Role of rare earth oxide particles on the oxidation behaviour of silicon carbide coated 2.5D carbon fibre preforms

Abstract

Silicon carbide (SiC) coated carbon fibre preforms are often reported to offer superior mechanical and oxidation resistance compared to those without such coatings, although the use of SiC is limited by its poor oxidation resistance in the presence of moisture, low oxygen partial pressures and/or temperatures above 1550 ​°C. In an attempt to overcome these limitations, the doping of a SiC coating with two rare earth (RE) oxides, Y2O3 and CeO2, both separately and in combination has been investigated with a view to improving the oxidation resistance. The coating was deposited using chemical vapour infiltration (CVI) of SiC onto the individual fibres within 2.5D carbon fibre preforms and the subsequent oxidation studies were undertaken in the range 1300–1700 ​°C with and without the presence of the RE oxide particles and with both continuous and isothermal oxidation behaviour being investigated. SiO2 growth rates were calculated for all the samples at different temperatures. Immiscible solid RE silicates were formed in the molten silica, which are believed to have enhanced the oxidation resistance by two different mechanisms: i) delays in the active oxidation of SiO2 by decreasing the evaporation of SiO and ii) enhancing the viscosity of molten SiO2, which further reduces the diffusivity of oxygen through the glassy phase.