液体介质处理对纳米隔热材料细观结构的影响
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摘要
为研究液体介质处理对纳米隔热材料细观结构的影响,并掌握材料结构对毛细管力的承受性,将纳米隔热材料分别在无水乙醇和去离子水中进行了浸泡和常温常压干燥处理。采用热导率测试结合SEM、N2吸附-脱附、光学显微镜等对材料处理前后的细观结构进行了表征,并以Kaganer双孔模型对气相热导率随环境气压的变化进行了描述。研究结果表明,材料固体骨架颗粒尺度和孔隙结构均不受无水乙醇处理的影响;去离子水处理后的材料固体骨架颗粒尺度虽未改变,但颗粒之间的接触面积有所增大,并且孔隙结构发生了两极分化,一部分变大,另一部分变小;处理前以及无水乙醇处理后,材料的孔隙结构均可以等效为70nm和300nm两种尺度的典型孔隙,占比分别约为81%和19%,而去离子水处理后的材料孔隙结构需要等效为30nm和60μm两种尺度的典型孔隙,占比分别约为58%和42%。
To investigate the effect of liquid-wetting on their microstructure and determine their structural stability to capillary tension,nano-porous thermal insulating materials were directly immersed in absolute alcohol or deionized water,and then they were dried under room temperature and atmospheric pressure.The microstructure of the materials was characterized by nitrogen adsorption-desorption,SEM and optical microscope,and the gas pressure dependence of their gaseous thermal conductivity was described by Kaganer model with two different pore sizes.The results indicate that the skeleton particle diameter and the pore size are not affected by wetting with alcohol.However,the interfacial area between adjacent skeleton particles increases and the pore size either increases or decreases via water wetting.For the alcohol-wetted material,two different equivalent pore sizes derived from its gaseous thermal conductivity are 70 nm and 300 nm and their contributions to the total porosity are about 82%and 18%,respectively.In case of the water-wetted material,two different equivalent pore sizes deduced from its gaseous thermal conductivity are 30 nm and 60μm and their contributions to the total porosity are about 58% and 42%,respectively.
To investigate the effect of liquid-wetting on their microstructure and determine their structural stability to capillary tension,nano-porous thermal insulating materials were directly immersed in absolute alcohol or deionized water,and then they were dried under room temperature and atmospheric pressure.The microstructure of the materials was characterized by nitrogen adsorption-desorption,SEM and optical microscope,and the gas pressure dependence of their gaseous thermal conductivity was described by Kaganer model with two different pore sizes.The results indicate that the skeleton particle diameter and the pore size are not affected by wetting with alcohol.However,the interfacial area between adjacent skeleton particles increases and the pore size either increases or decreases via water wetting.For the alcohol-wetted material,two different equivalent pore sizes derived from its gaseous thermal conductivity are 70 nm and 300 nm and their contributions to the total porosity are about 82%and 18%,respectively.In case of the water-wetted material,two different equivalent pore sizes deduced from its gaseous thermal conductivity are 30 nm and 60μm and their contributions to the total porosity are about 58% and 42%,respectively.
引文
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[29]MOREL B,AUTISSIER L,AUTISSIER D,et al.Pyrogenic silica ageing under humid atmosphere[J].Powder Technology,2009,190(1-2):225-229.
[30]BRINKER C J,SCHERER G W.Sol-gel science:The physics and chemistrry of sol-gel processing[M].New-York:Academic Press,1990:237.
[31]杨海龙,王钦,王晓婷,等.压汞和气体吸附在纳米超级隔热材料孔隙结构表征中的应用研究[J].复合材料学报,2013,30(S1):273-278.YANG H,WANG Q,WANG X,et al.Study on mercury porosimetry and gas sorption for pore structure characterization of nano-porous super thermal insulating materials[J].Acta Materiae Compositae Sinica,2013,30(S1):273-278(in Chinese).
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[33]KAGANER M G.Thermal insulation in cryogenic engineering[M].Jerusalem:IPST Press,1969:1-200.
