An Investigation In Ambient Pressure Drying Preparations Of Methyltriethoxysiliane Based Aerogel Monoliths With Enhanced Mechanical Property And Effective Thermal Insulation

The ambient pressure drying preparation of silicon-based aerogel monoliths is less expensive.As a type of light weight and porous nanomaterials,silicon-based aerogels have wide application prospects.It is of great significance to improve the mechanical property of silicon-based aerogel monoliths for practical applications.In this work,the methyltriethoxysilane(MTES)hydrolysis and gelation processes were systematically studied by selecting MTES as a silicon precursor,ethanol as a solvent,and ammonia as a catalyst for the water to ethanol volume ratios of 0.9,1.0 and 1.5.Accordingly,the time for complete MTES hydrolysis(tH)and time for gelation(tG)were determined.The effects of ammonia amount,aging time,aging temperature and drying temperature on the structures and properties of MTES-based aerogel monoliths were investigated by orthogonal experiments.The synthesis route for the ambient pressure drying preparation of MTESbased aerogel monoliths possessing a good integrality,low density,highly efficient thermal insulation and excellent mechanical property was developed.The influences of improving preparation procedures on the mechanical property of MTES-based aerogel monoliths are discussed.The experimental results revealed that the completion degree of MTES hydrolysis process could be quantitatively characterized by variation of silicon-oxygen-carbon(Si-OC)characteristic band in infrared(IR)spectrum.The time corresponding to the disappearance of Si-O-C characteristic band is taken as the time for complete MTES hydrolysis(tH).On the other hand,the gelation process could be quantified by measuring the viscosity-time curve in which the time corresponding to the maximum viscosity was determined as the gelation time(tG).As a result,an effective control of the sol-gel process was achieved.Based on the obtained values of tH and tG,the orthogonal experiments were carried out.It was found that when the water to ethanol volume ratios were 1.0 and 1.5,the as-prepared aerogels under the optimized parameters had the bulk densities of 0.101 g·cm-3 and 0.083 g·cm-3 with the thermal conductivities of 0.043 W·m-1·K-1 and 0.046 W·m-1·K-1,respectively.The average compression moduli of 79.1 kPa and 59.2 kPa for the water to ethanol volume ratios were 1.0 and 1.5 were also obtained,respectively,which were increased by an order of magnitude compared with the preparation procedure before the improvement in both cases.In addition,the compressive stress-strain curves recorded from the aerogels prepared with the water to ethanol volume ratios of 1.0 and 1.5 exhibited nearlinear and linear responses,respectively,during the tests from specimens being loading to being destroyed.Accordingly,the optimized parameters for the water to ethanol volume ratios of 1.0 and 1.5 were determined to be the hydrolysis time of 140 min and 120 min,the ammonia amounts of 0.18 mL and 0.24 mL,and the gelation time of 99 min and 32 min,respectively.The temperatures during the MTES hydrolysis and gelation processes were fixed to 26℃ with the aging temperature of 55℃,the aging time of 48 h,the drying temperature of 80℃ and the drying time of 24 h.