US3804726A - Electroplating processes and compositions - Google Patents

Abstract

THIS INVENTION RELATES TO A PROCESS AND COMPOSITION FOR THE PREPARATION OF AN ELECTRODEPOSIT WHICH CONTAINS AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT AND WHICH ALSO MAY CONTAIN IRON, WHICH COMPRISES PASSING CURRENT FROM AN ANODE TO A CATHODE THROUGH AN AQUEOUS PLATING SOLUTION CONTAINING AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF COBALT COMPOUNDS AND NICKEL COMPOUNDS AND WHICH MAY ALSO CONTAIN IRON COMPOUNDS TO PROVIDE COBALT, NICKEL AND FERROUS IONS FOR ELECTRODEPOSITING COBALT, NICKEL NICKEL-COBALT ALLOYS, NICKEL-IRON ALLOYS, OR NICKEL-COBALT-IRON ALLOYS THE IMPROVEMENT COMPRISING THE PRESENCE OF AN EFFECTIVE AMOUNT OF BORIC ACID AND AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF MANNITOL, SORBITOL, AND DULCITOL IN A SINGLE OR COMBINED CONCENTRATION OF 2 GRAMS PER LITER TO 100 GRAMS PER LITER FOR A TIME PERIOD SUFFICIENT TO FORM A SOUND METAL ELECTROPLATE UPON SAID CATHODE SURFACE.

Description

United States Patent 3,804,726 ELECTROPLATING PROCESSES AND COMPOSITIONS Frank Passal, Detroit, Mich, assignor to M & T Chemicals Inc., Greenwich, Conn. No Drawing. Filed April 23, 1973, Ser. No. 353,310 Int. Cl. C23h 5/08, 5/32, 5/46 US. Cl. 204-43 T 23 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process and composition for the preparation of an electrodeposit which contains at least one metal selected from the group consisting of nickel and cobalt and which also may contain iron, which comprises passing current from an anode to a cathode through an aqueous plating solution containing at least one member selected from the group consisting of cobalt compounds and nickel compounds and which may also contain iron compounds to provide cobalt, nickel and ferrous ions for electrodepositing cobalt, nickel, nickel-cobalt alloys, nickel-iron alloys, or nickel-cobalt-iron alloys the improvement comprising the presence of an effective amount of boric acid and at least one member selected from the group consisting of mannitol, sorbitol, and dulcitol in a single or combined concentration of 2 grams per liter to 100 grams per liter for a time period suflicient to form a sound metal electroplate upon said cathode surface.

This invention relates to improved processes and compositions for the electrodeposition of nickel, cobalt, and alloys one with another and with iron. More particularly, this invention relates to the use of new additives to improve the buffering capacity of nickel, cobalt, and alloy plating baths containing nickel and/or cobalt and to facilitating the plating of iron-containing alloys of nickel, cobalt, and nickel-cobalt.

BACKGROUND OF THE INVENTION One of the most serious problems with commercial nickel plating is the precipitation of basic ferric salts with the main sources of iron being as an impurity in the nickel anode materials used, from solution attack on ferrous basis metal parts being plated, from chemicals used for bath makeup and replenishment and from tap water used to replenish water lost by evaporation at the usual plating bath temperatures. When these basic ferric salts precipitate, particularly when pH values of about 3.8 electrometric or higher are reached, they tend to clog anode bags which interferes with free circulation of solution between anode and cathode compartments leading to partial anode polarization (resulting in liberation of oxygen or chlorine or both which attack and decompose organic additives thus adversely affecting performance and increasing operating costs). The precipitate also tends to clog filter media thereby markedly slowing down rates of filtration; this results in frequent and expensive filter cleaning and repacking, and also may result in inferior quality of deposits due to particle roughness, etc. If the concentration of the suspended precipitate in the bath reaches too high a value the precipitate may be electrophoretically codeposited with the nickel resulting in pitting, dull grainy areas, etc., particularly on shelf" areas.

In the electrodeposition of nickel, cobalt or nickel cobalt from a variety of electroplating baths the anode current efliciency under average operating conditions is about 100%. The cathode efliciency, however, is about 95% resulting in evolution of hydrogen at the cathode thereby resulting in the increase in hydroxyl (OH-) ion content in the bath which causes an increase in bath pH. If the pH exceeds an optimum range, say 3.8 to 4.2 for semi-bright or bright-nickel plating or electroforming ap-, plications, the limiting current density may be decreased i.e. the current density at the cathode where burnt or powdery, unsound deposits may be produced, especially on high curent density edges or corners or projections of articles being plated. This necessitates periodic, and under high volume plating, rather frequent additions of an appropriate acid, such as sulfuric or hydrochloric or sulfamic acid, to lower the pH to a value within optimum limits.

