Alkali-activation reactivity of chemosynthetic Al2O3-2SiO2 powders and their 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra

摘要

Pure Al2O3-2SiO2 powders were prepared by sol-gel and coprecipitation methods,and their alkaliactivation reactivities were compared.The alkali-activation reactivity of the powder prepared by the sol-gel method was higher than that of the powder prepared by the coprecipitation method.The powders were investigated by 27AI and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy（MAS NMR） to understand the relationship between their structure and alkali-activation reactivity.The 27Al MAS NMR data showed that the five-coordinate AI content of the powder prepared by the sol-gel method was higher than that of the powder prepared by coprecipitation.The higher content of five-coordinate Al corresponded to higher alkali-activation reactivity.The 29Si MAS NMR data showed that for the powder prepared by the sol-gel method,silicon was replaced by aluminum at secondary coordination sites of the central Si atoms during calcination.However,for the powder prepared by single-batch coprecipitation,the main change was from a low degree of polycondensation to a high degree of polycondensation.