A material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified based on their physical and chemical properties, or on their geological origin or biological function. Materials science is the study of materials and their applications.
Raw materials can be processed in different ways to influence their properties, by purification, shaping or the introduction of other materials. New materials can be produced from raw materials by synthesis.
Classification by use
Materials can be broadly categorised in terms of their use, for example:
- Building materials are used for construction
- Building insulation materials are used to retain heat within buildings
- Refractory materials are used for high-temperature applications
- Nuclear materials are used for nuclear power and weapons
- Aerospace materials are used in aircraft and other aerospace applications
- Biomaterials are used for applications interacting with living systems
Material selection is a process to determine which material should be used for a given application.
Classification by structure
In engineering, materials can be categorised according to their microscopic structure::15–17
- Ceramics: non-metal, inorganic solids
- Glasses: amorphous solids
- Metals: pure or combined chemical elements with specific chemical bonding behavior
- Polymers: materials based on long carbon or silicon chains
- Hybrids: combinations of multiple materials, for example composites.
Classification by properties
Materials can be compared and classified by their large-scale physical properties.
Mechanical properties determine how a material responds to applied forces.
Materials may degrade or undergo changes of properties at different temperatures. Thermal properties also include the material's thermal conductivity and heat capacity, relating to the transfer and storage of thermal energy by the material.
Materials can be compared and categorised by any quantitative measure of their behavior under various conditions. Notable additional properties include the optical, electrical and magnetic behavior of materials.:5–7
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