Ni-P and Ni-P-Re coatings were produced in the electroless deposition process from aqueous succinate baths composed of: NiSO4·7H2O, NaH2PO2·H2O,C4H6O4, Na2C4H4O4·6H20 and NH4ReO4 in the case of Ni-P-Re alloy deposition. All used chemicals were of analytical grade. In Table 1 the experimental conditions has been collected together with the chemical composition of the exemplary coatings. The appropriate pH values were controlled by either sulphuric acid or ammonia addition.The influence of electrolyte pH on P and Re amounts as well as NH4ReO4concentration on Re amount within the produced coatings has been described in.
Table1 Electroless plating process conditions applied to produce the Ni-P and Ni-P-Re coatings on copper substrates with their chemical composition.
It is possible to deposit the coatings when the pH is varying from 3.0 to 6.5. If the pH is higher than 6.5 nickel hydroxide precipitates, while at pH lower than 3.0 the electroless deposition process is not taking place. Within the range of 3.0-5.5 the P content in the coating decreases almost linearly with the increase of bath pH, and at higher values(above 5.5) maintains constant in both Ni-P and Ni-P-Re coatings. This trend is hold when rhenium is added to the Ni-P but not nickel. The nickel content decreases remarkably with the addition of rhenium, which reveals that the co-deposition of rhenium occurs competitively with nickel and independently of phosphorus. It is also to be noticed that there is a maximum of the deposition rate for both types of coatings in between 4.5 and 5.0 pH value and rhenium content in the coating increases with the increase of bath pH up to 5.0.
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