US3577330A - Process for producing electrorefined nickel having controlled size - Google Patents

Abstract

AN IMPROVED PROCESS FOR PRODUCING ELECTROREFINED NICKEL CATHODE MATERIAL OF CONTROLLED DIMENSION AND SUBSTANTIAL THICKNESS WHEREIN THE NICKEL IS DEPOSITED UPON A SUBSTANTIALLY FLAT, PERMANENT METAL CATHODE MANDREL SUCH AS STAINLESS STEEL, AND HAVING CONDUCTIVE ISLANDS OF CONTROLLED SIZE DEFINED ON THE SURFACE THEREOF, E.G., BY THE USE OF INTERCONNECTING LINES OF NONCONDUCTIVE RESIST, FROM A NICKEL ELECTROEFINING CATHOLYTE CONTAINING CONTROLLED AMOUNTS OF SULFUR DIOXIDE AND A LEVELING AGENT TO FACILITATE ADHERENCE OF THE ELECTRODEPOSITED NICKEL UPON THE MANDREL SURFACE BY CONTROLLING THE STRESS LEVEL THEREIN TO A TENSILE VALUE NOT EXCEEDING ABOUT 6,000 POUNDS PER SQUARE INCH AND THEREAFTER STRIPPING THE NICKEL DEPOSIT FROM THE MANDREL TO RECOVER ELECTRODEPOSITED NICKEL IN SIZES CORRESPONDING TO THE ORIGINAL AREAS OF THE CONDUCTIVE ISLANDS AND TO RECOVER THE MANDREL IN A CONDITION SUITABLE FOR FURTHER PLATING.

Description

United States Patent 3,577,330 PROCESS FOR PRODUCING ELECTROREFINED NICKEL HAVING CONTROLLED SIZE Burton Bower Knapp, Allendale, N..l., and Leander Ernest Cupp, Port Colborne, Ontario, Canada, assignors to The International Nickel Company, Inc., New York, N.Y. No Drawing. Continuation-impart of application Ser. No. 338,309, Jan. 17, 1964. This application Nov. 17, 1967, Ser. No. 683,801

Int. Cl. C2211 1/14; C23b 7/08 U.S. Cl. 204-112 7 Claims ABSTRACT OF THE DISCLOSURE An improved process for producing electrorefined nickel cathode material of controlled dimension and substantial thickness wherein the nickel is deposited upon a substantially flat, permanent metal cathode mandrel such as stainless steel, and having conductive islands of controlled size defined on the surface thereof, e.g., by the use of interconnecting lines of nonconductive resist, from a nickel electrorefining catholyte containing controlled amounts of sulfur dioxide and a levelling agent to facilitate adherence of the electrodeposited nickel upon the mandrel surface by controlling the stress level therein to a tensile value not exceeding about 6,000 pounds per square inch and thereafter stripping the nickel deposit from the mandrel to recover electrodeposited nickel in sizes corresponding to the original areas of the conductive islands and to recover the mandrel in a condition suitable for further plating.

The present application is a continuation-in-part application of a copending U.S. application Ser. No. 338,- 309, filed J an. 17, 1964, now abandoned.

The present invention relates to the production of electrolytic nickel and, more particularly, to a process for producing electrolytic nickel in subdivided form.

It is well known that the standard commercial high purity nickel (99.4+% nickel) is usually provided in the form of cathode sheets from an electrorefining operation. These sheets are usually about 28 inches by 38 inches in major dimension and are about inch thick. In many industrial operations, these cathode sheets can be employed directly. However, in many other industrial operations, nickel must be provided in smaller sizes because the standard size cannot conveniently be used. The standard cathode sheets can be sheared to provide the smaller sizes required in operations such as induction furnace melting of nickel-containing alloys, nickel stock for electroplating using titanium baskets to hold the nickel stock, etc. However, it is desirable to provide electrolytic nickel in smaller sizes directly from the electrorefining operation while at the same time maintaining or improving the efficiency of the nickel electrorefining operation, and, thus, to eliminate the cost factors involved in shearing the standard cathode nickel sheets. The production of electrolytic nickel is well known and is described, for example, in the Renzoni U.S. Pat. No. 2,394,874.

It has now been discovered that through the use of a permanent cathode mandrel of special design, electrolytic nickel pieces of any desired size can be produced directly in the electrorefining operation while maintaining the efficiency of the operation at a high level.

It is an object of the present invention to provide a process for producing electrolytic nickel of controlled small size.

