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Phase Equilibria in the System CaO‐BaO‐WO 3
Author(s) -
KREIDLER ERIC R.
Publication year - 1972
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1972.tb13419.x
Subject(s) - eutectic system , phase diagram , isothermal process , ternary numeral system , phase (matter) , tetragonal crystal system , solid solution , materials science , solubility , crystallography , mineralogy , analytical chemistry (journal) , chemistry , thermodynamics , crystal structure , metallurgy , microstructure , physics , organic chemistry , chromatography
The 1200°C isothermal section of the system CaO‐BaO‐WO 3 was studied in detail. The system contains one ternary compound, Ba 2 CaWO 6 , which can exist in binary equilibrium with BaO, CaO, Ba 3 WO 6 , Ba 2 WO 5 , BaWO 4 , and Ca 3 WO 6 . The composition range of solid solutions based on the ternary compound extends from Ba 2 CaWO 6 to Ba 1.86 Ca 1.14 WO 6 at 1200°C. Solid solubility along the binary join BaWO 4 ‐CaWO 4 was studied in the interval 1000° to 1340°C. Maximum solid solubilities occur at the eutectic temperature (1340°±10°C) and are 18 mol% CaWO 4 in BaWO 4 and 3.5 mol% BaWO 4 in CaWO 4 . A phase diagram is given for the BaWO 4 ‐CaWO 4 system. Evidence is presented which shows that Ba 2 WO 5 is a stable phase, and the BaO‐WO 2 phase diagram is revised accordingly. There are 3 polymorphs of Ba 2 WO 5 related by rapid reversible inversions at 1385°±5° and 1490°±10°C. The low‐temperature form of Ba 3 WO 6 . is tetragonal (α=8.65(2) Å and c =16.43(4) Å), not cubic as previously reported. The compounds Ca 6 WO 9 , BaW 2 O 7 , BaCa 2 WO 6 , Ba 5 CaW 2 O 12 , and Ba 1.5 Ca 1.5 WO 6 reported in earlier studies were not confirmed.