COBALT-CONTAINING ANODIC FILMS ON VALVE METALS

It is shown that when microplasma discharges occur on valve metals in an aqueous electrolyte containing alkali-metal polyphosphate and cobal t(II) phosphate as the base, this gives rise to colored anodic films w hose surface layers can contain as much as 30 wt % of cobalt ions. On an aluminum alloy, the anodic film contains spinel CoAl2O4, Co2O3, and AlPO4. In the case of titanium and niobium alloys, and zirconium, the anodic film typically contains compounds of the Co(II)Co(III)Me(PO4)x MeOy type. For zirconium, the characteristic compound is NaZr2(PO4)2. Some physico-chemical characteristics 'of the anodic structures are de scribed.