Synthesis Of Calcium Silicate Power By Hydrothermal Method

As the wider use of calcium silicate material,the demand of calcium silicate material's performance is higher and higher,and calcium silicate material synthesized by dynamic hydrothermal method due to its good performance and favored.In this paper,industrial sodium silicate or silica sand as the silicon source,industrial lime as a calcium source,tobermorite and xonotlite synthesized by dynamic hydrothermal method.Phase generating rules,microstructure conversion,the change of particle size and bulk density all discussed,the process conditions and mechanism for its synthesis were investigated.At the same time,xonotlite roasted and prepared the first grade wollastonite,which providing theoretical support and practical guidance for their application to industrial production.The main results are showed as follows.Silica sand can be reacted directly with sodium hydroxide solution,and sodium silicate solution with a small amount of impurities can be prepared.The higher reaction temperature,the longer reaction time,and the greater excessive number of reaction,all lead to the higher mole ratio of silicon oxide to sodium oxide in solution.The best dissolution conditions of silica sand are as follows:dissolution temperature is 180?,dissolution time is 2h,and the reaction of silica sand to sodium hydroxide solution excess number is 15%.In dissolution process of industrial sodium silicate,with the increase of the mass ratio of SiO2 to Na2O,sodium hydroxide concentration,and reaction temperature,the solubility of sodium silicate were changed better and the mole ratio of silicon oxide to sodium oxide in solution increased.The best dissolution conditions of industrial sodium silicate are as follows:the mass ratio of SiO2 to Na2O is 0.83,the concentration of sodium hydroxide is 120g/L,reaction temperature is 95 ?,and dissolution time is 4h.Tobermorite can be synthesized from synthetic sodium silicate solution and digestant calcium hydroxide slurry by hydrothermal method.Product is poorly crystalline C-S-H(I)type calcium silicate hydrate gel when the temperature at 90 ??120 ?,then it turns into good crystalline flake tobermorite at 160?,continue to raise the temperature to 200 ? tobermorite turns into fibrous xonotlite with large ratio of length to diameter.When the temperature at 90?-160?,the particle size of products roughened and specific surface area reduced.When the temperature change from 90 ? to 160?,the particle size of products gradually refined and specific surface area increased,and with the temperature increase bulk density decreased.The crystalline properties of products were changed better and the bulk density of products increased when the C/S is 0.7?0.8.The crystalline properties of products were changed poor and the bulk density of products decreased in synthetic tobermorite process when the C/S from 0.8 to 1.0.The particle size of products gradually refined with the increase of the C/S.The particle size of products refined when the L/S change from 2.7 to 4 and gradually roughened at 4-5.Bulk density decreases with the increase of L/S.Prolonging the reaction time is conducive to the crystallization and formation of tobermorite.The optimal conditions for the synthesis of tobermorite are as follows:sodium silicate solution and digestant calcium hydroxide slurry synthesis method,C/S is 0.8,reaction temperature is 160?,reaction time is 4-8h.Xonotlite can be synthesized from tobermorite by hydrothermal method at high temperature.With the increase of time,the crystallinity of xonotlite increases.The main composed of product is xonotlite,and it also contains a small amount tobermorite.In the direct synthesis of xonotlite process,the temperature is 240?,C/S is 0.8,L/S is 15 and reaction time is 5h,silica sand and lime can reacted very well.Product mainly is xonotlite of spherical secondary particles structure,and a very small amount of unreacted silica sand.The optimal conditions for the synthesis of xonotlite are as follows:tobermorite hydrothermal transition temperature is 240?,transition time is 5-10h,the ratio reaction of liquid to solid is 8.In the direct synthesis of tobermorite process,the temperature is 160?,C/S is 0.8 and reaction time is 10h,silica sand and lime can't reacted well,a large number of silica sand unreacted,only a small amount of tobermorite generated.Xonotlite can be synthesized by three ways,the first one is C-S-H(I)type calcium silicate hydrate gel? tobermorite ?xonotlite,the second one is C-S-H(I)type calcium silicate hydrate gel? xonotlite,and the third one is directly synthesized from silica sand and lime.The structure of synthesized xonotlite is intertwined fibrous aggregates formed porous spherical structure.Wollastonite with fibrous structure can be obtained from xonotlite by roasting at 900 ?for 2h,which the ratio of length to diameter is above 10,some can reach as much as 20 or more.Wollastonite's whiteness above 90%,which produced from industrial sodium silicate and industrial lime,and own low content of impurities,its ignition loss is 2.50%and the composition can meet the requirements of frist grade wollastonite.