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Effect of Reducing Atmosphere on Minerals and Iron Oxides Developed in Fired Clays: The Role of Ca
Author(s) -
MANIATIS Y.,
SIMOPOULOS A.,
KOSTIKAS A.,
PERDIKATSIS V.
Publication year - 1983
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.1151-2916.1983.tb10561.x
Subject(s) - gehlenite , wollastonite , calcite , ferrous , chemistry , mineralogy , mineral , quartz , aragonite , mössbauer spectroscopy , calcareous , clay minerals , spinel , metal , chemical engineering , materials science , metallurgy , geology , crystallography , raw material , organic chemistry , phase (matter) , paleontology , engineering
The transformations induced in two clays differing in Ca content, by firing under reduced conditions up to 1080°C, were studied by X‐ray diffraction, scanning electron microscopy, Mossbauer, and magnetization measurements. In the calcareous clay , gehlenite forms at lower temperatures (900°C) and, in addition, wollastonite forms at higher temperatures (1080°C). Ferric iron persists even under strongly reducing conditions and its presence is attributed to trapping in gehlenite. Extensive vitrification is observed in the non‐calcareous clays . Ferrous iron, produced by dissociation of iron oxides, is partly dissolved into the vitreous matrix and partly incorporated into the spinel mineral hercynite. The key role of Ca in controlling the above transformations was verified by studying the clays after removal or addition of calcite. The interaction of Ca with the clay constituents and its progressive attack on the quartz grains forming wollastonite zones was observed with the electron microscope. The bulk magnetic properties of the samples depended principally on the amount of iron oxides present, which in turn were strongly affected by firing temperature and type of clay. Metallic iron was detected in strongly reducing atmospheres.