US2392708A - Method of making sulphur-containing nickel anodes electrolytically - Google Patents

Description

Jan. 8, 1946. H. E. TscHoP METHOD OF MAKING SULPHUR-CONTAINING NICKEL ANODES ELECTROLYTICALLY Filed Aug. 9, 1941 IN V EN TOR.

A TTORNEYS.

Patented .inn. 8, 1946 UNITED "STATES" PATENT OFFICE mo mom oALLr- ANODES ELECTROLYTI- niu-i-y Edwin Tschop, Huntington, W. Va, assignor to The International Nickel Company, Inc.. New York, N. Y., a corporation of Delaware Application .August 9,1941, Serial-No. 406,115

In Canada June 13, 1941 8Claims. (01.204-292) The present invention relates to nickel plating anodes and, more particularly, to electrodeposited nickel plating anodes containing sulphur and a process therefor.

The development of the nickel plating indus-- try has been accompanied by careful consideration-of the eflect of the composition of the nickel anode upon the plating produced. The earliest nickel anodes contained appreciable amounts of iron and in the earliest days of nickel plating many platers held that the presence of cobalt was advantageous. In the last 25 or 30 years it has been found that nickel anodes containing small amounts of critical elements provided amore satisfactory anode from an operating standpoint than the anodes of the earlier days of the industry. While Spencer has stated:

It may be observed that the general tendency is toward the development and use ofan anode of the highest possible purity containing the lowest possible amounts of carbon, oxygen, iron, silicon, and other contaminating elements.

t t i I i 8 O .0

nickel. In other words, the metal should be clean when etched and examined under the microscope, or, if it is not absolutely clean, the

insolubles should be present in a few 1arge,disconnected particles." [The Metal Industry (London) January 22, 1937, p. 142, column 1, lines 10-14 from the bottom; p. 144,-column 1, line 7 from the bottom to column 2, line 14] the art has found that anodes containing critical amounts of some or all of these elements are far superior from an operating standpoint to anodes devoid of or containing as little as possible, of

these so-called contaminating elements. For example, one of the gravest problems confronting ity which nickel anodes of high purity develop. Several years ago it was proposed to incorporate in nickel anodes a critical amount of sulphur or a critical amount of oxygen or both in order to provide smooth corrosion and to eliminate passivity. .Such anodes have been described and have been provided for the art (Geiger U. 8. Patents Nos hgslfiw and 1,941,257).- However, such. anodes in the past have only been produced by melting electrolytic nickel' and incorporating the necessary amount of sulphur in ways well known to those-skilled in the art. It will be appreciated that the production of electrolytic nickel containing the necessary amount of sulphur would, from an economic standpoint, be a considerable advance in the progress of the art. However, so far as Iain aware, no one has proposed or disclosed a process whereby massive deposits of nickel may be obtainedelectrolytically which contain sulphur in a form providing the corrosion characteristics of sulphur when incorporated during melting and suitable for use as anodes in the electrodeposition of nickel plating for protective and/or decorative purposes.

While it is a fact that thin films of nickel containing extremely small amounts of sulphur have been deposited electrolytically on various base -metals for decorative 'or protective purposes, the

problem of electrodepositing massive nickel containing sulphur and suitable for use as anodes in electroplating, has not been solved heretofore. Those skilled in the art will readily appreciate that many factors affect the production of massive deposits of nickel electrolytically which do not arise in the deposition of thin films of nickel.-

It is customary in electroplating base metals with nickel for protective and/or decorative purposes to provide the base metal with a very thin film of nickel which in most instances has a thickness of about 0.0001 inch and rarely reaches a thickness of 0.001 inch. Incontrast to these very thin films of nickel. anodes for use in the electrodeposition of these thin films of nickel for protective, and/or decorative purposes generally have a thickness of at least about 5 inch and in many instances a thickness of the order of an inch. Furthermore, in the usual electroplating of thin illms for protective and decorative purthe manufacturer of nickel anodes is the passivposes the thin film or nickel is supported by the base metal and consequently the physical characteristics of the film of nickel do not play such an important part. Nickel anodes, on the other hand, must have suflicient strength to support their ownweight and must withstand the usual stresses encountered in shipping and in handling the anodes in and out of the electroplating bath.

Nickel anodes therefore of themselves must not be brittle to the degree that the anodes would shatter and become useless during the usual vicissitudes of comercial handling. Furthermore, the problems of depositing thick coatings of nickel are recognized and the experts in the art readily understand and agreethat beyond a certain thickness many problems arise which have not been solved. (Kugel U. 5. Patent No. 665,: 915.)

The characteristics of a nickel anode which are of primary importance to the electroplater but do not enter into an evaluation of nickel electrodeposits for decorative and/or protective purposes are the activity of the anode at highpI-I, the character of the corrosion, the amount of sludge, the character of the sludge and the tendency of the sludge from some anodes to become detached from the corroding anode in small pieces which float or migrateto the work'being plated. It will be readily appreciated that the producer of articles electroplated with nickel for protective or decorative purposes usually is not interested in the, foregoing characteristics of the protective or decorative plating. Applicant is only aware of one article in the technical literature which discusses the anodic properties of a nickel electro-deposit comparable to the conventional decorative or protective film of electroplated nickel. In an article published in Mitteilungen des Forschungsinstituts and Probieramt fur Edelmetalle for July, 1936, E. Raub discusses the use of insoluble anodes such as lead and rustproof steel by German electroplaters. The following quotation is from a translation of that article: I

