基于新型防热机理的防热材料的设计与试验验证

Design and Experimental Verification of Thermal Protective Materials Based on the New Thermal Protective Mechanism

传统的防热材料大多是依靠材料自身的高熔点"忍受"热流或依靠缓慢烧蚀来被动地延长寿命的,这些材料因其密度大或耐氧化不足等问题已经不能满足飞行器设计者的期望,突破传统的被动式防热的思路从防热机理的源头上探索新的思路或许可以找到可行的技术途径。作者设计了一个新的材料体系——耗散防热材料,即在石墨中加入还原性金属,在烧蚀过程中还原性金属耗散热量,同时耗散外界的氧,自发生成氧化物陶瓷膜。新的材料设计的思想是"利用"热流而不是单纯"忍受"热流,初步试验验证表明,在廉价的石墨渗入耗散剂——铝制备的耗散防热材料,在2 900℃,4 MW/m2热焓值烧蚀下,线烧蚀率仅为传统C/C的1/10。其耗散防热原理包含了以往的汇热防热、辐射防热、烧蚀防热、发汗防热等防热形式,增加了相变反应防热,是一种新的防热原理,这种高效能、低成本的材料预计具有很好的应用前景,也将推动非平衡条件下的金属化学基础理论突破。本材料研究的科学问题,涉及高温、高压、高速气流冲刷等非平衡状态的化学反应问题、金属流动问题等,这些问题的研究必将推动材料科学与传热学、流体力学、燃烧化学、气动力学等学科的交叉互动和新的发展。

Innovation design of the new ablation resistance materials should be focus on the source of the heat protection mechanism, because it is almost the high melting point or slow ablation rate to ＂endure＂ heat flow or prolong use life for the present traditional thermal protection materials, whose large density or ablation rate can not meet the strict requirement of future vehicle designer. The author designed a new material system--dissipation thermal protection materials--infiltra- ting reducing metal to graphite, whose dissipative agent dissipate heat and oxygen in ablation, and generate a kind of ce- ramic membrane to protect matrix. The new idea is to ＂make use of＂ , not ＂endure＂ heat flow, and the preliminary test results show that the liner ablation rate of the composite infiltrating A1 （ as dissipative agent） to graphite is 1/10 of that of C/C in the condition 2 900 ℃, enthalpy values of 4 MW/m^2 , whose cost is only 1/50 of C/C ! Dissipation thermal protection is a new form of thermal protection which includes phase transition besides sink heat, radiation, ablation, transpiration etc. The composite is expected to be very attractive for its good property and low cost, and it faces different problems of reaction rate and metal flowing etc. in the supercritical state-high temperature, high pressure and high speed airflow from the present ablation resistance materials only at high temperature, while it is believed that research on these problems will surely promote the interaction of material science, heat transfer, fluid mechanics, cumbustion chemistry and gasdynamics.