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Sulfuric acid

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Sulfuric acid/ Sulphuric acid

IUPAC name[hide]

Sulfuric acid

Other names[hide]

Oil of vitriol

Identifiers

CAS number 7664-93-9

ChemSpider 1086

UNII O40UQP6WCF

EC number 231-639-5


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UN number 1830

KEGG D05963

ChEMBL CHEMBL572964

RTECS number WS5600000

Jmol-3D images Image 1

SMILES

[show]

InChI

[show]

Properties

Molecular formula H2SO4

Molar mass 98.079 g/mol

Appearance Clear, colorless, odorless liquid

Density 1.84 g/cm3, liquid

Melting point 10 C, 283 K, 50 F

Boiling point 337 C, 610 K, 639 F

Solubility in water miscible

Acidity (pKa) 3, 1.99

Viscosity 26.7 cP (20 C)

Hazards

MSDS

External MSDS

EU Index 016-020-00-8

EU classification

Toxic (T)

Corrosive (C)

Dangerous for the environment (N)

R-phrases R35


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S-phrases (S1/2)S26S30S45

NFPA 704

032W

Flash point Non-flammable

Related compounds

Related strong acids

Selenic acid

Hydrochloric acid

Nitric acid

Related compounds

Sulfurous acid

Peroxymonosulfuric acid

Sulfur trioxide

Oleum

Supplementary data page

Structure and

properties n, r, etc.

Thermodynamic

data

Phase behaviour

Solid, liquid, gas

Spectral data UV, IR,NMR, MS

(what is this?) (verify)

Except where noted otherwise, data are given for materials in

theirstandard state (at 25 C, 100 kPa)

Infobox references

Sulfuric acid (alternative spellingsulphuric acid) is a strongmineral acid with themolecular formula H2SO4. Its historical name is vitriol. The salts of sulfuric acid are called

sulfates. Sulfuric acid is soluble in waterat all concentrations.

Sulfuric acid has many applications, and is a central substance in thechemical industry.Principal uses include lead-acid batteries for cars and other vehicles, ore processing, fertilizermanufacturing, oil refining, wastewater processing, and chemical synthesis.


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[edit] History

This section's factual accuracy is disputed. Please help to ensure that disputedfacts are reliably sourced. See the relevant discussion on the talk page. (November2009)

John Dalton's 1808 sulfuric acid molecule shows a central sulfur atom bonded to threeoxygen atoms.

The study of vitriol began in ancient times. Sumerians had a list of types of vitriol that theyclassified according to substance's color. Some of the earliest discussions on the origin and

properties of vitriol are in the works of the Greek physicianDioscorides (first century AD)and the Roman naturalist Pliny the Elder(2379 AD). Galen also discussed its medical use.

Metallurgical uses for vitriolic substances were recorded in the Hellenistic alchemical worksofZosimos of Panopolis, in the treatisePhisica et Mystica, and the "Leyden Papyrus x".[1]

Arab alchemists like Jabir Ibn Hayyan (c. 721 c. 815 AD), Al-Razi (865 925 AD), and

Jamal Din al-Watwat (d. 1318, wrote the bookMabhij al-fikar wa-manhij al-'ibar),included vitriol in their mineral classification lists. Ibn Sina focused on its medical uses and

different varieties of vitriol.[1]

Sulfuric acid was called "oil of vitriol" by medieval European alchemists. There are mentionsto it in the works ofVincent of Beauvais and in the Compositum de Compositis ascribed toAlbertus Magnus. A passage from Pseudo-Gebers Summa Perfectionis was long consideredto be the first recipe for sulphuric acid, but this was a misinterpretation.

[1]

In the 17th century, the German-Dutch chemist Johann Glauberprepared sulfuric acid byburning sulfur together with saltpeter(potassium nitrate, KNO3), in the presence of steam. As

saltpeter decomposes, it oxidizes the sulfur to SO3, which combines with water to producesulfuric acid. In 1736, Joshua Ward, a London pharmacist, used this method to begin the first

large-scale production of sulfuric acid.

In 1746 in Birmingham, John Roebuckadapted this method to produce sulfuric acid in lead-

lined chambers, which were stronger, less expensive, and could be made larger than thepreviously used glass containers. This lead chamber process allowed the effectiveindustrialization of sulfuric acid production. After several refinements, this method remainedthe standard for sulfuric acid production for almost two centuries.

