Influence of hydrothermal treatment on the microstructure and oxidation resistance of a Zn4B2O7 center dot H2O (4ZnO center dot B2O3 center dot H2O) coating for C/C composites

摘要

Antioxidant modification for C/C composites by in situ hydrothermal synthesise at 140 degrees C of a 4ZnO center dot B2O3 center dot H2O crystallite coating has been successfully achieved. The influence of hydrothermal time on the phase composition, microstructure of the as-prepared Zn4B2O7 center dot H2O (4ZnO center dot B2O3 center dot H2O), and its antioxidant modification for C/C composites were investigated. Samples were characterised by XRD, SEM, isothermal oxidation test and TG-DSC. Results show that, 4ZnO center dot B2O3 center dot H2O crystalline coating is achieved on the surface of C/C composites after the hydrothermal treatment at 140 degrees C for time in the range of 2-12 h. A smooth and crack-free 4ZnO center dot B2O3 center dot H2O layer can be obtained when the hydrothermal time reaches 8 h. Isothermal oxidation test demonstrates that the oxidation resistance of C/C composites is improved. The as-modified composites exhibit only 1.52 g.cm(-2) weight loss after oxidation at 600 degrees C for 15 h, while the non-modified one shows a 6.57 g.cm(-2) weight loss after only 10 h oxidation. For the uncoated C/C composite the oxidation rate is approximately linear with time (non-protective oxidation), thus at 15 h exposure one can estimate the mass loss to be 6.57 g.cm(-2) after 10 h for direct comparison with the coated samples.