Multiparametric Dissolution of Thorium-Cerium Dioxide Solid Solutions

The dissolution of Th1-xCexO2 solid solutions samples prepared by thermal conversion of oxalate precursors was studied by varying independently several parameters (such as chemical composition, leachate acidity, leaching temperature, firing temperature, and crystallization state). The relative effects of these parameters on the normalized dissolution rate were examined. Either the obtained partial order related to the roton activity (n = 0.50 +/- 0.01) or the activation energy (E-A = 57 +/- 6 kJ.mol(-1)) suggested that the dissolution was mainly driven by surface reactions occurring at the solid/liquid interface. Conversely to that observed for Th1-xUxO2 and Ce1-xNdxO2-x/2 solid solutions, the chemical composition did not induce strong modifications of the chemical durability of the leached samples. While the initial normalized dissolution rate slightly depended on the elimination of crystal defects for firing temperatures below 800 degrees C, it was mainly independent of the crystallite size (T >= 900 degrees C). The role of crystal defects (then that of preparation conditions) appeared thus important to consider since they contributed to modifications of the normalized dissolution rates of the same order of magnitude than that of the leachate acidity.