Hydrothermal Synthesis And Preparation Of Thermal Insulation Materials Based On Hydrated Calcium Magnesium Silicate

Hydrated calcium silicate?known as calcium silicate hydrate,tobermorite,and xonotlite,etc.?is the main inorganic gelling material and component of insulation material.Ca and Mg are the same main group elements with similar chemical properties in the nature which may form silicate symbiotic or associated minerals easily.Therefore,the utilization of calcium resources will be affected by magnesium-containing minerals.The available research generally consider that the product of Mg²⁺is mainly Mg?OH?₂ and little amount of Mg²⁺take part in the reaction of silicates.However,the previous research of our group has proved that certain amount of Mg²⁺could enter into the structure of hydrated calcium silicate to form calcium magnesium silicate hydrate under hydrothermal condition.In this study,the crystal structure and formation process of hydrated calcium magnesium silicate were investigated the phase composition,thermal stability and microscopic morphology of hydrated calcium magnesium silicate were characterized.The mechanism,as well as the effects of Mg²⁺on the crystal structures of hydrated calcium magnesium silicate was clarified by the analytical software such as Peak Fit,Diamond and Maud structural refinement.The formation of hydrated calcium magnesium silicate was determined by the evolution process of xonotlite and Mg-xonotlite under different reaction times and addition of Mg?OH?₂.Finally,the spherical hydrated calcium magnesium silicate was prepared by hydrothermal synthesis.Also,the insulation board of hydrated calcium magnesium silicate was prepared by compression forming method.The main works are as follow.?1?Hydrated calcium magnesium silicate was synthesized by hydrothermal method.The effect of Mg²⁺on the crystal structure of hydrated calcium silicate was studied.The results showed that Mg²⁺concentrated in the?202?crystal plane of the xonotlite,resulting in an overlapping peak in the corresponding position of XRD pattern.The d-spacing of?001?and?202?decreases about 0.03?,and the d-spacing of?200?reduces 0.26?.The reason is that the Ca3 and Ca4 sites in xonotlite crystal structure were occupied by Mg²⁺,which result in the larger displacement of Si3 than Si1 and Si2.The transformation of Mg-xonotlite to?-wollastonite had two stages at low temperature and high temperature,which led to increasing the crystallinity and slimming of Mg-xonotlite.?2?The transformation of mineral phases during the synthesis under the condition of hydrothermal at different Mg²⁺additions,temperatures and silicon sources were studied.The results show that a small amount of Mg²⁺can stabilize tobermorite,and the time for the conversion of tobermorite from to xonotlite is doubled.The conversion process is accompanied by the remaining Mg²⁺entering the xonotlite to form Mg-xonotlite.The crystallinity of Mg-xonotlite increased,and then decreased with the increased content of Mg?OH?₂ when quartz powder was used as silicon source.Maximum was Q²/Q³=2.03 in Ca_0.91Mg_0.09Si.The limit solidification of Mg?OH?₂ in xonotlite is 5.27 wt%..The formation of xonotlite underwent a process of C-S-H?I??tobermorite?xonotlite.With the addition of Mg?OH?₂,the Mg-tobermorite was formed with the combination of Mg²⁺and tobermorite,which stabilized the tobermorite and hinders the formation of xonotlite.Mg²⁺enters xonotlite through an ion-exchange channel.Mg²⁺entered through the Q³ defect of the xonotlite,lowering the crystallinity of xonotlite and forming a lower crystallinity of Mg-xonotlite.?3?The spherical particles of hydrated calcium magnesium silicate were synthesized by dynamic hydrothermal method,and then thermal insulation board was prepared by compression forming.The results showed that when 2.24?m quartz powder was used as one of the raw materials,the optimum condition for the preparation of Mg-xonotlite was heating the raw materials at 220°C for 10h.When 10?m quartz powder was used,the optimum condition was heating the raw materials at 220°C for 24h.When the mass ratio of water to solid was 40,secondary particles were formed into spheres with a particle size of 40-60?m under the stirring rate of 250 r/min.The solid solution of Mg²⁺increased the crystallinity of the xonotlite.The mean free path l_p of the phonon was larger and the thermal conductivity of the hydrated calcium magnesium silicate insulation board increased,which had a negative effect on the thermal insulation performance.