Photographic processing devices such as stainless steel racks and tanks are cleaned to remove contaminants such as silver by contacting the devices with a cleaning solution comprising water, a mineral acid such as nitric acid, a soluble cerium (IV) salt such as ceric ammonium nitrate, and acetic acid. The cleaning solutions have a pH no greater than 1. The acetic acid inhibits the formation of a brown stain on in the stainless steel.
The present invention is directed to compositions for removing silver soil from the surface of objects. These compositions contain a reducing agent, and an alkaline source, and may optionally contain various other components including a chelating agent, cleaning agent, filler, an anti-corrosion agent, a defoaming agent, an odorant, a dye, an antioxidant, or a bleaching agent. Methods of using the compositions are also disclosed, wherein the object to be cleaned is contacted with the composition and the object is then washed with an aqueous solution.
A metal surface which has been cleaned using an alkaline based solution is treated with an acidic solution which contains rear earth ions to remove any smut which may have been produced during the alkaline cleaning. A coating is formed on the cleaned surface using a different acidic solution containing rare earth cations which have multiple valence states. When the surface is reacted with coating solution, an increase in the pH at the metal surface indirectly results in precipitation of a rare earth metal such as cerium onto the surface. Alternatively, after the removal of the smut, the surface may be coated using a painting technique.
A process for forming a conversion coating on the surface of a metal, including: contacting the metal with an acidic solution containing an oxidant in order to initiate growth of a metal oxide cell structure on the metal surface; contacting the metal with water for a period of time sufficient to thicken the oxide and form a metal oxide containing layer of a desired thickness; and treating the metal with one or more rare earth elements in order to impregnate and substantially seal the metal oxide.
A process and an aqueous, acidic solution for forming a rare earth element containing coating on the surface of a metal, said solution including effective quantities of: (a) one or more rare earth element containing species including at least one rare earth element capable of having more than one higher valence state, as herein defined; and (b) one or more additives selected from the groups including: i) aqueous metal complexes including at least one peroxo ligand; and ii) metal salts or aqueous metal complexes of a conjugate base of an acid in which the metals are selected from Transition Elements and Group IVA elements of the Periodic Table as herein defined.
An aqueous acidic solution for forming a rare earth element containing conversion coating on the surface of a metal, said solution being chromate-free and including effective quantities of at least one rare earth element (as herein defined) containing species, an oxidant and at least one accelerator, comprising a metal selected from Groups VA and VIA of the Periodic Table.
