Dissolution Kinetics of Titanium Pyrochlore Ceramics at 90?C by Single-Pass Flow-Through Experiments

Corrosion resistances of titanium-based ceramics are quantified using single-pass flow-through (SPFT) experiments. The materials tested include simple pyrochlore group (B2Ti2O7, where B=Lu^3+ or Gd^3+) and complex multiphase materials that are either pyrochlore- (PY12) or zirconolite-dominated (BSL3). Experiments are conducted at 90?C over a range of pH-buffered conditions with typical duration of experiments in excess of 120 days. Apparent steady-state dissolution rates at pH=2 determined on the Gd2Ti2O7 and Lu2Ti2O7 samples indicate congruent dissolution, with rates of the former (1.3x10^-3 to 4.3x10^-3) slightly faster than the latter (4.4x10^-4 to 7.0x10^-4 g m^-2 d^-1). Rates for PY12 materials into pH=2 solutions are 5.9x10^-5 to 8.6x10^-5 g m^-2 d^-1. In contrast, experiments with BSL3 material do not reach steady-state conditions, and appear to undergo rapid physical and chemical corrosion into solution. At faster flow-through rates, dissolution rates display a shallow amphoteric behavior, with a minimum (4.6x10^-5 to 5.8x10^-5 g m^-2 d^-1) near pH values of 7. Dissolution rates display a measurable increase (~10X) with increasing flow-through rate indicating the strong influence that chemical affinity asserts on the system. These results step towards an evaluation of the corrosion mechanism and an evaluation of the long-term performance of Pu-bearing titanite engineered materials in the subsurface.