US2625507A - Method of electrodepositing nickel - Google Patents

Description

Jan. 13, 1953 s. A. MAYPER METHOD OF ELECTRODEPOSITING NICKEL Filed 001;. 16, 1945 1 G I F FIG.2.

mvnn'ron, STUART A. MAYPER,

AT TORNEY Patented Jan. 13, 1953 METHOD OF ELECTRODEPOSITIN G NICKEL Stuart A. Mayper, New York, N. Y., assignor to the United States of America as represented by the United States Atomic Energy Commission Application October 16, 1945, Serial No. 622,636

2 Claims.

bath consists essentially of nickel chloride and nickel sulfate buffered with boric acid. Efforts have been made to subject this and other nickelcontaining baths to electrolysis for producing a finely divided deposit of nickel. Such efforts have been unsuccessful despite the use of high current densities and the regulation of other plating conditions such as pH and temperature in an attempt to force such a finely divided deposit to occur. As a consequence it has been necessary heretofore to produce nickel powder by other means such as pyrometallurgical processes usually starting with nickel carbonyl, or by the reduction of various nickel compounds such as nickel formate ornickel oxalate. Such pyrometallurgical or reduction processes have been excessively complicated, difficult to control, 'expensive, and occasionally dangerous, such as the one involving the use of nickel carbonyl which a very poisonous gas.

Accordingly, it is a principal object of the preseht invention to provide a practical method for electroiyzing a bath containing nickel ions to produce a pulverulent or finely divided deposit of nickel.

It is another object of the invention to provide a process of the foregoing general nature which is simple and reliable, which does not require excessive current densities or excessive power consumption, which employs an inexpensive electrolyte as well as conventional anodes, and which may be operated to provide a nickel powder of a desired particle size.

Finally, it is another and more specific object of the invention to provide an acidic bath containing nickel ions, which bath may be electrolyzed to produce the desired pulverulent nickel deposit while keeping the deposit of flakes or massive nickel to a minimum and. while avoiding precipitation of nickel compounds in the bath.

Other objects and advantages of this invention will appear in the following description and ap- "@Elld'fid claims, reference being had to the accompanylng draw'mgs forming a part of this ifi ation til a e ke reference charact 2 designate corresponding parts in the two views. Fig. 1 is a perspective view showing one form of apparatus adapted to carry out the present invention. This view has parts broken away in" order to show more clearly the structure of the cathodes and anodes. Fig. 2 is a diagrammatic or schematic view indicating, in particular, one wiring circuit for supplying current to the electrodes and also indicating the relative position of the electrodes.

Referring to the drawings and particularly to Fig. 1, the reference numeral I0 indicates a container for holding the bath or solution to be electrolyzed. In the drawings, the tank H1 is shown while empty in order to better illustrate various parts of the apparatus which normally are at least partlysubmerged in the electrolyte. Naturally, this tank, when in operation is filled or at least partially filled with the electrolyte. The tank or container [0 is preferably of a conventional type normally employed for the electrodeposition of a metal. For example, a tank usually used for electrolyzing plating baths intended to plate out or deposit nickel in a massive form may be employed. In this connection, I have used a wooden tank lined with glass as shown at H, although a cast metal or weldedsheet-metal tank of a sturdy construction may also be employed satisfactorily. The tank should be lined with a non-conducting or insulating material such as rubber. If a metal tank is used the electrodes should not contact the tank as shown in Fig. 1. Any suitable means may be used for suspending or supporting the electrodes while electrically isolating them from objects other than the electrical circuit supplying them with current. a

The electrolyte consists essentially of an aqueous solvent or medium containing a soluble nickel compound, a soluble ammonium compound, and a soluble compound of an alkali or alkaline earth metal. More particularly, I'prefer to employ a solution of nickel chloride, ammonium "chloride and sodium chloride. Initially, that is prior to the electrolysis of the bath, the molar concentration of the ammonium compound'and'that of the sodium compound should be approximately 'equal whereas the nickelcompound should be present in a concentration about it; that of the "concentration was approximatelyfi; molar and the concentration of each of the ammonium chloride and the sodium chloride was approximately one molar. A bath made up in this way is acidic in character; and if properly prepared prior to electrolysis the pH of the bath should fall within the range of 2 to 6 inclusive, that is, the hydrogen ion concentration should be within the range of 10- to 10- molar. However, it may be necessary to add hydrochloric acid or some other acid or acid-forming substance to the solution from time to time during the electrolysis, or after the solution has been used for electrolysis, in order to maintain the pH within the above-mentioned range. If need be, hydrochloric acid or its equivalent may be added to the solution initially if it is found that, for some reason the solution does not possess the desired acidity. On the other hand, if the solution is too acidic or becomes too acidic, ammonium hydroxide or some other suitable basic substance may be added in order to bring the pH within the range of 2 to 6 inclusive.

