| Solubility products of Y₂O₃ and Eu₂O₃ were measured by the potentiometric titration method in molten KCl-LiCl eutectic at 743K. Measured titration curves clearly showed the formation of new types of soluble intermediate oxychloride complex ions, Y₄O_5Cl_(x+1)^-(x-1) and Eu₂OCl_(x+3)^-(x-1), before in situ precipitation of those rare earth oxides. Oxides thus formed seemed to be far more reactive than Chose in their standard state, thereby explaining the discrepancies between measured and calculated solubility products. The equilibrium formation constants for the intermediate oxychloride complex ions, Y₄O_5Cl_(x-1)^-(x-1) and Eu₂OCl_(x+3)^-(x-1) were 10^(-35.01) and 10^(-3.88), respectively. The solubility products for Y₂O₃ and Eu₂O₃ were also determined, being 10^(-19.73) and 10^(-6.63), respectively. From those results the potential pO^(2-) diagrams for Y and Eu were constructed. |
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