| A three dimensional porous silica aerogel(SiO2)is a kind of nano-porous materials with a large surface area,high porosity,low density,low thermal conductivity.Because of these special properties,SiO2 aerogel has a very wide applications in optical,electrical,thermal insulation,environmental protection,catalysis,chemical and other fields.In this study,preparation of the SiO2 aerogel via ambient air dry method and its composite insulation materials were systematicly investigated.First,hydrophobic SiO2 aerogel was prepared used water glass as starting materials by sol-gel method through the surface modification and the solvent replacement followed by atmospheric drying.According to the experimental rusults,the optimized preparation parameters of hydrophobic SiO2 aerogel was determine.The typical processure is as follows.The mixture of the water glass and water with a ratio of 1:5 was catalyzed by the 1:9 hydrochloric acid to form Sol,then it aged for 3 days,immersed in distilled water and anhydrous ethanol for 1 day respectively in sequence,to removal of the sodium ions(Na+),chloride(CI-)from the gel,and to replace water by ethanol.After that,three methylchlorosilane(TMCS)was used to modify the gels to forming the hydrophobic suface of SiO2,followed by hexane replacement until the water in gel was completely removed,then dried at 150?.The high quality SiO2 aerogel was obtained with a density of 0.1g·cm-3,porosity of 95.5%,and thermal conductivity of 0.018?0.022W/M·K which is 1?3 times lower than the commercial thermal insulation materials.Additionally,the obtained SiO2 aerogel has a large surface area of 472.5m2·g-1 and high pore volume of 3.47cm3·g-1 with an average pore diameter of 27.5nm.The X-ray diffraction analysis(XRD)shows the synthesied aerogel is an amorphous SiO2 with a nanoporous structure and possesses a good thermal stability-400? by t hermal analysis(TG-DSC)The infrared spectrum analysis(FT-IR)indicated that there are a large amount of Si-O-Si-(CH3)3 functional groups on the SiO2 aerogel surface,which is the main reasons for the SiO2 hydrophbic.Secondly,SiO2 aerogel/acrylic resin composite coating was prepared,acrylic resin was used as film forming materials,SiO2 aerogel powder was used as inorganic functional filler.The basic performance tests show that the composite coating has a good chemical stability and mechanical properties.Insulation performance test showed that the insulation performance of composite coatings increased with the amount of the SiO2 aerogel.When the SiO2 aerogel content reaches 20%,the heat insulation effect is best.Although the addition of SiO2 aerogel reduced the visible light transmittance through composite,it has a very good shielding effect on UV light.The hydrophobility of composite increased with the amount of SiO2 addition.The contact angle of is upto 118.80 when the amount of SiO2 aerogel reaches 20%.Due to the presence of-CH3 groups and a small amount of Si-OH groups in the SiO2 aerogels,it has a strong binding force with acrylic resin.Finally,aluminium phosphate binder was synthesized using aluminum hydroxide(AI(OH)3)and phosphate(H3PO4)as starting materials.And then SiO2 aerogel composite insulation block materials were prepared using magnesium oxide as curing agent.through adjusting the contents of the components and other parameters,the effect of the ratio of Al(OH)3 and H3PO4 in binder,the contents of curing agent and SiO2 aerogel on the properties of the composites were determined.The optimized preparation conditions is that the ratio of Al(OH)3 and H3PO4 in binder is 3g:50ml.The adding amount of curing agent is 9g and SiO2 aerogel is 2g to each 3ml binder.The compressive strength of the composites is 2.81 MPa,moisture absorption rate is 0.92%,and contact angle is 133.3°.Infrared analysis and thermal analysis prove the presence of AIPO4,MgHPO4 in the SiO2 aerogel composite insulation block samples.Insulation performance test shows it have a good heat insulation effect. |
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