Sulfuric acid created by John Roebuck's process only approached a 3540%concentration.[citation needed] Later refinements to the lead-chamber process by French chemistJoseph-Louis Gay-Lussac and British chemist John Glover improved the yield to 78%.[citationneeded]

However, the manufacture of some dyes and other chemical processes require a more


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concent ted product

cit

ti

Throughoutthe 18th century, thi could only be made bydry di tilling mineral in a techni ue similarto the originalalchemical processes. Pyrite (iron

disul ide, FeS2) was heated in airto yield iron (II) sul ate, FeSO4, which was oxidi ed byfurther heating in airto form iron(III) sulfate, Fe2(SO4)3, which, when heated to 480 C,

decomposed to iron(III) oxide and sulfurtrioxide, which could be passed through watertoyield sulfuric acid in any concentration. However, the expense ofthis process prevented the

large-scale use of concentrated sulfuric acid.

In 1831, British vinegarmerchant Peregrine Phillips patented the contact process, which wasa far more economical process for producing sulfurtrioxide and concentrated sulfuric acid.Today, nearly all ofthe world's sulfuric acid is produced using this method.

[edi i l erties

[edit] Grades of sulfuri acid

Although nearly 99% sulfuric acid can be made, this loses SO3 atthe boiling pointto produce

98.3% acid. The 98% grade is more stable in storage, and is the usual form of whatisdescribed as "concentrated sulfuric acid." Other concentrations are used for different

purposes. Some common concentrations are:2][3]

Mass fraction

H2SO4

Density

(kg/L)

Concentration

(mol/L)Common name

10% 1.07 ~1 dilute sulfuric acid

2932% 1.251.28 4.25battery acid(used in leadacid batteries)

6270% 1.521.60 9.611.5chamber aci

ertilizer aci

7880% 1.701.73 13.514 t

wer aci

Gl er aci

9598% 1.83 ~18 concentrated sulfuric acid

"Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced bythe lead chamber process, chamber acid being the acid produced in lead chamberitself(


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Pure sulfuric acid is a viscous clear liquid, like oil, and this explains the old name of the acid('oil of vitriol').

Commercial sulfuric acid is sold in several different purity grades. Technical grade H2SO4 isimpure and often colored, but is suitable for making fertilizer. Pure grades such as UnitedStates Pharmacopoeia (USP) grade are used for makingpharmaceuticals and dyestuffs.

Analytical grades are also available.

[edit] Polarity and conductivity

Anhydrous H2SO4 is a verypolarliquid, having a dielectric constant of around 100. It has ahigh electrical conductivity, caused by dissociation throughprotonating itself, a processknown as autoprotolysis.[4]

2 H2SO4 H3SO+4 + HSO4

The equilibrium constant for the autoprotolysis is[4]

Kap(25C)= [H3SO+4][HSO4] = 2.7104.

The comparable equilibrium constant forwater, Kw is 1014

, a factor of 1010

(10 billion)smaller.

In spite of the viscosity of the acid, the effective conductivities of the H3SO+4

and HSO

4 ions are high due to an intra-molecular proton-switch mechanism (analogous to theGrotthuss mechanism in water), making sulfuric acid a good conductor. It is also an excellentsolvent for many reactions.

The equilibrium is actually more complex than shown above; 100% H2SO4 contains thefollowing species at equilibrium (figures shown as millimoles per kilogram of solvent):HSO4 (15.0), H3SO+4 (11.3), H3O

+(8.0), HS2O

7 (4.4), H2S2O7 (3.6), H2O (0.1).[4]

[edit] Chemical properties

[edit] Reaction with water

The hydration reaction of sulfuric acid is highly exothermic. One should always add the acidto the waterrather than the water to the acid. Because the reaction is in an equilibrium thatfavors the rapid protonation of water, addition of acid to the water ensures that the acidis thelimiting reagent. This reaction is best thought of as the formation ofhydronium ions:


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H2SO4 + H2O H3O+

+ HSO4

K1 = 2.4 x 106

(strong acid)HSO4

+ H2O H3O+ + SO4

2 K2 = 1.0 x 10-2 [5]

HSO4-is the bisulfateanion and SO4

2-is thesulfate anion. K1 and K2 are the acid dissociationconstants. Because the hydration of sulfuric acid is thermodynamically favorable, sulfuricacid is an excellent dehydrating agent, and is used to prepare many dried fruits. The affinity

of sulfuric acid forwateris sufficiently strong thatit will remove hydrogen and oxygen atomsfrom other compounds; for example, mixing starch (C6H12O6)n and concentrated sulfuric acidwill give elementalcarbon and water which is absorbed by the sulfuric acid (which becomesslightly diluted):

(C6H12O6)n 6nC + 6n H2O

The effect ofthis can be seen when concentrated sulfuric acid is spilled on paper; thecellulose reacts to give aburnt appearance, the carbon appears much as soot would in a fire.

