Improvement of thermal-insulation and erosion-resistance properties of a carbon phenolic composite by incorporation of ZrO 2 fabric

Abstract

In this study, maximum back wall temperature and erosion rate of both the carbon phenolic composites (C-Ph) and ZrO₂ fabric incorporated carbon phenolic composites (Z-C-Ph) are evaluated after oxy-acetylene flame test to assess the effect of ZrO₂ fabric incorporation on the thermal and erosion properties of the composite. Theoretical estimation of back wall temperature is also carried out using ANSYS 15.0. Theoretical as well as experimental estimation shows that the heat affected zone of composite during oxy-acetylene flame test is wider and deeper for the C-Ph than those of the Z-C-Ph composite owing to the higher thermal conductivity and lower density of the C-Ph than those of the Z-C-Ph composite. Theoretically estimated maximum back wall temperatures (∼500°C for C-Ph and ∼450°C for Z-C-Ph) are found to be similar with the experimentally determined maximum back wall temperatures (516 ± 106°C for C-Ph and 428 ± 70°C for Z-C-Ph). The effects of several other parameters such as surface roughness of the sample, presence of blind drilled holes on the composite sample, char formation thickness on the maximum back wall temperature and erosion rate of both the composites are also studied. It is, in general, observed that the maximum back wall temperature and erosion rate is relatively higher for C-Ph (516 ± 106°C, 0.020 ± 0.007 mm/s, respectively) than those of Z-C-Ph (428 ± 70°C, 0.016 ± 0.003 mm/s, respectively). The percentage reduction of experimentally measured thermal conductivity and erosion rate due to ZrO₂ fabric incorporation in C-Ph composite is found to be ∼40% and ∼28%, respectively. Post-test examination with SEM reveals that more severe crack formation in the matrix and more matrix/carbon fibre de-bonding are observed in case of C-Ph than those in case of Z-C-Ph. Presence of blind drilled holes mitigates delamination thus increases thermal conductivity and renders the increase of back wall temperature. The higher char formation thickness causes decrease in the maximum back wall temperature since char reduces thermal conductivity. Smoother front surface in general causes lower heat absorption from the oxy-acetylene flame and thus decrease both the front/back wall temperature and erosion rate in case of C-Ph. However, smoothening of the surface by machining causes exposure of ZrO₂ fabric and subsequent reaction of ZrO₂ with char (C) which causes formation of highly porous char, ZrC and gaseous CO. This causes increase in the erosion rate due to greater char removal and consequently increase in back wall temperature for Z-C-Ph.