High-temperature phase transition and the activity of tobermorite

The high-temperature phase transition of tobermorite was investigated by TGA/DSC, X-ray diffraction and Infrared spectroscopy (IR), respectively. The experimental results showed that Si-OH bonds were cleaved at 724 A degrees C and dehydroxylation occured at the same time, implying that the crystal structure of tobermorite was broken. As a result, the dehydroxylation tobermorite was metastable state, exhibiting obviously hydrolysis activity. The suspension was alkaline and Ca2+ ions content reached a maximum value 4.76% after heat treatment at 724 A degrees C. The dehydroxylation tobermorite had potential reactive activity due to the strong hydrolysis activity. The disordered structure recombined to wollastonite, and the crystal structure became ordering and stable at 861 A degrees C Finally, 2M-wollastonite structure can be found in the sample as the temperature reached up to 1 000 A degrees C.