US2125229A - Electrodeposition of metals - Google Patents

Description

Patented July 26, 1 938 UNITED STATES PATENT OFFICE ELECTRODEPOSITION 0F METALS a corporation of Ohio No Drawing. Application October 21, 1936, Serial No. 106,816

11 Claims.

Various so-called addition agents have been proposed from time to time for inclusion in nickel plating baths in order to control or affect the character of the electrolytically deposited metal. One principal objective in such modification of the plating bath has been to increase the brightness or luster of the deposited metal, particularly where deposited as a plate on another metallic base. Such a bright nickel plate is not only desirable per se, but it is particularly advantageous where it is destined for use as the base for an electrolytically deposited chromium plate, since if the nickel plate does not requireto be polished and buffed, a thinner plate gives the same protection as aheavier gray plate some of which must be taken off in polishing, and again a very considerable saving in time and in cost in the production of plated articles becomes possible, whether with nickel plate per se or with additional chromium finish.

While it has long been known that the addition of certain substances to the electrolytic plating bath will cause the nickel to be deposited as a more or less smooth, lustrous plate, with many such addition agents the current density has to be kept very low, lower than desirable for commercial usage. In many cases, also, the results tend to be variable or at least it is too diiiicult to maintain proper balance of the ingredients in order to continuously plate out the nickel in the bright form desired.

Also, a tendency has been noted that the deposited nickel plate in some instances, because of the presence of a film or an apparently passive state perhaps, fails to take properly a bright superposed chromium plate where the nickel is to serve as a base for the latter.

Among the objects of the present invention is the provision of a nickel plating bath and process which will produce superior bright ductile nickel plate under commercial conditions, i. e., wherein the current density may be of commercial rate, with the plate deposited rapidly as well as uniformly to any desired thickness and without pitting. Another object is the provision of a plating bath and process capable of indefinite operation, and exactness of control, as the condition of the bath can be ascertained instead of having to depend upon unknown and unascertainable colloidal conditions. A further object is the provision of bright nickel plate in such manner as to insure the proper deposit of a superposed bright chromium plate, if desired.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the composition of ingredients and steps hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be used.

We have discovered that the addition to a nickel plating bath of usual composition of an agent making available selenium or tellurium produces very remarkable results, more especially in the brightening effect had on the deposited plate. The surface of such deposited metal is surprisingly brilliant and mirror-like, even when the deposit is relatively thick. Such bright nickel is obtainable even where the surface of the underlying metal is dull, e. g., a steel surface.

The electrolytic bath as to its metal-providing components may be of usual or desired composition, i. e., be a solution of so-called nickel salts, for instance nickel sulphate with an admixture of a relatively smaller amount of nickel chloride and a further small amount of boric acid. An-

other well known electrolyte comprises a solution of nickel sulphate and sodium sulphate with relatively small amounts of ammonium chloride and boric acid added.

The addition to any such electrolyte of a suitable selenium or tellurium compound has the brightening effect above noted. The selenium or tellurium may be added in the form of acid compounds as S802, T602, HzSeOa, HzSeO4, salts of these acids, Na2SezO3, KCNSe, etc. or as organic selenides or tellurides or organic selenium oxygen or tellurium oxygen compounds, as for instance organic seleninic acids, selenonic acids, (also salts thereof) selenols, and similar tellurium compounds. However, the organic compounds have in general been found less desirable than the simpler inorganic forms because of difliculty of preparation and of odor or other unpleasant property. Selenic acid is particularly advantageous, as it dissolves in relatively high concentration and is not critical in operating conditions, and will plate at a pH of 6, giving higher efflciency and less tendency for hydrogen co-deposit and brittleness. In general, less selenium or tellurium will be required at high pH to obtain brightness, and in practice the pH may range from 1.5 to 6, or as limited by the bath itself, and the optimum may be as desired in commercial practice, for instance generally 3.0 to 4.5. The current density rate may range as desired in practice from ten to one hundred fifty amperes per square foot in some cases and usually twenty to fifty amperes per square foot, and similarly, the effect or temperature is not critical, the usual temperature ranges of fronr;30-to 60 0., preferably around 50" C.,;iaeing applicable.

Where operating an electrolyte of low nickel concentration at low current density, a brightening efiect may be obtained with as little as 0.001 per cent of SeOz or its equivalent selenium content. In more concentrated solutions, however, the amount may be up to 0.1 per cent, and for general purposes may range from 0.005 to 0.05 per cent for desirable results. Similar concentrations of tellurium apply; within the limits of solubility or dispersibility of its compounds.

