US2533532A

US2533532A - Electrodeposition of nickel

Info

Publication number: US2533532A
Application number: US639869A
Authority: US
Inventors: Jr William B Stoddard
Original assignee: Champion Paper and Fibre Co
Current assignee: Champion Paper and Fibre Co
Priority date: 1946-01-08
Filing date: 1946-01-08
Publication date: 1950-12-12
Anticipated expiration: 1967-12-12

Description

Patented Dec. 12, 1950 ELECTRODEPOSITION OF NICKEL William B. Stoddard, in, Hamilton, Ohio, as-

Signor to The Champion Paper and Fibre Com pany, Hamilton, Ohio, a corporation of Ohio No Drawing. Application January 8, 1946, Serial No. 639,869

3 Claims. 1

This invention relates to the electrodeposition of nickel and has particular reference to methods of procuring deposits of specified hardness by suitably controlling the composition of the plating bath and the conditions of electrodeposition. It has particular utility in the electrodeposition of nickel for the purpose of building up and salvaging undersized metal parts and in the electroformation of nickel parts of various types and specifically in the electroformation of nickel sheets or strips of considerable size.

In the usual nickel platingart, the primary interest has been in securing good adherence to the base metal, in avoiding porosity of the deposit, and in recent yea-rs in obtaining nickel deposits which are bright as deposited and require no butting. Such deposits are in general quite thinusually less than 0.001 inch in thickness-and the decorative features are important. The physical properties, such as tensile strength, ductility, etc. in such deposits are normally of little interest.

It is evident from the physical characteristics of metallic nickel that it would be highly useful as a material for electrolytically building up undersized or worn parts by deposition on bearing or wearing surfaces, and for electroforming objects or machine parts which are subject to wear or mechanical stress, if it were possible to accurately predetermine and satisfactorily control the physical properties of the electrodeposit so that the desired strength hardness, and other physical properties, could be dependably secured and uniformly maintained within the required limits. Examples of parts which could be salvaged by properly controlled electrodeposition of nickel thereon, are rotating and sliding bearings and various parts subjected to wear and more or less localized pressure, impact and/or vibration. Electroformation, if it could be properly controlled, would find util ty in the production of wide variety of parts dillicult to construct with the desired properties, by conventional methods.

Endless nickel belts have been proposed for the continuous casting of cellulosic or other films or of coating on paper as described in Patent No. 1,719,166. Belts for these purposes must possess a unique combination of physical properties. They must have a relatively high tensile strength and yet stand repeated flexing around the necessary pulleys without damage. The surface must be smooth and must be hard enough not to be marred by the action of press rolls or any other action incident to normal use. The belt must also be substantially uniform in thickness and in physical properties throughout its extent. Rolled nickel belts have not been available in sufiicient width, length, quality, and uniformity to meet the requirements of this art. Electrodeposition has for some time been considered as ofiering a desirable method oiforming such belts, but so far as I amv aware they have not hereto fore been successfully produced in the required sizes with the desired strength and hardness and the necessary uniformity.

I have now discovered that by properly selecting and controlling the composition of the elec trolytic bath and the conditions of electrodeposition, it is possible to deposit nickel of substantially uniform physical properties and to secure deposits of any predetermined desired degree of strength, hardness, and ductility, within rather wide limits. Of course, as is well known, these properties are not independently variable, but greater hardness is accompanied by higher tensile strength and lower ductility, and measurements of hardness, because of their convenience and non-destructive nature, are commonly used as an indication of strength. Hence accurate control of the hardness may be used as a means for securing deposits of predetermined, uniform strength and ductility within narrow tolerances, even where wide variations in hardness itself are permissible.

It is known to be possible by use of solutions containing considerable proportions of ammo.- nium chloride, to secure nickel deposits which possess a high degree of hardness. My process, however, operates to give deposits of controlled predetermined hardness within a range somewhat below that of these highly hard deposits. a range wherein satisfactory predetermination and control of hardness has not heretofore been possible, and which covers values of strength, hardness, resistance to impact, and freedom from brittleeness which render the deposits highly useful in electroformed objects which must possess considerable strength, and in reclaiming worn or mismachined parts which have hardness within this range for resistance to wear, shock, and fatigue. In order to secure deposits of such predetermined physical properties, I use a modification of the well known Watts bath containing the formats radical in addition to the usual nickel sulfate, nickel chloride, and boric acid{ and to precisely control and maintain constant the con 3 of the factors included in the formula.

