METHOD OF TREATMENT OF A SURFACE OF AN ARTICLE

摘要

A method of treatment of a surface of an article, comprises the step of bringing the surface into contact with a gas which is substantially free of water and contains a gaseous metal halide. The metal halide has the formula MXn or M2X2n-2 where M is a metal, each X is a halogen and n is the highest valence state of M in combination with X. Oxygen or a source of oxygen is present at the contact zone and the temperature of at least one of the gas and the surface is such that there is formed on the surface a layer which is oxide of M or which converts into oxide of M on subsequent heating. Colouring effects can be obtained at the treated surface, or the oxide layer improves subsequent processing, such as coating, phosphatizing or chromatizing. TiCl4 and ZrCl4 are examples of the metal halide.