Mechanical, thermal and ablative properties of zirconia, CNT modified carbon/phenolic composites

Zirconium oxide (Zirconia) coating on carbon fabric (C-fabric) was developed by using zirconia sol. C-fabrics having different weight percentages (wt%) of zirconia namely 0 wt% (Blank), 3.5 wt%, 6.5 wt% and 9.5 wt% were used to make Zirconia–Carbon–Phenolic (Zr–C–Ph) composites. Similarly, 0.5 wt% multiwalled carbon nanotube (CNT) dispersed phenolic resin was used to make CNT–C–Ph composite. Thermal conductivity, ILSS and flexural strength were measured for the prepared composites. Based on the initial results, subsequently a functionally graded carbon–phenolic composite (FG-C–Ph) having CNT–C–Ph composition up to certain thickness followed by Zr–C–Ph composition for the remaining thickness was made. Thermal insulation and ablative properties for blank C–Ph, Zr–C–Ph, FG-C–Ph were studied using plasma arc jet test which was carried out at a heat flux of 4.0 MW/m2 for 30 s. Results from the plasma arc jet test show that, the temperature drop across the Zr–C–Ph composite was found to be highest while it was least for the blank. However the ablation rate was found to be highest for the FG-C–Ph while it was least for the blank. Ablation mechanisms for all the tested composites are proposed based on the SEM and XRD studies