| abstract |
Valve metals eg Al, Ti, Ta, Zr, Nb and valve metal based alloys are anodized efficiently in a substantially non-aqueous formation electrolyte comprising a polar aprotic solvent and an electrolyte-soluble source of phosphate ions to provide high quality dielectric oxide coatings. Titanium and titanium based alloys may be anodised at a current density of not greater than 2 milliamperes/cm<2>. Preferred formation electrolytes for use in this process contain phosphoric acid and an acid-ionizing amine eg pyridine or urea or tetramethyl urea and have resistivities in the range of 1,000-30,000 ohms per cubic centimeter and breakdown voltages in excess of 200 volts. Suitable polar aprotic solvents include dimethyl formamide, dimethylsulfoxide, N-methyl-2-pyrrolidone and 4-butyrolacetone. |