Question

Why are ceramics brittle? Can your answer also explain polymer behavior below its glass transition temperature? Why or why not?

Answer 1

Brittleness of Ceramics:

Most of the ceramics are brittle. This is due to the mixed ionic-covalent bonding that holds the constituent atoms together. At the high (or above glass transition) temperature, the ceramics behaves as a viscous liquid and not in the brittle manner. And hence it is easy to form glass into different shapes at elevated temperatures. So most of the ceramics are brittle at room temperature, but not necessarily at elevated temperatures.

Polymer behavoir below glass transition temperature:

Glass transition temperature is a temperature at which ductile-brittle transision of material ocurs. different glass transition temperatures of different polymers allow the polymer to be better suited for applications than others.

Below glass transition temperature, the polymer becomes hard, brittle. The material behavior for time scales corresponding to the temperature below glass transition state gives an impression of being glassy. Below Tg, the deformation of material is primarily elastic and the behavior is categorized as glassy. The total deformation is low and is completely recovered after removal of the load. This behavior show little or no binder or lubricant capability. The material has stronger tendancy to fracture than to deform.