IL22129A - Plating with chromium - Google Patents

Description

NOVEL PROCESS.

This invention relates to chromium plating* More particularly it relates to a novel technique for suppressing the evolution of fumes from chromium plating baths.

As is well known to those skilled in the art, chromium plating may be effected from baths which contain chromic acid and sulfate (typically introduced as sulfuric acid) together with other ingredients or additives including those whic may control or regulate the plating characteristic of the ba^h. Typical of such regulating additives may be strontium sulfate and potassium silicofluoride with or without additions of excess strontium ion (introduced as SrC03, SrCrO4 etc.) or excess potassium ion (introduced as K2Cr04, K2Cr207, etc.) which may make the bath a high speed bath which is self-regulating with respect to catalyst anion.

During chromium plating from such baths, there is a very vigorous evolution of hydrogen from the cathode and of oxygen from the anodej as these gases escape, they carry into the atmosphere substantial amounts of entrained chromium plating solution containing chromic acid, hydrofluoric acid, sulfuric acid, etc. sufficient to produce a variety of toxic effects on personnel engaged in the operation of the bath. Cumulative effects of these fumes may cause irritation of the respiratory tract, perforation of the nasal septum or lung cancer.

The evolved gases together with the entrained chemicals therefore pose a serious problem. Particularly because they are toxic to operating personnel and because they are also corrosive to equipment or harmful to other nearby plating baths, such as that used to plate nickel, it is desired to operate in manner to minimize or eliminate the evolution of the objectionable constituents of these gases into the surrounding atmosphere. Prior art attempts to accomplish these desiderata by means of mist-suppressing organic additives have been only partially successful. Most of the prior art additives have been organic surfactants which operate by building up a high head of foam on the chromium plating bath restricting the entrainment of liquids in the evolved hydrogen and oxygen. As operations continue, the foaming properties of these prior art additives decreases mainly because they deteriorate or decompose under the severe action of the electrolyte. As a result, their value as fume suppressants may decrease.

Those skilled in the «rt have attempted to develop inexpensive fume suppressants characterized by a long life during which the composition may permit maintenance of a fixed, predetermined blanket of foam on the surface of the plating bath,. Attempts ftave also been made to develop a fume suppressant which was not characterized by the fact that the inadvertent or accidental addition of an excess of material might result in an excess of foam which might result in overflow of the dangerously corrosive contents of the bath or which, because said foam contained a mixture pf hydrogen and oxygen, might react implosively when ignited by the electrical arcing commonly encountered in the plating operation.

It is an object of this invention to provide a novel fume suppressant system for electroplating baths characterized by its ability to economically generate a foam blanket of controlled thickness « Other objects will be apparent to those skilled in the art on inspection of the following description In accprdance with certain of its aspects, the novel composition of this invention which is characterized by its ability to controllably develop and maintain over an extended period of time a fixed predetermined optimum thickness of foam may comprise an anti-misting amount of a mixture of a sulfonated 2-alkylbenzimidazole and a disulfonated alkyl diphenyl oxide « In accordance(^with certain other aspects of this invention, it may be possible to effect chromium plating in a bath containing chromic add and sulfate wherein substantial quantities of gas' may be liberated from the electrodes by the process which comprises maintaining a chromium plating bath containing chromic acid and sulfate, maintaining therein an anti-misting amount of a mixture of a sulfonated 2-alkylbenzimidazole and a disulfonated alkyl diphenyl oxide, and plating chromium onto a cathode in said bath.

Typically chromium plating baths with which this invention may be employed may commonly have the following illustrative composition,.

PREFERRED COMPONENT AMOUNT g/l g/l I chromic acid 15O-5Q0 250 sulfate ion 1-10 2,5 (e.g. from sulfuric acid) II chromic acid 150-500 250 sulfate ion 0.5-5 1 (e.g. from sulfuric acid) silicofluoride ion 1-10 2 (e.g. from H2SiF6) III chromic acid 150-500 400 sulfate ion 1-5 2 (e.g. from strontium sulfate) silicofluoride ion 2-8 5 (e.g. from H2SiF6) The novel fume suppressant or anti-misting agent of this invention may include a disulfonated alkyl diphenyl oxide, typically having the following formulas wherein R is a hydrocarbon radical having 6-18 carbon atoms, n is 0-1, and X is a cation selected from the group consisting of hydrogen, ammonium and metals.

