Study On The Combustion Stability Of Gas-generating Agents Based On Different Preparation Processes

Quality defects such as explosion,intermittent combustion,and flameout constantly occur in process of unstable combustion of gas-generating agents.Combustion stability is very essential in the quality assessment of gas-generating agents,which is technical index to get the gas-generating agent ignited reliably in critical moments such as car accident and instant fire extinguishing.As the material properties,formula,and charge structure are determined,the preparation process of the gas-generating agent is especially crucial to the combustion stability.In this study,a dynamic combustion process evaluation model has been established with three parameters of completeness of combustion,combustion temperature and flame area,and analyzed the effects of several mostly-used preparation processes on the combustion stability of gas-generating agents comprehensively.Herein,three kinds gas-generating agents of potassium nitrate/5-aminotetrazole,potassium nitrate/nitroguanidine,and potassium nitrate/melamine were chosen as research object,whose optimal ratios were determined by changing the ratio of the agents through oxygen balance.Different preparation methods were applied for their characteristics.The gasgenerating agents of potassium nitrate/5-aminotetrazole were prepared by mechanical mixing method,evaporative crystallization method,and freeze-drying method.The potassium nitrate/nitroguanidine gas-generating agents were prepared by mechanical mixing method,cooling crystallization method,and freeze-drying method.The potassium nitrate/melamine gasgenerating agents were prepared by mechanical mixing method and freeze-drying method.all samples above were tested for the combustion stability.The freeze-dried agents of potassium nitrate/5-aminotetrazole gas-generating agents,potassium nitrate/nitroguanidine gas-generating agents,potassium nitrate/melamine gasgenerating agents all show certain advantages in combustion performance through constant volume combustion and residual residue rate.Their maximum combustion pressure reaches98.89 MPa,90.15 MPa,63.40 MPa,and the residue rate was 2.55%,3.44%,and 3.72%,respectively.The combustion temperature of the freeze-drying gas-generating agent is more stable than samples prepared by other methods.The images of the burning flame show that the flame disturbance is small and the flame shape is fixed when the freeze-dried agent burns.According to the images of the combustion flame,a method to analyze and evaluate flame stability is proposed,which is based on the quantification of the flame area.The stable combustion time of the freeze-drying agents of the three systems is 52.07%,71.76%,and 35.19%longer than that of the mechanical mixture,and the standard deviation values of the combustion stability section are low as 7.75,1.90,and 5.92,respectively.Herein,a new method of co-freeze-drying was proposed based on freeze-drying method,which pre-dissolved the binder,oxidant and combustible into a mixed solution and then freezedried.In this way,the same formulation as the potassium nitrate/melamine gas generator was prepared,and the combustion stability was tested.Compared with the freeze-drying method,the method simplifies the wet mixing steps,and the prepared medicament shows good combustion stability.Through scanning electron microscopy(SEM),X-ray diffractometer(XRD),Fourier infrared spectroscopy(FT-IR)thermogravimetric-differential scanning calorimeter(TG-DSC)characterization,it is found that the three system agents are different from The new crystal structure of the mechanical mixing of the oxidizer and the reductant,and the formation of cocrystals prove that the freeze-drying method improves the mixing degree and mixing method of the medicament from a microscopic point of view,thereby improving the combustion stability of the medicament.