History of Glass

History of glassFrom Wikipedia, the free encyclopediaJump to: navigation, search

Roman Cage Cup from the 4th century A.D.

Ancient Greek glass amphora, Hellenistic period, Altes Museum, Berlin

The history of glassmaking can be traced back to 3500 BCE in Mesopotamia.

Contents

[hide]

1 Origins of glass making 2 History by culture

o 2.1 India (Hindu Kingdoms) o 2.2 China o 2.3 Romans o 2.4 Anglo-Saxon world o 2.5 Islamic world o 2.6 Medieval Europe o 2.7 Murano glassmaking

3 Chronology of Advances to Production Methods [27] 4 See also 5 References 6 Further reading

[edit] Origins of glass making

Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Old Kingdom Egypt.[1] Because of Egypt's favorable environment for preservation, the majority of well-studied early glass is found there, although some of this is likely to have been imported. The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working slags or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.[2]

During the Late Bronze Age in Egypt (e.g., the Ahhotep "Treasure") and Western Asia (e.g. Megiddo [3] ) there was a rapid growth in glass-making technology. Archaeological finds from this period include colored glass ingots, vessels (often colored and shaped in imitation of highly prized hardstone carvings in semi-precious stones) and the ubiquitous beads. The alkali of Syrian and Egyptian glass was soda ash, sodium carbonate, which can be extracted from the ashes of many plants, notably halophile seashore plants: (see saltwort). The earliest vessels were 'core-wound', produced by winding a ductile rope of glass round a shaped core of sand and clay over a metal rod, then fusing it with repeated reheatings. Threads of thin glass of different colors made with admixtures of oxides were subsequently wound around these to create patterns, which could be drawn into festoons by using metal raking tools. The vessel would then be rolled flat ('marvered') on a slab in order to press the decorative threads into its body. Handles and feet were applied separately. The rod was subsequently allowed to cool as the glass slowly annealed and was eventually removed from the center of the vessel, after which the core material was scraped out. Glass shapes for inlays were also often created in moulds. Much early glass

production, however, relied on grinding techniques borrowed from stone working. This meant that the glass was ground and carved in a cold state.

By the 15th century BCE extensive glass production was occurring in Western Asia, Crete and Egypt and the Mycenaean Greek term ku-wa-no-wo-ko meaning "worker of lapis lazuli and glass" (written in Linear b syllabic script) is attested.[4][5] It is thought the techniques and recipes required for the initial fusing of glass from raw materials was a closely guarded technological secret reserved for the large palace industries of powerful states. Glass workers in other areas therefore relied on imports of pre-formed glass, often in the form of cast ingots such as those found on the Ulu Burun shipwreck off the coast of modern Turkey.

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. It picked up again in its former sites, in Syria and Cyprus, in the ninth century BCE, when the techniques for making colorless glass were discovered. The first glassmaking "manual" dates back to ca. 650 BCE. Instructions on how to make glass are contained in cuneiform tablets discovered in the library of the Assyrian king Ashurbanipal. In Egypt glass-making did not revive until it was reintroduced in Ptolemaic Alexandria. Core-formed vessels and beads were still widely produced, but other techniques came to the fore with experimentation and technological advancements. During the Hellenistic period many new techniques of glass production were introduced and glass began to be used to make larger pieces, notably table wares. Techniques developed during this period include 'slumping' viscous (but not fully molten) glass over a mould in order to form a dish and 'millefiori' (meaning 'thousand flowers') technique, where canes of multi-colored glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect. It was also during this period that colorless or decolored glass began to be prized and methods for achieving this effect were investigated more fully.[6]

According to Pliny the Elder, Phoenician traders were the first to stumble upon glass manufacturing techniques at the site of the Belus River. Georgius Agricola, in De re metallica, reported a traditional serendipitous "discovery" tale of familiar type:

"The tradition is that a merchant ship laden with nitrum being moored at this place, the merchants were preparing their meal on the beach, and not having stones to prop up their pots, they used lumps of nitrum from the ship, which fused and mixed with the sands of the shore, and there flowed streams of a new translucent liquid, and thus was the origin of glass."[7]

This account is more a reflection of Roman experience of glass production, however, as white silica sand from this area was used in the production of glass within the Roman Empire due to its low impurity levels.

During the first century BCE glass blowing was discovered on the Syro-Palestinian coast, revolutionising the industry. Glass vessels were now inexpensive compared to pottery vessels. The conquest of Judea by the Romans in 63 BCE [8] paved the way for the growth of the use of glass products that occurred throughout the Roman world. Glass became the Roman plastic, and glass containers produced in Judea and by the Jewish population in Alexandria [9] spread through out the Roman Empire. With the discovery of clear glass (through the introduction of manganese

oxide), by the Jewish glass blowers in Alexandria ca. AD 100, the Romans began to use glass for architectural purposes. Cast glass windows, albeit with poor optical qualities, began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii. Over the next 1,000 years glass making and working continued and spread through southern Europe and beyond.

[edit] History by culture

[edit] India (Hindu Kingdoms)

Indigenous development of glass technology in South Asia may have begun in 1730 BCE.[10] Evidence of this culture includes a red-brown glass bead along with a hoard of beads dating to that period, making it the earliest attested glass from the Indus Valley locations.[10] Glass discovered from later sites dating from 600–300 BCE displays common color.[10]

Chalcolithic evidence of glass has been found in Hastinapur, India.[11] Some of the texts which mention glass in India are the Shatapatha Brahmana and Vinaya Pitaka.[11] However, the first unmistakable evidence in large quantities, dating from the 3rd century BCE, has been uncovered from the archaeological site in Takshashila, ancient India.[11]

By the first century C.E., glass was being used for ornaments and casing in South Asia.[11] Contact with the Greco-Roman world added newer techniques, and Indians artisans mastered several techniques of glass molding, decorating and coloring by the succeeding centuries.[11] The Satavahana period of India also produced short cylinders of composite glass, including those displaying a lemon yellow matrix covered with green glass.[12]

[edit] China

Main article: Ancient Chinese glassThis section requires expansion.

[edit] Romans

Roman glassMain article: Roman glass

Glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts. Glass was used primarily for the production of vessels, although mosaic tiles and window glass were also produced. Roman glass production developed from Hellenistic technical traditions, initially concentrating on the production of intensely colored cast glass vessels. However, during the first century AD the industry underwent rapid technical growth that saw the introduction of glass blowing and the dominance of colorless or ‘aqua’ glasses. Production of raw glass was undertaken in geographically separate locations to the working of glass into finished vessels,[13][14] and by the end of the first century AD large scale manufacturing, primarily in Judea and by the Jewish population of Alexandria[15] , resulted in the establishment of glass as a commonly available material in the Roman world.

[edit] Anglo-Saxon world

Main article: Anglo-Saxon glass

Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was even used in jewelry.[16] In the 5th century AD with the Roman departure from Britain, there were also considerable changes in the usage of glass.[17] Excavation of Romano-British sites have revealed plentiful amounts of glass but, in contrast, the amount recovered from 5th century and later Anglo-Saxon sites is minuscule.[17] The majority of complete vessels and assemblages of beads come from the excavations of early Anglo-Saxon cemeteries, but a change in burial rites in the late 7th century affected the recovery of glass, as Christian Anglo-Saxons were buried with fewer grave goods, and glass is rarely found. From the late 7th century onwards, window glass is found more frequently. This is directly related to the introduction of Christianity and the construction of churches and monasteries.[17][18] There are a few Anglo-Saxon ecclesiastical[19] literary sources that mention the production and use of glass, although these relate to window glass used in ecclesiastical buildings.[17][18][20] Glass was also used by the Anglo-Saxons in their jewelry, both as enamel or as cut glass insets.[21][22]

[edit] Islamic world

Main article: Islamic glass

Arabic Lanters in Khan el-Khalili, Cairo

The Arab poet al-Buhturi (820–897) described the clarity of such glass, "Its color hides the glass as if it is standing in it without a container."[23]

Stained glass was also first produced by Muslim architects in Southwest Asia using colored glass rather than stone.[citation needed] In the 8th century, the Persian chemist Jabir ibn Hayyan (Geber) scientifically described 46 original recipes for producing colored glass in Kitab al-Durra al-Maknuna (The Book of the Hidden Pearl), in addition to 12 recipes inserted by al-Marrakishi in a later edition of the book.[24]

By the 11th century, clear glass mirrors were being produced in Islamic Spain.

[edit] Medieval Europe

A 16th-century stained glass window

Glass objects from the 7th and 8th centuries have been found on the island of Torcello near Venice. These form an important link between Roman times and the later importance of that city in the production of the material. Around 1000 AD, an important technical breakthrough was made in Northern Europe when soda glass, produced from white pebbles and burnt vegetation was replaced by glass made from a much more readily available material: potash obtained from wood ashes. From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use.[25]

Until the 12th century, stained glass – glass to which metallic or other impurities had been added for coloring – was not widely used, but it rapidly became an important medium for Romanesque art and especially Gothic art. Almost all survivals are in church buildings, but it was also used in grand secular buildings.

The 11th century saw the emergence in Germany of new ways of making sheet glass by blowing spheres. The spheres were swung out to form cylinders and then cut while still hot, after which the sheets were flattened. This technique was perfected in 13th century Venice.

The Crown glass process was used up to the mid-19th century. In this process, the glassblower would spin approximately 9 pounds (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 feet (1.5 m) in diameter. The disk would then be cut into panes.

Domestic glass vessels in late medieval Northern Europe are known as Forest glass.

[edit] Murano glassmaking

Main articles: Murano glass and Venetian glass

The center for luxury Italian glassmaking from the 14th century was the island of Murano, which developed many new techniques and became the center of a lucrative export trade in dinnerware, mirrors, and other items. What made Venetian Murano glass significantly different was that the local quartz pebbles were almost pure silica, and were ground into a fine clear sand that was combined with soda ash obtained from the Levant, for which the Venetians held the sole monopoly. The clearest and finest glass is tinted in two ways: firstly, a natural coloring agent is ground and melted with the glass. Many of these coloring agents still exist today; for a list of coloring agents, see below. Black glass was called obsidianus after obsidian stone. A second method is apparently to produce a black glass which, when held to the light, will show the true color that this glass will give to another glass when used as a dye.[26]

The Venetian ability to produce this superior form of glass resulted in a trade advantage over other glass producing lands. Murano’s reputation as a center for glassmaking was born when the Venetian Republic, fearing fire might burn down the city’s mostly wood buildings, ordered glassmakers to move their foundries to Murano in 1291. Murano's glassmakers were soon the island’s most prominent citizens. Glassmakers were not allowed to leave the Republic. Many took a risk and set up glass furnaces in surrounding cities and as far afield as England and the Netherlands.

