Study On Preparation Of Xonotlite Thermal Insulating Materials From SiO₂ Gel Byproduct Of Zirconium Oxychloride

With the rapid development of industrialization and urbanization,the shortage of resources and the deterioration of the environment are becoming increasingly serious.The urgent tasks on hands are to implement energy-saving and emission reduction,to strengthen ecological environmental construction and to develop the recycling economy.Cyclic utilization of industrial Solid Wastes and application of energy-saving new materials had been paid more attention in the realm of Science and Technology.In this research,Xonotlite-type thermal insulation materials were prepared using Zr-containing Silica Residue,a byproduct of zirconium oxychloride.A feasible way was provided,which combines the advantages of environment and economy,for comprehensive utilization of Zr-containing Silica Residue to effectively solve the problem of environmental pollution,and to prepare Xonotlite thermal insulation material with low costs.This paper makes research mainly on pretreating and activating of Zr-containing Silica Residue,hydrothermal conditions,transformation process of synthesizing Xonotlite,mechanism of synthesizing secondary particles,preparing Xonotlite-type thermal insulation materials and testing physical properties and so on.The technical route and method of preparation of Xonotlite-type thermal insulation material using Zr-containing Silica Residue are been initially established.Direct-washing,waste-alkali-liquor neutralization and lime neutralization were to treat Zr-containing Silica Residue.Impurity removing and activicating effects of different method were investigated by XRD,FT-IR and SEM techniques.It was shown that the[SiO4]4-polymerization degree of the silica gel treated by lime neutralization can be reduced,and the reactivity of the gel is enhanced correspondingly,which contribute to synthesizing of Xonotlite.Xonotlite was synthesized by the dynamic hydrothermal reatction of nCaO:nSiO2 in the molar ratio of 1:1 and the mass ratio of water-solid of 30:1 at 200? for 6h with stirring speed 100r/min.The length of synthesizing xonotlite fiber are between 3?12?m,and the ratio of length-diameter is between 40?60.Through adjusting water-solid ratio to 35,Xonotlite secondary hollow particles were well synthesized at 210? for 6h.On the basis of slurry containing secondary hollow particles,insulation materials was prepared through pressure filtration and suction molding by adding 4%alkali-resistanting glass fibers and 3%methyl cellulose as reinforcing agents.The results showed that bulk density is 0.084g/cm3,the porosity reaches as high as 97%and thermal conductivity is only 0.0305 W/(m-k)by the characterization of samples.All of the proporties are far more than the other insulation materials.The mechanism of transformation of xonotlite was disscused by analysing changes of phases and crystal morphology through XRD,SEM at different stages.It turned out that no tobermorites occurred in the whole process of synthesis,and the reaction between silica gel and lime combine to form amorphous CSH first,which subsequently became semi-crystalline CSH(I),and then it transformed into xonotlite.And introducing additional cation affected the transformation of target product in synthesis system.Al3+ can generate Al-tobermorite,Zr4+ can promote the growth of xonotlite fibers and Si4+(quartz)can improve the formation of secondary particles.