A study of the crystallization of ZrO2 in the sol-gel system:: ZrO2-SiO2

ZrO2-SiO2 sol-gel powders were produced using tetraethoxysilane (TEOS) and zirconium propoxide. After gellation, the ZrO2 crystallization process was investigated using X-ray diffraction (XRD), thermal analysis (DTA/TGA), and scanning electron microscopy (SEM), Fresh gels were amorphous. Thermal treatments were carried out from 100 to 1400 degreesC for a total annealing time of 182 h, Tetragonal zirconia, Z(t) was the first phase to crystallize, between 300 and 500 degreesC. Crystallization temperature was lower for zirconia-rich compositions, increasing as silica content was raised. DTA analysis showed that Z(t) crystallization occurred in two stages. Complete tetragonal-monoclinic zirconia transformation occurred near 1000 degreesC, and was clearly observed only in ZrO2-rich compositions (> 80%). Silica remains amorphous until 1200 degreesC, when ZrSiO4 formation took place, A metastable sol-gel phase diagram was proposed to show the crystallization process between 100 and 1400 degreesC. (C) 2001 Academic Press.