SURFACE NI2-GEL-DERIVED TETRAGONAL AND MONOCLINIC ZRO2 MATRICES( DIFFUSION IN SOL)

Tetragonal and monoclinic ZrO2 gel matrices have been synthesized from the zirconium n-propoxide-acetylacetonewater-isopropanol system. Surf ace Ni2+ ion diffusion in these sol-gel-derived tetragonal and monocli nic zirconia matrices have been studied with Fourier transform infrare d spectroscopy, differential thermal analysis and X-ray photoelectron spectroscopy (XPS). It is found that the Ni2+ metal ion diffuses into the ZrO2 continuously over the temperature range of 400-600 degrees C for both tetragonal and monoclinic ZrO2 matrices, and later forms a th ermodynamically stable Ni2+/ZrO2 solid solution at the elevated calcin ation temperatures. Higher Ni2+ surface contents in tetragonal ZrO2 ar e measured by XPS, indicating a larger specific surface area for tetra gonal gel matrix. In addition to the +2 oxidation state, +3 for Ni is also detected in Ni/ZrO2 systems. The atomic ratio of Ni2+/Ni3+ varies and peaks at 700 degrees C in the tetragonal ZrO2. However, in the mo noclinic case, the ratio remains constant throughout the course of exp eriments. Diffusion thermodynamic quantities are investigated and the diffusion activation energy determined for Ni2+ ion in ZrO2 matrices i s 0.40 eV. The oxidation states of surface metals (Ni and Zr) and crys tallinity of the system during the phase transformation are also addre ssed.