Effects Of HMX Polymorphs Match On Its Sensitivity And Thermal Decomposition Properties

The brisant explosive HMX, with high detonation velocity, high explosion heat and high burst pressure, was widely used in explosives and propellants. The industrial-grade sample which has relatively lower sensitivity is with the β crystal form, and the sensitivity of a-HMX is very high. In the actual production process, in order to meet the application requirements of different products, some explosives must be added deterrents (such as warheads) to reduce the sensitivity, and some explosives need to added sensitizers (such as emulsion explosives) to increase the sensitivity. However, deterrents and sensitizers are generally non-energetic components, and they will lead to the reduction of energy. We can control the sensitivity by matching the polymorphs of HMX samples, so that the sensitivity requirements of different explosives will be meted without reducing the energy of explosives. The results are as follows.Firstly, the solubility of the industrial-grade P-HMX was investigated in the mixture solution of acetic acid and water. The solubility of HMX would enlarge with the increase of acetic acid in the mixed solution, and it would also increases with temperature rising. When the volume ratio of acetic acid and water was1:0, the solubility of β-HMX could reach the maximum value0.428g at95℃. However, when the volume ratio of acetic acid and water was1:9at25℃, the solubility of β-HMX is minimum.Secondly, we employed the saturated solution-cooling crystallization method to research the crystal transformation ability of industrial-grade β-HMX. The mixture solution of50mL acetic acid and50mL water was heated to the situation of boiling,0.5g HMX was added to the boiling solution dissolving for2h, and then the saturated solution was put in20℃water bath for cooling. After that, the crystals were filtrated and washed by de-ionized water. At last, the washed crystals were dried at50℃in a vacuum oven. The synthesized sample was characterized by the X-ray Diffraction (XRD) and the scanning electron microscopy (SEM). The results showed that β-HMX can be changed to a-HMX through the saturated solution-rapid cooling crystallization method, and the morphology of a-HMX particles were like slender rods.Thirdly, the percentage of crystal conversion had been optimized. It is affected by the mass of industrial-grade β-HMX, the volume ratio of acetic acid and water in the mixture solution, initial temperature and the cooling time. Based on the above four factors, we taked the orthogonal design method to achieve the best technology parameter. The result showed that the100%conversion of industrial-grade p-HMX to α-HMX can be achieved on the conditions of0.4g HMX, cooling for3h, volume ratio being1:1, and initial water temperature being95℃.Finally, the friction sensitivity, impact sensitivity and thermal performance of the HMX samples were researched. Results showed that the higher amount of a-HMX, the friction and impact sensitivities were higher, and the thermal decomposition heat was higher.