| Solid propellant gas generators(SPGG),as a new kind of halon alternative extinguishing technology,has attracted considerable attentions in recently years due to its high efficiency,green and easy storage at atmospheric pressure.However,there are some shortcomings when using it,such as the high combustion temperature and the mutual restriction between combustion rate and pressure,which further limit its applications and development.5-Amino-1H-Tetrazole(5-AT),as the important component of solid propellant,its pyrolysis and combustion behaviors can influence the functions of the system directly,and further effect the work efficiency of SPGG fire extinguishing technology.Thermal decomposition deemed as the initial stage for the combustion process,which plays a crucial role in the whole process of combustion,can make a significant sense for combustion.In order to the better understand and optimize the pyrolysis and combustion characteristics of 5-AT and enhance its applicability for SPGG fire extinguishing technology,some work have been carried out in this paper.Firstly,the micron-sized boron and copper powder are selected as the catalysts to modify the pyrolysis of 5-AT.Both the solvent/non-solvent,water suspension and ball-milling methods are also applied to treat the surface of 5-AT sample,which are used to coated these catalysts on the surface of 5-AT to catalyze the pyrolysis for 5-AT.And the kinetic methods are employed to calculate the kinetic triplet for 5-AT pyrolysis,which is aimed to deeply enhance the exploration for the thermal decomposition behaviors and optimization mechanism of 5-AT.Simultaneously,5-AT is mixed with different oxidants based on the zero-oxygen balance principle,and the copper oxide is selected as the catalyst to explore the temperature characteristics of combustion,which is aimed to study a type of 5-AT-based solid propellant with lower combustion temperature.The results show that the pyrolysis of 5-AT in the first stage is almost unaffected by the modification methods and catalyst.The catalytic effects of catalysts are mainly reflected on the latter stages.The most obvious effect on the pyrolysis behaviors is reflected in the third stage of 5-AT due to the occurrence of the exothermic reaction.In terms of the catalytic effect and modification method,it is found that the pyrolysis steps of 5-AT are shorted from three to two under the catalytic actions of micron-sized copper powder.After being modified by the water suspension and the solvent/non-solvent methods,the activation energies of the latter two stages for 5-AT are reduced by 18.3 k J/mol and 10.9 k J/mol respectively,which illustrates that the suspension method shows a better modification effect.Furthermore,the same water suspension modification method is applied to compared the effect of the two catalysts.The results show that the activation energies of5-AT are reduced by 37.9 k J/mol and 307.2 k J/mol respectively for the latter two stages under the catalytic action of micron-sized copper powder compared with boron powder,which illustrates that micron-sized copper powder shows a better catalytic effect than boron powder.As for the initial pyrolysis stage,after being modified with the solvent/non-solvent method,the results shows that nano-sized copper powder can promote the pyrolysis of 5-AT,and the activation energies are reduced by 9 k J/mol compared with nano-sized boron powder.Moreover,the pyrolysis model has been changed from F4 to F2 and F3 model respectively.As for the thermal safety parameters,the use of nano-sized copper oxide as the catalyst tends to be safer than nano-sized copper powder,and 5-AT shows a faster reaction rate under the catalytic action of the nano-sized one.After being modified by the ball milling method,the nano-sized copper powder shows a better catalytic effect than nano-sized copper oxide,with the activation energies reduced by 10.3 k J/mol.At the same time,the reaction model is both changed from F4 to F2 model.The use of nano-sized copper powder as a catalyst is safer than nano-sized copper oxide,and it also speeds up the5-AT pyrolysis reaction rate.From the perspective of combustion characteristic,this paper is focused on the study of propellant samples mixed with 5-AT and oxidizers to constitute the propellant components.It is found that the combustion temperature of 5-AT propellant with the form of tablets is closer to the theoretical burning temperature compared to the powder ones,possibly due to the higher density of tablet samples.As for the mixture of 5-AT and strontium nitrate,its burning behaviors in the form of powder could largely reduce the catalytic effect of copper oxide compared with the tablets.With respected to potassium nitrate,the copper oxide could not only promote the combustion,but also increase the combustion temperature.For basic copper nitrate,its burning behaviors in the form of tablets could increase the catalytic effect of copper oxide compared to the form of powder.In this paper,the micron-sized boron powder and copper powder are firstly employed as catalysts.And then solvent-non-solvent and water suspension methods are used to modify 5-AT,which is aimed to make the catalyst being coated on the surface of 5-AT to catalyze its pyrolysis process.In contrast,it is found that the micron-sized copper powder has a better catalytic effect,and the water suspension method has a better modification effect.Secondly,ball milling and solvent-non-solvent method are used as the modification methods,and nano-sized copper and copper oxide powders are introduced as the catalysts to explore the effect of modification methods and catalysts on the pyrolysis of 5-AT in the initial stage.Results show that the pyrolysis in the initial stage of 5-AT is greatly affected by the modification method and catalyst.Finally,5-AT is mixed with three kinds of oxidants,and nano-sized copper oxide is used as a catalyst to investigation the combustion temperature.Studies have found that nano-sized copper oxide can reduce the combustion temperature of 5-AT mixed with strontium nitrate and basic copper nitrate,and has the opposite catalytic effect on the combustion temperature of 5-AT/potassium nitrate mixture.The conclusions could provide several valuable directions and references about the further understanding,exploration,design and applications of 5-AT-based solid propellant in the future. |
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