engleski

NICKEL-TiO2 COMPOSITE COATINGS – SURFACE CHARACTERIZATION

Nickel coatings onto brass substrate were produced from conventional suspensions consisted from a conventional nickel sulphate bath and fine TiO2 particles (dp < 1µm) kept in suspension by magnetic stirrer. Composite coatings were obtained at different current densities and different concentrations of particles in suspensions for a constant process time and constant temperature. Composite coatings were characterised by means of optical and SEM micrographs, by XRD analysis as well as by determining surface roughness parameters. Metallographic analysis has also been done. Coatings obtained from the pure electrolyte under the same other experimental conditions served as an standard for comparison. It was found that the presence of TiO2 particles in the electrolyte cause an embedment of particles into deposited metal, changing physical characteristics of produced composite. Particles were embedded as smaller or bigger agglomerates at the surface rather than individual ones. Current density and particles concentration in electrolyte both determine the amount of embedded particles into the coating thus affecting the surface quality. Certain irregularities appear on the surface in the form of whiskers and nodules at higher particles concentration as well as at higher current density. Also, under these conditions, a certain rugosity of the surface was remarked as a reflection to the electrolyte streamlines that exist due to the suspension stirring. Metallographic analysis showed uniform distribution of particles through the coating. Surface roughness analysis has revealed trends in the measured values of amplitude roughness parameters. In the group of samples with composite coatings obtained at different current densities highest values of measured roughness parameters were recorded at 6 A dm-2 and lowest values at 10 A dm-2. As for group of samples with coatings obtained at different concentrations of TiO2 particles higher values of measured roughness parameters were observed at lower values of TiO2 concentrations. However, relation between the geometry of the profiles and different current densities i.e. concentrations of particles has not been noted.

nickel; composite coatings; titania (TiO2) particles; surface roughness; optical and SEM analysis

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