Yoshiharu Nagai

Corrosion Resistance of Decorative Platings Deposited from Cobalt Citrates

CASS and corrodkote tests on a decorative plating containing an intermediate cobalt layer from citrates were conducted to examine its high corrosion resistance processes.Following conclusions were drawn:(1) Corrosion surroundings had effects on the formation of small blisters.(2) The electrode potential between each two plating layers had effects on the formation of small blisters under definite surroundings.(3) The undercoating of cobalt layer should be electrochemically nobler than the bright nickel.(4) The preferred processes for high corrosion resistance of decorative platings were as follows:Cu……Co……bright Ni……regular CrCu……semi-bright Ni……Co……bright Ni……regular Cr and their modifications.

Cobalt Platings from Double Salt Bath with Pb Anode

In order to obtain economical cobalt platings for decorative purpose of high corrosion resistance, investigations were made for replacing the semi-bright layer of triple nickel platings by copper and replacing thin sulfur rich layer by cobalt.By using Pb anode and CoSO4. 7aq. solution or double salt bath, the process was examined for Co++ concentration for higher throwing power and higher current density by the determination of cathodic current efficiency and continuous pH determination of the controlled bath. The control of pH was made by neutralization of the solution around the anode with CaCO3, CoCO3, or Pb(OH)2 PbCO3 or addition of ammonium acetate to the plating bath.The results obtained were as follows:(1) The highest throwing power was obtained from the solution containing 0.6mol/l of Co++.(2) The factor most effective for the current density was the variation in pH.(3) Co++ concentration had no effect on the current efficiency at pH=4 in a range of 0.4-0.7mol/l.(4) The value of pH was required to be kept at above 4.(5) The method of keeping pH value at constant was to neutralize the solution around the anode with Pb(OH)2. PbCO3 or to activate the anode by the addition of ammonium acetate to the plating bath. The optimum conditions of the bath components for the latter method were as follows:CoSO4.7aq. 0.6mol/l(NH4)2SO4 0.4mol/l(NH4)O2C2H3 0.4mol/lAnode Pb(containing Sn)pH 4-4.5

Corrosion Cell of Cobalt Electrodeposited from Double Salt Type Bath

For the estimation of corrosion resistance of composite platings, including a cobalt layer, the changes of the following factors with the progress of time were determined. The specimens used were cobalt from double salt type bath, copper from sulfate bath, and bright nickel. The tests were made on the following factors.(a) Spoutaneous electrode potential of each specimen in CASS solution.(b) Mixed potential of a combined specimen in CASS solution.(c) Electromotive force between any two specimens in various accelerated corrosion solutions or in natural water.The following conclusions were drawn from the consideration of experimental results.(1) The Plating order for the most Suitable was as follows: Cu at fast, Co the next, and bright Nickel at last. The order of the Potentials was as follows:Cobalt was least noble, Copper was the next, and bright nickel was noblest(2) In chloride rich surroundings, the electromotive force between bright nickel and cobalt was larger than that detween any other specimens; therefore, copper layer was protected by cobalt layer.(3) In chloride poor surroundings, copper layer was also protected by cobalt layer since copper layer was the noblest in these surroundings.(4) By reasons of the above facts, the composite plating including a cobalt layer was suitable for preparing articles used in various different surroundings.

Elimination of Organic Impurities in Bright Nickel Plating Bath by Sorption by Crushed Coconut-core Active Carbon

The sorption of coconut-core active carbon for automatic elimination of organic impurities, oxidized or reduced substances of 2-butyne-1·4-diol, in bright nickel plating bath was investigated.The results obtained were as follows:1) The sorption points of acidic impurities and alcoholic ones were different each other.2) Much more 2-butyne-1·4-diol (brightener) was sorbed than its oxidized or reduced substances (acidic or alcoholic impurities).3) The process of automatic or semi-automatic elimination of the organic impurities was preferable to conduct in the following order of sequence.(a) Passing through 30g/l of coconut-core active carbon of 30-50 mesh about 5 times for elimination of the brightener.(b) Adding 0.1g/l of KMnO4 to the solution.(c) Dissolving the precipitate obtained (MnO2) with 0.143ml/l of 30% H2O2.(d) Passing through the active carbon layer, used in the process of (a), more than 9 times for more than 1hr.

