US3374154A - Electroforming and electrodeposition of stress-free nickel from the sulfamate bath - Google Patents

Description

United States Patent 3,374,154 ELECTROFORMING AND ELECTRODEPOSITION 0F STRESS-FREE NICKEL FROM THE SULFA- MATE BATH Hugh L. McCutchen, Warwick, N.Y., assignor to The International Nickel Company, New York, N.Y., a corpoi-anion of Delaware No Drawing. Filed July 12, 1965, Ser. No. 471,431 5 Claims. (Cl. 204-3) The present invention is directed to a method for electrodepositing nickel and, more particularly, to a method for electroforming nickel to provide a nickel deposit having a controlled stress level and good appearance.

In U.S. patent application Ser. No. 368,651, now US. Patent No. 3,326,782, a nickel sulfamate plating bath and method for electrodepositing nickel therefrom is described. The bath described in the aforementioned patent application is characterized by a special high concentration of nickel sulfamate, i.e., the concentration of nickel sulfamate in the bath is about 500 to about 700 grams per liter (g.p.l.). It is pointed out in the said patent application that very high cathode current densities may be employed in the bath and that the internal stress level in the deposit produced therefrom can be controlled by means of bath temperature and cathode current density. The special bath and method may also be employed to produce bright nickel deposits by controlling the current density to relatively low levels. In order to produce deposits having substantially zero internal stress, i.e., having an internal stress level in the range of about 1,000 pounds per square inch (p.s.i.) compressive to about 1,000 p.s.i. tensile, the current density may be correlated with bath temperature when the bath contains about 550 to about 650 g.p.l. of nickel sulfamate as shown in the following table:

Cathode current density-amperes per square foot to provide in deposit an internal stress level of 1000 p.s.i. compressive to 1000 p.s.i. tensile Bath Temperature, C.:

55 110 to 125 60 160 to 180 65 210 to 240 70 260 to 290 When the current density employed is at a lower level than that given in the foregoing table, the internal stress in the resulting deposit becomes more strongly compressive. Deposits produced under the foregoing conditions using the bath described in the aforementioned US. patent application are not bright and it is found that when a bright deposit is desired that the current density should not exceed about 70 amperes per square foot (a.s.f.) in instances wherein no organic brightening agents are employed. Whensuch current densities are employed to achieve a bright deposit the stress level is strongly compressive, for example, being on the order of about 14,000 p.s.i. compressive when the deposit is formed from a bath containing about 600 g.p.l. nickel sulfamate operated at 60 C. using a cathode current density of 50 a.s.f. This is undesirable in many applications, for example, in electroforming wherein it is desired that the internal stress level of the deposit be substantially zero to avoid dimensional changes in the deposit.

Nickel sulfamate plating baths according to the disclosure in the aforementioned patent application have been operated on a commercial scale in a number of installations with good success. It is found that the temperature-current density control needed to provide deposits of substantially zero stress from the concentrated nickel sulfamate bath have imposed undesirable limitations in certain areas. For example, in the production of electrotypes using matrices made of certain plastics, it is required that the bath temperature not exceed about F. (49 C.) or the dimensions of the matrix will change. Again, in the electroforming of complex shapes (as distinguished from fiat surfaces), it is undesirable to employ high cathode current densities since non-uniform thicknesses of electrodeposited nickel are then encountered. Furthermore, the high concentration of nickel sulfamate in the bath results in high viscosity which apparently contributes to pitting in the deposits. Other disadvantages flowing from operation of the said bath at the required temperature levels of 55 C. (131 F.) or 60 C. F.) are an increased bath hydrolysis rate and increased evaporation loss.

A need accordingly has arisen to provide a means whereby a deposit having an internal stress level of substantially zero may be produced using the current densities and bath temperatures conventionally employed in electroforming, i.e., current densities of the order of about 10 to about 100 a.s.f. and temperatures as low as 100 F. A method for electrodepositing nickel has now been discovered whereby nickel may be electrodeposited from a sulfamate bath in the absence of special organic addition agents which will have a substantially zero internal stress and which will have a good appearance.

It is an object of the present invention to provide a method for electroforming nickel having a substantially zero internal stress and having good appearance.

It is a further object of the present invention to provide a method for electrodepositing nickel from a sulfamate bath wherein no special organic addition agents are employed and wherein the bath may be utilized over long periods of time.

