Preparation, characterization, surface chemistry and corrosion properties of nickel-transition metal-phosphorus alloys produced by autocatalytic reduction.

摘要

Autocatalytic or electroless deposition of Ni-P film alloys has been reviewed and considered as a model for the deposition of ternary alloys such as Ni-TM-P where TM is W-Mo and Cr.; This study is a comprehensive analysis of the parameters that influence each one of the steps involved in a successful deposition. It starts in the preparation of the substrate to be plated; special attention is given to the mechanical polishing, degreasing and chemical activation. The degree of cleanliness provides the film's quality of adherence.; The bath's chemical composition is explained in terms of the role played by each of the bath components such as Ni and P, complexing agents, buffers, stabilizers and other additives. The most important parameters that influence the rate of deposition and the film's properties are temperature, pH and concentration of the components in the plating bath.; The characterization of the autocatalytic film was done from the structural, chemical composition and surface chemistry perspectives. X-ray Diffraction, (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) techniques were used in this study.; Two chapters are devoted to the study of chemical and electrochemical mechanisms of autocatalytic deposition of Ni-TM-P and chemical kinetics. From the experimental results it can be said that the deposition of Ni-W-P is mostly a chemical mechanism; deposition of Hi-Mo-P is governed by both chemical and electrochemical mechanisms and Ni-Cr-P deposition is only possible when the process is controlled by an electrochemical mechanism. The reducing power of hypophosphite is larger when the mechanism is purely chemical; therefore, Ni-Cr-P is difficult to deposit in an autocatalytical (chemical) way. To over-ride this difficulty additions of boron compounds are recommended in this study.; Corrosion results show that structure or chemical composition alone are not sufficient to provide excellent corrosion resistant properties for electroless films. In Ni-W-P crystalline samples with 18-20.8 wt.% W showed higher corrosion rates than amorphous samples with lower W contents, while crystalline samples without W showed the highest corrosion rates. Ni-Mo-P behaves differently from Ni-W-P. While decreasing the amorphicity, molybdenum per se provides a better shield against corrosion than tungsten; therefore, amounts around 5 wt.% Mo are enough to equalize the effect of the structural atomic organization on the corrosion resistance which is not the case for tungsten in Ni-W-P. Even though it was not possible to deposit Ni-Cr-P, it is possible to infer that with the standard bath composition it will not be possible to produce amorphous Ni-Cr-P ({dollar}>{dollar}9 Wt% P) but the Ni-Cr-P (low P alloy) obtained will also have remarkable corrosion properties because of the presence of chromium.