[34]ZENG S Q,HUNT A,GREIF R.Mean free path and apparent thermal conductivity of a gas in a porous medium[J].Journal of Heat Transfer,1995,117(3):758-761.
[35]WIENER M,REICHENAUER G,BRAXMEIER,et al.Carbon Aerogel-Based High-Temperature Thermal Insulation[J].International Journal of Thermophysics,2009,30(4):1372-1385.
[36]ERTL G,KNOZINGER H,WEITKAMP J.Preparation of solid catalysts[M].Weinheim:WILEY-VCH Verlag GmbH,1999:89.
[2]RAO A V,KULKARNI M M,AMALNERKAR D P,et al.Surface chemical modification of silica aerogels using various alkyl-alkoxy/chloro silanes[J].Applied Surface Science,2003,206(1-4):262-270.
[3]PISAL A A,RAO A V.Development of hydrophobic and optically transparent monolithic silica aerogels for window panel applications[J].Journal of Porous Materials,2017,24(3):685-695.
[4]IHARA T,JELLE B P,GAO T,er al.Aerogel granule aging driven by moisture and solar radiation[J].Energy and Buildings,2015,103:238-248.
[5]JENSEN K I,SCHULTZ J M,KRISTIANSEN F H.Development of windows based on highly insulating aerogel glazings[J].Journal of Non-Crystalline Solids,2004,350:351-357.
[6]BAETENS R,JELLE B P,GUSTAVSEN.Aerogel insulation for building applications:A state-of-the-art review[J].Energy and Buildings,2011,43(4):761-769.
[7]WAGH P B,INGALE S V.Comparison of some physicochemical properties of hydrophilic and hydrophobic silica aerogels[J].Ceramics International,2002,28(1):43-50.
[8]RAO A V,HARANATH D.Effect of methyltrimethoxysilane as a synthesis component on the hydrophobicity and some physical properties of silica aerogels[J].Microporous and Mesoporous Materials,1999,30(2-3):267-273.
[9]KATO H,MIYASHITA W,NOMURA,et al.Observation of shrinkage of silica aerogel during capillary condensation of4 He[J].Journal of Low Temperature Physics,2007,148(5-6):621-625.
[10]SANZ-MORAL L M,RUEDA M,NIETO A,et al.Gradual hydrophobic surface functionalization of dry silica aerogels by reaction with silane precursors dissolved in supercritical carbon dioxide[J].The Journal of Supercritical Fluids,2013,84:74-79.
[11]LI W,WILLEY R J.Stability of hydroxyl and methoxy surface groups on silica aerogels[J].Journal of Non-Crystalline Solids,1997,212(2-3):243-249.
[12]BARNYAKOV A Y,BARNYAKOV M Y,BARUTKIN V V,et al.Influence of water on optical parameters of aerogel[J].Nuclear Instruments and Methods in Physics Research Section A:Accelerators,Spectrometers,Detectors and Associated Equipment,2009,598(1):166-168.
[13]ANAPPARA A A,RAJESHKUMAR S,MUKUNDAN P,et al.Impedance spectroscopic studies of sol-gel derived subcritically dried silica aerogels[J].Acta Materialia,2004,52(2):369-375.
[14]MINER M R,HOSTICKA B,NORRIS P M.The effects of ambient humidity on the mechanical properties and surface chemistry of hygroscopic silica aerogel[J].Journal of NonCrystalline Solids,2004,350:285-289.
[15]LAKATOSA.Investigation of the moisture induced degradation of the thermal properties of aerogel blankets:Measurements,calculations,simulations[J].Energy and Buildings,2017,139:506-516.
[16]GURAV J L,RAO A V,NAGARGI D Y.Study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogel dried at ambient pressure[J].Journal of SolGel Science and Technology,2009,50(3):275-280.
[17]MIYASHITA W,YONEYAMA K,NOMURA R,et al.Liquefaction of 4 He in aerogel[J].Journal of Physics and Chemistry of Solids,2005,66(8-9):1509-1511.
