US2457061A - Method for bonding a nickel electrodeposit to a nickel surface - Google Patents

Description

Patented Dec. 21, 1948 METHOD FOR BONDING A NICKEL ELEC- TRODEPOSIT TO A NICKEL SURFACE Ralph Crysler McQuire, Port Colborne, Ontario, Canada, assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application December 18, 1945, Se-

rial No. 635,774. In Canada October 25, 1945 7 Claims.

1 The present invention relates to the treatment of a nickel starting sheet or other nickel surface ,in order to secure adherence thereto of a subsequent nickel electro-plating and to the product obtained by such treatments.

The art has recognized the broad problem of securing satisfactory adherence or bonding between a nickel surface and a nickel electro-plating. For example, U. S. Patent No. 2,001,385 discloses certain attempts which have been made in the art, such as the immersion of a nickel starting sheet in a dilute acid solution without application of electric current. An important feature of the process in U, S. Patent No. 2,001,385 is immersion of the starting sheet in the dilute acid bath for several hours. Another U. S. patent, No. 2,299,054, discloses the anodic treatment of a nickel starting sheet in a sodium cyanide solution to remove oxide film adhering thereto; the process disclosed therein also involves a cathodic treatment in the same cyanide solution prior to the electro-deposition of nickel. I am aware that other processes have been proposed and 'attempted for the cleansing and activation of other metal bases, for example iron, prior to the electrodeposition of a metal plating thereon. However, none of these proposals and attempts has provided a satisfactory solution to the problem of securing an adequate bond between a nickel surface and a nickel electro-plating. This will be readilyrecognized by reference to an article by Pinner, Soderberg and Baker in Modern Electroplating, 1942, page 237, in which the authors point out the difficulty in obtaining a good bond between a ductile nickel coating and a relatively thin brittle coating deposited from a high-sulfate nickel bath.

I have discovered a commercially feasible process for securing adequate bonding between a nickel surface and a nickel plating subsequently applied thereto. My novel process is well adapted to commercial production due to relatively short workin time and great economy in the use of treating reagents.

It is an object of the present invention to provide a process for securing adequate bonding between a nickel surface and a nickel electroplating.

It is within the purview of the present invention to provide an electro-deposited nickel cathode integral with and securely bonded to a nickel starting sheet.

The present invention further aims to secure a high degree of economy by providing for periodic recovery of certain of the reagents used in the bonding process.

The present invention further contemplates the provision of a plurality of coherent bonded layers of electro-deposited nickel upon a metal article.

The scope of the present invention likewise includes the removal of a passive film from a nickel surface prior to the electro-depositi'on of nickel thereon.

Various other objects, advantages and features of the present invention will become apparent from the followin description.

Broadly speaking, the present invention involves the anodic treatment of a nickel surface in an aqueous acid bath containing a significant concentration of cupric ions. The anodic treatment must be carried out within a critical current density range in order to obtain the improved results obtainable with the present invention. After the anodic treatment, the nickel surface is immediately given a water rinse and immersed in a nickel plating tank in which a nickel plating is deposited upon and securely bonded to the anodically treated nickel surface. It will be apparent to those skilled in the art that the nickel surface receiving the anodic treatment may be a nickel starting sheet, a prior nickel plating, a cast or machined nickel surface, or a wrought nickel surface.

I have observed that copper is deposited in sponge form at the cathode during anodic treatment of the nickel. In order to maintain an adequate concentration of cupric ions in the bath, I prefer to interrupt the anodic treatment at intervals and pass compressed air through the bath whereby the sponge copper is redissolved. In this manner, I secure a high degree of economy in operation. Another method that may be employed to maintain the desired concentration of cupric ion in the bath is to add to the bath at controlled rate, a copper solution having a controlled composition; thus in this manner, the cupric ion content of the bath may be maintained within the desired range by replacement of the copper being removed at the cathode with out interruption of the current.

