Preparation And Properties Of RDX-based Spherical Composite Energetic Materials By Microcapsule Technology

In recent years,with the rapid development of modern weapon systems,solid propellants have developed towards high-energy,insensitive,safe and environmentally friendly directions.The effective way to improve the energy of propellant is to add high explosives to its formula,or adjust and control the oxygen balance in the formula.This article first refines cyclotrimethylnitrosamine（RDX）to provide raw materials for its subsequent coating;Then the RDX/AP/alginate copper composite energetic materials were prepared by microencapsulation granulation technology with biological gel copper alginate as the substrate based on the proportion of zero oxygen balance.The main research content of this article is as follows:（1）Submicron sized RDX particles were prepared using the solvent anti solvent method using high-frequency vibration and electrostatic repulsion.The effects of solution concentration,solvent non solvent ratio,surfactant type and concentration on the morphology and particle size distribution of RDX were studied.By designing a single factor experiment,RDX crystals with uniform crystal particles and smaller particle sizes were prepared.Performance characterization of the samples under the optimal experimental conditions:the average particle size of RDX is370 nm,and the activation energy of refined RDX is 148.19 k J·mol^-1;The mechanical sensitivity of recrystallization refined RDX has increased by 3 J and 12 N respectively in terms of ultimate impact energy and friction pressure compared to the raw material,resulting in a significant improvement in safety.（2）Based on zero oxygen balance,RDX/AP/alginate copper composite energetic materials under different oxygen balance were prepared,and their properties were characterized.The results show that the particle sizes of the composite materials are all between 450 and 550μm.With the increase of RDX content,the obtained sample has a more uniform shape and size,and the surface coating is more dense.RDX,AP,and copper alginate coexist well in the composite material.The activation energy of the composite in zero oxygen balance reached 269.50 k J·mol^-1,and the mass loss was the largest after the thermal decomposition reaction,reaching 97.64%,which made the reaction more complete;The thermal decomposition rate constant is 5.00 at high temperature and 6.89×10^-16 at room temperature,most active in high-temperature environments and most stable at room temperature;The mechanical sensitivity of the samples coated with copper alginate decreased and their safety performance improved.（3）The RDX/AP/alginate copper composite energetic materials with different copper content of alginate were prepared under the proportion of zero oxygen balance,and their morphology was spherical.With the increase of sodium alginate content,the surface gel coating became more dense,and the content of copper in the particles gradually increased.Compared with RDX,the thermal decomposition peak temperature of composite materials has been advanced,and the activation energy and pre exponential factor have been significantly increased.When the copper alginate content is 8 wt%,the activation energy reaches 497.6k J·mol^-1.It has the greatest difference in thermal decomposition rate between room temperature and high temperature conditions,is most stable at room temperature,and reacts most violently at high temperature;According to TG-DTG,when the copper alginate content is 8 wt%,the reaction time is shortest and the maximum decomposition rate reaches 272.47%/min.The mechanical sensitivity of composite materials gradually decreases with the increase of copper alginate content,and the safety performance is improved.（4）Through microencapsulation granulation technology,single factor experiment was designed to obtain the optimal process conditions for preparing RDX/AP/alginate copper composite energetic materials under zero oxygen balance:nozzle diameter 300μm.The concentration of sodium alginate is 2%,the temperature is 20℃,the feeding rate is 8 m L/min,the vibration frequency is 720 Hz,and the vibration amplitude is 3.The sample obtained using freeze-drying technology has a more uniform and dense coating,an ultimate impact energy of7.5 J,a friction pressure of 128 N,lower mechanical sensitivity,and better safety performance.Compared with the RDX/AP/copper alginate composite material prepared by direct method,the composite material prepared by microcapsule granulation technology has better safety performance.