Electrophoretic deposition of binary energetic composites

This work utilizes electrophoretic deposition (EPD) as a facile and effective method to deposit binary energetic composites. In particular, micron-scale aluminum and nano-scale copper oxide were co-deposited as a thin film onto a conductive substrate without the use of surfactants. For comparative purposes, films of this energetic mixture were also prepared by drop-casting (DC) the premixed suspension directly onto the substrate, then allowing the liquid to dry. The structure and microscopic features of the two types of films were compared using optical and electron microscopies. The films prepared using EPD had an appreciable density of 2.6 g/cm³, or 51% the theoretical maximum density, which was achieved without any further processing. According to the electron microscopy analysis, the EPD films exhibited much more uniformity in composition and film thickness than those produced by DC. Upon ignition, the EPD films resulted in a smoother and faster combustion event compared to the DC films. The dispersion stability was improved by adding water and decreasing the particle concentration, resulting in dispersions stable for >30 min, an ample amount of time for EPD. Patterned electrodes with fine feature sizes (20 × 0.25 mm) were then combined with EPD to deposit thin films of thermite for flame propagation velocity studies. The fastest velocity (1.7 m/s) was observed for an equivalence ratio of 1.6 ± 0.2 (Al fuel rich composition). This peak value was used to investigate the effect of film mass/thickness on propagation velocity. The deposition mass was varied from 20 to 213 μg/mm², corresponding to a calculated range of film thicknesses from 9.8 to 104 μm. At lower masses, a flame did not propagate, indicating a critical mass (20 μg/mm²) or thickness (9.8 μm). Over the range of thicknesses, in which self-propagating combustion was observed, the flame velocity was found to be independent of sample thickness. The lack of a thickness dependence suggests that under these particular conditions heat losses are negligible, and thus the velocity is predominantly governed by the intrinsic reactivity and heat transfer through the material.