Bonding properties of C/C composites based on polyborosilazane ceramic precursor films

Liquid polyborosilazane, solid polyborosilazane, Si, and Sb₂O₃ were used as inorganic fillers to prepare low-temperature-cured and high-temperature-applicable polyborosilazane adhesive films. The mechanical properties of the bonded C/C composites were tested at 25 °C after treatment at different temperatures from room temperature to 1400 °C. The results showed that the addition of Sb₂O₃ significantly improved the mechanical properties of the adhesive, which was mainly due to the formation of borosilicate glass in the high-temperature melting decomposition system of Sb₂O₃, and the oxidation produced volume compensation. The shear strength of the bonded specimens gradually decreased from 12 MPa at curing to 4.18 MPa at 600 °C; then it increased up to 8.06 MPa at 1000 °C. When the temperature exceeds 1000 °C, the value decreases again. In general, the bonding strength of C/C composites at 1200 °C remains above 4 MPa. The adhesion strength of Si-modified polyborosilazane adhesive film was 4.88 MPa at 1000 °C, indicating that it should be suitable for joining C/C composites for high-temperature applications.