ABSTRACT
Ceramics can cover natural as well as artificial materials, e.g. minerals, rocks, cement gels and glasses, as well as sintered clays which give us our traditional ceramics. The basic ceramic material usually degrades slowly, and is a long-lived component, whereas the fixing mechanisms are often highly stressed and, if corrosion occurs, failure is dramatic. Increases in the strength of ceramic materials can be achieved by minimizing glassy regions, through which crack propagation is dramatic, and also by manipulating the size and structure of crystals. Rounded cracks then lead to a tear out of material, the rounded micro cracks transform in to shallow tips and the degradation is progressive. In ceramics there are two systems of bonding, covalent and ionic. Covalent bonding is by far the strongest of all chemical bonds, involving the pairing of electrons shared between two atoms. A great deal of the bonding occurring in compounds is intermediate in nature between the two pure bonding types.
