| abstract |
The invention provides a process for cleaning a metal surface including the steps of: (a) contacting the metal surface with an alkaline cleaning solution in order to remove contaminants such as dirt and grease; and (b) contacting said metal surface with an acidic, rare earth ion containing cleaning solution thereby to remove smut formed on said metal surface by step (a). The process may be used to prepare a metal surface for a subsequent coating process which includes the further step of: contacting the metal surface with an aqueous, acidic, rare earth ion containing coating solution including rare earth cations capable of having more than one valence state, resulting in an increase of the pH of the coating solution in the region of the metal surface to a value sufficient to precipitate one or more compounds of the rare earth element, thereby to cause the compound of the rare earth element to precipitate in a coating on the metal surface. The present invention also provides an acidic, rare earth ion containing aqueous cleaning solution for use in step (b) of the process of the invention, said solution including ions of one or more rare earth elements in an amount effective to remove smut from a metal surface previously contacted with an alkaline cleaning solution. The invention also extends to a metal surface, treated by the process of the invention. |