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.