Schematic of EPD cell used in this work. Also shown is an example of a patterned electrode before and after deposition.
Top and cross-sectional image of nano-Al/CuO composite. Elemental mapping is included to exemplify the homogeneous mixing of the particles brought forth by using this technique.
Actual equivalence ratio measured by ICP-OES (Φ) as a function of the weighed equivalence ratio in the precursor dispersion (Φd). Note that a linear relationship exists, and this is used to convert the data to actual equivalence ratio.
Propagation velocity as a function of equivalence ratio. This was repeated using two field strengths, 10 V/cm and 40 V/cm. The peak reactivity occurs at Φ = 1.7 in both cases. Also notice the 25% drop in reactivity near Φ = 2.0.
Equilibrium calculations for Al/CuO as a function of equivalence ratio. The Al2O3 oxide shell was included, and these are constant enthalpy and pressure calculations done using CHEETAH v6.0 with the JCSZ library and Al (s) omitted.
Conceptual model of fuel and oxidizer transport towards one another during combustion. The fuel and oxidizer are assumed to be infinite sheets with finite thickness of xf and xo.
(a) Representative cross-sectional profiles of thermites for different deposition times. The thickness of the 5 s deposition profile has been amplified to illustrate the features. (b) Optical images of the same strips. From this data, the optically measured strip width was mapped to the thickness measured by profilometry, so that the strip width can be directly used to correlate to thickness.
Propagation velocity as a function of thickness, and at the optimum equivalence ratio of Φ = 1.7. The data showed a two-plateau behavior, with nearly an order of magnitude difference in velocity. In the transitional regime, the velocity scaled linearly with thickness.
A series of images from the combustion event. The top series corresponds to a slow velocity, the middle to an intermediate velocity, and the bottom series a fast velocity. Particles were observed to be transported further and further ahead of the flame as the velocity increased. The plane where particles could be observed is superimposed as the dotted line, and the flame position (on the substrate) is denoted by the solid line. The circled regions show ignition which presumably occurs as molten clusters are forwardly advected and ignite unreacted material.
Particle advection analysis using a thin slit mounted above a sample. The x,y coordinates of 100 random particles were recorded over 2-3 frames (20-40 μs), and were used to estimate a linear velocity. The velocity distribution is plotted from this analysis.
Electron microscope images of advected particles captured near the slit in Figure 10. This was done at the optimum equivalence ratio of Φ = 1.7, but was also repeated at a more fuel-rich condition of Φ = 2.8, where the temperature is predicted to drop below the melting temperature of Al2O3. The particles at Φ = 1.7 are observed to be micron-scale and in surface contact, indicating a reactive sintering mechanism occurred. At Φ = 2.8, characteristically larger clusters were seen which contained Al, Cu, and O.
Schematic of a thin thermite film with thickness t. Gases are produced within the outlined control volume, and will then escape in the z-dimension at a rate governed by Fickian diffusion in a porous medium.
Relative value of non-dimensional number A, and what it implies for energy transport.
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