[edit] Chronology of Advances to Production Methods[27]

1226 - "Broad Sheet" first produced in Sussex 1330 - "Crown Glass" first produced in Rouen, France. "Broad Sheet" also produced.

Both were also supplied for export 1620 - "Blown Plate" first produced in London. Used for mirrors and coach plates. 1678 - "Crown Glass" first produced in London. This process dominated until the 19th

century 1688 - "Polished Plate" first produced in France (cast then hand polished) 1773 - "Polished Plate" adopted by English at Ravenshead. By 1800 a steam engine was

used to carry out the grinding and polishing process 1834 - "Improved Cylinder Sheet" introduced by Robert Lucas Chance, based on a

German process of partial remelting of cut glass cylinders. This type of glass was used to glaze the The Crystal Palace of the Great Exhibition. The process was common until WW1.

1843 - An early form of "Float Glass" invented by Henry Bessemer, pouring glass onto liquid tin. Expensive and not a commercial success.

1847 - "Rolled Plate" introduced by James Hartley. This allowed a ribbed finish. This type of glass was often used for extensive glass roofs such as within railway stations

1888 - "Machine Rolled" glass introduced allowing patterns to be introduced

1898 - "Wired Cast" glass invented by Pilkington for use where safety or security was an issue. This is commonly given the misnomer "Georgian Wired Glass" but greatly post-dates the Georgian era.

1903 - "Machine Drawn Cylinder" technique invented in USA. Manufactured under licence in UK by Pilkington from 1910 until 1933.

1913 - "Flat Drawn Sheet" technique developed in Belgium. First produced under licence in UK in 1919 in Kent

1923 - "Polished Plate" first appeared in UK. Commonly used for large panes such as on shopfronts.

1938 - "Polished Plate" process improved by Pilkington, incorporating a double grinding process to give an improved quality of finish

1959 - "Float Glass" launched in UK. Invented by Sir Alistair Pilkington.

Glass recyclingFrom Wikipedia, the free encyclopedia

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The examples and perspective in this article deal primarily with the United Kingdom and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page.

Public glass waste collection point in a neighborhood area for separating colorless, green and amber glass

3R Concepts

Waste Disposal Hierarchy o Reduce o Reuse o Recycle

Barter Dematerialization Downcycling Dumpster diving Ecodesign Ethical consumerism Freeganism Extended producer responsibility

Industrial ecology Industrial metabolism Material flow analysis Product stewardship Simple living Upcycling Zero waste

Recyclable materials [show]

Glass recycling is the process of turning waste glass into usable products. Glass waste should be separated by chemical composition, and then, depending on the end use and local processing capabilities, might also have to be separated into different colors. Many recyclers collect different colors of glass separately since glass retains its color after recycling. The most common types used for consumer containers are colorless glass, green glass, and brown/amber glass.

Glass makes up a large component of household and industrial waste due to its weight and density. The glass component in municipal waste is usually made up of bottles, broken glassware, light bulbs and other items. Adding to this waste is the fact that many manual methods of creating glass objects have a defect rate of around forty percent. Glass recycling uses less energy than manufacturing glass from sand, lime and soda. Every metric ton of waste glass recycled into new items saves 315 additional kilograms of carbon dioxide from being released into the atmosphere during the creation of new glass.[1] Glass that is crushed and ready to be remelted is called cullet.

Contents

[hide]

1 Glass reuse 2 Glass collection 3 Glass recycling

o 3.1 United Kingdom 3.1.1 Secondary uses for recycled glass

o 3.2 United States o 3.3 Germany

4 See also 5 References 6 External links

[edit] Glass reuse

Reuse of glass containers is preferable to recycling according to the waste hierarchy. Refillable bottles are used extensively in many European countries, Canada and until relatively recently, in

the United States. In Denmark 98% of bottles are refillable and 98% of those are returned by consumers.[2] A similarly high number is reported for beer bottles in Canada.[3] These systems are typically supported by container deposit laws and other regulations. In some developing nations like India and Brazil, the cost of new bottles often forces manufacturers to collect and refill old glass bottles for selling carbonated and other drinks.

[edit] Glass collection

Vehicle emptying a glass bank in Europe

Glass collection points, known as Bottle Banks are very common near shopping centres, at civic amenity sites and in local neighborhoods in the United Kingdom. The first Bottle Bank was introduced by Stanley Race CBE, then president of the Glass Manufacturers’ Federation and Ron England in Barnsley on 6 June 1977;[4]

Bottle Banks commonly stand beside collection points for other recyclable waste like paper, metals and plastics. Local, municipal waste collectors usually have one central point for all types of waste in which large glass containers are located. There are now over 50,000 bottle banks in the United Kingdom.[5]

Most collection points have separate bins for clear, green and amber/brown glass. Glass reprocessors require separation by colour as the different colours of glass are usually chemically incompatible. Heat-resistant glass like Pyrex or borosilicate glass should not be disposed of in the glass container as even a single piece of such material will alter the viscosity of the fluid in the furnace at remelt.

[edit] Glass recycling

[edit] United Kingdom

The 600 ml beer bottle is the standard reused bottle in Brazil. It was extended from beer to popular carbonated drinks.

752,000 tons of glass are now recycled annually in the United Kingdom.[5] Glass is an ideal material for recycling and where it is used for new glass container manufacture it is virtually infinitely recyclable. The use of recycled glass in new containers helps save energy. It helps in brick and ceramic manufacture, and it conserves raw materials, reduces energy consumption, and reduces the volume of waste sent to landfill.[6]

[edit] Secondary uses for recycled glass

In the United Kingdom, the waste recycling industry cannot consume all of the recycled container glass that will become available over the coming years, mainly due to the colour imbalance between that which is manufactured and that which is consumed. The UK imports much more green glass in the form of wine bottles than it uses, leading to a surplus amount for recycling.

The resulting surplus of green glass from imported bottles may be exported to producing countries, or used locally in the growing diversity of secondary end uses for recycled glass.[7] Cory Environmental are presently shipping glass cullet from the UK to Portugal.[8]

The use of recycled glass as aggregate in concrete has become popular in modern times, with large scale research being carried out at Columbia University in New York. This greatly enhances the aesthetic appeal of the concrete. Recent research findings have shown that concrete made with recycled glass aggregates have shown better long term strength and better thermal insulation due to its better thermal properties of the glass aggregates.[9] Secondary markets for glass recycling may include:

Glass in ceramic sanitary ware production Glass as a flux agent in brick manufacture Glass in astroturf and related applications (e.g. top dressing, root zone) material or golf bunker

sand Glass in recycled glass countertops Glass as water filtration media Glass as an abrasive

Mixed glass waste streams can also be recycled and converted into an aggregate. Mixed waste streams may be collected from materials recovery facilities or mechanical biological treatment systems. Some facilities can sort out mixed waste streams into different colours using electro-optical sorting units.

[edit] United States

This section includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (August 2008)

Rates of recycling and methods of waste collection vary substantially across the United States because laws are written on the state or local level and large municipalities often have their own, unique systems. Many cities do curb-side recycling meaning that they collect household recyclable waste on a weekly or bi-weekly basis that residents set out in special containers in front of their homes.

Apartment dwellers usually use shared containers that may be collected by the city or by private recycling companies which can have their own recycling rules. In some cases, glass is specifically separated into its own container because broken glass is a hazard to the people who later manually sort the co-mingled recyclables. Sorted recyclables are later sold to companies

In 1971 the state of Oregon passed a law requiring buyers of carbonated beverages (such as beer and soda) to pay five cents per container as a deposit which would be refunded to anyone who returned the container for recycling. This law has since been copied in nine other states including New York and California. The abbreviations of states with deposit laws are printed on all qualifying bottles and cans. In states with these container deposit laws, most supermarkets automate the deposit refund process by providing machines which will count containers as they are inserted and then print credit vouchers that can be redeemed at the store for the number of containers returned. Small glass bottles (mostly beer) are broken, one-by-one, inside these deposit refund machines as the bottles are inserted. A large, wheeled hopper (very roughly 1.5m by 1.5m by 0.5m) inside the machine collects the broken glass until it can be emptied by an employee.

[edit] Germany

In 2004, Germany recycled 2,116,000 tons of glass. Reusable glass or plastic (PET) bottles are available for many drinks, especially beer and carbonated water as well as softdrinks (Mehrwegflaschen). The deposit per bottle (Pfand) is €0.08-€0.15, compared to €0.25 for recyclable but not reusable plastic bottles. There is no deposit for glass bottles which do not get refilled.

FiberglassFrom Wikipedia, the free encyclopediaJump to: navigation, search

Bundle of fiberglass

Fiberglass, (also called fibreglass and glass fibre), is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called "fiberglass" in popular usage. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of fiberglass was only made possible with the invention of finer machine tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World's Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. This was first worn by the popular stage actress of the time Georgia Cayvan.

What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a genericized trademark. A somewhat similar, but more expensive technology used for applications requiring very high strength and low weight is the use of carbon fiber.

Contents

[hide]

1 Fiber formation 2 Chemistry 3 Properties

o 3.1 Safety 4 Glass-reinforced plastic 5 Uses 6 Role of recycling in fiberglass manufacturing 7 See also 8 Notes and references 9 External links

[edit] Fiber formation

Glass fiber is formed when thin strands of silica-based or other formulation glass is extruded into many fibers with small diameters suitable for textile processing. The technique of heating and drawing glass into fine fibers has been known for millennia; however, the use of these fibers for textile applications is more recent. Until this time all fiberglass had been manufactured as staple (a term used to describe naturally formed clusters or locks of wool fibres). The first commercial production of fiberglass was in 1936. In 1938 Owens-Illinois Glass Company and Corning Glass Works joined to form the Owens-Corning Fiberglas Corporation. When the two companies joined to produce and promote fiberglass, they introduced continuous filament glass fibers.[1] Owens-Corning is still the major fiberglass producer in the market today.[2]

The types of fiberglass most commonly used are mainly E-glass (alumino-borosilicate glass with less than 1 wt% alkali oxides, mainly used for glass-reinforced plastics), but also A-glass (alkali-lime glass with little or no boron oxide), E-CR-glass (alumino-lime silicate with less than 1 wt% alkali oxides, has high acid resistance), C-glass (alkali-lime glass with high boron oxide content, used for example for glass staple fibers), D-glass (borosilicate glass with high dielectric constant), R-glass (alumino silicate glass without MgO and CaO with high mechanical requirements), and S-glass (alumino silicate glass without CaO but with high MgO content with high tensile strength).[3]

[edit] Chemistry

The basis of textile-grade glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2)n. It has no true melting point but softens at 2,000 °C (3,630 °F), where it starts to degrade. At 1,713 °C (3,115 °F), most of the molecules can move about freely. If the glass is then cooled quickly, they will be unable to form an ordered structure.[4] In the polymer, it forms SiO4 groups that are configured as a tetrahedron with the silicon atom at the center and four oxygen atoms at

the corners. These atoms then form a network bonded at the corners by sharing the oxygen atoms.