A more dramatic reaction occurs when sulfuric acid is added to a tablespoon of white sugarinabeaker; a rigid column of black, porous carbon will quickly emerge. The carbon will smell

strongly ofcaramel due to the heat generated. Although less dramatic, the action ofthe acid

on cotton, even in diluted form, will destroy the fabric.

[edit] Other reactions

As an acid, sulfuric acid reacts with mostbasesto give the corresponding sulfate. For

example, the blue coppersaltcopper(II) sulfate, commonly used forelectroplating and as afungicide, is prepared by the reaction ofcopper(II) oxide with sulfuric acid:

CuO (s) + H2SO4 (aq) CuSO4 (aq) + H2O (l)

Sulfuric acid can also be used to displace weaker acids from their salts. Reaction with sodium

acetate, for example, displaces acetic acid, CH3COOH, and forms sodium bisulfate:

H2SO4 + CH3COONa NaHSO4 + CH3COOH

Similarly, reacting sulfuric acid withpotassium nitrate can be used to produce nitric acid anda precipitate ofpotassium bisulfate. When combined with nitric acid, sulfuric acid acts bothas an acid and a dehydrating agent, forming the nitroniumion NO+2, which is importantin nitration reactions involving electrophilic aromatic substitution. Thistype of reaction, where protonation occurs on an oxygen atom, is importantin many organicchemistry reactions, such as Fischer esterification and dehydration of alcohols.

Concentrated sulfuric acid reacts with sodium chloride, and gives hydrogen chloridegas and

sodium bisulfate:

NaCl + H2SO4 NaHSO4 + HCl

Concentrated sulfuric acid also dehydrates sugar, leaving a porous blackcarbon mass behind.Sulfuric acid does nottake partin this reaction, butitdecomposesthe sugar. During thisreaction heatis produced and water vaporis given off. Reaction is as follows:

C12H22O11 12C + 11H2O


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Sulfuric acid reacts with most metals via a single displacement reaction to produce hydrogengas and the metal sulfate. Dilute H2SO4 attacks iron, aluminium, zinc, manganese,magnesium and nickel, but reactions with tin and copperrequire the acid to be hot andconcentrated. Lead and tungsten, however, are resistant to sulfuric acid. The reaction with

iron shown below is typical for most of these metals, but the reaction with tin produces sulfurdioxide rather than hydrogen.

Fe (s) + H2SO4 (aq) H2 (g) + FeSO4 (aq)Sn (s) + 2 H2SO4 (aq) SnSO4 (aq) + 2 H2O (l) + SO2 (g)

These reactions may be taken as typical: the hot concentrated acid generally acts as anoxidizing agent whereas the dilute acid acts a typical acid. Hence hot concentrated acid reactswith tin, zinc and copper to produce the salt, water and sulfur dioxide, whereas the dilute acidreacts with metals high in the reactivity series (such as Zn) to produce a salt and hydrogen.This is explained more fully in 'A New Certificate Chemistry' by Holderness and Lambert.

Benzene undergoes electrophilic aromatic substitution with sulfuric acid to give thecorresponding sulfonic acids:[6]

[edit] Occurrence

Pure sulfuric acid is not encountered naturally on Earth, due to its greataffinity for water.

Apart from that, sulfuric acid is a constituent ofacid rain, which is formed by atmosphericoxidation ofsulfur dioxide in the presence ofwater i.e., oxidation ofsulfurous acid. Sulfurdioxide is the main byproduct produced when sulfur-containing fuels such as coal or oil are

burned.

Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as iron sulfide.The resulting water can be highly acidic and is calledacid mine drainage (AMD) or acid rockdrainage (ARD). This acidic water is capable of dissolving metals present in sulfide ores,which results in brightly colored, toxic streams. The oxidation ofpyrite (iron sulfide) bymolecular oxygen produces iron(II), or Fe

2+:

2 FeS2 (s) + 7 O2 + 2 H2O 2 Fe

2+

(aq) + 4 SO2

4 (aq) + 4 H+

The Fe2+

can be further oxidized to Fe3+

:

4 Fe2+

+ O2 + 4 H+

4 Fe3+

+ 2 H2O

The Fe3+ produced can be precipitated as thehydroxide orhydrous oxide:


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Fe3+

(aq) + 3 H2O Fe(OH)3 (s) + 3 H+

The iron(III) ion ("ferric iron") can also oxidi e pyrite:

FeS2 (s) + 14 Fe3+

+ 8 H2O 15 Fe2+

(aq) + 2 SO24 (aq) + 16 H

+

When iron(III) oxidation of pyrite occurs, the process can become rapid.pH values belowzero have been measured in ARD produced by this process.

ARD can also produce sulfuric acid at a slower rate, so thatthe acid neutralizing capacity(ANC) ofthe aquifer can neutralize the produced acid. In such cases, the total dissolvedsolids (TDS) concentration ofthe water can be increased from the dissolution of mineralsfrom the acid-neutralization reaction with the minerals.

