Direct Imaging and Simulation of the Interface Reaction of Metal/Metal Oxide Nanoparticle Laminates

One of the difficulties in understanding how powder composites of reactive fuel/oxidizer systems behave is the lack of control of the mixing length. In this study, we have prepared Al/CuO particle laminates using a direct writing approach. With as little as 10 wt % polymers, we were able to obtain free-standing microscale particle-based laminates. Using these composites, we were able to image the cross section of the laminates to directly probe the interface reaction with high-speed microscopic imaging and pyrometry. We show quantitatively how the burn rate can be altered by changing the layer thicknesses of the printed laminates and under high-speed microscopy imaging asymmetry heat transfer resulting in fingering in the temperature profiles in the reaction front. Numerical simulations of the heat and mass transport processes are able to reproduce the finger-structured reaction fronts. We find that for Al/CuO particle-based laminates, the lateral O-2 diffusion rate from the CuO layer to the Al layer appears to be rate-limiting. The finger-like profiles appear due to the combined effects from the faster propagation of the interfacial reaction over the bulk, and the thermal diffusivity differences between the Al/CuO layers. Interestingly we see no evidence of layer intermixing even on postcombustion inspection. These results are to our knowledge the first imaging of interface reactions between particle composites and provide a valuable testbed for probing mechanisms and validating models.

Automated summary

This study prepared Al/CuO particle laminates using a direct writing approach and investigated the interface reaction through high-speed microscopic imaging and pyrometry. The burn rate can be altered by changing the layer thicknesses of the laminates, and fingering heat transfer in the temperature profiles was observed. Numerical simulations reproduced the finger-structured reaction fronts. The lateral O-2 diffusion rate from the CuO layer to the Al layer was found to be rate-limiting. The imaging of interface reactions between particle composites provides valuable insights and validation for models.