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 ST EST AST

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. ST EST AST

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 tree 2. The speed of growth 3. The water content of the wood Other properties of wood that may influence the choice of this material include: 1. Aesthetic appeal 2. Hardness, elasticity, resilience, and toughness 3. Low thermal and electrical conductivity 4. Ease with which it can be worked 5. Its colours 6. Its lightness relative to its strength ST EST AST

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. ST EST AST

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. ST EST AST

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. ST EST AST

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. ST EST AST

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 ST EST AST

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. ST EST AST

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. ST EST AST

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 ST EST AST

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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 ST EST AST

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 ST EST AST

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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 ST EST AST

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 ST EST AST

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. ST EST AST

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. ST EST AST

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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. ST EST AST

Checkup Workbook  Pg ST EST AST