Anthony J. Perrotta

Kinetics of the reactive spreading of molten aluminum on ceramic surfaces

The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.

Hydrotalcite formation on aluminum sheet and powder

We have observed the formation of the hydrotalcite-like phase of lithium dialuminate, LiAl 2 (OH) 6 OH · 2H 2 O, and also the carbonate analog, by the oxidation of aluminum sheet and also aluminum powder in aqueous lithium hydroxide or lithium carbonate solutions. A secondary phase, bayerite, was also observed following the oxidation process, except when the aluminum was treated with lithium oxalate solutions where it is the principal phase. Results have been obtained for the time required to form a passivating film to hydrogen formation as a function of temperature and oxidizing solution. Grazing incidence x-ray diffraction of aluminum sheet samples, combined with polycrystalline x-ray diffraction on similarly treated aluminum powder, were used to evaluate the formation of the films. Both transmission and reflectance infrared absorption spectra on powder and sheet samples were used to support the x-ray observations. Scanning and transmission electron microscopies show morphological differences between preparations, film thicknesses of 10–20 μm, and also film defects. Additional SIMS analysis determined the relative lithium and aluminum concentrations in the films, suggesting that a higher concentration of lithium occurs when lithium carbonate is present in the reacting solutions.