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Dissolution of A2Ti2O7 (A = Y3+, Gd3+, or Lu3+) Pyrochlore by Experiment at pH = 2, T = 90°C: Evidence for Solubility Control Using a Linear Free Energy Model

  • J. P. Icenhower (a1), B. P. McGrail (a1), W. J. Weber (a1), B. D. Begg (a2), N. J. Hess (a1), E. A. Rodriguez (a1), J. L. Steele (a1), C. F. Brown (a1) and and M. J. O'Hara (a1)...

Abstract

We performed a series of dissolution experiments with well-characterized pyrochlore ceramics with the formula A2Ti2O7, where A = Y3+, Gd3+, or Lu3+ in H2O- and D2Obased solutions [pH(D) = 2] at 90°C. Normalized log10 dissolution rates (g·m−2·d−1) in H2O-based solutions increase from Lu2Ti2O7 (−3.2 to –3.3) to Gd2Ti2O7 (−2.6 to –2.9), to Y2Ti2O7 (−1.9 to –2.0). Rates in D20-based solutions are indistinguishable from rates in H2O, indicating that release of elements is probably not diffusion controlled. A recent dissolution model, based on ligand-exchange reactions, suggests that the rate of reaction should increase in inverse order of the cation field strength: Lu < Y < Gd (where the cation denotes the appropriate pyrochlore composition), which is not observed. Evaluation of the thermodynamic stability of the three solids was performed using a linear free-energy model and reported free energies of formation. The calculations indicate that reactivity should follow in the progression Lu < Gd < Y, as observed in the dissolution experiments. Our data indicates, therefore, that dissolution models based on ligand-exchange reactions may not be strictly applicable to simple pyrochlore minerals.

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Dissolution of A2Ti2O7 (A = Y3+, Gd3+, or Lu3+) Pyrochlore by Experiment at pH = 2, T = 90°C: Evidence for Solubility Control Using a Linear Free Energy Model

  • J. P. Icenhower (a1), B. P. McGrail (a1), W. J. Weber (a1), B. D. Begg (a2), N. J. Hess (a1), E. A. Rodriguez (a1), J. L. Steele (a1), C. F. Brown (a1) and and M. J. O'Hara (a1)...

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