A technique of in situ SiO2 preparation in silicon-based ablationresistant material by sol-gel method was established.The preparing processes were as follows:first

vulcanizates were prepared by mechanical mixing of silicone rubber

fumed silica and other fillers.Secondly

the vulcanizates were swelle in tetrahydrofuran (THF) at 30°C for 12 h

and subsequently subjected to soaking in the tetraethylorthosilicate (TEOS) for 24 h.Thirdly

the swollen vulcanizates were put into the aqueous solution of n-butylamine at 50°C for 48 h in order to conduct the hydrolysis and condensation reactions of TEOS.Finally

the resultant vulcanizates were dried for several days at 50°C under a reduced pressure.SEM photographs indicated that silicon dioxide particles prepared by sol -gel method were spherical

and the particle size distribution was in the range of 40～60 nm

but the in situ SiO2 was dispersed differently in the vulcanizates

which was enriched in the surface than the inside.So the content of in situ SiO2 was the average of the materials. Compared to the conventional silicafilled vulcanizates which were prepared by mechanical mixing of the silica particles

the new vulcanizates with the in situ SiO2 showed better properties.The results showed that the tensile strength and the ablation rate were improved apparently when the average amount of in situ SiO2 increased.The tensile strength of the siliconbased ablation-resistant material containsing 13.7% in situ SiO2 was about 5.82 MPa

and the ablation rate was 0.071 mm/s.