Takeo Ishida

Studies on Adsorption Behavior of Addition Agents used for Copper Electroplating by Measuring Differential Capacity of Electrical Double Layer

The adsorption behavior of addition agents used for electroplating of copper in acid copper sulfate bath was studied on a dropping mercury electrode relating to their concentration and electrode potential by measuring differential capacity of electrical double layer.The potentials were measured by using Hg/Hg2SO4, 1N H2SO4 as a reference electrode. The zero charge potential of Hg electrode in 1N H2SO4 was estimated as zero volt for further discussion.By the addition of thiourea (TU) or acetyl thiourea to 1N H2SO4, new peaks of capacity appeared at +0.6V and +0.75V.When phenylthiourea was added to the same solution, the maximum of differential capacity at +0.15V appeared to decrease considerably.These effects could be explained by the adsorption of TU and its derivatives on the surface of mercury electrode at rather positive potential.Sodium β-naphthalene sulfonate (NS) and trisodium 1, 3, 5-naphthalene sulfonate had the similar effects on capacity-potential (C-E) curve, in which a minimum of differential capacity was observed at +0.3V and a maximum of that at -0.3V in the both agents. However, disodium 1, 5-naphthalene sulfonate gave a minimum at +0.3V and a maximum at 0V.When TU and NS were concurrently added to 1N H2SO4, C-E curve was found as the sum of the each individual curve of each single addition agent. Therefore, it was concluded that there was no specific interaction between the adsorptions of TU and NS.When benzotriazole was added to 1N H2SO4, the maximum at +0.15V in C-E curve remarkably decreased. By the addition of polyacrylamide, the differential capacity of electrical double layer noticeably increased at E>+0.55V and the maximum at +0.15V decreased.It was found that methyl-isothiourea, glycine, and l-cystine had no effects on C-E curve in 1N H2SO4.

The Effects of Sodium Naphthalene Sulfonates on the Electrodeposition of Nickel from Nickel Sulfate Bath

By the oscillographic determination of the potential decay curves, analysis was made on the resistance polarization, the differential capacity of double layer, and the activation overpotential with respect to the inhibitor action of naphthalene sulfonates in the electrodeposition of nickel from nickel sulfate bath.It was found that naphthalene sulfonates had no specific effects on the resistance polarization as well as on the activation overpotential in the electrodeposition of nickel. However, the dependence of the differential capacity of double layer upon the electrode potential in the presence of naphthalene sulfonates was very significant even though there were no special relations between the differential capacity and the number or positions of sulfonategroups in naphthalene ring.

Corrosion Resistance of Chromate Films on Zinc Electrodeposits

Study was made to establish the new chromate process in which zinc deposits were plated first using a proper addition agent followed by the chromate treatment using dilute chromate solutions.The bright zinc deposits were treated with the following types of chromate solutions:A) CrO3 200g/l, H2SO4 20g/l B) Na2CrO7 200g/l, H2SO4 10g/lC) CrO3 10g/l, H2SO4 0.5g/l D) CrO3 5g/l, Cr2(SO4)3 10g/lThe determination of the corrosion resistance was conducted by both Neutral Salt Spray Test (JIS Z-2371) and also by the pulse polarizer method.Using dilute chromate solutions such as, C) and D), golden yellow films were obtained whose protective power is fairly good and comparable with those obtained from the conventional chromate solutions such as, A) and B).Comparative tests revealed that all the chromated zinc deposits stood up to the salt spray test for 96hrs. (JIS Specification), but the zinc plated panels treated with concentrated chromate solutions exhibited a smaller rust area after the conclusion of the test (336hrs.).It was also found that the pulse polarizer method could be applied for the evaluation of the protective power of the chromated zinc deposits.

