Study On The Preparation And Performances Of Nano Oxidants By Low Temperature Spray Freeze Drying Method

Ammonium nitrate(AN)and ammonium perchlorate(AP)are two important oxidants that are widely used in propellants,industrial explosives and pyrotechnics.With the development of propulsion technology,high burning rate is required.The results show that reducing the particle size of solid oxidant can significantly improve the combustion performance of solid propellant.In order to reduce the particle size of AN and AP to the nanometer size,thus further improving AN and AP performance.In this paper,nano AN and nano AP were successfully prepared by ultra-low temperature spray freeze-drying method,and the chemical purity,crystal structure,thermal decomposition properties,sensitivity properties and hygroscopic properties of the prepared nano AN and nano AP were studied.At the same time,the application of nano AN and nano AP in propellant was investigated.The main research contents are as follows:Firstly,AN and AP with particle size less than 100nm were prepared by ultra-low temperature spray freeze-drying method.The nano AN and nano AP samples were characterized by SEM,EDS,XRD,IR and XPS,and the thermal decomposition and sensitivity characteristics of the prepared nano AN and nano AP were studied.The results show that the micro morphology of nano AN is spherical,and the micro morphology of nano AP is long strip.The molecular structures,surface elements and crystal phases of nano AN and nano AP are consistent with those of raw AN and raw AP,respectively.The thermal decomposition activation energy of nano AN is 92.11k J·mol^-1,which is only 5.43k J·mol^-1lower than that of raw AN,indicating that the thermal stability of nano AN is basically unchanged.The thermal decomposition activation energy of nano AP is 128.14k J·mol^-1,which is 18.68k J·mol^-1lower than that of raw AP,indicating that the thermal stability of nano AP decreases.Nano AN is very insensitive to mechanical action.The falling height(H₅₀)of 10kg falling ball is greater than 110cm,and the explosion percentage(P)of friction sensitivity is 16%.The characteristic drop height(H₅₀)of 5kg drop ball is 71cm,and the explosion percentage(P)of friction sensitivity is 96%,which is increased by 14.5%and 56%respectively compared with the raw AP.Secondly,the hygroscopicity of nano AN and nano AP samples was tested.The surface of nano AN and nano AP were coated with 2%octadecylamine,0.5%and 1%oleic acid,0.5%and 1%KH550 and 3%PMMA(polymethyl methacrylate).The results show that the moisture absorption rate of raw AN is 8.87%,and that of nano AN is 15.44%.Compared with nano AN,the moisture absorption rate of modified nano AN decreases by 9.52%,30.51%,35.75%,35.10%,38.73%and 19.17%respectively.The moisture absorption rate of raw AP was 1.15%,and that of nano AP was 4.36%.Compared with nano AP,the moisture absorption rate of modified nano AP decreased by 19.27%,29.36%,59.63%,41.29%,67.66%and52.29%respectively.Finally,the application of nano an and nano AP in propellants was explored,and the thermal decomposition properties,sensitivity and energy characteristics of propellants containing nano an and nano AP were studied.The results show that the DSC curves of CMDB-4 propellant samples show two exothermic decomposition peaks.A large exothermic peak appeared at about 190?corresponding to the thermal decomposition of NC and DGTN,and a small exothermic peak appeared at about 275?corresponding to the thermal decomposition of HMX and AN.Each DSC curve of the HTPB-6 propellant sample has only one exothermic peak,and the peak shape of the exothermic peak is sharp.The main decomposition products of CMDB-4 propellant are H₂O,N₂,CO,NO,CO₂,N₂O.The main decomposition products of HTPB-6 propellant are H₂,H₂O,N₂,CO,CO₂,N₂O,and it is speculated that HCl is generated.With the increase of nano AN content,the value of H₅₀of CMDB propellant increases and the friction sensitivity decreases.In contrast,as the percentage of nano AP increases,the value of HTPB propellant H₅₀becomes smaller and the friction sensitivity increases.In terms of energy performance,the standard specific impulse Isp of CMDB and HTPB propellants are 2439.5N·s·kg^-1and 2449.3N·s·kg^-1,respectively.The combustion products of CMDB propellant contain the most H₂O,while the combustion products of HTPB propellant contain the most CO and H₂.