Typical1 R radicals which may be employed may be alkyl radicals including hexyl, octyl, nonyl, dodecyl, and octadecyl radicals, preferably octyl, nonyl, and dodecyl radicals. The R radicals may preferably be the same. X may typically include sodium, ammonium, hydrogen, potassium, lithium, trivdent chromium, calcium, strontium, barium, magnesium, nickel, iron, and copper. X may preferably be The sulfonated alkyl diphenyl oxide in the highly acid and strongly oxidizing bath is believed to exist in the form of the acid radical having the formula The sulfonated alkyl diphenyl oxide as produced and utilized may be a mixture of compounds containing the noted substituents. In a typical commercial mixture, such as that available under the Dow Chemical Company trademarks DOWFAX 2A1, or BENAX 2A1, the sulfonic acid groups may be primarily substituted in the position ortho to the ether-bearing carbon, and the alkyl chain may be primarily substituted in the posit on para to that, carbon. The commercial product may be a. mixture of mono- and dialkyl substituted products.

A preferred composition may be a mixture :¾>f the d sulfonated salts of monododecyl diphenyl oxide and didodecyl diphenyl oxide. The d sodium and dipotassium sa^ts may be preferred.

The novel fum -suppressant or anti-misting agent of this invention may include a sulfonated 2-alkylbenzimidazole which may typically have the structure M0,S wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal cartjon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R* is a non-aromatic hydrocarbon radical containing at least 3 carbon atoms; RT » is selected from the group consisting of hydrogen, alkyl, aryl, arqlkyl, omega-sulfonated alkyl, sulfonated aryl, and sulfonated aralkyl; R? r is selected from the group consisting of hydrogen, alkyl and aralkyl; Y is a water-soluble anion; and a is 0-1» The sulfonated benzimidazoles which contain alkenyl, cycloalkyl and cycloalkenyl substituents in the 2-position will be understood to be embraced by the term "sulfonated 2-alkyl benzimidazole" as used in the context of this invention.

In the sulfonated 2-alkylbenzimidazole, the group Ar may be phenyl or naphthyl, and preferably it may be phenyl.

The cation M may be hydrogen, ammonium, or a metal. Typically M may be selected from the group consisting of hydrogen, ammonium, sodium, potassium, lithium, trivalent chromium, calcium, strontium, barium, magnesium, nickel, iron, and copper. Preferably, M may be an alkali metal e.g. sodium, potassium, ammonium and lithium.

The group Rf may be a non-aromatic hydrocarbon containing at least 3 carbon atoms. Preferably, R' may be selected from the group consisting of alkyl, cycloalkyl, alkenyl, and cycloalkenyl radicals. Preferably, R may contain at least 8, say 8-18 carbon atoms. Preferred RT groups may include n-octyl, isooctyl, nonyl, decyl, undecyl, tridecyl, pe tadecyl, heptadecyl, octjadecyl, 4-ethylcyclohexyl, octenyl, nonenyl, undecenyl, tridecenyl, pentadecenyl, heptadecenyl, 4-amylcyclohexenyl, etc.

The group R" may be hydrogen, alkyl, aryl, aralkyl, omega-sulfonated alkyl, sulfonated aryl or sulfonated aralkyl. Preferably R»* may be omega-sulfonated alkyl, sulfonated aryl or sulfonated aralkyl and most preferably R* ' may be selected from the group consisting of omega-sulfonated lower alkyl (i.e. an alkyl containing less than about 6 carbon atoms), sulfonated phenyl and sulfonated benzyl. The sulfonate group contained in the R» « group may typically be of the form M03S- wherein M is as defined supra and preferably wherein M is alkali metal, e.g. sodium, potassium, ammonium or lithium.

The group R' « « may be hydrogen, alkyl or aralkyl.

Preferably, R> ' ? may be selected from the group consisting of hydrogen, lower alkyl (i.e. an alkyl containing less than about 6 carbon atoms) and benzyl. Most preferably, R» ' 1 may be benzyl.

The group Y may be a solubilizing anion, typically a water-soluble anion. Preferably, Y may be selected from the group consisting of bromide, iodide, sulfate, acetate, methosulfate, ethosulfate, citrate, and perchlorate.

The sulfonated 2-alkylbenzimidazoles which may be present in the novel compositions of this invention may contain a quaternary nitrogen atom. Thus, a may be 1 and the compound may be a qiiaternized sulfonated 2-alkylbenzimidazole. When a is 0, the compound as added may contain no quaternized nitrogen atom. When the sulfonated 2-alkylbenzimidazole is added to the plating bath as an unquaterniezed compound, it may be converted in the acid bath to a quaternary compound.

