Metrohm’s ProcessLab atline analysis system is a robust solution for monitoring the nickel sulfate and hypophosphite concentrations as well as the alkalinity in electroless nickel plating baths. All relevant process parameters are available immediately after sampling. Implemented right on the production floor, ProcessLab brings the lab to the process allowing plating baths to be operated more economically and ecologically.
A complexometric titration is used for the fully automatic determination of the nickel concentration. A Cu-EDTA buffer solution is added to a bath aliquot and then titrated against an EDTA solution using a copper-selective electrode. The nickel consumption in the nickel plating bath is determined from the EDTA consumption.
The hypophosphite concentration is determined by iodometric back-titration. The sample is acidified and then treated with a defined amount of iodine solution. The excess iodine that is not consumed by the hypophosphite is then back-titrated against a thiosulfate solution using Metrohm’s Pt-Titrode. The hypophosphite concentration in the nickel plating bath is calculated from the initial amount of iodine present and the consumed thiosulfate.
In contrast to orthophosphate, considerably greater interference by a product that increases the salt content results from the self-enriching sulfate, which impairs crystal formation and the relevant coating properties such as corrosion resistance, hardness and resistance to abrasion. Sulfate is precipitated as barium sulfate by the addition of barium chloride, and the excess barium is back-titrated against EDTA in the same way as the nickel determination described above.
The alkalinity is determined by a simple titration with hydrochloric acid using a combined pH glass electrode. The sulfuric acid produced during the coating process reduces the acid-binding ability of the bath and requires the addition of extra sodium hydroxide or ammonia.