Effect of Calcium Fluoride Addition on Densification and Microstructure of Reaction-Sintered Indian Clay-Alumina Mixtures
A mullite compound was prepared using Indian clay and reactive alumina following a reaction-sintering route in the presence of a calcium fluoride (CaF2) additive. 0.25, 0.50, and 1.00 mass-% CaF2 was added to the mullite (stoichiometric) forming batch and the batches were sintered at temperatures of 1550, 1600, and 1650°C for 2 h. The batch without CaF2 completed the reaction at 1600°C whilst a relative density of 97% of the theoretical density of mullite was attained at 1650°C/2 h, whereas with 0.25 mass-% CaF2 the batch completed the reaction at 1550°C and achieved the same relative density at 1600°C/2 h. A bimodal distribution of elongated lath-shaped primary mullite and equiaxed secondary mullite was found in the secondary electron image of the 0.25% CaF2-containing batch sintered at 1650°C/2 h. The microstructures of the CaF2-containing batches are discussed.
Keywordskaolinite calcium fluoride reaction sintering primary mullite secondary mullite
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