It is another object of the present invention to provide a method for electrodepositing nickel from a sulfamate bath wherein the bath is maintained in a condition for producing nickel deposits having the desired properties over long periods of time without the necessity for making additions to the bath.

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

Broadly speaking, the present invention comprises a method for electro-depositing nickel having a controlled stress level and having a good appearance over a long period of time which comprises establishing an aqueous acid sulfamate bath containing about 55 to about 1 10 g.p.l. of nickel, up to about 90 g.p.l. sulfate ion, up to about 25 g.p.l. chloride ion, a buffering amount of boric acid, having a temperature of about 100 F. to about F., and passing current through said bath at a cathode current density up to about 300 a.s.f., e.g., about 10 to about 100 ash or' about 200 a.s.-f., while subjecting .at least a portion of said bath to anodic oxidation. Advantageously, the anodic oxidation contemplated in accordance with the invention is accomplished by providing in the plating bath a control anode, which is insoluble therein, such as a platinum or platinized titanium or platinized tantalum anode, and passing about 0.25% to about 4%, or, more advantageously, about 0.25% to about 2%, e.g., about 1% to about 2%, of the total plating current through said control anode. Most conveniently, a separate power supply is provided for the control anode, since control and positioning of the insoluble anode in the bath are thereby facilitated. When the control anode has a platinum surface, it usually is operated at a potential of about 1.1 to about 1.6 volts as measured by a probe and asatur-ated calomel reference electrode. As the current passed through the control anode is increased in proportion to the total plating current, stress in the deposit tend to become more compressive. With regard to other practical operating factors, a reduction in bath nickel concentration, an increase in bath pH or an increase in bath chloride ion concentration within the ranges given hereinbefore will affect the stress level in the deposit in the tensile direction. A reduction in bath temperature or an increase in cathode current density will also affect stress level in the deposit in the tensile direction more strongly. For example, in the case of a bath operated at 140 F. and containing about 110 g.p.l. of nickel as nickel sulfamate and about 40 g.p.l. boric acid at pH 4.0 with active anodes and with about 1.2% of the plating current supplied to a platinum control anode, a substantially Zero stress level in the deposit was obtained at a cathode current density of about 180 a.s.f. and the bath could be operated almost indefinitely without measurable change in bath pH. When the cathode current density was reduced to 100 a.s.f., the tress level in the deposit was about 6,000 p.s.i. compressive and when the cathode current density was increased to about 265 a.s.-f., the stress level in the deposit was increased to about 6,000 p.s.i. tensile. A similar bath operated at the same temperature with about 0.6% of the plating current supplied to a platinum control anode provided a substantially zero stress level in the deposit at a cathode current density of about .150 a.s.f., whereas at a cathode current density of 100 a.s.f., the stress level in the deposit was about 4,000 p.s.i. compressive and at a cathode current density of about 205 a.'s.f., the stress level in the deposit was about 4,000 p.s.i. tensile. Minor acid additions were needed periodically to control bath pH during the runs made with 016% of the plating current supplied to the control anode. Another bath containing about 80 g.p.l. of nickel as nickel sulfamate, about 40 g.p.l. of boric acid, having a pH of 4.0 and operated at 120 F. with about 1. 1% of the plating current supplied to the platinum control anode yielded a substantially zero stress in the deposit at a cathode current density of about 43 a.s.f. When this bath was operated with a cathode current density of about a.s.f., other conditions being the same, the internal stress level in the deposit was about 12,000 p.s.i. compressive, whereas when the cathode current density was increased to about 50 a.s.f., the internal stress level in the deposit was about 3,000 p.s.i. tensile.

