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The crystallisation of chromite‐magnesiochromite spinels from a calcium magnesium aluminosilicate glass: Nucleation, crystal growth and final crystal sizes
Author(s) -
Packter A.,
Robson M. J.
Publication year - 1980
Publication title -
kristall und technik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0023-4753
DOI - 10.1002/crat.19800150906
Subject(s) - spinel , nucleation , crystallization , crystal growth , chromite , crystal (programming language) , aluminosilicate , materials science , mineralogy , magnesium , calcium aluminosilicate , crystallography , chemical engineering , chemistry , metallurgy , programming language , biochemistry , organic chemistry , computer science , engineering , catalysis
The crystallisation of chromite‐magnesiochromite spinels was studied from a calcium magnesium aluminosilicate glass (a simulated slag) containing 3 to 12 percent total iron oxides and 0.3 to 1.5 percent chromium(III) oxide, at temperatures from 1400° to 700 °C. – Spinel crystallisation occurred in glasses with 3–7 percent FeO and 0.7–1.1 percent Cr 2 O 3 . At temperatures 1100 °C and above, the nucleation was rapid and crystal numbers very high, at FeO contents above 3 percent and Cr 2 O 3 contents above 0.7 percent; at 1056° and 1000 °C however, the crystal numbers reached some optimum values but then decreased as clinopyroxene crystals grew onto and enveloped the spinel microcrystals. In these glasses, the crystal lengths varied with growth time according to the relation, l t = 2 k g t α = R g 1 t α , where α = 0.7–1.0: this time dependence was a compromise between a relation for dendritic growth and one for facetted growth. The growth rates generally increased about five to seven times for 160 °C temperature rise: the energy of activation for the spinel crystal growth was then estimated as 180 ± 60 kJ mole −1 . – No spinel crystals were observed in glasses with more than 7 percent FeO content, only clinopyroxene crystals. Probably, these latter had nucleated rapidly and grown onto spinel microcrystals, while the spinel microcrystals were still of < 0.1 μm size.