REDUCTION OF CREVICE CORROSION IN BIPOLAR CHLORINE DIAPHRAGM CELLS BY LOCATING THE CATHODE SCREEN AT THE CREVICE AND MAINTAINING THE TITANIUM WITHIN THE CREVICE ANODIC

摘要

1445903 Bi-polar electrolytic cells PPG INDUSTRIES Inc 19 July 1974 [20 July 1973] 32055/74 Heading C7B A bi-polar electrolyzer has a plurality of diaphragm cells electrically and mechanically connected in series for brine electrolysis to yield caustic soda and chlorine, formed by bi-polar units 11 each comprising: a peripheral wall 21 with flanges 23, 25 at each end and a backplate 31 inside, combining an anolyte chamber 43 fabricated of, preferably clad with, an anolyte-resistant material 27, e.g. a film-forming metal such as Ti, Zr, Hf, V, Nb, Ta, W, or alloy thereof and a catholyte chamber 57 fabricated of a catholyte-resistant material; anodes 41 e.g. extending from the anodic side 33 of the backplate; cathodes 51 e.g. including fingers 53 and backscreen 55 extending from the cathodic side 35 of the backplate; a diaphragm (not shown) mounted on the cathodes which separates the chambers; a joint 61 with gasket 71 between the respective anolyte and catholyteresistant materials of the peripheral walls having a crevice formed within in which corrosion is reduced by maintaining the surface of the anolyteresistant material within the crevice anodic, e.g. by maintaining the surface at a potential 2 to 4 volts which is between its passivation and anodic breakdown potential; preferably the cathode is in contact with the catholyte-resistant material within the crevice by extending therein. Chlorine and hydrogen recovered from chambers 43, 57 are vented respectively through pipes 19, 17. The Ti cladding in the joint may contain 2% Ni or be coated with Ta.