Exploiting kaolinite-alumina heteroaggregation in Pickering emulsion stabilisation and porous mullite fabrication

Clay particles have gained considerable attention as a potential option for stabilising Pickering emulsions in recent years, which are promising templates for the development of porous ceramics intended for high temperature applications. However, the development of porous ceramics using this approach requires control over a number of factors such as stability, microstructure, rheology, and processability of the Pickering emulsions. In this work, we discuss a versatile approach for formulating porous mullite ceramics from emulsions stabilised by oppositely charged kaolinite and alumina particles. In this process, we exploit the electrostatic heteroaggregation phenomena in the oppositely charged mixed colloidal particle system. The aggregates formed by electrostatic interaction readily adsorb to the interface created during emulsification and favor the formation of highly stable Pickering emulsions. The influence of parameters such as concentration of each particle in the mixture, pH, and total particle concentration on the microstructure of Pickering emulsions are studied. We further show that processable Pickering emulsions can be engineered by in-situ surface modification of the hetero-aggregates using a short-chain amphiphile. Porous mullite ceramic is obtained by drying and sintering the optimised emulsion formulation. The phase evolution, microstructure, and porosity of the resulting ceramic are characterised. The macroporous mullite developed through this approach can be used as thermal insulator due to low thermal conductivity and tailored microstructure.