Solid propellant burn rate characterization: Effect of copper chromite blend with oxidiser and its storage

This work details the study conducted on composite solid propellants with activated copper chromite (ACR) as burn catalyst for its burn rate change with time due to the interaction of ammonium perchlorate (AP) with ACR. One of the hypotheses cited for burn rate reduction is the conversion of chromite in ACR to chromate by an electrolytic reaction with moisture in the presence of ammonium perchlorate. This hypothesis was studied by a design of experiments which includes blending ammonium perchlorate and ACR, Aluminum and ACR, stand alone ACR in raw material stage and the blends storage with time. The effect of moisture in AP is addressed by comparing undried and dried AP in the blends. The blended raw materials were characterized by Thermogravimetric analysis, Particle Size Distribution, surface area measurement, Scanning Electron Microscopy and chromium estimation. Results show that the conversion of chromium from chromite to chromate is very minimum in the presence of AP. Propellant samples are prepared with these blends at different time intervals to understand viscosity, mechanical properties and burn rate behavior with raw material storage. Experimental results show burn rate shows an opposite trend of increase with blend storage of 6 months. A plausible explanation for this observation is presented in the paper correlating the experimental conditions.