Abstract:

Potassium feldspar was hydrothermally decomposed with CaO as an additive, and then tobermorite nano-scale powder was synthesized. The effective factors on the synthesizing reaction were the mole ratio of CaO/(SiO₂+AlO_1.5), reaction temperature and reaction time. The experimental results showed the tobermorite was crystallized well with the mole ratio of CaO/(SiO₂+AlO_1.5) in the range of 0.75 to 1.00, at the reaction temperature of 230 to 250 ℃ for 5 to 8 hours. The research data obtained in this study demonstrate that the reactive mechanism of the potassium feldspar's dissolution cannot be explained solely on the basis of ion exchange or aluminosilicate depolymerization reaction. The dissolution of potassium feldspar and the crystallization of tobermorite in hydrothermal system are considered possibly as a three-step process. At first, the potassium feldspar decomposes and gives rise to Si-rich and Al-deficient surface precursor complexes, secondly, the precursor complexes（SiO_2·nH₂O）decompose and further to form C-S-H gel and hydrogarnet phases, and at last, the C-S-H gel and hydrogarnet are converted into the tobermorite.

Key words: hydrothermal reaction at low temperature, potassium feldspar, tobermorite, reactive mechanism