| abstract |
This invention includes improvements to a method for forming a chemical conversion coating on ferrous metal substrates, to the chemical solutions used in the coating and to the articles coated thereby. A first oxidation applies a molecular iron/oxygen-enriched intermediate coating, such as a dicarboxylate or phosphate, to a ferrous substrate. A coloring procedure (a second oxidation) follows the first oxidation procedure, using a heated oxidizing solution that reacts with the iron and oxygen enriched intermediate coating to form magnetite (Fe 3 O 4 ). The result is the formation of a brown or black finish. An appropriate rust preventive topcoat may seal the substrate. The finish affords protection, a degree of lubricity to aid assembly, break-in of sliding surfaces, provides anti-galling protection and an adherent base for paint finishes. Improvements to the first oxidation include a broader range of operating conditions, the addition of a hydroxylamine accelerator or a wetting agent, and operation by slurry deposition. Improvements to the second oxidation include a broader range of operating conditions, and the addition of a sequestrant or thio-based accelerator. |