Research On The Thermal Autocatalytic Decomposition Characteristics And Thermal Safety Of Energetic Materials

The catalytic thermal decomposition of energetic materials is a reaction that the products act as catalysts in the reaction process.The kinetics of this type of reaction is special with a sudden release of heat.This type of reaction reacts violently and its destruction is great,which gets great attention of domestic and foreign scholars.A certain amount of decomposition products will be produced if the energetic materials is heated unexpectedly or after a long-term storage(thermal history),and for autocatalytic reaction the aforementioned products will seriously affect the thermal safety of energetic materials.This paper mainly focused on the research of the identification of catalytic thermal decomposition of energetic materials,reaction kinetics and thermal security,etc.In this study,simulations were conducted on select substances using the first-order reaction model(F1)and the general autocatalytic reaction model(Cn).Based on the results of the simulation,the theoretical basis of the thermal history method for determining the autocatalytic decompositions of energetic materials were studied.The method was used to identify the autocatalytic reaction properties of energetic materials for the first time in this study.The isothermal DSC measurements and Swiss method were also employed to validate the reliability of the proposed thermal history method.The results showed that the decomposition of 2-Ethylhexyl nitrate(EHN),ammonium nitrate(AN)and the AN-based industrial explosives such as emulsion explosives,ANFO,expanded ammonium nitrate explosive proceed according to the nth order law.The explosives such as Pentaerythritol tetranitrate(PETN),nitrocellulose(NC),hexanitrohexaazaisowurtzitane(CL-20),3-nitro-1,2,4-triazol-5-one(NTO),cyclotetramethylene tetramine(HMX),nitroguanidine(NQ),trinitrotoluene(TNT)and ammonium nitrate explosive,they decomposed autocatalytically.The influence on the dynamic DSC curves was significant based on data in the autocatalytic reactions.Thermal stability was decreased with a lower initial temperature and peak temperature.The results of this study indicated that the proposed thermal history method can be successfully used to quickly and effectively identify the autocatalysis characteristics of energetic materials.EHN,PETN,NC,NTO,CL-20 and NQ were tested by dynamic DSC runs,while HMX and TNT were tested by isothermal DSC experiments.The kinetic parameters and the parameter values of thermal safety were also calculated based on the DSC curves.The results showed that the initial decompistion temperature,TD8,TD24 and SADT of EHN,PETN and NC were much lower than other types of energetic materials,which meaned their possibility of thermal explosion were higher.The experiments with thermal history method for EHN and NC were conducted at different heating rates,the results showed that the thermal history resulted in a significant reduction of the activation energy of NC in the initial thermal decomposition and a reduction of its thermal safety.The slow cook-off experiments were carried out to investigate the critical temperature of the thermal decomposition of the large cartridge emulsion explosives.The results indicated that the critical temperature obtained in slow cook-off experiments were generally lower than the initial temperatures from DSC.For the large cartridge emulsion explosives with diameter of 70 mm,the the critical temperature was 170 ? at the heating rate of 3?·h-1.It is a dangerous temperature for the production of the large cartridge emulsion explosives and it should cause our attention.The accelerating rate calorimeter(ARC)was used for thermal analysis of EHN,NC and PETN.The results showed that the temperature versus time curve of EHN was liner,while NC and PETN were S-type.For the nth order reaction and autocatalytic reaction,the effects of the sample mass were different,and the difference could also be used as a method to identify the catalytic reaction.The initial decomposition temperature of EHN,NC and PETN were 145.5,145.2 and 150.8? respectively,which were far less than the values obtained from DSC experiments.Compared with the DSC experiments,the heat release from the ARC experiments were much lower while the thermal safety temperature such as TD8,TD24 and SADT were higher.The TG-DSC-QMS method was used to measure the weight loss,heat,the MS of gas products simultaneously in the decomposition process of NQ,HMX,NTO and research department explosive(RDX),while the non-linear multivariate regression were used to fit the TG curves of them.The results indicated that the decomposition process of NQ could be described by the reaction modelA(?)B(?)C,and the reaction mechanism of the first step was Fn while the second was Cn.The decomposition process of NTO and RDX could be described by the A(?)B;A(?)Cmodel,and the reaction mechanism of the two parallel step were Fn and Cn respectively.For HMX,the best fit result was the A(?)B model,whose reaction mechanism was Cn.The above results also proved the presence of autocatalytic reaction in the decomposition of the four above-mentioned energetic materials.