Where anode area is not adequately maintained or where excessively high currents per unit volume are used the anodes may partially polarize resulting in evoluiton at the anode of oxygen or chlorine (from chloride-com taining baths) or both. It is thus possible, therefore, that the anode current efiiciency may be lower than the cathode etficiency thereby resulting in an accumulation of excess hydrogen ions (H'*) in the bath resulting in a tendency toward decreasing pH to a value below optimum limits. Under such circumstances not only will the anodically evolved 0 or C1 tend to decompose organic bath additives to adversely affect plating characteristics such as deposit luster etc. but the pH must be periodically increased to a value within recommended limits. Since this necessitates the addition, generally, of a carbonate of the metal or metals being plated, or of a hydroxide or carbonate or bicarbonate of a bath compatible cation, such as Na or Ca or Sr or Ba, and since these materials are either sparingly soluble or slowly reactive or may cause localized precipitation of basic nickel salts they obviously cannot be added directly to the plating bath during operation. The usual modus operandi is to add one or more of these materials in incremental portions in the filter which is rather inconvenient since it involves the use of a filter feed special attachment andwhich may be also troublesome since it may disturb the filter cake (filter aid+activated carbon etc.) and introduce particles into the plating bath which may cause roughness of electrodeposits. It would therefore be highly desirable to modify the bath composition so as to increase the bulfering capacity of the bath so as to counteract in some significant degree a tendency either for rising or falling pH. The usually added boric acid does help to buffer the cathode film i.e. the thin layer of solution immediately adjacent to the cathode, but it provides rather poor buffering action for the body of the plating bath.

A bath which is particularly sensitive to pH is one for plating semi-bright or bright cobalt involving the use of one or more organic additives. If the. pH becomes too high i.e. in the range of 3.8 to 4.2 or higher there is a strong tendency toward obtaining unsightly and unsatisfactory nonuniform, brownish, stained deposits in the high current density end of the range.

It is an object of this invention to improve the buffering characteristics and thereby the pH stability of baths for the electrodeposition of semi-bright or bright nickel, cobalt, alloys of nickel and cobalt, alloys of nickel and iron and alloys of nickel-cobaltiron. A special object of this invention is to provide processes and compositions for the production of sound electrodeposits containing nickel and/or cobalt and iron over a wide range of concentrations of additives without substantial precipitation of basic ferric salts. Other objects of the invention will be apparent from the following detailed description of the invention.

DETAILED DESCRIPTION In accordance with certain of its aspects, this invention relates to a process for the preparation of an electrodeposit which contains at least one metal selected from the group consisting of nickel and cobalt and which may also contain iron, which comprises passing current from an anode to a cathode through an aqueous plating solution containing at least one member selected from the group consisting of cobalt compounds, nickel compound, and which may also contain iron compounds to provide cobalt, nickel and iron ions for electro-depositing cobalt or nickel, or alloys of both and also iron alloys of each or both, the improvement comprising the presence of 2 grams per liter to 100 grams per liter, in single or combined concentration, of at least one member selected from the group consisting of mannitol, sorbitol, and dulcitol for a time period sufi'lcient to form a sound metal electroplate upon said cathode surface. Mannitol, sorbitol and dulcitol are optical isomers having the following formula:

HOCH (CHOH) CH OH The baths may contain an effective amount of at least one member selected from the group consisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliary brightener (d) anti-pitting agent The substrates on which the nickel-containing, cobaltcontaining, nickel-cobalt-containing, nickel-iron-containing or nickel-cobalt-iron containing electrodeposits of this invention may be applied may be metal or metal alloys such as are commonly electrodeposited and used in the art of electroplating such as nickel, cobalt, nickel-cobalt, copper, tin, brass, etc. Other typical substrate basis metals from which articles to be plated are manufactured may include ferrous metals such as steel; copper; tin and alloys thereof such as with lead; alloys of copper such as brass, bronze, etc.; zinc, particularly in the form of zinc-base die castings; all of which may bear plates of other metals, such as copper, etc. Basis metal substrates may have a variety of surface finishes depending on the final appearance desired, which in turn depends on such factors as luster, brilliance, leveling, thickness, etc. of the cobalt, nickel, or iron containing electroplate applied on such substrates. 7

The term primary brightener" as used herein is meant to include plating additive compounds such as reaction products of epoxides with alpha-hydroxy acetylenic alcohols such as diethoxylated 2 butyne-l,4-dio1 or dipropoxylated 2 butyne-l,4-diol, other acetylenics, N- heterocyclics, active sulfur compounds, dye-stuffs, etc. Specific examples of such plating additives are:

1,4-di- (fl-hydroxyethoxy)-2-butyne 1,4di- (B-hydroxy-y-chloroprop oxy) -2-butyne 1,4-di-(fi-,'y-epoxypropoxy)-2-butyne 1,4-di- (fi-hydroxy- -butenoxy)-2-butyne 1,4-di-(2'-hydroxy-4'-oxa-6'-heptenoxy)-2-butyne N-1,2-dichloropropenyl pyridinium chloride 2-butyne-1,4-diol /CH:CH2CN] CHzCHzCN fuchsin posits. However, best results are obtained when primary brighteners are used with either a secondary brightener,

a secondary auxiliary brightener, or both in order to provide optimum deposit luster, rate of brightening, leveling, bright plate current density range, low current density coverage, etc.