The reference numeral 12 designates the cathodes employed to assist in the electrolysis of the bath. In the preferred embodiment of the invention, each of these cathodes was formed of a sheet of stainless steel since this .materail operates effectively and is readily obtainable. However, other metallic or current conducting materials may be employed provided that they are not attacked by the bath, for instance, nickel or copper sheets may be used. The arrangement of the cathodes is important and is discussed hereinafter; one typical installation being best illustrated schematically by Fig. 2. It is preferable that the cathodes [2 be so constructed that they may easily be removed from the solution; and any suitable lifting mechanism (not shown), automatic or otherwise, for conveniently removing the cathodes from the solution may be utilized. At the plane or area where each of the cathodes meets the surface of the bath, there tends to be considerable foaming and gas evolution during the electrolysis. This usually results in a lowered effective cathode current density, and sometimes causes flaking and otherwise tends to produce an undesirable kind of electrodeposition at this plane or area. In order to minimize such undesired electrodeposition and such foaming and the like, it is preferable to reduce the area of the cathode at the point that it enters the bath; for example, the cathode may be cut out or shaped so that only a narrow connecting piece or neck 13 passes through the surface of the bath. This preferred structure for the cathode is best illustrated in Fig. l. The electric conductor or wire connecting the cathode to the source of current is preferably fastened at the neck [3.

As illustrated in particular in Fig. 2, I prefer to employ two types of anodes, the principal type being a nickel-bearing or nickel-containing anode which is corroded by electrolysis of the solution to provide the necessary replenishment of the nickel in the bath during. the electrolysis. Preferably, a plurality of these nickel-bearing or nickel-containing anodes are provided, two such anodes being shown in the drawings at I4, 14. These anodes consist of a sheet of nickel provided with suitable extensions or cars at their tops for supporting the anodes in position. in the manner best illustrated in Fig. 1. Preferably, sheets of electrolytic nickel are employed. How- ,7 ever, it is not necessary that the nickel anodes be in sheet form. Other conventional nickel anodes may be used, such, for example, as relatively thick or heavy rods which are suspended by a hook extending over a copper rod which is,

in turn, supported by the edges of the tank. Baskets containing nickel may be used and, in fact, any suitable means for placing a soluble nickel-bearing anode in the electrolyte and supplying it with the necessary current may be employed.

The other anodes shown generally at 15, I5 (in Figure 2) are secondary or auxiliary anodes; and they are formed of some current carrying material which is insoluble in the electrolyte. For this purpose I have preferred to use carbon, although other materials which are below nickel in the electromotive series may be used, if such materials are not attacked by the bath when used. Materials of this character which are practical are not numerous, thus making carbon the only acceptable and readily available material that I know of; but a number of other materials may be used, nevertheless, such as silver or platinum. While any suitable means of supporting the carbon rods or auxiliary electrodes l9, l9, may be employed, I have preferred to employ a shallow metal trough or holder, I6 (Fig. 1), into which the upper ends of the electrodes, 19, extend. The electrodes are held within the trough or holder, I6, by solder or some similar substance adapted to .securely retain them in place, and at the same time to conduct electricity. Preferably, the conduction is attached to the trough. 6, for electrically connecting the anodes i5, 5, to the source of current.

The preferred arrangement for the anodes and cathodes is shown in the diagrammatic view (Fig. 2). An operable system may be set up while utilizing other arrangements of the anodes and cathodes, but I have found from experience that this particular arrangement operates very effec tively and this arrangement comprises one feature of my invention. It will be observed, in particular, that the auxiliary carbon anodes are located at either end of the bath, and that each nickel anode is confronted on both sides by the steel cathodes. Preferably, the cathodes and anodes are spaced apart substantially uniformly and the distance between them which I employed was approximately four to five inches. This particular spacing of the anodes and cathodes is not especially critical. However, it will be readily appreciated that the necessary current densities (discussed hereinafter) are achieved at a lower voltage if the electrodes are placed nearer together; and correspondingly, it requires a higher voltage to attain this current density if the electrodes are spaced farther apart. When the correct proportion of anode current (also discussed hereinafter) is carried by each type of anode, I have found that the above described arrangement provides substantially equal current densities at all of the faces of the cathodes. This is desirable for present purposes, but in conventional plating baths was not necessary or was not achieved.

