JNTU B.Tech III NON-METALLIC MATERIALS Previous Question Paper (August - 2022 - R18)

Metallic materials are substances characterized by high electrical and thermal conductivity, luster, ductility, and malleability, resulting from the presence of delocalized electrons in a metallic lattice. Common examples include iron, copper, aluminum, and gold. Non-metallic materials are substances that lack these metallic properties; they are generally poor conductors of heat and electricity, often brittle in solid form, and include ceramics, polymers, and composites. Examples include plastics, glass, wood, and rubber.

Polymerization is a chemical process in which small molecules called monomers react together to form long, chain-like structures known as polymers. The mechanism typically follows three distinct stages: initiation, propagation, and termination.

1. Initiation: An initiator molecule decomposes to create a reactive species (usually a free radical) that attacks the double bond of a monomer, creating an active center.
2. Propagation: The active monomer reacts with subsequent monomers, extending the chain length rapidly as the reactive site transfers to the end of the growing chain.
3. Termination: The process ends when two growing chains collide and combine, or react with an impurity, neutralizing the active sites and stopping further growth.

A common example is the addition polymerization of ethylene (monomer) to form polyethylene (polymer), where the double bond in ethylene opens to allow covalent bonding between repeating units.