Abstract
In the paper, the lime-barium and lime-zinc glazes used in Southern and Eastern Africa Mineral Center (SEAMIC) ceramic unit in Tanzania were investigated for the production of high temperature raw glazes in Cameroon. The base Seger formula used was 0.3KNaO, 0.3CaO, 0.4ZnO or BaO; xAl2O3 and ySiO2. Different Al2O3/SiO2 formula ratios for glossy and matt glazes were tested with raw materials from Cameroon and Tanzania. In the Cameroonian glazes, a local pegmatite (quartz, microcline, albite) with low coloured oxides replaced an albitic feldspar in the Tanzanian glazes. The other materials were kaolin, limestone, silica and barium carbonate or zinc oxide. The glazes were tested at Seger Cone 7 (1240℃) on stoneware slabs (made up of the same feldspathic glaze material: 18%, silica sand or quartz 27%, ball clay 40% and kaolin 15%) from both Tanzania and Cameroon materials. From results obtained, zinc oxide acted as a more vigorous flux than barium carbonate at cone 7, which is obvious in the glazes with pegmatite (with high quartz content). At a Seger formula of Al2O3/SiO21:10, transparent glazes were obtained. In these glazes the alumina content was lower and when increased to higher Seger ratios 1:4.7 - 8.7, the gloss was lowered to matt-luster due to fine crystal formation.
Highlights
Glazes constitute a fundamental material to the success of the ceramic industry
The lime-barium and lime-zinc glazes used in Southern and Eastern Africa Mineral Center (SEAMIC) ceramic unit in Tanzania were investigated for the production of high temperature raw glazes in Cameroon
Different Al2O3/SiO2 formula ratios for glossy and matt glazes were tested with raw materials from Cameroon and Tanzania
Summary
Glazes constitute a fundamental material to the success of the ceramic industry. During recent years, the demands of shorter firing cycles and easy control of surface microstructure have called for the use of fritted compositions. Glaze is similar to glass but with a more complex system because it deals with more components; 7 or 8 oxides in significant amounts are common [1,2,3,4,5,6]. The complication with glazes is accentuated by the fact that a thin layer is applied to a ceramic body and the glaze body interaction may result in faults. Such faults like cracks (at times voluntary) can affect the aesthetics and technical properties of the product. For every given body composition, it is important to test the ideal glaze based on aesthetics and properties envisaged
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