The term secondary brightener as used herein is meant to include aromatic sulfonates, sulfonamides, sulfonimides, sulfinates, etc. Specific examples of such plating additives are:

(l) saccharin (2) trisodium l,3,6-napthalene trisulfonate (3) sodium benzene monosulfonate (4) dibenzene sulfonimide (5 sodium benzene monosulfinate Such plating additive compounds, which may be used singly or in suitable combinations, have one or more of the following functions:

(1) To obtain semi-lustrous deposits or to produce substantial grain-refinement over the usual dull, matte, grainy, non-reflective deposits from additive free baths.

(2) To act as ductilizing agents when used in combination with other additives such as primary brighteners.

(3) To control internal stress of deposits, generally by making the stress desirably compressive.

(4) To introduce controlled sulfur contents into the electrodeposits to desirably afiect chemical reactivity, potential ditfernces in composite coating systems, etc. thereby decreasing corrosion, better protecting the basis metal from corrosion, etc.

The term secondary auxiliary brightener as used herein is meant to include aliphatic or aromatic-aliphatic olefinically or acetylenically unsaturated sulfonates, sulfonamides, or sulfonimides, etc. Specific examples of such plating additives are:

( 1) sodium allyl snlfonate (2) sodium-3-chloro-2-butene-l-sulfonate (3) sodium fl-styrene sulfonate (4) sodium propargyl sulfonate (5) monoallyl sulfamide (H NSO NHCH CH=CH (6) diallyl sulfamide NH-Allyl [02S :l

NH-Allyl (7) allyl sulfonamide Such compounds, which may be used singly (usual) or in combination have all of the functions given for the secondary brighteners and in addition may have one or more of the following functions:

(1) They may act to prevent or minimize pitting (probably acting as hydrogen acceptors).

(2) They may cooperate with one or more secondary brighteners and one or more primary brighteners to give much better rates of brightening and leveling than would be possible to attain with any one or any two compounds selected from all three of the classes:

(1) primary brightener;

(2) secondary brightener; and

(3) secondary auxiliary brightener used either alone or in combination;

(3) They may condition the cathode surface by catacooperating additives (usually of the primary brightener type) may be substantially reduced, making for better economy of operation and control.

Among the secondary auxiliary brighteners one may also include ions or compounds of certain metals and metalloids such as zinc, cadmium, selenium, etc. which, although they are not generally used at present, have been use to augment deposit luster, etc. Other cooperating additives of Organic nature which may be useful are the hy- 5 droxy sulfonate compounds of US. Pat. No. 3,697,391 i.e. typically, sodium formaldehyde bisulfite, the function of which is to make baths more tolerant to primary brightener concentrations, to increase tolerance toward metallic impurities such as zinc, etc.

The term anti-pitting agent as used herein is meant to include a material (different from and in addition to the secondary auxiliary brightener) which functions to prevent or minimize gas pitting. An anti-pitting agent may also function to make the baths more compatible with contaminants such as oil, grease, etc. by their emulsifying, dispersing, solubilizing, etc. action on such contaminants and thereby promote attaining of sounder deposits. Anti-pitting agents are optional additives which may or may not be used in combination with one or more members selected from the group consisting of a primary brightener, a secondary brightener, and a secondary auxiliary brightener. Preferred anti-pitting agents may include sodium lauryl sulfate, sodium lauryl ether sulfate and sodium di-alkylsulfosuccinates.

Typical nickel-containing, cobalt-containing, and nickelcobalt-containing bath compositions which may be used in combination with effective amounts of about 2 grams per liter to 100 grams per liter of the mannitol, sorbitol, or dulcitol compounds and elfective amounts of about 01005-02 grams per liter of the primary brighteners, with about 1.0-30 grams per liter of the secondary brightener, with about 05-10 grams per liter of the secondary auxiliary brightener, and with about 0.05-1 gram per liter of anti-pitting agent, described herein are summarized below.

Typical aqueous nickel-containing electroplating baths (which may be used in combination with effective amounts of cooperating additives) include the following wherein all concentrations are in grams per liter (g./l.) unless otherwise indicated:

TABLE I.-AQ,UEOUS NICKEL-CONTAINING ELECTRO- PLATING BATES Minimum Maximum Preferred Component:

- Nickel sulfate 200 500 300 Nickel chloride 30 80 45 Boric acid-.." 35 55 45 pH (eleetromet 3 5 4 When ferrous sulfate (FeS .7H O) is included in the foregoing bath the concentration is about 5 grams per liter to 80 grams per liter.

