Novel Superhybrid Composites of Boric Acid Modified Phenol Formaldehyde Resin for Supersonic Re-entry Vehicles

YutikaBadhe, Balasubramanian K*

Department of Materials Engineering, Defence Institute of Advanced Technology, DRDO DIAT(DU), Ministry of Defence, India 411025.

*Email:

Keywords: Ablative, High Temperature, Supersonic, Phenol Formaldehyde

ABSTRACT

Critical and challenging missions which involve entry into the atmospheres of gas giant planets or re-entry in earth’s atmosphere, are subjected totremendous pressures and extremely high temperature environments of above 2000C.Such missions require ablative materials as thermal protection systems for re-entry vehicles to ensure that they do not incinerate during reentry. Ablative materials play a strategic role in the aerospace industry and the excerption of the proper candidate is strictly related to the char retention capability. Heritage carbon phenolic is an efficient ablative material with low coefficient of thermal expansion and high thermal shock resistance.

The present study focuses on modification of conventional Phenol Formaldehye resin with Boric Acid by in-situ polymerization of PF with 1, 5, 10, 40, 50 wt% Boric Acid and assessment of its ablative properties for effective ablation. These composites were subjected to severe thermal conditions such as Oxy-Acetylene Flame at ∼2300 °C for 60 s, according to ASTM E 285. The mass loss and dimensional change before and after ablation wereestimated to calculate ablation rate. Boric Acidmodified Phenol Formaldehyde (B-PF) exhibited diminished erosion rate compared to the pristine PF under similar conditions.Pristine PF is incapable to hold the turbostratic carbon together against the prevailing oxy-acetylene conditions, leading to major erosive losses. In case of 50 wt% B-PF hybrid composites, the linear ablation rate curtailed by 72% while the mass ablation rate by about 38%, by the virtue of Borate Glass formed on the surface at high temperatures which was affirmed by FESEM. Augmented char residue (53%), which was quantified by TGA at 800°C,and the impermeability of gases across the glass provide an exemplary barrier for oxygen diffusion and temperature conduction. This prevents further decomposition and oxidation, thus enhancing the ablation resistance of the B-PF composites.This hybrid composite with superior ablation resistance finds potential applications in spacecrafts to protect rocket nozzles during atmospheric re-entry, ship hulls from propellant gas erosion, heat shield from laser beams, and protection of land-based structures from high heat environments.