Films of zinc oxide and related compounds [ZnO, ZnO(OH)5, Zn(OH)Cl9] are electrodeposited cathodically in aqueous zinc chloride solutions using dissolved oxygen as a precursor. The influence of the precursor concentrations, pH, and deposition temperature on the growth, composition, and properties of the films are investigated by means of in situ techniques: voltammetry electrochemical quartz-crystal microgravimetr surface pH, and ex situ techniques: X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The deposition mechanism is analyzed in terms of electrochemically induced surface precipitation due to an increase of local pH resulting from the oxygen reduction reaction. This approach allows us to explain the formation of either zinc hydroxychloride compounds or zinc oxide from their calculated solubility diagrams. In conditions of the formation of ZnO, a dramatic effect of temperature is observed, with a transition between amorphous insulating zinc oxyhydroxide to well-crystallized and conducting zinc oxide when the temperature increases (Ttran,jtjon 50 °C).

Communications ADVANCED MATERIALSConsequently, the initial precipitation of Ti and A1 or Ni and A1 in segregated phases, followed by an exothermic reactive-sintering process between the Ti and A1 or Ni and A1 nanocomponents produced the sintered microstructures. Crystallite growth was restricted to nanometer dimensions because diffusion distances for the reaction were short and reaction temperatures were only transiently high.In summary, we report the first general chemical synthesis of nanocrystalline aluminide intermetallics. The method uses readily available starting materials, a simple solutionbased processing technique, and low applied temperatures. The small crystallite sizes and sintered microstructures result directly from the chemical pathway followed and the participation of a nanoscale reactive-sintering event. In a separate study,t211 we have induced Ni and A1 to react and precipitate in the same amorphous phase in the solutionphase step, which precludes a subsequent reactive sintering and results in a non-sintered nanocrystalline microstructure. Consequently, grain size and microstructure are amenable to chemical control. We will report the results of these experiments and the mechanical properties of densified nanocrystalline aluminide compacts in the near future.