1979 Volume 87 Issue 1011 Pages 558-564
Change in length of phase-separated borosilicate glass rods were measured during acid leaching. Remarkable swell or shrinkage was observed in relation to the composition of glass, and the conditions of heat treatment and leaching.
Sample subjected to the heat treatment for a short time shrank in the course of acid leaching. With prolonged heat treatment shrinkage turned into swelling and reached the saturated value. This value was constant independently of the heat treating temperature. The heat treating time (t3) necessary to reach the saturated value, however, become shorter with higher heat treating temperature. Logarithm of t3 was linearly proportional to the reciprocal absolute temperature of heat treatment. Experimental activation energy obtained from t3 was 62kcal/mol.
Samples subjected to the heat treatment for a short time produced evident cracks during acid leaching, presumably due to the insufficient development of silica skeleton.
When the Na2O/B2O3 in glass was in the range from 0.2 to 0.4, the saturated values appeared with the swells. Beyond this range, shrinkage and cracks increased remarkably. At the ratio of 0.4, the amount of 4-coordinated borons are known to become maximum, and it is assumed that, above this ratio, silica skeleton is broken resulting in the shrinkage and crack.
Saturated values of the swell reduced when alumina was added to the glass, and it has been found out that neither swell nor shrinkage took place at about 3.5% of alumina added.
