| The successful recovery of the“Falcon 9”booster rocket indicates that reusable rockets that reduce use costs and improve utilization efficiency have become one of the important trends in the development of future aerospace industry.As a result,People have put forward the requirements for thermal protection materials that can withstand multiple ablation.In this paper,phenolic resin is used as the matrix phase,and the carbon fiber braid is used as the reinforcing phase.The vacuum assisted impregnation process and the sol-gel method were adopted.The Si O2/phenolic gel network interpenetrating structure was constructed,and the material was filled with Zr Si2.The preparation and characterization of a carbon-based braid-reinforced inorganic modified phenolic ablation material was carried out,and a gradient anti-heat insulation integrated material that can withstand secondary ablation was prepared and related characterization was carried out.First,phenolic aerogels with different solid content and curing agent content were prepared by the sol-gel method.The preparation process and drying process that can prepare aerogels with complete structure and low shrinkage were adjusted.When the solid content increases from 10%to 20%,the density correspondingly increases from 0.071g/cm3 to 0.243g/cm3.The content of the curing agent has no direct effect on the density of the aerogel.Comprehensive comparison,when the ratio of curing agent content to resin content is 1/10,a low-shrinkage phenolic aerogel can be prepared.Secondly,phenolic resin was used to configure organic sol,and ethyl orthosilicate was used to configure inorganic sol.The silicon-modified phenolic hybrid aerogel with different silicon content was prepared by the co-gel method.The Si O2/phenolic gel network interpenetrating structure was constructed.The hybrid aerogel has a bi-continuous structure with a gel skeleton and pores,and the size of the gel particles and pores are nanometers.With the increase of silicon content,the Si element content increased from 0.51%to 13.27%.Si O2 was uniformly distributed in nanometers,and the increase of Si O2 content did not destroy the interpenetration of the gel network.The density of the hybrid aerogel has no obvious change and remains at about 0.15g/cm3.The micropore content of the hybrid aerogel has a tendency to increase first and then decrease.The vibration peak intensity of Si-O bond at 1100cm-1 and 464cm-1 is increased,but there is no XRD diffraction peak.The carbon residue rate at 1300℃increases from 41.46%to 60.19%.Finally,the hybrid aerogel is used as the matrix phase,and the carbon fiber braid with high/low density double-layer structure is used as the reinforcing phase.The dense layer of the braid is filled with Zr Si2,and the unmodified phenolic/carbon fiber is prepared by a vacuum-assisted impregnation process.Composite materials（RF-C）,silicon modified phenolic/carbon fiber composites（Si-RF-C）and Zr Si2 filled silicon modified phenolic/carbon fiber composites（Zr Si2-Si-RF-C）.The resin in the composite material infiltrates the fiber well.Zr Si2 is mainly dispersed in the material in the form of micron-level aggregates.Carbon fiber is prone to structural damage after being oxidized.Si O2 and Zr Si2 can effectively increase the carbon residue rate after pyrolysis of the material.The average mass ablation rate of RF-C after twice ablation for 25s is 0.058g/s,the average linear ablation rate is 0.094mm/s;the average mass ablation rate of Si-RF-C is 0.046g/s,the average the linear ablation rate is0.074mm/s;the average mass ablation rate of Zr Si2-Si-RF-C is 0.026g/s,and the average linear ablation rate is 0.042mm/s.The back temperature of RF-C after the first ablation was 102.8℃,and the back temperature after the second ablation was446.4℃.The back temperature of Si-RF-C after primary ablation was 96.2℃,and the back temperature after secondary ablation was 282.5℃.After the material is modified by inorganic material,the ablation rate and back temperature of the material are obviously reduced.The inorganic filler realizes the compaction and enhancement of the carbonized layer,and improves the material’s anti/heat insulation performance. |
