A computational model of anaerobic reactions in metallic multilayered systems with an equimolar composition of zirconium and aluminum is developed. The reduced reaction formalism of M. Salloum and O. M. Knio, Combust. Flame 157(2): 288–295 (2010) is adopted. Attention is focused on quantifying intermixing rates based on experimental measurements of uniform ignition as well as measurements of self-propagating front velocities. Estimates of atomic diffusivity are first obtained based on a regression analysis. A more elaborate Bayesian inference formalism is then applied in order to assess the impact of uncertainties in the measurements, potential discrepancies between predictions and observations, as well as the sensitivity of predictions to inferred parameters. Intermixing rates are correlated in terms of a composite Arrhenius law, which exhibits a discontinuity around the Al melting temperature. Analysis of the predictions indicates that Arrhenius parameters inferred for the low-temperature branch lie within a tight range, whereas the parameters of the high-temperature branch are characterized by higher uncertainty. The latter is affected by scatter in the experimental measurements, and the limited range of bilayers where observations are available. For both branches, the predictions exhibit higher sensitivity to the activation energy than the pre-exponent, whose posteriors are highly correlated.
A computational model is developed to describe the evolution of the temperature field in a nanocalorimeter that comprises inert material layers on which a nanoscale Ni/Al bilayer has been deposited. The model incorporates a reduced continuum description of mixing and heat release in the Ni/Al bilayer, and of the energy equation in the inert layers. Due to the small thicknesses of individual layers that are several orders of magnitude smaller than the corresponding length, a simplified, transient, homogeneous representation of the temperature field can be adopted. The resulting lumped model is valid over short enough timescales, which are nonetheless sufficiently large to capture the formation reaction. By using experimental observations of the evolution of the temperature on the surface of the nanocalorimeter, the model is used to estimate the transient heat release rate. Assuming an Arrhenius model for the mixing between Ni and Al, the estimated heat release rate is used to determine the Arrhenius pre-exponent and activation energy of the atomic diffusivity. Computed results indicate that the present approach provides a promising means of characterizing atomic diffusion rates. Limitations arise, however, due to the low amplitudes of the heat release term at low temperature, and also due to phase-change effects, which make the heat release rate unobservable in the neighborhood of the melting temperature of individual constituents. For the present system, reliable estimates are extracted for temperatures ranging from about 600 K to the Al melting temperature.
A palladium catalyst (Pd-Cs) encapsulated metalloporphyrin network PIZA-1 thin film with bifunctional properties has been developed through a modified epitaxial layer-by-layer encapsulation approach. Combining the oxidation activity of Pd-Cs and the acetalization activity of the Lewis acidic sites in the PIZA-1 thin film, this bifunctional catalyst of the Pd-Cs@PIZA-1 thin film exhibits a good catalytic activity in a one-pot tandem oxidation-acetalization reaction. Furthermore, the surface components can be controlled by ending the top layer with different precursors in the thin film preparation procedures. The catalytic performances of these thin films with different surface composites were studied under the same conditions, which showed different reaction conversions. The result revealed that the surface component can influence the catalytic performance of the thin films. This epitaxial encapsulation offers a good understanding of the tandem catalysis for thin film materials and provides useful guidance to develop new thin film materials with catalytic properties.
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