Another object of the invention is to provide a special permanent mandrel for use as cathode in a nickel electrorefining cell.

The invention also contemplates providing a process for producing electrolytic nickel having :a low level of internal stress.

Other objects and advantages of the invention will become apparent from the following description.

Generally speaking, the present invention contemplates a process for producing electrolytic nickel in subdivided form which comprises immersing in an electrorefining bath a permanent, i.e., reusable, metal cathode mandrel having conductive islands defined on the surface thereof, electrodepositing nickel upon said cathode under conditions of low stress to provide electrolytic nickel deposits having substantial thickness upon said conductive islands, removing the plated cathode mandrel from said bath and removing the deposited nickel from said mandrel, so as to recover the mandrel for reuse.

The conductive islands are defined on the surface of the permanent metal cathode mandrel by means of interconnecting areas of nonconductive material. The mandrel may be provided in a number of ways. Thus, interconnecting lines of nonconductive or resist material at least as wide as the thickness of metal to be deposited upon the mandrel (i.e., generally about /s to 4 inch) may be applied to the surface thereof to define isolated conductive areas, or islands, of the desired size and shape. The nonconductive resist material may be in the form of an adherent paint, varnish, lacquer, tape, etc., which will be retained on the mandrel surface and will be compatible with the electrorefining bath. Materials having a plastic or rubber base, e.g., epoxy resin,s acrylics, polyethylenes, etc., are examples of such resists. The conductive cathode metal mandrel may be, for example, pure nickel or a nickel-chromium or nickel-chromium-iron alloy containing about 8% to 30% chromium, at least 8% nickel and up to about 74% iron, such as the well-known 18-8 stainless steel. Electroformed nickel is also satisfactory as the mandrel metal. In order that the mandrel will be sufiiciently rugged to withstand repeated reuse, it is usually about 0.020 inch or about 0.040 inch up to about or about /8 inch thick. The mandrel may be sufliciently thin, e.g., up to about inch thick, to be readily flexed for stripping the nickel deposit therefrom or may be considerably thicker and stiffer, e.g., about inch thick. A pattern of interconnecting lines which are depressed with respect to a major face of the mandrel may be embossed in the thinner mandrel sheets and the embossed lines may be filled or coated with resist. In such an instance, the mandrel may be made of two embossed sheets placed back-to-back so that plating may be conducted simultaneously upon both sides of the mandrel. Such embossed lines also perform the function of stifiening the thinner mandrel. It is advantageous to electroform mandrels containing such depressed interconnecting lines in a metal such as nickel. It is an advantage from the operating standpoint to employ the thicker and heavier mandrel sheets in electrorefining practice since good contact to the cathode bus bar is thereby achieved and the problem of warping and shorting in the plating tank is avoided. In order to promote adherence of the electrodeposited nickel to the mandrel, the mandrel surface advantageously has a surface finish in the range of about 10 to about microinches. Such a surface finish can be provided by the mill or can be obtained by means such as scratch brushing, light sand blasting, etc.

In carrying the invention into practice, it is preferred to deposit electronickel in a low-stress condition so that satisfactory adherence of the electrolytic nickel upon the exposed cathode areas will be achieved. Thus, it is advantageous that the tensile stress level in the deposit be not higher than about 6,000 pounds per square inch (p.s.i.) and between about 8,000 psi. compressive and about 6,000 p.s.i. tensile as measured by the Brenner-Senderoff contractometer. When stress is controlled to this low level, cathode nickel segments as large as about 2 inches by 2 inches can be produced without encountering separation of the cathodenickel segments from the cathode sheet during the plating operation. It will be appreciated that the size of the conductive cathode areas, or islands, which may successfully be employed without encountering undesirable separation of the electrolytic nickel segments deposited thereon, varies in relation to the stress level which is maintained in the deposit. Thus, when lower tensile stress levels than 6,000 p.s.i. are maintained in the deposit, cathode nickel segments inch to inch in thickness and larger than 2 inches by 2 inches can be produced successfully, i.e., without encountering separation of the deposit from the mandrel during the plating operation. A tendency for lifting of nickel electrodeposits having a rectangular shape at corners of conductive islands has been observed. Accordingly, it is advantageous to employ conductive islands having a circular or elliptical shape.

