There are two types of electrolyte for chromium electroplating: the Sergent bath and the chromate solution containing fluorine compound. The Sergent bath is an acidified chromate solution consisting of some 250 g/liter CrO~, and easy to operate. However, the current efficiency for chromium deposition is low, about 10% or less. Metal deposition no longer takes place if the electric circuit is once interrupted. This is probably due to rapid passivation of the metal surface, and it is troublesome. Therefore, the Sergent bath is inadequate for some applications, such as the barrel plating.Of the modified solutions containing fluorine compound, the fluosilicate bath, consisting of CrO~, H~SO4, and sodium hexa-fluosilicate Na2SiFs, is most popular, although other electrolytic solutions, such as those containing fluoborate, for example, are also used. The current efficiency for metal deposition from the fluosilicate bath (FS bath, hereafter) is somewhat large compared to that from the Sergent bath because of the difference of the catalytic activity in both solutions. Metal deposition from the FS bath is able to continue even if the electric current is switched off during operation. It is of importance from the practical viewpoint.A number of scientific papers on the chromium electroplating have been published since Mfiller proposed the mass transport through the oxide film formed on the cathode surface (1). However, the mechanism on the chromium electrodeposition has not yet been fully established.Lead and its alloys, such as Pb-Sn and Pb-Sb, are employed as the anode in both the Sergent bath and the FS bath (2, 3). A lead dioxide layer formed on the surface prevents the anode from corrosion. At the open-circuit potential or at zero current, however, the oxide layer changes to lead chromate, and the cell voltage becomes high. This is caused by an extremely high resistance of the PbCrO4 layer. The consecutive formation of PbO, Pb(OH)2, PbCrO4, and PbO2 on the lead anode immersed in the chromium electroplating bath has been pointed out on the respective potentials before oxygen evolution, but no significant effect of addition of sulfuric acid to the chemical composition of the oxide layer has been found (4).The corrosion rate of the Pb alloy anode in the Sergent bath is in the range 1-10 mg/Ah, depending on the alloy composition, the casting, and the operating conditions, but the anode consumption in the FS bath is great. According to the laboratory test, the corrosion rates of a Pb-2% Sn alloy anode in the Sergent bath and the FS bath were 5 and 12 mg/Ah, respectively, under normal conditions. With the plant experiences, the grain boundaries of *Electrochemical Society Active Member.alloy are attacked, fine particles go away into the solution, and a part of these solids precipitate on the cell bottom which is troublesome for the cell operation.The lead alloy anode is consumed by two factors: the chemical attack and the physical degradation. The anode surface is dissolved gradually by electrolysis or by the faradaic curre...

The demand for chlorine for water and waste treatment is increasing because of the increase of water consumption, a large amount of waste water discharge, and governmental regulations. Transportation and handling of chlorine cylinders and containers are strictly controlled to avoid hazard. As a result, on-site electrolytic production of hypochlorite becomes important for disinfection of drinking water, oxidation of sewage, chlorination of cooling water in process plants, and other uses. There are now a number of publications and patents on hypochlorite cells and the electrodes to be used (1-13).A hypochlorite cell must be simple in operation with minimum maintenance for a year or more. The energy consumption is also an important factor.In an electric power station located by the sea, saline water containing some 3% NaC1 is fed to the hypochlorite cell and is chlorinated prior to being sent to the heat exchangers in the plant. Because of the low salt concentration, oxygen evolution occurs, and this reduces chlorine current efficiency. Also, sea water contains Mg and Ca ions, which deposit at the cathode, resulting in high cell voltage. Periodic acid cleaning removes the scale, but affects the electrodes, especially the anode coating, and in some cases the electrode activity is not restored.Pretreatment of sea water prior to electrolysis is preferable, but it is expensive and complicated. Therefore, durable anodes having such characteristics as low chlorine overvoltage and high oxygen overvoltage in sea water must be developed to improve the operating performance of hypochlorite cells. Experimental ProcedureTwo types of the platinized Ti anodes were used as controls. One was Pt-plated Ti sheet prepared by conventional electroplating (hereafter referred to as "regular Pt/Ti"). The other was also a Pt-plated Ti sheet and had a large surface area ("modified Pt/Ti") (14). The average ~hickness of the Pt coating was 3 ~m.The modified Pt/Ti sheet was painted with a solution containing a metal chloride, such as RuC13 or IrCl.~, depending on the oxide catalyst proposed, dried in air, and then fired at 500~ for few minutes to deposit the oxide on the Pt layer (MODE| In this work, the Ir oxideloaded material was used mostly.Full-scale experiments were conducted in an electric power plant located at Tokyo Bay. The flowsheet is illustrated in Fig. 1, Eight cells were operated in series and parallel connections; the sea water was fed to the top end of the cell series, electrolyzed, and mixed together at the outlet. The chlorinated sea water was sent to the heat exchangers in the plant. Each hypochlorite cell employed was equipped with five anodes and six cathodes (carbon steel plate) in parallel. There were no separators. The design capacity of the cell is as follows. The effective area of * Electrochemical Society Active Member. electrode was 80 cm wide and 45 cm high each. The anode-to-cathode gap was 5 mm. The current density was 15 A/din 2 at 5.4 kA total current load. The cell voltage was 5.5 z 0.5V. The solution flow rate...