Microwave Hydrothermal Synthesis and Characterisation of Aluminum Substituted Tobermorite

Abstract

To solve the long-time problems facing the preparation of aluminum substituted tobermorite (Al-tobermorite)， microwave hydrothermal synthesis is increasingly recognized as an available alternative thanks to its volumetric heating nature. The synthesis of aluminum substituted tobermorite（Al-tobermorite）was carried out under the microwave hydrothermal condition using silica, calcium hydroxide and aluminum hydroxide as raw materials. Effects of different ratios of Al in place of Si on the microstructure of Al-tobermorite were investigated. Following this, mechanism of microwave heating on the crystal structure formation of Al-tobermorite was proposed. Results show that under the microwave hydrothermal synthesis condition (220℃, 1.5h), as the Al/Si ratio was increased, the substitution of Al and Si in the crystal structure of tobermorite happened to form Al-tobermorite, and the optimal Al/Si ratio for the preparation of Al-tobermorite was 0.15, and the Al/Si ratio over 0.15 would lead to the further conversion of Al- tobermorite into hydrous calcium aluminite garnet.

Keywords: Al-tobermorite, Microwave hydrothermal synthesis, Al/Si ratio, Microstructure