In accordance with the invention, thenickel surface to be treated is immersed as anode in an acid treating bath containing a significant concentration of cupric ions. stated, the nickel surface may be a nickel starting sheet on which nickel is deposited, the resultant cathodic electro-deposit being suitable for subsequent use as an anode in a plating bath. On the other hand, in many cases, it is desirable to deposit a nickel plating upon a previously electrodeposited nickel surface. In such a case, the

As previously expression "nickel surface' would of course, refer to the nickel plating first applied to the base metal and upon which nickel plating. a subsequent nickel plating having good bond characteristics is deposited. In other instances, the nickel surface may consist of machined or cast nickel upon which it is desired to deposit a nickel plating.

The composition of the bath has an important efiect particularly upon the character of the bond between the nickel surface and the subsequently applied nickel plating. To obtain adequate bonding between a nickel electro-plating to a nickel surface, as contemplated by the present invention, it is preferable that the bath contain about 90 to about 200 grams per liter of sulfuric acid. However, as stated hereinafter, satisfactory results can be obtained by employing a bath having a smaller or greater concentration of sulfuric acid. Thus, the lower limit for sulfuric acid concentration in the bath is about grams per liter. A sulfuric acid concentration exceeding 200 grams per liter may be employed. However, when sulfuric acid concentrations exceeding. 200 grams per liter are employed, it is necessary to remove nickel from the bath before the acid is consumed.

Thus, it is preferred to employ a bath having a sulfuric acid concentration of about 90 to about 200 grams per liter.

In accordance with the invention, about 0.5 to about grams per liter of cupric ion in the form of any water soluble source of copper ion is added to any one of the acid baths previously described. However, the preferred range of cupric ion concentration is from about 2 to about 10 grams per liter. The presence of the requisite quantity of cupric ion is essential if proper bonding of the nickel surface to the subsequently applied nicked electro-deposlt is to be obtained. In the absence of cupric ion in the bath, a dark, thin sludge is formed upon the nickel surface and satisfactory adherence .of a subsequent nickel plating to the nickel surface is not obtained.

The nickel surface to be treated is immersed as anode in a treating bath having the aforedescribed composition. It is essential to maintain a current density not exceeding about 25 amperes per square foot, if the subsequent nickel plating is to be properly bonded to the nickel surface. Preferably, a current density range of about 10 to 25 amperes per square foot should be employed. If the critical upper limit of anodic current density is exceeded, a glossy surface is produced having extremely poor bonding properties. That is to say, if. a nickel plating is deposited upon a nickel surface which has been treated in one of the foregoing all-sulfate acid baths containing cupric ion at a current density greater than about 25 amperes per square foot, the electro-deposited nickel has a pronounced tendency to separate from the treated nickel surface upon shearing. A current density below about 10 amperes per square foot may be used and satisfactory bonding properties of the nickel surface obtained, but it is preferred that at least 10 amperes per square foot be employed as a lower current density prolongsthe time of treatment and is, accordingly, uneconomical.

In view of the relatively close position of iron and nickel in the electromotive series, and their position in the periodic table, it would generally be expected that the present invention would also be applicable to the treatment of iron surfaces. However, I have determined that iron surfaces cannot be satisfactorily treated at current densities below about 25 amperes per square foot, as

required by the present invention, whereas nickel surfaces are satisfactorily treated at such current densities. difference in the anodic behaviour of iron and nickel which is not apparent from the relative position of these two elements in the electromotive series.

For best results, the treatment bath should be maintained at a temperature of about 60 to about 100 F. However, the temperature employed is not critical, and accordingly, higher or lower temperatures than 100 F. and 60 F. respectively may be employed.

The voltages required in the operation of the process vary with electrode spacing and current density. Preferably, the anode to cathode spacing is about 3 inches and a tank voltage of about 2 to about 8 volts is required. Agitation of the bath has little or no effect upon the operation of the process and, accordingly, is preferably not used in order to reduce the cost of the treatment.

The nickel surface is anodically treated for at least 2 minutes; an anodic treatment of about 5 minutes has been found to produce the improved results contemplated by the present invention. A longer period of treatment than 5 minutes may be employed, but entirely satisfactory results are obtained with a time of treatment of about 2 to about 5 minutes. The treated nickel surface is about 60 minutes after removal of the treated surface from the rinse tank. In the event it is not desired to apply the nickel plating within this period, the nickel surface should be kept immersed in a bath which will prevent the formation of a passive film on the nickel surface. Thus the nickel surface may be immersed in a bath of clear water until plating is begun. Otherwise satisfactory bonding of the treated nickel surface to the electro-deposit of nickel is not obtained due to formation of a passive film on the treated nickel surface.