"More suitable than the use of insoluble' anodes is the following process which also is the basis of a proposal of the Langbein-Pfanhauser Werke of Leipzig. Metallic nickel is made electrolytically from nickel salts, which in general are not so diflicultto procure as metallionickel, which then is used as anode in the galvanic nickel bath. The process is of course inconvenient and The pure nickel used in industry in the United States is supplied in the form of electrodeposited plates or sheets about one-fourth inch in thickness and cut up in squares of suitable size. It has the typical structure of such deposits in that it consists of groupings of parallel elongated crystals, their size and shape apparently being dependent on the uniformity or non-uniformity of the electric current, composition of the solution, temperature, and other such factors. Any change in these will alterthe rate of deposition and the crystal size. If the current is stopped, metal deposition will cease, and re-solution of nickel from the cathode may occur, or copper or other metal impurities in the solution may deposit by immersion, with formation of a film of Y oxides or basic salts on the surface. When deposition is resumed, a newlayer of crystals of different orientation will be formed, probably with weak'adherence to the underlying metal. This is one reason why cathode sheet nickel would be unsatisfactory for use as. anodes.

i i I l U Because of. the internal stresses de- I particles which-would interfere with smooth platmakes nickel plating expensive but nevertheless better than insoluble anodes in a process for elec-' troplating protective or decorative films of nickel. A mere recitation of these characteristics of a nickel anode impresses the fact that the mere deposition of nickel electrolytically as a thin film for decorative or protective purposes does not provide the art with the answer to these questions: Will electrolytically deposited nickelcontaining sulphur be active at high pH [pH 4.0(Q) Will such nickel corrode smoothly? Will the amount of sludge be excessive? Will the sludge adhere to the anode and only break away therefrom in chunks of such size as to sink to the bottom of the tank? It is equally manifest that other questions of similar scope still remain unanswered after the unpremedltated deposition of sulphur in thin films of nickel for decorative or protective purposes is known. In fact, Spencer in his article in The begiven a slight annealing treatersto relieve such stresses and produce as uniform in grain size as possible.

commercial point of view it is questionable whether the cost of depositingsuch an anode v and annealing it: would be low'enough to make it economically practicable."

While no "organization ofllcially has agreed upon the specifications with which nickel anodes, must comply to be acceptable by the trade, there is generala'gr'eement among not only the users of nickel anodes, but also the producers thereof. regarding'certain characteristics which a nickel anode must have to be acceptable by the trade. Thus, it isa' 'agreed that a nickel anode should havea highdegree of purity and be substantially free from or at least only contain a practical minimum of those elements, such as copper, manganese, iron and zinc, which enter the bath and are plated on the article together with the nickel. It is claimed that an amount of copper and/or iron above a certain percentage in a nickel electrodeposit will cause dark streaks. Furthermore, the presence of manganese is considered to be highly detrimental in that it is considered to affect the corrosion resistance of the nickel deposit adversely. Thus, some experts in the art specify that an anode shall contain lessk than 0.005 per cent manganese.

In addition, the anode should be soluble in the bath under the plating conditions used-and have a high anode efliciency which means that the pH of the electrolyte can be easily maintained. In maintaining the operating pH of a nickel electroplating bath. it is always desirable "to do this by adding sulphuric acid to the bath seem, therefore, that cathode In addition a nickel anode must dissolve with a minimum amount of sludge remaining and the I nature of the sludge should be such that all of it can be retained by an anode bag. If bags are not being used, the sludge should adhere to the anode and build up in sufficient thickness in order to entrap any small particles of loose metallics which may come from the anode. Furthermore, when a layer of sludge does drop off, it should be dense and heavy so that it immediately sinks to the bottom of the plating tank. However, in all first class plating shops the injurious effect on the deposit, which can readily be caused by particles of metallics and sludge, is recognized. Consequently, all types of anodes are bagged and at the same time the electrolyte is continuously or intermittently filtered through a filter medium with the result that the electrolyte is practically 1 free from suspended matter.

The art has agreed that a nickel anode should dissolve in such a manner that practically no metallic particles are evolved since it has deflnitely been proven that these metallic particles can cause rough work. The commercial importance of percentages of loose nickel is perhaps better realized when it is appreciated that certain large purchasers of nickel anodes have purchased anodes on a specification of .a maximum loose nickel of 0.04 per cent of the total weight of anode the anodes cease to corrode smoothly and uniformly. In many instances they become covered with a soft, spon y, metallic "hide or "skin on the surface or the metal may remain hard and firm but selective corrosion takes place, causing furrows or grooves in the anode face. The pH at which the surface becomes rough or spongy has been defined as the upper limit of smooth cor-.

rosion or its activity limit.

A nickel anode should be free from metallurgi cal defects, such as longitudinal or-transverse cracks, commonly termed fire cracks, and slag pockets or gas holes.

During the normal corrosion of the anode it has been found that the areas around such defects corrode at. aslightly higher rate than the body of the anode with the result that the bar ma corrode completely through at these spots, causing an unused section to fall to the bottom of the tank. Therefore, since it is highl desirable and economical-to have as little scrap loss as possible, the anode bars should be free of such defects mentioned above.

Likewise, a. nickel anode should have a size and shape so that a maximum amount of surface is exposed and at the same time require only a small amount of tank space. The shape and size should alsobesuchastobeeasilyhandledandtobe attached to the anode bus bar by means of anode hooks. For the above reasons the elliptical shape of the anodes now being used in the trade is pretty much standardized. By this shape it is possible to produce a section which contains about one pound of nickel per linear inch.

There are three main types of anodes being used in large tonnages in'the plating industry today. depolarized, both 99 per cent plus, which are elliptical in shape and'are of such a section that the weight is approximately one pound per linear inch, the 99 per cent plus cast carbon anodes which are also elliptical in shape but have a slightly larger cross section arid weigh more than one pound per inch, and electrolytic nickel anodes.

Finally, a' nickel anode'should have a good, clean surface and be free from mechanical and metallurgical defects in the as purchased" condition. The surface layer of an anode should be prepared. either by pickling or "deskinning (ac- I tivating) so that it begins to dissolve immediately when placed in the plating circuit.

