| In order to reduce the energy consumption and time for producing tobermorite,comparatively,microwave hydrothermal synthesis technology has more advantages.Therefore,in this paper,study on the microwave hydrothermal synthesis of tobermorite,Al-tobermorite and fly ash based tobermorite was carried out.Subsequently,the samples prepared under microwave hydrothermal condition were characterized by XRD,SEM,TG-DTG,NMR,TEM and nitrogen adsorption,which was then compared those prepared under conventional hydrothermal condition.The main conclusions are as follows:(1)The suitable conditions for microwave hydrothermal synthesis are:Ca/Si ratio of0.83,liquid-solid ratio of 30m L/g,synthesis temperature of 220℃,synthesis time of 1.5h.The time for producing tobermorite under microwave hydrothermal condition is only about 9%of that for producing tobermortie under conventional hydrothermalcondition.According to XRD,the crystallinity of tobermorite synthesized by microwave hydrothermal method is inferior to that of traditional hydrothermal method.The morphology of tobermorite obtained under microwave hydrothermal condition looks like small sheets of stacked honeycomb,while the tobermorite obtained under conventional hydrothermal condition appears the shape of whisker.(2)The suitable Al/Si ratio for synthesizing Al-tobermorite is 0.15.The specific surface area and pore volume of Al-tobermorite synthesized under microwave hydrothermal condition are larger than those synthesized under conventional hydrothermal condition.Al-tobermorite appears long sheet,but the width of cross section of Al-tobermorite synthesized under microwave hydrothermal condition is slightly larger than that under conventional hydrothermal condition.The results of FTIR and NMR show that Al replaces the silicon at Q~2 and Q~3 positions in the Al-tobermorite structures prepared under microwave or conventional hydrothermal conditions.TEM results indicate that as the content of aluminum ion increases,the crystallinity of tobermorite increases and the lattice constant c value increases.(3)Most of the products in the samples made from fly ash are Al-tobermorite,which appears long sheets.In comparison,the fly ash based tobermorite crystal synthesized under microwave hydrothermal condition is finer,with smaller average pore size and larger specific surface area,and its suitable synthesis time is 3h,which is only half of the time for synthesizing tobermorite under conventional hydrothermal condition. |
