Investigation of Al/CuO multilayered thermite ignition

International audienceThe ignition of Al/CuO multilayered material is studied experimentally to explore the effect of heating surface area, layering and film thickness on the ignition characteristics and reaction performances. After the description of the micro-initiator devices and ignition conditions, we show that the heating surface area has to be properly calibrated to optimize the nanothermite ignition performances. We demonstrated experimentally that a heating surface area of 0.25 mm 2 is sufficient to ignite a multilayered thermite film of 1.6 mm wide by a few cm long, with a success rate of 100%. A new analytical and phenomenological ignition model based on atomic diffusion across layers and thermal exchange is also proposed. This model considers that CuO first decomposes into Cu 2 O, the oxygen diffusing across Cu 2 O and Al 2 O 3 layers before reaching the Al layer where it reacts to form Al 2 O 3. The theoretical results in terms of ignition response times confirm the experimental observation. The increase of the heating surface area leads to an increase of the ignition response time and ignition power threshold (go/no go condition). We also evidence that for any heating surface area, the ignition time rapidly decreases when the electrical power density increases until an asymptotic value, named minimum response ignition time, which is a characteristic of the multilayered thermite itself. At the stoichiometric ratio (Al thickness is half of CuO one), the minimum ignition response time can be easily tuned from 59 µs to 418 ms by tuning the heating surface area. The minimum ignition response time increases when the bilayer thickness increases. Not only this work gives a set of micro-initiator design rules to obtain the best ignition conditions and reaction performances but it also details a reliable and robust MEMS process to fabricate igniters and it brings new understanding of phenomena governing the ignition process of Al/CuO multilayers