Carbon-carbon composite manufactured by deposition of pyrocarbon (PyC) through chemical vapor infiltration (CVI) has the key issue of being process parametric sensitive which necessitates the detailed study of the effect of process parameters on the rate of PyC deposition. Conventional method of studying the parametric effect by changing one variable at a time keeping the other variables constant has a limitation of more number of experiments and missing the interaction effect among the variables. Here, the effect of process parameters including temperature, pressure, methane gas flow rate, and nitrogen gas flow rate on the mass gain and PyC deposition was studied by Taguchi method, a statistical optimization method, which has the advantage of very few experiments performed at specific pairs of process parameters only. The experiments were performed at three levels of the process parameters. Carbon-Carbon composite material is processed through the CVI process where PyC was deposited on porous carbon fiber preforms at various process conditions as per the Taguchi method. The impact of gas residence time, Reynolds number, Prandtl number, and Peclet number were also investigated. It was observed that the CVI process parameters significantly affect the rate of PyC deposition. Optimized CVI process parameters are essential for achieving a high rate of PyC deposition to reduce the processing time. The findings have revealed that a higher PyC deposition rate arises under high temperatures, pressure, methane gas flow rate, and optimal nitrogen gas flow rate. The effect of the critical interaction of the CVI process parameters on the rate of PyC deposition was also obtained. Based on the experimental studies, process guidelines are proposed for the densification of carbon fibers preform to realize C/C composite products.

Silica phenolic ablative composites are used in many high-temperature applications like rocket/missile solid motor nozzles, space re-entry vehicles, and so forth. As ablative composite with lower thermal conductivity and density can save considerable cost, a hybrid silica phenolic ablative composite was developed by establishing a novel processing methodology using chopped silica fiber, phenolic resin, and hollow glass microsphere. The thermophysical properties of the developed hybrid composite are analyzed and established the scientific know-how. The developed composites, with 36% lower density, displayed 50% lower thermal conductivity and 50% lower thermal diffusivity than standard silica phenolic composite. Since a proper thermal conductivity model for a three-component composite with matrix, fiber, and hollow glass microsphere is not available, the most suitable model for the developed composite is established.

Silica phenolic composites are used as thermal protection systems for high temperatures applications like atmospheric re-entry modules, rocket nozzles etc. Lightweight silica phenolic composites (SPGB) were developed using chopped silica fibre, phenolic matrix, and hollow glass microspheres through a compression moulding technique to achieve a cost advantage in thermal protection systems. Ablative properties were evaluated using an Argon plasma jet at a stagnation heat flux of 500 W/cm2. The mass-loss and erosion rates under plasma exposure reduced up to 48% and 32%, respectively, with the addition of hollow glass microspheres. The heat of ablation of composites increased up to 33%. The thermal degradation behaviour of raw materials and SPGB composites was investigated through thermogravimetric analysis, and the scientific know-how was established. Compressive behaviour under uniaxial loading was evaluated, and the theoretical model for the developed three-component composite was established.

Carbon-Fibre-Carbon matrix composites having high thermal conductivity per unit density is a competitive material for thermal management for aerospace applications. Due to anisotropic nature of Carbon-Carbon(C-C) composites, the thermal conductivity in the thickness direction which is dominated by the matrix carbon is comparatively low. In the present study, work is carried to increase the thermal conductivity in the thickness direction of 2D-CC composites. Multi-Walled Carbon Nanotubes (MWNT) were functionalised and dispersed in Phenolic Resin. C-C composites were densified with MWNT dispersed Phenolic Resin through impregnation, curing & carbonisation cycle. CNT-CC composites were densified through Chemical Vapor Infiltration process and further graphitised. The effects of MWNT in amorphous carbon for thermal conductivity were investigated. The result shows that Multi Walled Carbon Nanotubes (MWNT) can induce the ordered arrangement of micro-crystallites in amorphous carbon leading to increase in thermal conductivity of the bulk composites. There exists an optimum MWNT concentration in resin to enhance the thermal conductivity of C-C composites in the perpendicular direction. However, excess MWNT in resin is disadvantageous to enhance the thermal conductivity due to problems like agglomeration, resulting in reduced thermal conductivity. This can be attributed to the interfacial contact resistance due to improper heat transmission channels arising due to agglomeration. Investigation has been carried out to study the effect of agglomeration for the thermal conductivity of the bulk composites