[edit] Extraterrestrial sulfuric acid

[edit] Venus

Sulfuric acid is produced in the upper atmosphere ofVenus by the Sun'sphotochemical

action on carbon dioxide, sulfur dioxide, and watervapor. Ultravioletphotons of wavelengthsless than 169 nm canphotodissociate carbon dioxide into carbon monoxide and atomicoxygen. Atomic oxygen is highly reactive. When it reacts with sulfur dioxide, a tracecomponent ofthe Venusian atmosphere, the resultis sulfurtrioxide, which can combine withwater vapor, anothertrace component of Venus's atmosphere, to yield sulfuric acid. In theupper, cooler portions of Venus's atmosphere, sulfuric acid exists as a liquid, and thicksulfuric acid clouds completely obscure the planet's surface when viewed from above. Themain cloud layer extends from 4570 km above the planet's surface, with thinner hazesextending as low as 30 km and as high as 90 km above the surface. The permanent Venusian

clouds produce a concentrated acid rain, as the clouds in the atmosphere of Earth producewater rain.

The atmosphere exhibits a sulfuric acid cycle. As sulfuric acid rain droplets fall downthrough the hotterlayers ofthe atmosphere's temperature gradient, they are heated up andrelease water vapor, becoming more and more concentrated. When they reach temperaturesabove 300C, sulfuric acid begins to decompose into sulfurtrioxide and water, both in the gas

phase. Sulfurtrioxide is highly reactive and dissociates into sulfur dioxide and atomicoxygen, which oxidizes traces of carbon monoxide to form carbon dioxide. Sulfur dioxideand water vapor rise on convection currents from the mid-level atmospheric layers to higheraltitudes, where they will be transformed again into sulfuric acid, and the cycle repeats.

[edit] Europa

Infrared spectra fromNASA's Galileo mission show distinct absorptions on Jupiter's moonEuropathat have been attributed to one or more sulfuric acid hydrates. Sulfuric acid insolution with water causes significantfreezing-point depression of water's melting point,down to 210 K (63 C), and this would make more likely the existence ofliquid solutions

beneath Europa's icy crust.The interpretation ofthe spectra is somewhat controversial. Someplanetary scientists preferto assign the spectral features to the sulfate ion, perhaps as part of

one or more minerals on Europa's surface.[7]


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[edit] Manufacture

Main articles: Contactprocess andWetsulfuric acid process

Sulfuric acid is produced from sulfur, oxygen and water via the conventionalcontact process

(DCDA

) orthe wet sulfuric acid process (WSA

).

[edit] Contact process (DCDA)

In the first step, sulfuris burned to produce sulfur dioxide.

S (s) + O2 (g) SO2 (g)

This is then oxidized to sulfurtrioxide using oxygen in the presence of a vanadium(V) oxidecatalyst.

2 SO2 (g) + O2 (g) 2 SO3 (g) (in presence of V2O5)

The sulfurtrioxide is absorbed into 9798% H2SO4to form oleum (H2S2O7), also known asfuming sulfuric acid. The oleum is then diluted with waterto form concentrated sulfuric acid.

H2SO4 (l) + SO3 H2S2O7 (l)H2S2O7 (l) + H2O (l) 2 H2SO4 (l)

Note that directly dissolving SO3in wateris not practical due to the highly exothermic natureofthe reaction between sulfurtrioxide and water. The reaction forms a corrosive aerosolthatis very difficultto separate, instead of a liquid.

SO3 (g) + H2O (l) H2SO4 (l)

[edit] Wet sulfuric acid process (WSA)

In the first step, sulfuris burned to produce sulfur dioxide:

S(s) + O2(g) SO2(g)

or, alternatively, hydrogen sulfide (H2S) gas is incinerated to SO2 gas:

2 H2S + 3 O2 2 H2O + 2 SO2 (518 kJ/mol)

This is then oxidized to sulfurtrioxide using oxygen with vanadium(V) oxide as catalyst.

2 SO2 + O2 2 SO3 (99 kJ/mol)(this is actually a reversible reaction)

The sulfurtrioxide is hydrated into sulfuric acid H2SO4:

SO3 + H2O H2SO4(g) (101 kJ/mol)


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The last step is the condensation of the sulfuric acid to liquid 9798% H2SO4:

H2SO4(g) H2SO4(l) (69 kJ/mol)

[edit] Other methods

Another method is the less well-known metabisulfite method, in which metabisulfite isplaced at the bottom of a beaker, and 12.6 molar concentration hydrochloric acid is added.The resulting gas is bubbled through nitric acid, which will release brown/red vapors. Thecompletion of the reaction is indicated by the ceasing of the fumes. This method does not

produce an inseparable mist, which is quite convenient.