During the operation of the process embodied by the present invention for anodic treatment of nickel surfaces, copper deposits in sponge form at the cathode, which cathode may be formed from nickel or any other suitable metal. In addition, a certain amount of nickel is dissolved from the nickel surface. Accordingly. the nickel content of the solution rises and the copper content decreases as the operation proceeds. When sufficient copper is deposited to lower the concentration of cupric ions in the bath to about 2 grams per liter, the anodic treatments are discontinued and compressed air is blown through the solution with the result that the copper is redissolved from the cathode and once more enters the solution thereby maintaining a minimum concentration of about 2 grams per liter of cupric ion in the bath at all times. A nickel concentration of as high as 60 grams per liter does not interfere with the operation of my novel anodic treatment bath. However, when a nickel concentration of about 50 grams per liter is attained, I prefer to treat the solution in a manner suitable for nickel recovery. Thus, great economy in the use of copper salts and recovery of nickel is obtained.

The following illustrative examples are provided These results indicate a marked in order that one skilled in the art may have a better understanding of practicing the present invention.

Example I A nickel starting sheet was immersed as anode in a bath containing about 100 grams per liter of sulfuric acid, and about 5 grams per liter of cupric ion in the form of copper sulfate. Anodic treatment was carried out for about 5 minutes at a temperature of about 80 F. and at a current density of about 15 amperes per square foot. After the anodic treatment was completed, the starting sheet was removed from the bath and given a water rinse. From the rinse tank, the starting sheet was immediately transferred to a nickel plating tank and nickel was plated thereon from a conventional Watts type bath until a deposit about 0.25 inch thick was obtained on each side of the startin sheet, giving a total deposit of 0.5 inch. The cathodic electro-deposit was removed from the plating tank and the degree of bonding between the nickel starting sheet and the nickel plate was tested. An entirely satisfactory degree of adhesion was obtained between the nickel starting sheet and the nickel electro-deposit, as no evidence of separation at the bond was observed when the following test was applied; a strip six inches long and one inch wide was cut from the cathode comprising the nickel starting sheet on both sides of which a thick nickel electro-plating of 0.25 inch was deposited. The edges of the cut strip were ground and etched to reveal the bond. The strip was then given a sharp right angle bend and the bond examined microscopically at a magnification of 100x. Adhesion was considered satisfactory if no separation of the nickel electro-plating from the nickel surface occurred. In cases wherein faulty adhesion results due to improper treatment of the nickel surface, the defect is not always noticeable after the grinding and etching operation, but evidence of separation at the bond is observed after application of the stress due to bending.

Example II An iron article having a nickel plating thereon was anodically treated in a bath containing about 100 grams per liter of sulfuric acid and about 5 grams per liter of cupric ion in the form of cupric sulphate. The anodic treatment was continued for about 5 minutes employing a temperature of about 80 F. and a current density of about amperes per square foot. Upon completion of this period of anodic treatment, the nickel plated article was removed from the bath and given a water rinse after which it was immersed in a Watts type plating solution as cathode and a second deposit of nickel plated thereon. An entirely satisfactory adherence of the two nickel platings was observed and the second nickel plating had substantially no tendency to strip or peel from the first nickel plating.

Although various concentration ranges for the reagents used in my novel process have been set forth in the foregoing description, it is to be understood that the invention is not to be limited to these specific ranges, particularly with regard to sulfuric acid. Thus, for example, the lower limit of sulfuric acid concentration set forth is about 10 grams per liter. It will be appreciated that the acid concentration of the bath decreases as the bath is used due to hydrogen ion discharge at the cathode. Accordingly, the initial concentration of sulfuric acid should be at least about 90 grams per liter to maintain sufficient acidity until the nickel ion concentration reaches about 50 grams per liter at which point it is preferred that the bath be treated for nickel recovery. However, a lower initial concentration of acid may be used if the bath is to be treated for nickel recovery before a nickel ion concentration of about 50 grams per liter is attained. Although the upper limit of acid concentration was chosen for economic reasons, greater concentration can be employed without departing from the spirit and scope of the present invention.