From the foregoing discussion it will be appreciated that the desirable characteristics and the characteristics of nickel anodes required by the art are entirely different from the desirable and required characteristics of protective and/or decorative nickel electrodeposits. For these reasons,

nickel anodes for use in the production of protective and/0r decorative nickel electroplate have contained addition agents and have not been 0 the highest nickel content possible.

While the art has recognized the advantages resulting from the incorporation-of small controlled amounts of substances other than nickel in nickel anodes, ior'example, oxygen, copper, sulphur, silicon etc., on the other hand, in the production of electrolytic nickel anodes in the past, every attempt has been made. to exclude from the cathode deposit all elements except nickel and cobalt. This has resulted in an electrolytic nickel which, with the years, has become purer until today electrolytic nickel has a purity greater than 99.80% (nickel plus cobalt) and is devoid of sulphur. Therefore, a problem confronted the' experts in the art, to wit: the incorporation of sulphur in electrodeposited nickel anodes without recourse to additional steps of melting electrolytic nickel, adding sulphur to the molten nickel and casting a sulphur-containing nickel ingot suitable for reduction to anodes. In other words,. if sulphur could be incorporated directly in an electrolytic nickel anode during It is another object of the present inventionto provide a means for producing electrolytic nickel containing sulphur within critical limits.

The" present invention also contemplates a novel nickel electrolyte from'which nickel containing sulphur can be electrodeposited.

It is a further obiect of the prwent invention to provide electrolytic nickel anodes containing sulphur within critical limits.

Other objects and advantages of'the present These are the rolled carbon and rolled inorganic materials.

invention will become apparent from the following description and drawing in which:

Figure 1 is a photomicrograph of a transverse section of conventional electrolytic nickel and Figure 2 is a photomicrograph of a transverse section of novel sulphur-containing active electrolytic nickel.

In its broadest aspect the present invention contemplates incorporating in the usual or con ventional or standard or other electrolytic bath for the production of electrolytically deposited nickel anodes, i. e., cathode-nickel anodes, an electrolyte soluble substance containing sulphur which during the electrodeposition of nickel will deposit sulphur with the nickel. While the particular form in which sulphur must be present in anickel anode to provide the good corrosion and activity during subsequent electroplating is not generally known, I have found that certain sulphur-containing materials give satisfactory results whereas others do not. Thus, for example, among the inorganic sulphur-containing compounds which are inefiective is sodium pyrosulphate. On the other hand, sodium thiosulphate is effective. Among the organic substances which are ineffective although containing sulphur, are trional and sulphonal while among the effective materials are thio-urea, methylene blue and others.

From my investigations it would appear that the conditions under which the electrodeposition' is carried out has a. bearing upon the amount of sulphur which is deposited together with the nickel. For example, nickel deposited at low pH and high current density from an electrolyte containing sodium sulphite contains no sulphur whereas nickel deposited at high pH and low current density from an electrolyte containing sodium sulphite contains about 0.015% sulphur. On the other hand, nickel electrodeposited at low pH and high cathode currentdensity and nickel electrodeposited at high pH and low cathode current density from nickel electrolytes containing sodium pyrosulphate contain practically no sul-' phur and corroded .unsatisfactorily at pH 4.0 (quinhydrone). When a deposit containing 0.015% sulphur such as that obtained from an electrolyte containing sodium sulphite is corroded under standard testing conditions ata pH of about 4.0 as determined by the quinhydrone electrode the corrosion is unsatisfactory. Nickel deposited at low pH and high current density from an electrolyte containing sodium bisulphite contained about 0.11% sulphur whereas nickel deposited from a similar electrolyte at 'high pH and low current density contained no sulphur and in both cases, the corrosion of the nickel anode thus produced was poor. In contrast to the foregoing, nickel deposits made from a bath containing sodium thiosulphate and deposited at low pH and high current density or high pH and low current density both contained sulphur and corroded anodically in a satisfactory manner. Thus'it will be seen that sulphur is not deposited with equal facility from all sulphur containing Nor is the mere presence of sulphur an assurance that the nickel deposit containing the sulphur will corrode anodically in a satisfactory manner.

It would appear that the activity at a high pH such as pH 4.0 (quinhydrone) is dependent not so much upon the presence of sulphur but upon the presence of at least a critical amount. Thus, during these investigations it has appeared that in order to have a good activity at high pH such as pH 5.5 (quinhydrone) it is necessary to have a minimum sulphur content in the cathode nickel anodes of at least about 0.011% and a maximum sulphur content in the cathode nickel anodes of about 0.05 to about 0.06%.

Illustrative of sulphur-containing compounds which may be employed for the purpose of introducing into cathode nickel sufllcient sulphur to ensure that the cathode nickel when employed as anode for electroplating for protective and decorative purposes at high pH such as pH 5.5 (quinhydrone) will have good activity are 5 types of sulphur-containing compounds. These sulphur compounds may be classified as (1) sulphonamides or substituted'sulphonamides having the type formula II R- S --NH:

where R is an aromatic radical such as that of benzene and its homologues and naphthalene and its homologues. (2) thio-urea and substituted thio-urea having the basic structure N-C-N/ I (3) phenthiazine compounds such as methylene blue having the basic structure (4) thiosulphates having a structure considered to be MO/ \S such as sodium thiosulphate and (5) dithiophosphates considered to have the basic structure (where R is a cyclic radical such as the cresol or phenol radical or where R may be an alicyclic radical) and M is an alkali metal such as the dithiophosphates well known to the art of concentrating minerals by flotation. These phosphorus and sulphur containing addition agents may be prepared from substances containing a hydroxyl group, such as alcohols or phenols or from substances containing carboxyl groups (COOH) the aldehyde group, (COH) or the ketone group. (C0).