Examples of preferred sulfonated 2-alky imidazole compounds which may be used in the novel fume-suppr ssant compositions of this invention may include: A. sodium 2-n-heptadecyl^"3-sulfophenylbenzimidazole sulfonate 8. sodium 2-n-heptadeeyl^3-sulfobenzylbenzimidazole sulfonate (3. potassium 2-n-octyl^"3-omega-sulfo-n-propyl- benzimidazole sulfonate D. sodium 1-benzyl 2-n-undecyl^-3-sulfobenzyl-sulfobenzimida olium bromide E. potassium l-anethyl^- 2-pentadecyl^ 3-sulfopheny - sul obenzimidazolium acetate F« sodium 1-ethyl, 2-nonyi^1 S-omega-sulfo-n-butyl-! sulfobenzimidazolium ethosulfate 6. ammonium 2-isooctyl- 3-sulfophenyl^ benzimidazole sulfonate In the plating bath, the sulfonated 2Talkyl benzimidazole is believed to exist in an ionized form such a / β N °O3S- Ar C-R' I R' ' It will be apparent to one skilled in the art that when R* ' also contains a sul onate group, this group may also be present in the ionized ^38 form. The nitrogen atoms of the imidazole ring may also be present as ionized quaternary nitrogens in the highly acidic plating bath.

In practice of this invention one may use a mixture containing 5-95, preferably 30-90, say 66 parts by weight of the disulfonated alkyl diphenyl oxide and 5-95, preferably 10-70, say 33 parts by weight of the sulfonated benzimidazole. These materials may be readily mixed together in powdered form or in aqueous solution; and stored or used as such. The solutions, may contain stabilizing amounts of a chromate or dichrornate, of e.g. sodium or potassium to inhibit growth of fungi or mold.

The two components of the novel fume-suppressant composition may be preblended prior to their addition to the bath, or they may be added thereto individually. When added individually, they may be added as a solid or in separate qqueous solutions. Preferably, they may be preblended prior to the addition. Preblending may be accomplished by physically mixing the solid materials or by dissolving both of them in the same aqueous solution. This solution may typically contain about 1-20%, say 10%, by weight of the fume-suppressant composition. The dry materials may also be blended and compressed, i.e. "pelletized"r preferably together vath a release agent, say sodium bicarbonate.

It has been discovered that when as little as 0.001 g1 (grams per liter) of the novel anti-misting composition is added to a chromic acid bath in the chromium plating process, the amount of mist and spray is substantially reduced. Although these additives are stable in chromic acid baths, they do decompose to a slight extent and over a period of time are "used ^ or depletedjVndrag out" of solution further contributes to this depletion. The minimum initial amount added to the bath is to a large extent governed by the contemplated replenishment rate. It is also in part governed by cost considerations, by the amount of plating current used and by the actual construction of the plating tanks. Baths containing this additive develop a stable foam blanket on the surface. It is desirable that this blanket should be stable and of substantial, yet not too great, thickness, which could be dangerous because of the large amount of entrapped oxygen and hydrogen. For this reason the geometry of the plating system affects the desired concentration of additive as it will affect the thickness of the foam blanket for a given volume of bath.

It is not contemplated that more than about 5g/l of the additive will be present in the bath at any one trime . The bath may contain about 0.001 g/l to 1.0 g/1. Larger amounts may be used but no apparent advantage may be realized thereby.

In, typical embodiments of this invention, the novel fume-suppressant composition may be present iri chromium plating baths in the amount of 0.001 to 1.0 g l of bath.

Preferably, the composition may be present in the amount of 0.002 to 0.05, say 0.01 g/l of bath.

It has been'-found that the anti-misting properties of the novel composition of this invention may endure over an extended period of time. This may be due in part to th,e unexpected synergistic action between the two components of the composition, thereby maintaining a substantially constant foam level for an indefinitely long period of time. It is a particular feature of this composition that presence pf considerable excesses of this material (as by inadvertent overdosage) do not cause build up of any substantially excessive amount of foam.

Practice of the invention may be observed from the following examples wherein the parts are parts by weight unless otherwise noted. In this first series of three comparative examples, three anti-misting agents were prepared.