In order to obtain the required low stress level in the deposit, a concentration of about 0.005 to about 0.02, e.g., about 0.009 to about 0.011, gram per liter (g.p.l.) of sulfur dioxide and about 0.01 to about 0.1 g.p.l. of a levelling agent, e.g., hydracarylonitrile, are maintained in the electrorefining electrolyte. A preferred electrolyte also contains about 40 to about 70 g.p.l. of nickel, about 20 to about 55 g.p.l. of chloride ion, about 65 to about 150 g.p.l. of sulfate ion, about to about 25 g.p.l. of boric acid, about 40 to about 60 g.p.l. of sodium ion, has a pH of about 3 to about 5, with the balance essentially water This electrolyte is operated at a temperature of about 100 F. to about 160 F. at a cathode current density of about 10 to about 35 amperes per square foot (a.s.f.).

After the cathode nickel has been grown to the desired thickness on the cathode, the plated cathodes are removed from the electrorefining cell and the crop of refined nickel is removed from the cathode sheet. It is found that, provided proper control of deposit stress level and mandrel surface finish are exercised, the nickel readily separates from the cathode sheet. Furthermore, the individual nickel segments are readily separable along the original resist lines present in the cathode sheet if, in fact, they are adherent one to another. In the case where the resist lines are about the same width as the thickness of the refined nickel deposit, it is found that a load of about 500 pounds applied normal to the surface of a nickel deposit stripped from the mandrel will sever a A inch thick deposit 12 inches long along a line grown across an original resist line inch wide. When the resist lines applied to the mandrel are Wider than the thickness of the final cathode product, there is little tendency for the individual nickel pieces to adhere to each other and such pieces may readily be recovered as such during the stripping operation.

The stripping operation itself may be conducted in a number of ways. Thus, flexible plated mandrels may be passed through rubber rolls to strip the deposit, or they may be flexed in any other convenient manner to strip the nickel deposit therefrom. Heavier, more rigid mandrels can be treated by vibration,hammering, etc., to remove the deposit therefrom. As an aid in the stripping operation, the mandrel may be treated before deposition of nickel thereon to reduce adherence of deposited nickel thereto. Thus, the mandrel may be dipped in a solution containing about 0.1 to about 1 g.p.l. of sodium dichromate for about one minute and then washed with water. This treatment is effective when used upon mandrels made of nickel, stainless steel and other nickel-chromium and nickelchromium-iron alloys. This treatment also assists in promoting the useful life of the mandrel.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better ap- 4 preciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLE I A nickel electrorefining electrolyte having a pH of about 4- containing about 56 g.p.l. nickel, about 54 g.p.l. chloride ion, about g.p.l. sulfate ion, about 50 g.p.l. sodium ion, about 15 g.p.l. boric acid, and the balance essentially water Was prepared. About 0.04 g.p.l. hydracrylonitrile and about 0.01 g.p.l. of sulfur dioxide were introduced into the bath. A flat stainless steel cathode mandrel having a smooth cold rolled surface, about Ms inch thick and having dimensions of about 29 by 40 /4 inches, was marked off with interconnecting lines of electroplating tape to provide conductive islands about 1 inch square. The minimum width of the tape was about A inch. The mandrel was degreased, inserted in the bath and plated with nickel using an average current density of 20 a.s.f. at a temperature of F. to provide a nickel deposit A3 inch thick on each side of the mandrel. The plated mandrel was then removed from the bath and the nickel deposit was readily stripped therefrom as individual pieces.

EXAMPLE II in Example I and with a current of about 7,000 amperes being supplied to the tank for time suflicient to provide deposits inch thick on each side of each mandrel. At this thickness, the areas of nonconducting tape were bridged over with nickel. The plated mandrels were removed from the bath and the deposits stripped therefrom by impact. The deposits were readily dividable along the locations corresponding to the original areas of nonconducting tape applied to the mandrel and had a roughly hexagonal outline.

The deposit produced according to Examples I and II had a stress level of about 1,000 p.s.i. tensile and was smooth and white.

The combination of the sulfur dioxide and hydracrylonitrile reagents to control stress level in the deposit is entirely compatible with the standard sulfate-chloride electrorefining bath and the purification cycle employed therewith and the bath can be maintained over long periods of time without diificulty.

The use of the combination of sulfur dioxide and hydracryonitrile as described hereinbefore in the electrorefining bath in accordance with the invention will introduce controlled amounts of sulfur, e.g., about 0.015% to 0.05% sulfur, and more preferably about 0.02% to about 0.025% sulfur, into the deposit and will result in electrolytic nickel having high activity.. This material is in a highly desirable physical form for use in titanium plating baskets. Furthermore, the material corrodes smoothly in conventional nickel electroplating baths without splitting since the product contains no physical interruptions such as the starting sheet contained within usual sheared electrolytic nickel. During plating, the material settles smoothly within the plating basket as the corrosion proceeds so that hangups, bridging and formation of voids in the nickel material within the basket are mitigated or are avoided altogether.