3 d tions of deposition, primarily the composition of the bath, the pH, the current density, and agitation of the bath. in using a bath of tiis cone position I have discovered that, within the limits of operation and with all other conditions unchanged: 1. A higher ratio of formate to total nickel gives a deposit of greater hardness and higher tensile strength; 2. A higher pH value gives a deposit of greater hardness and higher tensile strength; 3. A higher current density gives a deposit of lesser hardness and lower tensile strength; 4. A higher degree of agitation of the a v=[50o.4+s0o roizsm gmg which V is Vickers hardness, CD is the oathode current density in amperes per square foot,

IEv is the ratio of formate to total nickel in the bath, and A is an agitation factor which has a value of about 1.0 for moderate agitation and a value from 1.6 to 2.0 or more for vigorous or turbulent agitation. It should be noted that this formula is only known to hold within limits which may be roughly expressed as follows: V between 100 and 400; F between 0.1 and 0.5 (though at high values of pH and of nickel content, saturation may be reached at values of F below 0.5) pH between 2.0 and 3.5; and CD bev tween 120 and 30.

The results obtained pursuant to the above formula are subject to further Variation to some degree with variations in other factors not included there-in, such as temperature, purity of the chemicals, and proportions of the ingredients in the bath-other than the ratioof formate to total nickel. Differences from the specified hardness which may result from differences from the assumed values in the above factors, can be cor rected by an appropriate change in one or more If the conditions as determined by the formula, when degree of hardness, one or more of'the conditions can be altered as required to secure the desired physical properties. The conditions to be changed and the direction and approximate magnitude of the change required can be seen by inspection of the formula.

,For example, the hardness may be increased creasing pH as described in the art does not ordinarily occur until the pH reaches a value of 4;.5 to 5.5 which is the usual approximate location of the point where the hardness ceases to decrease and begins to increase with increases in pH. This known increase in hardness with increasing pH above 5.5 in the usual baths is so rapid, however, and the hardness is so sensitive to minute changes in pH, that in the past adjust- :5; merit of the pH has not been considered practical as a means for controlling the hardness of the deposit. The increase of hardness with increase of pH in the present process is sufficiently gradual that adjustment of pH constitutes a rather sensitive control of hardness.

Alternatively, as is apparent from the formula; the conditions can be adjusted to give deposits of greater or lesser hardness without making 7 any change in the composition or acidity of the bath. For instance, increased hardness can be secured by decreasing the current density or vice versa, which is the reverse of the effect noted by some observers when using baths of composition slightly different from that herein disclosed. Otherwise the hardness can be increased by increasing the degree of agitation. So far as I am aware this effect of varying the degree of agitation has never been observed in the use of the prior art nickel plating baths. 1' find, however, where it is desired to produce nickel deposits having closely specified physical properties, that this is frequently a convenient method of securing the desired hardness of the deposit. If, when a run is started, tests of the hardness show a failure to meet the specifications, it is usually a simple matter to change the degree of agitation and this alone is often adequate to make the desired correction without changing any of the more diflicultly alterable conditions. If it is not sufficient, an additional change in current density will generally serve to complete the adjustment, if the composition of the bath has been suitably chosen at the start.

Ascan be seen from the formula, the lower the current density the greater the increase in hardness which results from a given decrease in current density. This is particularly the case at high ratios of formate to-total nickel and with vigorous agitation. This fact must be borne in mind in the practice of the process of the present invention. It is especially significant when making deposits on irregularly-shaped surfaces. Un less suitable precautions are taken in such cases,

the current density in deep depressions and sharp re-entrant angles may be but a fraction of that at the high points on the surface. The resulting dilferences in hardness of the deposit in the high and low areas may become intolerable and in ex tried do not result in a deposit of the specified treme cases the deposit in the lowest areas may become so hard and brittle that spontaneous cracking occurs. To avoid these difliculties when deposits of irregular shape are to be made,'the current density should be equalized so far as possible over the entire surface of the cathode by suitable known methods, and the formate to nickel ratio and the degree of agitation kept low enough that the unavoidable variations in current density do not cause excessive variations in hardness.

Nickel sulfate and nickel chloride are the primary nickel-carrying ingredients of the Watts bath. For purposes of the present invention, ratio of nickel sulfate (NiSO4'7H2O) to nickel chloride (NiClz-GHzO) in the bath is not critical,

as satisfactory results have been obtained With solutions wherein this ratio differed as greatly as from about 2/1 to about 8/1. This ratio does,

however, appear to have some effect on the hardness of the deposit, greater proportions of chloride tending to yield harder deposits and smaller proportions of chloride tending to yield softer deposits. Not only the ratio between the amounts of these ingredients but also the total amount of each may be varied considerablyin aerate:

operations under this invention. baths having a total nickel (Ni) content as high as 66 and as low as 32 grams per liter having been used successfully, though the actual limits for practical open ation are apparently considerably wider.

