Reticulated three-dimensional network ablative composites for heat shields in thermal protection systems

Abstract

Successful utilization of thermosetting resins as ablative materials for heat shields in thermal protection systems (TPS) has newer contemporary materials, surpassing the conventional resins in terms of thermal and physical properties. The present study demonstrates similar progress in ablative heat shielding materials, putting forward capable replacements for existing phenolic system. A novel three-dimensional network composed of a dihydric resorcinol formaldehyde (RF) has been synthesized successfully by modification with boric acid via an effortless and facile polymerization technique. The ablation and thermal properties were investigated with primary and cheap, yet effective test methods like the oxy-acetylene flame test, which explored the ablation rate in terms of mass loss and dimensional change, showing 40% and 70% curtailment respectively. X-Ray diffraction studies confirm the formation of insulative, turbostratic, carbonaceous char formed upon resin pyrolysis with peaks at 24° and 44° attributing to (002) and (100) for turbostratic carbon formed during pyrolysis. FTIR studies reveal change in the intensity and shifts in the peaks for pristine RF for the boric acid modified RF including stretch vibrations at 1429 and 1380 cm⁻¹ corroborating modification of the ring. Atomic Force Microscopy showed the surface roughness which up surged with an increase in the concentration of boric acid in the system, making the composite sensitive to mechanical depletion due to increase reactivity. Interesting morphologies of the sample after ablation were observed with FESEM exposing glassy nanospheres of borate in the periphery and porous char of the depleted zone. Pristine RF has a char yield of 42%, which increased to 68% for 50 wt% of boric acid in RF at 800 °C, quantified by the TGA studies. Mathematical models and energy balance equations were idealized for the exchange in energies at the surface of the ablator. The results determined that the modification of the 3D network of the resin justifies its competency to replace conventional materials demonstrating augmented ablation resistance with faster reaction mechanisms.