Phase Equilibria in the System BaO‐SrO‐SiO 2

Phase equilibria in the system BaO‐SrO‐SiO 2 in air were established using conventional solid‐state techniques. The phase relations in the boundary system SrO‐SiO 2 were completed by determining the liquidus temperatures for the SrO‐rich portion of the diagram. The known compounds, SrSiO 3 , Sr 2 SiO 4 , and Sr 3 SiO 3 , melted congruently at 1580°±15°, 2325°±15°, and 2170°±15°C, respectively. Simple binary eutectics exist between (1) Sr 2 SiO 4 and Sr 3 SiO 5 at 2150°±15°C and ∼27 mol% SiO 2 and (2) Sr 3 SiO 5 , and SrO at 2080°±15°C and ∼23 mol% SiO 2 . All Alkemade lines were established for the ternary system; two of these joins were examined in detail because of extensive solid‐solution regions. On the Ba 2 SiO 4 ‐Sr 2 SiO 4 join, a maximum solubility of ∼70 mol% Sr 2 SiO 4 in Ba 2 SiO 4 appears to exist at 2100°±15°C, the eutectic reaction temperature. A two‐phase region apparently connects the eutectic reaction isotherm with a high‐temperature polymorphic transition (α′±α) of Sr 2 SiO 4 . Below this transition temperature, a complete solid‐solution series exists between Ba 2 SiO 4 and α′‐Sr 2 SiO 4 . The BaSiO 3 ‐SrSiO 3 , join contains limited solid‐solution regions at the extremities which arise from the solid solubility of 40 mol% SrSiO 3 in the high‐temperature (β) polymorph of BaSiOs 3 and 20 mol% BaSiO 3 in SrSiO 3 at 1210°±15°C. The only ternary compound isolated, BaSrSi 3 O 8 , has a lower limit of stability at 1220°±3°C and melts incongruently at 1275°±3°C.