, In the preparation of cathode nickel containing sulphur for direct use as anodein the electrodeposition of nickel for protective and/or decorative purposes it has been found that 4 factors, to" wit: concentration of sulphur-containing addi-" tion compound, cathode current density, DH of the bath and temperature; influence the amount of sulphur deposited with the cathode nickel. or course, solubility of the sulphur-bearing addi tion agent in the electrolyte also has an effect upon the amount of sulphur introduced into the cathode nickel. Furthermore, when the sulPhur-. bearing addition agent forms insoluble precipi tates or an oily reaction product with thecon- 'stituents of the electroplating bath, unsatisfactory results are usually obtained. Thus, when insoluble reaction products or oily reaction products are formed with the constituents of the bath in some instances these reaction products migrate to the cathode and the cathode nickel thus produced may be very rough and porous due to the presence of the precipitated reaction products in the electrolyte.

The four factors enumerated above aflect the sulphur content of cathode nickel when deposited from a bath containing a sulphonamide or substituted sulphonamide generally as follows:

The sulphurcontent of the cathode nickel increases first rather rapidly with theconcentration until the concentration of soluble sulphonamide in the electrolyte reaches a value of about 0.35 gram per liter. Thereafter the sulphur content of the cathode nickel increases quite slowly with increased concentration of sulphonamide. The sulphur content of cathode nickel is affected ne ligibly by the cathode current density when this class of sulphur bearing compound is employed.

The sulphur content of cathode nickel varies with the pH being high at low pH and low at high pH when sulphonamides or substitutedsulphonamides are employed. In the presence of sulphonamides or substituted sulphonamides the sulphur content of cathode nickel increases with decrease in temperature. The foregoing is clearly evident from the following tabulations:

Erncr or Concrnrxerror'r or SULPHUR-BEARING Anmrrox AGENT (SULPHONAMIDES on SUss'rI- rursn Sunrnommunrs) Conmrrorra-pH, 2.5 (quinhydroue). Cathode current density, 30 amperes per square foot. Temperature, 45 C.

Concentration Activity of of sulphur- Per cent sulca ode bearing addiphur in cathnickel at. H tion agent, in ode nickel 5.5 (quin ygrams per liter drone) 0.05 0.012 Passive 0.15 0.034 Fair 0.35 0.042 Good 0. 50 0. 045 Good 1.00 0.047 Good Errscr or CURRENT Dsnsnr CONDITIDNBr-DH, 2.5 -(quinhydrone). Temperature, 45 .0.

Concentration of sulphurbearing addition compound, 1.00 gram per liter.

Actiilrgdy of .Current den- Per cent snl- 6 city (amperes phur in cath- "5 g square foot) ode nickel 2 i hy drone) i 0. 045 Good 30 0. 047 Good 50 0. 049 Good Errrc'r or VARrA'rroN or 2H CONDl'l'l0Ns.-Cathode current density, 30 amperes per squ re foot. Tcmperature,45 C. Concentrationoisnlphurbearingaddition m per liter.

- Actlvityof pn (quin- 55mg 1 flo fincks el 8 D hydrone) ode nickel (q drone) 0.056 Good M 11041 Good o 0.035 Fair 0.025 Panlve eity, 38 amperes per square foot.

Low rH-Hma Crmanrr Dnrsrrr Conpnroim-Low pH, pH 2.5. High current density, 30 amperes ggg square loot. Temperature, 45 C. Concentration of 3111 huring addition agent, 0.25 grams per liter 0! electrolyte. P sting time, 48 hours.

. Activity of .if'h t. .Tit" Sulphur bearing addition agent 5 2 23 nickel (31:111-

hy one) Para toluene sulphonamide 0. 040 Good Ortho toluene sulphonamide. 0. 044 Good Dichlorarnine 'l (ortho or para tolue 0.011 Fair phondichlorarnine) Benzene sulionamidem; 0. 057 Good 1 Dichloramine T has a low solubility in solutions of low pH.

HIGH PH-LOW CURRENT DENSITY CoNm'rror rsPpH, 5.5 (quinhydrone). Cathode current density,

Err-nor or VARIATION nw Tauranaruar:

Connmona- H 2.5 ulnh drone). Cathode current denp (q y Concentration of sulphur-bearing addition agent, 1.00 gram per liter.

Percent of Temperasulphur in .5 g ture, C. cathode pH 5.5 (quinnickel hydwne) 3o 068 very good 5 0. 047 Good The sulphur content of cathodenickel produced in an electrolyte containing thio-urea or substituted thio-urea varies (1) substantially linearly with the concentration of sulphur bearing addition compound; (2) with the current density. The sulphur content'of cathode nickel increases slightly with increased pH and with decrease in temperature when thin-urea or substituted thin-urea is employed.

Erracr or Vemrr'ou nr CONCINTRATION or SULPHUR BEARING Annrrrorr Adam Connrrroua-pfl, 2.5 (quinhydrone). Cathode current density 30 amperes per square foot. Temperature, :50 C.

Concentration of thiourea m cathode m nickel 0.05 (Hi2: 0. l0 0. 15 0.810 0. 2o 0. 410 0. 25 0.405

minor or VARIATION IN CURREN DENSITY CoNm'rroNs-pH,

EFFECT or VARIATIONS IN PH Current Percent density, sulphur in amperes per cathode square toot nickel 2.5 (quinhydrone). Temperature, 50 C. Concentration of thio-urea, 0.10 gram per liter.

CoNmrroNs.--pH, 2.5 (quinhydrone). Cathode current density,

30 arnperes per square foot. of thin-urea, 0.10 gram per liter.

Temperature, 50 C.

Percent pH (quinsulphur in hydrone) cathode nickel Concentration EFFECT or VARIATION IN TEMPERATURE CoNmT1oNs.pH, 2.5 (quinhydrone). Cathode current density, 30 aniperes per square foot. Concentration of thio-urea, 0.10 gram per liter.

