Enhancement of thermal stability‐insulation performance of hyper porous materials is the premier issue to design of novel porous thermal protection systems. Boron‐containing monolithic novolac xerogels (BCNXs) were synthesized using sol–gel networking of novolac resin with hexamethylenetetramine (HMTA) and boric acid at the solvent saturated vapor atmosphere (SSVA). The aim was to elucidate the effect of higher crosslinking density and thermal stable boron containing chemical bonds on the microstructure, thermal conductivity, and thermal oxidation stability of novolac xerogels. The results of FESEM and BET analysis showed that the microstructural characteristics of xerogels are significantly depend on the HMTA and boric acid concentration. The thermogravimetric results were analyzed using characteristic kinetic temperature (CKT)‐characteristic kinetic temperature range (CKTR) approximations. The effect of micromorphology of xerogels on the thermal conductivity was investigated. The effective thermal conductivity of samples were in the range of 0.031–0.048 W/m K.

中文翻译：

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含硼整体酚醛清漆干凝胶的微观结构性质，隔热和热降解行为

增强超多孔材料的热稳定性和绝缘性能是设计新型多孔热保护系统的首要问题。使用酚醛清漆树脂与六亚甲基四胺（HMTA）和硼酸在溶剂饱和蒸气气氛（SSVA）的溶胶-凝胶网络合成了含硼的整体酚醛清漆干凝胶（BCNX）。目的是阐明较高的交联密度和热稳定的含硼化学键对线型酚醛干凝胶的微观结构，热导率和热氧化稳定性的影响。FESEM和BET分析的结果表明，干凝胶的微观结构特征显着取决于HMTA和硼酸浓度。使用特征动力学温度（CKT）-特征动力学温度范围（CKTR）近似值分析热重分析结果。研究了干凝胶的微观形态对热导率的影响。样品的有效导热系数在0.031–0.048 W / m K的范围内。