Add time:07/20/2019         Source:sciencedirect.com

Electroless gold deposition onto Ni-P substrates from a bath containing dicyanoaurate ions and sodium hypophosphite as a reducing agent has been studied and the mechanism of this process has been proposed. A number of simultaneous reactions occur in the bath studied. One of them is the gold cementation on nickel. The cementation is accompanied by an overstoichiometric dissolution of the substrate, which is initiated by the formation of the Au-Ni galvanic couple. Ni2+ ions pass into solution and then are reduced resulting in the codeposition of nickel with gold in the course of Au plating. Electrochemical studies have shown that pure gold does not catalyze the oxidation of hypophosphite. Both nickel from the substrate and nickel codeposited with gold act as a catalyst of the hypophosphite oxidation coupled with the gold plating. Simultaneously, the freshly reduced nickel dissolves gradually in the plating bath due to its high chemical activity in the cementation. Auger spectroscopy, transmission and scanning microscopies were used to investigate the composition, morphology and microstructure of the gold films deposited. The property test results show that the coatings possess better characteristics (protective ability, wear resistance and adhesion) in comparison with those of the electroplated gold films with the same thickness. The improved characteristics can partially be attributed to the fine grained structure of the films and to the presence of nickel in the subsurface zone. The thickness of good quality coatings is limited to 0.3 μm. Possible reasons for film growth ceasing are discussed.

We also recommend Trading Suppliers and Manufacturers of dicyanoaurate (cas 14950-87-9). Pls Click Website Link as below: cas 14950-87-9 suppliers