Phase relations in the Ta2O5-WO3-SiO2 system

Subsolidus relations and liquidus boundaries in the Ta2O3-WO3-SiO2 system at temperatures ranging from 1200 °C to 1500 °C were investigated. Phase diagrams were constructed. Compounds with stoichiometries of Ta22W4O67, Ta2WO8 and Ta16W18O94 formed in the Ta2O5-WO3 subsystem at 1200 °C. SiO2 was compatible with each of the compounds. A solid solution with a formula of (1 − x) Ta2O5·xWO3 formed on the Ta2O5-WO3 line in the compositional range of Ta2O5:WO3 > 11:4. SiO2 had a maximum solubility of 25% SiO2 in the solid solution. Liquid phase first appeared in the WO3-rich corner at 1300 °C. As the temperature was increased up to 1500 °C, the liquidus area boundary gradually expanded towards the SiO2- and the Ta2O5-rich corners.