Sulfuric acid can be produced in the laboratory by burning sulfur in air and dissolving the gas

produced in a hydrogen peroxide solution.

SO2 + H2O2 H2SO4

Prior to 1900, most sulfuric acid was manufactured by the chamber process.[8]

As late as1940, up to 50% of sulfuric acid manufactured in the United States was produced by chamber

process plants.

[edit] Uses

Sulfuric acid production in 2000

Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acidproduction is a good indicator of its industrial strength.[9] World production in 2001 was 165million tons, with an approximate value of US$8 billion. The major use (60% of total

production worldwide) for sulfuric acid is in the "wet method" for the production ofphosphoric acid, used for manufacture ofphosphatefertilizers as well as trisodium phosphatefor detergents. In this method, phosphate rock is used, and more than 100 million tonnes are

processed annually. This raw material is shown below as fluorapatite, though the exactcomposition may vary. This is treated with 93% sulfuric acid to producecalcium sulfate,hydrogen fluoride (HF) andphosphoric acid. The HF is removed as hydrofluoric acid. The

overall process can be represented as:

Ca5F(PO4)3 + 5 H2SO4 + 10 H2O 5 CaSO42 H2O + HF + 3 H3PO4

Sulfuric acid is used in large quantities by the iron and steelmaking industry to removeoxidation, rust and scale from rolled sheet and billets prior to sale to theautomobile andwhite goods (appliances) industry. Used acid is often recycled using a Spent AcidRegeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas,fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide (SO2)


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and sulfurtrioxide (SO3) which are then used to manufacture "new" sulfuric acid. SARplantsare common additions to metal smelting plants, oil refineries, and otherindustries where

sulfuric acid is consumed in bulk, as operating a SARplantis much cheaperthan therecurring costs of spent acid disposal and new acid purchases.

Ammonium sulfate, an important nitrogen fertilizer, is most commonly produced as a

byproduct from coking plants supplying the iron and steel making plants. Reacting theammonia produced in the thermal decomposition ofcoal with waste sulfuric acid allows theammonia to be crystallized out as a salt (often brown because ofiron contamination) and soldinto the agro-chemicals industry.

Anotherimportant use for sulfuric acid is forthe manufacture ofaluminum sulfate, alsoknown as paper maker's alum. This can react with small amounts of soap onpaper pulp fibersto give gelatinous aluminum carboxylates, which help to coagulate the pulp fibers into a hard

paper surface. Itis also used for making aluminum hydroxide, which is used atwatertreatment plants to filteroutimpurities, as well as to improve the taste ofthe water.Aluminum sulfateis made by reactingbauxite with sulfuric acid:

Al2O3 + 3 H2SO4 Al2(SO4)3 + 3 H2O

Sulfuric acid is used for a variety of other purposes in the chemicalindustry. For example, itis the usual acid catalyst forthe conversion ofcyclohexanone oximeto caprolactam, used formaking nylon. Itis used for making hydrochloric acid from salt via the Mannheim process.Much H2SO4is used inpetroleum refining, for example as a catalyst forthe reaction ofisobutane with isobutyleneto give isooctane, a compound that raises the octane rating ofgasoline (petrol). Sulfuric acid is also importantin the manufacture ofdyestuffs solutions andis the "acid"in lead-acid (car) batteries.

Sulfuric acid is also used as a general dehydrating agentin its concentrated form. SeeReaction with water.

[edit] Sulfur-iodine cycle

The sulfur-iodine cycleis a series ofthermo-chemical processes used to obtain hydrogen. It

consists ofthree chemical reactions whose net reactantis waterand whose net products arehydrogen and oxygen.

2 H2SO4 2 SO2 + 2 H2O + O2 (830 C)

I2 + SO2 + 2 H2O 2 HI + H2SO4 (120 C)

2 HI I2 + H2 (320 C)

The sulfur and iodine compounds are recovered and reused, hence the consideration oftheprocess as a cycle. This process is endothermic and must occur at high temperatures, soenergy in the form of heat has to be supplied.

The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-basedeconomy. It does not require hydrocarbonslike current methods ofsteam reforming.


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The sulfur-iodine cycle is currently being researched as a feasible method of obtaininghydrogen, but the concentrated, corrosive acid at high temperatures poses currentlyinsurmountable safety hazards if the process were built on a large scale.

[edit] Safety

[edit] Laboratory hazards

Drops of 98% sulfuric acid char a piece of tissue paper instantly

The corrosive properties of sulfuric acid are accentuated by its highlyexothermic reactionwith water. Burns from sulfuric acid are potentially more serious than those of comparablestrong acids (e.g. hydrochloric acid), as there is additional tissue damage due to dehydrationand particularly secondary thermal damage due to the heat liberated by the reaction withwater.