Percent Temperasulphur in ture, C. cathode nickel The sulphur content of cathode nickel electrodeposited in baths containing substituted phenthiazine compounds such as methylene blue (1) varies. directly with the concentration of the phenthiazine compound; (2) decreases with increase of cathode current density; (3) increases slightly with increase or-decrease of pH from a ature.

EEEEcT E VARIATION IN CoNcnNTRATIoN or SULPHUR-BEARING AnnITIoN AGENT L median pH and increases with a rise in temper- CONDI'I'IONs.-pH, 2.5 (quinhydrone). Cathode current density 30 amperes per square foot. Temperature, 40 C.

a s??? Percent Methylene sulphur in Blue, grams cathode I per nickel EFFECT OF VARIATION IN CATHODE CURRENT DENSITY CONmTroNs.pH 2.5 (quinhydrone). Tem e ture 40 C. Concentration of Methylene Blue, 0.25 gram per Cathode cur- Percent rent density, sulphur in amperes per cathode square foot nickel l0 0. 115 0. 083 so I 0.074

Concentration of thiof ffff sulphate in caghode fig nickel EFFECT or VARIATION IN PH CoNniTioNs.-Cathode current density, .30 amperes per square foot. Temperature, 40 C. Concentration of Methylene Blue,

The sulphur content of cathode nickel produced in electrolytes containing sodium thiosulphate (1) varies directly with the concentration,

. (2) is slightly affected by cathode current density, (3) varies considerably with high or low pH from a median pH, and (4) increases slightly with decrease in temperature.

v35 EFFECT OF VARIATION IN CONCENT ATION or SULPHUR-BEARING AnnITIoN AGENT CoNmTIoNs.pH, 2.5 (quinhydrone). Cathode current density, 30 amperes per square foot. Temperature, 40 C.

EFFECT or VARI TION IN CURRENT DENSITY CONDnToNa-pH, 2.5 (quinhydrone). Temperature, 40 0.

Concentration of thiosul'phate. 0.10 gram per liter.

Current Per cent density in sulphur and amperes per cathode square foot nickel EFFECT or VARIATION IN PH CoNnrrIoNs.-Cathodecurrent density, 30 amperes per square foot. Ten perature, 40 0. Concentration of thlcsulphate, 0.10

gram per liter.

Percent of (quln- S p in ydrcne) cathode nickel I Addition agent crystallized out in part from the colder solution.

j aeea'roe Enter or vlumrron m Turns-run:

Commons-p3, 2.5 (quinh drone). Cathode current density, N amperiis per square foot. oncentration of thiosulphate, 0.10

gram per ter.

' Percent Temperasulphur in ture, C. cathode nickel Cdumrrona-pH, 2.6 (quinhydrone). Cathode current density. 30 amperes per square foot. Temperature, 40 C.

Concentratlon of dipsiz tzt. m sass... p ur n cadii igii fi 13211 5 phateL gmms per liter EFFECT OF VARIATION IN CA'IHCDE CURRENT DENSI'fY Commons-pH, 2.6 (quinhydrone). Temperature, 40 Concentration of dithiophosphate, 0.20 gram per liter.

' EFFECT O! VARIATION IN PH CorimrroNa-Cathdde current density, .30 amperes per square foot- Temperature, 40 C. Concentration of dithiophosphate, 0.20 gram per liter.

Percent Percent pH (quinsulphur m phosphorus hydrous) cathode in cathode nickel nickel Emc'r or-Vaurarron m TIIPlRATURE Counrriosa-pH, 2.6 (quinhydrone). Cathode cim'entdensity, 80 amperes per square foot. Concentration of dithlophosphate,

0.20 gra W Temp zfg i s ature, in i cathode C. 't ode nickel kel The preferred operating conditions for each of the foregoing classes of sulphur-bearing addition compounds are summarized in the tollowins tabulations:

sulplhonamldes and substituted sulphpnamides,

pH-about 2.0 to about 2.5 (quinhydrone) Current density-about to about 50 amperes p r square foot Temperature-about 25 C- to about 40 C.

Concentration of sulphonamide-about 1.00 gram per square foot.

per liter Thin-urea and substituted tlu'o-ureas Substituted phenthiazine addition agents pH-about 2.5 to about 4.5 (quinhydrone) Current density-about 10 to about 50 amperes per square foot Temperatureabout 30 to about 50 C.

Concentration of substituted phenth'iazine compound-about 0.10 to about 0.20 gram per liter Thiosulphate addition agents about 0.20 gram per liter Dithiophosphate addition agents pH-about 1.7 to about 5.5 '(quinhydrone) Current density-about 10 to about 50 amperes per square foot Temperature-about 20 to about 40 0.

Concentration of dithiophosphate-about about 0.25 gram per liter From the'foregoing it will be appreciated that sulphur-bearing cathodic nickel can be electrodeposited from conventional nickel electrolytes such as electrolytes containing about 84 grams of nickel per liter, about 13 to 14 grams of chloride per liter and about 14 to 15 grams of boric acid per liter and containing about 0.2 of a gram to .about 1 gram per liter of sulphur-bearing electrolyte soluble compound. The electrodeposition' of the novel sulphur-bearing cathodic nickel can be carried out at a pH of about 1.7 to about 5.5 at a temperature of about 20 to about 50 C. at a current density of about 10 to about 50 amperes It would appear that the sulphur present in the electrolytically produced nickel anode should 'be present in the anode principally in the sulphide form. I have foundthat it would appear that those anodes which have satisfactory activity at high pH [pH 4.0 (Q) and above] when analyzed for total sulphur by the acid evolution method contain sulphur in the sulphide form. That is to say for example,the total sulphur as determined as barium sulphate was 0.045% and the sulphur determined by acid evolution was 0.041 to 0.045%. It would appear from these results that all, or practically all the sulphur of the electrolytically produced nickel anodes was in sulphide form. These anodes had satisfactory activity at pH 4(Q) and above, corroded smoothly and produced small amounts of sludge containing small amounts of metallic nickel. Consequently, such anodes are acceptable to the trade from all technical considerations.

