Effect of ageing on ammonium perchlorate with activated copper chromite as a burn-rate modifier

Abstract

Ammonium perchlorate (AP) is a predominantly used oxidiser in composite solid propellants, with its burning and decomposition characteristics heavily influenced by catalyst type and concentration. This study investigates the ageing of AP with low-concentration Activated Copper Chromite (ACR) as a catalyst. AP pellets containing 0.4 % ACR, representative of typical industrial class propellant compositions, underwent accelerated cyclic ageing equivalent to four years of natural ageing. Subsequently, aged ACR was extracted and added into fresh AP and pelletized. The resulting pellets are characterised using burn rate tests, TGA, and DTA analyses. Results indicate a 12.3 % average decrease in burn rates upon ageing, alongside deteriorated decomposition characteristics compared to AP with un-aged ACR. The decomposition characteristics of AP with aged ACR are found to be shifting toward the pure AP decomposition characteristics. This shift indicates that the ageing process alters the decomposition properties of the AP–aged ACR mixture, causing it to behave like AP during decomposition. The activation energy of AP, AP+raw ACR and AP+aged ACR also shows similar trends in changes in activation energy proving deterioration in catalytic performance on AP. Ammonium TPD testing reveals a loss in the strength of Lewis acid sites in aged ACR, suggesting reduced efficiency. Additionally, Energy-Dispersive Spectroscopy Analysis demonstrates an increase in oxygen content in aged ACR. XRD tests show increase in copper oxide upon ageing of ACR and decrease in the percentage of copper chromium oxide. Propellants with raw and aged ACR were made and burn rates were measured. Burn rates were found to decrease in case of propellants with aged ACR. These findings underscore the importance of understanding the ageing process in AP-ACR systems and its implications for propellant performance.