Dynamic oxidation mechanism of carbon fiber reinforced SiC matrix composite in high-enthalpy and high-speed plasmas

This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite (Cf/SiC) in high-enthalpy and high-speed plasmas. The results highlighted a transition of passive/active oxidations of SiC at 800–1600 °C and 1–5 kPa. Specially, the active oxidation led to the corrosion of the SiC coating and interruption of the SiO2 growth. The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas. In the transition and passive domains, the SiC dissipation was negligible. By multiple dynamic oxidations of Cf/SiC in the domains, the SiO2 thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO2. In addition, the mechanical properties of the SiC coating/matrix and the Cf/SiC were maintained after long-term dynamic oxidations, which suggested an excellent thermal stability of Cf/SiC serving in thermal protection systems (TPSs) of reusable hypersonic vehicles.

Preparation of nano-SiO2 compound antioxidant and its antioxidant effect on polyphenylene sulfide

Polyphenylene sulfide (PPS) is easily oxidized at high temperature, which greatly limits its applications. In this study, a nano-SiO2 compound antioxidant (SiO2-g-AO) was prepared and incorporated into PPS by melt compounding to obtain PPS/SiO2-g-AO composites. SiO2-g-AO was prepared by reacting 3-(3,5-di-tert-butyl-4-hydroxyphenyl) (antioxidant AO) with an aminosilane coupling agent (KH792). Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA) confirmed that the antioxidant AO was successfully immobilized on the surface of SiO2 and the thermal stability was improved. Scanning electron microscopy (SEM) images showed that SiO2-g-AO was uniformly dispersed in PPS. It has been found that the crystallinity and mechanical properties of PPS composites improved, and the dynamic oxidation induction temperature (OIT) increased in the range of 16.7°C–21.1°C. A synergistic anti-oxidation model of nanoparticles and antioxidants, namely a multi-stage antioxidant system, was established by comprehensive analysis of experimental results. The synergistic anti-oxidation model provides a new idea for the antioxidant modification of polymer composites.