Effects of complexing agents on acidic electroless nickel deposition

Our previous study reported the influences of different complexing agents on electroless nickel (EN) by examining the properties of the deposits. In the present work, the effects of four common-used complexing agents on EN deposition rate and the stability of solution pH values were examined, either with an acetic pH buffer agent or absent of them. It is indicated that the pH buffering effect of them is dominative when the EN solution is lack of the pH buffer. Under this situation, the EN deposition rate increases with the concentration of complexing agents increasing. The EN deposition rate decreases with further adding the complexing agent when the solution already has enough pH buffer capability. Electrochemical impedance spectroscopy obtained during EN deposition illustrates that, in this case, the enhanced reaction resistance is the main reason for a lower deposition rate. However, the influence of polarization caused by mass transfer is not negligible at high complex ratio for sodium citrate and malic acid EN solutions.