The presence of boric acid in the bath appears to stabilize conditions somewhat and to make for more. uniform deposition, but its precise mode oil functioning is obscure. It does not appear to act as a buffer in the range of pH that I'employ, though that is commonly considered to be its function in the usual Watts bath. If desired, the boric acid may be omitted entirely but I prefer to use from about to about grams perliter.

Formates have in the past been used occasionally in nickel plating baths as buffers andbrightening agents. The proportions used have not been considered critical and so far as I am aware, formates have never served the purposes or the present invention as a control of the "physical properties of the deposit. In the present inven tion the ratio of the weight of formate; computed as the formic acid radical (COOH) to the weight of the total nickel (Ni) in the bath, is one of the primary factors used in the control of the physical properties of the nickel deposit and should accordingly be properly chosen at thestartand should be carefully maintained throughout the time of deposition.

In general the most desirable temperaunesare round between and F. though the usable range of temperatures appears to be quite wide-- temperatures from about 110 up to about F. having been used successfully. These figures, however, do not appear to constitute definite limits though it is found that at temperatures much above 160 F. the vaporization of formic acid becomes excessive and at temperatures much below 110 F. the useful range of current density becomes unduly restricted.

Though the invention is not necessarily limited its use to non-contaminated solutions, the re sults herein described are those which have been secured in solutions substantially free from contaminants, the effects of which in the deposition of nickel are well known. Ammonium, sodium,

and potassium ions, for example, have the effect of hardening the deposit and if present in considerable proportion in the bath may increase the hardness beyond the range contemplated in the present invention. It may be noted in particular that, because of the deleterious effect of lead in the solution and because of the solubility of lead in formic acid, lead-lined tanks and equipment should be avoided. Suitable rubber lined tanks and equipment are recommended-for containing the solution, and high silicon iron has been found suitablefor pipes, pumps, etc. It is well to continuou'siy filter and purify the solution during electrodeposition. In this connection the use of activated charcoal or clay has sometimes been found advantageous. Copper, zinc, etc. may be removed from the bath, before using, by known methods which employ low current density electrolysis.

During the deposit-ion the composition of the bath tends to change. Ordinarily the nickel concentration tends to build up due to the differ ence between the anode and cathode efiiciencies.

This in itself is not harmful but the correspondthe decrease in the acidity should be compensated by periodic additions of acid-su1furic acid is satisfactory for the purpose-4:1 order to maintain the pH value within the required limits; The forl'l'iat to-tota-l nickel ratio should' also be carefully 6 watched and may be controlled by addition of formic acid when necessary due to increase of nickel. content, volatilization of the formic acid, orto other cause. a I The following examples will. serve to illustrate the practical use of the invention.

Example 1.--A precision machine part of considerable size and value had been rejected because a cylindrical bearing surface about 4 inches in diameter and 3 inches long had been machined to a diameter slightly less than the specified low limit. The part was made of chrome-nicke1-molybdenum alloy steel heat treated to give it a Rockwell C hardness of about 32. (corresponding approximately to a Vickers hardness of about 305', in accordance with pub.- lished conversion tables) to resist the extreme loads and vibration towhich it would be sub- .iected in use, and it was required that the repaired surface have substantially the same hardness. In order to salvage the part, the cylindrical bearing surface was built up slightly above and ground down to the correct dimension, using the present invention to give a deposit of nickel having hardness substantially the same as that of the steel itself. For this urpose a plating bath of the following composition was used:

NiSQr'THzO -grams 158.94 NiCIz-GHzO l do 53.64 NiCCOOH)2'2H2O do..- 31.65 H3130: do 25.61 Water liter 1 The total nickel in the bath was approximately 57.5 grams per liter and the ratio of formats to total; nickel was approximately 0.268. After preparing the base metal .so that the electro-deposited nickel would adhere strongly thereto,

nickel was deposited from this bath onto the undersized cylindrical. surface. During the deposi tion the pH of the bath was maintained at a value between 2.75 and 2.80 and the temperature at about 140 R, the cathode current density was maintained at 100 amperes per square foot within close limits and a substantially constant condition of turbulence was maintained in the solu tion. After about two hours the deposit had reached a sufficient thickness of about 0.010 inch. When tested, the deposit showed the desired hardness of from 31 to 33 on the Rockwell C scale (corresponding approximately to Vickers hardness values between about 296 and 316). When dressed to the required dimensions the part of hardness on the Rockwell C scale. Had a test deposit not shown hardness within the specified limits, the degree ofagitation and if necessary the current density, could have been altered to give the required degree of hardness, before starting deposition on the part to be salvaged.