The vitreous and crystalline states of silica (glass and quartz) have similar energy levels on a molecular basis, also implying that the glassy form is extremely stable. In order to induce crystallization, it must be heated to temperatures above 1,200 °C (2,190 °F) for long periods of time.[1]

Molecular Geometry of Glass

Although pure silica is a perfectly viable glass and glass fiber, it must be worked with at very high temperatures, which is a drawback unless its specific chemical properties are needed. It is usual to introduce impurities into the glass in the form of other materials to lower its working temperature. These materials also impart various other properties to the glass that may be beneficial in different applications. The first type of glass used for fiber was soda lime glass or A glass. It was not very resistant to alkali. A new type, E-glass, was formed; this is an alumino-borosilicate glass that is alkali free (<2%).[5] This was the first glass formulation used for continuous filament formation. E-glass still makes up most of the fiberglass production in the world. Its particular components may differ slightly in percentage, but must fall within a specific range. The letter E is used because it was originally for electrical applications. S-glass is a high-strength formulation for use when tensile strength is the most important property. C-glass was developed to resist attack from chemicals, mostly acids that destroy E-glass.[5] T-glass is a North American variant of C-glass. A-glass is an industry term for cullet glass, often bottles, made into fiber. AR-glass is alkali-resistant glass. Most glass fibers have limited solubility in water but are very dependent on pH. Chloride ions will also attack and dissolve E-glass surfaces.

Since E-glass does not really melt, but soften, the softening point is defined as "the temperature at which a 0.55–0.77 mm diameter fiber 235 mm long, elongates under its own weight at 1 mm/min when suspended vertically and heated at the rate of 5°C per minute".[6] The strain point is reached when the glass has a viscosity of 1014.5 poise. The annealing point, which is the temperature where the internal stresses are reduced to an acceptable commercial limit in 15 minutes, is marked by a viscosity of 1013 poise.[6]

[edit] Properties

Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(m·K).[7]

The strength of glass is usually tested and reported for "virgin" or pristine fibers—those that have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity.[5] Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber.[4] Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks.[4] There is a correlation between bending diameter of the filament and the filament diameter.[8] The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

[edit] Safety

Fiberglass has increased in popularity since the discovery that asbestos causes cancer and its subsequent removal from most products. However, the safety of fiberglass is also being called into question, as research shows that the composition of this material (asbestos and fiberglass are both silicate fibers) causes similar toxicity as asbestos.[9][10][11][12]

1970s studies on rats found that fibrous glass of less than 3 micrometers in diameter and greater than 20 micrometers in length is a "potent carcinogen".[9] Likewise, the International Agency for Research on Cancer found it "may reasonably be anticipated to be a carcinogen" in 1990. The American Conference of Governmental Industrial Hygienists, on the other hand, says that there is insufficient evidence, and that fiberglass is in group A4: "Not classifiable as a human carcinogen".

The North American Insulation Manufacturers Association (NAIMA) claims that fiberglass is fundamentally different from asbestos, since it is man-made instead of naturally-occurring.[13] They claim that fiberglass "dissolves in the lungs", while asbestos remains in the body for life. Although both fiberglass and asbestos are made from silica filaments, NAIMA claims that asbestos is more dangerous because of its crystalline structure, which causes it to cleave into smaller, more dangerous pieces, citing the U.S. Department of Health and Human Services:

Synthetic vitreous fibers [fiber glass] differ from asbestos in two ways that may provide at least partial explanations for their lower toxicity. Because most synthetic vitreous fibers are not crystalline like asbestos, they do not split longitudinally to form thinner fibers. They also generally have markedly less biopersistence in biological tissues than asbestos fibers because they can undergo dissolution and transverse breakage.[14]

A 1998 rat study found that the biopersistence of synthetic fibers after one year was 0.04–10%, but 27% for amosite asbestos. Fibers that persisted longer were found to be more carcinogenic.[15]

[edit] Glass-reinforced plastic

Main article: Glass-reinforced plastic

Glass-reinforced plastic (GRP) is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine glass fibers. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass). Thermosetting plastics are normally used for GRP production—most often unsaturated polyester (using 2-butanone peroxide aka MEK peroxide as a catalyst), but vinylester or epoxy are also used. Traditionally, styrene monomer was used as a reactive diluent in the resin formulation giving the resin a characteristic odor. More recently alternatives have been developed. The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.[3][16]

As with many other composite materials (such as reinforced concrete), the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the glass fibers are very strong in tension but have no strength against compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well.[17] The two materials may be used uniformly or the glass may be specifically placed in those portions of the structure that will experience tensile loads.[3][16]

[edit] Uses

Uses for regular fiberglass include mats, thermal insulation, electrical insulation, sound insulation, reinforcement of various materials, tent poles, sound absorption, heat- and corrosion-resistant fabrics, high-strength fabrics, pole vault poles, arrows, bows and crossbows, translucent roofing panels, automobile bodies, hockey sticks, surfboards, boat hulls, and paper honeycomb. It has been used for medical purposes in casts. Fiberglass is extensively used for making FRP tanks and vessels.[3][16] Fiberglass is also used in the design of Irish stepdance shoes.[18]

[edit] Role of recycling in fiberglass manufacturing

Manufacturers of fiberglass insulation can use recycled glass. Owens Corning's fiberglass has 40% recycled glass. A recycling program begun in 2009 in Kansas City, Kansas, will ship crushed recycled glass, called cullet, to the Owens Corning plant that will use it as raw material for fiberglass making

GlassFrom Wikipedia, the free encyclopedia

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This article is about the material. For other uses, see Glass (disambiguation).

Moldavite, a natural glass formed by meteorite impact, from Besednice, Bohemia

A modern greenhouse in Wisley Garden, England, made from float glass

Clear glass light bulb

Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.[1]

Strictly speaking, a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising.[2][3][4][5][6] Many glasses contain silica as their main component and glass former.[7] The term "glass" is, however, often extended to all amorphous solids (and melts that easily form amorphous solids), including plastics, resins, or other silica-free amorphous solids. In addition, besides traditional melting techniques, any other means of preparation are considered, such as ion implantation, and the sol-gel method.[7] Commonly, glass science and physics deal only with inorganic amorphous solids, while plastics and similar organics are covered by polymer science, biology and further scientific disciplines.

Glass plays an essential role in science and industry. The optical and physical properties of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art.

Contents

[hide]

1 History

2 Glass production o 2.1 Glass ingredients

2.1.1 Composition and properties o 2.2 Contemporary glass production o 2.3 Glassmaking in the laboratory o 2.4 Sol-gel science/technology

3 Silica-free glasses 4 Physics of glass

o 4.1 Glass versus a supercooled liquid o 4.2 Behavior of antique glass o 4.3 Physical properties

4.3.1 Optical properties 4.3.2 Color 4.3.3 Optical waveguides

5 Modern glass art o 5.1 Museums

6 See also 7 References 8 Bibliography 9 External links

[edit] History

Main article: History of glass

The history of creating glass can be traced back to 3500 BCE in Mesopotamia.

[edit] Glass production

Main articles: Glass production and Float glass

[edit] Glass ingredients

Quartz sand (silica) as main raw material for commercial glass production

Oldest mouth-blown window-glass in Sweden (Kosta Glasbruk, Småland, 1742). In the middle is the mark from the glassblower's pipe.

Pure silica (SiO2) has a "glass melting point"—at a viscosity of 10 Pa·s (100 P)—of over 2300 °C (4200 °F). While pure silica can be made into glass for special applications (see fused quartz), other substances are added to common glass to simplify processing. One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass.[8] Soda-lime glasses account for about 90% of manufactured glass.

Most common glass has other ingredients added to change its properties. Lead glass or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eye glasses. Large amounts of iron are used in glass that absorbs infrared energy, such as heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.

Another common glass ingredient is "cullet" (recycled glass). The recycled glass saves on raw materials and energy. However, impurities in the cullet can lead to product and equipment failure.

Finally, fining agents such as sodium sulfate, sodium chloride, or antimony oxide are added to reduce the bubble content in the glass.[8] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

[edit] Composition and properties

There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.

The presence of non-bridging oxygens lowers the relative number of strong bonds in the material and disrupts the network, decreasing the viscosity of the melt and lowering the melting temperature.

The alkaline metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility however decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance.[9] Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.

Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and therefore is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.[10]

Addition of fluorine lowers the dielectric constant of glass. Fluorine is highly electronegative and attracts the electrons in the lattice, lowering the polarizability of the material. Such silicon dioxide-fluoride is used in manufacture of integrated circuits as an insulator. High levels of

fluorine doping lead to formation of volatile SiF2O and such glass is then thermally unstable. Stable layers were achieved with dielectric constant down to about 3.5–3.7.[11]

[edit] Contemporary glass production

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.[8]

After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.[12] Container glass for common bottles and jars is formed by blowing and pressing methods. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).

[edit] Glassmaking in the laboratory

A vitrification experiment for the study of nuclear waste disposal at Pacific Northwest National Laboratory.

Failed laboratory glass melting test. The striations must be avoided through good homogenization.

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali oxides and hydroxides, alkaline earth oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[13] Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.[13][14]

In order to make glass from materials with poor glass forming tendencies, novel techniques are used to increase cooling rate, or reduce crystal nucleation triggers. Examples of these techniques include aerodynamic levitation (cooling the melt whilst it floats on a gas stream), splat quenching (pressing the melt between two metal anvils) and roller quenching (pouring the melt through rollers).

See also: Optical lens design, Fabrication and testing of optical components

[edit] Sol-gel science/technology

Main article: Sol-gel

[edit] Silica-free glasses

Besides common silica-based glasses, many other inorganic and organic materials may also form glasses, including plastics (e.g., acrylic glass), amorphous carbon, metals, carbon dioxide (see below), phosphates, borates, chalcogenides, fluorides, germanates (glasses based on GeO2), tellurites (glasses based on TeO2), antimonates (glasses based on Sb2O3), arsenates (glasses based on As2O3), titanates (glasses based on TiO2), tantalates (glasses based on Ta2O5), nitrates, carbonates and many other substances.[7]

Some glasses that do not include silica as a major constituent may have physico-chemical properties useful for their application in fibre optics and other specialized technical applications. These include fluoride glasses (fluorozirconates, fluoroaluminates), aluminosilicates, phosphate glasses, borate glasses, and chalcogenide glasses.

