Cerium Dioxide Surface Characterization and Determination of Surface Density by Potentiometric Fast Titration

Abstract

Cerium dioxide has been used as a Pu analogous to study Pu-Th mixed oxide fuels behavior, (Th, Pu)O-2, known as "Th-MOX". They are considered as possible advanced nuclear fuels for Generation-IV Fast Reactors aiming the burning and reprocessing of Pu stocks generated on U cycle. The use of Pu in Mixed-Oxide Fuel (MOX) will generate less fission products than U dioxide fuels. Before performing the study of Th sorption behavior, it is necessary to identify essential parameters as surface coordination sites density, surface charge and the equilibrium constants of the functional surface groups of hydrous oxide. Cc oxide has been characterized by the BET (Brunauer-Emmett-Teller) method to measure the specific surface area using N-2(g), by XRD (X-Ray Diffraction) to verify the crystalline structure, by SEM (Scanning Electron Microscopy) to analyze how well the pellets have been sintered, by AFM (Atomic Force Microscopy) to study the roughness, and by potentiometric titration to determine the surface sites density.

Potentiometric titrations were carried out both on a suspension of ceria colloids and on pellets. After the measurements, both proton intrinsic affinity constants and OH surface groups were compared. The experiments were developed in a wide range of pH and at different ionic strengths. The sites density values measured for ceria in 0.1 M NaClO4 media were 52.0 +/- 5.5 and 2.3 +/- 0.1 sites.nm(-2), for colloids and pellet, respectively. The hysteresis cycle obtained with pellets between acid/alkaline directions is rather important because indicates the tendency to retain other elements in his matrix.