Definitions of Material Types

• Metals are malleable and ductile, with high electrical and thermal conductivity. Examples include iron, aluminium, and gold.
• Ceramics are generally hard, strong in compression, weak in shearing and tension, and resistant to heat and harsh chemical environments. Examples include brick, glass, and porcelain.
• Polymers are usually flexible, lightweight, and have a wide range of thermal and electrical conductivities. They can be found in many everyday items such as plastics and rubber.
• Composites are a combination of two or more constituent materials with significantly different physical or chemical properties. Examples include fibreglass and carbon fibre composites.

Characteristics of Material Types

• Metals exhibit metallic bonding, leading to tightly packed atomic structures that allow electrons to move freely, resulting in high conductivity.
• Ceramics are generally composed of ionic and covalent bonds, leading to a crystalline structure of tightly packed atoms, yielding properties like brittleness and heat resistance.
• Polymers are made up of long chains of repeating molecular units. These chains can be arranged in various ways, resulting in different properties for the material.
• Composites have a blend of properties from the different constituent materials, making them tailored for specific applications by combining the strengths and mitigating the weaknesses of the constituent materials.

Common Uses of Material Types

• Metals are widely used in construction (steel for buildings), transport (aluminium for aeroplane bodies), and in electrical wiring due to their high conductivities.
• Ceramics are often used in kitchenware (pottery), in electronics (as insulators), and in buildings (bricks, tiles).
• Polymers, due to their flexibility and light weight, are commonly used in packaging (plastics), clothing (polyester), and technology devices (insulation on wires).
• Composites find application in aircraft and spacecraft (carbon fibre composites), sports equipment (carbon fibre tennis rackets), and in vehicles (glass-reinforced plastic body panels).

Factors Affecting Material Selection

• Cost is a crucial factor in material selection, with metals generally costing more than polymers and composites.
• The function of the item to be made will heavily influence material choice, as each material type has characteristics that lend themselves to different uses.
• Availability of materials can also affect selection decisions. Rare and hard-to-source materials may be unsuitable for mass production.
• Environmental considerations, such as energy consumption during production and disposal, also influence material selection. For example, the production of new polymers consumes more non-renewable resources and produces more waste compared to recycling existing polymers.