Effects of Bath Compositions and Brighteners on Corrosion Resistance of Bright Nickel Plating

The effects of bath compositions and brighteners on corrosion resistance of bright nickel plating were studied. The results obtained were as follows:(1) The interaction between the concentrations of nickel sulfate and nickel chloride had no effects on corrosion resistance.(2) The interaction between the cathodic current density and the concentration of total nickel had effects on corrosion resistance. Higher corrosion resistance was obtained under the conditions of lower concentration of total nickel and lower cathodic current density, or the higher concentration of total nickel and the higher cathodic current density.(3) Corrosion resistance was varied according to the kind and concentration of brighteners in double nickel plating.(4) The interaction between the kind of brighteners and cathodic current density had effects on corrosion resistance.(5) However, in CASS test of triple nickel plating, the kind of brighteners and cathodic current density had no effects on corrosion resistance.

Corrosion Resistance of Substrate Plated with Bright Nickel Deposit

Microscopic observation, measurement of hardness, CASS and EC tests, and measurement of corrosion potential were conducted to examine the effects of polishing, tension, bending, and welding of substrates for the specimens plated with bright nickel deposit.The results obtained were as follows:1) Corrosion resistance was lower with the increase in surface roughness of the substrate and the effect was greater with the decrease in thickness of plated layer.2) The electrodeposited surface was rougher in the initial stage of deposition when the original substrate surface was rougher and the effect was greater with the increase in current density.3) The tension of the substrate had little effects on electrodeposited layer and corrosion resistance.4) On bending of the substrate, a few rough points were observed in the initial stage of deposition. Non-uniform distribution of hardness was revealed on account of the bending deformation in parts, by which corrosion resistance was lowered.5) The defects in welding of the substrates had effects on corrosion pattern.As mentioned above, the treatments of substrate in plating works had little effects on corrosion resistance. Whereas, combination of unsatisfactorily controlled factors such as defects in current density, purity of solution, and brighteners seemed to have greater effects on corrosion resistance.

Effects of Impurities on Properties of Bright Nickel Plating

Effects of organic and metallic impurities in bright nickel plating bath on the corrosion resistance and surface appearance of nickel-chromium plating were examined.Organic compounds were the substances supposed to be produced by oxidation or reduction of 2-butyne-1·4 diol. Metallic impurities included Cu (II), Zn (II), and Mn (II).CASS and SO2 tests were conducted on the corrosion resistance for organic impurities, but CASS test only for metallic impurities.The follwing conclusions were drawn from the results of experiments.The accumulated oxidized impurities, in particular, acetylene-dicarboxylic acid, tartaric acid, an glycolic acid had worse effects on the properties of nickel-chromium plating than reduced impurities. The following results were obtained.1) Decrease in corrosion resistance of ncikel-chromium platings.2) Decrease in leveling power of nickel deposits.3) Formation of milky semi-bright deposits.It was suggested the allowable limits of the contents of metallic impurities with respect to corrosion resistance and appearance were as follows:Zn (II) up to 0.05g/l Cu (II) up to 0.02g/l and Mn (II) up to 5g/l

Study on the Reaction of Chrome Oxide by Cuprous Cyanide

As it was known that Cr+6 is reduced by the reaction with cuprous cyanide, the difference of reductions between the reaction with sodium cuprous cyanide and that with cuprous cyanide powder was studied.The above study was applied for the waste water treatment of plating shops. The waste water, consisting of the mixture of cyanide and chrome oxide, was acidified with sulfuric acid (pH=2-2.5), and then treated by aerating tower.