Study On Properties Of Explosives Containing Light Metal Hydrides

The energy design of mixed explosives breaks the limitation of traditional systems,and the development of non-ideal explosivesystem with oxidants-combustible agents is an importantmethod to improve the explosiveenergy.Light metal hydrides with high hydrogen content and high calorific values are expected to be new fuels of mixture explosive.Lithium hydride?LiH?andlithiumborohydride?LiBH₄?are promising potential metallic hydrogen storage materials.Due to the characteristics of largehydrogen storage,high reaction activityand highcombustion heat,theycan enhance the reactivity of1,3,5-trinitro-1,3,5-trazinane?RDX?,1,3,5,7-tetranitro-1,3,5,7-tetrazocane?HMX?and ammonium perchlorate?AP?in the structure and formula of explosives and then their energy release can be improved.In this paper,RDX,HMX and AP were the main explosive researched,while LiH and LiBH₄were as fuel additives.According to the insufficient storagestability in the design of explosive containing light metal hydrides,the coating and water-resisting mechanism of inert polymer materials were studied by molecular dynamic simulations.And then the coating process was operated by polycarbonate?PC?and paraffin wax coating on the surface of LiH andLiBH₄ and the stability of hydrides was improved.The interaction mechanism between LiH,LiBH₄ and RDX,HMX,AP was studied by means of molecular dynamics simulation,DSC,XPS,microcalorimetry,cook off tests and so on.Furthermore,the explosive formulas and structures with light metal hydrides were designed and prepared,and the explosionperformances of mixture explosivescontaining light metal hydrides were studiedsubsequently.The peak overpressure and impulse of explosion shock wave were obtained and analyzed.The main research contents are as follows:1.In order to solve the poor environmental stability of LiH?LiBH₄,the absorption situations of water molecules on the surface of inert materials?PPXC,PC?werefirstly analyzed by molecular dynamic simulation to study the hydrophobic mechanism.Based on the theoretical forecast,the multi-layer coating process of LiBH₄ and LiH was carried out with PC and the common inert material paraffin wax commonly used in explosives.Results show that acompact layer of organics is successfully coated on the surface of LiBH₄;while paraffin wax and PC coated on LiBH₄and LiH particles do not affect significantly the crystal form and the thermodynamic performance.The C and O elements were detected on the surface of coated LiBH₄.The coated degree of inert materials on LiBH₄was 98%and the environmental stability was improved by 66%in the weighing tests while the stability of LiH was 40%improved which laid the foundation for its further application.2.The surface interaction of HMX/LiH/coating materials?paraffin wax,PC,PPXC?was studied by molecular dynamic simulations.Compared with the binding energy,the intermolecular function patterns and mechanics properties of energetic systems,the improving effect of inert materials were evaluated such as extension and ductility of the explosive.The mechanisms of improving the ductility and toughness to the explosive system by the coating material were evaluatedand the binding mechanisms in the energetic systems at the molecular level were analyzed.The hydrogen bonds between the H atoms in PC and the Li atom,the carbonyl O atoms in the PC and the H atoms in HMX molecule were strongerand the main binding form.3.The thermal reaction mechanism of the decomposition of RDX,HMX and AP with LiH,LiBH₄ were studied by DSCtests.The addition of a certain amount of LiBH₄ changes the thermal decomposition mechanism of RDX.RDX decomposed directly without the melting process,and the initial decomposition temperature was about 50?in advance.There were two reaction stages between LiBH₄ and RDX.First,the released hydrogen catalyzed the decomposition reaction of RDX,and then the degradation products of RDX and LiBH₄ reacted with each other.The addition of LiH had little effect on the melting process and the decomposition peak temperature of RDX,but the high content of LiH changed greatly the decomposition peak temperature and the peak shape of RDX.After adding 5%LiH,the decomposition temperature peak of AP was advanced by 82.4?.With the increase of the addition amount,the decomposition peak shifted to low temperature which meant the reactivity between AP and LiH was violent.LiH or LiBH₄had little effect on the melting process and the decomposition peak temperature of HMX.Li₂CO₃ was detected by XPS analysis of LiH and HMX/LiH systems,which was the product of LiH hydrolysis.The appearance of Li₂CO₃ peak and the disappearance of N element in HMX/LiH system after DSC test were the result of the reaction between LiH and the decomposition products of HMX during the DSC test.The results showed that LiH and LiBH₄ had strong catalytic effect on RDX and AP decomposition,and the compatibility of coated LiH,LiBH₄ with three explosives was improved.4.The interaction performance of AP/LiBH₄ system was analyzed by microcalorimetry and cook-offtests.Due to thermal analysis of AP/LiBH₄ system by microcalorimetry test,the released heat was almost the same for LiBH₄ and AP/LiBH₄mixed powder of equal mass below 100?,it implied that there was no instant interaction between LiBH₄ and AP,but mainly the hygroscopic reaction of LiBH₄ itself.The cook-off tests show that there are two-stage reactions for AP/LiBH₄ grain system.The first stage is hydrolysis of LiBH₄,and then AP was used as oxidant to react with the reducing gas products generated in the first stage as an oxidizer.The self-accelerating decomposition temperature of AP/LiBH₄ grain is 270?,the explosion is mainly due to the decomposition of AP,and the explosion energy of AP/LiBH₄ system is higher than AP.This provides an important reference for the design of the oxidant-flammable system containing such light metal hydrides.5.High energetic explosives containing LiH and LiBH₄were designed and prepared,and the explosion characteristics were studied.Results show that:compared with traditional TNT,HMX based explosives,the explosion shock wave overpressure of explosives containing light metal hydrides presents a higher level?3%⁸3%?at 2⁵ m away from the explosion center.The instant damaging power is higher and the reduction of overpressure wave is slower.The detonation reaction time is prolonged and then the impulse is greatly improved than traditional TNT,HMX explosives.Li₂CO₃ powder is the combustion product of Li-H compounds and is also the main solid product of HMX/Li-H system.The generation of Li₂CO₃ and the heat release process is deduced the reason for the increase of HMX/Li-H detonation energy.