A typical sulfamate-type nickel plating bath which may be used in practice of this invention may include the following components:

When ferrous sulfate (FeS0 .7H O) is included in the foregoing bath the concentration is about 5 grams per liter to 80 grams per liter.

vA typical chloride-free sulfate-type nickel plating bath which may be used in practice of this invention may include the following components:

TABLE III Minimum Maximum Preferred When ferrous sulfate (FeSO .7H O) is included in the foregoing baths the concentration is about 5 grams per liter to grams per liter.

It will be apparent that the above baths may contain compounds in amounts falling outside the preferred minimum and maximum set forth, but most satisfactory and economical operation may normally be effected when the compounds are present in the baths in the amounts indicated. A particular advantage of the chloride-free baths of Tables III and IV, supra, is that the deposits obtained may be substantially free of tensile stress and may permit high speed plating involving the use of high speed anodes.

The following are aqueous cobalt-containing and c0- balt-nickel-containing electroplating baths in which the combination of effective amounts of one or more cooperating additives according to this invention will result in beneficial AQUEOUS COBALT-CONTAINING AND COBALT-NICKEL- CONTAINING ELEOTROPLA'IING BATES [All concentrations in g./l. unless otherwise noted] Maximum Minimum Preferred V. Cobalt bath:

00804-7 H20 400 200 300 COC12-6 1120---- 75 15 60 113303.; 50 37 45 VI. Cobalt bath:

00804 7 20 500 300 400 N 2101 50 15 3O HsBOam 50 37 45 VII. High chloride cobalt bath:

C0 z-fi z 500 200 I 300 HaBOa 50 37 I 45 X. Suliamate cobalt bath: 7 p

00(O2SNH2)2 400 200 290 CoCh-fi H2O.-

When ferrous sulfate (FeSO .7.H O) is included in the foregoing baths the concentration is about 5 grams per liter to 80 grams per liter.

Preferred cobalt-containing bath compositions may contain at least about 30 g./l. of CoCl .6H O, and typically, 2*0-50 g./l. of CoCl .6H O. Other compounds which have abath compatible cation (i.e. a cation which does notinterfere with the operation of the bath) which will provide at least 7.5 g./l. of chloride ion, Cl- (and preferably a minimum of about 9 g./l. of C) may also be used.

The pH of all of the foregoing illustrative aqueous nickel-containing, cobalt-containing, nickel-cobalt-containing, and vnickel-cobalt-iron-containing compositions may be maintained during plating at pH values of 2.5 to 5.0, and preferably from about 3.0 to 4.0. During bath operation, the pH may normally tend to rise and may be adjusted with acids such as hydrochloric acid or sulfuric acid, etc.

Operating temperature ranges for the above baths may be about 30 to 70 C. with temperatures within the range of 45 to 65 C. preferred.

Agitation of the above baths during plating may consist of solution pumping, moving cathode rod, air agitation or combinations thereof. For applications involving the deposition of alloys containing iron from baths in which the iron is predominantly in the ferrous (divalent) state of valency, it is preferable to use very mild agitation i.e. moving cathode rod, to minimize air oxidation of ferrous to ferric iron.

Anodes used in the above baths may consist of the particular single metal being plated at the cathode such as nickel or cobalt for plating nickel or cobalt respectively. For plating binary or ternary alloys such as nickel-cobalt, nickel-iron or nickel-cobalt-iron, the anodes may consist of the separate metals involved suitably suspended in the bath as bars, strips or small chunks in titanium baskets. In such cases the ratio of the separate metal anode areas is adjusted to correspond to the particular cathode alloy composition desired. For plating binary or ternary alloys one may also use as anodes alloys of the metals involved in such a percent weight ratio of the separate metals as to correspond to the percent weight ratio of the same metals in the cathode alloy deposits desired. These two types of anode systems will generally result in a fairly constant bath metal ion concentration for the respective metals. If with fixed metal ratio alloy anodes there does occur some bath ion imbalance, occasional adjustments may be made by adding the appropriate corrective concentration of the individual metal salts. All anodes are usually suitably covered with cloth or plastic bags of desired porosity to minimize introduction into the bath of metal particles, anode slime, etc. which may migrate to the cathode either mechanically or electrophoretically to give roughness in cathode deposits.

The following examples are submitted for the purpose of illustration only and are not to be construed as limiting the scope of the invention in any way.

EXAMPLE 1 A nickel electroplating bath composition was prepared by combining in water the following ingredients to provide the indicated concentrations (in g./l. unless indicated otherwise).

A polished brass panel was scribed with a horizontal single pass of 2/0 grit emery to give a band width of about 1 cm. at a distance of about 2.5 cm. from the bottom of the panel. After cleaning the panel, including the use of a thin cyanide copper strike to assure excellent physical and chemical cleanliness, it was plated in a 267 ml. Hull Cell, at a 2 ampere cell current for minutes, at a temperature of 50 C. and using magnetic stirring. The resulting deposit was uniformly fine-grained, glossy in appearance, with excellent ductility and a very slight uniform background haze. The leveling was only fair.

