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The System CaO–“CaCr 2 O 4 ”–CaAl 2 O 4 in Air and under Mildly Reducing Conditions
Author(s) -
Kaiser Arno,
Sommer Burkhard,
Woermann Eduard
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.tb04211.x
Subject(s) - solidus , chromium , aluminate , chromate conversion coating , calcium oxide , chromite , ternary operation , calcium , materials science , phase (matter) , ternary numeral system , metallurgy , inorganic chemistry , mineralogy , chemistry , cement , organic chemistry , alloy , computer science , programming language
The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca 5 Cr 3 O 12 , Ca 3 (CrO 4 ) 2 , and Ca 5 (CrO 4 ) 3 ) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ ‐CaCr 2 O 4 , is observed. In the CaO‐rich section of the CaO–Al 2 O 3 –Cr 2 O 3 system a ternary intermediate phase, chrome‐haüyne, Ca 4 [(Al,Cr 3+ ) 6 O 12 ](Cr 6+ O 4 ), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca 6 Al 4 Cr 2 O 15 , coexists with CaO, CaCr 2 O 4 , chrome‐haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al 2 O 3 system is insignificant.