Influence of simulated waste oxides on the durability of a borosilicate glass

Abstract

Although the numerous papers on the chemical durability of nuclear waste glasses, more work is needed to understand the effects of waste oxides on the glass durability. This is due to the great variety of possible compositions and to the wide leaching conditions [1]. We have prepared the N. 189 glass (England), B, to which we have added 10% and 20% of SrO, Cs 2O, U 3O 8. Furthermore we studied the effects on B of an addition of 4% ZnO [2]. All the glasses were grounded and passed through 40 and 60 mesh sieves to obtain approximately the same surface for the same weight. Powders were leached by water at 70 °C for times varying from 1 day to 24 days and the solutions were analyzed by means of conventional methods. SiO 2 B 2O 3 Li 2O Na 2O SrO Cn 2O U 3O 4 ZnO Loss% B 55.5 29.2 5.0 10.3 - - - - 72.9 SR1 50.4 26.6 4.5 8.4 8.1 - - - 83.1 SR2 46.2 24.3 4.2 8.6 16.7 - - - 87.7 CS1 50.4 26.5 4.6 9.4 - 9.1 - - 91.7 CS2 46.2 24.3 4.2 8.6 - 16.7 - - 97.1 U1 50.4 26.6 4.5 9.4 - - 9.1 - 73.5 U2 46.2 24.3 4.2 8.6 - - 16.7 - 75.9 ZN4 53.3 28.0 4.8 9.8 - - - 4.0 15.3 In the Table I are reported the sample compositions and the percentage of mass leached out after 24 days. In any case the waste ions make poorer the base glass with a maximum for the cesium containing glass. On the contrary the zinc ions, even if in a very low amount, allow very increased resistance to the corrosion [3]. As example in Figs. 1 and 2 are reported the quantitites of SiO 2 and Na species leached out in the course of the experiment. It must be pointed out that the zinc containing glass continues to dissolve in an appreciable way. This is due to the fact that after 24 days the glass mass is ▪ ▪ not negligible. On the contrary, the other glasses after 24 days are dissolved up to 97%. The different behaviour of the cesium and zinc containing glasses is evidenced also by Figs. 3, and 4, which show the SEM photographs of leached glasses. IR technique can show the effect of leaching on the glass structure. In Fig. 5 we can see that water transforms the silicate amorphous structure of the glass B in a structure very similar to the vitreous silica [4].