| Ammonium nitrate（AN）materials are hazardous chemicals,and they are the main ingredient of common fertilizer,industrial raw materials and energetic materials,such as explosives and solid propellant.These materials play an important role in the industry,agriculture and national defense in our country,thus its safe production,storage,transportation and utilization concern the stability of the national production and economic development.Many AN explosive accidents have happened in the world since the 20th century.These accidents mainly occurs in the process of production,transportation and storage,and usually cause many casualties and huge economic losses.Thus,the development of fire extinguishing,inert and explosion suppression technique for AN by studying the thermal decomposition and dynamics behavior of AN and its combustion reaction mechanism are important and significant.It is beneficial to maintain public security of inflammable and explosive materials in chemical industry park and other places,and to secure the safety of the people and ensure the security of the state property.This thesis has been supported by the National Key Technologies Research and Development Program of China（No.2017YFC0804907 and No.2016YFC0802801）and the National Natural Science Foundation of China（No.51374164）.Based on the systematic research and in-depth analysis of the related research results,theoretical analysis and experimental research are used in this study,including kinetics of thermal decomposition and self-accelerating decomposition temperature of AN,the influence of typical inhibitors on the thermostability and explosibility of AN,structural characteristics and the evolved products of optimized inhibitors,and mechanical sensitiveness of optimized inhibitors on the AN.Firstly,the thermal decomposition behavior and thermal stability of AN under different conditions are systematically studied,including in an open pan and a closed pan,different mass,atmospheres,heating rates,gas flow rates.The evolved decomposition gases of AN in air and nitrogen are analyzed with a quadrupole mass spectrometer.Thermal stability of AN in different environment,mass,atmospheres,heating rates and gas flow rates are studied by differential scanning calorimetry,thermogravimetric analysis and safety parameter evaluation.Kinetic parameters（thermal decomposition and apparent activation energy）and self-accelerating decomposition temperature（SADT）of AN are calculated by Vyazovkin method.Experimental results show that the thermal decomposition of AN in closed environment is more complex than that in the open environment.The major evolved decomposition gases in air are H2O,NH3,N2O,NO,NO2 and HNO3,while in nitrogen,H2O,NH3,NO and HNO3 are the major components.Compared with nitrogen atmosphere,lower initial and end temperatures,higher heat flux and broader reaction temperature range are obtained in air.Meanwhile,higher air gas flow rate tends to achieve lower reaction temperature and poorer thermal stability of AN.SADT of AN in air is much lower than that in nitrogen.10 kinds of typical inhibitors are primarily selected from the commonly used fire extinguishing agent in order to screen their suppression on fire and explosion of AN.The thermal stability and thermal decomposition of AN and its mixtures with various concentration of additives are systematically investigated by DSC-TG analysis and the reaction mechanism of AN and its mixtures are speculated.Experimental results show that ammonium monohydric phosphate（AMP）,ammonium dihydrogen phosphate（ADP）,ammonium sulfate（AS）,potassium sulfate（PS）,potassium carbonate（PC）and calcium carbonate（CC）can slow down the thermal decomposition reaction of AN in a certain extent,thus these additives are beneficial to the thermal stability of AN.In order to analyze the inhibition effect and mechanism of the additive on the thermal decomposition characteristics of AN,the surface morphology,thermal stability and thermal decomposition of AN and its mixtures（ADP,AS,PS and CC）with various concentration are investigated by SEM,TG-MS and TG-FTIR analysis.TG-MS experimental results show that the major evolved decomposition gases of AN and its mixtures are different.The evolved gas types are varied with additives.TG-FTIR experimental results showed that N2O are the major evolved decomposition gases of AN.Meanwhile,the generation of NO and NO2 obviously lag in the AN mixture,thus the thermal decomposition of AN can be inhibited by ADP.It is considered that the ADP,AS,PS and CC are effective inhibitors for AN,which can effectively enhance the thermal stability of AN.Explosive sensitivity of optimized inhibitors on AN are studied by breaking point tester,shock sensitivity tester and friction sensitivity tester,and 5 seconds explosion delay period temperatures（breaking point values）and explosion probability of AN and its mixtures are obtained.Experimental results showed that the breaking point values of AN are markedly improved by ADP,AS,PS and CC,and the values of AN mixtures are all lower than AN in the sensitivity experiments.The critical temperatures of AN hot spot are increased by inhibitors,thus,mechanical sensitivity of AN is inactivated by these inhibitors.It is considered that the ADP,AS,PS and CC have marked inhibiting effect on explosive sensitivity of AN,thus they can effectively enhance the thermal stability of AN,CC has the best effect.This research proves that reasonable changes of storage conditions will influence AN’s thermostability,which is helpful to its safe production,storage,transportation and utilization.The optimized inhibitors are low-cost and efficient suppression on the fire and explosion of AN.Thermal decomposition and inhibition mechanisms of AN materials can provide theoretical support for the further research and development of fire-extinguishing materials and technologies for AN. |
