Solid state reactions in the ZrO2 · SiO2 - αAl2O3 system

Solid state reactions between ZrO2· SiO2 and αAl2O3 in mixed powders were studied by quantitative X-ray diffraction, density measurements and qualitative EDAX. Data were obtained at temperatures ranging from 1400 to 1600° C for 5 h; the initial molar ratios of the reactants (Al2O3/ZrO2 · SiO2) varying from 0 to 5. The results indicate that: (1) ZrO2· SiO2 and αAl2O3 react and form ZrO2, crystalline 3Al2O3 · 2SiO2 and a noncrystalline mullite phase; (2) the non-crystalline mullite phase is an important transitional phase towards equilibrium under subsolidus conditions. In the experimental conditions used the amount of the non-crystalline phase varies by as much as about 15%. This phase is of great importance in the mechanisms of reaction sintering between ZrO2 · SiO2 and αAl2O3.