GB1134620A - Method of producing a platinum group metal or alloy electrode - Google Patents

Abstract

1,134,620. Electro-depositing or chemical plating platinum group metals or alloys. AJINOMOTO CO. Inc. April 28, 1967 [May 19, 1966], No. 19810/67. Headings C7B and C7F. A platinum group metal electrode suitable as an anode in alkali metal chloride electrolysis in a mercury cell is produced by (a) forming on a clean surface of a metal-containing base such as Ti, Zr or magnetic iron oxide an alloy layer comprising a Pt-group metal or alloy, i.e. Pt, Rh, Ir, Pd, Os and/or Ru, and an alloyable non-Ptgroup metal or alloy, e.g. Cu, Ni, Au, Fe, Ag, Pb, Mn and/or Co, (b) dissolving the non-Ptgroup metal or alloy from the alloy layer and (c) plating the resulting Pt-group metal or alloy coated base with the same or a different Pt-group metal or alloy. Step (a) may be effected by electro-deposition using a plating bath containing ions of the required Pt-group and non-Pt-group metals; initially the base may be plated with the Pt-group metal. A Pt electro-plating bath is specified as comprising 5 g/l H 2 Pt Cl 6 .6H 2 O, 45 g/l NH 4 H 2 PO 4 , 240 g/l (NH 4 ) 2 HPO 4 , with or without 0À4 g/l Cu Cl 2 (for Pt-Cu plating), the cathode current density being 0À3 A/dm<SP>2</SP> . Alternatively, the base surface may be electro-plated with the Pt-group metal, followed by plating with the non-Pt-group metal, heating e. g. at 700‹ C. in an inert gas to diffuse the layers and quenching. Conventional electro-plating baths are specified for Cu, Ni, Ag, Au and Fe. Step (b) may be effected chemically, e. g. by immersing the coated base in an acid such as HNOs, HCl or H 2 SO 4 or alkali such as alkali metal hydroxide, or electrochemically, e. g. by electrolysing an alkali metal chloride of concentration 300 g/l using the coated base as anode and mercury as cathode with an anode current density of 100 A/dm<SP>2</SP>. Step (c) may be effected by electro-plating as in (a) for Pt-group metal, or chemical plating such as by chemical reduction or enamelling, e.g. using a solution comprising 2À6g H 2 Pt Cl 6 À6H 2 O or 0À26g Rh Cl 3 .3H 2 O or 0À18g Ir Cl 3 .3H 2 O, 0À04 ml each of 35% HCl and 25% H 3 BO 4 solution, 20 ml ethanol, 10 ml lavender oil and 8 ml turpentine oil, and heating; the latter may also be used for step (a) and may additionally contain 0À21g Cu Cl 2 (0À1 Cu) for Pt-Cu enamel or 0À1g NiCl 2 .6H 2 O for Pt-Ni enamel. The base may be initially cleaned with boiling HCl, or (KCl+NaCl) fused salt followed by 50% H 3 PO 4 .