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The offect of polyoxyethyleneglycole (PEG) on the copper deposition and dissolution were studied in an acid copper sulfate bath as a function of electrode potential, polymerization degree of PEG and Cl - concentrations. In the presence of Cl - , PEG adsorbed on the copper surface to give an adhesive film causing remarkable suppression of the reaction current in the wide potential range of copper deposition and dissolution. While, in the Cl - free solution, PEG suppressed the reaction current in the potential range less negative than -150mV vs Cu 2 +* /Cu . Only the PEG which has the polymer ions are grasped in PEG molecules.

The covering powers of chromium platings from both of the plating baths of low and high concentrations were studied.The following results were obtained:(1) The covering power by the Hull Cell Test was much higher in the bath of low concentration than in that of high concentration.(2) On the contrary, the covering power by the parallel or bend cathode process was lower in the bath of low concentration than in that of high concentration.(3) The above two contradictory phenomena were due to the fact that the current was likely to be concentrated along the edges of the specimen so that the current density in the center was lowered; and the lowering degree of the current density was greater in the bath of low concentration than in that of high concentration.

Activities of fluoride and foluorosilicate in chromium plating baths were studied by using a fluoride electrode, and the following results were obtained.(1) In chromium plating baths, the activity of fluoride was less than that of the additional fluoride. The reason for this was that F-+H+→HF.(2) The activity of fluoride well corresponded with the value calculated from pH of the plating bath and ionization constant of HF, 7.2×10-4.(3) The activity of fluorosilicate was quite the same as that of fluoride at concentrations of less than 10-3mol/l or at higher pH. The reason was that the fluorosilicate was completely decomposed at low concentrations, and it was decomposed to fluoride at higher pH as follows:SiF62-+6OH-→6F-+[Si(OH)6]2-(4) The difference between activities of fluoride and fluorosilicate under other conditions was due to the formation of complex salt by fluorosilicate.

Improving the method of “colorimetric determination of NL-I of H-V W-M Co.”, a volumetric chemical analysis of naphthalene sulphonats in nickel plating baths was devised.As naphthalene sulphonate is quantitatively oxidised in hot solution of K2Cr2O7-H2SO4, when heated for 2.5 minutes after the white fume of H2SO4 begins to be generated, chloride ion and second class brighters in nickel baths are also oxidized by K2Cr2O7, so that it is found that there is no trouble in heating naphthalene sulphonates in acidic solution with H2SO4 until the appearence of white fume of H2SO4. Thus the chroride ion and second brighters are eliminated before adding K2Cr2O7.The both results of “Colorimeter determination of NL-I visual composition method” and this method coincide farely well.Reproducing of this action is pretty good, and the equivalent of 8 Mol K2Cr2O7 seems to correspond to 1Mol naphthalene sulphonate, regardless of the number of sulphonate radicals.

The bath voltages of chromium plating were studied at various concentrations of CrO3 and under various plating conditions.The following results were obtained:(1) A higher bath voltage was required for a CrO3 bath of lower concentration. When the voltage of CrO3 250g/l bath was taken as the standard, the voltage required was about 2 times for 50g/l bath, about 4 times for 25g/l bath, and about 6 times for 12.5g/l bath at 1l beaker test.(2) Assuming that the hypothetical value of resistance voltage of chromium plating bath calculated from its conductivity is Eohm and the real value is E'ohm, the following relation was derived:k=Eohm/E'ohm=K/K'=(2.4±0.2)l1/3where K and K': Hypothetical and real cell constants, respectivelyl: Distance between electrodes(3) Accordingly, k was called cell constant ratio.

The self-regulation of sulfate concentration by the addition of Sr2+ to a chromium plating bath saturated with SrSO4 was studied. The following results were obtained: (1) Since SrSO4 is a strong acid salt, the solubility of SrSO4 in low pH solution such as a chromium plating bath was not much higher than that in its aqueous solution. (2) The SO4 concentration could freely be regulated by the addition of SrCO3 to the chromium plating bath. (3) The decrease in the solubility of SrCO3 conformed to “common-ion effect” in the chromium plating bath, but not in the aqueous solution. It would be more clear by assuming activity instead of concentration. Namely, the ionic strength was higher and steady in the chromium plating bath and was supposed to be proportional to CrO3 concentration; but it was changeable in the aqueous solution. (4) For example, the solubility of SrSO4 (as SO4) was 1.4g/l in chromium plating bath containing 50g/l of CrO3 at 55°C. When SrCO3 of 6.0g/l was added to the bath, the SO4 concentration became 0.5g/l, by which the plating bath for self-regulating SO4 was prepared.

