Thermodynamic Analysis of the CaO–Y2O3–ZrO2–Ti–Fe2O3 System as a Precursor for SHS-Produced Pyrochlore-Based Ceramics

Resumo

The paper reports on the thermodynamic analysis of the CaO–Y₂O₃–ZrO₂–Ti–Fe₂O₃ system as a precursor for SHS-produced pyrochlore-based ceramics. Adiabatic combustion temperature T_ad and equilibrium concentration of pyrochlore were first calculated for the quasi-ternary system Y₂O₃–ZrO₂–(Ti + Fe₂O₃) containing no CaO. It was found that, in the presence of CaO, a best yield of Zr-enriched pyrochlore ceramic can be reached within the following domain of green compositions (wt %): CaO 2.5–5.0, Y₂O₃ 22.5–35.0, ZrO₂ 7.5–22.5, and (40% Ti + 60% Fe₂O₃) 45.0–60.0; within this domain, T_ad = 2100–2400°K. Although in control experiments T_ad was found to be within the range 1700–1970 K, nevertheless the combustion products always showed the presence of pyrochlore-based ceramic, as predicted by thermodynamic analysis.