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| In this paper, xonotlite was synthesized by CaO and amorphous SiO2 powder in hydrothermal method. Thermal behavior of the xonotlite was characterized by Differential Scanning Calorimetry/Thermo Gravimetric (DSC/TG), and X-ray powder diffraction (XRD) was used to investigate the crystalline phase. The insoluble matter of the xonotlite in diluted hydrochloric acid and activity of Ca2+ ions in the xonotlite were measured to characterize the chemical behavior. The morphology and composition of the xonotlite and insoluble matter were tested by Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS). The crystalline phase of the synthetic sample was xonotlite at the temperature under 873K. From 873K to 1023K, the xonotlite phase could lose hydroxyl, at 1023K, the xonotlite transformed to wollastonite. During the dehydroxylation process of xonotlite, the Ca2+ ions could be activated and then resulted in the dissolution rate of Ca2+ ions increased from 2.75wt% to 4.81wt%, and the content of insoluble matter, which was composed of silicon, was also increased. The insoluble matters were proved to be porous, whose maximum BET surface area was 670m2/g and the most probable distribution pore size was 0.57nm. The porosity of the insoluble matters could be attributed to the selective dissolution of the activated xonotlite due to the weaken of the coordination between Ca2+ and the silicon skeleton. |
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| Keywords:xonotlite; thermal behavior; activated Ca2+ ions; insoluble matter; porous silicon; selective dissolution |
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