The danger is greater with more concentrated preparations of sulfuric acid, but even the

normal laboratory "dilute" grade (approximately 1 M, 10%) will char paper by dehydration ifleft in contact for a sufficient time. Therefore, solutions equal to or stronger than 1.5M are

labeled "CORROSIVE", while solutions greater than 0.5 M but less than 1.5 M are labeled"IRRITANT". Fuming sulfuric acid (oleum) is not recommended for use in schools as it is

quite hazardous.

The standard first aid treatment for acid spills on the skin is, as for othercorrosive agents,irrigation with large quantities of water. Washing is continued for at least ten to fifteenminutes to cool the tissue surrounding the acid burn and to prevent secondary damage.Contaminated clothing is removed immediately and the underlying skin washed thoroughly.

Preparation of the diluted acid can also be dangerous due to the heat released inthe dilutionprocess. The concentrated acid is always added to water and not the other way around, to take

advantage of the relatively high heat capacity of water. Addition of water to concentratedsulfuric acid leads to the dispersal of a sulfuric acidaerosol or worse, an explosion.

Preparation of solutions greater than 6 M (35%) in concentration is most dangerous, as theheat produced may be sufficient to boil the diluted acid: efficient mechanical stirring and

external cooling (such as an ice bath) are essential.

On a laboratory scale, sulfuric acid can be diluted by pouring concentrated acid onto crushedice made from de-ionized water. The ice melts in an endothermic process while dissolving

the acid. The amount of heat needed to melt the ice in this process is greater than the amount


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of heat evolved by dissolving the acid so the solution remains cold. After allthe ice hasmelted, further dilution can take place using water.

[edit] Industrial hazards

Although sulfuric acid is non-flammable, contact with metals in the event of a spillage can

lead to the liberation ofhydrogen gas. The dispersal of acid aerosols and gaseous sulfurdioxide is an additional hazard of fires involving sulfuric acid.

Sulfuric acid is not considered toxic besides its obvious corrosive hazard, and the mainoccupational risks are skin contactleading to burns (see above) and the inhalation of aerosols.Exposure to aerosols at high concentrations leads to immediate and severe irritation oftheeyes, respiratory tract and mucous membranes:this ceases rapidly after exposure, althoughthere is a risk of subsequentpulmonary edemaiftissue damage has been more severe. Atlower concentrations, the most commonly reported symptom of chronic exposure to sulfuricacid aerosols is erosion ofthe teeth, found in virtually all studies:indications of possiblechronic damage to the respiratory tract are inconclusive as of 1997. In the United States, the

permissible exposure limit (PEL) for sulfuric acid is fixed at 1 mg/m:limits in othercountries are similar. There have been reports of sulfuric acid ingestion leading to vitaminB12 deficiency with subacute combined degeneration. The spinal cord is most often affectedin such cases, butthe optic nerves may show demyelination, loss ofaxons and gliosis.

[edit] Legal restrictions

International commerce of sulfuric acid is controlled underthe United Nations ConventionAgainst Illicit Traffic in Narcotic Drugs and Psychotropic Substances, 1988, which listssulfuric acid under Table II ofthe convention as a chemical frequently used in the illicitmanufacture of narcotic drugs or psychotropic substances.[10]

In the US sulfuric acid is included in List II ofthe list of essential or precursor chemicalsestablished pursuantto the Chemical Diversion and Trafficking Act. Accordingly,transactions of sulfuric acidsuch as sales, transfers, exports from and imports to the United

Statesare subjectto regulation and monitoring by the Drug EnforcementAdministration.

[11][12][13]

http://en.wikipedia.org/wiki/Sulfuric_acid

Alloy

From Wikipedia, the free encyclopedia

Jump to:navigation, searchThis article is aboutthe t pe ofmaterial. Forthe specification language, seeAlloy

(specification language). For alloyedwheels, see alloy wheel.


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Steel is a metal alloy whose major component is iron, with carbon content between 0.02%and 2.14% by mass.

An alloy is a metallicsolid solution composed of two or more elements. Complete solidsolution alloys give single solidphase microstructure, while partial solutions give two ormore phases that may or may not be homogeneous in distribution, depending on thermal(heat treatment) history. Alloys usually have different properties from those of the componentelements.

Alloy constituents are usually measured by mass.

