Construction And Application Of Nano-thermite With Core-shell Like Structure

With the systematic development of advanced initiating explosive devices,more requirements are put forward for the performance of initiating explosive devices in terms of strong efficacy,controllable energy release and reduction sensitivity.There are some limitations to meeting the above-mentioned requirements in traditional initiating explosives.Aiming at the above three properties of initiating explosive,a series of research on the coating of nano-Al powder（nano-Al@TA、nano-Al@C）,the selection of composite/new oxidants oxidant（Fe_xO_y、C/CuO、NaIO₄）,construction structure with highly reactive of oxidant/reductant（core-shell like structure）were conducted.Three nanothermites of Al@Fe₂O₃@Fe₃O₄,Al/C/CuO,and Al@NaIO₄ with a core-shell like structure were prepared.And the thermal property,constant volume combustion property,magnetic property and sensitivity of the three nanothermites are discussed in detail.Al@Fe_xO_y can be directly used as a charge in micro-propulsion and has low friction sensitivity.Al/C/CuO shows lower electrostatic sensitivity（electrostatic ignition energy is 10.11 mJ）,and significantly improves the heat release of NH₄ClO₄（about 2.84 times）.Al@NaIO₄ can be directly filled into the detonator to detonate RDX,and the impact sensitivity and electrostatic sensitivity are low.The above system realizes the application of directly using a single thermite formula in initiation,catalysis and micro-propulsion.The specific research contents and conclusions are as follows:Study on stability and reaction activity of nano-Al.Firstly,the basic properties of nano-Al（100 nm）are discussed,and an easier TEM method is proposed to quantify the activity of nano-Al,which is 82.2%.Combined with the thermal oxidation process of nano-Al and Arrhenius equation,the room temperature limit thickness of oxide film on the surface of nano-Al particles is 4 nm.Then the effect of temperature or moisture on the activity of nano-Al was studied.The results showed that nano-Al could exist stably at≤300 ℃ or 4 h by dispersed in water,which was related to the oxidation resistance of the dense oxide layer on the surface.Based on the results,nano-Al was coated by TA and C by spray drying-calcination method.Compared with pure nano-Al,the exothermic peak temperature of the oxidation reaction is advanced by 26 ℃ and 20 ℃ respectively,and the exothermic enthalpy of the oxidation reaction is increased by518.55 J·g^-1 and 215 J·g^-1.The coated nano aluminum powder can prevent the further oxidation of the core of nano-Al and improve the reaction activity of nano-Al.Study on the application in micro-propulsion of space-constraint and reduction friction sensitivity of Al/Fe₂O₃.Firstly,core-shell Al@Fe_xO_y nanothermites with different particle sizes and components were prepared by mixed solvothermal method with changing the reaction time（4h,6h,8h,10h）.When the reaction time is 8 h,the maximum heat release of the sample is1060 J·g^-1,which is 1.98 times more than that of Al/Fe₂O₃.When the reaction time is 4 h and10 h,the pressure value of constant volume combustion can be maintained stability in 100.36μs and 113.38μs respectively,and the result shows that it is suitable for the application of micro-propulsion of space-constraint.In addition,the friction sensitivity of Al@Fe_xO_y is lower than Al@Fe₂O₃ is due to the electrons of Fe₂O₃@Fe₃O₄ can transfer rapidly between the two oxidation states of iron that it is difficult to form hot spots in the crystal.The formula shows different regular combustion parameters and micro-propulsion performances and realizes the performance regulation of and the reduction of friction sensitivity.To reduce the electrostatic sensitivity and promote the thermal decomposition of AP of Al/CuO,the s-CuO and s-C/CuO with skeleton structure were prepared by spray drying-calcination method.Compared with pure AP,the promoting effect of s-CuO on the thermal decomposition of AP is reflected in the advanced temperature of the high-temperature decomposition process which is about 56 ℃ and the increase of heat release which is increased by 1.4 times.s-C/CuO makes the thermal decomposition reaction rate of AP faster,and changes from two steps exothermic to one step exothermic,the exothermic heat is significantly increased by 2.6 times,and the temperature of the high-temperature decomposition process is advanced by about 82.7 ℃,indicating that the composite oxidant has a better effect than the single oxidant on promoting the thermal decomposition of AP.The addition of nano-thermite Al/s-CuO and Al/s-C/CuO greatly promoted the thermal decomposition process of AP,which also changed from two steps exothermic to one step exothermic.The exothermic heat increased by 2.84 times and the temperature of the high-temperature decomposition process was advanced to about 79.2℃.At the same time,due to the existence of C and skeleton structure,the conductivity and thermal conductivity of the Al/CuO system are increased,the electrostatic sensitivity is effectively reduced and the safety is improved.The electrostatic ignition energy of Al/s-CuO is10.11 mJ,which the electrostatic sensitivity is about 34 times lower than the reported in the literature which is 0.3 mJ.A single thermite formula is designed through system formula and structure design,which can be directly used for initiation.NaIO₄ was selected as an oxidant for nano-thermite,Al/NaIO₄ and Al@NaIO₄ with two different structures were prepared by physical mixing and spray drying.The maximum pressurization rates in the combustion cell of Al/NaIO₄ and Al@NaIO₄ are 1.91 GPa·s^-1 and 2.94 GPa·s^-1,respectively（1.67 times than that of Al/CuO and3.36 times than that of Al/Al/Fe₂O₃ under the same conditions）,and the burning rates are 561m·s^-1 and 731 m·s^-1,respectively（5.7 times than of Al/CuO under the same conditions）.Because several gaseous species can form during the multistep decomposition of NaIO₄,the reaction rate of the sodium periodate systems is significantly faster than other nano-thermites.In No.8industrial detonator,93 mg Al@NaIO₄ can detonate secondary explosive RDX completely,and the detonating effect can reach the level of primary explosive LA.Under strong constraints,93mg Al/NaIO4 can detonate explosive FOX-14.The core-shell structure nano-thermite shows higher reaction activity.In addition,the sodium periodate systems have low impact sensitivity and electrostatic sensitivity,and good resistance to the humid environment,which is of great significance for preparation,use and storage.