Preparation And Properties Of Insensitive Ultra-fine Ammonium Perchlorate Used In High Burning Rate Propellant

Ultra-fine ammonium perchlorate (AP) is widely used as oxidant in high burning rate of solid propellant. But the mechanical sensitivity of ultrafine AP is high, and it is easy to absorb moisture caking which causes inconvenience in preparation and application of high burning rate solid propellant. Here, our team completed two major projects.On the one hand, by air-impact-grinding, three kinds of ultra-fine AP composite particles were prepared. On the other hand, through improvements of the traditional jet mill equipment and process optimization, we explored the massive processes of the spherical ultra-fine AP preliminarily, and prepared spherical ultra-fine AP successfully. The main works are as follows:Firstly, Nano-graphite, graphite and carbon black were chosen as insensitive modifiers, and three ultra-fine-AP composite particles were prepared by airflow-impact-grind-complexing. Preparation process can be divided into two steps, modifier premixed up with AP and airflow-impact-grind-complexing.The premix process parameters were as follows:the mass ratio of AP and modifier was 200:1, the weight of the stainless steel balls was 10 kg, the cylinder speed was 20 r·min-1, the mixing time was 0.5 h. The process parameters of airflow-impact-grind-complexing are as follows:main gas pressure was 0.5 MPa and the secondary gas pressure was 0.4 MPa. The size and morphology, crystal and purity of the samples were tested, the results show that the crystalline form of insensitive ultra-fine AP composite particles is consistent with the feedstock,which proves that the complex process belongs to the physical changes, and does not generate new chemical substances. The size of ultra-fine AP composite particles is between 2-3 μm, meeting the requirements of the use of high burning rate propellant.Secondly, the thermal decomposition properties of insensitive ultra-fine AP composite particles were studied.The results show that the modifiers act a catalytic action to the decomposition. Compared with other samples,the pyrolysis peak of sample AP-1 shift to a lower temperature,and with a small time frame, a steep peak, indicating that the decomposition reaction is faster and the heat is also very focused, which meets the requirements of high burning rate propellant combustion performance. The moisture absorption and anti-caking properties, powder characteristics and mechanical sensitivity of ultrafine composite particles were tested. The results show that these ultra-fine composite particles are difficult to absorb moisture and be agglomerated, and have better fluidity. Besides, the safety performance has been improved.Thirdly,spherical ultra-fine AP wre prepared by improving the jet mill and exploring new technological conditions massively, the conditions were as follows:the primary gas pressure was 0.75 Mpa, auxiliary gas pressure was 0.7 Mpa, the feed rate was 30 kg·h-1, the material tube height was 40 mm, milling fist and then grinding. The size and morphology, the crystal form, the purity and structure of the sample were characterized and the hygroscopic properties the sense of fluidity and mechanical properties wre studied. The results show that the particle size of spherical ultrafine particle prepared by the new process is about 2.5 μm, the morphology is spherical, and with lower moisture absorption, better fluidity.The most important is that the mechanical sensitivity is relatively lower.