Preparation And Performence Of Alumina-silica Aerogel And Composites For Thermal Insulaton

Fiber-reinforced Alumina-silica aerogel composites become an important part in high performance insulation fields for its low bulk density, low thermal conductivity, and well mechanics performance and for its extensive prospective application in aerospace, missile, energy industry, chemical, metallurgy, and fire protection, etc.Both Al₂O₃-SiO₂ aerogel and flexible fiber-reinforced Al₂O₃-SiO₂ aerogel composites which had high resisting temperature, high surface area and low bulk density were synthesized via sol-gel and supercritical drying process by using alumina s-butoxide (ASB) and tetraethoxysilane (TEOS) as precursor. The aerogel's structure was characterized by nitrogen adsorption, SEM, FTIR, DSC-TGA. The mechanism and thermal insulation properties of the compositions were characterized by self-established equipment, thermal conductometer(plate method) and electron omnipotence examination. And established ANSYS Model of composites.The influences of different type of organic alumina alkoxide, conten of ethanol and waer on property of Al₂O₃ sol were discussed. The stabilization and clear aerogels were synthesized when H2O/ASB molar rate was 0.6, alumina s-butoxide (ASB) was precursor by mixing round 45min at 60 degree. Gelation time prolong as conten of ethanol increases. The moler rate of Al₂O₃ sol was established, ASB/EtOH/H2O =1:8¹6:0.6.The structure and high tempreture stability property of Al₂O₃-SiO₂ aerogel was investigated. It was indicated that Al₂O₃-SiO₂ aerogel had a spathic boehmite structure, low density (minimum 0.047g/cm3), high hole ratio (bigger than 96%), high sueface area (maximal 766m2/g). Al₂O₃-SiO₂ aerogel sufferedγ-AlOOH(boehmite)→γ-Al₂O₃→?Mullite change when temperature increased from normal temperature to 1200 degree. As the SiO₂ joined Al₂O₃ aerogel, the surface area of Al₂O₃-SiO₂ aerogel was increaser comparing pure Al₂O₃ aerogel. The surface area of Al₂O₃-SiO₂ aerogel which had well tempreture stability property, increased from 156m2/g to 444.5m2/g at 1000 degree, and 73m2/g o 73m2/g at 1200degree.The influences of different Al/Si molar rate on structure and performance of Al₂O₃-SiO₂ aerogel were also investigated. As the Al/Si molar rate decreased, the surface area increased and then decreased at 1000 degree, when the Al/Si molar rate was 3:1 and 4:1, it had higher surface area 381.6m2/g and 444.5m2/g, respectively. As the Al/Si molar rate decreased, weight loss of Al₂O₃-SiO₂ aerogel was increased and the number of Al-O-Si bond was decreased, that lead high tempreture stability property of aerogel receded. It was indicated that Al₂O₃-SiO₂ aerogel had a better colligation performance when Al/Si molar rate was 3:1 by analysing. It could be used at 1000 degree long time, it was boehmite structure after SCFD andγ-Al₂O₃ structure at 600¹100 degree and mullite structure at 1200 degree. This aerogel's average aperture was 44.6nm, adsorption isotherm belonged toâ…£species.Availability thermal conductivity of Aerogel was calculated by using geometry model and experimen data. SiO₂ aerogel and Al₂O₃-SiO₂ aerogel composites had minimum availability thermal conductivity 0.012W/m·K and 0.030W/m·K at normal temperature. The density of aerogel augmented could reduce high temperature thermal conductivity, but it had a little effect than advanced exinction coefficient by joining another substance.The influences of different Al/Si molar rate, aerogel dencity and fiber bulk density on heat insulation performance of Al₂O₃-SiO₂ aerogel were also investigated. Al/Si molar rate had a little effect on heat insulation performance, and it was better when Al/Si molar rate was 3:1. As the aerogel density and fiber bulk density increased, the heat insulation performance of Al₂O₃-SiO₂ aerogel composites gather head. When Al/Si molar rate was 3:1, aerogel dencity was 0.072g/cm3, fiber bulk density was 0.25g/cm3, Al₂O₃-SiO₂ aerogel composites had better heat insulation performance, whoes thermal conductivity was 0.062W/m·K at 1000 degree, reduced 61% compared with mullite fiber felt.The influences of different aerogel dencity and fiber bulk density on mechanism performance of Al₂O₃-SiO₂ aerogel composites which Al/Si molar rate was 3:1 were investigated. As the aerogel density increased, the mechanism performance from strength to strength, but the tenacity performance was decreased, when aerogel density was 0.072g/cm3, the Al₂O₃-SiO₂ aerogel composites had better mechanism performance, bengding strength, tensile strength and compressive strength of 25% strain was 0.42, 0.53, 0.45MPa, respectively.Examining the thermal insulation properties of flat Al₂O₃-SiO₂ aerogel composites. Composites'cool face temperature was 437 degree by heating up 640s at 1000 degree, corresponding 484 degree of Al₂O₃ aerogel composites. Simulated the examination data by ANSYS software, it was indicated that examination data and simulation data were consistent when surface film coefficient h was 2W/m2·K.