Nanoscale investigation of surfaces exposed to a thermite spray

A thermite spray gun was recently developed as a means for discharging the reaction products and intermediates of the highly exothermic thermite reaction. The thermite spray gun was inspired by more widely used hydrocarbon spray guns with the modification that the reactants are in the solid phase. This device has been used in conjunction with a heat flux sensor to examine the energy transfer characteristics of the spray. The current study broadens the previous work of thermite sprays by examining the influence of reactant composition on heat flux characteristics as well as the penetration behavior of the ejected spray evaluated with atomic force microscopy (AFM). Specifically, the apparatus was loaded with a fuel lean (Φ = 0.61) and a fuel rich (Φ = 1.52) Al-Fe2O3 thermite and both nanometric and micron-scale reactants were investigated. The gas generating, fuel rich nano-thermite exhibited slight ablation of the silicon substrate, exhibiting 7.5 times shorter exposure to the thermite spray, and an order of magnitude faster spray velocity as compared to the non-gas generating, fuel lean nano-thermite. The micron-thermite demonstrated comparatively more ablation of the silicon substrate such that it was determined particle size plays an important role in surface removal with micron-scale particles also producing higher heat fluxes and surface temperatures.

Research highlights
► Influence of stoichiometry and reactant particle size were studied for thermal sprays.
► For nano-thermites, a fuel rich mixture removed 10% more Si off substrate's surface.
► The micron-thermite spray transferred more energy than its nano-thermite counterpart.
► Silicon exposed to a micron-thermite spray showed significant surface modifications.