Under extremes of pressure and temperature solids may exhibit large structural and physical changes which can lead to polyamorphic phase transitions.[15] In 2006 Italian scientists created an amorphous phase of carbon dioxide using extreme pressure. The substance was named amorphous carbonia(a-CO2) and exhibits an atomic structure resembling that of silica.[16]

[edit] Physics of glass

See also Physics of glass

Unsolved problems in physics

What is the nature of the transition between a fluid or regular solid and a glassy phase? What are the physical mechanisms giving rise to the general properties of glasses?

The amorphous structure of glassy Silica (SiO2) in two dimensions. No long range order is present, however there is local ordering with respect to the tetrahedral arrangement of Oxygen (O) atoms around the Silicon (Si) atoms.

The standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching.[3]

[4][5][17] If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at the glass transition temperature Tg. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.[18] As in other amorphous solids, the atomic structure of a glass lacks any long range translational periodicity. However, due to chemical bonding characteristics glasses do possess a high degree of short-range order with respect to local atomic polyhedra.[19] It is deemed that the bonding structure of glasses, although disordered, has the same symmetry signature (Hausdorff-Besicovitch dimensionality) as for crystalline materials.[20]

[edit] Glass versus a supercooled liquid

Glass is generally classed as an amorphous solid rather than a liquid.[17][21] Glass displays all the mechanical properties of a solid. The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity of amorphous materials). From a more commonsense point of view, glass should be considered a solid since it is rigid according to everyday experience.[22]

Some people consider glass to be a liquid due to its lack of a first-order phase transition [21] [23] where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. However, the glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are continuous.[20] Despite this, the equilibrium theory of phase transformations in solids does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.[5]

Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature.[24] A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.

[edit] Behavior of antique glass

The observation that old windows are often thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a matter of centuries. It is then assumed that the glass was once uniform, but has flowed to its new shape, which is a property of liquid.[25]

In actuality, the reason for this is that when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not, however, absolutely flat; the edges of the disk became thicker as the glass spun. When actually installed in a window frame, the glass would be placed thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window.[26] Occasionally such glass has been found thinner side down or thicker on either side of the window's edge, as would be caused by carelessness at the time of installation.[27]

Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centred in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.

Several other points exemplify the misconception of the "cathedral glass" theory:

Writing in the American Journal of Physics, physicist Edgar D. Zanotto states "...the predicted relaxation time for GeO2 at room temperature is 10 32 years . Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer."[28] (1032 years is many times longer than the estimated age of the Universe.)

If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more — but this is not observed. Similarly, prehistoric obsidian blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).[21]

If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.[21]

There are many examples of centuries-old glass shelving which has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.

Some glasses have a glass transition temperature close to or below room temperature. The behavior of a material that has a glass transition close to room temperature depends upon the timescale during which the material is manipulated. If the material is hit it may break like a solid glass, but if the material is left on a table for a week it may flow like a liquid. This simply means that for the fast timescale its transition temperature is above room temperature, but for the slow one it is below. The shift in temperature with timescale is not very large however, as indicated by the transition of polypropylene glycol of -72 °C and -71 °C over different timescales.[18] To observe window glass flowing as liquid at room temperature we would have to wait a much longer time than any human can exist. Therefore it is safe to consider a glass a solid far enough below its transition temperature: Cathedral glass does not flow because its glass transition temperature is many hundreds of degrees above room temperature. Close to this temperature

there are interesting time-dependent properties. One of these is known as aging. Many polymers that we use in daily life such as polystyrene and polypropylene are in a glassy state but they are not too far below their glass transition temperature as opposed to rubber which is used above its glass transition temperature. Their mechanical properties may well change over time and this is serious concern when applying these materials in construction. In general for polymers there is a relation between the glass transition temperature and the speed of the deformation.

[edit] Physical properties

See also: List of physical properties of glass

[edit] Optical properties

Glass is in widespread use largely due to the production of glass compositions that are transparent to visible wavelengths of light.

In contrast, polycrystalline materials in general do not transmit visible light.[citation needed] The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light. Light entering a polycrystal is repeatedly scattered until it re-emerges from the surface in random directions. This subsurface scattering mechanism,[29][30] together with scattering by surface irregularities, gives rise to diffuse reflection and hence, although it does not absorb light, the polycrystal is not transparent. This mechanism, which causes objects to be opaque, is a crucial mechanism for vision, because most objects are seen by our eyes through their diffuse reflection.[31]

Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material.[citation needed] The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface.[citation needed] These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing (colored, see below).[citation needed]

Glass has the ability to refract, reflect and transmit light following geometrical optics, without scattering it, and it is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5.[citation needed] According to Fresnel equations, the reflectivity of a sheet of glass is about 4% per surface (at normal incidence), and its transmissivity about 92%.[citation

needed]

[edit] ColorMain article: Glass coloring and color marking

See also: Transparent_materials#Absorption of light in solids

Common soda-lime float glass appears green in thick sections because of Fe2+ impurities.

Many glasses have a chemical composition which includes what are referred to as absorption centers. This may cause them to be selective in their absorption of visible lightwaves (or white light frequencies). They absorb certain portions of the visible spectrum, while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected back or transmitted for our physical observation. This is what gives rise to color.

Thus, color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses).[7] Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt%[32] produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black.[33] Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide.

[edit] Optical waveguidesMain article: Waveguide (optics)

The propagation of light through a multi-mode optical fiber.

A laser bouncing down an acrylic rod, illustrating the total internal reflection of light in a multimode optical fiber.

Optically transparent materials focus on the response of a material to incoming light waves of a range of wavelengths. Frequency selective optical filters can be utilized to alter or enhance the brightness and contrast of a digital image. Guided light wave transmission via frequency selective waveguides involves the emerging field of fiber optics and the ability of certain glassy compositions as a transmission medium for a range of frequencies simultaneously (multimode optical fiber) with little or no interference between competing wavelengths or frequencies. This resonant mode of energy and data transmission via electromagnetic (light) wave propagation, though low powered, is relatively lossless.

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The index of refraction is a way of measuring the speed of light in a material. (Note: The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in a given medium. (The index of refraction of a vacuum is therefore equal to 1, by definition). The larger the index of refraction, the more slowly light travels in that medium. Typical values for core and cladding of an optical fiber are 1.48 and 1.46, respectively.

When light traveling in a dense medium hits a boundary at a steep angle, the light will be completely reflected. This effect is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles will be propagated. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.

Optical waveguides are used as components in integrated optical circuits (e.g. light-emitting diodes, LEDs) or as the transmission medium in local and long haul optical communication systems. Also of value to materials science is the sensitivity of materials to thermal radiation in

the infrared (IR) portion of the EM spectrum. This infrared homing (or "heat-seeking") capability is responsible for such diverse optical phenomena as "night vision" and IR luminescence.

[edit] Modern glass art

Main article: Studio glass

A vase being created at the Reijmyre glassworks, Sweden

Paperweight with items inside the glass, Corning Museum of Glass

A glass sculpture by Dale Chihuly, “The Sun” at the “Gardens of Glass” exhibition in Kew Gardens, London. The piece is 13 feet (4 metres) high and made from 1000 separate glass objects.

Glass tiles mosaic (detail).

From the 19th century, various types of fancy glass started to become significant branches of the decorative arts. Cameo glass was revived for the first time since the Romans, initially mostly used for pieces in a neo-classical style. The Art Nouveau movement in particular made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy important names in the first French wave of the movement, producing colored vases and similar pieces, often in cameo glass, and also using lustre techniques. Louis Comfort Tiffany in America specialized in secular stained glass, mostly of plant subjects, both in panels and his famous lamps. From the 20th century,

some glass artists began to class themselves as in effect sculptors working in glass, and as part of the fine arts.

Several of the most common techniques for producing glass art include: blowing, kiln-casting, fusing, slumping, pate-de-verre, flame-working, hot-sculpting and cold-working. Cold work includes traditional stained glass work as well as other methods of shaping glass at room temperature. Glass can also be cut with a diamond saw, or copper wheels embedded with abrasives, and polished to give gleaming facets; the technique used in creating Waterford crystal.[34] Art is sometimes etched into glass via the use of acid, caustic, or abrasive substances. Traditionally this was done after the glass was blown or cast. In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mould with the image already on the surface of the glass. This reduced manufacturing costs and, combined with a wider use of colored glass, led to cheap glassware in the 1930s, which later became known as Depression glass.[35] As the types of acids used in this process are extremely hazardous, abrasive methods have gained popularity.

Objects made out of glass include not only traditional objects such as vessels (bowls, vases, bottles, and other containers), paperweights, marbles, beads, but an endless range of sculpture and installation art as well. Colored glass is often used, though sometimes the glass is painted, innumerable examples exist of the use of stained glass.

[edit] Museums

Apart from historical collections in general museums, modern works of art in glass can be seen in a variety of museums, including the Chrysler Museum, the Museum of Glass in Tacoma, the Metropolitan Museum of Art, the Toledo Museum of Art, and Corning Museum of Glass, in Corning, NY, which houses the world's largest collection of glass art and history, with more than 45,000 objects in its collection.[36]

The Harvard Museum of Natural History has a collection of extremely detailed models of flowers made of painted glass. These were lampworked by Leopold Blaschka and his son Rudolph, who never revealed the method he used to make them. The Blaschka Glass Flowers are still an inspiration to glassblowers today.[37]

[edit] See also

Aluminium oxynitride Ceramic engineering Colloidal crystal Fiberglass Fulgurite Glass transition Glass recycling Glazier History of glass Nanomaterials

Optical fiber Magnifying glass Superglass Transparent materials Tektite Volcanic glass Vitrification Vitrified sand Devitrification Prince Rupert's Drops

[edit] References

1. ̂ Douglas, R. W. (1972). A history of glassmaking. Henley-on-Thames: G T Foulis & Co Ltd. ISBN 0854291172.

2. ̂ ASTM definition of glass from 1945; also: DIN 1259, Glas – Begriffe für Glasarten und Glasgruppen, September 1986

3. ^ a b Zallen, R. (1983). The Physics of Amorphous Solids. New York: John Wiley. ISBN 0471019682.4. ^ a b Cusack, N. E. (1987). The physics of structurally disordered matter: an introduction. Adam

Hilger in association with the University of Sussex press. ISBN 0852748299.5. ^ a b c Elliot, S. R. (1984). Physics of Amorphous Materials. Longman group ltd.6. ̂ Horst Scholze (1991). Glass – Nature, Structure, and Properties. Springer. ISBN 0-387-97396-6.7. ^ a b c d Werner Vogel (1994). Glass Chemistry (2 ed.). Springer-Verlag Berlin and Heidelberg

GmbH & Co. K. ISBN 3540575723.8. ^ a b c B. H. W. S. de Jong, "Glass"; in "Ullmann's Encyclopedia of Industrial Chemistry"; 5th

edition, vol. A12, VCH Publishers, Weinheim, Germany, 1989, ISBN 3-527-20112-5, pp. 365–432.9. ̂ Eric Le Bourhis (2007). Glass: Mechanics and Technology. Wiley-VCH. p. 74. ISBN 3527315497.

http://books.google.com/?id=34W4ZNDBHqQC&pg=PA64&dq=%22borate+glass%22&cd=1#v=onepage&q=%22borate%20glass%22.

