Effect of composition on the short-term and long-term dissolution rates of ten borosilicate glasses of increasing complexity from 3 to 30 oxides

Ten borosilicate glass compositions consisting of a ternary sodium borosilicate containing increasing numbers of some of the key elements (Al, Ca, Zr, Ce) present in nuclear glasses were leached in pure water at 90 degrees C and monitored for up to 14 years. They were then characterized to establish correlations between the glass composition and the short- and long-term alteration rates. We first qualitatively explain the variations of the initial dissolution rate by structural considerations. Then we evidence a qualitative inverse correlation between the initial and residual rates. This counterintuitive result is in fact related to the effect of gel reorganization on the diffusive properties of the passivating layer. Since no equilibrium can be reached between glass and solution, these long-term experiments help in understanding how glasses behave once the solution is saturated with respect to the main glass formers. Very efficient synergy between Ca and hardener elements (Al or Zr) leads to the lowest residual rates, compared with glasses having only one of the two categories of elements. We also confirm the detrimental effect of precipitation of silicate minerals on the residual rate. (C) 2012 Elsevier B.V. All rights reserved.