The self-regulation of fluorosilicate concentration by the addition of K+ to a chromium plating bath saturated with K2SiF6 was studied. The following results were obtained: (1) Since K2SiF6 is a strong acid salt, the solubility of K2SiF6 in low pH solution such as a chromium plating bath was not much higher than that in its aqueous solution. (2) The decrease in the solubility of K2SiF6 conforming to “common-ion effect” did not agree to the following dissociation. K2-SiF6→2K++SiF62-. (3) The reason was explained by the following hydrolysis of K2SiF6: K2SiF6+H2O→2K++SiF5(OH)2-+HF. The dissociation of a fluorosilicate having higher solubility such as Na2Si F6 was as follows: Na2SiF6→2Na++SiF62-. Whereas, the dissociation of a fluorosilicate having lower solubility such as BaSiF6 was as follows: BaSiF6+2H2O→Ba2++SiF4(OH)22-+2HF. The results of experiments well agreed with the basis of these dissociations. (4) For example, the solubility of K2SiF6 was 10g/l in chromium plating bath containing 250g/l of CrO3 at 55°C. Therefore, the plating bath for selfregulating SiF6 was prepared by the addition of a small amount of K2CO3 to the bath. The solubility of K2SiF6 was 7g/l in low concentration chromium plating bath containing 50g/l of CrO3 at 55°C. Since the optimum concentration of K2SiF6 in this bath is 0.6g/l, 27.5g/l of K2CO3 shall be added to get the self-regulating bath. However, this composition was not adequate for the chromium plating bath owing to the increase of pH value.

The authors examined the changes in number of crack meshes, crack width, plateau size, etc. of a part of chromium deposit, which had been subjected to sucsessive electrolytic etching. The examination was conducted by a serial photomicrography. The following results were obtained. The increase in number of crack meshes and the decrease in plateau size of chromium deposit electrolytically etched were proportional to a certain unit thicness of the deposit; this phenomenon reveals that the presence of cracks of chromium deposit was separated by unit thickness of the deposit, which is referred to as the “thickness of unit crack layer”, hereinafter. The “thickness of unit crack layer” was thinner when the cracks were more dense, but was thicker when the cracks were sparser. Moreover, it was related with the “critical thickness” observed in the measurement of the stress of chromium deposit. When the etching was further promoted, each of the number of crack meshes and plateau size tended to a constant value, at which the thickness was several times as large as that of the “thickness of unit crack layer”.

In electroless copper plating solution, the reaction among copper sulfate, Rochelle salt, and sodium hydroxide is shown by the following equation:Reaction of deposition of copper is shown by the following equation:When this solution is settled for a time, sodium hydroxide is decomposed by the reactions shown in the following two equations:NaOH+CO2→NaHCO3…… (3)NaOH+2HCHO→HCOONa+CH3OH…… (4)It is derived from the four equations mentioned above that 4 mol or more of sodium hydroxide, 1 mol or more of Rochelle salt, and 2 mol or more of formalin are required for the deposition of 1 mol of copper.Rate of deposition of copper is proportional to the temperature and the amounts of copper sulfate and sodium hydroxide in plating solution. However, self-decomposition of the solution will take place with the increase of the above amounts or temperature rise. The rate is promoted by mechanical stirring of the plating solution, which will prevent self-decomposition.For preventing self-decomposition in the solution of high concentration, it is effective to add 1-3g/l of potassium cyanide to the solution. However, as the effects of the addition, the rate of deposition is lower and blackish brown deposit in initial stage has much less adhesive power.

When the following pretreatments are applied in ABS resin, electroless copper having good adhesive property can be obtained as an undercoating for electroplating.Chemical roughing CrO3 33g/l, conc. H2SO4 800cc/l, 60-70°C, 1min↓Water rinsing Neutralization 10% NaOH, room temp.↓Water rinsing Sensitizing SnCl2⋅2H2O 40g/l, conc. HCl 70cc/l, room temp. 1min↓Water rinsing Activating AgNO3 1.5g/l, conc. NH4OH 1.2cc/l, room Temp., 1min↓No rinsing↓Reducing 10% (vol.), formalin solution, room temp., a few sec.↓Drying 60-70°C↓No rinsing Electroless copperWhen such pretreatments are applied, costly mechanical roughing process can be omitted and noble metals for activation are not needed, further more, the quality is far superior to the ones which are treated for activation with noble metals such as Pd or Au.

