WET CHEMICAL SYNTHESIS OF ZRO2-SIO2 COMPOSITE POWDERS

Gels of composition xZrO(2)(1-x)SiO2, with x = 10, 20, 30 and 40 vol%, have been prepared by a wet chemical method using fumed silica and zi rconyl chloride as precursors. Thermogravimetric analysis (TG) and dif ferential thermal analysis (DTA) show that weight loss is caused by re lease of the absorbed water and decomposition of the Zr(OH)(4) gels. G els were heat-treated for 2 h at 500, 700, 900, 1100 and 1350 degrees C, and the products examined using infra-red (IR) spectroscopy. The in creasing intensity of the peak at 800 cm(-1) in the IR spectra with in creasing temperature is attributed to the formation of Si-O-Si bonds a mong different SiO2 particles, which means that the SiO2 particles gro w bigger with increasing temperature. The DTA exothermic peak as well as the IR results reveal that the crystallization of tetragonal zircon ia (t-ZrO2) begins at about 900 degrees C, which is confirmed by X-ray diffraction (XRD). XRD curves also suggest that the silica matrix con tributes to the thermal stability of t-ZrO2. The stability of t-ZrO, i s interpreted by the particle-size effect. (C) 1996 Elsevier Science L imited.