The chemical species and equilibria in electroless copper plating baths consisting of copper sulfate, EDTA, glycine, hexacyanoferrate and formaldehyde were investigated by visible-spectrum measurements at 25°C. Chemical species were mainly CuOHL3-, CuL2-, G-, M-, MG2-, HMG-, CuLG3-, CuLfe6-, fe4-, L4- and HL3- at pH11.75∼12.50, where H4L=EDTA, HG=glycine, HCHO+H2O=HM and Fe (CN)4-=fe4-. Glycine and formaldehyde form condensation products such as HMG-, resulting in a decrease in the concentration of free formaldehyde, but the concentration of M-, the electrochemically active species of formaldehyde, increased in the high pH region. Three mixed-complexes were found in the solution: CuL2-, and OH- formed CuOHL3-([CuOHL3-] [H+]/[CuL2-]=10-11.8, molar absorptivity ε730=45); CuL2- and G- formed CuLG3- ([CuLG3-]/[CuL2-] [G-]=101.5, ε730=45.5); and CuL2- and fe4- formed CuLfe3-([CuLfe3-]/[CuL2-] [fe4-]=101.2, ε490=315). The concentrations of CuLG3- and CuLfe4- were considerably lower than the other Cu (II) -EDTA complexes.
An investigation was made of polarization characteristics for electroless copper plating baths consisting of copper sulfate, EDTA, formaldehyde, glycine, potassium hexacyanoferrate (II) and triethanolamine. Mixed-potential theory was confirmed from experimental results including local potential-current relationships for copper deposition. Formaldehyde accelerated the rate of copper deposition. The addition of glycine brought about a substantial decrease in the local current for the oxidation of ormaldehyde, as well as in that for copper deposition. Hexacyanoferrate (II) retarded the anodic reactions. It also retarded the property of ormaldehyde to accelerate copper deposition, while accelerating the deposition in itself. Triethanolamine accelerated the oxidation of formaldehyde near the rest potential.
Measurements of current density-potential (I-E) curves and AC impedance during electrodeposition of Cu-Zn alloys showed that Zn was codeposited only under conditions of diffusion-limited Cu deposition in the case of baths without histidine. This was confirmed by the characteristics of the I-E curves and by the characteristic Warburg impedance behavior. In the case of the baths containing histidine, on the other hand, Zn was codeposited under conditions where Cu deposition was not diffusion-controlled. I-E curves and double layer capacitances suggest that the adsorbed histidine suppressed Cu deposition and markedly increased the surface concentration of Cu+ adions. The adsorbed histidine suppressed Cu deposition even at negative potentials sufficient for Zn codeposition in the alloy baths Therefore, the rate of Cu deposition in the alloy baths was so small that it did not exceed the diffusion limited current of Cu2+ ion at negative potentials sufficient for Zn codeposition and this resulted in the smooth Cu-Zn alloy deposits. Data from AC impedance measurements suggest that an adsorbed intermediate plays an important role in alloy deposition processes from the baths containing histidine.
The effect of the addition of EDTA complexing agent on the electrodeposition of tin-lead alloy from gluconate baths was investigated. The addition of EDTA to baths containing additives was found to suppress the preferential deposition of lead in the low current density region. Measurement of partial polarization curves for tin-lead alloy plating baths showed that the addition of EDTA to baths containing additives shifted the potential of lead deposition in the less noble direction, but had little effect on the current values for hydrogen evolution. As the concentration of sodium gluconate in the bath was increased, the lead content of deposits increased and the current efficiency decreased. When the EDTA-to-lead concentration ratio in the bath was increased, on the other hand, the lead content of the deposits decreased and the current efficiency increased. These results suggest that the formation of the complex of lead ion with gluconic acid and EDTA occurred in the solution.
Since it has been found in our previous studies that Ti-added cold rolled steel sheets, when they have been ground, may exhibit inferior phosphatability, the effects of pre-phosphating-treatment, and Ni or F concentration in the phosphating reagents were investigated. It was found that the oxidative effect of F and ClO3 on phosphatability differed greatly, but that other effects were minor. In order to ascertain the etching capacity of two phosphating reagents, the solubility of Fe in the phosphating reagents without Zn ion was examined. The result confirmed the evident difference in Fe solubility between the two types of phosphating.
In a field of metallic cementation, there are many methods of introducing penetrating elements into solid metals in the vapor phase. After the cementation, however, it is frequently impossible to determine the original position of the solid metal surface, and such cases, it is impossible to use ordinary interdiffusion coefficients to plot the concentration penetration curve. Accordingly surface-fixed reference coordinates were employed to analyze the penetration of zinc in the vapor phase into pure copper specimens. The method was also applicable to the penetration of zinc into copper-nickel alloy specimens, an example of diffusion in a ternary metallic systems.