A 57Fe Mössbauer study of black coring phenomena in clay-based ceramic materials

The black discoloration sometimes found in the interior cores of iron-containing clay-based ceramic materials was studied in three different samples by XRD, elemental analysis and 58Fe Mossbauer spectroscopy. The primary cause of black coring is locally reducing conditions in the interior of the bod...

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Bibliographic Details
Published in:Journal of materials science 1990-06, Vol.25 (6), p.2937-2942
Main Authors: MACKENZIE, K. J. D, CARDILE, C. M
Format: Article
Language:English
Subjects:
Applied sciences
Bricks, roofing tiles, pottery
Building materials. Ceramics. Glasses
Ceramic industries
Chemical industry and chemicals
Exact sciences and technology
Heavyclay products, whiteware
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Summary:The black discoloration sometimes found in the interior cores of iron-containing clay-based ceramic materials was studied in three different samples by XRD, elemental analysis and 58Fe Mossbauer spectroscopy. The primary cause of black coring is locally reducing conditions in the interior of the body resulting from incomplete oxidation of carbonaceous impurities and results in the formation of Fe2+, but the presence of discrete lower iron oxides or iron metal was not confirmed. Instead, the Fe2+ occurs as a lattice substituent of the normal products of the high-temperature ceramic reactions (as ferroan pyroxenes, olivines or feldspars, depending on the chemical composition and reaction conditions). The dark core reflects the deeper colour of these ferrous minerals, which are not present in the oxidised material of the outer rim. 17 refs.
ISSN:0022-2461
1573-4803