[18]KATO H,MIYASHITA W,NOMURA R.Observation of shrinkage of silica aerogel during capillary condensation of4 He[J].Journal of Low Temperature Physics,2007,148(5-6):621-625.
[19]HEINEMANN U.Influence of water on the total heat transfer in ‘evacuated’insulations[J].International Journal of Thermophysics,2008,29(2):735-749.
[20]MERZBACHER C I,BARKER J G,SWIDER K E,et al.Effect of re-wetting on silica aerogel structure:A SANS study[J].Journal of Non-Crystalline Solids,1998,224(1):92-96.
[21]HUSING N, SCHUBERT U. Aerogels-airy materials:chemistry,structure,and properties[J].Angewandte Chemie International Edition,1998,37,22-45.
[22]KWON J,JANG C H,JUNG H,et al.Effective thermal conductivity of various filling materials for vacuum insulation panels[J].International Journal of Heat and Mass Transfer,2009,52(23-24):5525-5532.
[23]FRICKE J,TILLOTSON T.Aerogels production,characterization,and applications[J].Thin Solid Films,1997,297(1-2):212-223.
[24]CAPS R,FRICKE J.Thermal conductivity of opacified powder filler materials for vacuum insulations[J].International Journal of Thermophysics,2000,21(2):445-452.
[25]SINGH H,GEISLER M,MENZEL E.Experimental investigations into thermal transport phenomena in vacuum insulation panels(VIPs)using fumed silica cores[J].Energy and Buildings,2015,107:76-83.
[26]YRIEIX B,MOREL B,PONS E.VIP service life assessment:Interactions between barrier laminates and core material,and significance of silica core ageing[J].Energy and Buildings,2014,85:617-630.
[27]BRUNNER S,WAKILI K G.Hints for an additional aging factor regarding the thermal performance of vacuum insulation panels with pyrogenic silica core[J].Vacuum,2014,100:4-6.
[28]HAERIED S,ANDERSON J,EINARSRUD M A.Thermal and temporal aging of TMOS-based aerogel precursors in water[J].Journal of Non-Crystalline Solids,1995,185(3):221-226.
[29]MOREL B,AUTISSIER L,AUTISSIER D,et al.Pyrogenic silica ageing under humid atmosphere[J].Powder Technology,2009,190(1-2):225-229.
[30]BRINKER C J,SCHERER G W.Sol-gel science:The physics and chemistrry of sol-gel processing[M].New-York:Academic Press,1990:237.
[31]杨海龙,王钦,王晓婷,等.压汞和气体吸附在纳米超级隔热材料孔隙结构表征中的应用研究[J].复合材料学报,2013,30(S1):273-278.YANG H,WANG Q,WANG X,et al.Study on mercury porosimetry and gas sorption for pore structure characterization of nano-porous super thermal insulating materials[J].Acta Materiae Compositae Sinica,2013,30(S1):273-278(in Chinese).
[32]REICHENAUER G,HEINEMANN U,EBERT H.Relationship between pore size and the gas pressure dependence of the gaseous thermal conductivity[J].Colloids and Surfaces A:Physicochemical and Engineering Aspects,2007,300(1-2):204-210.
[33]KAGANER M G.Thermal insulation in cryogenic engineering[M].Jerusalem:IPST Press,1969:1-200.
[34]ZENG S Q,HUNT A,GREIF R.Mean free path and apparent thermal conductivity of a gas in a porous medium[J].Journal of Heat Transfer,1995,117(3):758-761.
[35]WIENER M,REICHENAUER G,BRAXMEIER,et al.Carbon Aerogel-Based High-Temperature Thermal Insulation[J].International Journal of Thermophysics,2009,30(4):1372-1385.
[36]ERTL G,KNOZINGER H,WEITKAMP J.Preparation of solid catalysts[M].Weinheim:WILEY-VCH Verlag GmbH,1999:89.