Preliminary tests of silicon carbide based concretes for hybrid rocket nozzles in a solar furnace

Abstract

This research is part of the PERSEUS project, a space program concerning hybrid propulsion and supported by CNES. The main goal of this study is to characterise silicon carbide based micro-concrete with a maximum aggregates size of 800μm, in a hybrid propulsion environment. The nozzle throat has to resist to a highly oxidising polyethylene (PE)/N2O hybrid environment, under temperatures ranging up to 2980K.The study is divided into two main parts: the first one deals with the thermo-mechanical characterisation of the material up to 1500K and the second one with an investigation on the oxidation behaviour in a standard atmosphere, under a solar flux up to 13.5MW/m2.Young’s modulus was determined by resonant frequency method: results show an increase with the stabilisation temperature. Four point bending tests have shown a rupture tensile strength increasing with stabilisation temperature, up to 1473K. Sintering and densification processes are primary causes of this phenomenon. Visco-plastic behaviour appears at 1373K, due to the formation of liquid phases in cement ternary system.High-temperature oxidation in ambient air was carried out at PROMES-CNRS laboratory, on a 2kW solar furnace, with a concentration factor of 15,000. A maximum 13.5MW/m2 incident solar flux and a 7–90s exposure times have been chosen. Optical microscopy, SEM, EDS analyses were used to determine the microstructure evolution and the mass loss kinetics. During these tests, silicon carbide undergoes active oxidation with production of SiO and CO smokes and ablation. A linear relation between mass loss and time is found. Oxidation tests performed at 13.5MW/m2 solar flux have shown a mass loss of 10mg/cm2 after 15s. After 90s, the mass loss reaches 60mg/cm2.Surface temperature measurement is a main point in this study, because of necessity of a thermo-mechanical-ablative model for the material. Smokes appear at around 5.9MW/m2, leading to the impossibility of useful temperature measurements by optical pyrometry.Micro-concrete is really interesting for the nozzle realisation, thanks to its workability, and its thermo-mechanical properties. After 30s, mass loss in micro-concrete is one half of pure α-SiC. This result is really interesting to study SiC-based concretes in oxidising environments, instead of sintered α-SiC.