Phase study of SiO₂-ZrO₂ composites prepared from polymorphic combination of starting powders via a ball-milling followed by calcination

The effects of SiO₂-ZrO₂ polymorphic combinations as starting powders and calcination temperature on phase composition of the SiO₂-ZrO₂ composites were studied. Stoichiometric (1:1 mol%) mixtures of the SiO₂-ZrO₂ composites were mechanically activated using a ball-milling for 5 h followed by calcinations at 1000, 1100 and 1200 °C for 3 h. The composites used in the present study were a-SiO₂+ a-ZrO₂, a-SiO₂+ t-ZrO₂, c-SiO₂+ a-ZrO₂ and c-SiO₂+ t-ZrO₂ which were symbolized by AA, AT, CA and CT, respectively. Prefixes a, t and c denote amorphous, tetragonal and cristobalite, respectively. The phase composition was determined by Rietveld analysis of X-ray diffraction (XRD) data using Rietica software. The identified phases for all calcined samples were a combination among t-ZrO₂, c-SiO₂, m-ZrO₂ and zircon (ZrSiO₄). Amorphous zirconia formed a transient tetragonal zirconia phase during heating, which reacted with silica to form zircon. The zircon phase was not found to form even at 1200 °C in the AT and CT mixtures and at 1100 °C in the CA mixture. The AA mixture in particular crystallized to form zircon at a lower temperature with more composition fraction than the others, ca 82.9 (14) mol%.