CONSEQUENCES OF FOREIGN SALT ADDITIVES ON THE STRUCTURE AND TEXTURE OF SOME METAL-OXIDES

The influence of foreign salt additives, namely (NH2)(2)CO and NH4NO3, on the structure and texture of ZrO2, Nb2O5, La2O3 and ThO2, produced by thermal decomposition of their nitrates, has been investigated. Th ermal behaviour of oxide precursors (metal nitrates) as well as additi ve salts (pure and impregnated into the oxides) was explored by thermo gravimetry. Accordingly, the calcination products of the additive-free and additive-containing oxides were obtained at the appropriate tempe ratures. The final oxide materials, with and without additives, were c haracterized by X-ray diffractometry. Slight structural modifications were detectable, viz. a retardation to crystallinity and particle size decrease. Texture assessment (surface area and porosity) was carried out via analysis of nitrogen adsorption isotherms (at -196 degrees C) adopting BET-and t-methods. The additives, particularly of urea, were found to improve notably the surface area and porosity. This was corre lated with the structural modifications conceded by the material bulk. (C) 1998 Elsevier Science B.V.