| As the accidents of pumps usually occurred in the production process of emulsion explosives, the phenomenon of thermal decomposition, local ignition and deflagration to detonation transition (DDT) process of emulsion explosives was analyzedThe local ignition test was investigated according to the French and American methods of UN test to simulate the properties of deflagration to detonation transition process of emulsion explosives. The results show that the DDT process can not happen under atmosphere condition. When hot-wire was used to ignite the emulsion explosives at different temperatures, it was shown that temperature had a very significant influence over the ignition sensitivity of emulsion explosives. Along with temperature increase, the ignition sensitivity raised.According to accelerating rate calorimeter (ARC) test results, thermal stability of emulsion explosives was affected by many factors. Different chemical structures and impurities of emulsifiers contributed to their significant influence on thermal ability. Oil material has little effect on the thermal stability for its boiling point exceeds ammonium nitrate decomposition temperature. In the production process of emulsion explosives, many inorganic salts were also used. Urea can obviously improve the initial decomposition temperature of ammonium nitrate and emulsion explosives. Sodium nitrate does not affect the thermal stability of ammonium nitrate and emulsion explosives whereas the presence of chloride and iron ions can significantly decrease the thermal stability of ammonium nitrate and emulsion explosives.The pressure data in the ARC test results could be used to judge the thermal stability. According to the ammonium nitrate and emulsion explosives test results, this justifies the use of pressure data in kinetic calculations. High pressure ARC was also used to analyze ammonium nitrate and emulsion explosives thermal stability. The results revealed that under pressure condition, initial decomposition temperature maintained while the decomposition reaction speed increased with the decomposition heat. Also the initial temperature of ammonium nitrate increased for the water inhibited the ammonium nitrate thermal decomposition.Emulsion explosives minimum burning pressure (MBP), which means self-sustained combustion pressure, was carried out by pressure vessel. Emulsion explosives formulation and testing method affected the MBP testing results significantly. A probable process of emulsion explosives ignition has several stages. First, under high temperature and pressure condition, water phase of emulsion matrix droplet began to boil when heating continued. Water vapor escaped from oil film of droplet, evaporated into the pressure vessel when water vapor pressure overcame the droplet surface tension. Second, ammonium nitrate and other inorganic salts crystallized in the droplet surface and underwent decomposition under continued heating. Third, active free radical of oil materials were generated under high temperature, and reacted with ammonium nitrate decomposition production. Finally, emulsion explosives realized ignition. When pressure value exceeded the MBP value, emulsion explosives realized self-sustained combustion. The fundamental reason of emulsion explosives MBP phenomena is that, dissociation reaction is a huge endothermic reaction and is dominant at the initial stage of ammonium nitrate decomposition reaction, which effects subsequent exothermic reaction. If the water can not be exported in the ignition process, test results of emulsion explosives MBP testing will be affected. There is a very good correlation between thermal stability and MBP test result of emulsion explosives.According to energy balance in the emulsion explosives ignition process, MBP model was established, which was commonly used to calculate the emulsion explosives formulations. The results were consistent with the results of MBP measurements. Therefore, the model is applicable to emulsion explosives MBP simulation calculations. |
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