Chemistry: electrical and wave energy – Processes and products
Patent
1988-10-18
1990-10-30
Tufariello, T. M.
Chemistry: electrical and wave energy
Processes and products
204 585, C25D 536, C25D 344
Patent
active
049666606
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a process enabling improvement of the adhesion of electrodeposits and purity of coatings in a process for the electrodeposition of aluminum on a metal sheet by use of a molten salt bath.
BACKGROUND OF THE ART
Electroplating of aluminum can be carried out with difficulty using a plating bath of an aqueous solution type, since aluminum has a large affinity for oxygen and shows a lower potential than hydrogen. For this reason, the electroplating of aluminum has hitherto been carried out using a plating bath of a non-aqueous solution type, in particular, a plating bath of an organic solvent type.
In regard to the plating bath of this organic solvent type, available as a plating bath that secures safety in operations is a molten salt bath comprised of an aluminum halide and an N-alkylpyridinium halide. It includes, for example, a molten salt bath comprised of an aluminum halide and an N-ethylpyridinium halide or a bath obtained by mixing an organic solvent in this bath (U.S. Pat. Nos. 2,446,331; 2,446,349; and 2,446,350). and a molten salt bath comprised of an aluminum halide and an N-butylpyridinium halide, or a bath obtained by mixing an organic solvent, capable of obtaining products having better appearance than those obtained by using the above plating baths even if the plating is carried out in a high current density (Japanese Unexamined Patent Publications No. 70592/1987 and No. 70593/1987, or U.S. Patent application No. 092,517/87).
This molten salt bath, though sometimes bringing about coatings partly having a problem in appearance, comes to a liquid near room temperature and makes it possible to carry out electroplating in the temperature range of approximately from 0.degree. to 150.degree. C. when a compound comprising a halogen atom selected from Cl, Br or I is used as the aluminum halide and a compound whose N-substituted alkyl group has 1 to 5 carbon atoms is used as the N-alkylpyridinium halide in amounts of from 40 to 80 mol % for the aluminum halide and from 20 to 60 mol % for the N-alkylpyridinium halide.
U.S. Pat. No. 2,446,349 discloses that the above molten salt bath dislikes water and oxygen, and presence of these results in oxidation of the bath to lower the quality of plating, thus requiring to bring its atmosphere into a dry and oxygen-free atmosphere. For this reason, also when a metal strip is continuously plated, it is necessary to take care that the water adhered on the strip in the course of a pretreatment of the plating may not be carried in the bath.
Since, however, when oxides exist on the strip, the oxides can not be removed unless an inorganic acid is used, the pretreatment must be carried out using a treatment solution of an aqueous solution type. This pretreatment is commonly carried out through the steps of degreasing, washing with water, pickling using an inorganic acid, washing with water, and, as occasion demands, strike plating, but drying is required before plating to prevent the water from being carried in the bath. This drying, because of an activated state on the surface of the strip, must be carried out in the dry and oxygen-free atmosphere before a good deposit adhesion can be obtained.
A generally available method for giving the dry and oxygen-free atmosphere is a method in which nitrogen gas or argon gas is used. However, this method, though not requiring to use gas in a large quantity in carrying out the plating in an experimental scale since there is less evaporation of water from the strip, requires to use gas in a large quantity in carrying out the continuous plating since there occurs the evaporation of water in a large quantity. Hence, in the case of the continuous plating, a step for carrying out drying in an atmosphere has hitherto been provided between the washing after pickling and the plating in a bath. This method, however, have had the problem that because of the activated state on the surface of the strip an oxide coating is formed thereon even if the drying is carried out in a short time, resulting in a
REFERENCES:
patent: 2446331 (1948-08-01), Hurley
patent: 2446349 (1948-08-01), Wier et al.
patent: 2446350 (1948-08-01), Wier
patent: 3136709 (1964-06-01), Smith
patent: 4101386 (1978-07-01), Dotzer
patent: 4747916 (1988-05-01), Kato et al.
Kikuko Akimoto
Kumiko Mori
Ryozo Akama
Setsuko Takahashi
Nisshin Steel Co. Ltd.
Tufariello T. M.
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