10. ̂ James F. Shackelford, Robert H. Doremus (2008). Ceramic and Glass Materials: Structure, Properties and Processing. Springer. p. 158. ISBN 0387733612. http://books.google.com/?id=ASIYuNCp81YC&pg=PA158&dq=%22glass+solders%22&cd=3#v=onepage&q=%22glass%20solders%22.

11. ̂ Robert Doering, Yoshio Nishi (2007). Handbook of semiconductor manufacturing technology. CRC Press. pp. 12–3. ISBN 1574446754. http://books.google.com/?id=PsVVKz_hjBgC&pg=SA12-PA3&dq=semiconductor+failure+microphotograph&cd=5#v=onepage&q=.

12. ̂ "PFG Glass". Pfg.co.za. http://www.pfg.co.za/about%20glass.htm. Retrieved 2009-10-24.13. ^ a b "Glass melting, Pacific Northwest National Laboratory". Depts.washington.edu.

http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html. Retrieved 2009-10-24.

14. ̂ Alexander Fluegel. "Glass melting in the laboratory". Glassproperties.com. http://glassproperties.com/melting/. Retrieved 2009-10-24.

15. ̂ P. F. McMillan (2004). "Polyamorphic transformations in liquids and glasses". Journal of Materials Chemistry 14: 1506–1512. doi:10.1039/b401308p.

16. ̂ carbon dioxide glass created in the lab 15 June 2006, www.newscientisttech.com. Retrieved 3 August 2006.

17. ^ a b S. A. Baeurle et al. (2006). "On the glassy state of multiphase and pure polymer materials". Polymer 47: 6243–6253&year=2006. doi:10.1016/j.polymer.2006.05.076.

18. ^ a b Folmer, J. C. W.; Franzen, Stefan (2003). "Study of polymer glasses by modulated differential scanning calorimetry in the undergraduate physical chemistry laboratory". Journal of Chemical Education 80 (7): 813. doi:10.1021/ed080p813. http://jchemed.chem.wisc.edu/Journal/Issues/2003/Jul/abs813.html.

19. ̂ P.S. Salmon (2002). "Order within disorder". Nature Materials 1 (2): 87. doi:10.1038/nmat737. PMID 12618817.

20. ^ a b M.I. Ojovan, W.E. Lee (2006). "Topologically disordered systems at the glass transition". J. Phys.: Condensed Matter 18: 11507–11520. doi:10.1088/0953-8984/18/50/007.

21. ^ a b c d Philip Gibbs. "Is glass liquid or solid?". http://math.ucr.edu/home/baez/physics/General/Glass/glass.html. Retrieved 2007-03-21.

22. ̂ "Philip Gibbs" Glass Worldwide, (May/June 2007), pp. 14–18

Laboratory glassware

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It has been suggested that Ground glass joint be merged into this article or section. (Discuss)

Brown glass jars with some clear lab glassware in the background

Three beakers, a conical flask, a graduated cylinder and a volumetric flask

Laboratory glassware refers to a variety of equipment, traditionally made of glass, used for scientific experiments and other work in science, especially in chemistry and biology laboratories. Some of the equipment is now made of plastic for cost, ruggedness, and convenience reasons, but glass is still used for some applications because it is relatively inert, transparent, more heat-resistant than some plastics up to a point, and relatively easy to customize. Borosilicate glasses—formerly called Pyrex—are often used because they are less subject to thermal stress and are common for reagent bottles. For some applications quartz glass is used for its ability to withstand high temperatures or its transparency in certain parts of the electromagnetic spectrum. In other applications, especially some storage bottles, darkened brown or amber (actinic) glass is used to keep out much of the UV and IR radiation so that the effect of

light on the contents is minimized. Special-purpose materials are also used; for example, hydrofluoric acid is stored and used in polyethylene containers because it reacts with glass.[1]

Contents

[hide]

1 Applications 2 Production 3 Service temperatures 4 Lubrication and sealing 5 Safety when using vacuums and Keck clips 6 Gentle & even heating - baths & alternatives 7 Glassware Joints

o 7.1 Ground glass joints 7.1.1 Conically tapered joints 7.1.2 Ball-and-socket joints

o 7.2 O-ring joints o 7.3 Threaded connections o 7.4 Glass-to-metal transition joints o 7.5 Hose connections

8 Glassware Valves o 8.1 Stopcock valve o 8.2 Threaded plug valve

9 Fritted glass 10 Cleaning laboratory glassware 11 Gallery 12 Notes

[edit] Applications

There are many different kinds of laboratory glassware items, the majority are covered in separate articles of their own; see the list further below. Such glassware is used for a wide variety of functions which include volumetric measuring, holding or storing chemicals or samples, mixing or preparing solutions or other mixtures, containing lab processes like chemical reactions, heating, cooling, distillation, separations including chromatography, synthesis, growing biological organisms, spectrophotometry, and containing a full or partial vacuum. When in use, laboratory glassware is often held in place with clamps made for that purpose, which are likewise attached and held in place by stands or racks. This article covers aspects of laboratory glassware which may be common to several kinds of glassware and may briefly describe a few glassware items not covered in other articles.

[edit] Production

Most laboratory glassware is now mass-produced, but many large laboratories employ a glass blower to construct specialized pieces. This construction forms a specialized field of glassblowing requiring precise control of shape and dimension. In addition to repairing expensive or difficult-to-replace glassware, scientific glassblowing commonly involves fusing together various glass parts—such as glass joints and tubing, stopcocks, transition pieces, and/or other glassware or parts of them to form items of glassware, such as vacuum manifolds, special reaction flasks, etc.

Various types of joints and stopcocks are available separately and come fused with a length of glass tubing, which a glassblower may use to fuse to another piece of glassware.

[edit] Service temperatures

Borosilicate glass, which makes up the majority of lab glass, may fracture if rapidly heated or cooled through a 150 °C (302 °F) temperature gradient. This is particularly true of large volume flasks, that can take hours to safely warm up. Gentle thermal cycling should be used when working with volumes more than hundreds of mls to two liters. Whenever working with borosilicate glass, it is advisable to avoid sharp transitions between temperatures when the heating and cooling elements have a high thermal inertia. Glassware can be wrapped with tinfoil or insulated with wool to smooth out temperature gradients.

500 °C (932 °F) is the maximum service temperature for borosilicate glass as, at 510 °C (950 °F), thermal strain begins to appear in the structures. Operation at this temperature should be avoided and only intermittent. Bear in mind that glassware under vacuum will also have around one atmosphere of pressure on its surface before heating and so will be more likely to fracture as temperature transitions increase. Vacuum operation should be used if the atmospheric temperatures required are above a few hundred degrees Celsius, as this often has a dramatic effect on boiling points; significantly lowering them.

Borosilicate anneals at 560 °C (1,040 °F), this removes built in stain in the glass.

At 820 °C (1,510 °F), borosilicate glass softens and is likely to deform. And at 1,215 °C (2,219 °F) it becomes workable.

Quartz glass is far more resilient to thermal shock and can be operated continuously at 1,000 °C (1,830 °F). Thermal strain appears at 1,120 °C (2,050 °F), annealing occurs at 1,215 °C (2,219 °F) and it becomes workable at 1,685 °C (3,065 °F).

It is common for students and those new to working with glassware to set hotplates to a high value initially to rapidly warm a solution or solid. This is not only bad practice, as it can scorch the contents, it will almost universally burst large flasks, and this is one of the reasons why large flasks are often heated in water, oil, sand and steam baths or using a mantle that surrounds most, or all, of the flask.

[edit] Lubrication and sealing

A thin layer of grease is usually applied to the ground-glass surfaces to be connected, and the inner joint is inserted into the outer joint such that the ground-glass surfaces of each are next to each other to make the connection. The use of grease helps to provide a good seal and prevents the joint from seizing, allowing the parts to be disassembled easily.[2]

Grease can be washed out of tapers by the flow of solvents past them. Reagents may react with the grease or it may leak from the tapers at higher temperatures. The latter is prone to occurring when the system is under vacuum. Grease leaking from tapers can, of coarse, contaminate an operation either passively or by actively reacting with something passing by. For these reasons, it is advisable to apply a light ring of grease at the fat end of the taper and not its tip, to keep the material away from insides of the glassware. If the grease smears over the entire taper surface on mating, too much is being used. Using greases specifically designed for this purpose is also a good idea, as these are often better at sealing under vacuum, thicker and so less likely to flow out of the taper, become fluidic at higher temperatures than Vaseline (a common substitute) and are more chemically inert than other substitutes.

Grease allows chemists to easily see when a taper is leaking, as bubbles can usually be seen flowing through the taper.

When contamination is a serious concern, PTFE (Teflon) sleeves and PTFE sealing rings can be used in between joints to fit them together instead of grease.[3] PTFE tape can also be used, but requires a little care when winding onto the joint to ensure a good seal is produced.

Keck clips and other clamping methods can be used to hold glassware together.

[edit] Safety when using vacuums and Keck clips

An ultimate vacuum produces a pressure of one atmosphere, approximately 14 psi, over the surface of the glass. The energy contained within an implosion is defined by the pressure difference and the volume evacuated. As most vacuum chemistry occurs with at least 90% of the atmosphere removed, the pressure difference is often negligible between laboratories; a typical diphragm pump, aspirator or rotary vane pump will remove this level of atmosphere. However, flaks volumes can change by orders of magnitude between experiments. Whenever working with liter sized or larger flasks, chemists should consider using a safety screen or the sash of a flow hood to protect them from shards of glass, should an implosion occur. Glassware can also be wrapped with spirals of tape to catch shards, or wrapped with webbed mesh more commonly seen on scuba cylinders.

Glass under vacuum becomes more sensitive to chips and scratches in its surface, as these form strain accumulation points, so older glass is best avoided if possible. Impacts to the glass and thermally induced strain are also concerns under vacuum.

Round bottom flasks more effectively spread the strain across their surfaces, and are therefore safer when working under vacuum. For the majority of work below a liter, the difference in flask form has little influence on its safety under vacuum; Erlenmeyer flasks can be used.

