Influence of calcination temperature of kaolin on the structure and properties of final geopolymer

In this paper, the structure of two types of metakaolins from kaolin calcined at 800 and 900 °C, respectively, and the obtained geopolymer were systematically characterized. It was found that calcination temperature had little effect on the environment of silicon atoms but had great effect on that of aluminum ones. 27Al NMR analysis showed that tetrahedral aluminums in the metakaolin from kaolin calcined at 800 and 900 °C were in different environment, of the type AlQ3(3Si) and AlQ4(4Si), respectively, leading to different environment of aluminum atoms in the resulted geopolymer. Aluminum atoms in the geopolymer based on metakaolin from kaolin calcined at 800 °C were in the types of tetrahedral and octahedral, and silicon atoms were in the types of tetrahedral Q4(3Al) together with a small amount of Q4(0Al). However, geopolymer based on metakaolin from kaolin calcined at 900 °C consisted of Q4(4Si) unit aluminum and Q4(3Al) unit silicon. The results revealed that the calcination temperature had a great effect on environment of the aluminum atoms of the metakaolin, thus led to the different structure and properties including mechanical strength and thermal conductivity of the post obtained geopolymer.