Question

a) Describe the glass transition temperature of polymers and ceramics

b) Compare and contrast the rules that underly the formation of crystalline structures in ceramics and polymers

Answer 1

a) Glass Transition Temperature (Tg) is one of the most important properties of a polymer and is the temperature region where thepolymer transitions from a hard, glassy material to a soft, rubbery material.

In the case of Ceramics glass transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state.

b) Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories – either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, and then sintering to form a solid body.

Crystallization of polymers is a process associated with partial alignment of their molecular chains. Polymers can crystallize upon cooling from the melt, mechanical stretching or solvent evaporation. The fraction of the ordered molecules in polymer is characterized by the degree of crystallinity, which typically ranges between 10% and 80%.Higher values are only achieved in materials having small molecules, which are usually brittle,