Preparation And Properties Of Core-shell Composite Energetic Material Prepared By The Suspension Spray Drying Method

With the never-ending changes and improvements of battlefield environment, all kinds of applications in reality require higher and higher performance on energetic material. In order to meet these requirements, the hot spot of energetic material has to develop toward a high-energy, insensitive, and high reliability direction. Some studies at home and abroad show that the safety performances of explosive can be improved by the core-shell coating on the energetic material with suitable material. At present, there are a number of traditional core-shell coating methods with their disadvantages respectively. However, spray drying technology are widely used in the material modification field, owning to its short drying time, fast circulating mass transfer speed, high spherical degree and other advantages. Therefore, the study of spray drying technology on core-shell coating has excellent use value and development prospects. The main work was showed as follows:(1)With the applied study of theories-numerical analysis, heat and numerical mass transfer and CFD, and the application of computational fluid dynamics software Fluent, this paper created a numerical simulation of air-spray drying process. By changing the spray drying parameters(inlet temperature、pressure、flow rate), this paper studied the trajectories of the particles in the drying tower, duration and particle diameter. The most suitable process conditions were put forward: the inlet temperature is from 353 to 358 K, the flow rate is from 4.5 to 6.0 mL/min, and the pressure is from 0.6 to 0.8 MPa.(2)Ultra fine CL-20 samples were prepared by a ultrasound-and spray–assisted precipitation method. CL-20 particle was influenced in the process of recrystallization by some factors, such as the nozzle diameter, ultrasound, solution concentration, and other factors. The optimal technology of refining CL-20 was obtained: nozzle diameter of 0.5 mm, the pressure of 0.6 MPa, the mixing time of 30 min, stirring speed 400 r/min, the proportion of solvent and non-solvent for 1:7, the solution of 0.3 g/mL. The ultra fine CL-20 was spherical or elliptical. The mean particle size of CL-20 was 597.6 nm and the type of CL-20 was ε phase. Compared with the raw CL-20, the drop height(H50) of the ultrafine CL-20 was increased from 19.20 to 28.12 cm.(3)Combining the technology of ultrasonic spray and spray drying, the suspension spray drying method was adopted to prepare the core-shell composite energetic material. Through dynamic contact angle experiments, surface tension, interfacial tension and adhesion work of CL-20 with binders were calculated; as a binder, Estane was determined to coat the CL-20 crystal. By comparing the effect of packaging, the technological conditions were optimized. After coating under such conditions, the impact sensitivity of samples was significantly suppressed, but the thermal stability was improved. Coated CL-20 crystal was still the ε-phase. Calculated by the XRD internal standard method, the ε-phase purity of CL-20/Estane was averaged as 95.02%.(4)HMX-based core-shell composite energetic materials were prepared using F2602、Estane and Viton as a binder, respectively. The effects of the suspension spray drying technological conditions on the particle size of core-shell composite energetic materials were investigated, including the inlet temperature, feed rate, solution concentration and etc. The particle morphology, particle size, and impact sensitivity of two samples were characterized by scanning electron microscopy(SEM), laser particle size analyzer and impact sensitivity test. The results showed that the selection of various parameters were closely related to the powder particle size of core-shell composite energetic material, among which the material liquid concentration had the most impact. By comparing and analyzing the coverage degree and the machine sensitivity of samples, cladded with F2602 works best.(5)By the orthogonal test, the three main factors influencing the particle morphology of RDX/Estane were investigated, including the inlet temperature, the feed rate and the flow rate. The optimal combination preparing the particle morphology of RDX/Estane was obtained: inlet temperature of 85 ℃, nitrogen flow of 347 L/h, the feed rate of 7.5 mL/min. Comparing the water suspension process and blend solution spray drying process, we could find that the suspension spray drying process and water suspension process was core-shell coating, but blend solution spray drying technology was composite coating.