2.
The influence of processing conditions on the morphology of calcium hexaluminate (CA
6) grains in Al
2O
3: 30 vol% CaO·6Al
2O
3 (CA
6) ceramic composites was investigated. Specimens were prepared by
in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA
6 grains developed a platelike morphology when CaCO
3 was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA
6 grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA
6 reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.Cement Nomenclature C
CaO
- A
Al
2O
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