In order to carry out electrolysis of the bath described above the anodes and the cathodes are connected to a suitable source of direct current in the manner indicated diagrammatically in Fig. 2. Preferably, a motor-generator set is employed as a source of direct current as indicated at 11 (Fig. 2) although batteries may be used; and suitable conductors, ammeters, voltmeters and the like are employed in a conventional manner. The quantity of current necessary and the current regulation is discussedhereinafter. The rheostat or variable resistance shown at 18 is used to regulate the ratio of total anode current which (46 to 276 amperes per square foot).

is carried by each type of anode. This ratio is also discussed further hereinafter. While one electrical circuit has been illustrated and described, it is to be understood that any suitable source of current may be employed and various wiring systems may be used.

During the electrolysis the cathoce current density should be relatively high as compared with the cathode current density of conventional plating baths, especially conventional nickel plating baths. Preferably, this current density is at least 0.05 ampere per square centimeter and may be as great as 0.30 ampere per square centimeter Generally speaking the anode current density will vary depending upon the quantity of nickel which is dissolving or has dissolved into the bath during the electrolysis. Naturally it is desirable to so govern or regulate the electrolysis that the quantity of nickel which dissolves from the anode willperiments to maintain this balance and also to maintain the proper cathode current density. The anodes carry the required quantity of current and complete the circuit, the current density of the anode not being regulated other than indirectly through regulation of the total current flowing in the circuit or by regulation of the cathode current density.

However, there is another factor which pertains to making the quantity of nickel that dissolves substantially equal to the quantity of nickel deposited. This is the proportion of the anode current which is carried by the nickel anodes to that which is carried by the carbon or other auxiliary anodes. I have found that this proportion, that is, the ratio of current carried by the nickel anodes to that carried by the carbon anodes, varied somewhat from run to run but fell within the range of approximately 1.5 to 2.5. As indicated above, one may determine the rate of nickel deposit; and within the aforementioned limits adjust the anode current density and. also the ratio of current carried by each type of anode to achieve the proper balance between nickel depositing, and that dissolving. Also, the proportion of the total current that is carried by each type of anode is of importance in achieving substantially uniform current densities at the cathodes. I have found that, when the anodes and cathodes are arranged as they are illustrated in the drawings, this substantially uniform current density may be attained if the ratio of current carried by the nickel anodes to that carried by the carbon anodes is roughly two to one. In this connection it will be observed that each nickel anode faces two cathode surfaces whereas each auxiliary anode facesbut dle stirrer maybe effectively employed for-this purpose. Instead of such 'stirring' means t: e bath may be circulated; for instance, it may be pumped. If need be or if it is desirable, the

solution making up the bath may be circulated through a filter press or other purifying means and returned to the tank [0, therebymaintaining an uncontaminated bath and at the same time circulating the bath during the electrolysis.

I have found that the temperature at which the electrolysis takes place is not particularly critical and does not appear to affect markedly the character of the powder deposited at the cathode. Accordingly, normal temperaturesfor ,electrolysis of baths of this general character may be employed and I have electrolyzed the baths at electrolyte temperatures ranging from approximately room temperature to C.

The nature of the deposit appears to'be materially affected by the length of the time'interval for which the deposit is permitted to build up or accumulate at the cathode. Generally speaking, the longer this time interval is, the larger will be the mean particle size. of the nickel particles deposited, and the shorter this interval the smaller the means particle size will be. Accordingly, the particle size may be governed or controlled by regulating the time interval for the depositing of the particles. In this connection, it is pointed out that the nickel collects at the cathode in theform of a packed clinging mass of small particles, this mass growing larger as the electrolysis proceeds. If the method is properly carried out few particles fall to the bottom of the bath. The table set forth hereinafter contains some typical results achieved by carrying out the present method, and thus indicates the relationship between the time interval of the accumulation of the particles and the particle size. In general, it may be stated that if the cathode is removed and scraped every 15 minutes (which is the preferred procedure) the -mean particle diameter will be '7 to 8 microns, at

half-hour intervals the mean diameter will be 9 to 10 microns, and after runs for 2 or 3 hours without removing the cathodes the mean diameter will be about 15 microns. Occasionally, especially if the cathodes are not removed or scraped for quite a long period of time, the oathode deposit may appear as coherent flakes or strips. However, these flakes or strips may easily ing procedure. The cathodes and anodes are arranged as indicated in the diagrammaticsketch and the electrolyte comprises a water solution of one mol of ammonium chloride, one mol of sodium chloride, and one-tenth of a mol of-nick-el to .cliloride per liter. This-bath iselectrolyzed'for one hour at a cathode current density of 0.25 to 0.30 ampere per square centimeter; and the-ratio of the current carried by the nickel anodes to that carried by the carbon anodes in 2:1. The pH is maintained within a range of 2 to 3 by the addition from time to time (if needed) of hydrochloric acid. The cathodes are removed every 15 minutes and scraped as clear as practicable of the powdered nickel which will cling to them as -a more or less hard-packed deposit.

