Study On The Activity Retention And Performance Of Nano-aluminum Powder

Nano-aluminum is one of the most important metal additives in modern solid propellant.It can reduce the diffusion limitation and increase the rate of oxidation in contribution to detonation velocity and pressure when compared to micro aluminum and regular aluminum.However,the high specific surface area and great surface energy make it easy to react with oxygen and water to form aluminum oxide(Al2O3)under ambient conditions.The 'dead weight' not only reduces the active aluminum contents,but also causes a lower energy density and other combustion properties in propellants.So,more efforts should be made to stablize nano-aluminum by coating passivation agents.In this paper,five passivation agents were used to prepare nano composite particles,which were nano Al/hydroxyl terminated polybutadiene(HTPB),nano Al/octadecylamine(ODA),nano Al/C,nano Al/Ni and nano Al/Ni/HTPB respectively.The effectiveness of these passivation agents was observed in this study.The main works are as follows:(1)Three different size nano-aluminum produced by electrical explosion method were introduced to study the reactivity and combustion characteristics in propellant.Results showed that the burning rates of propellant containing nano-aluminum were remarkably increased by 25.2%-57.0%when compared to micro aluminum.Among the three kinds of nano-aluminum,the performance of aluminum about 80 nm is the best in burning test.(2)The most reactive nano-aluminum(80 nm)was coated with HTPB by a simply solvent evaporation.TEM results showed that nano-aluminum was encapsulated by HTPB with a layer of 3 nm.FTIR results showed that HTPB molecule may probably bind to the surface of nano-aluminum through the-OH.Reactivity preservation analysis showed that the active aluminum content of Al/HTPB nanocomposite particles changed marginally in air for 40 days.When introduced to the propellant,the burning performance of aged Al/HTPB sample was nearly the same as the newly one.So the coating of HTPB on surface of aluminum can prevent nano-aluminum from further oxidation and preserve its reactivity.(3)Nano-aluminum produced by liquid chemical method was coated with ODA,C,Ni and Ni/HTPB.These materials played a good performance in passivating nano-aluuminum when compared to Al2O3.However,the effectiveness of ODA and Ni was poorer as the nano-aluminum continued oxidation in a month.When C and HTPB were introduced to coat aluminum and Al/Ni respectively,the reactivity of resulting Al/C and Al/Ni/HTPB has been maintained in air for a month.So C and HTPB were proved to be favorable caps for nano-aluminum.