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Liquidus–Solidus Phase Relations in the System CaO─CrO─Cr 2 O 3 ─SiO 2
Author(s) -
Villiers Johan P. R.,
Muan Arnulf
Publication year - 1992
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.1151-2916.1992.tb04191.x
Subject(s) - liquidus , solidus , chromium , calcium silicate , calcium oxide , silicate , mineralogy , phase (matter) , ternary operation , mineral redox buffer , metal , analytical chemistry (journal) , chemistry , chromite , oxide , materials science , inorganic chemistry , metallurgy , oxygen , alloy , chromatography , computer science , composite material , organic chemistry , programming language
Phase relations in the system CaO–chromium oxide–SiO 2 were determined (a) in equilibrium with metallic chromium and (b) at various oxygen pressures in the range of ∼ 10 −10 to 10 −13 atm. Two ternary phases occur on the liquidus surface in equilibrium with metallic chromium, viz, the garnet Ca 3 Cr 2 Si 3 O 12 (uvarovite), and CaCrSi 4 O 10 of the gillespite‐type structure and in which essentially all the chromium is present in the divalent state (Cr 2+ ). Furthermore, a previously reported binary calcium chromite phase “X” of approximate composition (Ca 0.4 Cr 0.6 )Cr 2 O 4 is stable also on the liquidus surface of the present system. The lowest liquidus and solidus temperatures in the system under these conditions (contact with metallic chromium) are significantly lower (by 100° to 200°C, depending on CaO/SiO 2 ratios of the melts) than those for the same system in air. Furthermore, there is considerable solid solution of chromium oxide in lime (CaO) and the various crystalline calcium silicates (pseudowollastonite, CaSiO 3 ; rankinite, Ca 3 Si 2 O 7 ; dicalcium silicate, Ca 2 SiO 4 ; tricalcium silicate, Ca 3 SiO 5 ), presumably by partial substitution of Cr 2+ for Ca 2+ toward hypothetical chromium analogs of each CaO‐containing phase, particularly in lime and Ca 2 SiO 4 . At the somewhat higher oxygen pressures imposed by the CO 2 ─H 2 gas mixtures of CO 2 /H 2 ratios of 1/24 and 1/8.1, the phases containing most of the chromium in the divalent state (CaCrSi 4 O 10 and (Ca 0.4 Cr 0.6 )Cr 2 O 4 ) do not appear on the liquidus surface, the primary phase area of garnet (uvarovite) decreases, the lowest liquidus and solidus temperatures increase noticeably (−50° to 100°C), and the amounts of chromium substituting in lime and the various crystalline calcium silicate phases (CaSiO 3 , Ca 3 Si 2 O 7 , Ca 2 SiO 4 , and Ca 3 SiO 5 ) decrease considerably from those observed for the system in equilibrium with metallic chromium. Combination of the data obtained under these reducing conditions with those previously reported for the system under more oxidizing conditions permits derivation of the general features of phase relations in the quaternary system CaO─CrO─Cr 2 O 3 ─SiO 2 .