' Example 2.--This example involves the electrolytic production of a long strip of sheet nickel =7 for makingran endless belt for use as a casting surface for films or coated paper. The hardness and tensile strength of strips for this use are desirablyhigh, but they must not be so high as to unduly decrease ductility and increase brittleness. Accordingly the plating bath consisted of 2900 gallons of solution prepared in the following proportions: V

NiSO4-7H2O grams 185 NiCla-GHzO d O 45 Ni(COOH)2-2H2O "do-" 35 H3303 d 30 Water liter 1 Thetotal nickel in the bath was approximately 61 grams per'liter, and the ratio of formate to total nickel was approximately 0.280. The pH of the solution was adjusted to 2.70 by the addition of sulfuric acid. A good grade of chemicals was used and care was taken throughout: to prevent contamination of the bath.

The cathode was in the form of a horizontally mounted cylinder 4 feet in diameter and 6 feet in length. The face was composed of l8'8 stainless steel containing 2 per cent oftmolybdenum, as described and claimed in my co-pending application Serial No. 538,537, filed'June 2, 1944, now abandoned. This face was carefully polished to a mirronfinish. This cathode was continuously rotated on its axis at a surface. speed of about three feet per hour. The-cathode was rotated in a rubber-lined tank containing the solution described to a depth to submerge about 85 per cent of the cylindrical surface. The anodes were in the form of rolled oval bars of nickel con- 'taining about 2 per cent of cobalt, spaced about inches from the face of the cathode and'bent to' conform to its cylindrical form, each 'bar being enclosed in a woven bag to prevent contamination of the solution. The tank was provided with inlet and outlet pipes through which the solution was circulated at the rate of about 35 gallons per minute by means of a Duriron pump. This, together with air agitation, provided" moderately vigorous agitation (corresponding toa value of A of about 1.4) in the liquor between the electrodes.

A rubber-covered plate and frame filter contain- 1 temperature at the desired value. The electrodes 6 were connected to a direct current generator which supplied direct current at. a potential of 9-10 volts and a rate of about 60 amperes per square foot of the submerged surface of the "cathode' As the cathode surface'emerged from .the plating bath, the electrodeposited nickel was "stripped therefrom as a continuous strip six feet wide and about 0.010 inch thick and was wound on a reel. During the 'run which lasted about 60 hours, a strip of nickel about 175 feet long was produced. It was found to have a tensile strength of about 130,000 pounds per square .inch (well within the limits specified for the strip), with V ltlOll of 4. to 4 per cent, and Vickers hardness of about 285 to 290, which corresponds to a Rockwell C hardness of about 30. The conditions initially established corresponding, in accordance with the formula, to a Vickers hardness of about 290, required no change in order to prod ces ip i h r e fieqe r si .8. Example 3.In this case the bath contained per liter; Grams NiSO4-7H2O NiClz-GI-IzO so 7 Ni(COOH)z'-2H2O 27.3

Grams per liter msol-vnz'o 24o NiClz-GI-lzO 45 HsB'Os 30 To this was added sufficient formic acid to give a ratio of-formate to, total'nickel of 0.l33,'and enough sulfuric acid to reduce the pH to 2.0. The deposition was then carried out at a current density of amperespersquare foot and a temperature of about lf1U F.,- using only a moderate degree c-f agitation which, as hereinbefore set forth, corresponds to a value of l for the agitation factor-Ain-the formula. The resulting deposit was found to have a Vickers hardness of 146 instead of the value of 1&2 expected from the establishment of the stated conditions in accordance with the formula. This is well within the limits of .error in hardness testing and accordingly answers the predetermined requirement.

Example 5.,In this case the deposit was to have a hardness intermediate between that of the deposit in Example 1 and that in Example 4; but somewhat harder than their mean. For this purpose the basic solution was; the same as that described'in Example 4, the ratio of formate to total nickel was the same, but the pH was in this case adjusted to 3.5 and the deposition-was carried out at a current density of only 30 amperes per square foot at a temperature of about F. The same moderate degree of agitation as in Example 4 was used in this case, corresponding to a value of 1 for the agitation factor A. The resulting deposit was found to have a Vickers hardness of 245 which was essentially the same as the value of 2 16 predicted to result from the establishment of the conditions named, in accordance with the formula.

While the invention has been described as related to the deposition of nickel, it is to be understcod as including nickel containing small percentages of cobalt, and has been used satisfactorilyin electrodeposition from commercial anodes which commonly contain some cobalt.

