Chemical Tempering of Glass

Surface defects are responsible for the limited glass resistance and its large scatter [6]. The creation of a compressive stress layer in the surface of the material can limit the formation or propagation of flaws and improve the mechanical properties thermal and chemical tempering of glass are two main methods for producing a compressive stress in the glass surface. The thermal method is widely used to make windows and other transparent flat structural components [2, 7],... 

Engineering judgment is also required in assessing the blast capacity of a glass-clad polycarbonate. Because in most cases the annealed, semi-tempered, or sodium-based chemically tempered glass does not contribute substantially to the blast load capacity of the cross section, it is conservative to base blast capacity upon the polycarbonate layers alone. 

Because of the transparency and chemical inertness of inorganic glasses, their uses in everyday life are ubiquitous. However, for many applications, especially where safety is concerned, as manufactured, glass is deemed to be too weak and brittle. Fortunately, glass can be significantly strengthened by a process referred to as thermal tempering, which introduces a state of compressive residual stresses on the surface (see Sec. 11.3.3). 

G. A. Chase, T.R. Kozlowski and R.P. Krause, Chemical strengthening of ophthalmic lenses, Am. J. Optom., 50 (1973) 470 and Suresh T. Gulati, Frangibility of Tempered Soda-Lime Glass Sheet, Proc. Glass Processing Days, Tampere, Finland 1997, p. 72,... 

The constant B is a dimensionless modiflcation factor accounting for free surface effects and stress gradients along the crack depth as the compressive surface stress diminishes into the bulk. For the depths of compressed zones encountered in toughened glass, B is approximately unity, but it must be emphasized that this is not true for chemically tempered glass where the stress profile is very steep. ... 

It would be unrealistic to expect that with present methods one can predict the atomic arrangements for any material simply by providing the chemical composition. There are several reasons for this. (1) No material is really in its thermodynamic equilibrium and the actual atomic structure reflects the history of the synthesis and processing of the material. The heat treatment of a steel, the growth of semiconductor devices by chemical vapor deposition, the tempering of silicate glasses, and the precipitation, calcination, and activation procedures of oxide-based heterogeneous catalysts provide illustrative examples for the complexity of the relationship between chemical... 

Such a control of the residual stresses is destructive, so non-destructive methods are preferred (Chapter 11). Notably, the Akeyoshi et al. (1967) approach for thermally tempered glasses can be generalized to chemically tempered glasses (Bouyne and Gaume, 2001). 

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