Deposited plate where the foregoing selenium or tellurium compound alone is added to the bath, while exceptionally bright, has a tendency to be brittle. Furthermore, the bath tends to become depleted, by cathodic deposition, ,of such agent at a rate which would militate against its use on ,a commercial scale. However, we have made the further important discovery that both the foregoing objections are overcome or controlled by the addition of an agentwhich we find greatly decreases the amount of selenium co-deposited with the nickel and in so doing increases the due-- tility of the deposit, such agent being ;a sulphonate of an aromatic hydrocarbon. As for instance benzene sulphonates, naphthalene sulphonates, diphenyl sulphonates; sulphuric acid reaction products of terpenes, etc. Thus we have found that naphthalene mono, di, and tri sulphonates, mixtures of these, benzene disulphonate, diphenyl sulphonates, etc., act particularly to control the rapidity with which the selenium or tellurium is co-deposited with the nickel and in that connection increasing the ductility of the deposit. Such agent we designate an agent for regulating the depletion of the {addition agent. In general, the amount of such control agent may range from 0.05 to 1 per cent, but larger amounts up to a saturated solution may be used.

In the selection of a sulphonic acid suitable for this use it seems best to choose those which are as free as possible from colloidal organic material present as impurities formed during the sulphonation, which has a brightening and embrittling eifect on the deposited nickel. i The pure sulphonates or commercial mixtures 05 sulphonates: suitable for use in the bath contribute very little to the brightness'of the plate and when used in the plating bath without addition of a selenium or tellurium compound produce a gray ductile plate. The deposit or" nickel obtained when a selenium or teliurium compound is added to such a bath ds mirror-bright and ductile. However,;if an impure-sulphonate containing dispersed er colloidal organic material be used which produces a bright plate itself, the addition of azselenium or tellurium compound may cause extreme brittleness.

Where a sulphonate as above mentioned is thus added along with a selenium or tellurium compound as specified, the deposited plate is found to be not only brilliantly mirror-like and free from milky-gray cloudiness, when deposited on a relatively smooth surface, but it also tends to level up and deposits brilliantly omunpolished surfaces and can be built up as thickly as desired. The deposit on analysis shows a content of selenium or tellurium, w d'iichever such agent is used, together with a content of sulphur derived from the sulphurhontaining radical of the organic addition agent. The amount of sulphur thus codep'nsited with the nickel will vary from a trace to several tenths of one per cent, usually from 0.01 to 0.1 per cent, depending upon the amount and kind of the organic agent employed in the bath. The amount of selenium or tellurium codeposited with the nickel will vary from a trace to several per cent, usually from 0.01 to 1 per cent;

depending upon the composition of the bath, the

tained less than .001 sulphur and 1.6 per cent, selenium and although bright was extrenj ely brittle.

In'general; we find 0.01 to 0.1 per cent of sulphur and 0.05 to 0.6 per cent of selenium (or corresponding amount of tellurium) in plates of proper brightness with ductility. We find also that by including in the electrolytic bath a substance or agent which lowers the surface tension a still better result is obtained. We have found sulphated higher alcohols of six or preferably eight or more carbon atoms, on up to about twenty, as for instance sulphated laufryl, oleyl, octy1, caprylic, cetyiic alcohols, etc., particularly advantageous for this in a bath which includes the above mentioned addition agents. Such agent we designate a surface-tension reducing agent. The criterion governing the amount of such latter agent to be added to the bath is afforded by the surface tension which may be determined by a suitable means, conveniently ior instance the Jaeger tensimeter, as described in Advanced Practical Physics for Students by B. A. Warnop and H. T. pages -143, (pub. by Methuen, London, 1927). Thus, where the bath would lllIlFfOI example, on the order of 60-70 dynes per centimeter as thus determined, it should be adjusted with the sulphated alcohol or the like to not in excess of 50 dynes per centimeter, and preferably below 40; 2

The following will serve as illustrative examples of our improved nickel plating bath utilizing one or more of the abo e described addition agents: 1

Oz. per gal. I. NiSO4,6HzO 32 NiC12,5H2O 4 HzBOs 5 pH may be about 4.0, and the temperature 30-60 C. V II. With similar amounts of nickel salts and boric acid as in Ex. I there is incorporated W SeOz 0. 01

Naphthalene di-sulphonic acid 1 Witli similar amounts of nickel salts and boric acid as in Ex. I there is incorporated TeOz 0. 025 IV. With similar amounts of nickel salts and boric acid as in Ex. I there is incorporated S802 i 0. 01 Naphthalene di-sulphonic acid 1 and lauryl alcohol sulphate 0.1 V. With similar amounts of nickel salts and boricacid as in Ex. I there is incorporated l SeOz 5 0. 01 Benzene di-sulphonic acidi. 1 and octyl alcohol sulphate 0. 2

araaaao 3 Oz. per gal. with the condition encountered where our newly VI. With similar amounts of nickel salts discovered brightening agent is employed.