In order to further illustrate the'present invention, the data secured as aresult-of a number of typical electrolysis operations carriedzout in accordance with the present invention are summarized in the table appearing immediately-bethe electrodes about four inches :and the tem- Jp'eraturle .ofthe bath "rose from room temperature at the start to about 50 C. after approximately tonehour.

TABLE Run.i-io-. 1 '2 '3 l c 7 (Ni-{+1. moi/1.0" 0.080 0.071 0.0818 0.1017 0.1158 0.1101 0.12 H s-c 2.5 2-0 2-3 '2-0 2-. as (NH4't7)[m0]/L V 0.94 1.04 :1. 4 1.18 1.10 1.22 (Na+)."moI/l-.-.- 0.85 0.555 0.34 0.32 0.82 0.31 0.81 Gnthode-area,-cm-. "-1,-341 30s 39s 30s 308 303 338 TctalcNurrenunitnun; .105 .110 103.5 110 103 103 icurren a 3 Rz1n W... 1. 1.83 2. 2.01 1 Cathode ourrenhdnm; 1 1 --sity,amp:/cm.' 0.0775 0.203 0.276 0.200 0.270 0.259 0.205 Time, hr 3,10 0.50 2.50 1.00 i 1. 00 1.00 100 .Meanvoitaga his 7.4 7.1 7.3 as 7.0 ?.1 Totalwatt-hr 2.030 .300 1,050 700 750 120 730 28.08 .03 59.58 550M415 .000 0.080 0.076 0.088 .145 0.175 0.108 0.104

microns. -4 9 7.7 8.0 7.;- .10 Specific surface, M lgh 0321" 0.17. 0.67, 0.57 0.46

"Deposit removed at fifteen-minute intervals.

:In orderto still .further explain my invention, the following theoretical considerations are pre- 'sented. .It will be understood that these considerations comprise my opinion or belief as to the .operation'of my method; and whether or not this opinion correct my method is successful and operable. .In .thefirst place, the electrolyte of the present invention is acidic in character. It is 'recognizediiniscientific circles that the morei'acidlc ai'solntion containing nickel and ammonium ions becomeathemor'e completely the complex nickelammonia ion'breaks down to provide a comparatively high concentration of free nickel ions in the solution. .Also'the comparatively low concentration of ammonium ions in the electrolyte employed in the present method tends to keep the number of complex nickel-ammonia ions low. As aLi-esulu my electrolyte contains a high concentration "of free or hydrated nickel ions as compared with other ammonium-containing nickel baths, particularly if such other baths are basic. ln-ifact, my bath is green or greenish in color (because of the presence of a relatively high concentration of nickel ions) as contrasted with the distinct blue color characteristic of the nickelammonia ion.

The-ammonium ionsinmy electrolyte serve one useful -purpose. "They insure that nickel compounds; especially nickel hydroxide, will not inadverte'ntly precipitate in the bath, particularly if'theibath should become comparatively basic in local areas during "the electroylsi's. The bath tends to become more-basic around the anodes. Normally, I 'oper'ateithe electrolyte at a pH of two or threeythat iaitis rather acid so that no parts of the bath wouldbecome suificiently basic (that is, liaising a pH of about' or above) to cause this undesired precipitation. However, one may operate with an electrolyte under less acidic conditions: and in any event it is desirable to utilize the ammonium ion in the electrolyte as a precaution.

The presence of the sodium ion has been found to aid in the depositing of the nickel in a finely divided state without the use of excessively high cathode current densities. One may achieve this desired deposition of the nickel as a powderwithout using any sodium ion at all; but it requires a considerably greater cathode current density, as

8 much as approximately :three times "the cathode current density employed when the sodium ion is present in the electrolyte, in order to deposit nickel in a finely divided powdered condition. Thus the current densities mentioned hereinbefore by way of exampleare lowfor the purpose of electrodepositing such finely divided nickel, although they are .high as compared with current densities used .for conventional plating operations.