. The novel sulphur-bearing cathodic nickel or electrolytic nickel'produced in accordance with the foregoing'disclosure has a novel microstructure which readily enables experts in the art to differentiate this novel sulphur-containingelec-f "of regular conventional sulphur-free electrolytic or cathodic nickel and is a typical specimen of regular or conventional sulphur-free electrolytic nickel. Fig. 2 is a reproduction of a photomicrograph taken at 500 diameters magnification of a transverse section of the novel active sulphurbearing electrolytic or cathodic nickel, and is ty'pical oi th'e'novel active sulphur-bearing electrolyticlnickel producedin accordance with the foregoing;disclosure.

The regular 'or conventional sulphur-free electrolytid'or cathodic nickel was electrodeposited from'a bath containing about 40 grams per liter of nickel, about 35 grams per liter of Na2SO4 and about grams per liter of boric acid at a pH of about 5.0(Q) at a temperature of about 57 C. and a current density of about 12 amperes per square foot.

The novel active sulphur-bearing electrolytic or cathodic nickel of Figure 2 can be produced in an electrolyte having about the same composition as the foregoing, but containing about 1 gram per liter of ortho benzoyl sulphonamide. The novel active sulphur-bearing cathodic nickel of Figure 2 had the following analysis:

Sulphur About 0. 030% as sulphide Copper About 0. 026% Iron About 0. 045% Cobalt About 0. 48

Nickel Balance In other words, the novel active sulphur-bearing cathodic nickelproduced in accordance with the foregoing disclosure contains about 0.030%

-. sulphur principally as the sulphide and the balance principally nickel except for a small amount of cobalt and incidental impurities. A typical analysis of conventional or regular sulphur-free electrolytic or cathodic nickel is as follows:

A comparison of Figs. 1 and 2 makes manifest the differences in microstructure which exist between regular sulphur-free electrolytic nickel and the novel active sulphur-bearing electrolytic nickel of the present invention. In Fig. 2 the presence of large amounts of nickel sulphide is plainly revealed and the photomicrograph shows that the nickel sulphide is mainly concentrated in the grain boundaries. There is no analogous structure discernible in the reproduction of the photomicrograph of a regular sulphur-free electrolytic nickel provided in Fig. 2. Thus, an inspection of the microstructure of the novel active sulphur-bearing electrolytic nickel of the prespurpose.

\ the operating conditions under which such sulphur-containing electrolytic nickel anodes may be produced are provided in the following illustrative examples.

- EXAMPLE, I

The anodes were deposited from a bath substantially equivalent to the conventional electrolyte commonly employed in the industry for this That is to say, an electrolyte was employed containing about 84.46 grams per liter of nickel, about 13.85 grams per liter. of chloride, and about 14.96 grams per' liter of boric acid. In other words, the electrolyte contained a source of nickel, an anode corroding agent and a buffer.

When an insoluble anode is used the anode corroding agent need not be present. Under such conditions conventional salts such as sodium sulphate may be incorporated to increase the con- To this electrolyte ductivity of the electrolyte. was added about 0.25 gram per liter of the sulphur-containing addition agent, in this instance sodium thiosuliphate. v The distance from the anode to the cathode was about 2- inches. The temperature during electrodeposition was between about 40 and about 45 C. A low pH of about 1.8 to about 3.0 was employed and the electrolyte was agitated by an air liftpump, An anode current density of 8 amperes per square foot and a high cathode current density of 27 amperes per square foot was employed. An electrodeposit of nickel weighing about 130 grams was obtained. Upon testing this cathodic nickel as an anode at a pH of about 4.0, it was found that this cathodic nickel deposited from a bath containing sodium thiosulphate had satisfactory activity andsatisfactory corrosion characteristics. Corrosion at pH 5.5 (Q) showed that after 18 hours the metal of the anode was still hard and firm, the anode had satisfactory activity and satisfactory corrosion properties. The anode produced cathodically in the bath containing sodium thiosulphate contained about 0.11% of sulphur practically all of which was present in a form reacting with HCl to form H28.

ExAmPLa II From the standard or conventional electrolyte containing about 0.25 gram per liter of orthobenzoyl-sulphonimide a deposit of about 116 grams of cathodic nickel was obtained after a run of about 46 hours. The pH of the electrolyte during this period of electrodeposition was about 1.9 to about 2.6. An anode current density of about 8 amperes per square foot and a cathode current density of about 27 amperes per square foot were employed. From the foregoing it will be seen that the electrolytic nickel anode thus produced was produced under conditions of low pH and high current density. This cathodic nickel was then corroded as an anode at a pH of about 4.0 (Q) at a temperature of about 40 to 45 C. at an anode current density of about 15 amperes per square foot and a cathode current density of about 4 amperes per squarefoot in an electrolyte containing 81.70 grams per liter of nickel, 13.12 grams per liter of chloride and 40.10 grams per liter of boric acid. The pH during the corrosion ranged from 4.0 to 4.3 (Q) and the anode lost about-38 grams during a corrosion of about 22 hours. The surface of the anode was covered completely with a. thin black film of sludge. The anodic metal was hard and firm at all points. The corrosion of the face of the anode was smooth and the anode was highly active. From all technical considerations this anode was highly satisfactory. This anode likewise was tested for corrosion characteristics in a hot Watts type test solution having a pH of about 5.5 (Q) at the initiation of the corrosion. After 22 hours of corrosion the anode was still active, was completely covered with a thin black film of sludge, the metal was hard and firm at all points and the corrosion of the face was smooth. Thus, this anode is considered to be highly active at high pHs above pH 4.0 (Q). The sulphur content of this anode was 0.054%.