I claim:

1. Inthe electrodeposition of nickel from a bath of the Watts type wherein the nickel sulproportion thereof, and other conditions of deposition, in accordance with the degree of Vickers hardness V specified for the deposit that and within limits about as follows: the ratio F of formate to total nickel between 0.1 and 0.5, the pH between 2.0 and 3.5, the current density CD between 120 and 30 amperes per square foot, and the agitation factor A between 1.0 corresponding to moderate agitation and 2.0 corresponding to turbulent agitation, and bringing the bath to a temperature of between 1 and 160 deg. Fahrenheit.

2. Method of preparing to make electrodeposits of nickel of approximately any predetermined specified hardness within the range of about 100 to about 400 Vickers, from a bath of the Watts type which is substantially free from formaldehyde and from sodium, otassium and ammonium ions, and wherein the nickel sulphate and nickel chloride are present in a ratio between 2:1 and 8:1, which comprises: including the formate radical to the extent, and making a test deposit under the conditions, determined by the formula:

in accordance with the specified value V of the Vickers hardness, at a temperature between 110 and 160 F., said conditions being within the following limits: the agitation factor A between 1.0 corresponding to moderate and 2.0 corresponding to turbulent agitation, the ratio F of formate to total nickel between 0.1 and 0.5, the pH between 210 and 3.5, and the current density between 30 and 120 amperes per square foot; then, while holding said conditions within said limits, making at least one of the following changes: increasing the ratio F of formate to total nickel in the bath, increasing the pH, decreasing the current density CD, increasing the agitation A, when greater hardness is required to more closely approximate said specified hardness, and vice versa, said changes being proportioned in accordance with said formula, to the dilference between the value of V specified and that of the test deposit.

3. Method of making electrodeposits of nickel of approximately any predetermined specified hardness between about 100 and about 400 Vickers, from a bath of the Watts type which is substantially free from formaldehyde and from sodium, potassium, and ammonium ions, and wherein the nickel sulphate and nickel chloride are present in a ratio between 2:1 and 8:1, which comprises: including the formate radical to the extent, and making a test deposit under conditions, determined by the formula:

in accordance with the specified value V of the Vickers hardness, at a temperature between 1 0 and 160 deg. Fahrenheit, said conditions being within the following limits: the agitation factor A between 1.0 corresponding to moderate and 2.0 corresponding to turbulent agitation, the ratio F of formate to total nickel between 0.1 and 0.5, the pH between 2.0 and 3.5, and the current density CD between 30 and amperes per square foot; then, while holding said condition within said limits, making at least one of the following changes: increasing the ratio F of formate to total nickel in the bath, increasing the pH, in creasing the agitation A, and decreasing the current density CD when greater hardness is required to more closely approximate said specified hardness, and vice versa, said changes being proportioned, in accordance with said formula, to the difference between the value of the hardness V specified and that of the test deposit; and thereafter electrodepositing nickel from said bath while maintaining the conditions of deposition substantially constant throughout the deposition process.

WILLIAM B. STODDARD, JR.

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

UNITED STATES PATENTS Number Name Date 2,026,718 Weisberg et al. Jan. '7, 1936 FOREIGN PATENTS Number Country Date 526,966 Great Britain Sept. 30, 1940 526,967 Great Britain Sept. 30, 1940 OTHER REFERENCES Modern Electroplating, published by Electrochemical Society, 1942, pp. 250, 253. Metal Industry, Feb. 9, 1940, p. 155.

Claims

1. IN THE ELECTRODEPOSITION OF NICKEL FROM A BATH OF THE WATTS TYPE WHEREIN THE NICKEL SULPHATE AND NICKEL CHLORIDE ARE PRESENT IN A RATIO BETWEEN 2:1 AND 8:1, WHICH IS SUBSTANTIALLY FREE FROM FORMALDEHYDE AND FROM SODIUM, POTASSIUM, AND AMMONIUM IONS, THE METHOD OF SETTING UP THE OPERATION TO YIELD DEPOSITS OF A PREDETERMINED SPECIFIED HARDNESS BETWEEN ABOUT 100 AND ABOUT 400 VICKERS, WHICH COMPRISES INCLUDING THE FORM ATE RADICAL IN TEH BATH ADN SO ESTABLISHING THE PROPORTION THEREOF, AND OTHER CONDITIONS OF DEPOSITION, IN ACCORDANCE WITH THE DEGREE OF VICKERS HARDNESS V SPECIFIED FOR THE DEPOSIT THAT,