On adding to the solution 2.3 =g./l. of sodium allyl sulfonate and repeating the plating test the resulting deposit was brighter and slightly better leveled as evidenced by the degree of obliteration or filling in of the emery scratches. I

On further adding to the solution of 50 mg./l. of 1,4- di-(fi-hydroxyethoxy)-2-butyne a brilliant, well-leveled, ductile deposit with slight tensile stress and excellent low current density coverage was obtained.

EXAMPLE 2 Example 1 was repeated using as the acetylenic primary brightener, 1,4-di-(,B-hydroxypropoxy)-2-butyne in place of 1,4-di-(,s-hydroxyethoxy)-2-butyne and essentially the same results were obtained.

EXAMPLE 3 Example 1 was repeated using as a primary brightener 20 mg./l. of N-allyl-quinaldinium bromide as a replacement for 1,4-di-(fi-hydroxyethoxy)-2-butyne and essentially the same results were obtained except that the degree of leveling was not as high.

EXAMPLE 4 A nickel-cobalt-iron electroplating bath was prepared as in Example 1 but containing only 40 g./l. of ferrous sulfateand in addition, containing 40 g./l. of cobalt sulfate heptahydrate (CoSO -7H O). The plating test sequence of Example 1 was then repeated with essentially the same results obtained.

EXAMPLE 5 EXAMPLE 6 A bath was prepared having the following concentration of salts to give atypical high chloride type bath:

I G./l. Nickel chloride 200 Nickel sulfate 50 Boric acid 40 Sorbitol 36 The additives of Example 1 were used in the sequence given in Example 1 and the ferrous sulfate was added in increments. Highly lustrous, ductile deposits having fair degree of leveling were obtained up to a ferrous sulfate concentration of about 50 g./l. Higher concentrations of ferrous sulfate resulted in partial milky, partially thin striated, non-uniform deposits indicating an upper limit to the useable ferrous iron content.

- EXAMPLE 7 The bath of Example 1 was then subjected to a 4 liter life test using conditions as follows:

Plating cell-5 liter rectangular cross-section (13 cm. x 15 cm.) made of Pyrex.

Solution volume-4 liters to give a solution depth, in absence of anode, of about 20.5 cm.

Temperature55 C. (maintained by immersing cell in a thermostatically controlled water bath).

Agitation-moving cathode rod.

Anode--single bagged titanium basket containing SD nickel squares.

Cathode-brass strip (2.54 cm. x 0.071 cm.) buffed and polished on one side and immersed to a depth of about 17.8 cm.horizontal bend 2.54 cm. from bottom and the next 2.54 cm. bent to give an internal angle on the polished side of cathode of about 45 polished side facing anode at an approximate distance of 10.2 cm. and scribed vertically in center with a 1 cm. wide band of a single pass of 2/0 grit emery paper scratches.

Cell current5.0 amperes.

Timesolution electrolyzed about 7 hours per day occasional cathodes plated for 30 minutes to evaluate deposit leveling, uniformity, ductility, luster (overall and in low current density recessed area).

Filtration-occasional batch.

Additions-the pH was periodically adjusted when necessary with dilute sulfuric acid to within a range of 3.0 to 3.5 electrometric; periodic replenishment additions of the primary brightener and the secondary auxiliary brightener were made to maintain deposit luster and leveling. The ferrous iron content of the bath was maintained with separate nickel and Armco iron anode systems in bagged titanium baskets with occasional corrective additions of ferrous sulfate, based on analysis for ferrous iron, to maintain the nickel and ferrous iron contents of the bath fairly constant.

The life test was run in excess of 1125 ampere-hours per 4 liters using a ampere cell current. Although a small amount of basic ferric salt precipitate formed its amount was small enough to be commercially handled and removed by continuous filtration. The main source of this basic ferric salt precipitate was its formation on the anode bags; the body of the solution remained quite clear. A typical deposit was plated for one hour on a stainless steel substrate to give a brilliant, relatively ductile, well-leveled deposit which was stripped off the substrate and analyzed. The deposit was found to contain about 50% by weight Ni and about 50% by weight Fe.

The deposits have the following general characteristics:

Brightness-very good and easy to maintain. Ductility-Excellent.

Internal stress-40w tensile.

Levelingfairly good (about same as bright cobalt). Hydrogen embrittlement by chromium plating-livery low. Pitting tendency-very low.

Smoothness of depositsexcellent.

EXAMPLE 8 Example 7 was repeated using a bath without sorbitol. Within a relatively short electrolysis time of several hours the bath assumed a muddy appearance on stirring due to formation of basic ferric salts. This condition manifested itself in the appearance of the deposits which showed micro-roughness and orange-peel and even a haze or dullness on shelf areas of the bent cathodes where the basic salt precipitate accumulated to a greater degree. This condition became progressively worse and the bath had to be taken out of operation at the end of about 1 65 ampere-hours of electrolysis.

