Mullite formation from mixtures of alumina and silica sols: mechanism and pH effect

Journal of the Brazilian Chemical Society

Carla C. Osawa¹  Celso A. Bertran¹ 

[1] ,Universidade Estadual de Campinas Instituto de Química Campinas SP ,Brazil

关键词: pH effect;    mullite formation;    alumina sol;    silica sol;   

DOI  :  10.1590/S0103-50532005000200019

来源: SciELO

【 摘 要 】

This work reports the effect of pH on the process of mullite formation from mixtures of alumina and silica sols. The pH of the mixtures determines the charges of particle surfaces and affects their interactions and distributions. Mullite formation from amorphous precursors with an Al:Si molar ratio of 1:3, prepared from the sols mixture, was not affected by pH. In this case, the higher concentration of silica determined its distribution around alumina, which led to tetragonal mullite formation, according to the Sundaresan and Aksay mechanism. However, for mullite formation from precursors with Al:Si = 3:1, the pH played an important role on the interactions between alumina and silica particles, as well as on the predominant aluminum species. At pH 1, octahedrically coordinated Al3+ ions predominated in the alumina sol while tetrahedrically coordinated Al3+ ions predominated in the sol at pH ~6. The interactions between silica and alumina particles and their distributions in these precursors determined the minimum temperature required for orthorhombic mullite formation.

【 授权许可】

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