Study On Stearate Improvement Of Thermal Decomposition,Safety And Anti-hygroscopic Properties Of Ultrafine Ammonium Perchlorate

Ammonium perchlorate（AP）is the main energy component of solid composite propellants,and improving the performance of AP is of great significance for promoting the development of aerospace and military chemistry.The smaller size of ultrafine ammonium perchlorate（UF-AP）has a faster burning rate,but the smaller size of AP will lead to increased moisture absorption and reduced safety performance,the contradiction between AP thermal decomposition and safety performance is also a difficult problem for the industry to reconcile.In this study,a high-efficiency and low-energy recrystallization method was proposed to refine AP,and the concept of superhydrophobicity was introduced to solve the problem of moisture absorption after refinement.The low surface energy material stearate was used to construct a core-shell structure composite of UF-AP/stearate,and the moisture absorption rate of UF-AP was inhibited by low surface energy and rough stearate shell layer.The stearate shell layer maintains its buffering effect at room temperature,which effectively reduces the sensitivity of UF-AP,when the temperature rises,it decomposes in situ on the surface of UF-AP to generate corresponding metal oxides and catalyze the thermal decomposition of UF-AP.The addition of stearate improves the thermal decomposition performance and safety performance of UF-AP at the same time,and solves the problem of contradiction between the two performances.The main contents of this study are:（1）In the aspect of AP refinement,based on the principle of solvent-nonsolvent method,a new spray recrystallization method was proposed to refine AP,and the influence of the selection and ratio of solvent and non-solvent on the refinement results was also explored.Through SEM characterization,the size and morphology of AP obtained when 5℃water was used as the non-solvent did not meet the requirements,while the UF-AP obtained when 5℃ethanol was used as the non-solvent were smaller in size and tended to be spherical,and the sizes were mostly distributed about 10μm,increasing the proportion of non-solvent cannot intuitively reduce the average size of UF-AP,and will lead to an increase in the proportion of smaller sizes.Subsequent characterization of the structure FT-IR and XRD did not change,indicating that this refinement method does not change the molecular structure and crystal form of AP,and DSC-TG proved that the high and low temperature decomposition peaks of UF-AP obtained after refinement are slightly advanced,and the process of thermal decomposition is smoother.Through the characterization of moisture absorption rate and sensitivity,it is proved that the problem of increased moisture absorption and reduced safety performance after AP refinement.（2）The method of compounding stearate and UF-AP through liquid phase deposition adopts the reaction of stearic acid and metal acetate to generate the corresponding stearate shell layer on the surface of UF-AP.It was preliminarily determined by SEM that the surface of UF-AP was coated with a layer of material,and then in-depth structural characterization FT-IR,XPS and XRD proved that the reaction proceeded normally and the core-shell structure,and the crystal form of UF-AP did not change,there is good compatibility between the two substances.In terms of anti-hygroscopic performance,the addition of stearate effectively inhibited the moisture absorption rate of UF-AP within 72 h,when the content of Cu SA was 5%,the moisture absorption rate of UF-AP decreased from 0.56%to 0.03%.In terms of safety performance,the stearate shell layer also greatly reduces the impact sensitivity and friction sensitivity of UF-AP,when the content of Cu SA was 5%,H₅₀ increased from 25.4 cm to 54.2cm,and P decreased from 96%to 12%,and the desensitization effect of the core-shell structure is better than that of the physically mixed composite.The thermal decomposition properties of the composites were characterized by DSC-TG,the thermal properties of the three stearate salts themselves were first studied,and it was found that they would melt at 100-120°C,and decompose when the temperature continued to rise,the corresponding metal oxides were generated in situ to catalyze the attachment to the surface of UF-AP and catalyze the thermal decomposition of UF-AP.The Cu O produced by the decomposition of Cu SA has excellent catalytic effect on UF-AP,when the Cu SA content is 5%,the high temperature decomposition peak of UF-AP can be advanced from 424.5℃to 305.9℃.The initial temperature of Co SA decomposition is slightly delayed,and the decomposition rate is also slightly slower,during decomposition,Co O products will be formed first,which will be further oxidized to Co₃O₄ at higher than 300℃,the peak of high temperature decomposition of UF-AP/Co SA（wt=5%）was advanced to 344.8°C.Due to the highest decomposition onset temperature and the decomposition rate is slow of Zn SA,resulting in the decomposition of Zn O can only advance the pyrolysis temperature of UF-AP to 370-380℃,and will not advance further with the increase of Zn SA content.Finally,the thermal decomposition mechanism of the complex of stearate and UF-AP was speculated by thermal analysis and combined infrared characterization.In a word,the compound of stearate and UF-AP successfully reduced the hygroscopic effect of UF-AP,which improved the safety performance of UF-AP and also cleverly catalyzed the decomposition of UF-AP through thermal properties.It is a way to comprehensively improve AP performance,which has great potential in future engineering applications.