Chromium-free or low-chromium metal surface passivation
AssigneeRichardson Chemical Company
InventorJoseph L. Greene
Life of this patent
Estimating the term…
Abstract
Substrates, especially those having plated metal surfaces, and subjected to passivation treatments in baths that incorporate one or more film-forming agents at least one of which does not require chromium and includes anions or cations of elements other than chromium. Typically, the anions or cations are introduced as bath-soluble salts which react with the plated surface of the substrate to form an adherent, coherent passivation surface film. Also present within these baths are a source of hydrogen ions and a bath-soluble carboxylic acid or derivative activator for enhancing the rate of the passivation reaction. Articles passivated in baths incorporating these film-forming agents have a hydrophobic surface that exhibits corrosion resistance and that typically has a bright finish.
Claims31
An acidic aqueous bath for the passivation treatment of a substrate having a metal surface, comprising:
- an organic activating agent, said organic activating agent being a carboxylic acid having between about 2 and about 12 carbon atoms and being selected from the group consisting of polyhydroxy carboxylic acids, polycarboxylic acids, bath-soluble derivatives thereof and combinations thereof, in combination with one or more bath-soluble film-forming agents, at least one of said agents being a chromium-free film-forming agent selected from the group consisting of fluoride salts, oxalate salts, malonate salts, succinate salts, and combinations thereof, said chromium-free film-forming agent including a nonchromium film-forming element that forms a thin, adherent and coherent hydrophobic passivation coating onto a substrate having a metal surface, said film-forming element being selected from the group consisting of aluminum, silicon, titanium, vanadium, iron, cobalt, molybdenum, cerium, and combinations thereof, said chromium-free film-forming agent being a bath-soluble fluoride complex including at least one of said non-chromium film-forming elements, and said organic activating agent, whether added as said film-forming agent, as said organic activating agent, or as any other bath additive, is present at a concentration up to about 0.3 weight percent, expressed as oxalic acid, per volume, based on the total bath volume, said bath including a strong acid and having an operative pH range between values high enough to avoid chemical polishing and etching of the metal surface and low enough to maintain a desired rate of passivation reaction.
In a bath for the passivation treatment of metal substrates, which bath includes a passivation composition having an activating agent and one or more film-forming agents including at least one film-forming element that reacts, in an acidic aqueous environment of the bath, with the metal substrate, the improvement comprising said passivation composition being a combination of a bath-soluble organic activating agent having between about 2 and about 12 carbon atoms and being selected from the group consisting of carboxylic acids, salts thereof, esters thereof, oxalate complex salts, malonate complex salts, succinate complex salts, and combinations thereof, together with a chromium-free film-forming agent selected from the group consisting of fluoride salts, oxalate salts, malonate salts, succinate salts, and combinations thereof, said chromium-free film-forming agent including a film-forming element selected from the group consisting of aluminum, silicon, titanium, vanadium, iron, cobalt, molybdenum, cerium and combinations thereof, said chromium-free film-forming agent being a bath-soluble fluoride complex including at least one of said film-forming elements, and said organic activating agent, whether added to the bath as said film-forming agent, as said organic activating agent, or as any other bath additive, is present at a concentration up to about 0.3 weight per cent, expressed as oxalic acid, per volume, based on the total bath volume, said bath including a strong acid and having an operative pH range between values high enough to avoid chemical polishing and etching of the metal substrate and low enough to maintain a desired rate of passivation reaction.
Dependencies are inferred from the claim text.