T-p[sub O[sub 2]] topologic analysis of phase relations in the system--CaO-CrO-Cr[sub 2]O[sub 3]-SiO[sub 2]
- Mintek, Randburg (South Africa). Mineralogy and Process Chemistry Div.
A temperature (T)-oxygen partial pressure (p[sub O[sub 2]]) topologic analysis of phase relations in the system CaO-CrO-Cr[sub 2]O[sub 3]-SiO[sub 2], involving divalent and trivalent chromium, was undertaken to determine the relative positions of isobaric invariant points and univariant lines in T-p[sub O[sub 2]] space. Liquidus phase relationships in equilibrium with metallic chromium, CO[sub 2]-H[sub 2] gas mixtures, and air were used to identify the univariant and invariant assemblages involving Cr[sup 2+] and Cr[sup 3+]. The T-p[sub O[sub 2]] grid was constructed using Schreinemakers 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[sub O[sub 2]] regions that were not experimentally investigated. For example, the effect of p[sub O[sub 2]] on the liquidus phase relationships involving CaSiO[sub 3] (wollastonite), Cr[sub 2]O[sub 3] (eskolaite), and Ca[sub 3]Cr[sup 3+][sub 2]Si[sub 3]O[sub 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[sup 2+]-bearing phases, (Ca[sub 0.4]Cr[sup 2+][sub 0.6])Cr[sup 3+][sub 2]O[sub 4] and CaCr[sup 2+]Si[sub 4]O[sub 10] as a function of temperature and p[sub O[sub 2]] and demonstrates the observed increase in liquidus temperatures with increasing p[sub O[sub 2]].
- OSTI ID:
- 6078312
- Journal Information:
- Journal of the American Ceramic Society; (United States), Journal Name: Journal of the American Ceramic Society; (United States) Vol. 76:9; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
MATHEMATICS
OXIDES
OXYGEN COMPOUNDS
PARTIAL PRESSURE
PHASE STUDIES
SILICON COMPOUNDS
SILICON OXIDES
TEMPERATURE DEPENDENCE
TOPOLOGY
TRANSITION ELEMENT COMPOUNDS