The solution was then filtered and 36 g./l. of sorbitol were added. In the place of the electrolytic nickel squares in a titanium basket used in previous tests there were suspended in the bath an elliptical cross section rolled depolarized anode containing carbon. On resuming the electrolysis excellent deposits were obtained for about 195 additional ampere-hours at the end of which electrolysis the deposits began to show partial dull graininess. During this second electrolysis the anode had formed a dark film of carbon. It was suspected that the change in plating characteristics had occurred due to partial anode polarization resulting in build up of ferric iron in excessive concentration. This was confirmed by analysis which showed the presence in solution of 3.5 g./l. of ferric iron. The remarkable factor was that even with this relatively high ferric iron content the bath had remained perfectly clear and free of basic iron precipitate although at the bottom of the container there was some accumulation of anode carbon flakes. Due to the soluble ferric iron which could impart a yellow color the solution had changed from a clear transparent green to a dark olive green in color and was opaque in appearance.

The pH of the solution was then adjusted to 3.0 electrometric and the solution was stirred at 140 F. with 40 grams of pure iron powder for 30 minutes. At the end of this period the solution was again clear green due to the reduction of ferric to ferrous iron by the iron powder. After filtration to remove the iron powder the bath was set up for electrolysis again, now using a bagged titanium basket containing electrolytic nickel squares (which apparently resist polarization better than rolled depolarized carbonized nickel with the mild agitation used) and the baths excellent plating characteristics were again restored. This sequence of tests indisputably proved the remarkable complexing and solubilizing effect of sor- 10 bitol on ferric iron under conditions where it would normally precipitate out as a basic salt.

There are two ways in which the buffering characteristics of a nickel, cobalt, or nickel-cobalt plating bath may be evaluated and these are the following:

(1) Taking a known volume of plating bath and adjusting the pH to some relatively low value. While stirring the bath, in which there is immersed a glass electrode-calomel electrode system connected to a pH meter to monitor pH, a solution of an alkali such as saturated sodium bicarbonate, is added in small increments and, after achieving equilibrium after each increment, the pH is read. This results in a series of pH readings and volume of alkali additions which may be plotted on rectangular coordinate graph paper as ordinates and abscissa respectively to give a buffering curve for the system. The greater the volume of alkali solutions required to change the pH from one value to another, say pH 2.0 to 5.0, the greater is the buffering capacity of the system. A 'visual indication of buffering capacity as produced by some adidtive (say mannitol, sorbitol. dulcitol) is the more rapid flattening out of the buffer curve, i.e., it becomes more nearly parallel with the abscissa.

(2) To electrolyze a bath containing no buffering improvement additive and one containing a buffering improvement additive, preferably in series, the solutions having equal volumes and operated at the same temperature, cell current, anode area, agitation, etc. The amount of acid required to readjust the pH to the starting value periodically for the two baths is then compared. The lower the acid consumption the higher is the degree of buffering capacity.

The following examples illustrate method 1 using as the plating bath a Watts type nickel plating bath having the following makeup composition:

G./l. Nickel sulfate 300 Nickel chloride 60 Boric acid 45 EXAMPLE 9 No additive Ml. sat. Na-HCO pH electrometric EXAMPLE 10 25 g./l. sorbitol 1 1 EXAMPLE -Continued Ml. sat. NaHCO pH electrometric EXAMPLE 11 25 g./l. dulcitol Ml. sat. NaHCO pH electrometric 0 1.70 2.5 1.85 5.0 2.00 7.5 2.35 10.0 3.20 12.5 3.75 15.0 4.10 17.5 4.30 20.0 4.50 22.5 4.70 25.0 4.80 27.5 4.90 30.0 0.05 35.5 5.20

EXAMPLE 12 25 g./l. mannitol Ml. sat. Nail-I00 pH electrometric 0 1.65 2.5 1.80 5.0 2.00 7.5 2.35 10.0 2.85 12.5 3.25 15.0 3.55 17.5 3.85 20.0 3.95 22.5 4.10 25.0 4.30 27.5 4.45 30.0 4.60 32.5 4.70 35.0 4.80 37.5 4.90 40.0 5.00

The following example shows that inositol which is C H (OH) or 1,2,3,4,5,6 cyclohexane hexol does not impart the degree of buifering capacity of the three compounds of this invention, viz. manitol, sorbitol, and dulcitol.

