RETENTION BEHAVIORS OF CARBON-CONTAINING SPECIES IN AS-PREPARED, WATER-TREATED, AND TRANSITION-METAL-CONTAMINATED ZRO2 GELS

Retention behaviours of carbon-containing species in ZrO2 gels derived from the Zr-n-propoxide-acetylacetone-water-isopropanol system have b een studied by the Fourier transform infrared (FT-IR) pellet technique . The carbon retention patterns based on evolution of FT-IR spectra at different calcination temperatures for ZrO2 gels are examined in deta il. It is found that the carbon retention behaviours for as-prepared g els and for thermal, water and transition metal (Ni2+) pre-treated ZrO 2 gels differ. For most captured carbon species, for example, solvent isopropanol and additive acetylacetone, carbon can be depleted at a re latively low temperature of about 400 degrees C. However, for lattice- included species, especially those incorporated into the lattice durin g the phase transition, a temperature around 900 degrees C is needed t o eliminate carbon in the gels. In the study of the effect of moisture on gel calcination, it is found that water treatment alone does not p rovide new routes for carbon retention in as-prepared ZrO2 gels. Howev er, when gels are pre-treated with Ni2+ and water, new forms of carbon -containing species can be observed. These forms are attributed to an inter-diffusion of Ni2+ and ZrO2 matrix and the catalytic effect of th e resultant solid solution, NiO-ZrO2, on the retained carbon species.