A Study On Fabrication Of Novel Thermites Film By Electrophoretic Deposition Method

Nano thermites are kinds of nanoenergetic composites often composed of aluminum nanoparticles and some oxidizer nanoparticles. Comparing with conventional thermites, nano thermites exhibit more excellent thermodynamic properties and combustion performance due to the nanoscale mixing. Therefore, nano thermites are of potential interests in yielding metal and alloy, welding, synthesizing novel materials and assembling initiating explosive devices. Nano thermite bridge films have recently received considerable attention for some special application in reactive bridge films with nanoenergetic composites in initiating explosive devices. As a result, fabrication of nano thermite film has been the topic of realizing the application of nano thermite to energetic bridge films.In this paper, several novel nano thermite films have been successfully fabricated by electrophoretic deposition(EPD). The suitable suspension media which is the key issue for successfully fabricating nano thermite film was introduced. The influence mechanism of kinetics of electrophoretic deposition for nano aluminum particles and nano oxide particles on composition of nano thermite film were investigated, and this mechanism were proved in fabrication of novel nano thermite films. The feasible approach for controlling composition of nano thermite film was also studied.The detail contents are as follow:Four nano thermite films, nano Al/Fe2O3 thermite film, nano Al/Co3O4 thermite film, nano Al/Ni O thermite film and nano Al/Mo O3 thermite film have been successfully fabricated by EPD. The suitable suspension media for nano Al/Fe2O3 thermite film is the mixture of acetylacetone and ethanol(1:1 vol.%), and the total solids loading in suspension is 1 g·L-1. The suitable suspension media for nano Al/Co3O4 thermite film is the mixture of acetylacetone and ethanol(1:1 vol.%) containing 0.00025 M nitric acid, and the total solids loading in suspension is 1 g·L-1. The suitable suspension media for nano Al/Ni O thermite film is the mixture of acetylacetone and ethanol(1:1 vol.%) containing 0.00025 M nitric acid, and the total solids loading in suspension is 2 g·L-1. The suitable suspension media for nano Al/Mo O3 thermite film is isopropyl alcohol containing 0.01g·L-1 polyethylene imine(PEI), and the total solids loading in suspension is 1 g·L-1.These four electrophoretic nano thermite films exhibit homogeneous mixing and improved interfacial contact between Al particles and oxide particles. For ano Al/Fe2O3 thermite film, nano Al/Co3O4 thermite film and nano Al/Ni O thermite film, the particle sizes of both Al and oxide in the deposit were still kept in nanoscale. For nano Al/Mo O3 thermite film, Al particles in the deposit was nanoscaled and Mo O3 particles was micron-sized.The theoretical calculaition of the kinetics of electrophoretic deposition reveals that the composition of nano thermite film would be affected by the behavior of electrophoretic deposition for nano aluminum particles and nano oxide particles. The composition keeps steady when the linear deposition kinetics dominates for both Al particles and oxide particles. The composition would change with deposition time when deposition kinetics for Al particles or oxide particles change into parabolic kinetics dominates. This conclusion is suitable for nano thermite films fabricated by electrophoretic deposition in this study. Linear relationship studies showed that a coefficient of proportionality between equivalence ratio in deposited films and that in suspension was observed for EPD of nano thermite. This linear relationship between Φs and Φd is an interesting feature, it makes facilely for further researching the optimum equivalence ratio in thermite film for purpose of enhancing combustion performance by adjusting equivalence ratio in suspension through linear translation.The thermodynamic properties of nano thermite films were significant influenced by the equivalence ratio. The theoretical heat of reaction for Al/Fe2O3 thermite film samples with Φd of 1.32 can be calculated to be 1582.6J·g-1. The theoretical heat of reaction for Al/Co3O4 thermite film samples with Φd of 1.56 can be calculated to be 1527.1 J·L-1. The theoretical heat of reaction for Al/Ni O thermite film samples with Φd of 1.23 can be calculated to be 931.1J·g-1. The theoretical heat of reaction for Al/Mo O3 thermite film samples with Φd of 1.47 can be calculated to be 1962.5 J·g-1.These four electrophoretic nano thermite films could be ignited and the combustion was self-sustaining. The combustion performance of nano thermite films was significant influenced by the equivalence ratio. The flame velocity for Al/Fe2O3 thermite film samples with Φs of 1.32 was 52.9 m·s-1. The flame velocity for Al/Co3O4 thermite film samples with Φs of 1.56 was 36.6 m·s-1. The flame velocity for Al/Ni O thermite film samples with Φs of 1.23 was 43.4 m·s-1. The flame velocity for Al/Mo O3 thermite film samples with Φs of 1.47 was 28.6 m·s-1.