When connecting glassware, it is often tempting to use Keck clips on every joint, but this can be dangerous if the system is sealed or the exhaust is in anyway restricted; e.g. by wash flasks or drying media. Many reactions and forms of operation can produce sudden, unexpected surges of pressure inside the glass. If the system is sealed or restricted, this can blow the glass apart. It is safer to only clip the joints that need holding together to stop them falling apart and to purposefully leave one or more unclipped; preferably those that are connected to lightweight, small objects like stoppers, thermometers or wash heads, that are pointing vertically upwards and not connected to other items of glassware. By doing so, any significant surge of pressure will cause these specifically chosen tapers to open and vent. This may seem counterintuitive, but it is safer and easier to deal with a controlled escape as opposed to the entire volume being uncontrollably released in an explosion.

[edit] Gentle & even heating - baths & alternatives

This is a prerequisite for a lot of laboratory work as it protects the work itself and decreases the possibility of thermal strain fracturing the glass; see service temperatures for more information on this.

A common method is to fill a bowl surrounding the flask with water, oil, sand or steam, or to use a wrap around heating mantle.

However, baths can be extremely dangerous if they spill, overheat or ignite, they have a high thermal inertia (and so take a long time to cool down) and mantles can be very expensive and are designed for specific flask volumes. There are two alternative methods that can be used instead, where appropriate.

When a heat sources minimum temperature is high, the glassware can be suspended slightly above the surface of the plate. This will not only reduce the ultimate temperature on the glass, it will slow down the rate of heat exchange and encourage more even heating; as there is no longer direct contact via a few points with the plate. Doing so works well for low boiling point operations.

If the glassware must be run at higher temperatures, a teepee setup can be used; so named as it looks a little like a tipi. This is when the glassware is suspended above the plate, but the flask is surrounded by a skirt of tinfoil. The skirt should start at the neck of the flask and drape down to the surface of the plate, not touching the sides of the flask. Having the base of the skirt cover the majority of the plates surface will effect better heat transfer. The flask will now be warmed indirectly by the hot air collecting under the skirt but, unlike simply suspending the glassware, it can now reach hundreds of degrees Celsius and is better protected from drafts.

Both these methods are useful as they are either cheaper or free, effective, safe and feature low thermal inertia transfer methods, meaning the chemist does not have to wait for a bath to cool down after use.

Baths are most useful when the heat source has little or no control over it. With the advent of variable temperature hotplates and wrap around mantles, their necessity has somewhat declined. The same can be said for many round bottom flask operations, which require the use of a bath.

[edit] Glassware Joints

[edit] Ground glass joints

Main article: Ground glass joint

In a lab experiment or process—such as a distillation or a reflux—ground glass joints make it possible to rapidly assemble the set-up from component glassware items in a leak-tight but non-permanent way. Using old technology, this was often done with rubber (or possibly cork) stoppers inserted between the component glassware items. Holes could be made in such stoppers to insert glass tubes or the ends of some glass items. However, rubber (and of course cork) are not as chemically inert or heat-resistant as glass and degrade with age. In order to connect the hollow inner spaces of the glassware components, these types of joints are hollow on the inside and open at the ends, except for stoppers.

Two general types of ground glass joints are fairly commonly used: joints that are slightly conically-tapered and ball and socket joints (sometimes called spherical joints).

Ground glassware should be disassembled as soon as it is safe to do so after a reaction, as this will help avoid the tapers seizing. Tapers will seize either from thermal activity or something from the reaction penetrating the taper and thickening upon cooling or exposure to the atmosphere. High concentrations of certain reactants can chemically seize a taper such that is essentially impossible to open. Exposure time plays a role in this occurring, and so should be minimized. PTFE sealing methods are also of use for such applications as they produce an intermediate layer between the glass that is highly inert and solid, meaning it can not be displaced and the glass can never come in contact with its mating taper.

[edit] Conically tapered joints

Conically tapered ground glass joints consist of a male and a female half[2] which are manufactured to a standard 1:10 taper. Apart from stoppers, most conically tapered joints are hollow to allow liquids or gases to flow through. An example of the use of conically-tapered joints is to join a round bottom flask, Liebig condenser, and oil bubbler together to allow a reaction mixture to be refluxed.

Conically tapered ground glass joints. Inner (male) joint shown on the left and outer (female) joint shown on the right. Ground glass surfaces are shown with gray shading. By putting them together in the direction of the arrows, they can be joined, usually with some grease applied to the ground glass surfaces.

[edit] Ball-and-socket joints

Here, the inner joint is a ball and the outer joint is a socket, both having holes leading to the interior of their respective tube ends to which they are fused. Ball and socket joints are used where some degree of free-play is necessary, such as when joining a cold trap to a gas manifold for a Schlenk line.[2]

Ground glass ball (left) and socket (right) joints. The ground glass surfaces are shown with gray shading. By putting them together in the direction of the arrows, they can be joined, with some grease applied to the ground glass surfaces.

For either standard taper joints or ball-and-socket joints, inner and outer joints with the same numbers are made to fit together. When the joint sizes are different, ground glass adapters may be available (or made) to place in between to connect them. Special clips or pinch clamps, known as Keck clips, may be placed around the union of the joints to help keep them together.

Grease is used to lubricate glass stopcocks and joints. Some laboratories fill them into syringes for easy application. Two typical examples: Left - Krytox, a fluoroether-based grease; Right - a silicone-based high vacuum grease by Dow Corning.

[edit] O-ring joints

There are also glass joints available sometimes which use an O-ring between them to form a leak-tight seal.[2] Such joints are more symmetrical in theory with a tubular joint on each side having a widened tip with a concentric circular groove into which an elastomer O-ring can be inserted between the two joints. O-ring joints are sized based on the inner diameter in mm of the joint. Since they can come apart rather easily, a clip or pinch clamp is needed to hold them together. The elastomer of the O-ring is more limited in high temperature resistance than other types of glass joints using high temperature grease.

Glass O-ring joints with elastomer O-ring in between. By putting them together in the direction of the arrows with an appropriately-sized O-ring placed in between in circular grooves on each joint (not shown on the joint on the left side for simplicity), they can be joined.

[edit] Threaded connections

Round slightly spiral threaded connections are possible on tubular ends of glass items. Such glass threading can face the inside or the outside. In use, glass threading is screwed into or onto non-glass threaded material such as plastic. Glass vials typically have outer threaded glass openings onto which caps can be screwed on. Bottles and jars in which chemicals are sold, transported, and stored usually have threaded openings facing the outside and matching non-glass caps or lids.

[edit] Glass-to-metal transition joints

Occasionally, it may be desired to fuse a glassware item to a metal item with a tubular pathway between them. This requires the use of a glass-to-metal transition joint. Most glass used in laboratory glassware does not have the same coefficient of thermal expansion as metal, so fusing the usual type of glass with metal is likely to result in cracking of the glass. These special transition joints have several short sections of special types of glass fused together between the metal and the usual type of glass, each having more gradual changes in thermal expansion coefficients.

[edit] Hose connections

Laboratory glassware, such as Buchner flasks and Liebig condensers, may have tubular glass tips serving as hose connectors with several ridged hose barbs around the diameter near the tip. This is so that the tips can have the end of a rubber or plastic tube mounted over them to connect the glassware to another system such as a vacuum, water supply, or drain. A special clip may be

placed over the end of the flexible tube surrounding the connector tip to prevent the hose from slipping off the connector.

A number of brands, including Quickfit, have begun using threaded connections for hose barbs. This allows the barb to be unscrewed from the glassware, the hose pushed on and the setup screwed back together. This helps avoid accidentally breaking the glass and potentially doing serious harm to the chemist, as will sometimes occur when pushing the hoses directly onto the glass.

[edit] Glassware Valves

A very common straight bore glass stopcock attached with a plastic plug retainer. This stopcock is in the side arm of a Schlenk flask.

Describing glassware can be complicated since manufactures provide conflicting names for glassware. For example ChemGlass calls a glass stopcock what Kontes calls a glass plug. Despite this it is clear there are two main types of valves used in laboratory glassware, the stopcock valve and the threaded plug valve. These and other terms used below are defined in detail since they are bound to conflict with different sources.

[edit] Stopcock valve

Stopcocks are often parts of laboratory glassware such as burettes, separatory funnels, Schlenk flasks, and columns used for column chromatography. The stopcock is a smooth tampered plug or rotor with a handle, which fits into a corresponding ground glass female joint. The stationary female joint is designed such that it joins two or more pieces of glass tubing. The stopcock has holes bored through it which allow the tubes attached to the female joint to be connected or separated with partial turns of the stopcock. Most stopcocks are solid pieces with linear bores although some are hollow with holes to simple holes that can line up the joints tubing. The stopcock is held together with the female joint with a metal spring, plastic plug retainer, a washer and nut system, or in some cases vacuum. Stopcocks plugs are generally made out of ground

glass or an inert plastic like PTFE. The ground glass stopcocks are greased to create an airtight seal and prevent the glass from fusing. The plastic stopcocks are at most lightly oiled.

Stopcocks are generally available individually with some length of glass tubing at the ports so that they can be joined by a glass blower into custom apparatus at the point of use. This is especially common for the large glass manifolds used in high vacuum lines.

More examples are featured in the gallery. This is a small sampling of stopcock valves; many additional variations exist in both plug boring and joint assembly.

[edit] Threaded plug valve

A standard solid threaded plug valve with a double o-ring upper seal and PTFE to glass seal at it base.

Threaded plug valves are used significantly in air-sensitive chemistry as well as when a vessel must be closed completely as in the case of Schlenk bombs. The construction of a threaded plug valve involves a plug with a threaded cap which are made so that they fit with the threading on a corresponding pieces of female glass. Screwing the plug in part way first engages one or more o-rings, made of rubber or plastic, near the plugs base which seals the female joint off from the outer atmosphere. Screwing the plug valve all the way in engages the plugs tip with a beveled constriction in the glass which provides a second seal. This seal separates the region beyond the bevel and the o-rings already mentioned.

With solid plugs a tube or area exists above and below the bevel and turning the plug controls access. In a number of cases its convent to fully remove a plug which can give access to the region beyond the bevel. Plugs are generally made of an inert plastic such as PTFE with and are attached to a threaded sleeve in such a way that the sleeve can been turned without spinning the plug. The contact with the bevel is made by an o-ring fitted to the tip of the plug or by the plug itself. There are a few examples where the plug in made of glass. In the case of glass plugs the joint contact is always a rubber o-ring but are still prone to shattering.

A thread T-bore plug valve used as a side arm on a Schlenk flask.

Not all plugs are solid. Some plugs are bored with a T-junction. In these systems the plug extends beyond the threaded sleeve and is designed to form an airtight fitting with glass tubing or hosing. The shaft of the plug is bored from beyond the threaded sleeve to a T-junction just before the bevel plug contact. When the plug is fully sealed region beyond the bevel is separated from the plug shaft as well as the bore which leads out of its shaft. When the plug bevel contact is released the two regions are exposed to each other. These valves have also be used as a grease free alternative to straight bored stopcocks common to Schlenk flasks. The high symmetry and concise design of these valves has also made them popular for capping NMR tubes. Such NMR tubes can be heated without the loss of solvent thanks to the valve's gas tight seal. NMR tubes with T-bore plugs are widely known as J. Young NMR tubes named after the brand name of valves most commonly used for this purpose. Images of J. Young NMR tubes and a J. Young NMR tube adapter are in the gallery.

