PREPARATION, CHARACTERIZATION AND PROPERTIES OF ELECTROLESS Ni-P-ZrO_2 COMPOSITES COATINGS

摘要

The study of composite electroless Ni-P coatings is pursued in order to obtain coatings on metal substrate with advanced properties such as high wear and corrosion resistance or as potential catalytic electrode materials for particular engineering uses. Composite NiP-ZrO_2 layers were prepared by simultaneous electroless codeposition of Ni-P and ZrO_2 on steel and brass substrate, from a reducing solution in which ZrO_2 particles were kept in suspension by stirring. The load of the particles in the bath was up to 5.0 g/l and the percentage on the surface of the coating reaches 16%. Deposits were characterized for its structure, morphology and hardness by means of scanning electron microscopy, microanalysis as well as X-ray diffraction. The obtained electroless coatings exhibit different morphology on different type of substrates, good adherence and physical properties such as high hardness, reaching 1400 HV after thermal vacuum treatment. The electrochemical linear polarization measurements in a corrosive NaCl 3.5% solution shows that, at the specific bath load (2.0 g/l), the favorable conditions for the formation of defects free composite deposit could be created. Hydrogen evolution reaction (HER) in alkaline media (1M NaOH) is-used to determine the electrocatalytic properties of plain Ni-P and composite Ni-P-ZrO_2 coatings. It has been found that this reaction is faster three to fivefold on the composite Ni-P-ZrO_2 electrode materials than on the plain Ni-P electrode surface and independent of the substrate material.