EXAMPLE III the pH and after a further 16 hours of electrodeposition, the pH of the electrolyte was 3.5.

Upon corroding the cathodic nickel produced by electrodeposition from a standard electrolyte containing about 0.25 gram per liter of methylene blue as its chloride initially for 22 hours as an anode, inspection of the corroded anode showed that the surface was dark all over and the activity ofthe anode good. Cathodic nickel produced in.

the bath containing methylene blue was then corroded in a hot Watts type electrolyte having a pH of about 5.5 (Q) at the start of the corrosion. After 22 hours of corrosion, the anode was covered with sludge but was still active. It is manifest therefore, that cathodic nickel electrodeposited from an electrolyte, containing methylene blue has good activity and is satisfactory for use as an anode in the electrodeposition of protective, decorative or utilitarian films of nickel. The electrodeposited nickel produced in the bath containing methylene blue contained about 0.104% sulphur.

EXAMPLE IV A second anode was prepared by cathodic deposition of nickel from a standard electrolyte containing 0.25 gram per liter of methylene blue. The cathodic nickel so obtained contained about 0.023 gram of sulphur present principally as the sulphide. This cathodic nickel upon corrosion at pH 4.0 and pH 5.5 (Q) made it manifest that such cathodic nickel is suitable for use as plating anodes in the deposition of protective, decorative and/or utilitarian films of nickel. This second methylene blue anode had good activity, satisfactory corrosion and only produced amounts .of sludge which are acceptable to the art.

EXAMPLE V The same standard electrolyte was employed as employed in Example 1 to which was added nickel so produced was corroded at about pH 4.0 (Q) employing an anode current density of about 15 amperes per square foot. was completely covered with a thin black film of sludge indicating uniform corrosion. A similar portion of cathodic nickel produced from a bath containing 0.25 gram per liter of thio-urea was EXAMPLE VI Cathodic nickel was deposited under the aforedescribed conditions at low pH and high current density from a standard electrolyte containing initially about 0.25 gram of a dithiophosphate sold under the trade name of Sodium Aerofloat.

Y The cathodic nickel thus produced when corroded After 8 hours further anodically at pHs 4.0 and 5.5 (Q) showed good activity and highly satisfactory corrosion characteristics. The sulphur content'of this anode was about 0.175 and the sulphur was present principally as a sulphide. The phosphorus content of this anode was about 0.103.

Other massive deposits suitable for use as anodes and'c'orroding ver satisfactorily at high pH such as 5.5 (Q) were obtained from a standard nickel electrolyte containing a dithiophosphate. An anode produced at high .pH and low current density contained about 0.30% sulphur, about 0.133% phosphorus and corroded very satisfactorily at pH 5.5 (Q).

EXAMPLE VII know, Thioflavine S is a methyl derivative of sulphonated primuline, and usually comes on the market as the sodium salt of the sulphonate. When cathodic nickel produced in a bath containing thioflavine S is corroded anodically at pHs 4.0 and 5.5 (Q), it is manifest that such metal is suitable for use as anode in nickel elec-.

troplating. This nickel is active at both pH 4.0 and 5.5 and the anode becomes covered with a black sludge.

Similar sulphur-containing materials derived from dehydro-thio-para-toluidine such as thiofiavine T may likewise be employed with equally satisfactory results. The anode produced cathodically in the bath containing thiofiavine S contained about 0.078% copper and about 0.033% sulphur, the sulphur being present principally as a sulphide.

The anodes produced as described hereinbefore had a thickness of about 0.2 centimeter or, in other words, about 0.08 inch. As those skilled in the art will readily understand, such deposits are many times the thickness of the average film of nickel deposited for protective, decorative and/or 0.25 gram per liter of thio-urea; The cathodic utilitarian purposes, and considerably thicker The anode than even the thickest films produced by the prior art for protective, decorative and/or utilitarian purposes. In general, cathodic nickel suitable for use as anodes in plating conventional gray nickel or in electrodepositing "bright" nickel may be produced employing standard nickel electrolytes as the basic bath and operating at pHs of about 1.5 to about 6.0(Q). at anode current densities of about 3.0 to about 100 amperes per square foot and cathode current densities of about 5.0 to about 100 amperes per square foot. The electrodeposition of such cathodic nickel may be carried out at temperatures of about 20 F. to about 200 F., preferably with agitation of the electrolyte.

From the foregoing, those skilledin the art will appreciate that in distinct contrast to the thin foil-like films conventional in nickel electroplating for protective, decorative and/or utilitarian purposes, by the process of the present invention it is possible to produce massive deposits of electrolytic nickel containing sulphur. As a result thereof, it is now possible to provide the art with active cathode nickel anodes containing sulphur or containing sulphur and copper which corrode satisfactorily with production of small amounts of sludge containing small amounts of metallics Iron and having good or excellent activity in electroplating baths of high pH. In other. words, the conventional process for producing nickel anodes comprising producing electrolytic nickel substan tially devoid of sulphur, melting the electrolytic nickel and adding sulphur to the molten nickel and finally casting the nickel containing sulphur as an ingot from which nickel anodes may be produced is no longer necessary, since it is now possible by means'of the present invention to produce cathode nickel containing sulphur or cathode nickel containing copper and sulphur directly in the electro-recovering bath.

It is of interest that even those anodes produced from electrolytes containing such organic compounds as thio-urea, methylene blue, thioflavine S ortliobenzoy'l sulphonimide, or dithiophosphates are substantially devoid of carbon. This fact, coupled with the fact that the sulphur in the novel anodes of the present invention is present principally in the sulphide form is indicative that the sulphur is combined with the "metal of the anode probabl as a nickel or copper sul-' phide or as both.

The composition of the novel anodes is illustrated by the followingexamples:

1 Nickel including incidental amounts of cobalt V "fore, may contain up to about 0.1% copper.

I have found that sulphur-bearing electrolytic nickel having the composition given hereinafter is suitable for electroplating anodes.