[edit] Fritted glass

A Büchner funnel with a sintered glass disc

Fritted glass is finely porous glass through which gas or liquid may pass. It is made by sintering together glass particles into a solid but porous body.[4] This porous glass body can be called a frit. Applications in laboratory glassware include use in fritted glass filter items, scrubbers, or spargers. Other laboratory applications of fritted glass include packing in chromatography columns and resin beds for special chemical synthesis.

In a fritted glass filter, a disc or pane of fritted glass is used to filter out solid particles, precipitate, or residue from a fluid, similar to a piece of filter paper. The fluid can go through the pores in the fritted glass, but the frit will often stop a solid from going through. A fritted filter is often part of a glassware item, so fritted glass funnels and fritted glass crucibles are available.[5]

Gas-washing bottle

Laboratory scale spargers (also known as gas diffusing stones or diffusors) as well as scrubbers, and gas-washing bottles (or Drechsel bottles [6]) are similar glassware items which may use a fritted glass piece fused to the tip of a gas-inlet tube. This fritted glass tip is placed inside the vessel with liquid inside during use such that the fritted tip is submerged in the liquid. To maximize surface area contact of the gas to the liquid, a gas stream is slowly blown into the vessel through the fritted glass tip so that it breaks up the gas into many tiny bubbles. The purpose of sparging is to saturate the enclosed liquid with the gas, often to displace another gaseous component. The purpose of a scrubber or gas-washing bottle is to scrub the gas such that the liquid absorbs one (or more) of the gaseous components to remove it from the gas stream, effectively purifying the gas stream.

As frits are made up of particles of glass that are bonded together by small contact areas, it is wise to avoid using them in strongly alkaline conditions, as these can dissolve the glass to some extent. This is not normally a problem, as the amount dissolved is usually minute, but the equally minute bonds in a frit can be rotted away, causing the frit to fall apart over time. As such, consideration should be given to using frits in such solutions and they should be rapidly and thoroughly rinsed when cleaning the glass with bases like KOH.

[edit] Cleaning laboratory glassware

There are many different methods of cleaning laboratory glassware. Most of the time, these methods [7][8] are tried in this order:

The glassware is soaked in a detergent solution to remove grease and loosen most contamination

Gross contamination and large particles are removed mechanically, by scrubbing with a brush or scouring pad.

o Alternatively, the first two steps may be combined by sonicating the glassware in a hot detergent solution

Solvents known to dissolve the contamination are used to rinse the glassware and remove the last traces

Acetone is often used for a final rinse of sensitive or urgently needed glassware as the solvent is miscible with water and forms a low boiling point azeotrope with it, encouraging the remaining aqueous phase to leave more rapidly and thoroughly; this is particularly important if the following work is moisture sensitive.

Glassware is often dried by suspending it upside down to drip dry on racks; these can include a hot air fan to blow the internals dry. Another alternative is to place the glassware under vacuum, lower the boiling points of the remaining volatiles.

If the glassware are still dirty, more drastic methods may be needed. This includes soaking the piece in a saturated solution of sodium or potassium hydroxide in an alcohol ("base bath"),[8] followed by a dilute solution of hydrochloric acid ("acid bath") to neutralize the excess base. Sodium hydroxide cleans glass by dissolving a tiny layer of silica, to give soluble silicates. Care should be taken using strongly alkaline solutions to clean fritted glassware, as this will degrade the frit over time.

More aggressive methods involving aqua regia (for removing metals from frits), piranha solution and chromic acid (for removing organics), and hydrofluoric acid baths are generally considered unsafe for routine use because of possible explosions and the corrosive/toxic materials involved.[8]

[edit] Gallery

A straight bore plastic stopcock sans female joint. Note its washer and nut system for attaching to its female joint.

A T-bore glass stopcock in a three way assembly. Two of the outlets end in plain hose adapters while the third ends in a male 14/20 ground glass joint. This stopcock is attached with an easily removed metal spring.

A double oblique bore glass three-way stopcock.

A single hole hollow glass stopcock held in place by vacuum.

A J. Young NMR tube attached to an adapter with a female 24/40 joint already greased. Note the hole resulting from the T-bore in the side of the PTFE plug.

A J. Young NMR tube from above looking down the hole that leads to the T-bore.

A Taper Joint Stopper with PTFE Sealing Ring. Optical transparency of the narrow sealing ring pressured by glass joint (right).

Factory glassFrom Wikipedia, the free encyclopediaJump to: navigation, search

A term used by collectors of Art glass to distinguish relevant items from the more individual or unique Studio glass and by studio glass artists to distinguish their work from the more standardised items which are generally made in larger glassworks. [1]

It's difficult to specify how large a glassworks would be before it's considered a factory but size is not the key indicator. The crucial distinction would be where there is a significant degree of specialisation or "division of labour" as opposed to the more hands-on working methods used by a single glass artist, with perhaps an assistant, in a studio.

Contents

[hide]

1 Exceptions o 1.1 Factory "Studio" Glass"

2 Standardised Production 3 Other Types of Glass made in Factories 4 See also 5 References and external links

[edit] Exceptions

Not all glass made in factories counts because more individual, limited edition or one-off pieces were made for a variety of reasons. Examples would include; experimental, "end-of-day" and apprentice pieces and "friggers" (test or trial pieces) but also special orders and one-off commissions.

[edit] Factory "Studio" Glass"

At Fenton, Dave Fetty, a factory glass worker for most of his career, was allowed to use specialist skills, learned before joining the factory, in limited editions of "offhand" pieces without the use of moulds.[2] Such pieces are more akin to Studio glass than "Factory Glass".

In the United Kingdom, Whitefriars and Caithness, have produced limited production "studio" lines alongside standard production in the same factory. At the ZBS glassworks in Czechoslovakia, there was a separate department for making more experimental studio type pieces which was later hived off and came to be called Libera. The small Skrdlovice works was used by designers in the communist era to test out their designs with short runs before some went

on to full production at other factories. The limited test items are much more prized by collectors but it's often difficult to be sure which ones these are and which ones were replicated in full production runs elsewhere.

[edit] Standardised Production

While, the exceptions would generally account for a very small proportion of overall production, the term applies, strictly speaking, only to the production which was standardised, where many workers would be involved in the making of each item.

[edit] Other Types of Glass made in Factories

The many other types of glass which are generally made in factories are usually referred to by their individual names; for example; Float glass (for windows) and "Glass Packaging" (bottles, jars and containers) and domestic Glassware.

Pressed glassFrom Wikipedia, the free encyclopediaJump to: navigation, search

Pressed glass standing dish in a cottage in Lund, Sweden

Pressed glass is a form of glass made using a plunger to press molten glass into mold. It was first patented by American inventor John P. Bakewell in 1825 to make knobs for furniture.

The technique was developed in the United States from the 1820s and in Europe, particularly France, Bohemia, and Sweden from the 1830s. By the mid-19th century most inexpensive mass-produced glassware was pressed. One type of pressed glass is carnival glass.

The method is also used to make beads.

Pressed glass beads

Glass tubeFrom Wikipedia, the free encyclopediaJump to: navigation, search

Glass tubes or glass tubing are hollow pieces of borosilicate used in laboratory glassware. They are commercially available in various thicknesses and lengths, according to unknown standards. Tubes are generally made from flint (clear) glass.

Glass tubes cannot be cut with scissors but by scoring with a diamond cutter, and bending, giving a break with a clean edge. The ends are preferably flame polished before use to remove the edge. Hose barbs can be added to give a better grip and seal when used with rubber tubing. Glass tubes can be bent by heating to red heat in a non-luminous Bunsen flame. The glass tubes are fitted to rubber bungs by drilled holes.

In the past, scientists constructed their own laboratory apparatus prior to the ubiquity of interchangeable ground glass joints. Today, commercially available parts connected by ground glass joints are preferred; where specialized glassware are required, they are made to measure using commercially available glass tubes by specialist glassblowers. For example, a Schlenk line is made of two large glass tubes, connected by stopcocks and smaller glass tubes, which are further connected to plastic hoses.

Laboratory equipment Glassware Beaker · Büchner funnel · Burette · Cold finger · Condenser · Conical measure · Cuvette · Dropping funnel · Eudiometer · Gas syringe · Graduated cylinder · Pipette · Petri dish · Pycnometer · Separatory funnel · Soxhlet extractor · Watch glass

FlasksBüchner · Erlenmeyer · Fleaker · Florence · Retort · Round-bottom · Schlenk · Volumetric

Tubes

Boiling · NMR · Test · Thiele · Thistle

Other

Agar plate · Aspirator · Autoclave · Biosafety cabinet · Bunsen burner · Calorimeter · Chemostat · Colony counter · Colorimeter · Laboratory centrifuge · Crucible · Eyewash · Fire blanket · Fume hood · Glove box · Homogenizer · Hot air oven · Incubator · Laminar flow cabinet · Magnetic stirrer · Meker-Fisher burner · Microscope · Microtiter plate · Picotiter plate · Plate reader · Retort stand · Safety shower · Spectrophotometer · Static mixer · Stir bar · Stirring rod · Scoopula · Thermometer · Vortex mixer · Wash bottle

Glass-to-metal sealFrom Wikipedia, the free encyclopediaJump to: navigation, search

Uranium glass used as lead-in seals in a vacuum capacitor

Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass encapsulated semiconductor diodes, reed switches, pressure tight glass windows in metal cases, and metal or ceramic packages of electronic components.

Contents

[hide]

1 Mercury seal 2 Platinum wire seal 3 Dumet wire seal 4 Copper tube seal 5 Copper disc seal 6 Matched seal 7 Molybdenum foil seal 8 Compression seal 9 Design aspects 10 References 11 See also

[edit] Mercury seal

The first technological use of a glass-to-metal seal was the encapsulation of the vacuum in the barometer by Torricelli. The liquid mercury wets the glass and thus provides for a vacuum tight

seal. Liquid mercury was also used to seal the metal leads of early mercury arc lamps into the fused silica bulbs.

[edit] Platinum wire seal

The next step was to use thin platinum wire. Platinum is easily wetted by glass and has a similar coefficient of thermal expansion as typical soda-lime and lead glass. It is also easy to work with because of its non-oxidibility and high melting point. This type of seal was used in scientific equipment throughout the 19th century and also in the early incandescent lamps and radio tubes.

