Preparation And Study On Phenolic Impregnated Poriferous Framework Ablators

New type, efficient and lightweight insulation integrated prevention ablative material is frontiers of the thermal protection system in the domain of aerospace research. Along with the rapid development of deep space technology to the planetary exploration direction, the study puts forward new requirements to high temperature ablative thermal protection materials. The low density reusable surface insulating material (RSI) such as LI–2200under high temperature and high pressure coupled thermal-mechanical loading, especially the existence of high shear load on the surface, can appear mechanical failure and severe caving. Obviously, the ordinary surface insulations under the environment of high heat flux can not realize the spacecraft protection function. In order to improve the reusable surface insulation ablation performance and high temperature resistant performance, this paper studies a new type of efficient ablative material--Phenolic impregnated poriferous framework ablators.This topic proposed to fill phenolic resin into the internal holes of ceramic fiber rigid heat shield. Compounding materials in accordance with their own advantages, exploring a more superior, comprehensive performance thermal protection materials.This topic uses the short cut quartz fiber and chopped carbon fiber as raw material, preparing two kinds of porous fiber framework. Fiber pulp was moulded by suction filtration and mould pressing method and then sintered through high heat. The quartz fiber framework has an extremely low density (0.20g/cm3~0.35g/cm3) and high porosity (85%~91%), the carbon fiber framework have a density range of0.15g/cm3~0.25g/cm3, porosity is between85%~92%. The observation of the quartz fiber framework by scanning electron microscope shows that quartz fiber distribute randomly along the direction of fiber layer, there was no orientation, pores are interconnected and its structure are irregular, stratification along fiber framework section orientation is obvious. With the increase of framework volume density, quartz fiber sintering bending phenomenon increases.Carbon fiber distribution in framework also has no orientation, bonding between fibers relies on water soluble phenolic resin, the pore structure of the framework is irregular. Mechanical performance test shows that fracture mechanism of compression failure conforms the characteristics of sag curve, the stress-strain curve shows an apparent compaction stage platform stress period for its typical brittle porous structure. The yield strength of the quartz fiber framework with density of0.20g/cm3is0.337MPa, the strength of the deformation of10%is0.472MPa; The yield strength of the carbon fiber framework with density of0.20g/cm3is0.355MPa, the strength of the deformation of10%is0.428MPa. Vacuum impregnation method is used in impregnating phenolic resin into the framework. We investigated the composites density influence with the concentration of impregnant and vacuum. Results show that the concentration of impregnant is the main factors influencing the final composite density. The compressive properties test results show that with the increase of the content of phenolic resin, the compression strength increases obviously, phenolic resin is the major load-carrying structure. Compared with the blank prefab body skeleton, compression strength of phenolic resin impregnated porous quartz fiber ablative material increases432%, compression strength of phenolic resin impregnated porous carbon fiber ablative material increases by569%.Thermal analysis was carried out on the products, and the results show that the heat insulation performance of the composite material is similar with the framework. Thermal conductivity of quartz fiber porous materials at room temperature is0.032W/m·K, Thermal conductivity of phenolic resin impregnated porous quartz fiber ablative material at room temperature increases to0.043W/m·K; Thermal conductivity of carbon fiber porous materials at room temperature is0.046W/m·K, and phenolic resin impregnated porous carbon fiber ablative material increases to0.067W/m·K.Oxyacetylene ablation experiment results show that mass ablation rate for the phenolic impregnated porous quartz fiber ablative materials is0.0070g/s under the condition of the heat flux density of406.84kW/m2. In the same conditions,the linear ablation rate is0.0364mm/s. Phenolic resin impregnated porous carbon fiber ablative material ablated120s under the condition of the heat flux density of659.83kW/m2has a mass ablation rate of0.0106g/s. Under the same conditions, linear ablation rate is0.0313mm/s.