Dimensionally stable coated electrode for electrolytic process, comprising protective oxide interface on valve metal base, and process for its manufacture

Claim 1

A method of manufacturing an anode for use in an electrolytic process, comprising a valve metal base and an outer coating of lead dioxide or manganese dioxide characterized by the steps of: (a) converting valve metal in the surface of said valve metal base into a protective layer of electrically conducting mixed oxide integrated with said surface by: (i) applying to said surface a solution containing 0.14 to 3.0 moles per liter of hydrogen chloride and 0.02 to 0.10 mole per liter noble metal chloride selected from chlorides of iridium, rhodium and ruthenium, said concentrations being selected to provide a molar ratio of hydrogen chloride to noble metal chloride of between about 3:1 and about 30:1; (ii) drying said solution on said surface slowly to achieve substantial reaction between said hydrogen chloride and said surface, thereby forming on said surface an intimate mixture of the valve metal chloride and the noble metal chloride in proportions consonant with said molar ratio; (iii) heating the thus treated valve metal base from (ii) in an oxidizing atmosphere at 400° C. to 600° C. until said intimate mixture has been converted into an electrically conducting mixed oxide integrated with the surface of said base; (iv) repeating this sequence of steps (i) through (iii) until enough of said conductive mixed oxide has been integrally grown on said surface to provide a protective layer for said valve metal base; and (b) applying an outer coating of lead dioxide or manganese dioxide onto said protective layer of electrically conducting mixed oxide.

Claim 2

A method of manufacturing an anode for use in an electrolytic process, comprising a valve metal base and an outer coating of lead dioxide or manganese dioxide characterized by the steps of: (a) converting valve metal in the surface of said valve metal base into a protective layer of electrically conducting mixed oxide integrated with said surface by: (i) applying to said surface a solution containing 0.14 to 3.0 moles per liter of hydrogen chloride and 0.02 to 0.10 mole per liter noble metal chloride selected from chlorides of iridium, rhodium and ruthenium, said concentrations being selected to provide a molar ratio of hydrogen chloride to noble metal chloride of between about 3:1 and about 30:1; (ii) drying said solution on said surface slowly to achieve substantial reaction between said hydrogen chloride and said surface, thereby forming on said surface an intimate mixture of the valve metal chloride and the noble metal chloride in proportions consonant with said molar ratio; (iii) heating the thus treated valve metal base from (ii) in an oxidizing atmosphere at 400° C. to 600° C. until said intimate mixture has been converted into an electrically conducting mixed oxide integrated with the surface of said base; (iv) repeating this sequence of steps (i) through (iii) until enough of said conductive mixed oxide has been integrally grown on said surface to provide a protective layer for said valve metal base; and (b) applying an outer coating of lead dioxide or manganese dioxide onto said protective layer of electrically conducting mixed oxide.