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T‐p O2 Topologic Analysis of Phase Relations in the System CaO–CrO–Cr 2 O 3 –SiO 2
Author(s) -
Nell Johan,
Villiers Johan P. R.
Publication year - 1993
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.1151-2916.1993.tb07754.x
Subject(s) - liquidus , chromium , phase diagram , analytical chemistry (journal) , thermodynamics , phase (matter) , mineralogy , chemistry , materials science , physics , metallurgy , organic chemistry , chromatography
A temperature ( T ) − oxygen partial pressure ( p O2 ) topologic analysis of phase relations in the system CaO–CrO–Cr 2 O 3 –SiO 2 , involving divalent and trivalent chromium, was undertaken to determine the relative positions of isobaric invariant points and univariant lines in T‐p O2 space. Liquidus phase relationships in equilibrium with metallic chromium, CO 2 –H 2 gas mixtures, and air were used to identify the univariant and invariant assemblages involving Cr 2+ and Cr 3+ . The T‐p O2 grid was constructed using Schreine‐makers rules for the disposition of univariant lines about an invariant point. The topological relationship between univariant lines and invariant points assists in the interpretation of phase relationships over the T‐p O2 regions that were not experimentally investigated. For example, the effect of p O2 on the liquidus phase relationships involving CaSiO 3 (wollastonite), Cr 2 O 3 (eskolaite), and Ca 3 Cr 2 3+ Si 3 O 12 (uvarovite) is clearly illustrated by the grid; these details are not borne out by the experimentally determined phase diagrams. The grid furthermore illustrates the stability fields of the Cr 2+ ‐bearing phases, (Ca 0.4 Cr 0.6 2+ )Cr 2 3+ O 4 and CaCr 2+ Si 4 O 10 as a function of temperature and p O2 and demonstrates the observed increase in liquidus temperatures with increasing p O2 .