Carbon Trace to about 0.02

' Trace Trace Trace Manganese Silicon Sulphur About 0.007 to about 0.11

Copper About 0.0025 to about 0.03 Nickel including incidental amounts of cobalt-..

Balance Carbon Trace Iron Trace Manganese I Trace Silicon Trace Sulphur About 0.030 to about 0.050 Copper About 0.010 Nickel including incidental amounts of cobalt-..

Balance In the foregoing tabulation when the term trace" is employed, I mean not more than about 0.01% iron, 0.005% manganese, and about 0.01% silicon. It is to be understood that this disclosure is not to be limited to the exact details shownand described for obvious modifications will occur to those skilled in the art.

Thus, the term dithiophosphates is to be understood to include those phosphorus and sulphur-containing organic substances which-are included in the type formula.

RIO

where R1 and R: may be the hydrocarbon residues of aliphatic alcohols, carboxylic acids, aldehydes and ketones as well as the hydrocarbon residues of such members of the, aromatic series as cresols, xylenols, 'naphthols and the like. .It is' likewise to be understood that as the sulphur content of the electrolyte decreases during the deposition of the electrolytic nickel containing sulphur, further amounts of the sulphur-containing addition agent as defined hereinbefore may be added to the fundamental nickel electrolyte if desirable. Furthermore, electrolytic nickel anodes as produced under the. conditions described hereinbeaddition, the term electrolyte soluble as applied to sulphur-bearing substances suitable for use in the aforedescribed process means sulphur-bearing compounds which are soluble in the electrolyte at the pH at which electrodeposition of the cathodic nickel takes place. As a further means of defining the electrolyte soluble sulphur-bearing substances suitable for use in the aforedescribed process, the reduction potential at unit activity may be employed. That is to say, elec- Balance 'trolyte soluble sulphur-'bearingsubstances capable of ionizing to sulphur-containing radicals having a reduction potential to hydrogen sulphide at unit activity of not more than that of thiosulphate, for example, not more than about 0.64

volt may be employed. Moreover, while the present invention has been described in conjunction with conventional nickel electrolytes containing a source of nickel, an anode corroding agent and a buifer'for use in conjunction with nickel anodes, those skilled in the art willappreciate that when insoluble anodes are employedand the electrolyte is the sole source of nickel, an anode corroding agent is not incorporated in the bath. Similarly, a suitable electrolyte is one containing about 40 'to about 84 grams of nickel per liter in the form taining sulphur which comprises immersing an anode and a starting sheet as cathode in an aqueous electrolyte comprising essentially nickel ions, sulphate ions, chloride ions, borate ions and about 0.05 to 0.25 gram per liter of alkali metal thiosulphate, said electrolyte being characterized by of the entire bath present solely as alkali metal thiosulphate. I

2. A bath suitable for the electro-deposition of nickel electro-plating anodes at least about 0.08 inch thick and containing sulphur within the range of 0.007 to 0.11% which comprises an aqueous electrolyte comprising essentially nickel'ions, sulphate ions, chloride ions, borate ions and about 0.05 to 0.25 gram per liter of alkali metal thiosulphate, said bath having a pH of about 1.9 to 5.5 and characterized by having the thiosulphate content of the entire bath present-solely as alkali metal thiosulphate.

3. A bath suitable forthe electro-depositlon of nickel anodes at least about 0.08 inch thick and containing sulphur within the range of 0.007 to 0.11% which comprises an aqueous electrolyte comprising essentially nickel ions, sulphate ions. chloride ions, borate ions and about 0.1 to 0.2 gram per liter of sodium thiosulphate, said bath having a pH of about 2.5 to 4.5 and characterized by having the thiosulphate content of the entire bath present solely as sodium thiosulphate.

4. A process for producing nickel anodes conhaving the thiosulphate content thereof present solely as alkali metal thlosulphate, maintaining said electrolyte at pH of about 1.5 to 6.0. and passing electric current at a cathode current density of about 5 to amperes per square foot between said ahodeand cathode until a cathodic electrodeposit at least about 0.08 inch thick and containing about 0.007to 0.11% sulphur is obtained, said cathodic electro-deposit being suitable in the asdeposited condition for subsequent use as an anode.

5. A process for producing nickel anodes containing sulphur which comprises immersing an anode and a starting sheet as cathode in an aqueous electrolyte comprising-essentially nickel ions, sulphate ions, chloride ions, borate ions and about 0.05 to 0.25 gram per liter of alkali metal thiosulphate, maintaining said bath at pH of about 1.9 to 5.5, and passing electric current at a cathode current density of about 10 to about 50 am-' peres per square foot between said anode and cathodeuntil a cathodic electro-deposit at least about 0.08 inch thickand containing about 0.007 to 0.11% sulphur is obtained, said cathodic electro-deposit being suitable in the as-deposited condition for subsequent use as an anode.

6. The process as set forth in claim 4 wherein the alkali thiosulphate is sodium thiosulphate.

taining sulphur which comprises immersing an 'anodeand a starting sheet as cathode in an aqueous electrolyte comprising essentially nickel ions, sulphate ions, chloride ions, borate ions and about 0.1 to 0.2 gram per liter of sodium thiosulphat'e, maintaining saidbath at pH of about 2.5 to 4.5, and passing electric current at a cathode current density of about 10 to 50 amperes per square foot between said anode and cathode until a cathodic electro-deposit at least about 0.08 inch thick and containing about 0.007 to 0.11% sulphur is obtained, said cathodic electro-deposit being suitable in the as-deposited condition for subsequent use as an anode.

HARRY EDWIN 'ISCHOP.

'7. The process as set forth in claim 5 wherein thealkali metal thiosulphate is sodium thiosulphate.

8. A process for producing nickel anodes con-.

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