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纳米隔热材料的热导率变化规律
杨海龙,胡子君,胡胜泊,王晓婷,孙陈诚
航天材料及工艺研究所,先进功能复合材料技术重点实验室,北京 100076
摘要:
为认识和掌握纳米隔热材料的热导率变化规律,以正硅酸乙酯(TEOS)为硅源、炭黑为遮光剂、石英纤维为增强体,采用溶胶-凝胶工艺结合超临界干燥技术制备了纳米隔热材料,并采用热导率测试仪、N2吸附-脱附、SEM、激光粒度仪对材料进行了表征。测试结果表明:未添加炭黑的材料常压热导率随表观密度的变化以203kg/m3为分界点,分界点之前随表观密度的增大线性降低,分界点之后则随表观密度的增大线性升高,并且后一阶段较前一阶段变化快。孔隙率相同时,常压热导率随炭黑含量的增加先降低后稍有升高,极限真空热导率逐渐降低,而常压条件下的气相热导率增大。在半对数坐标系中,气相热导率随环境气压的下降而降低,并且依据降低速率可以划分为三个阶段,101.325~30kPa之间下降最快,且变化值约为6mW/(m·K);30~0.1kPa之间下降较快,且变化值约为2mW/(m·K);0.1~0.01kPa之间下降最慢,且基本可以忽略不计。材料常压热导率最低值为16.62mW/(m·K),添加5wt%的炭黑后可以进一步降低至14.50mW/(m·K)。
关键词:  纳米隔热材料  热导率  炭黑  极限真空  气压
DOI:10.12044/j.issn.1007-2330.2019.02.006
分类号:TB332,TB34
基金项目:国家“973”计划项目 2015CB655200 国家“973”计划项目(2015CB655200)
Thermal Conductivity Variation of Nano-Porous Thermal Insulating Materials
YANG Hailong,HU Zijun,HU Shengbo,WANG Xiaoting,SUN Chencheng
Science and Technology on Advanced Functional Composites Laboratory,Aerospace Research Institute of Materials & Processing Technology,Beijing 100076
Abstract:
To understand the variation of their thermal conductivity, nano-porous thermal insulating materials loaded with carbon black and silica fiber were synthesized from tetraethylorthosilicate (TEOS) via a sol-gel process followed by supercritical drying, and they were characterized by thermal conductivity tester, nitrogen adsorption-desorption, SEM, laser particle size analyzer. Test results indicate that the thermal conductivity of the materials without carbon black at atmospheric pressure declines linearly and then rises linearly with increasing apparent density, and the lowest value appears at apparent density of 203 kg/m3. The variation rate of thermal conductivity in the rising region is higher than that in the declining region. With the increase of doped carbon black, the thermal conductivity of the resulting materials with the same porosity at atmospheric pressure decreases first and then increases slightly, their thermal conductivity under ultimate vacuum drops, and their gaseous thermal conductivity at atmospheric pressure grows. In semilogarithmic coordinate, the gaseous thermal conductivity reduction of the resulting material as a function of gas pressure can be divided into 3 stages according to decreasing rate, it decreases rapidly by 6 mW/(m·K) from 101.325 to 30 kPa and then decreases slowly by 2 mW/(m·K) from 30 to 0.1 kPa, while the reduction between 0.1 and 0.01 kPa can be neglected. The lowest thermal conductivity of these materials at atmospheric pressure is only 16.62 mW/(m·K) and it can be further reduced to 14.50 mW/(m·K) via doping 5 wt% carbon black into these materials.
Key words:  Nano-porous thermal insulating material  Thermal conductivity  Carbon black  Ultimate vacuum  Gas pressure