MS – Module I
Classification of Materials Three basic groups of solid engineering materials based on atomic bonds and structures: * Metals * Ceramics * Polymers Classification can also be done based on either properties (mechanical, electrical, optical), areas of applications (structures, machines, devices). Further we can subdivide these groups. According to the present engineering needs: Composites, Semiconductors, Biomaterials
Metals * Characteristics are owed to non-localized electrons (metallic bond between atoms) i.e. electrons are not bound to a particular atom. * They are characterized by their high thermal and electrical conductivities. * They are opaque, can be polished to high lustre. The opacity and reflectivity of a metal arise from the response of the unbound electrons to electromagnetic vibrations at light frequencies. * Relatively heavier, strong, yet deformable. E.g.: Steel, Aluminium, Brass, Bronze, Lead, Titanium, etc.
Ceramics * They contain both metallic and nonmetallic elements. * Characterized by their higher resistance to high temperatures and harsh environments than metals and polymers. * Typically good insulators to passage of both heat and electricity. * Less dense than most metals and alloys. * They are harder and stiffer, but brittle in nature. * They are mostly oxides, nitrides, and carbides of metals. * Wide range: traditional (clay, silicate glass, cement) to advanced (carbides, pure oxides, non-silicate glasses). E.g.: Glass, Porcelain, Minerals, etc.