Geothite as Propellant Grade Catalyst – Preparation and Characterisation

Abstract

The increasing demand for higher acceleration during the first 100 seconds of rocket ascent drives rocket propellant designers to explore advanced materials. One key area of focus is the development of combustion catalysts for composite solid propellants. While iron oxide is a commonly used catalyst in solid propellants globally, detailed data is scarce because its formulation is often tailored to specific fuel-oxidizer compositions. This paper aims to develop high surface area propellant-grade iron oxides with a modified version of the David and Welch method. Our approach is twofold: first, we alter the process conditions of the David and Welch method and prepare high surface area propellant-grade iron oxides; second, we extensively characterised the prepared catalyst and conducted propellant level trials. Lowering the process temperature and using hot air oven in one experiment and open-air drying in another resulted in the formation of iron oxyhydroxide structures. Structural analysis was performed using X-ray diffraction (XRD) supplemented by Mossbauer, FTIR, EDS, and Raman spectroscopies. The surface morphology was examined using field emission scanning electron microscopy (FESEM), and specific surface area was measured using the BET method where higher surface area of approximately 100 m²/g was achieved. Iron oxy hydroxide particles were needle-like, non-agglomerated and amorphous in nature. The propellant viscosity and viscosity build-up rate showed no abnormalities, indicating no adverse effects on rocket castability and pot life. Similarly, the uniaxial mechanical properties (tensile strength, elongation at break, Young’s modulus, and hardness) were within acceptable limits for existing propellants. However, the iron oxyhydroxide prepared using open-air drying exhibited low viscosity build-up, reduced Young’s modulus, and hardness, likely due to surface moisture reducing the presence of curative in the polymer network. Burn rate measurements were conducted using acoustic emission (AEBR) and ultrasonic emission (UBR) techniques, which also assessed burn rate sensitivity and pressure index. The results indicate that both the samples enhanced burn rate and pressure index compared to a catalyst-free sample.