The effect of suspension bath composition on the composition, topography and structure of electrolessly deposited composite four-component Ni-W-P-ZrO2 coatings

Composite four-component Ni-W-P-ZrO2 coatings were electrolessly deposited from a bath with different concentrations of aminoacetic acid (glycine-the complexing agent), sodium tungstate(VI) and zirconium(IV) oxide at different pH values. Concentration distribution curves were determined for nickel-aminoacetic acid complexes as a function of the bath pH at different metal ion/complexing agent concentration ratios. It has been shown that the bath pH and the complexing agent concentration have the strongest effect on the composition and structure of the coatings. As the bath pH is lowered and the aminoacetic acid concentration is increased, the phosphorous content in the coating increases. In composite four-component Ni-W-P-ZrO2 coatings (similarly as in electroless two- and three-component nickel coatings), as the phosphorous content in the coating increases, the crystallinity of the coating decreases. Diffraction patterns deposited at pH 5 have only one peak corresponding to nickel: Ni(1 1 1) at 2Θ = 44°. In the diffraction patterns at pH 8 one can observe sharp peaks for 5 crystalline planes: (2 0 0), (2 2 0), (3 1 1), (2 2 2) and dominant (1 1 1). After heat treatment at 400 °C for 1 h a nickel phosphide (Ni3P) phase appears (besides the crystalline nickel phase) in the coatings. Heat treatment also results in an increase in crystallite size from 1.5 to 2.0 to about 3.0 nm.