EXAMPLE 13 25 g./l. inositol 12 Ml. sat. NaHCO pH 17.5 4.95 20.0 5.10 22.5 5.20

To summarize Examples 9 to 13 inclusive in terms of ml. of sat. NaHCO required to raise the pH from 2 to 5 the following can be calculated:

Ml. 1) No additive 14 (2) Sorbitol 25 (3) Dulcitol 25 (4) Mannitol 35 (5) Inositol 12.5

. G./l. Cobalt sulfate 300 Cobalt chloride 60 Boric acid 45 EXAMPLE 14 No additive Ml. sat. NaHCO pH 0 1.60 1 1.65 3 1.85 6 3.10 8 4.05 9 4.30 10 4.40 11 4.50 12 4.60 14 4.70 16 4.80 18 4.90 20 5.00

EXAMPLE 15 25 g./l. sorbitol Ml. sat. NaHCO pH 0 1.65 1 1.70 3 1.75 6 2.20 8 2.70 10 3.20 12 3.50 14 3.75 16 3.95 18 4.15 20 4.30 22 4.45 24 4.55 26 4.70 28 4.80 30 4.85 33 5.00 36 5.10 40 5.25

It can be seen from Examples 14 and 15 that to increase the pH from 2 to 5 there are required about 16 ml. Without additive and about 29 ml. for 25 g./l. sorbitol respectively indicating the pronounced increase in buffering capacity produced by sorbitol.

13 To illustrate the beneficial effects of sorbitol on a sulfamate type nickel plating bath as used commonly for electroforming the following examples are given:

G./l. Nickel sulfamate 375 Nickel chloride 6 Boric acid 37.5

EXAMPLE 16 No additive Ml. sat. NaHCO pH 1.65 1 1.70 2 1.75 3 1.80 5 1.85 7 2.00 10 2.15 12.5 2.35 15.0 2.85 18.0 4.05 20.0 4.40 22.0 4.55 25.0 4.85 30.0 4.95- 35.0 5.10

EXAMPLE 17 25 g./l. sorbitol Ml. sat. NaHCO pH 0 1.65 1 1.70 2 1.75 5 1.80 10 2.05 12.5 2.20 15.0 2.45 20 3.20 22.5 3.60 3.80 28 4.10 30 4.25 4.50 4.75 4.95 5.05

It may be seen from Examples 16 and 17 that it required in going from pH 2 to 5 about 23 ml. with no additive and about 40 ml. with 25 g./l. sorbitol.

EXAMPLE 18 A 4-liter life test was run using the following conditions:

Plating cell-5 liter rectangular cross-section (13 cm. x 16 cm.) made of Pyrex.

Solution volume--4 liters to give a solution depth, in absence of anode, of about 20.5 cm.

Temperature- C. (maintained by immersing cell in a thermostatically controlled water bath).

Agitation-filtered air through a glass and polyethylene s ider.

Anode---single bagged titanium basket containing electrolytic nickel squares.

Cathode-brass strip (2.54 cm. x 20.3 cm. x 0.071 cm.) buffered and polished on one side and immersed to a depth of about 17.8 cm.-horizontal bend 2.54 cm. from bottom and the next 2.54 cm. bent to give an internal angle on the polished side of cathode of about 45 polished side facing anode at an approximate distance of 10.2 cm. and scribed vertically in center with a 1 cm. wide band of a single pass of 2/0 grit emery paper scratches.

Cell current-5 .0 amperes.

Time--solution electrolyzed about 7 hours per day-- occasional cathodes plated for 30 minutes to evaluate deposit leveling, uniformity, ductility, luster (overall and in low current density recessed area).

The bath composition was as follows:

Nickel sulfate g /l 300 Nickel chloride g./l 60 Boric acid g./l 45 Sorbitol g /1 25 pH, 4.0 electrometric. Sodium saccharinate (0.6H 0) g./l 3.2 Sodium allyl sulfonate ..g./l-.. 2.3 Dipropoxylated 2 butyne-1,4-diol m'g./l 50 Sodium di-n-hexylsulfosuccinate g./l 0.25

The above solution was operated for a total of 670 ampere-hours with periodic replenishment of organic additives. Early in the life test it was found that the pH stabilized at a value of about 4.3 and this pH was allowed to remain at this value except that on two widely sepa rated days a small amount, less than 5 ml., of 1-1 connoticed in deposit appearance or phsyical properties indicating that besides stabilizing pH sorbitol was essentially inert in its action on bath performance. Mannitol and dulcitol would produce essentially the same effect. Sorbitol would be preferred for commercial large scale use because of its ready availablity and substantially lower cost than mannitol and dulcitol.

Although this invention has been illustrated by reference to specific embodiments, modifications thereof which are clearly within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. In a process for the preparation of an electrodeposit which contains at least one metal selected from the group consisting of nickel and cobalt, and which may also contain iron, which comprises passing current from an anode to a cathode through an aqueous acidic plating solution containing at least one member selected from the group consisting of nickel compounds, cobalt compounds, and ferrous compounds providing ions for electrodepositing nickel, cobalt, nickel-cobalt alloys, nickeliron alloy, or nickel-cobalt-iron alloy, the improvement comprising the presence of boric acid and at least one compound selected from the group consisting of mannitol, sorbitol, and dulcitol in single or combined concentration of 2 grams per liter to grams per liter.

