Influence of hydrothermal synthesis condition on xonotlite crystal morphology

This investigation was made to examine how the conditions of hydrothermal synthesis influence the crystal structure of xonotlite and its morphology. For synthesis we used amorphous silica fume and SiO2/CaO molar ratio equal to 1.0, water-solids ratio W/S = 10 and W/S = 15. The samples were cured hydrothermally in the rotation autoclave with mixing rod for 2 and 4 hours at 200 °C. The products were characterized by X-ray diffraction, differential thermal analysis, thermogravimetry, SEM, atomic force microscopy and mercury intrusion porosimetry. The low W/S ratio and mixing intensity had a decisive effect on processes of formation of xonotlite. During the 4-hour synthesis at W/S = 15, well formed xonotlite fiber of 0.2 mm diameter was obtained. Under the same conditions, but at W/S = 10, the obtained xonotlite was poorly formed, with fiber of 0.07 mm diameter. The mercury intrusion porosimetry method was used to examine and compare the surface of synthesized xonotlite. In the case of well formed xonotlite, the surface equals to 8.027 m2/g and that of poorly formed xonotlite 22.328 m2/g. The investigation of pressed xonotlite powder by XRD shows the rise in diffraction peak intensity (0.700; 0.324) nm and the drop in diffraction peak intensity (0.308; 0.184) nm. With tobermorite, there is a rise in diffraction peak intensity (1.13; 0.542) nm