Characterization of thin film thermite ofr varying binder/solvent systems

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2013-08

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There is a current need for low cost heat sources for a variety of applications, from local joining and welding, to providing local heat for power sources. In this work, powders of magnesium and manganese dioxide were mixed with a fuorpolymer or paran

binder and blade cast onto a stainless steel foil substrate. The three binder-solvent systems investigated were Polyvinylidene Fluoride (PVDF) and Methyl Pyrrolidone (NMP), Viton A and Acetone, as well as paraffin and xylene. Films were prepared by mixing the energetic composites with the binder and solvent to create a 40% solids content suspension, and then casting onto stainless steel foil to a 200 microns wet film thickness. In this study, binder content and type was varied, and calorific output and open

fame propagation speed were investigated for each mixture ratio. It was found that calorific output increased with increasing binder content, to a maximum observed

value of 954 calories per gram, indicating participation of the binder in the exothermic reaction. Flame speed was shown to decrease with increasing binder content, with a

maximum recorded value of 0.14 m/s for unconfined tests. This may reflect the lower heat transfer of the binder, or a mechanism that blocks propagation with increasing binder content. Confined tests were also conducted for the PVDF/NMP system, with a maximum recorded fame speed of 3.46 m/s. High speed video of the flame propagation shows significant gas generation ahead of the flame front, which may explain the observed difference between fame speeds for confined and unconfined test configurations, as the ejecta plume preheats the material in advance of the flame front.

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