Research on Preparation of Nano-SiO_2 and the Influences of Nano-SiO_2 and Silica Fume on OPC

Abstract: The characteristic, structure, preparation methods of nano-SiO2, merits and demerits of these methods are summarized in the thesis after looking up the literatures at home and abroad. Its application in the fields of rubber, plastics and building materials are also recounted. In addition, developing situation in our country, the kinds and properties for high-performence OPC(Ordinary Portland cement) at home and abroad are also summed up. Then the methods of solid-phase preparation of nano-SiO2 and study orientation of nano-SiO2 composite cement are posed.The properties of nanometer materials, for instance, surface-effect, small-size effect and so on, were presented in nano-SiO2. And high activities of reacting chemically with cement matrix existed in nano-SiO2. In this thesis, the effective combination nanometer technology theories with cement hydrate theories are approched and the effect of nanometer inducement hydrate was firstly put forward. The feasibility of preparation nano-SiO2 composite cement was discussed here.With the use of test methods of TEM, SEM, TG/DTA, XRD and IR, the influences on the properties in azeotropic distillation and direct dry during preparing nano- SiO2 powder are studied. The results show that thewater in silica gel can be effectively removed by azeotropic distillation and the formation of hard agglomerates in the drying process is prevented. The particles of nano-SiO2 powder are amorphous and average particle diameters are in the range of 20 to 30 nm.After studying the activities of nano-SiO2 and silica fume individully, they are mixed into highly active additives and added to ordinary Portland cement for approaching composite modified effect. After testing the properties of macroscopic mechanics, anti-penetrability and porosity in modified hardening slurry, compressive strength, anti-penetrability and porosity are obviously improved and the activities of nano-SiO2 powder are higher than these of silica fume. When mixing them, these activities are even excellent. There are dense microstructure, thick interwoven net-C-S-H and fewer defects in modified hardening slurry. The nano-SiO2 powder can evidently absorb the Ca (OH) 2 phases in the slurry.According to the above-mentioned studies, the reactive mechanism of nano-SiO2 in the slurry is approched. New thinking of preparing nano-SiO2 with the help of method of solid phase reaction and up-to-date concept of nanometer inducement hydrate effect are put forward here…
Key words: nano-SiO_2; azeotropic distillation method; composite modified cement; nanometer inducement hydrate effect.

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