Studies On Pyrolysis Dynamics And Combustion Characteristics Of 5-amino-1H-tetrazole Based Solid Propellants

With lots of excellent properties,solid propellant gas generators(SPGG)has appealed widespread attention.The four attributes(large amounts of inert gas generation,atmospheric storage,application in conjunction with liquid fire extinguishing agent,release on demand)are what makes SPGG attractive and promising for Halon alternative fire suppression technology.However,as the main component inside SPGG,the 5AT/Sr(NO3)2 propellant has several drawbacks(such as high exhaust gas temperature,and unstable burning rate)weakening the fire-fighting efficiency and limiting its promotion and use.Based on the background of SPGG,we take the high nitrogen energetic material,5-aminotetrazole,and its propellant mixed with strontium nitrate as the research object.By means of adding positive/negative catalysts into 5AT/Sr(NO3)2 propellant,we study the effect of two variations(particle size,and transition metal oxide catalysts)on combustion properties of 5AT/Sr(NO3)2 propellant,and reveal the modifying mechanism of different variation on propellant combustion properties from the perspective of pyrolysis mechanism.The aim of this paper is to explore a novel 5AT/Sr(NO3)2 propellant formula with low exhaust gas temperature,low pressure exponent,and fast burning rate.Firstly,the green energetic material,5AT,was chosen as the study object,and its thermal decomposition and mechanism were discussed.TG-DSC analysis was conducted to compare the thermal stability of prepared 5AT samples with different particle sizes.The resistance to heat of 5AT sample with smaller particle size seemed to be weaker.Combined with the analysis of surface microtopography,and specific surface area,it was found that this phenomenon mainly resulted from the higher surface energy,and faster heat transfer rate of small particle.Additionally,the thermal decomposition mechanism of 5AT was found to be diffusional(D1)model.Besides,the catalyze mechanism of three kinds of transition metal oxide(short for TMO,including nanosized Fe2O3,nanosized CuO,and nanosized NiO)on 5AT samples was explored,by the means of TG-DSC-IR-MS measurement,BET analysis,and SEM imaging method.The presence of TMOs could accelerate the thermal decomposition rate of 5 AT.It was owing to the fact that the formation of CN bond was hindered,while the breaking of CN bond was strengthened with the TMOs addition.To conclude,the heat sensitivity of 5AT samples with smaller particle size,and TMOs addition tends to be strong,and needs more attention during the production,transportation,storage process.Secondly,the mixture of 5AT/Sr(NO3)2 propellant was set as study object,and its pyrolysis mechanism was analyzed with the method of TG-MS technology.Its thermal decomposition could be divided into four stages as follows.The 5AT decomposed into HN3,NH2CN,and melamine in the first stage.Then melamine continued to decompose with the generation of HCN,melem,and melam.In the 3rd stage,melem proceeded to decompose into NH2CN,HN3,HCN.etc,as well as reacted with the undecomposed Sr(NO3)2 to generate HCHO,and CO2.Afterwards,the decomposition of Sr(NO3)2 occurred with the generation of SrO,and nitrogen oxides.Finally,several methods were employed to study the modifying effect of catalysts on 5AT/Sr(NO3)2 propellant combustion performance,including TG-DSC,combustion temperature profile tests,burning rate measurements,thermal conductivity tests,and SEM photography.Compared to the propellant formula without additives,the formula with the addition of 20%CaCO3 exhibited a smaller activation energy,a lower decomposition temperature,and a faster burning rate in the former reaction stage,which was due to the increased specific surface area of condensed phase caused by the CaCO3 addition.In contrast,the formula with the CaCO3 addition performed a higher thermal decomposition temperature,a higher activation energy,and a much lower burning rate in the latter reaction stage,which resulted from the agglomeration effect in gas phase as a result of CaCO3 addition.In conclusion,although a plateau combustion effect and a low burning temperature have been achieved with the presence of CaCO3,a bad burning rate behavior has also been exhibited,which was harmful to the suppression efficiency of SPGG technology.The 5AT/Sr(NO3):propellant with the presence of TMOs displayed a fast burning rate as well as a low combustion temperature,and the variation tendency conformed to the relationship of thermal conductivity.The study on the modifying mechanism showed that the presence of TMOs could change the heat transfer and surface area in condensed phase,meanwhile alter endothermic/exothermic heat in gas phase,achieving a synergistic effect between condensed phase reaction and gas phase reaction.Additionally,the propellant with the addition of micron-sized Fe2O3 showed a faster burning rate than the one with nano-sized Fe2O3.The agglomeration and coverage effect when Fe2O3 particles dispersed among propellants were detected.Thence,when nano-particles applied as burning rate modifiers,some surface modification treatment was recommended to deal with the additives,such as electrochemical dissolution.Based on the study of 5AT/Sr(NO3)2 propellant in this paper,a safe,scalable,inexpensive,and excellent propellant formula has been obtained.The novel formula has satisfied combustion performance optimization for traditional 5AT/Sr(NO3)2 propellant,and achieved a balance among a low combustion temperature,a fast burning rate,and low pressure exponent.This study is of great significance to improve the suppressant efficiency for 5AT/Sr(NO3)2 propellant employed in SPGG device,accelerate the market application for SPGG technology,and promote the development for Halon alternative fire-fighting technology.