Various types of point defects are: 1. Vacancy 2. Interstitialcy 3. Frenkel Defect 4. Impurity Atoms. A point defect is a very localised disruption in the regularity of a lattice. It is a defect of dimensions just like a point (zero dimensions). The size of the defect could be one atom, or two atomic diameters, which is just like a [...]
Vacancies have been seen to be thermodynamically stable in crystalline solids above 0°K, and that their number increase exponentially with the increase of temperature, as illustrated in Fig. 4.8 for aluminium. To understand this, the usual concept of Gibbs free energy for metal-system is used. In a perfect crystal, all lattice sites are occupied by atoms so that no vacancies [...]
The following points highlight the three main surface defects in crystals. The types are: 1. Free Surfaces 2. Grain Boundaries 3. Stacking Faults. Surface defects are defects of two dimensional nature in the mathematical sense (that is, they have two dimensions). These are areas of distortions that lie about a surface, having a thickness of a few atomic diameters (that [...]
Pores, voids and blow holes are defects in solid castings. Voids can be regarded as an agglomeration of vacancies. Pores are discontinuities or holes in solid parts. Such defects normally form during freezing due to one or combination of both the factors: (i) Evolution of dissolved gas at the solid-liquid interface. (ii) Decrease in volume that occurs during freezing in [...]