Impressed current protection of titanium or titanium alloy in acid aqueous solution

  • Inventors:
  • Assignees: M & T Chemicals Inc
  • Publication Date: March 26, 1969
  • Publication Number: GB-1146443-A

Abstract

1,146,443. Preventing corrosion of titanium; electro-plating. M. & T. CHEMICALS Inc. April13, 1966 [April 14, 1965], No.16247/66. Headings C7B and C7E. Titanium or an alloy containing at least 90% Ti is protected from etching while immersed in an aqueous acid solution by placing it in intimate electrical contact with a low hydrogen overvoltage metal having a hydrogen overvoltage equal to or less than that of massive nickel and maintaining on the titanium or alloy a cathodic current density of 0À1 to 2 amps/sq. dm. The low hydrogen overvoltage metal which may be Pt, Pd, Rh, Ir, Au or Ni (including black nickel and electroless nickel) may be placed in intimate contact with the titanium or alloy by overlaying with a foil or a thin foraminous sheet of the metal, or by hot-melt dipping, dusting with metal powder followed by fusing, by immersion plating, by applying a foraminous sheet of a high hydrogen overvoltage metal e.g. steel itself coated with a low hydrogen overvoltage metal such as Pt or Pd, or by electroplating. Water-soluble compounds suitable for use in electro-plating are chloroplatinic acid or its potassium salt, platinum chloride, platinum diamino dinitrite, tetrammine platinous chloride or fluoride, potassium chloroplatinite, palladium dichloride, palladium nitrate, rhodium chloride, iridium tetrachloride, chloroiridic acid, chloroauric acid, gold chloride, and gold cyanide. Electro-plating is effected at temperatures of 20 to 90‹ C. with a cathode current density of 0À5 to 5 amps. /sq.dm. for 0À2 to 5 minutes to give deposits of thickness 0À05 to 0À5 Á which may be porous or even form discrete islands. Strips of Ti alloy containing 2% by weight Pd electro-plated with 0À15 Á Pt from an acid aqueous chloroplatinic acid solution suffered no loss in weight when made cathodic at a current density of 0À8 amp. /sq.dm. in a chromic acid plating bath containing silicofluoride and sulphate catalyst ions. Titanium or alloy so protected may be used for heating coils or elements, heat exchanger coils, partitions, stirrers or as sheets, rods or Ti-clad sheets in such chromium electro-plating baths. Reference is made also to protection in chromic acid plating baths containing simple fluoride, fluoaluminate, fluotitanate or fluoborate catalyst ions.

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