Abstract
A12O3 nanoparticle reinforced nickel can be produced by electrolytical co-deposition of nickel and alumina nanoparticles under direct current (DC) plating conditions from electrolytical nickel baths in which alumina nanopowders are dispersed [1-8]. It is also known that high current density favors the formation of fine grained nickel films due to an increasing nucleation rate of nickel nuclei on the growing film with increasing current density [e.g. 9]. Recent investigations also showed that when alumina nanoparticles are added to the electrolytical bath, besides incorporating in the growing nickel film these particles inhibit growth of nickel nuclei and therefore allow deposition of nanocrystalline Ni/Al2O3 composite films with an average nickel matrix grain size around 30 nm under DC conditions [6]. It was also found by transmission electron microscopy (TEM) investigations that the size distribution of the codeposited nanoparticles is nearly the same as that of the employed nanopowder prior deposition and therefore size selection during embedding of particles in the film is negligible [7]. This is of importance when uniform composite films are required. However, when these films are plated under pulsed direct current (PDC) conditions where the pulse length allows only limited growth of nickel nuclei, large nanoparticles or parts of particle agglomerates might not be sufficiently embedded by growing nuclei during one pulse to be trapped on (in) the film. Therefore these particles might escape from the surface before the next pulse occurs, which not necessarily promotes a continuous growth of the same nuclei. Furthermore under PDC conditions the ion concentrations in the cathode film are fluctuating, which will also affect the growing film in a different manner than in the case of DC plating. Under those conditions the homogeneity of the particle distribution and the particle size distribution in the PDC plated films might be different from those in the DC plated composites. This issue is the subject of current investigations in our laboratories and we present first results on the plating of Ni/Al2O3-composite films under PDC conditions.
Published Version
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