Preparation Of Energetic Hollow Microcapsules And Detonation Properties Of Its Sensitized Emulsion Explosives

Energetic additives could significantly increase the explosive power of emulsion explosives?EE?,which has been widely concerned by researchers at home and abroad.However,ultrafine energetic additives were incompatible with EE,which not only increased the explosion power of EE,but also reduced the security and stability of EE.These defects limited the promotion and use of high-energy EE to a certain extent.In order to solve the compatibility of energetic additives with EE and improve the security and storage stability of EE,we designed and prepared a new kind of dual functional energetic hollow microcapsules?EHMs?via the microcapsule encapsulation technology with energetic additives and blowing agent,poly?methyl methacrylate??PMMA?as core and shell,respectively.EHMs with hollow structure were formed by thermal expansion.Firstly,the EHMs of PMMA encapsulated AC/TiH₂ were prepared by an improved suspension polymerization-thermal expansion method with methyl methacrylate?MMA?,azodicarbonamide?AC?and TiH₂ powder as monomer,blowing agent and core material,respectively.The laser particle size analysis showed that the particle size of the EHMs,with a mean particle size of 116 ?m,which was significantly larger than that of the raw material TiH₂.Optical microscope?OM?and scanning electron microscope?SEM?results showed that the EHMs had good spherical morphology and core-shell structure,and a single EHM contained multiple TiH₂ particles.The thermal expansion experimental results showed that the particle size of EHMs did not change much after expansion,indicating that the expansion effect of using solid AC as the blowing agent was not well,and it still needed to be improved.In order to improve the expansion rate of EHMs and simplify the encapsulation and synthesis process,the liquid blowing agents and TiH₂ were directly encapsulated in the polymer microcapsules by one-step suspension polymerization to prepare EHMs.To prepare EHMs which are suitable for use as sensitizers of EE,the influences of EHMs preparation process?dispersing time and speed,the species and composition of blowing agents,dispersant category,core content and etc?on the particle size,the initial expansion temperature,surface morphology and thermal stability of microcapsules were studied by using particle size analyzer,SEM,OM and TGA.The experimental results showed that the increase of dispersing time and speed can significantly reduce the particle size of EHMs and make the particle size distribution more concentrated.The EHMs could not be formed by using polyvinyl alcohol as dispersant.The EHMs,which were prepared by using nanometer magnesium hydroxide?Mg?OH?₂?as inorganic dispersant,had good spherical morphology.By optimizing the core-shell mass ratio of MMA/TiH₂,the surface morphology of the prepared microcapsules could be controlled.The initial expansion temperature of EHMs was related to the type of blowing agent encapsulated in the microcapsules core.EHMs with different initial expansion temperatures could be prepared by combining different types of blowing agents.The microcapsules expansion rate was positively correlated with the content of expansion agent.Meanwhile,TiH₂ could improve the thermal stability of EHMs.After adding TiH₂ into the microcapsules,the stability of EHMs increased with the increasing amount of TiH₂ in the core.The detonation performances of EE sensitized by EHMs were studied by the brisance and detonation velocity experiments.Compared with the GMs sensitized EE,the brisance of the EHMs sensitized EE were increased 45%.This was due to that TiH₂ in EHMs were used as energetic additives to improve the detonation heat and detonation reactivity of the explosive.Compared with the GMs-TiH₂ sensitized EE,the brisance and detonation velocity of the EHMs sensitized EE were increased 3%.This was because the hollow structures in EHMs could act as "hot spots",the internal hollow structure of EHMs could save the volume occupied by energetic additives TiH₂,which increased the charge density and enhanced the detonation performance of EE.The TG-DSC analyzer was used to analyze the EE with 6%EHMs,and TG and DSC curves under different heating rates were measured to obtain the activation energy and other thermodynamic parameters.The experimental results showed that the activation energy of the EHMs sensitized EE was significantly higher than that of GMs-TiH₂ sensitized EE at the same conversion rate,indicating that the thermal stability of the EHMs sensitized EE was significantly better than that of GMs-TiH₂ sensitized EE.The thermal stability of EE could be improved by the presence of polymer film.Figure[36] table[10] reference[95]...