Kinetics of glass corrosion in acid solutions

The interaction of simulated nuclear waste borosilicate glass with acid solutions (pH = 2, PH = 4) was studied under static conditions (i.e. without refreshment of corroding solution) at 30, 60 and 90 degrees C. Tests with stirred and unstirred solution were compared. The rate of glass dissolution (given by the rate of SiO2 transfer into the solution) and the rate of glass leaching (represented by the rate of sodium transfer into the solution) were significantly higher at lower PH and in stirred solution. The first phenomenon can be explained by the more extensive opening of glass structure al lower pH. The second phenomenon can be caused by the creation of thin solution layer adjacent to the glass surface in the case of unstirred corroding media. The SiO2 and sodium concentration in this layer are then higher in comparison to the bulk solution. Due to this fact the driving force of glass matrix dissolution and sodium leaching are lower than in the case of stirred solution. The temperature dependencies of the initial rate of glass matrix dissolution and of the sodium diffusion coefficient can be described using equations of Arrhenius' type.