The Effect Of Impurities On The Thermal Decomposition Characteristics Of Nitrate

Nitrate is generally composed of metal ion or ammonium ion(NH4+)and nitrate ion(NO3-),belongs to nitric acid derived ionic compounds,and is widely used in industry and agriculture.Because of its strong oxidation property,it is identified as dangerous goods category 5.1.It is strictly prohibited to be stored and transported with acids,reducing agents,inflammable substances,active metal powders,etc.,and keep it away from heat source.Although there are strict requirements for the production,storage,transportation and use of nitrate,fire and explosion accidents caused by nitrate have occurred frequently,and are extremely destructive,causing a large number of casualties and heavy economic losses.Scholars at home and abroad have been paying continuous attention to the study of its thermal risk.The mechanism of hot spot formation and its induction process caused by impurity intervention are not very clear.Therefore,two kinds of nitrate,ammonium nitrate(AN)and guanidine nitrate(GN),were selected to study the influence of impurities,such as water,diesel oil,wood powder and Fe2O3,on their thermal decomposition characteristics during production,storage,transportation,and use.Thermogravimetry and derivative thermogravimetry method(TG-DTG)was used to explore the thermal decomposition characteristics of nitrate under the action of impurities,and the activation energy was calculated by FWO and KAS methods.The CR method was used to explore the optimal reaction mechanism function,and the thermodynamic theory was used to solve the relevant thermal safety parameters,providing theoretical reference for the study of the thermal risk of nitrate and theoretical support for its safety application.(1)Ammonium nitrate exhibits one-step weight loss in the temperature range of 400-650K.The average extrapolated onset temperature and extrapolated end temperature are 538.30K and 577.73K respectively at different heating rates,and the decomposition mechanism of ammonium nitrate is best reflected by the Zero-order(F0)model.Ammonium nitrate containing water or diesel shows a two-step weight loss,and the extrapolated onset temperature is delayed.The extrapolated onset,peak and extrapolated end temperatures of ammonium nitrate containing wood powder are all advanced.The extrapolated onset temperature of ammonium nitrate containing Fe2O3 is relatively lagged behind,but the overall effect is not significant.The presence of impurities reduces the activation energy of ammonium nitrate and promotes its decomposition process to some extent.(2)Guanidine nitrate exhibits one-step weight loss in the temperature range of 450-700K.The average extrapolated onset temperature and extrapolated end temperature are 580.28K and 607.78K respectively at different heating rates,and the decomposition mechanism of guanidine nitrate is best reflected by the Avrami-Erofeev(A2)model.Guanidine nitrate containing water or diesel shows a two-step weight loss,and the extrapolated onset temperature is delayed,the activation energy increases,and the difficulty of the reaction increases with the degree of reaction.The extrapolated onset,peak and extrapolated end temperatures of guanidine nitrate containing wood powder are all advanced,the activation energy is reduced,and the difficulty of the reaction decreases with the degree of reaction,indicating that the thermal risk is further increased.The extrapolated onset temperature of guanidine nitrate containing Fe2O3 is advanced and the activation energy decreases,which promotes the decomposition to some extent.(3)The spontaneous ignition temperature and self-accelerating decomposition temperature of ammonium nitrate are 519.71K and 502.35K respectively.The presence of water,wood powder and Fe2O3 reduces thermal safety and increases thermal risk of ammonium nitrate.The spontaneous ignition temperature and self-accelerating decomposition temperature of guanidine nitrate are 548.10K and 530.15K respectively.The presence of wood powder and Fe2O3 reduces thermal safety and increases thermal risk,so try to avoid contact with them and strictly control the ambient temperature to avoid thermal runaway caused by heat accumulation.