Contents

[hide]

y 1 Theoryy 2 Terminologyy 3 Historyy 4 See alsoy 5 Referencesy 6 External links

[edit] Theory

Alloying a metal is done by combining it with one or more other metals or non-metals thatoften enhances its properties. For example,steel is stronger than iron, its primary element.The physical properties, such as density, reactivity, Young's modulus, and electrical andthermal conductivity, of an alloy may not differ greatly from those of its elements, butengineering properties such as tensile strength

[1]and shear strength may be substantially

different from those of the constituent materials. This is sometimes due to the sizes of theatoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, andsmaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation.


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Sometimes alloys may exhibit marked differences in behavior even when small amounts ofone element occur. For example, impurities in semi-conducting ferromagnetic alloys lead to

different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura.[2][3]

Some alloys are made by melting and mixing two or more metals. Bronze, an alloy ofcopper

and tin, was the first alloy discovered, during theprehistoric period now known as thebronzeage; it was harderthan pure copper and originally used to make tools and weapons, but was

later superseded by metals and alloys with better properties. In latertimes bronze has beenused forornaments,bells, statues, andbearings. Brassis an alloy made from copperand zinc.

Unlike pure metals, most alloys do not have a single melting point, but a melting range inwhich the materialis a mixture ofsolid and liquid phases. The temperature at which melting

begins is called the solidus, and the temperature when melting isjust complete is called theliquidus. However, for most alloys there is a particular proportion of constituents (in rarecases two)the eutectic mixturewhich gives the alloy a unique melting point.

[edit] Terminology

The term alloy is used to describe a mixture of atoms in which the primary constituentis ametal. The primary metalis called the base orthe matrix. Ifthere is a mixture of only twotypes of atoms, not counting impurities, such as a copper-nickel alloy, then itis called abinary alloy. Ifthere are three differenttypes of atoms forming the mixture, such as iron,nickel and chromium, then itis called a ternary alloy.An alloy with four constituents is aquaternary alloy, while a five-part alloy is termed a quinary alloy. Since the percentage ofeach constituent can be varied, with any mixture the entire range of possible variations iscalled asystem. In this respect, all ofthe various forms of an alloy containing only twoconstituents, like iron and carbon, is called a binary system, while all ofthe different alloycombinations possible with a ternary alloy, such as alloys ofiron, carbon and chromium, iscalled a ternary system.

[4]

When a molten metalis mixed with another substance, there are two different mechanismsthat can cause an alloy to form, called atom exchange and the interstitialmechanism. Therelative size of each atom in the mix plays a primary role in determining which mechanismwill occur. When the atoms are relatively similarin size, the atom exchange method usuallyhappens, where some ofthe atoms composing the metallic crystals are replaced with atoms of

the other constituent. With the interstitial mechanism, one atom is usually much smallerthanthe other, and so cannot successfully replace an atom in the crystals ofthe base metal. Thesmaller atoms become trapped in the spaces between the atoms in the crystal matrix, calledthe interstices.[5]

Alloys are often made in orderto alterthe mechanical properties ofthe base metal, to inducehardness, toughness, ductility, or other desired properties. While most metals and alloys can

be work hardened by inducing defects in their crystal structure, caused byplasticdeformation, some alloys can also have their properties altered by heattreatment. Nearly allmetals can be softened by annealing, which repairs the crystal defects, but not as many can behardened by controlled heating and cooling. Many alloys ofaluminum, copper, magnesium,titanium, and nickel can be strengthened to some degree by some method of heattreatment,

but few respond to this to the same degree thatsteel does.[5]


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At a certain temperature, the base metal of steel, iron, undergoes a change in the arrangementof the atoms in its crystal matrix, called allotropy. This allows the small carbon atoms to enterthe interstices of the crystal. When this happens, the carbon atoms are said to be insolution,or mixed with the iron. If the iron is cooled slowly, the carbon atoms will be forced out of

solution, into the spaces between the crystals. If the steel is cooled quickly, the carbon atomsbecome trapped in solution, causing the iron crystals to deform when the crystal structure

tries to change to its low temperature state, inducing great hardness.[5]

In practice, some alloys are used so predominantly with respect to their base metals that thename of the primary constituent is also used as the name of the alloy. For example, 14karatgold is an alloy of gold with other elements. Similarly, the silverused injewelry and thealuminium used as a structural building material are also alloys.

The term "alloy" is sometimes used in everyday speech as a synonym for a particular alloy.For example, automobile wheels made of an aluminium alloy are commonly referred to assimply "alloy wheels", although in point of fact steels and most other metals in practical useare also alloys.

[edit] History

This section requires expansion with:History of early intentional alloy use, History of science of modern metallurgical alloys.

A meteorite is shown below a hatchet that was forged from meteoric iron.

