Study On Preparation And Hygrothermal Performance Of Silica Aerogel Composites For Thermal Insulation

Building energy consumption accounts for a very high share of social total energy consumption,and the proportion in heating and air conditioning of building energy consumption is as high as 50%⁶0%.So reducing the loss of heat?cold?in the maintain comfortable indoor thermal environment process,the insulation measures of walls,roofs,windows and doors of heating and air conditioning building and supplying heating,cooling pipe should be taken.Thus a lot of energy was reduced and further increased the energy utilization.It could reduce energy consumption of building by application of thermal insulating material and improve the effect of the building energy efficiency.However there exist a series of problems in most of thermal insulating materials such as strong moisture absorption,water absorption and high permeability and so on.Thus heat preservation material moisture content is very high.what is more,it would lead to thermal conductivity much higher and corrosion of the wall.So it is necessary to research and prepare one new kind of high performance thermal insulation material of moisture absorption rate of small and strong resistance to wet.By wash water cotton fiber,glass fiber and aluminum silicate fiber of three kinds of fiber mat as enhancement materials respectively,a series of aerogel composites were successfully fabricated reinforced via sol-gel process and drying at ambient pressure.Different aerogel composite materials were prepared under different preparing parameters including ratio of sol and aging time.And alcohol gel compressive performance,density,microstructure and thermal conductivity of composite materials were tested.The relationship between performance of composite materials and preparing parameters were studied.The results showed that maximum compressive strength of alcohol gels is 67.7N.It can obtained more lower density?0.105g?cm-3?and higher porosity?94.5%?of aerogel,specific surface area of 952m²?g^-1,average pore size of 16.77 nm by expand the amount of EtOH 1 times of SiO₂ sol.And thermal conductivity of composite materials is 0.0173W·m^-1·K^-1.Then thermal conductivity of composite material based on three kinds of fiber mat are 0.0174,0.0206,0.0214W·m^-1·K^-1 and all has reached the requirement of super insulation.The thermal conductivity of washing water cotton fiber mat/aerogel composite materials is the lowest.Hygroscopicity of aerogel composite material was tested by weighing method.The results showed that the moisture absorption rate of all composites is very low and it is about 0.5%²%.In addition,thermal conductivity of composites hardly increased after moisture absorption.Then according to the classical adsorption model equation such as Langmuir and Freundlich,BET,D-R and D-A and described the process of adsorption of water vapor of composites.It was found that D-A equation is suitable for the adsorption model,and correlation coefficient of the adsorption equation is over 0.99.The moisture permeability of aerogel composite material was also tested,including wet flow density and moisture permeability.The result showed that volume ratio of sol and fiber influenced on moisture permeability of composite material the most.The moisture permeability of composite material is minimum when the volume ratio of sol and fiber is 1.2.And its moisture permeability is 0.0174g?m-2?Pa^-1?h^-1 and water vapor permeability coefficient is 1.940?10-3g?m^-1?Pa^-1?h^-1.Because moisture permeability of composites was bigger than wall materials.And it could satisfy the requirement for water vapor to difficult in and easy out in external wall thermal insulation system and will not hinder the migration of water and steam in the wall.The hygrothermal performance of all aerogel composite material was studied in the paper.And it was obtained that a new type of aerogel insulation material of ultra-low thermal conductivity,low moisture absorption rate and resistance wet.And it can still maintain heat insulation performance after moisture absorption very well.So it has a good application prospect of aerogel composite material at building heat insulation in high humidity area like guangzhou and chongqing.