I. This agent was the ULTRAVON WG brand of the Sodium salt of 2-n-heptadecyl,,- 3-sulfobenzyl benzimidazole sulfonate .

II . This agent was the DOWFAX 2A1 brand of the mixture of d sodium salts of monododecyl diphenyl oxide disulfona e and didodecyl diphenyl oxide d sulfonate; and III . This agent was a mixture of 5 %-50% of each of the agents of Examples I and II .

Each of these compositions was added in amount of 1 g/1 to one liter of a chromium plating solution having the following composition.

Component Concentratio gA chromic acid 225 sulfate 1 silicofluoride 2 The solutions were electrolysed at about 45eC. -at 3 amperes during the day, and allowed to stand at *t5°C. without electrolysis overnight and over the weekend. During the 120 hour test, the solutions were electrolyzed for a total of 20 hours. Duiing the tests, the solutions were intermittently electrolyzed at higher current density (5 amperes) for 5 minutes at each of the hereinafter noted times. The foam at the end of these 5 minute periods was evaluated on the following basis. 0 - no foam 1 -■ very little foam 2 little foam 3 - moderately little foam - moderate foam moderately high foam 6 - high foam 7 - excessive foam 8 - very excessive foam FOAM RATING Honrs at ,°C. I II III 1 7 4 5 2.5 7 4 5 7 3 5 7.5 7 2 6 32 7 0 7 7 ' 5 0 4 77 5 0 1 80 4 0 0 100.5 3 0 0 A rating of 5-6 is preferred. A rating of 4 or below or 7 or above is undesirable. A rating below 3 or of 8 is unsatisfactory. From this table, it will be observed that the composition III of this invention permitted attainment of a desirable moderate foam blanket to about 75 hours while the composition II gave a satisfactory blanket for only 5 hours. The composition I gave undesirably high foam at the controlled concentrations of the test. It is particularly noteworthy that composition III gave a foam of substantially uniform thickness over a long period of time, while the foams produced by I and II varied widely or were excessive over the same period of time.

It is a further advantage of the novel compositions of this invention that they may produce less sulfate build-up in a commercial bath than fume-suppressants previously used. Sulfate ion is produced when the fume-suppressant breaks down in the plating bath. Since the compositions of this invention (e.g. Composition III) may be effective for 6-8 times as long as previously used agents, they need not be added as frequently, and sulfate build-up may be thereby reduced.

It is a feature of this invention that use of the novel anti-misting agents ofi this invention is characterized by lower initial cost of production, production of more foam per unit weight of additive, longer foam life, lower _ concentration threshold of effectiveness, wider usable concentration range of operation, and their ability to produce durable foams of controlled and substantially constant thickness, over extended periods of usage.

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

Claims (1)

1. HAY particularly described and ascertained the nature of our said invention and in what manner the same is to be declare that we claim Compositions capable of developing and maintaining over extended period of time a fixed fume suppressant foam blanket of the desired thickness on electroplating which compositions contain a of a sulfonated benziraidazole and a disulfonated alkyl Compositions as claimed in Claim containing the sulfonated benzimidazole in a proportion of 5 to preferably 10 to by and the disulfonated alkyl diphenyl oxide in a proportion of 95 to preferably 90 to 30 Compositions as claimed in Claim 1 or wherein disulfonated alkyl diphenyl oxide is one having the formula where is an alkyl group containing carbon is or a metal and n is 0 or Compositions as claimed in Claim 2 or wherein the sulfonated benzimidazole is one having the formula a a where Ar is a phenyl or naphthyl ring incorporated into the structure through vicinal carbon of said an lower sulfonated phenyl or benzyl is hydrogen or a lower alkyl or benzyl Y is a and a is 0 or Compositions as claimed in any of Claimsl to the sulfonated benzimidazole is sodium hep sodium sulfonate or sodium bensimidasole Compositions as claimed in any of Claims 1 to wherein the disulfonated alkyl diphenyl oxide is a mixture of disodium monododecyl diphenyl oxide and diphenyl oxide Compositions capable of developing and maintaining over an extended period of time a fixed foam blanket of the desired thickness on electroplating baths substantially as described A process for electrodeposlting from a chromium plating wherein to preferably to g l of a composition according to any of the preceding Claims is maintained in the A process for electrodeposlting chromium a chromium plating substantially as described A bath for the of containing to preferably to grams per liter of a composition according to any of Claims 1 to insufficientOCRQuality