Nano-silica modified lightweight and high-toughness carbon fiber/phenolic ablator with excellent thermal insulation and ablation performance

Lightweight and high-toughness carbon fiber/phenolic ablator(CFPA)is required as the Thermal Protection System(TPS)material of aerospace vehicles for next-generation space missions.To improve the ablative properties,silica sol with good particle size distribution prepared using tetramethoxysilane(TMOS)was blended with natural rubber latex and deposited onto carbon fiber felt,which was then integrated with phenolic aerogel matrix,introducing nano-silica into the framework of CFPA.The modified CFPA with a low density of 0.28—0.31 g/cm3exhibits strain-in-fracture as high as 31.2%and thermal conductivity as low as 0.054 W/(m·K).Furthermore,a trace amount of nano-silica could effectively protect CFPA from erosion of oxidizing atmosphere in different high-temperature environments.The oxyacetylene ablation test of 3000°C for 20 s shows a mass ablation rate of 0.0225 g/s,a linear ablation rate of 0.209 mm/s for the modified CFPA,which are 9.64%and 24.82%lower than the unmodified one.Besides,the long-time butane ablation test of 1200°C for 200 s shows an insignificant recession with mass and linear ablation rate of 0.079 g/s and 0.039 mm/s,16.84%and 13.33%lower than the unmodified one.Meanwhile,the fixed thermocouple in the test also demonstrates a good thermal insulation performance with a low peak back-face temperature of 207.7°C,12.25%lower than the unmodified one.Therefore,the nano-silica modified CFPA with excellent overall performance presents promising prospects in high-temperature aerospace applications.

Monetary Policy and Borrowers'Loan Defaults:Research Based on Data from Ren re ndai

This paper uses Renrendai data to study the relationship between monetaryj policy and the default behavior of borrowers,and analyzes the transmission channels.The research shows that tight monetary policy will lead to a significant increase in a borrower s probability to default,and this effect will continue for several months.There may be two transmission channels:(i)monetary policy changes a debtor s liquidity through credit and balance sheet channels,which directly affects their current repayment behavior;and(ii)monetary policy may affect a borrower s investment,production and profitability,thus changing their long-term solvency.The paper also finds that the repayment behavior of productive borrowers is more susceptible to monetary policy than consumptive borrowers,and that the default behavior of borrowers in coastal provinces is more susceptible to monetary policy than of borrowers in inland provinces.These findings provide new evidence for understanding how monetary policy affects individual behavior and its transmission mechanisms.