Salt bath composition based on alkali nitrates for oxidizing fer

Details Salt bath composition based on alkali nitrates for oxidizing fer Salt bath composition based on alkali nitrates for oxidizing fer

1995-01-20

1996-05-07

Silverberg, Sam

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

C23C 204

Patent

active

055142265

ABSTRACT:
A salt bath composition is adapted to form a layer of magnetite Fe.sub.3 O.sub.4 on the surface of ferrous metal parts, including nitrided ferrous metal parts, to protect the underlying iron against corrosion. This layer is impermeable and of good crystalline order, as indicated by a deep black color and a corrosion potential greater than 1 000 mV. The composition includes at least nitrate anions and sodium and lithium cations, the latter in a proportion by weight relative to the bath between 0.1% and 5%, preferably between 0.5% and 1.75%. Preferred compositions contain sodium, potassium and lithium cations and nitrate, carbonate and hydroxyl anions, within the following percentage ranges:

REFERENCES:
patent: 2639244 (1953-05-01), Vordahl et al.
patent: 3912547 (1975-10-01), Gaucher et al.
patent: 4006043 (1977-02-01), Gaucher et al.
patent: 4292094 (1981-09-01), Kunst et al.
patent: 4448611 (1984-05-01), Grellet et al.
Penjagina, "Passivierung von Eisen und Nickel in geschmolzenen Carbonaten", erkstoffe und Korrosion, Nov. 1, 1972, vol. 23, No. 11, p. 1046.
Akihiko Satomi, "Surface treatment of iron member for increasing corrosion and wear resistance", Patent Abstracts of Japan, Dec. 21, 1982, vol. 6, No. 261.

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