Preparation And Properties Of Ceramifiable Silicone Thermal Protection Composite

With the development of aerospace technology and the need of national defense technology,hypersonic long-endurance spacecraft put forward higher requirements for the long-term oxidation resistance of thermal protection materials.The existing phenolic composites have a large ablation amount in long-term oxidation environment,and seriously damage the thermal protection effect.In response to this problem,the ceramifiable silicone composites with excellent thermal oxidation stability are studied in this paper,providing guidance for it application in the field of large-scale thermal protection of spacecraft.Firstly,four kinds of polysiloxanes?PSQ?with different monomer ratios were synthesized using vinyltrimethoxysiloxane and dimethyldimethoxysiloxane.The molecular structure,process properties and thermal stability of PSQ were characterized by FTIR,¹H-NMR,²⁹Si-NMR,GPC,MALDI-TOF-MS,DSC and TG,combined with various properties,PMVSQ31was chosen as the matrix of ceramifiable composite,and its gel time,viscosity,curing kinetics and cracking reaction were investigated,the results show that PMVSQ31 had a good process window,and the curing process was determined to be 100?/0.5h,130?/0.5h,150?/3h.After heat treatment in muffle furnace,the original morphology can be kept relatively regular,and the residual rate was high,with quartz ceramics formed by inorganic transformationSecondly,titanium boride,calcium carbonate,magnesium carbonate,alumina,mica powder and glass powder were selected to compose the six-component ceramic filler system?F6?.Through the analysis of the ceramic properties of the F6 system and the ceramic castable with different proportions,the optimum formula of ceramic filler was determined as F6-Z3.On this basis,the effects of short cut quartz fiber?CQF?and resin matrix on the ceramization effect of castable were investigated.The results show that the increase of CQF content and resin silicon content can significantly improve the macroscopic morphology,quality and dimensional stability of the material after heat treatment.The mechanism of in-situ ceramization at high temperature was characterized by SEM,XRD and EDS.It was found that a certain thickness of ceramic protective layer was formed on the surface of the material,and MgAl₂O₄,Al₂Si₂O₅ and other ceramic phases were formed in situ.Finally,the process parameters affecting the PSQ prepreg were studied,and the scraping method was determined to be the preparation method of dry PSQ prepreg,the solvent content and mixed resin content of pregreg were controlled at 10%and 700 g/m² respectively,the storage time should not exceed 20 days.Ceramifiable silicone composites?SDC?were prepared by moulding pressing with inclined-placing,and its mechanical properties,thermophysical properties and ablation properties were characterized and evaluated,it was found that the material has excellent mechanical strength and modulus after heat treatment.After ablation,the surface of the sample is flat,without macro-cracking and layer-uncovering,it has excellent long-term oxidation resistance.It can be used as resin-based thermal protection composites in big area ablative shield application of spacecraft.