Uv–vis diffuse reflectance spectroscopy-driven quantification of nano-MnO2 dispersion for catalytic thermal decomposition and combustion optimization in ammonium perchlorate composites

Abstract

Ammonium perchlorate (AP) is widely used in propellants, acting the key power source of rockets and missiles. Improving the thermal decomposition efficiency of AP by introducing nanocatalysts is of great significance for enhancing the performance of propellants. However, nanoparticle agglomeration and the lack of reliable dispersion characterization methods hinder their practical application. The current challenge is to establish methods for accurately characterizing the dispersion of nanocatalysts in energetic materials and to develop efficient, agglomeration-resistant nanocatalysts. In this study, nano-MnO₂/superfine AP composites with different nano-MnO₂ dispersions were prepared and characterized by manual wet grinding and mechanical grinding methods. UV–Vis diffuse reflectance spectroscopy was innovatively employed to quantitatively assess the dispersion homogeneity of MnO₂ nanoparticles, revealing a direct correlation between dispersion and catalytic activity. It was found that the nano-MnO₂ dispersions in nano-MnO₂/superfine composites can be effectively characterized according to the absorbance of solid UV–Vis of composites. The better the dispersion of nano-MnO₂ is, the better the catalytic effect of nano-MnO₂ on the thermal decomposition and combustion of superfine AP and superfine AP/Al composites will get. In the optimal dispersion state, the peak temperature of superfine AP decomposition can be increased by 105 ℃. Thus, the combustion intensity, flame area, combustion time and combustion temperature of superfine AP/Al composites are improved, which can be attributed to the highly dispersed nano-MnO₂ accelerating the decomposition process of superfine AP. Mechanistic studies indicate that well-dispersed MnO₂ facilitates redox cycling during AP decomposition, promotes intermediate conversion, and enhances oxygen release. On the other hand, nano-MnO₂ dispersity is enhanced, agglomeration is reduced, desorption sites are increased, and thermal decomposition of superfine AP is enhanced. The results of this study demonstrate the importance of dispersibility of nanocatalysts to catalyze energetic materials and provide a method to describe the dispersibility of nanocatalysts. It is expected to provide reference for the development of characterization technology of nanocatalysts and broaden the wide and practical application of nanocatalysts in the field of energetic materials.