Advantageously, the nickel material employed at the anode in accordance with the invention is an active nickel containing a small amount of an activating agent such as aboutv 0.02% to about 0.04% sulfur, since such anode materials have a limiting anode current density of about 500 a.-s.f. even in chloride-free sulfamate plating bath-s such as a nickel sulfamate plating bath containing about 450 g.p.l. of nickel sulfamate, about 30 g.p.l. of boric acid and the balance essentially water. The bath may contain chloride ion in an amount up to about g.p.l., e.g., about Zero g.p.l. to about 5 g.p.l., as the chloride ion tends to decrease anode passivity. Chloride ion concentrations exceeding about 25 g.p.l. are undesirable because internal stress in the deposit is thereby undesirably increased in the tensile direction. In producing the bath contemplated in accordance with the invention, the content of nickel sulfamate should be at least about 300 g.p.l. (55 g.p.l. of nickel) up to about 600 g.p.l. (109 g.p.l. of nickel) to provide a bath capable of yielding sound deposits of good appearance employing plating currents at the cathode current densities contemplated herein. The pH of the bath may be from about 3 to about 5 in order to avoid undesirable bath hydrolysis on the one hand and to avoid undesirable stress increases in the deposit on the other. More advantageously, the pH is from about 4 to about 4.5 because the pH control is then facilitated. The bath contains a buffering agent such as boric acid in amounts up to saturation, e.g., about 25 or about g.p.l. up to about to about g.p.l. of boric acid. The bath is operated at a temperature of at least about 100 F. up to about 170 F, e.g., about 120 F. to about 140 F. This temperature range includes the range of 100 F. to 120 P. which is necessary for the production of electrotypes and provides satisfactory plating rates and the production of sound deposits.

The process contemplated in accordance with the invention provides a ready means for controlling the stress level in the deposit. Deposits produced at substantially zero internal stress have a bright matte appearance. Brighter deposits can be produced at more compressive stress levels by increasing the anodic oxidation supplied to the bath. The brightest deposits produced without addition agents are characterized by a slight haze but are satisfactory as the basis for a chromium deposit of acceptable quality. The bright matte deposits may readily be placed into a condition for plating high quality chromium thereon by employing an intermediate conventional bright nickel layer.

It is an advantage of the invention that baths may be employed which contain nickel as nickel sulfate in amounts u to approximately the amount of nickel added as nickel sulfamate while still obtaining deposits having a low stress level. Sulfate-sulfamate baths are materially less expensive than all-sulfamate baths. Additions of sulfate ion to the bath appear to move the stress level in the deposit in the tensile direction.

The invention is particularly advantageous in relation to electroforming processes wherein it is known that a substantially zero internal stress, i.e., an internal stress between about 1,000 p.s.i. compressive and about 1,000 p.s.i. tensile, is advantageous. The invention accomplishes this result and at the same time provides a nickel deposit having good appearance. The cathode current density employed in accordance with the invention is generally at least about 20 a.s.f. to provide an acceptable plating rate, but usually does not exceed about 200 a.s, f. because it then becomes more difficult to produce sound stressfree deposits, particularly with the more dilute baths and the lower operating temperatures.

In order to give those skilled in the art a better understanding of the advantages of the invention, the following illustrative example is given:

Example A bath containing about 300 g.p.l. of nickel sulfamate (about 55 g.p.l. nickel ion), about 40 g.p.l. of boric acid and the balance essentially Water was prepared. The bath had a pH of about 4 and was operated at a temperature of about F. An active nickel sla-b anode containing about 0.03% sulfur and having a surface area of about 72 square inches was inserted in the bath. In addition, a platinum anode having an effective surface area of about 1 square inch was also inserted in the bath and each of the anodes was provided with a separate current supply. A cathode having an effective area of about 48 square inches Was also inserted in the bath. Current was passed through the bath at a cathode current density of about 20 a.s.f. Current was passed to the nickel anode at an impressed voltage of about 2.2 volts and the plating current was 6.6 amperes. The current supplied to the platinum anode was about 0.42% of the plating current. The bath was operated for about 2 4 hours during which time a nickel deposit about 0.024 inch thick was produced on the cathode. The cathode was removed from the bath and the nickel deposit thereon was found to have a bright matte appearance. The deposit produced under these conditions had a zero internal stress level by the spiral contractometer method. The bath was thereafter operated for a total of 20,000 ampere hours and it was found that during the course of this time no material change in internal stress of the deposit occurred. Small periodic acid additions were made to control bath pH during the run. When the identical bath was operated only with active nickel material over a period of about ampere hours, i.e., without the insoluble platinum anode, the resulting deposit was gray and had a stress level of about 14,000 p.s.i. tensile. Again, when a similar bath was operated over a period of 20,000 ampere hours using only high purity (99.9%

nickel) nickel slab anode material and with a chloride ion addition to the bath of about 5 g.p.l. to maintain anode activity, the resulting deposit was gray and had a stress level of about 8,000 p.s.i. tensile. In each of the latter two instances, periodic acid additions were made to control bath pH.

