Research On The Forming Mechanism Of Sodium Azide Gas Generating Agent Residue

The active sodium generated in the combustion process of sodium azide gas generator,which has a tendency to coagulate and form two-phase flow with gas,has a risk of the concentration of thermal stress in internal and external equipment and the blockage of gas-producing passage.Accordingly,improving the pore structure of grain residue is necessary,and can effectively immobilize the active sodium in situ.In this paper,in the processing of formation based on the high azide of sodium azide/iron oxide formula,the sodium azide's residue and its influencing factors were systematically studied.The mechanism of three processes on thermal decomposition,active sodium oxidation and residue agglomeration of sodium azide residue formation was studied by using the ignition experiment of glass tube generator.The effects of various factors on the three processes of residue forming were studied by means of internal ballistic calculation software?REAL?,scanning electron microscopy?SEM?method,energy dispersive X-ray spectroscopy?EDX?method,X-ray diffractio?XRD?method and plasma?ICP?method,by which the macro-morphology,micro-morphology,composition and content distribution of residue were analyzed.In addition,three means of alloy,coating and burning rate adjustment were used to improve the mechanical properties of grain residue and decrease the residue.The DSC-TG results showed that thermal decomposition has an influence on the formation of sodium azide residue.The sodium azide with high thermal decomposition activation energy,whose grain burns regularly along the vertical end of the grain and formation structure of the grain residue is complete,has in-situ immobilization effect on the active sodium by the pore structure of the residue.On the contrast,the grain of sodium azide with low thermal decomposition activation energy,burns nonlinearly and irregularly along the contact surface with high temperature airflow,resulting in fast burning rate and that the active sodium condenses and unites along the airflow direction.The single factor analysis method was used to study the effect of oxidant type and content on the oxidation process of sodium azide active sodium.The enthalpy of formation of Sr?NO₃?₂?KClO₄ and NaClO₃ is high,causing the poor micro-morphology of residue and fast burning rate,while MnO₂ with high melting point oxidation products improves the structural strength of the grain and has good slagging effect.The four metal oxides Al2O3,TiO₂,MgO and MoS₂ all have an efficiently effect on reducing residue,whose pore structure is obviously fused,showed that the oxidation product enhances the structural properties of the residue.The residue rate of Al₂O₃ is less than 1%,showed slow burning rate has a significant slagging effect.The higher the content of oxidant,the thicker coating layer of sodium azide cell,the better the slagging.The effects of six slag-forming agents on the agglomeration of sodium azide residues were discussed.The traditional slag-forming agents,including silica and kaolin,had limited effect on in-situ fixation of residues.Talc powder has medium burning rate and good slagging effect.Boron nitride and silicon nitride have flame retardant effect,whose burning rate is slow and residue rate is less than 1%,showed that they have good effect on the formation of sodium azide residue accordingly.The residue rate of B₂O₃ is less than1%,showed the residue structure strength has a significant slagging effect in the condition of quick burning rate.The content of slagging agent is not the better for the formation of sodium azide residue,which for example,would increase the burning rate,temperature and pressure with a large number of primary fuels,being conducive to sodium azide residue.The means of alloy increasing melting point of residue found that silicon and titanium have a good slagging effect,which keeps the pore structure"stalactite"shape with obvious fusion.The formation of sodium silicate and silicon nitride in the combustion process of Si is beneficial to slagging.The effect of boron and iron on reducing residue was not obvious,while boron could react with nitrogen to produce boron nitride and iron can obviously decrease the burning rate.In the whole slagging effect of silicon,boron,titanium and their compounds on sodium azide:elements>nitrides>organic compounds>oxides.Sodium azide raw materials were coated with one-component polyurethane and boron modified phenolic resin,found that they had certain residue reduction effect.On the basis,three formulations of sodium azide were designed,found that the synergistic effect of multiple components on reducing sodium azide residue was better than that of single component.