Tailoring combustion of composite solid propellants by CoxTiyOz nano-catalysts synthesized from a chemical route

Abstract

Binary metal oxide particles Co_xTi_yO_z with different elemental compositions were synthesized by liquid-phase precipitation and high-temperature calcination. How the difference in elemental content influenced the morphology, crystal structure, and catalytic action on the thermal decomposition of ammonium perchlorate (AP) was investigated. And the influence of Co_xTi_yO_zs on AP + Al composite fuel ignition and combustion was investigated with laser ignition and a high-speed camera. The results show that for a Co : Ti ratio of 4 : 1, the particles appear as sheet-like particles with a diameter of ∼250 nm and a thickness of ∼15 nm, showing agglomeration. At a 2 : 1 ratio, most calcined particles are sheet-like, with a few large rod-like and particle-like morphologies. The sheet-like particles have diameters of around 250 nm, while rod-like particles exceed 600 nm in diameter with micrometric lengths, and particle-like entities measure 100 nm. At a 1 : 1 ratio, the predominant morphology is rod-like, with some smaller particle-like entities attached to the surface; rods have diameters close to 1 micron, and attached particles range from 100 to 400 nm. At 1 : 2, the particles are primarily coarser rods, with diameters exceeding 3 microns, with small particles adhering to the rod surface. The rods mainly consist of titanium, whereas the attached fine particles are primarily cobalt, with oxygen distributed uniformly across particles. The Co_xTi_yO_z-1 powder with a Co : Ti atomic ratio of 4 : 1 has a predominant phase of Co₃O₄. In Co_xTi_yO_z-2, Co_xTi_yO_z-3, and Co_xTi_yO_z-4, with Co : Ti ratios of 2 : 1, 1 : 1, and 1 : 2, respectively, the particles contain Co₃O₄, TiO₂, and CoTi₂O₅, with Co₃O₄ forming sheet-like particles, TiO₂ forming rods, and CoTi₂O₅ forming spherical particles. With Co_xTi_yO_z as catalysts, the heat release peak temperature of AP thermal decomposition decreased from 453.02 °C to 334.92 °C, 325.19 °C, 336.08 °C, and 356.89 °C for Co_xTi_yO_z-1, Co_xTi_yO_z-2, Co_xTi_yO_z-3, and Co_xTi_yO_z-4, respectively, with reductions of 118.10 °C, 127.83 °C, 116.94 °C, and 96.13 °C compared to pure AP thermal decomposition. The total heat release of AP catalyzed by Co_xTi_yO_z-1, Co_xTi_yO_z-2, Co_xTi_yO_z-3, and Co_xTi_yO_z-4 is 1152.53 J g⁻¹, 1118.60 J g⁻¹, 1070.60 J g⁻¹, and 1136.76 J g⁻¹, respectively. For the sample catalyzed by Co_xTi_yO_z, the rapid weight loss stage ends at 340.11 °C, 331.19 °C, 342.28 °C and 367.39 °C with a total weight loss of 98.22%, 98.55%, 98.47% and 98.49%. AP demonstrates maximum decomposition rates at 334.92 °C, 325.59 °C, 336.71 °C, and 355.32 °C, with decomposition rates of 15% min⁻¹, 14% min⁻¹, 13% min⁻¹, and 13% min⁻¹. The combustion process of Co_xTi_yO_z-2 + AP + Al composite fuel can be divided into five stages: ignition, lighting, steady combustion, decay, and extinguishment. As the content of Co_xTi_yO_z-2 particles in the Co_xTi_yO_z-2 + AP + Al mixture increases from 0.5 wt% to 1 wt% and then to 2 wt%, the ignition delay times are 128 ms, 97 ms, and 84 ms, respectively. When the content of Co_xTi_yO_z-2 is 0.5 wt%, the flame area during steady combustion does not show a significant increase. When the content is increased to 1 wt%, the flame area increases significantly and exhibits a pronounced jet-like structure. When the concentration of Co_xTi_yO_z-2 reaches 2 wt%, there is no further increase in the flame area. Of all the composite oxide particles, Co_xTi_yO_z-2 demonstrated the relatively optimal catalytic performance for AP.