The Chemical Durability of SiO_2-B_2O_3-Na_2O System Glasses (The 2nd Report)

The chemical durability of SiO_2-B_2O_3-Na_2O system glasses was studied in this paper. The thirty kinds of glasses in this system were fused in the electric furnace. The fused glasses were powdered into the particles of 35-60 meshes (Tyler), and 2g of them were immersed in 50ml water of 30,50 and 70℃, while being stirred during 10,20,40 and 80 minutes respectively. Then the amounts of alkali dissolved into the water were measured by 0.01N HCl. The results were as follows. (1) The experimental data were tested by analysis of variance, and it was found that log of dissolved amounts was linear function of log of dissolving time, and was linear function of reciprocal of absolute temperature of the water. (2) In the case of Na_2O mol constant, the dissolving phenomena were very simple. That is, the dissolved amounts increased considerably with increasing B_2O_3/SiO_2. (3) In the case of SiO_2 mol constant, the dissolving phenomena were very complex. Namely, there were maximum and minimum value of dissolved amounts. (4) Generally, the glasses in the outer domain of exsolution were more durable than the glasses in the inner domain.