Bronze axe 1100 BC

The use of alloys by humans started with the use ofmeteoric iron, a naturally occurring alloyofnickel and iron. As no metallurgic processes were used to separate iron from nickel, thealloy was used as it was.[6] Meteoric iron could be forged from a red heat to make objectssuch as tools, weapons, and nails. In many cultures it was shaped by cold hammering intoknives and arrowheads. They were often used as anvils. Meteoric iron was very rare andvaluable, and difficult for ancient people to work.

[7]


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Iron is usually found as iron ore on Earth, except for one deposit of native iron in Greenland,which was used by the Inuit people. Native copper, however, was found worldwide, along

with silver, gold andplatinum, which were also used to make tools,jewelry, and other objectssince Neolithic times. Copper was the hardest ofthese metals, and the most widely

distributed. It became one ofthe mostimportant metals to the ancients. Eventually, humanslearned to smelt metals such as copper and tin from ore, and, around 2500 BC, began alloying

the two metals to formbronze, which is much harderthan its ingredients. Tin was rare,however, being found mostly in GreatBritain. In the Middle East, people began alloyingcopper with zincto formbrass.[8]Ancient civilizations made use ofthe information containedin modern alloy constitution diagrams, taking into accountthe mixture and the various

properties it produced, such as hardness, toughness and melting point, under variousconditions oftemperature and work hardening.

[9]

The first known smelting ofiron began in Anatolia, around 1800 BCCalled the bloomeryprocess, it produced very soft butductilewroughtiron and, by 800 BC, the technology hadspread to Europe. Pig iron, a very hard but brittle alloy ofiron and carbon, was being

produced in China as early as 1200 BC, but did not arrive in Europe untilthe Middle Ages.These metals found little practical use untilthe introduction ofcrucible steel around 300 BC.

These steels were of poor quality, and the introduction ofpattern welding, around the 1stcentury AD, soughtto balance the extreme properties ofthe alloys by laminating them, tocreate a tougher metal.

[9]

Mercury had been smelted from cinnabarforthousands of years. Mercury dissolves manymetals, such as gold, silver, and tin, to form amalgams, (an alloy in a soft paste, orliquidform at ambienttemperature). Amalgams have been used since 200 BCin China for platingobjects with precious metals, called gilding, such as armorand mirrors. The ancientRomansoften used mercury-tin amalgams for gilding their armor. The amalgam was applied as a

paste and then heated untilthe mercury vaporized, leaving the gold, silver, ortin behind.[10]

Mercury was often used in mining, to extract precious metals like gold and silver from theirores.

[11]

Many ancient civilizations alloyed metals for purely aesthetic purposes. In ancientEgypt andMycenae, gold was often alloyed with copperto produce red-gold, oriron to produce a bright

burgundy-gold. Silver was often found alloyed with gold. These metals were also used tostrengthen each other, for more practical purposes. Quite often, precious metals were alloyedwith less valuable substances as a means to deceive buyers.

[12]Around 250 BC, Archimedes

was commissioned by the king to find a way to checkthe purity ofthe gold in a crown,

leading to the famous bath-house shouting of"Eureka!" upon the discovery ofArchimedesprinciple.

[13]

While the use ofiron started to become more widespread around 1200 BC, mainly due to

interruptions in the trade routes fortin, the metalis much softerthan bronze. However, verysmall amounts ofsteel, (an alloy ofiron and around 1% carbon), was always a byproduct ofthe bloomery process. The ability to modify the hardness of steel by heattreatment had beenknown since 1100 BC, and the rare material was valued for use in tool and weapon making.Since the ancients could not produce temperatures high enough to fully meltiron, the

production of steelin decent quantities did not occur untilthe introduction ofblister steelduring the Middle Ages. This method introduced carbon by heating wroughtiron in charcoalforlong periods oftime, butthe penetration of carbon was not very deep, so the alloy was notvery homogenous. In 1740, Benjamin Huntsman began melting blister steelin a crucible to


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even outthe carbon content, creating the first process forthe mass production oftool steel.Huntsman's process was used for manufacturing tool steel untilthe early 1900s.[14]

With the introduction ofthe blast furnace to Europe in the Middle Ages, pig iron was able tobe produced in much higher volumes than wroughtiron. Since pig iron could be melted,people began to develop processes of reducing the carbon in the liquid pig iron in orderto

create steel. Puddling was introduced during the 1700s, where molten pig iron was stirredwhile exposed to the air, to remove the carbon by oxidation. In 1858, Sir Henry Bessemerdeveloped a process of steel making by blowing hot airthrough liquid pig iron to reduce thecarbon content. The Bessemer process was able to produce the firstlarge scale manufactureof steel.[14] Once the Bessemer process began to gain widespread use, other alloys of steel

began to follow, such as mangalloy, an alloy of steel and manganese, which exhibits extremehardness and toughness.[15]

Synthetic polymers:

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