The theory underlying the present invention is not understood but it is, nevertheless, found that operation of the process as described hereinbefore provides a means for electrodepositing nickel having a controlled stress level and a good appearance over a long period of time. The level of stress in the deposit can be controlled to be substantially zero or to a stress level within a range from about 14,000 p.s.i. compressive to about 10,000 p.s.i. tensile by appropriate control of operating conditions. Attempts to duplicate the results obtained through the controlled electrolytic oxidation of the bath as described hereinbefore by means of chemical oxidizing agents have been unsuccessful. Thus, it has been determined that peroxide ion, persulfate ion, and dithionate ion additions to the bath have no effect. It appears likely that the special effects yielded in accordance with the invention are associated in some unexplained way with a special state of oxidation obtained electrolytically. Regardless of the true explanation for the unusual effects provided in accordance with the invention, the method as described hereinbefore provides a means for producing nickel deposits having controlled low stress levels and good appearance while Operating the bath and process over extended periods of time.

It will be appreciated that the usual impurities known to be deleterious in nickel plating baths should be controlled to low levels in the bath operated in accordance with the invention. These impurities include iron, copper, zinc, lead, chromium, etc. Lead cannot be used as the material for the control anode contemplated in accordance with the invention since lead sulfamate is a soluble salt. The effects of impurities and their removal from nickel plating baths is discussed, for example, in the handbook Practical Nickel Plating, Second Edition, 1959, published by The International Nickel Company, Inc.

Usual oxidizable organic addition agents such as brighteners, levellers, anti-pitters, etc., become oxidized by the control anode yielding solid products which are removed by filtration of the bath. Such agents accordingly cannot be employed in the process provided in accordance with the invention.

The control anode advantageously is platinum or a platinum-surfaced metal such as titanium or tantalum. The control anode must act as a polarized anode in the bath and must not introduce harmful metal ions thereinto. Carbon can be employed as the control anode, although care is needed to remove carbon particles from the bath by filtration. Advantageously, the control anode is operated at a potential sufficient to liberate gas, e.g., oxygen. Chlorine does not form at the control anode due to the presence of sulfamate in the bath.

It is to be appreciated that when nickel sulfamate is introduced into solution in an amount equivalent to 55 g.p.l. nickel, about 178.5 g.p.l. of sulfamate (NH SO is introduced and that when 110 g.p.l. of nickel is introduced as nickel sufamate, about 357 g.p.l. of sulfamate (NH SO is introduced.

The process provided in accordance with the invention may be employed in the electroforming upon a conductive mandrel of complex shapes such as coffee pots and other utensils and of simpler shapes such as record stampers and the like and can be employed in decorative nickel plating or in any other application wherein control of stress level in the deposit is of value. The nickel deposits produced in accordance with the invention are ductile and soft after a heating to a red heat, e.g., about 1000 F.

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.

I claim:

1. The process for electrodepositing nickel having a controlled stress level which comprises establishing an aqueous acid sulfamate bath having a pH of about 3 to about 5 and containing about 55 to about 110 grams per liter of nickel, up to about grams per liter of sulfate ion, up to about 25 grams per liter of chloride ion, a buffering amount of boric acid and a temperature of about F. to about 170 F. and passing a plating current through said bath at a cathode current density up to about 300 amperes per square foot from an active nickel anode to a cathode immersed therein While subjecting said bath to anodic oxidation by supplying current in the amount of about 0.25 to about 4% of the plating current to an insoluble anode immersed in said bath to produce a nickel deposit having a controlled internal stress level over along period of bath operation.

2. The process for electrodepositing nickel having a controlled stress level which comprises establishing an aqueous sulfamate bath having a pH of about 3 to about 5 and containing about 55 to about grams per liter of nickel, up to about 90 grams per liter of sulfate ion, up to about 25 grams per liter of chloride ion, about 25 to about 40 grams per liter of boric acid, and having a temperature of about 100 F. to about F., and passing a plating current through said bath at a cathode current density up to about 300 amperes per square foot from an active nickel anode to a cathode immersed therein while subjecting said bath to controlled anodic oxidation by supplying current in the amount of about 0.25% to about 4% of the plating current to an insoluble control anode immersed in said bath to produce a nickel deposit having a controlled internal stress level.

