Surface Catalyticity Properties Testing And Characterization Methods Of Thermal Protection Materilas

Aerosphere environment is the most complicated and dangerous region for hypersonic flight of vehicles, the realization and guarantee is thermal protection technology, which demands the precise prediction of service thermal environment and material thermal response. With the enhancement of flight speed, incoming flow is decelerated by the shock wave compression or viscous retardation, which leads to the amounts of thermal energy transform from kinetic energy, arising the “high temperature gas effects”. The consequence of the effects is not only emerge severe aerodynamic heating for vehicle surfaces, but also the intense nonlinear coupling effects with vehicle surface materials by obvious high temperature flowing of the “non-equilibrium effect”. On one hand, the aerothermodynamic environment will change the material surface properties, on the other hand, material response will affect the aerothermodynamic load on a great extent which vehicle bears, the aerodynamic thermal/mechanical properties and thermal protection of vehicles will be affected seriously, which is becoming a huge challenge to high temperature mechanical properties of thermal protection materials, and prove to be the common difficulty and “task killer” to develop the hypersonic vehicles.The current main thought of solving thermal protection problems is the new thermal protection materials preparation and structure optimization from the view of materials and structure, respectively, to satisfy the service demands of aerothermodynamic loading. However, because of the restriction of new materials research and development and the high mobility structure properties, promoting substantially the thermal/mechanical/ablative properties through material composition control and structure optimization is difficult. As a consequence, effective solutions should from the point of environment which thermal protection materials service, exploring the coupling effects between aerothermodynamic and materials, governing the aerothermodynamic loading from coupling effects actively, reducing the thermal protection materials service temperature under the same aerothermodynamic environment, in order to relieving the pressure of thermal protection materials substantially. In the coupling effects, the main resource of aerothermodynamic loading is the catalytical reaction which occurs between atoms in high temperature gases on material surfaces. Flight experiments results of the USA, Europe and Japan indicated that, heating from surface catalytical reaction can be contribute as much as50%of the total aerothermodynamic loading. For this reason, effective reducing the material surface catalyticity properties, will greatly reduce the requirement of thermal protection materials, break the constraint of limited thermal protection candidate materials so that expand the material option systems for the thermal protection system of hypersonic flight significantly, and offer the new development space for thermal protection materials.In this dissertation, the research from the coupling effect between aerothermodynamic environment and materials, emphasize the core question of “thermal protection surface catalytical reaction”, introducing three critical scientific issues, which are “Synchronized in situ characterization method of thermal protection materials catalysis, oxidation and emission”,“Evolution rule and coupling effects of material surface properties” and “Material surface catalytical mechanism and key influence parameters”. Based on the guiding ideology of physical mechanics using the experiment characterization, atomic spectral diagnosis, material property analysis and physical model, conduct the characterization and evaluation research of thermal protection materials surface catalyticity properties:(1) From the mechanism of catalytical reaction and based on the atom concentration loss, developing the catalyticity properties experimental testing and characterization methods. Building the surface catalyticity properties experimental testing system which allows the independent regulation of pressure, temperature and atom concentration. Based on the spectral diagnosis technology, construct the atom concentration spatial discrimination online testing device, and the non-contact material surface temperature, morphology and emissivity synchronized in situ testing system, which offering the experimental foundation for the mechanism research, characterization and evaluation of thermal protection materials surface catalyticity properties, as well as the design of new kinds of thermal protection materials.(2) Based on the characterization method demand of oxygen atom concentration testing, built the oxygen atomic emission spectrum testing method. The oxygen atom spatial concentration distribution in the reaction cavity was obtained and demonstrated using Kapton mass loss method. The numerical simulation of oxygen atom concentration distribution under different condition was conducted. The oxygen atom concentration spatial distribution law in reaction cavity can be evaluated precisely. Based on this, the research of oxygen atom spatial distribution of typical thermal protection materials under room and high temperatures was conducted.(3) The influence of temperature, pressure, oxygen atom concentration and surface roughness on the oxidation behavior of ZrB2-SiC material, and the oxidation evolution rule was analyzed. The differences of oxidation behavior were analyzed through the comparison with low pressure oxygen molecule oxidation and high frequency plasma wind tunnel oxidation. Based on these oxidation experimental data, corresponding oxygen atom oxidation model of ZrB2-SiC material was built. By determine the consumption of oxygen atoms during oxidation reaction, the oxidation disturbance to surface catalyticity properties was analyzed from the four aspects of temperature, atom consumption, surface composition and oxidation reaction time.(4) Surface catalyticity properties testing and evaluation aimed at typical ultra high temperature ceramic ZrB2-SiC material was conducted. Influence rules and mechanism of catalyticity properties was obtained from the environmental properties (temperature, pressure and oxygen atom concentration) and material surface property (roughness and composition).Catalytical testing results was analyzed and predicted using E-R, L-H models. By comparing with foreign literature data, the effectiveness of testing methods, experimental technique testing results can be demonstrated.(5) The ZrB2-SiC material catalytical experimental testing basd on energy method was conducted on high frequency plasma wind tunnel. By comparing the results between wind tunnel and the atom loss method in laboratory, difference between these two methods was systematic analyzed from environmental parameters, material response, testing accuracy and so on. Based on the principle of heat equilibrium, heat equilibrium characterization method was built on the basis of experimental testing devices. The material surface catalyticity propertly was obtained and the experimental catalytical testing system was completed.In this paper, based on the interdisciplinary fusion of material science, surface physical chemistry, plasma dynamics expanded from physical mechanics, spectral physics, engineering thermodynamics and experiment/numerical simulation, the characterization methods of thermal protection material surface coupling response property, the material surface catalysis, oxidation and emission testing and evaluation technology, as well as the oxidation evolution and catalytical reaction mechanism of thermal protection materials have made a breakthrough, which offers thermal protection technological reserve for endoatmosphere high speed flight vehicles, reusable reentry transportation system, manned space flight and deep space exploration, and offers scientific foundation for future aerospace vehicle technology development. By the interdisciplinary cross, the source and comprehensive innovation abilities is elevated.