Hydrothermal Synthesis Of Calcium Silicate Powder By Additive Strengthening

Calcium silicate powder has many advantages,such as small bulk density,low thermal conductivity,high heat tolerance,high strenth and good adsorption and so on,so it is used widely in building materials,insulation materials,filler in paper and rubber,decontamination,biomedical materials and other fields.With the development of calcium silicate materials's application,we have a higher requirements on its performance.In this paper,we select several kinds of additives that some are commonly used in the hydrothermal synthesis of calcium silicate and others are additives which are used to guide the growth of crystal in the process of calcium carbonate production and are chosen by the similarity of crystalline and ion in the reaction system.The technics of dynamic hydrothermal synthesis was used to prepare xonotlite and tobermorite by using industrial lime and quartz sand as the raw material.The influence rule of different additives about the physical and chemical properties consisting of the phase composition,crystal structure,microstructure,particle size,bulk density,oil absorption,water absorption and true density of calcium silicate powders were systematically studied,and explore the influence rule of different additives in the hydrothermal synthetic process of calcium silicate powder.The main results are as following:This paper has studied on the effects of inorganic and organic additives in the hydrothermal synthetic calcium silicate.Inorganic additives include ZrOCl2,STT,V2O5 and Na4P2O7,and organic additives have cetrimonium bromide(CTAB),citric acid and polyethylene glycol.In the synthesis process of xonotlite,CTAB,V2O5 and Na4P2O7's products are respectively kilchoanite,calcium vanadate and hydroxyapatite,and reduce the content of xonotlite.While citric acid,polyethylene glycol,ZrOCl2 and STT can promote the formation of xonotlite,and it occurs scawtite in the products of citric acid and polyethylene glycol.Through analyzing the microstructure,it can generate the powder that is a irregular shape,concave slope in the surface and honeycomb structural xonotlite with no additive,STT can promote to generate a large number of xonotlite which is well-crystallized,smooth and globular,and ZrOCl2 can promote the formation of the plate-like xonotlite with a spinulose surface,a loose structure,a clear fiber-like morphology,and plenty of fibers are scattered around.Compared with no additive,STT can increase the crystallinity,grain size of the(112)crystal face and specific surface area of the xonotlite,and reduce its particle size,bulk density,and the absorption of oil and water,in which the descend range of bulk density is maximum.In the synthesis process of tobermorite,STT increase the content of synthesis tobermorite.CTAB,citric acid,ZrOCl2,V2O5 and Na4P2O7 are not conducive to the formation of tobermorite.Polyethylene glycol inhibition the synthesis of tobermorite.Compared with no additive,STT can also enhance the crystallinity,grain size of the(220)crystal face and the absorption of oil and water of the tobermorite powder,reduce its particle size and bulk density,in which the descend range of bulk density is larger.Based on the above analysis,STT is determined to be the best additive for the hydrothermal synthesis of xonotlite and tobermorite.It has studied on the influencing rules of the hydrothermal synthetic calcium silicate when the amount of STT is between 0%to 8%.With the continuous increasing amount of STT,the content of xonotlite,the grain size of the(112)crystal face and crystallinity all increase firstly and then decrease;The particle size of product becomes big when adding a little,and then it first thick hind fine with the continuous increasing;The plate-like xonotlite is changed from a thick and short one to be slender fiber;The bulk density and true density decrease firstly and then increase,the oil absorption value keeps decreasing and the water absorption rate is about 80%.With the increase of STT,the content of tobermorite increase firstly,then decrease and increase again finally,the grain size of the(220)crystal face increase firstly and then decrease,and the crystallinity of tobermorite constantly rise;The effect of particle size is the same as the one in the process of synthesizing xonotlite with STT;The microstructure of tobermorite is change from honeycomb irregularity to spherical,porous structure,and then transform into being dense lamellar;The bulk density and true density increase firstly,then decrease and increase again finally,and the oil and water absorption have a opposite change.Based on the above analysis,4%is the optimal added content of STT for the hydrothermal synthesis of xonotlite and tobermorite.The effect of reaction time on the synthesis of calcium silicate by hydrothermal method has been studied when adding 4%STT.With prolonging reaction time,on the one hand,the content of xonotlite,the specific surface area,oil absorption volue and water absorption rate of powder constantly heighten,and the particle size,bulk density and true density continually decrease,and the plate-like xonotlite fibers are thinner and longer.On the other hand,the content of reactant is gradually reduced in the beginning process of synthesis tobermorite,but it can't compound tobermorite.The particle size,oil absorption volue and water absorption rate of tobermorite powder are increasing and its specific surface area,bulk density and true density gradually decrease,and its blocky granule gradually disappear with the gradually agglomeration of flocculus forming lamelliform tobermorite.At the same time,we have compared the synthetic effect in the same time without adding additives.To synthesise xonotlite,The results show that STT can accelerate the transformation of tobermorite into xonotlite;The powder's bulk density and particle size are lower because of the smaller microscopic particles and the more hollow structure among the plate-like xonotlite consisting of more slender fibers;The oil absorption volue and water absorption rate of xonotlite with STT are small than that with no additive.With regard to synthesise tobermorite,STT can delay the crystallization of tobermorite when the reaction time is less than 4 hours,and the microscopic particles of the tobermorite is more dispersed and more existence forms.STT can accelerate the reaction process of tobermorite when the reaction time is between 4 hours and 8 hours;STT is more suitable for the refinement of tobermorite powder and the specific surface area of its powder is greater;It also turned out that the more content of tobermorite is,the less bulk density and true density and the bigger oil absorption volue and water absorption rate.