[edit] Dumet wire seal

In 1911 the Dumet-wire seal was invented which is still the common practice to seal copper leads through soda-lime or lead glass. If copper is properly oxidised before it is wetted by molten glass a vacuum tight seal of good mechanical strength can be obtained. Simple copper wire is not usable because its coefficient of thermal expansion is much higher than that of the glass. Thus, on cooling a strong tensile force acts on the glass-to-metal interface and it breaks. Glass and glass-to-metal interfaces are especially sensitive to tensile stress. The Dumet-wire is a copper wire with a core of an iron-nickel alloy with a low coefficient of thermal expansion. This way it is possible to make a wire with a coefficient of radial thermal expansion which is slightly lower than the linear coefficient of thermal expansion of the glass, so that the glass-to-metal interface is under a low compression stress. About 27% of the volume of the wire is copper. It is not possible to adjust the axial thermal expansion of the wire as well. Because of the much higher mechanical strength of the iron/nickel-core compared to the copper, the axial thermal expansion of the Dumet-wire is about the same as of the core. Thus, a shear stress builds up which is limited to a safe value by the low tensile strength of the copper. This is also the reason why Dumet is only useful for wire diameters lower than about 0.5 mm. In a typical Dumet seal through the base of a vacuum tube a short piece of Dumet-wire is butt welded to a nickel wire at one end and a copper wire at the other end. When the base is pressed of lead glass the Dumet-wire and a short part of the nickel and the copper wire are enclosed in the glass. Then the nickel wire and the glass around the Dumet-wire are heated by a gas flame and the glass seals to the Dumet-wire. The nickel and copper do not seal vacuum tight to the glass but are mechanically supported. The butt welding also avoids problems with gas-leakages at the interface between the core wire and the copper.

[edit] Copper tube seal

Another possibility to avoid a strong tensile stress when sealing copper through glass is the use of a thin walled copper tube instead of a solid wire. Here a shear stress builds up in the glass-to-metal interface which is limited by the low tensile strength of the copper combined with a low tensile stress. The copper tube is insensitive to high electrical current compared to a Dumet-seal because on heating the tensile stress converts into a compression stress which is again limited by the tensile strength of the copper. Also, it is possible to lead an additional solid copper wire through the copper tube. In a later variant, only a short section of the copper tube has a thin wall and the copper tube is hindered to shrink at cooling by a ceramic tube inside the copper tube.

If large parts of copper are to be fitted to glass like the water cooled copper anode of a high power radio transmitter tube or an x-ray tube historically the Houskeeper (not Housekeeper!) knife edge seal is used. Here the end of a copper tube is machined to a sharp knife edge, invented by O. Kruh in 1917. In the method described by W.G. Houskeeper the outside or the inside of the copper tube right to the knife edge is wetted with glass and connected to the glass tube.[1] In later descriptions the knife edge is just wetted several millimeters deep with glass, usually deeper on the inside, and then connected to the glass tube.

If copper is sealed to glass, it is an advantage to get a thin bright red Cu2O containing layer between copper and glass. This is done by borating. After W.J. Scott a copper plated tungsten wire is immersed for about 30 s in chromic acid and then washed thoroughly in running tap water. Then it is dipped into a saturated solution of borax and heated to bright red heat in the oxidizing part of a gas flame. Possibly followed by quenching in water and drying. Another method is to oxidize the copper slightly in a gas flame and then to dip it into borax solution and let it dry. The surface of the borated copper is black when hot and turns to dark wine red on cooling.

It is also possible to make a bright seal between copper and glass where it is possible to see the blank copper surface through the glass, but this gives less adherence than the seal with the red Cu2O containing layer. If glass is melted on copper in a reducing hydrogen atmosphere the seal is extremely weak. If copper is to be heated in hydrogen-containing atmosphere e.g. a gas flame it needs to be oxygen-free to prevent hydrogen embrittlement. Copper which is ment to be used as an electrical conductor is not necessarily oxygen-free and contains particles of Cu2O which react with hydrogen that diffuses into the copper to H2O which cannot diffuse out-off the copper and thus causes embrittlement. The copper usually used in vacuum applications is of the very pure OFHC (oxygen-free-high-conductivity) quality which is both free of Cu2O and deoxidising additives which might evaporate at high temperature in vacuum.

[edit] Copper disc seal

In the copper disc seal, as proposed by W.G. Houskeeper, the end of a glass tube is closed by a round copper disk. An additional ring of glass on the opposite side of the disc increases the possible thickness of the disk to more than 0.3 mm. Best mechanical strength is obtained if both sides of the disk are fused to the same type of glass tube and both tubes are under vacuum. The disk seal is of special practical interest because it is a simple method to make a seal to low expansion borosilicate glass without the need of special tools or materials. The keys to success are proper borating, heating of the joint to a temperature as close to the melting point of the copper as possible and to slow down the cooling, at least by packing the assembly into glass wool while it is still red hot.

[edit] Matched seal

In a matched seal the thermal expansion of metal and glass is matched. Copper-plated tungsten wire can be used to seal through borosilicate glass with a low coefficient of thermal expansion which is matched by tungsten. The tungsten is electrolytically copper plated and heated in

hydrogen atmosphere to fill cracks in the tungsten and to get a proper surface to easily seal to glass. The borosilicate glass of usual laboratory glassware has a lower coefficient of thermal expansion than tungsten, thus it is necessary to use an intermediate sealing glass to get a stress-free seal.

There are combinations of glass and iron-nickel-cobalt alloys (Kovar) where even the non-linearity of the thermal expansion is matched. These alloys can be directly sealed to glass, but then the oxidation is critical. Also, their low electrical conductivity is a disadvantage. Thus, they are often gold plated. It is also possible to use silver plating, but then an additional gold layer is necessary as an oxygen diffusion barrier to prevent the formation of iron oxide.

While there are Fe-Ni alloys which match the thermal expansion of tungsten at room temperature, they are not useful to seal to glass because of a too strong increase of their thermal expansion at higher temperatures.

Reed switches use a matched seal between an iron-nickel alloy (NiFe 52) and a matched glass. The glass of reed switches is usually green due to its iron content because the sealing of reed switches is done by heating with infrared radiation and this glass shows a high absorption in the near infrared.

The electrical connections of high-pressure sodium vapour lamps, the yellow lamps for street lighting, are made of niobium alloyed with 1% of zirconium.[2]

Historically, some television cathode ray tubes were made by using ferritic steel for the funnel and glass matched in expansion to ferritic steel. The steel plate used had a diffusion layer enriched with chromium at the surface made by heating the steel together with chromium oxide in a HCl-containing atmosphere. In contrast to copper, pure iron does not bond strongly to silicate glass. Also, technical iron contains some carbon which forms bubbles of CO when it is sealed to glass under oxidizing conditions. Both are a major source of problems for the technical enamel coating of steel and makes direct seals between iron and glass unsuitable for high vacuum applications. The oxide layer formed on chromium-containing steel can seal vacuum tight to glass and the chromium strongly reacts with carbon. Silver-plated iron was used in early microwave tubes.

It is possible to make matched seals between copper or austenitic steel and glass, but silicate glass with that high thermal expansion is especially fragile and has a low chemical durability.

[edit] Molybdenum foil seal

Another widely used method to seal through glass with low coefficient of thermal expansion is the use of stripes of thin molybdenum foil. This can be done with matched coefficients of thermal expansion or unmatched after Houskeeper. Then the edges of the strip also have to be knife sharp. The disadvantage here is that the tip of the edge which is a local point of high tensile stress reaches through the wall of the glass container. This can lead to low gas leakages. In the tube to tube knife edge seal the edge is either outside, inside, or buried into the glass wall.

[edit] Compression seal

Another possibility of seal construction is the compression seal. This type of glass-to-metal seal can be used to feed through the wall of a metal container. Here the wire is usually matched to the glass which is inside of the bore of a strong metal part with higher coefficient of thermal expansion.

[edit] Design aspects

Also the mechanical design of a glass-to-metal seal has an important influence on the reliability of the seal. In practical glass-to-metal seals cracks usually start at the edge of the interface between glass and metal either inside or outside the glass container. If the metal and the surrounding glass are symmetric the crack propagates in an angle away from the axis. So, if the glass envelope of the metal wire extends far enough from the wall of the container the crack will not go through the wall of the container but it will reach the surface on the same side where it started and the seal will not leak despite the crack.

Another important aspect is the wetting of the metal by the glass. If the thermal expansion of the metal is higher than the thermal expansion of the glass like with the Houskeeper seal, a high contact angle (bad wetting) means that there is a high tensile stress in the surface of the glass near the metal. Such seals usually break inside the glass and leave a thin cover of glass on the metal. If the contact angle is low (good wetting) the surface of the glass is everywhere under compression stress like an enamel coating. Ordinary soda-lime glass does not flow on copper at temperatures below the melting point of the copper and, thus, does not give a low contact angle. The solution is to cover the copper with a solder glass which has a low melting point and does flow on copper and then to press the soft soda-lime glass onto the copper. The solder glass must have a coefficient of thermal expansion which is equal or a little lower than that of the soda-lime glass. Classically high lead containing glasses are used, but it is also possible to substitute these by multi-component glasses e.g. based on the system Li2O-Na2O-K2O-CaO-SiO2-B2O3-ZnO-TiO2-BaO-Al2O3.

Disadvantages

Uses lamps for light, lamps need to be replaced on average once every year and a half to two years[citation needed]. Current models with LED lamps reduce or eliminate this. Estimated lifetime of LED lamps is over 100,000 hours.

Fixed number of pixels, other resolutions need to be scaled to fit this. This is a limitation only when compared with CRT displays.

The Rainbow Effect: This is an unwanted visual artifact that is described as flashes of colored light seen when the viewer looks across the display from one side to the other. This artifact is unique to single-chip DLP projectors. The Rainbow Effect is significant only in DLP displays that use a single white lamp with a "color wheel" that is synchronized with the display of red, green and blue components. LED illumination systems that use discrete red, green and blue LEDs in concert with the display of red, green and blue components at high frequency reduce, or altogether eliminate, the Rainbow effect.

Disadvantages

The Screen-door effect: Individual pixels may be visible on the large screen, giving the appearance that the viewer is looking through a screen door.

Possibility of defective pixels Poor black level: Some light passes through even when liquid crystals completely untwist, so the

best black color that can be achieved is a very dark gray, resulting in worse contrast ratios and detail in the image. Some newer models use an adjustable iris to help offset this.

Not as slim as DLP projection television Uses lamps for light, lamps may need to be replaced Fixed number of pixels, other resolutions need to be scaled to fit this Limited viewing angles

Disadvantages

Heavy and large, especially depth-wise If one CRT fails the other two should be replaced as well to maintain color and brightness

balance Susceptible to burn-in because CRT is phosphor-based Needs to be 'converged' about every year Has focus problems