Corrosion of ISG fibers in alkaline solutions

The corrosion behavior of glass fibers synthesized from the International Simple Glass ( ISG ) reference ingot, an international High‐Level Waste ( HLW ) borosilicate glass standard, is reported. Bundles of glass fibers were submerged in 120 mL of four different solutions of initial pH values ( pH i ) of 9.5, 10.5, 11.5, and 12.5 for static corrosion testing. While all the experiments reached a residual corrosion rate after ~50 days, which remained approximately constant for the duration of the pH i 9.5‐11.5 experiments, the pH i 12.5 experiment underwent a Stage II → III dissolution transition after 57 days. This transition was preceded by a decrease in the Al concentration in solution followed by an increase in B and Si concentration in the leachate. Zeolite NaP2 was observed to form on these fibers via scanning electron microscopy and X‐ray diffraction—the crystallinity of the fibers was estimated to be ~40%‐45% (relative to amorphous component) after the Stage II → III transition. Transmission electron microscopy cross‐sectional imaging of sampled fibers revealed several porous layers on the pH i 9.5‐11.5 samples, and a more aggressive alteration mechanism in the pH i 12.5 fibers. Potential markers that indicate a transition from Stage II →Stage III corrosion are shown to occur based on experimental observations.