MICROSTRUCTURE DEVELOPMENT OF REACTIVE ALUMINAS

While most aluminas are purified and calcined in downstream operations, there are practical limits to the purity levels that can be achieved. Impurities such as CaO, SiO2 and Na2O are very common, and typical purity levels are in the 99.0-99.8% range. In order to produce high-quality microstructures...

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Bibliographic Details
Published in:Ceramic Industry 2015-04, Vol.165 (4), p.30-32
Main Authors: Lawrence, A, Kundu, A, Harmer, M, Compson, C, Atria, J, Bullard, T
Format: Magazinearticle
Language:English
Subjects:
Alumina
Aluminum oxide
Ceramics industry
Computer programs
Electron back scatter diffraction
Grain growth
Magnesium
Magnesium oxide
Microstructure
Purity
Raw materials
Roasting
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Summary:While most aluminas are purified and calcined in downstream operations, there are practical limits to the purity levels that can be achieved. Impurities such as CaO, SiO2 and Na2O are very common, and typical purity levels are in the 99.0-99.8% range. In order to produce high-quality microstructures in technical ceramics, MgO is often added to reactive alumina powders to control the level of abnormal grain growth. An attempt was made to evaluate the microstructural evolution of two commercial reactive alumina powders with similar overall purity level. Pressed and sintered samples were analysed by SEM and EBSD. Grain sizes were measured and calculated using the EBSD software. The results showed that simply adding more MgO to a sample will not solve the problem of abnormal grain growth. The sample with the lowest CaO content had the best microstructure, showing that CaO has a dominant role in driving microstructure development. With a lower CaO content, less MgO will be needed to homogenise the microstructure.
ISSN:0009-0220
2328-4072