Mechanism of the antioxidation effect of α-Fe2O3 on silicone rubbers at high temperature

摘要

The high temperature resistance of silicone rubber (SR) could be significantly improved by adding hematite (α-Fe _(2) O _(3) ). In this study, the variation of α-Fe _(2) O _(3) and polysiloxanes was investigated by ultraviolet-visible absorption spectroscopy, X-ray diffraction, M?ssbauer spectroscopy, and ~(29) Si NMR spectroscopy after SR aging for 12 h in air at 350 °C. The results indicate that Fe ~(3+) is reduced to Fe ~(2+) by organic free radicals (R˙) in the process of aging. Fe ~(3+) captures R˙ to protect the polysiloxanes from being destroyed and is transformed into Fe _(3) O _(4) . Moreover, magnetic Fe _(3) O _(4) is only found in the inner layer of SR; however, it is not detected in the outer layer. Therefore, a new mechanism of antioxidation is proposed: on the outer part of SR, the reduction–oxidation cycle of Fe ~(3+) is formed because of sufficient oxygen; however, inside the SR, α-Fe _(2) O _(3) is gradually reduced to Fe _(3) O _(4) .