and boric acid as in Ex. I there is For example, cathodic cleaning in 'a regular incorporated cleaning solution containing borax iseffective in Teoz 0.02 some cases, especially if a small amount of glu- Alpha-naphthalene sulphonic-acid- 0. 2 co'se or sugar be added, but not infrequently the Lauryl alcohol sulphate 0. 1 film condition appears to be of such a thickness VII. With similar amounts of nickel salts that cleaning in this manner cannot be effected and boric acid as in Ex. I there is in any reasonable length of time. incorporated We also have tried adding copper cyanide to $602 0.01 the cleaner, depositing a film of copper and re- 3 oz. per gal. of a water solution of moving such film with chromic acid either in the a nickel-neutralized product of chromic acid bath or by a pretreatment, as well the action of 2 parts of 20 per as plating on a film of zinc and stripping this cent oleum on 1 part of naphthawith hydrochloric acid. Here again the cleaning lene at 160 C. for 2 hours, the is ineffective if the film condition is bad. nickel-neutralized solution being We have found, however, that by the following of such concentration as to be procedure the nickel plate can be quickly and equivalent to Bper cent naphthaeffectively put in condition for the superposed lene, and additionally there is chromium plate, viz., by placing the nickel plated incorporated lauryl alcohol sularticle in a solution of sodium cyanide, and then phate 0. 1 using the metal plated article as an anode, pass- VIII. NiSO4,6HzO 32 ing an electric current therethrough at a voltage NiCl2,6H2O 4: o ro 2 to 10 volts for a period of about 1 H 30 5 second; we then reverse the current making the Selenic acid 0.1 a piece athode for a few seconds up to several IX. With similar amounts of nickel salts minutes. There is no definite time limit for such and boric acid as in Ex. I there is last mentioned step (cathodic treatment), but incorporated ordinarily 15-30 seconds will be quite suificient. Selenlc acid 0.1 A suitable sodium cyanide solution will contain 23 Naphthalene di-sulphonic acid 1 ounces per gallon and the solution may be used X. With similar amounts of nickel salts at room temperature or warm, as desired.

and boric acid as in Ex. I there is We find that by making the piece anode in a incorporated sodium cyanide solution, the objectionable film Selenic acid 0.1 effect is removed, but apparently the nickel sur- Naphthalene di-sulphonic acid 1 face is left passive. However, by making the piece and lauryl alcohol sulphate 1 first anode and then cathode, the surface film XI. With similar amounts of nickel salts is q y pp d g e nodic treatand boric acid as in Ex. I there is ment and the surface of the metal then reactiincorporated vated by the cathodic treatment. Where the Selenic acid 0.1 shapes are very complicated, it may be necessary Benzene di-sulphonic acid, 1 to continue the anodic treatment for as long as and octyl alcohol sulphate 0, 2 or even seconds before reversing the current XII. With similar amounts of nickel salts and subjecting to the cathodic treatment.

and boric acid as i 1 th is Where the foregoing cleaning procedure is folincorporated lowed, the chromium covers exceptionally well Selenic acid o. 1 and it should be noted that such procedure is not 3 per of a water Solution f necessarily limited to the treatment of bright a nickepneutralized product of nickel plate produced with our improved addit action of zparts of 20 per t; tion agents, but is found highly beneficial in oleum on 1 part of naphthalene cleaning nickel plate produced from the regular t 1 0 for 2 hours, t i k lplating bath and then buffed as a preliminary neutralized solution being of such step t chromium P concentration as t b equivalent, In place of using a cleaning solution containing t 3 per c t aphth l e, a d simply sodium cyanide, as specified above, we additionally there is incorporated may substitute soda ash in part for such sodium lauryl h l 5u1phate 0,1 cyanide and seemingly obtain results that are x111. With similar amounts of nickel salts t about s good- An example of such modified d b ri a id as i x, 1 there 1 solution would comprise approximately 4 ounces incorpgrated of sodium cyanide and 4 ounces of soda ash to a KCNse 0 05 gallon of water. We have also found that sodium Alphamaphthalene sulphomc acid 0 2 formate can be substituted in large part for the Octyl alcohol sulphate 0, 2 s ium cy nid and t t a good cleaning bat-h can v In t such as 1X there is be had using only 1 or 2 ounces of sodium cyanide incorp'omted ethyl 1 1d 0 03 to 6 or 7 ounces of sodium formate per gallon of instead of the KCNSe.

Where another metal is to be superposed on the bright nickel plate deposited from our improved composition of bath, as for example where chromium is to be plated over the nickel by the usual process, while various more or less familiar methods of cleaning of the plated surface have been heretofore employed, none of these have been wholly satisfactory, particularly in dealing water. In the case of each of the named ingredients, or combination of ingredients, for the cleaning solution, it may be desirable to increase the conductivity of the latter by the addition of conducting salts. This would be more especially the case where the nickel plated article to be cleaned is of complicated shape, such as a radiator shell or the like.

