Investigation of the ignition and combustion characteristics of Al@AP incorporated with graded aluminum powder

The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders, while simultaneously safeguarding their energy properties. In this paper, a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique. The thermal behavior, ignition and combustion characteristics were comprehensively evaluated and compared. The experimental results showed that with the varying inclusion of the graded Al, the heat of reaction exhibited a significant change, ranging from 9090 J·g⁻¹ to 11036 J·g⁻¹, which was strongly dependent on the particle size of Al. The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP, resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7 °C in the peak temperature of the HTD. Furthermore, the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s⁻¹, which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate. Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP, and the combustion images clearly indicated an incomplete combustion tendency for this sample. In contrast, a well-designed gradation of Al powders, such as a combination of fine Al powders with a particle size below 5 μm, has proven to be the most conducive to enhancing the combustion efficiency of the composites.