3. The process for electrodepositing nickel having a controlled stress level which comprises establishing an aqueous sulfamate bath having a pH of about 4 to about 4.5 and containing about 55 to about 110 grams per liter of nickel, up to about 90 grams per liter of sulfate ion,

.up to about 25 grams per liter of chloride ion, about 25 to about 40 grams per liter of boric acid and having a temperature of about 100 F. to about 170 F. and passing a plating current through said bath. at a cathode current density of about 10 to about 200 amperes per square foot from an active nickel anode to a cathode immersed therein while subjecting said bath to controlled anodic oxidation by supplying current in the amount of about 0.25 to about 4% of the plating current to an insoluble control anode immersed in said bath to produce a nickel deposit having a controlled internal stress level.

4. The process for electrodepositing nickel having a controlled stress level which comprises establishing an aqueous sulfamate bath having a pH of about 4 to about 4.5 and containing about 55 to about 1.10 grams per liter of nickel, up to about 90 grams per liter of sulfate ion, up to about 25 grams per liter of chloride ion, about 25 to about 40 grams per liter of boric acid and having a temperature of about 100 F. to about 170 F. and passing a plating current through said bath at a cathode current density of about 20 to about 200 amperes per square foot from an active nickel anode to a cathode immersed therein While subjecting said bath to controlled anodic oxidation by supplying current in the amount of about 0.25 to about 2% of the plating current to a control anode having a platinum surface immersed in said bath to produce a nickel deposit having a controlled internal stress level.

5. The process for electroforming nickel having a controlled low internal stress level which comprises establishing an aqueous nickel sulfamate bath having a pH of about 4 to about 4.5 and containing about 55 to about 110 grams per liter of nickel, up to about 25 grams per liter of chloride ion, about 25 to about 45 grams per liter of boric acid and having a temperature of about 100 F. to about 170 F. and passing a plating current therethrough at a cathode current density of about 10 to about 200 amperes per square foot from an active nickel anode to a conductive electroforrning mandrel immersed therein While subjecting said bath to controlled anodic oxidation by supplying current in the amount of about 0.25% to about 2% of the plating current to a control anode having a platinum surface immersed in said bath to produce a nickel deposit having a controlled low internal stress level.

References Cited UNITED STATES PATENTS 2,625,507 1/1953 Mayper 204-49 XR 2,706,170 4/1955 Marchese 20449 XR 3,326,782 6/1967 Kendrick et a1. 20449 XR 8 FOREIGN PATENTS 9/1940 Great Britain.

OTHER REFERENCES Hammond, R. A. F., Nickel Plating From Sulphamate Solutions, The International Nickel C0. (Mond) Ltd., pp. 1-24, 1962.

Kendrick, R. 1., High-Speed Nickel Plating From Sulphamate Solutions, transactions of the Institute of Metal Finishing, Proceedings of the 6th International Conference on Electrodeposition and Metal Finishing, pp. 235245, 1964.

HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner.

Claims (1)

1. THE PROCESS FOR ELECTRODEPOSITING NICKEL HAVING A CONTROLLED STRESS LEVEL WHICH COMPRISES ESTABLISHING AN AQUEOUS ACID SULFAMATE BATH HAVING A PH OF ABOUT 3 TO ABOUT 5 AND CONTAINING ABOUT 55 TO ABOUT 110 GRAMS PER LITER OF NICKEL, UP TO ABOUT 90 GRAMS PER LITER OF SULFATE ION, UP TO ABOUT 25 GRAMS PER LITER OF CHLORIDE ION, A BUFFERING AMOUNT OF BORIC ACID AND A TEMPERATURE OF ABOUT 100*F. TO ABOUT 170*F. AND PASSING A PLATING CURRENT THROUGH SAID BATH AT A CATHODE CURRENT DENSITY UP TO ABOUT 300 AMPERES PER SQUARE FOOT FROM AN ACTIVE NICKEL ANODE TO A CATHODE IMMERSED THEREIN WHILE SUBJECTING SAID BATH TO ANODIC OXIDATION BY SUPPLYING CURRENT IN THE AMOUNT OF ABOUT 0.25% TO ABOUT 4% OF THE PLATING CURRENT TO AN INSOLUBLE ANODE IMMERSED IN SAID BATH TO PRODUCE A NICKEL DEPOSIT HAVING A CONTROLLED INTERNAL STRESS LEVEL OVER A LONG PERIOD OF BATH OPERATION.