We have also found that in place of subjecting the article first to anodic and then to cathodic treatment, satisfactory results can also be obtained by using an alternating current superimposed upon a direct current so as to obtain a cathode efiect in excess of the anode efiect. This, however, requires a somewhat more elaborate electrical set-up than simple current reversal, which we regard as providing the more practical procedure.

By following the steps of the process hereinbefore described, including the addition -to a nickel plating bath of a selenium or tellurium compound, an organic sulphonate as noted as a regulating agent and a surface tension reducing agent, preferably a sulphated higher alcohol as indicated to avoid pitting, a very superior bright nickel plate is obtained which possesses not only the desired characteristic of brilliant smoothness, but which can be built up to any desired thickness and is free from brittleness, i. e., is surprisingly ductile, so that the plated article can be bent without any evidence of crackling. Furthermore, the bright nickel plated articles thus produced, even where of intricate design, will, when cleaned in accordance with the preferred procedure described above and further subjected to the standard chromic acid chromium plating process, take a superposed chromium plate perfectly.

This application is a continuation, in part and as to common subject matter, of our application Serial No. 74,340, filed April 14, 1936.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

We therefore particularly point out and distinctly claim as our invention:

1. An electro-deposition bath, comprising an acid nickel electrolyte and an amount of a brightening addition agent selected from the group consisting of compounds of selenium and tellurium, soluble in the electrolyte, sufficient to produce a brilliant but normally brittle deposit and an amount of an aromatic sulphonate suificient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

2. An electro-deposition bath, comprising an acid nickel electrolyte and an amount of selenium compound brightening addition agent, soluble in the bath, sufiicient to produce a brilliant but normally brittle deposit and an amount of a benzene sulphonate suflicient to counteract the normal embrittling efi'ect of said brightener compound and to render the deposit ductile.

3. An electro-deposition bath, comprising an acid nickel electrolyte and an amount of selenium compound brightening addition agent, soluble in the bath, suflicient to produce a brilliant but normally brittle deposit and an amount of a naphthalene sulphonate sufficient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

4. An electro-deposition bath, comprising an acid nickel electrolyte and an amount of selenium compound brightening addition agent, soluble in the bath, suiiicient to produce a brilliant but normally brittle deposit and an amount of a naphthalene disulphonate sufficient to counteract the normal embrittling effect of said brightener compound and to render the deposit ductile.

5. An electro-deposition bath, comprising an acid nickel electrolyte and an amount of selenium compound brightening addition agent, soluble in the bath, sufiicient to produce a brilliant but normally brittle deposit and an amount of a mixture of naphthalene mono, diand tri-sulphonates sufllcient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

6. An electro-deposition bath, comprising an acid nickel electrolyte to which there has been added an amount of selenium dioxide sufiicient .to produce a brilliant but normally brittle deposit,

an amount of a naphthalene sulphonate material containing a naphthalene di-sulphonate sufficient to counteract the normal embrittling effect of said brightener compound and to render the deposit ductile and a minor amount of a sulphate of an aliphatic alcohol having from eight to twenty carbon atoms in the molecule.

7. An electro-depositi'on bath comprising an acid nickel electrolyte containing as a brightening addition agent an amount'of a selenium compound, soluble in the electrolyte, equivalent to the addition of from about 0.001% to about 0.10% of selenium dioxide and an amount of a naphthalene sulphonate in excess of about 0.05% and suflicient to counteract the embrittling efi'ect of the amount of selenium compound present in the bath and render the deposit ductile.

8. The process of electro-depositing nickel in brilliant and ductile form from an acid nickel electrolyte containing an amount of a brightening addition agent selected from the group consisting of compounds of selenium and tellurium, soluble in the electrolyte, sufiicient to produce a brilliant but normally brittle deposit and an amount of an aromatic sulphonate sufiicient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

9. The process of electro-depositing nickel in brilliant and ductile form from an acid nickel electrolyte containing in solution an amount of selenium compoundbrightening addition agent suflicient to produce a brilliant but normally brittle deposit and an amount of a benzene sulphonate suflicient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

10. The process of electro-depositing nickel in brilliant and ductile form from an acid nickel electrolyte containing in solution an amount of selenium compound brightening addition agent suflicient to produce a brilliant but normally brittle deposit and an amount of a naphthalene sulphonate sufllcient to counteract the normal embrittling efiect of said brightener compound and to render the deposit ductile.

11. The process'of electro-depositing nickel in brilliant and ductile form from an acid nickel electrolyte containing in solution an'amount of selenium compound brightening addition agent suflicient to produce a brilliant but normally brittle deposit and an amount of a naphthalene di-sulphonate suificient to counteract the normal embrittling efiect of "said brightener compound and to render the deposit ductile.

WILLIAM J. HARSHAW. KENNETH E. LONG.