Degradation of Al₂O_3f/SiO₂ composites exposed to Na₂SO₄ environment and MMH/N₂O₄ bipropellants test

Abstract

Al2O3f/SiO2 composites were fabricated efficiently using sol‐gel process. The degradation behavior exposed to Na2SO4 environment at 1100℃ and MMH/N2O4 bipropellants test were investigated and compared. The results showed that the strength of Al2O3f/SiO2 composites gradually decreased as the ratio of Na2SO4:water increased; the strength of the composites was only 23.56 MPa at 20% (Na2SO4:water), which suggested that the composites maintained lower strength. Cracks began to appear in SiO2 matrix, and the structure of Al2O3f/SiO2 composites could be corroded which would corrode the SiO2 matrix, leaving naked fibers. Developing a protective layer with higher stability for Al2O3f/SiO2 composites would be considered for long time use. The composites showed higher ablation resistance to MMH/N2O4 bipropellant test; the flexural strength was (77.15 ± 4.56) MPa and the retention ratio was 98.7%. The degradation of Al2O3f/SiO2 composites was promoted owing to the thermal‐mechanical and chemical factors. SiO2 matrix became weak and fragile at elevated temperature; some SiO2 matrix became loosened and porous after being washed away through the shearing of MMH/N2O4 bipropellants, which prevented cracks from penetrating Al2O3 fibers. With ongoing test, the fibers were worsened by thermal‐mechanical corrosion.