The Technological World. 2.Categories of Materials and their Properties Let’s have a closer look at the following materials and their properties: 1. Wood.

The Technological World

2. Categories of Materials and their Properties Let’s have a closer look at the following

materials and their properties:1. Wood and Modified Wood

2. Ceramics

3. Metals and Alloys

4. Plastics

5. Composites

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2.1 Wood and Modified Wood Wood is a material obtained by harvesting

and processing trees. Hardwood comes from deciduous trees

such as maple, oak, and birch Softwood comes from coniferous trees

such as spruce, pine and fir.

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Solid Oak Furniture

Solid Oak Furniture

Maple Baseball Batt

Oak Flooring

Properties of Wood The mechanical properties depend on the type

of wood and vary due to:1. The species of tree2. The speed of growth3. The water content of the wood

Other properties of wood that may influence the choice of this material include:

1. Aesthetic appeal2. Hardness, elasticity, resilience, and toughness3. Low thermal and electrical conductivity4. Ease with which it can be worked5. Its colours6. Its lightness relative to its strength

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Modified Wood Modified wood is treated wood or wood

made from wood mixed with other substances.

Common products include plywood, particle board and fibreboard

These are sheets, chips, or fibres of wood that are glued together in sheets.

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Particle Board

Degradation and Protection of Wood Unprotected wood can degrade swiftly. Since wood is an organic substance, many fungi,

microorganisms, and insects can infest the wood, feed off it and cause it to rot.

Wood can be painted, stained, varnished or treated with other protective coatings to help prevent its deterioration.

Treated wood is made resistant to rot by: Dipping it in an alkaline solution containing copper. This

wood usually has a greenish colour. Heating it to a high temperature.

Some woods, such as cedar, have a natural resistance to rot.

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Treated wood

Cedar Docks and Decks

Ceramics

2.2 Ceramics A ceramic is a solid material obtained by

heating inorganic matter containing various compounds, usually oxides.

When the raw material is heated, the water evaporates, and the bonds between the constituent compounds are rearranged. A ceramic is always solid at room temperature.

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Traditionally, most ceramic objects were made out of clay and sand. Sand is used for making glass.

Although other materials are now used, clay and sand are still widely used as they are both plentiful and inexpensive.

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Properties of Ceramics The properties of ceramic objects vary with the

raw material and the method of baking. The following properties make ceramics a good

choice for many objects: Low electrical conductivity – used as insulators High degree of hardness – used as building materials

and cutting tools Heat resistance and low thermal conductivity – dishes

and cookware as well as thermal insulators Resistance to corrosion – used in ducts for fumes or

water Fragility – most are very fragile, but some can be

made so resilient they are used in engines

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Ceramics can be fragile

The Degradation and Protection of Ceramics Although ceramics are generally very durable,

some acids and bases can have a degrading effect on them

Archeologists have found ceramic pieces that are thousands of years old and are still in remarkably good condition.

Glazes can be used to protect the ceramics A thermal shock (a sudden change in

temperature) can cause damage to a ceramic object.

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2.3 Metals and Alloys A metal is a material extracted from a

mineral ore. Metals are usually shiny in appearance and are good conductors of heat and electricity.

The pure metal is rarely used. An alloy is a mixture of a metal with one

or more other substances, which may be metallic or nonmetallic. The mixture of materials results in more desirable properties.

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Metals and Alloys

Alloy Bike Frames

There are two main types of alloys:Ferrous alloys whose main component is

iron.Nonferrous alloys whose main component is

a metal other than iron

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The Degradation and Protection of Metals and Alloys

The main cause for metal and alloy degradation is oxidation, where the material reacts with oxygen. This is commonly referred to as rusting.

The material can be protected by coating it with a substance that isolates it from the oxygen in the air: Metallic coatings: zinc, chrome, gold, silver, nickel,

aluminum, lead Other coatings: paint, enamel, grease, resin

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Oxidation of Metals

Rustproofing

Techniques That Enhance the Properties of Metals and Alloys Steel heat treatments are methods of

enhancing certain mechanical properties of steel through periods of heating.

These methods include: Quench hardening – hardens the steel Tempering – hardens the steel Annealing – returns the original properties by

removing the stress created by deforming (welding) All of these methods work by rearranging the

crystals within the material

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Plastics

2.4 Plastics Plastics are made from fossil fuels

(petroleum and natural gas) Monomers are extracted from the fossil

fuels and are arranged into long chains called polymers.

Plastic is a material made of polymers, to which other substances may be added to obtain certain desirable properties.

The invention of plastics lead to a revolution in world of materials

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Types of Plastics A thermoplastic is a plastic that becomes soft

enough when heated to be molded or remolded and that hardens enough when cooled to hold its shape. Most plastic objects are made of this type. Most thermoplastics can be recycled

A thermosetting plastic is a plastic that remains permanently hard, even when heated. Often harder and more resilient than thermoplastics Include melamine and polyesters Cannot be recycled in Quebec

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The Degradation and Protection of Plastics

Plastics tend to degrade over time. This process is usually slow, but can be detected as cracks and changes in colour appear.

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Composites

2.5 Composites A composite is formed by combining materials

from different categories to obtain a material with enhanced properties.

A composite has two main parts: the matrix and the reinforcement.

The matrix is the body of the material. It surrounds and supports the reinforcement and gives the object its shape.

The reinforcement is inserted into the matrix to strengthen the object.

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Kevlar is a composite

The Degradation and Protection of Composites The degradation of composites usually

takes one of two forms:1. The deformation or fracture of the matrix or the

reinforcement.

2. The loss of adherence between the matrix and the reinforcement.

The speed of degradation depends on the type of matrix and reinforcement and the conditions of use.

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Checkup Workbook

Pg 201-208

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