Study On Ignition Performance And Process Of Selective Laser Sensitive Composite System

Laser ignition technology has the advantages of strong electromagnetic interference resistance,easy multi-way ignition,non-destructive self-inspection of the system,and isolation of charge and power supply.It is one of the main development directions of pyrotechnics.Laser pyrotechnics require that the agents used have the characteristics of high laser sensitivity,insensitivity to other energy stimuli,and short delay time.However,the current laser explosives have the problem of high laser sensitivity and high thermal sensitivity,which will affect the safety of laser explosives to a certain extent.Therefore,it is extremely important to study energetic materials sensitive to laser and thermal insensitivity and their reaction mechanism.Aiming at this problem,this paper proposes the design idea of laser-thermal differential reaction,and constructs a laser characteristic sensitivity composite energetic system based on nano-thermite and HMX.The laser and heating wire ignition ignition characteristics and reaction process of the composite system were studied,and the laser-thermal differential reaction mechanism was revealed.The control method of photothermal differential performance and the action characteristics of the composite system were explored.The main contents and conclusions are as follows:（1）The design idea of laser-thermal differential reaction is put forward:due to the differences of the temperature rise process for the composite systems,which compose of component A and B with different laser absorption properties,will under the action of light and heat,the reaction process of the composite system will differ.The components of composite energetic materials with laser-sensitivity must have the following three conditions:laser absorption performance（A:strong,B weak）,reaction temperature（A:high,B:low）and specific reaction form（A:combustion or detonation under a certain energy level,B:thermal decomposition）.（2）The selected component A is nano-thermite Al/Cu O（Al:Cu O:NC=25:75:3）,with the reaction temperature of 526℃and the laser absorption of 86%approximately;The component B is HMX crystal,with the thermal decomposition temperature of 241℃and the laser absorption of about 22%approximately.The physical and chemical properties of the two components meet the basic design requirements of laser-thermal differential performance.The composite energetic system based on thermite and HMX was constructed and prepared..（3）The laser and heating wire ignition properties of five samples of nano-thermite,HMX,composite system,B/KNO3 and HMX/CB were studied respectively.The results show that the laser ignition thresholds of the composite system,nano-thermite and B/KNO₃ are all 17W,and the corresponding ignition delay times are 5.6ms,7.5ms and 9.4ms,respectively.HMX/CB and HMX cannot be ignited by laser（75W）;The heating wire ignition thresholds of nano-thermite and B/KNO₃ are both 4.5A,and the corresponding ignition delay times are 7.8ms and 8.4ms,respectively,while the composite system,HMX/CB and HMX cannot be ignited by the heating wire（6A）.The laser sensitivity of the composite system with nano-thermite mass ratio of 15%-50%is similar to that of nano-thermite,B/KNO₃,but the thermal sensitivity is much lower than that of nano-thermite,B/KNO₃ and other ignition powders,which verifies that it has the characteristics of being sensitive to laser and thermally insensitive.（4）The reaction process of the composite system under the action of laser and heating wire was studied.The experimental results show that the laser ignition process of the composite system is as follows:the nano-thermite component absorbs most of the energy under the action of the laser to reach the ignition temperature first,and then ignites to further ignite the HMX crystal.Thermal analysis experiments showed that when the mass proportion of nano-thermite was less than 60%,the exothermic peak of the thermite reaction could not be observed in the composite system;product analysis showed that when the composite system was heated to300°C,HMX was completely decomposed and the Cu O content was significantly reduced.The thermal action reaction mechanism of the composite system is as follows:HMX crystal first undergoes thermal decomposition,and its decomposition products CO and Cu O undergo a reduction reaction,which makes the nano-thermite ineffective,resulting in the failure of the system to be ignited.（5）The simulation results show that the spherical composite owns better laser-thermal differential performance;Increasing the difference of laser absorptivity,thermal resistance of heat transfer medium,particle size and film thickness will greatly enhance the laser-thermal differential performance of the composites;Reducing the total heat capacity of component A will improve the laser-thermal differential performance and shorten the action delay time;Increasing the total heat capacity of component B can improve the laser-thermal differential performance,but it will increase the action delay time.The laser-thermal differential performance of the composite system can be controlled by the changing the particle size of HMX crystal:the composite system composed of 300-μm,200-μm and 100-μm HMX crystal features the laser ignition threshold power of 17W,43W and 59W,respectively,which means the selectivity to laser power.（6）In order to verify the superiority of the laser ignition of the composite system,a laser ignition flyer detonator was designed.The composite system,nano-thermite and B/KNO₃ were used as the primary charge to compare the performance characteristics of the detonator..The action time of composite system and nano-thermite are 0.17ms and 0.45ms,respectively,which are much lower than that of B/KNO₃（22ms）.The average impact velocity of the flyer driven by the composite system is 1100m·s^-1,which is higher than the 337m·s^-1 of B/KNO₃.Nano-thermite cannot effectively drive the flyer.