Colouring anodically oxidised aluminium - after electrochemical colouring, by immersion in silicon- or phosphorus heteropolyacids of molybdenum or tungsten

摘要

Combination-colouring of Al or Al alloy articles, following anodic oxidn. and electrolytic colouring in an acid soln. of a metal salt with AC 1-50v for 0.1-15min., is effected by immersing the article in an aq. soln. of a heteropolyacid of Si or P with Mo or W, whereby, without supplying current, an electrochemical reaction sets in with the previously electrolytically incorporated metal ions which are more electronegative than Cu in the electromotive series. Method is used for forming decorative and/or wear-and weather-resistant coatings for internal and external use. Durable gray shades are obtd. Heteropolyacid can be prepd. in situ by reacting Na molybdate or tungstate with Na silicate or phosphate and HCl in an aq. soln.