Although the present invention has been described in conjunction with certain preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such variations and modifications are to be considered to be within the purview of the present invention and the scope of the appended claims.

I claim:

1. A method for obtaining improved bonding of anickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an aqueous acid bath consisting of about 10 to about 200 grams per liter of sulfuric acid, copper sulfate in an amount to provide about 0.5 to about 30 grams per liter of cupric ion in said bath and the balance essentially water at current densities of about 10 to about 25 amperes per square foot; and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit to said nickel surface of said article is obtained.

2. A method for obtaining improved bonding of a nickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an aqueous acid bath consisting of about 10 to about 200 grams per liter of sulfuric acid, copper sulfate in an amount to provide about 0.5 to about 30 grams per liter of cupric ion in said bath and the balance essentially water at current densities of about 10 to about 25 amperes per square foot; maintaining said article with said anodically treated nickel surface in a water bath to retain said nickel surface of said article in an active condition; and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit to said nickel surface of said article is obtained.

3. A method for obtaining improved bonding of a nickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an aqueous acid bath consisting of about to about 200 grams per liter of sulfuric acid, copper sulfate in an. amount to provide about 2 to about 10 grams per liter of cupric ion in said bath and the balance essentially water at current densities of about 10 to about 25 amperes per square foot; removing said article having said nickel surface from said bath; and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electrodeposit to said nickel surface of said article is obtained.

4. A method for obtaining improved bonding of a nickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an aqueous acidbath consisting of about 90 to about 200 grams per liter of sulfuric acid, copper sulfate in an amount to provide about 2 to about grams per liter of cupric ion in said bath and the balance essentially water at current densities of about 10 to about 25 amperesper square foot; removing said article having said nickel surface from said bath; rinsing said anodically treated nickel surface of said article; maintaining said article with said anodically treated nickel surface in a water bath to retain said nickel surface of said article in an active condition; immersing said article having said nickel surface in a nickel electro-plating bath and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit to said nickel sur face of said article is obtained. 7

5. A method for obtaining improved bonding of a nickel electro-deposit to an articlehaving a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an' aqueous acid bath consisting of about 90 to about 200 grams per liter of sulfuric acid, copper sulfate in an amount to provide about 0.5 to about 30 grams per liter of cupric ion in said bath and the balance essentially water at current densities of about 10 to about 25 amperes per square foot; removing said article having said anodically treated nickel surface from said bath; rinsing said anodically treated nickel surface of said article; and electrodepositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit' to said nickel surface of said article is obtained.

. 6. A method for obtaining improved bonding of a nickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 2 to about 5 minutes in an aqueous acid bath balance essentially water at current densities of about 10 to about 25 amperes per square foot; removing said article having said anodically treated nickel surface from said bath; rinsing said anodically treated nickel surface of said article; immersing said article having said anodically treated nickel surface in a nickel electro-plating bath and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit to said nickel surface of said. article is obtained.

'7. A method for obtaining improved bonding of a nickel electro-deposit to an article having a nickel surface which comprises anodically treating said article having said nickel surface for about 5 minutes in an aqueous acid bath consisting of about grams per liter of sulfuric acid, copper sulfate in an amount to provide about 5 grams per liter of cuprlc ion in said bath and the balance essentially water at a current density of about 15 amperes per square foot;

removing said article having said anodically 7 treated nickel surface from said bath; rinsing said anodically treated nickel surface of said article; immersing said article having said anodically treated nickel surface in a nickel electro-plating bath and electro-depositing nickel on said anodically treated nickel surface of said article whereby an improved bonding of a nickel electro-deposit to said nickel surface of said article is obtained.

RALPH CRYSLER MCQU'IRE..

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 694,699 Ulke Mar. 4, 1902 1,417,896 Fletcher May 30, 1922 1,793,936 Knauss Feb. 24, 1931 2,001,385 Gronningsaeter May 14, 1935 OTHER REFERENCES Iron Age of Sept. 26, 1940, PD. 19, 20. Iron Age of Oct. 3, 1940, pp. 32, 33.