2. The process of claim 1 wherein said nickel compounds are nickel sulfate and nickel chloride.

3. The process of claim 1 wherein said nickel compounds are nickel sulfamate and nickel chloride.

4. The process of claim 1 wherein said cobalt compounds are cobalt sulfate and cobalt chloride.

5. The process of claim 1 wherein said cobalt compounds are cobalt sulfamate and cobalt chloride.

6. The process of claim 1 wherein said ferrous compound is ferrous sulfate or ferrous chloride.

7. A. process for the preparation of an iron alloy electrodeposit which contains at least one metal selected from the group consisting of nickel and cobalt which comprises passing current from an anode to a cathode through an aqueous acidic plating solution containing boric acid, ferrous sulfate, or ferrous chloride, and at least one member selected from the group consisting of cobalt compounds and nickel compounds providing cobalt and/or nickel ions for electrodepositin'g cobalt and/or nickel and iron containing in combination an effective amount of:

15 (l) at least one member selected from the group of cooperating additives consisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliary brightener and (d) anti-pitting agent; and (2) grams per liter to 50 grams per liter in single or combined concentration of at least one member of the group consisting of mannitol, sorbitol, and dulcitol;

for a time period sufiicient to form a sound metal electroplate upon said cathode surface.

8. The process of claim 7 wherein said nickel compounds are nickel sulfate and nickel chloride.

9. The process of claim 7 wherein said cooperating additives are sodium saccharinate, sodium allyl sulfonate, 1,4-di-(p-hydroxyethoxy)-2-butyne, and sodium lauryl sulfate.

10. The process of claim 7 wherein said cooperating additives are sodium saccharinate, sodium allyl sulfonate, 1,4-di-(B-hydroxypropoxy)-2-butyne, and sodium lauryl sulfate.

11. In a process for the preparation of an electrodeposit which contains at least one metal selected from the group consisting of nickel and cobalt which comprises passing current from an anode to a cathode through an aqueous acidic plating solution containing at least one member selected from the group consisting of nickel compounds and cobalt compounds, the improvement comprising the presence of boric acid and at least one member selected from the group consisting of mannitol, sorbitol, and dulcitol in a single or combined concentration of 2 grams per liter to 100 grams per liter.

12. The process of claim 11 wherein said nickel compounds and said cobalt compounds are nickel and cobalt sulfates, sulfamates, and chlorides.

13. In an aqueous acidic electroplating solution containing at least one member selected from the group consisting of nickel compounds, cobalt compounds, and ferrous compounds, providing ions for electrodepositing nickel, cobalt, nickel-cobalt alloy, nickel-iron alloy, or nickel-cobalt-iron alloy, the improvement comprising the presence of boric acid and at least one compound selected from the group consisting of mannitol, sorbitol, and dulcitol in single or combined concentration of 10 grams per liter to 50 grams per liter.

14. The composition as claimed in claim 13 wherein said nickel compounds are nickel sulfate and nickel chloride.

15. The composition as claimed in claim 13 wherein said nickel compounds are nickel sulfamate and nickel chloride.

16. The composition as claimed in claim 13 wherein said cobalt compounds are cobalt sulfate and cobalt chloride.

17. The composition as claimed in claim 13 wherein said cobalt compounds are cobalt sulfamate and cobalt chloride.

18. The composition as claimed in claim 13 wherein said ferrous compound is ferrous sulfate or ferrous chloride.

19. An aqueous acidic electroplating solution which contains boric acid, ferrous sulfate or ferrous chloride, and at least one member selected from the group consisting of cobalt compounds and nickel compounds providing cobalt and/or nickel ions for electrodepositing cobalt and/or nickel and iron containing in combination an effective amount of:

(1) at least one member selected from the group of cooperating additives consisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliary brightener and (d) anti-pittting agent; and

(2) 10 grams per liter to grams per liter in single or combined concentration of at least one member of the group consisting of mannitol, sorbitol, and dulcitol.

20. The composition of claim 19 wherein said nickel compounds are nickel sulfate and nickel chloride.

21. The composition of claim 19 wherein said cooperating additives are sodium saccharinate, sodium allyl sulfonate, 1,4-di-(fl-hydroxyethoxy)-2-butyne, and sodium lauryl sulfate.

22. The composition of claim 19 wherein said cooperating additives are sodium saccharinate, sodium allyl sulfonate, 1,4 di (p-hydroxypropoxy)-2-butyne, and sodium lauryl sulfate.

23. In an aqueous acidic electroplating solution containing at least one member selected from the group consisting of nickel compounds and cobalt compounds, the improvement comprising the presence of boric acid and at least one member selected from the group consisting of mannitol, sorbitol, and dulcitol in single or combined concentration of 2 grams per liter to 100 grams per liter.

References Cited UNITED STATES PATENTS 3,677,912 7/1972 Passal 204-49 3,697,391 10/1972 Passal 204-43 T GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 204-48, 49