Compositional effects on long-term dissolution of borosilicate glass

Abstract

Calculations have been performed to determine why, in static dissolution tests, the experimentally observed formation of a zeolite, such as analcime, causes a rapid increase in the dissolution rate for some glasses but not for others. The results of these calculations with a series of simple glasses show that there is a strong dependence on the Al content of the glass. For ratios of Si/(Si + Al) < 0.7, the amount of glass that has to dissolve for analcime to cause the dissolution rate to increase is 100–1000 times less than for glasses with higher ratios of Si/(Si + Al). Other glass components such as Na, Ca, B and Li are less effective at changing the rate of dissolution, although a minimum amount of Na needs to be present in the glass for analcime to form. These effects may be calculated for multi-component glasses by use of a simple six-component glass, although experimental verification is necessary to show that a six-component glass can be used. We also discuss the reasons why the effect of analcime precipitation on the silicon concentration in solution may be experimentally difficult to determine.