ABSTRACT
Ceramics and refractories are inherently brittle materials. The reason for this behavior is that the bonding in them is predominantly ionic or predominantly covalent. For plastic deformation, which is required for ductile fracture, there should be dislocation movement. In ionic compounds, formation of dislocation itself is difcult, because, for neutrality of the material, a pair of dislocations should simultaneously form. One should carry negative charge, and the other, positive. This is a difcult thing. If at all a dislocation forms, it requires simultaneous movement of the oppositely charged dislocations. This is still more difcult. In the case of covalent bonds, they are directional and strong. There is no question of any line defect, such as a dislocation, forming. Therefore, any question of dislocation movement does not arise. Ceramic and refractory materials fail by the sudden fracture of their atomic or ionic bonds. Hence, the failure of ceramic and refractory materials can be discussed in terms of the failure of brittle materials. In other words, the theory of brittle materials’ fracture can be applied to ceramics and refractories.