Each component in the lead-tin fluoborate plating bath would be quantitatively analyzed by the following procedures simply and correctly.Pb: After the excess of EDTA being added to the bath, Sn++ was oxidized with H2O2. Then, the solution was masked with triethanolamine and back titrated with Zn++ at pH=10 using BT as indicator.Sn++: After Pb was precipitated with H2SO4, titrated by iodometry.Free HBF4 and Free H3BO3: After Pb was precipitated with Na2SO4, free HBF4 was determined by alkaline titration with pH-meter to pH=3.5 as the end point. Then, pH was made to 7.0, mannite was added to it, and free H3BO3 was determined by alkaline titration to pH=8.0 as the end point.Hydroquinone: Precipitate was filtered off from the solution after the determination of HBF4 and H3BO3 and titrated with Ce+4 using ferroin as indicator after made acidic with H2SO4.Lead and tin in the deposit could be determined by the following procedures.Pb: Lead-tin plated layer was dissolved by a remover such as Enstrip TL and the excess of EDTA was added to the solution. Then, tin was masked with triethonolamine and back titrated with Zn at pH=10.Sn: The above solution wa made acidic with HCl and back titrated with Zn at pH=5 in the warm state using PV as indicator to determine Sn+Pb. Then, Sn was calculated.

Experiments were conducted to find the optimum bath composition and plating condition for obtaining a bright chromium plating from CrO3 baths of concentrations lower than 50g/l.The following results were obtained:(1) The optimum bath composition for bright chromium plating was CrO3/H2SO4/Na2SiF6=100/1/1 and the concentration of CrO3 was 25-50g/l.(2) The plating conditions seemed to be almost the same as those of the normal bath of 250g/l CrO3. However, the range for brightness was narrower with the decrease in CrO3 concentration of the bath.(3) Chromate films appeared on the surface of the chromium plating from CrO3 baths of low concentrations. The films could be removed by dipping for a short period in the plating bath after deposition.

Stress of the chromium deposit obtained from various baths, at different temperature and current density, was measured with Brenner and Senderoff's contractometer, to study the relation between the stress and other properties, such as brightness, hardness, cracks and corrosion resistance.Result:(1) In chromium plating at a certain current density, the luster of the deposit changes gradually in the order from “mat” to “frosted, ” then to “bright, ” and finally to “milky, ” depending on the change of temperature. Stress of the thin deposit is very small with “mat, ” rapidly increases with “frosted, ” then becomes maximum with “bright” and decreases again with “milky.” It is supposed that the smaller the grainsize of the deposite is, the brighter is the luster.Stress of the thicker deposite becomes smaller, depending on brightness, and finally compressive at “bright.” This phenomenon can be explained by the exceptionally good micro-throwing power of chromium plating in the cracks of the deposited. Many theories have been so far discussed upon the brightness of chromium plating, but the good micro-throwing power is supposed to be one of the reasons for brightness as in the case of nickel plating.(2) The facts that its iso-hardness curve resembles its iso-stress curve and that the brighter the deposit is, the higher is the stress, suggest that the hardness of chromium deposit should have much to do with its stress.(3) Cracks produced in the cromium deposit are supposed to be caused by its initial big stress. this means that the stress is greater than the tensile strength. In fact, when the initial stress is small, few or not cracks occur. Such deposits can be obtained from the bath of concentrated CrO3, high ratio of CrO3/H2SO4, and higher temperature, which can also be considered as right plating conditions to get a deposit of good corrosion resistance.(4) Initial stress of the chromium deposit from the bath of SiF6 and CR-110 is comparatively greater than that from Sargent bath. Stress of the thicker deposit is smaller, which usually has fine cracks and brighter luster.(5) The deposit from the bath with selenic acid has smaller stress and fewer cracks, but its brightness becomes poor.

Some relations beween hardness and stress was found to exist in nickel deposits as follows:1) Of the nickel deposit from the bath without brightener the hardness (Hv 180-370) and stress (15-65×103psi) are proportional.2) Of the deposit from Watt's bath added with the first class brightener the stress is changed to compressive stress and its hardness is increased. In this case, the bigger the compression stress (-2- -13×103psi) is, the greater is the hardness (Hv 200-500).3) In general, of the deposit from the bath containing both the first and second class bightener, hardness (Hv 450-700) and stress (-10-50×103psi) is increased with an increase of the secomd class brightener.4) In all the above three cases, the bigger the stress is, the greater is the hardness.5) Agitation of the bath generally causes the hardness and stress to increase.6) Of the deposit from the bath added with some kind of surface active agent the stress is decreased, but the hardness increased.

Stress in electrodeposition was measured by means of the same equipment as described in the first report, and under various electrolytic conditions using Watt's type bath, plain bath, all chrolide bath, and sulphamate bath.The result is as follows:(1) Effects of temperature, current density, pH, Ni++, and Cl- on the stress were almost the same as reported by Brenner and others. The value of stress in Watt's type was the lowest when H3BO3 was about 30g/l.(2) MgSO4⋅7H2O of 0-200g/l or Cu++ and Zn++ of 0-0.05g/l had almost nothing to do with the stress.(3) Some organic impurities increase the stress.(4) When Watt's type bath or all chloride bath was air-agitated, the stress was increased about 7×103 p. s. i.