Measurements of Sulfuric Acid in Chromium Plating Bath by Means of Current-Potential Curve

There are four steps in the current-potential curve in the electrolysis of chromic acid solution containing sulfuric acid. It has been known that the current in the second step is a linear function of the quantity of the sulfuric acid. But they have not been used for the measurement of sulfuric acid owing to the poor reproducibility.In the present study, the reproducible results were obtained by raising the current in every 15 seconds using the clean Pt electrode for the measurement of cathode potential.It was found that there was a linear relationship between the quantity of SO42- and the limiting diffusion current in the electrolysis of CrO3 solution without Cr3+, but no remarkable effect of concentration of CrO3 in the range of 100-300g/l on the limiting current.The current was decreased as the concentration of Cr3+ increased when Cr3+ was present in the solution. However, upon electrolytic oxidation of the solution, the limiting current corresponding to the SO42- was found to return to its original value. The limiting current was also found to increase by the agitation of the solution which could be explained by the velocity of the diffusion of SO42- to the electrode surface.

The Effect of the Acetylenic Addition Agents on the Cathode Potential during Electrolysis and their Levelling Action in the Nickel Plating Bath

The fundamental study of the levelling action of the acetylenic addition agents was made by measuring the cathode potential during electrolysis and the levelling power defined as a proportion of the deposit thickness obtained at the edges and the recesses of the notches (60°, 90°, 120° and 150°).The addition agents used were propargyl alcohol, butyne-1, 4-diol, methyl butynol, methyl pentynol and dimethyl hexynediol. The results obtained were as follows:(i) When the acetylenic addition agents were added, the increase in the cathode potential toward the negative side was observed, especially with the agitation of the electrolytic solution. There were some differences in the increasing trend of the cathode potential among them. Propargyl alcohol, methyl butynol and methyl pentynol gave the most remarkable increase in the cathode potential, butyne-1, 4-diol intermediate and dimethyl hexynediol lesser extent. In all cases the more the addition agents, the more increased the cathode potential.(ii) The narrower the angles of the recesses, the better the levelling power. There existed some relationship between the levelling power and the increase of the cathode potential, that is, the more increased the cathode potential, the better the levelling power was. It is suitable to use so much amount of the addition agent as to increases the cathode potential toward the negative side within the range of 30-60mV.

Study on the Bright Cadmium Plating (Effect of Addition Agents on the Formation of Bright Deposits)

Effect of addition agents on the formation of bright cadmium deposits from the cadmium cyanide baths has been studied.Cathode polarisation measurements were carried out in the presence of several addition agents and, at the same time, the deposits obtained from these baths were analyzed by electron diffraction method and also by microscopic method, in order to elucidate the characteristics of the crystal structures with respect to the formation of bright deposits.The results obtained are as follows:1) The presence of very small amounts of metallic salts, such as Ni, Co, Fe, Cu, Zn and Hg, in the cadmium cyanide baths, did not remarkable affect the deposition potentials of cadmium, while they gave more positive values of hydrogen deposition potentials in the case of Ni, Co and Fe.2) Addition of organic compounds, such as gelatin, peptone, dextrine, turkey red oil, heliotropine and coumarin, generally resulted in higher polarisation potentials of cadmium to give 30-100mV. at 1amp./dm2.3) Addition of organic compounds in conjunction with metallic salts usually made the cathode potentials more negative to give 70-150mV. at 1amp./dm2.4) In the absence of addition agents, cadmium cyanide baths gave the matt deposits which usually have no preferred orientation of the crystals. Metallic salts were ineffective in changing the grain size or the preferred orientation of the crystals.5) Most organic compounds tested had an effect on the crystal growth of the deposits as revealed by the ability to reduce the grain size and to change the type and/ or degree of the preferred orientation of the crystals.6) Use of organic compounds in conjunction with metallic salts had a marked effect on the crystal growth to bring the bright deposits which have the specific preferred orientation of the crystals.Even though there was no direct relationship between the degree or the type of the preferred orientation and the brightness of the deposits, the main effect in promoting brighter deposits appears that the crystal habits are altered so as to lead to the development of the smooth surface which has fine grains and the preferred orientation of crystals in the deposits.