SURAM MOHAN KUMAR, (PhD) 3
Assistant Professor, Dept. of ME, AVNIET, Hyderabad, India
All engineering disciplines need to know about materials. Even the most immaterial like
software or system engineering depend on the development of new materials, which in turn alter
the economics, like software-hardware trade-offs. Increasing applications of system engineering
are in materials manufacturing (industrial engineering) and complex environmental systems.
Classification of Materials
Like many other things, materials are classified in groups, so that our brain can handle the
complexity. One could classify them according to structure, or properties, or use. The one that
we will use is according to the way the atoms are bound together:
Metals: The valence electrons are detached from atoms, and spread in an 'electron sea' that
"glues" the ions together. Metals are usually strong, conduct electricity and heat well and are
opaque to light (shiny if polished). Examples: aluminum, steel, brass, gold.
Semiconductors: The bonding is covalent (electrons are shared between atoms). Their electrical
properties depend extremely strongly on minute proportions of contaminants. They are opaque to
visible light but transparent to the infrared. Examples: Si, Ge, GaAs.
Ceramics: Atoms behave mostly like either positive or negative ions, and are bound by
Coulomb forces between them. They are usually combinations of metals or semiconductors with
oxygen, nitrogen or carbon (oxides, nitrides, and carbides).Examples: glass, porcelain, many
Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually
based on H, C and other non-metallic elements. They decompose at moderate temperatures (100
– 400 C), and are lightweight. Other properties vary greatly. Examples: plastics (nylon, teflon,
polyester) and rubber. Other categories are not based on bonding. A particular microstructure