Method of increasing corrosion resistance of metals and alloys by treatment with rare earth elements
US6068711A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 27, 1997 |
| Grant date | May 30, 2000 |
| Priority date | — |
| Expiry date | May 27, 2017 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC23C22/68
- WIPO fieldSurface technology, coating
- WIPO sectorChemistry
Abstract
There is provided a method for treating the surface of metals such as nickel based or high alloy steels, austenitic and ferritic stainless steels, copper and aluminum alloys to increase their corrosion resistance by modification of the metal surfaces to inhibit cathodic corrosion processes. In a single step treatment process the metals are immersed into a heated aqueous composition containing a rare earth salt substantially free of any halide compound. Increased corrosion resistance is obtained using nitrates of yttrium, gadolinium, cerium, europium, terbium, samarium, neodymium, praseodymium, lanthanum, holmium, ytterbium, dysprosium, and erbium nitrates. The rare earth salt is present in the range from about 2% by weight to saturation of the solution. The composition includes a pH-modifying substance such as nitric acid to adjust the pH in the range 0.5 to about 6.5 to attack the surface to remove oxides facilitating deposition of the rare earth. For aluminum alloys the pH is maintained between 4.5 to 6.5, for nickel based alloys and austenitic stainless steels the pH is maintained between 0.5 to 3.5 and between pH 2.0 to 4.5 for ferritic stainless steels. The surface can also be…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.