Crystalline and pore structure of zirconia-based sorbents: 1. Zirconia-alumina solid solution

Abstract

An 8ZrO₂ · Al₂O₃ solid solution of zirconia and alumina is studied by X-ray and neutron diffraction, small-angle neutron scattering, and nitrogen sorption. The samples are synthesized by the sol-gel method and then subjected to heat treatment at temperatures T _an of 450, 600, and 950°C for 6–8 h. The first two samples are identified as X-ray amorphous, while the third sample has a complete crystalline structure (predominantly tetragonal phase, space group P4₂/nmc). The size of the coherent scattering region is 10–20 nm. The small-angle neutron scattering curves exhibit a pronounced peak; the peak position is shifted to low momentum-transfer values with increasing annealing temperature. The presence of a peak suggests that there is a certain correlation in the distribution of solid-phase particles in the sample volume. The density-density correlation functions are numerically established from the experimental small-angle scattering cross sections by the inverse Fourier transform method. The correlation lengths, volume fractions of the nanoparticles (pores), and specific surface areas of the samples are determined. As the annealing temperature rises, the characteristic pore size increases from 3.0 to 7.3 nm and the specific surface area of the samples decreases from 134 to 45 m²/g. It is speculated that the samples contain a significant amount of pores with a size of less than 1 nm.