HYDROTHERMAL ROUTE TO PURE PHASE ZRO2 - INTERFACIAL REACTIVITY BY XPS AND ELECTROCHEMICAL DETERMINATIONS

The precipitation of pure monoclinic ZrO2 from acid solutions of zirconium salts aged at 100 degrees C was investigated. The rate of nucleation depends not only on the initial pH and pZr but also on the nature of the precursor salt and the electrolyte concentration [Cl-]. All the different experimental conditions adopted yielded monoclinic ZrO2, without metastable polymorphs. Analyses of the samples by thermogravimetric analysis and differential thermal analysis revealed both physisorbed and chemisorbed water. X-ray photoelectron spectroscopy showed the coordination of the surface cations to be regular and gave the stoichiometry and density of surface sites. The reactivity of the electrical double layer of the products was assessed by obtaining charge versus pH curves of aqueous suspensions. The value of the point of zero charge, determined electrochemically, was compared with data from other sources.