While I have described my invention principally in connection with the use in the electrolyte of nickel chloride, ammonium chloride and sodium chloride, there are other compounds which may be used in place of these substances. The nickel chloride, of course, supplies the necessary nickel'ion concentration; but other soluble nickel compounds adapted to deposit or plate nickel from a solution by electrolysis are satisfactory. For example, nickel sulfate or nickel nitrate may'be utilized. .1 have preferred to use sodium chlorideas the reagent for aiding in the deposition of the nickel powder at the comparatively low current densities mentioned hereinbefore; but other compounds may be employedior this purpose. Such compounds include various soluble compounds of an alkali metal or an alkaline-earth metal, that is, compounds of metals falling within either of groups I and II of the periodic arrangement of elements sometimes referred to as Mendelyeevs Periodic Table." However, in using the compounds of the alkalineearth metals and to a lesser extent the compounds of the alkali metals, it should be'kept in mind that the compounds used should .not .form insoluble precipitate when introduced into the electrolyte.

While I have preferred to use ammonium chloride, this compound was merely a convenient source of ammonium ion for the electrolyte. Accordingly, other ammonium compounds adapted to provide such ions to the electrolyte when dissolved therein can be used; and in fact any soluble ammonium compound that does not produce undesirable side reactions in the bath is satisfactory.

While I preferred to employ a pH of 2 to 3 and cathode current densities of 0.25 to 0.30 ampere per square centimeter, I can employ a pH within the range of 2 to 6 inclusively and can use a current density varying from 0.05 to 0.30 ampere per square centimeter, as pointed out hereinbefore.

Having illustrated and described my invention and having explained the principles thereof, it will be understood nevertheless that, within the scope of the appended claims, the invention may be practiced otherwise than specifically illustrated and described. Furthermore, the phraseology or terminology employed herein is for purposes of description and not of limitation; for it is not intended to limit the invention beyond the requirements of the prior art.

I claim:

1. A method of producing finely divided nickel having a mean particle size between 7 and 15 microns which comprises providing a solution containing nickel, ammonium and sodium ions in the respective approximate proportions of 0.1 to 1.0 to 1.0, providing a nickel anode and an inert anode in said solution, maintaining a oath ode current density from 0.05 to0.30 ampere per square centimeteron a cathode in said solution fora tune interval between 15 minutes and 3 hours, maintaining the nickel ion concentration approximately constant by adjusting the total anode current so that the ratio of current carried by said nickel anode to that carried by said insoluble anode is between 2.5 and 1.5 to 1, and maintaining the pH of said solution between 2 and 6 inclusive.

2. A method of producing finely divided nickel having a mean particle size of approximately 7 microns which comprises providing a solution containing nickel ions, ammonium ions, and sodium ions in molar ratio of 0.1 to 1.0 to 1.0, providing a soluble nickel anode and an insoluble anode in said solution, maintaining a cathode current density within the range of 0.25 and 0.30 ampere per square centimeter for a time interval of approximately 15 minutes, maintaining the nickel ion concentration approximately constant by adjusting the total anode current so that the ratio of current carried by said nickel anode to that carried by said insoluble anode is approximately 2 to 1, and maintaining the pH of said solution within the range of 2 to 3 inclusive.

STUART A. MAYPER.

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

UNITED STATES PATENTS OTHER REFERENCES Modern Electroplating, Special Volume of the Electrochemical Society, pages 237, 239-242, 244- 249 (1942).

Trans of The American Electrochemical Society, vol. 58, pages 387-394, 397 (1930)

Claims (1)

1. A METHOD OF PRODUCING FINELY DIVIDED NICKEL HAVING A MEAN PARTICLE SIZE BETWEEN 7 AND 15 MICRONS WHICH COMPRISES PROVIDING A SOLUTION CONTAINING NICKEL, AMMONIUM AND SODIUM IONS IN THE RESPECTIVE APPROXIMATE PROPORTIONS OF 0.1 TO 1.0 TO 1.0, PROVIDING A NICKEL ANODE AND AN INERT ANODE IN SAID SOLUTION, MAINTAINING A CATHODE CURRENT DENSITY FROM 0.05 TO 0.30 AMPERE PER SQUARE CENTIMETER ON A CATHODE IN SAID SOLUTION FOR A TIME INTERVAL BETWEEN 15 MINUTES AND 3 HOURS, MAINTAINING THE NICKEL ION CONCENTRATION APPROXIMATELY CONSTANT BY ADJUSTING THE TOTAL ANODE CURRENT SO THAT THE RATIO OF CURRENT CARRIED BY SAID NICKEL ANODE TO THAT CARRIED BY SAID INSOLUBLE ANODE IS BETWEEN 2.5 AND 1.5 TO 1, AND MAINTAINING THE PH OF SAID SOLUTION BETWEEN 2 AND 6 INCLUSIVE.

Images