It will be appreciated that the method contemplated in accordance with the present invention provides a number of advantages over the conventional method of shearing a cathode into suitable size. Thus, cathode nickel plated to predetermined size is readily distinguished on the basis of its physical appearance from sheared nickel. Thus, the individual nickel pieces have greatly reduced amounts of sharp edges as compared to the sheared product and have a characteristic peripheral elevated ridge on the outer face of each piece, i.e., the face in contact with the bath, which apparently is created by the lines of resist present on the mandrel. In addition, the method also provides a ready means for applying an identifying mark to each individual piece. This may readily be done by embossing the conductive islands on the flexible mandrel with an identifying mark which is then reproduced in the deposit. As an economical advantage, the shearing costs such as are attendant to shearing large nickel cathodes to the desired size are eliminated. Furthermore, the step of providing a nickel starting sheet as a separate operation is eliminated since the cathode nickel is grown to its full size in a single operation in accordance with the contemplation of the present invention.

It will also be appreciated that the electrolytic nickel produced in accordance with the invention is of substantial thickness, e.g., at least about inch up to about /2 inch or even thicker, whereas the nickel thickness employed in decorative nickel plating is of a much lower order, e.g., only about one to about two thousandths of an inch.

Although the present invention has been described in conjunction with 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 modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. In the method for electrorefining nickel, the improvement for producing electrorefined nickel cathode material of controlled dimension which comprises immersing in an electrorefining electrolyte a substantially flat, permanent metal cathode mandrel having a surface finish in the range of about to about 100 microinches and having conductive islands of controlled size defined on the surface thereof, electrodepositing nickel to a substantial thickness upon the surface of said mandrel while facilitating adherence of said electrodeposited nickel upon said mandrel by introducing into said electrolyte controlled proportions of sulfur dioxide and hydrocrylonitrile to control the stress level in said nickel cathode within the range of about 8,000 pounds per square inch compressive to about 6,000 pounds per square inch tensile, removing the plated mandrel from the bath and stripping the nickel deposit therefrom to recover electrodeposited nickel in sizes corresponding substantially to the original areas of said conductive islands and to recover said mandrel in a condition suitable for further plating.

2. The method according to claim 1 wherein said electrolyte is a sulfate-chloride electrolyte containing about 0.005 to about 0.02 gram per liter of sulfur dioxide and about 0.01 to about 0.1 gram per liter of hydracrylonitrile.

3. The method according to claim 2 wherein the sulfur dioxide content of the electrolyte is about 0.009 to about 0.011 gram per liter.

4. The method according to claim 1 wherein the mandrel is made of a metal from the group consisting of nickel and alloys containing about 8% to about 30% chromium, at least 8% nickel, and the balance up to about 74% iron.

5. The method according to claim 1 wherein the mandrel is made of stainless steel.

6. The method according to claim 1 wherein the conductive islands in the mandrel are defined by interconnecting lines of nonconductive resist material.

7. The method according to claim 6 wherein said conductive islands are circular or elliptical in shape.

References Cited UNITED STATES PATENTS 2,773,816 12/1956 Wesley et-al. 20412 2,706,170 4/ 1955 Marchese 2043 2,392,708 1/ 1946 TSChOp 204292 3,419,901 12/1968 Nordblom 20410 3,094,476 6/ 1963 Francis 20412 OTHER REFERENCES Modern Electroplating, 1963, Lowenheim, pp. 270-272.

Technology of Electrodeposition, 1962, Vagramyan et al. p. 267.

Tech. Proceedings A.E.S., 1963, Borchert, p. 44.

HOWARD S. WILLIAMS, Primary Examiner R. L. ANDREWS, Assistant Examiner U.S. Cl. X.R. 20410 Patent No. 1,577,330 Dated Mi 4 1971 Inventofls) B It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 41, for "99.4+%" read -99.9+%-.

Column 2, line 30, for "resims" read --resins,--.

Signed and sealed this 1 9th day of October 1 971 (SEAL) Attest:

EDWARD M .FLET CHER, JR. ROBERT GOI'TSGHALK Attesting Officer Acting Commissioner of Patents