クーロスタット法による無電解ニッケルめっき速度のモニタリング

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A computer-aided coulostatic method was employed for the in-situ monitoring the deposition rate of electroless nickel. The relationship between deposition rate (ielp) and polarization resistance (Rp) was given by the equation; ielp=K/Rp. The K-values were empirically determined from pairs of ielp and Rp values, which were measured both by weight gain due to electroless plating and also by the coulostatic method. The K-value relating to the electroless nickel deposition was found to be 10-20mV depending on temperature, pH and acetate concentration as well as stirring, but it was substantially independent of hypophosphite concentration. Once a K-value was established, the deposition rate could be successfully monitored by this method. The empirical K-value agreed fairly well with theoretical one which was calculated from Tafel slopes (ba, bc) measured by the galvanostatic trangent and a modified coulostatic method by using the equation; K=ba·bc/2.3 (ba+bc). The increase in K-value with rising pH was essentially ascribed to an increase in Tafel slopes. The pH dependence of the Tafel slopes was more pronounced in cathodic reactions than in partial anodic reactions. The coulostatic method is found to be useful not only for monitoring the deposition rate of electroless nickel, but also for elucidating the mechanisms of the deposition process.
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