Cobalt Platings from Double Salt Bath with Pb Anode:Studies on Improvement in Corrosion Resistance of Decorative Platings from Cobalt Baths with Insoluble Anode (Part 1)

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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
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