Preparation And Properties Of SiO₂ Aerogel Matrix And The Composites

Silica aerogel,formed by the accumulation of SiO₂ particles,is a nanostructured material with three-dimensional porous network structure.Because of its unique structure of low density,excellent heat insulation properties,high specific surface area and high porosity,SiO₂ aerogels have great value in the field of building insulation materials.At present,two main routes are commonly used for drying to prepare SiO₂ aerogels: Supercritical drying and ambient pressure drying.But the supercritical drying methods have remained considerably dangerous and costly,and its own low strength,brittleness,easy to crack and other defects of SiO₂ aerogels limit its application.Therefore,it is of great significance and practical value to prepare low density and high performance SiO₂ aerogels by controlling reaction conditions under ambient pressure drying.In this paper,the two-step sol-gel method was used to optimize the preparation of low-density SiO₂ aerogels under ambient pressure drying.The results showed that when the ratio of raw materials was TEOS: EtOH: H2 O = 1 : 5: 6,hydrolysis and condensation at 50°C,aging after the use of volume concentration of 8% TMCS n-hexane solution modified 4h,at this time to obtain the density of silica aerogel is only 0.138 g /cm3.Further use of TMCS as a surface modifier,changed the hydrophobic properties of aerogel,making its pore structure more uniform and dense,while making the thermal stability of aerogel increased.Because the mechanical properties of the aerogels are poor and the structure is easy to be destroyed,the aerosol was enhanced by the chopped glass fiber.The results showed that the thermal conductivity of the composites can be as low as 0.0234W/?m·K?,compressive strength and bending strength was up to 1.895 MPa,1.27 MPa,so that its strength significantly improved.Considering the thermodynamic properties of the composites,the optimum amount of chopped glass fiber was 5%,the thermal conductivity of the composite was 0.0257W/?m·K?,the compressive strength and bending strength are 1.04 MPa,0.93 MPa.Considering the difference between the size of the glass fiber and the aerogel,the nano-scale CNTs were selected as the enhanced phase to further improve the performance of the aerogel.The results showed that the addition of trace CNTs can help to weaken the heat radiation heat transfer process.The thermal conductivity of the reinforced SiO₂ aerogels was only 0.0211,which was lower than the thermal conductivity of pure aerogels,compressive strength,bending strength up to 1.98 MPa,1.811 MPa.And the thermal conductivity of CNTs-enhanced SiO₂ aerogels was only 0.0211W/?m·K?,which was lower than that of pure aerogels.The compressive strength and bending strength were up to 1.98 MPa and 1.811 MPa.The mechanical properties of the composites prepared by the short chopped glass fiber / CNTs composites were better than that of the single kind of material reinforced aerogels.When the amount of short chopped glass fibers was 5%,the addition of CNTs was 2%,the composite enhanced silica aerogels composites have the best mechanical properties of compressive strength of 2.367 MPa and flexural strength of 1.95 MPa.