US3041257A

US3041257A - Chromium electroplating

Info

Publication number: US3041257A
Application number: US51770A
Authority: US
Inventors: Jr Richard P Cope; John R Drobne
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-08-25
Filing date: 1960-08-25
Publication date: 1962-06-26
Anticipated expiration: 1979-06-26

Description

3,041,257 Patented June 26, 1962 This invention relates to the electrodeposition of chromium from aqueous acidic hexavalent chromium baths and has particular reference to aqueous acidic hexavalent chromium baths comprising a stable additive composition for the bath which is capable of reducing substantially the formation of spray and mist during electrolysis.

It is well known in the art that large quantities of hydrogen are evolved at the cathodes and largequantities of oxygen and ozone are evolved at the insoluble anodes during the electrodeposition of chromium from aqueous acidic hexavalent chromium solutions or baths. An undesirable spray and mist of chromic acid is given off from the bath as the-many gasfbubbles formed by the relatively large quantities of hydrogen, oxygen and ozone burst violently at the. surface of the bath.

, The spray and mist that is given oil? during electrolysis is of considerable volume, and is highly toxic to the workers in and around the area of the spray. Furthermore, the mist is highly corrosive to nearby equipment, and has a deleterious contaminating effect on other plating baths in the vicinity.

Many attempts have been made by those skilled in the art to prevent or to minimize substantially the formation of this highly undesirable sprayand mist during the electrodeposition of chromium from aqueous acidic hexavalent chromium solutions. The methods proposed heretofore have not been entirely satisfactory.

This invention is concerned particularly with providing a stable additive composition for acidic hexavalent chromium baths which is capable of minimizing substan tially the formation of spray and mist during electrolysis of such baths with insoluble or highly polarized anodes, and to provide a new and improved hexavalent chromium v plating bath.

For a complete understanding of this invention, reference is made to the following detailed description.

In accordance with this invention stable additive compositions for aqueous acidic hexavalent chromium electroplating baths have been found that are highly satisfactory in preventing substantially the formation of spray and mist during electrolysis.

Chromium elect'ropolating baths are well known in the art, and basically they comprise chromium trioxide, C chrornic acid or chromic anhydride, Water, and a catalyst. There would be no chromium deposited from the bath without the catalyst. The addition of a suitable catalyst in the ratio of about 1 part by Weight to 100 parts by weight of chromic acid produces a satisfactory working solution. The above ratio can be varied to meet different plating conditions. Thus, the ratio has been varied by those skilled in the art from about 1:60 to 1:250. V

The catalyst'employed in the chromium electroplating bath can be a sulfate, usually introduced into the bath by the addition of sulfuric acid.

Sorhe common formulations are as follows: (i) 33 ounces of chromic acid per gallon of electrolyte and 0.33

ounce of sulfuric acid (98%) per gallon of electrolyte; (ii) 54 ounces of chromic acid per gallon of electrolyte and 0.54 ounce of sulfuric acid (98%) per gallon of electrolyte; and (iii) 40 ounces of chromic acid per gallon of electrolyte and 0.40 ounce of sulfuric acid (98%) gallon of electrolyte.

formation of spray Chromium electroplating baths can be prepared by supplying CrO in the form of chromic anhydride or in the form of compounds containing cations which do not affect adversely the bath characteristics. Such compounds include the chromates, dichromates, and polychromates of potassium, sodium, magnesium and calcium. The CrO can be added in the form of chromic acid and/or dichromic acid in solution. Where alkali metal cations are present, the bath should not be neutralized in excess of of the dichromate end-point.

Sulfate ions can be added in the form of sulfuric acid as above set forth or as a sulfate salt or salts with a cation that does not affect adversely the characteristics of the bath. Examples of such cations include potassium, sodium, calcium, strontium, magnesium, and chromium.

Silicofiuoride ions can be added to the bath to maintain and to regulate the catalyst acid radical content of the bath. Silicofiuoride ions can be added in the form of fiuosilicic acid. Also, they can be added as silicofluoride salt or salts with a cation that does not affect adversely the bath characteristics such as potassium, sodium, magnesium, and chromium. The silicofluoride ion is usually present in an amount equal to about 1% to 2% of the chromic acid concentration.

The examples below are illustrative of typical bath formulations.

Example I Ounces per gallon Chromic acid (CrO 27 to 67 Strontium sulfate 0.8-1 to 2.01 Potassium silicofiuoride 2.16 to 5.36

Example II Chromic acid (CrO 40 Sulfuric acid 0.24 Fluosilicic acid; 0.40

The stable additive compositions of this invention are soluble in conventional aqueous acidic hexavalent chromium baths and will and mist. Furthermore, the additive compositions are stable'to the extremely powerful oxidizing conditions that exist at the insoluble anodes during the electro-deposition of chromium from such baths.

The stable additive composition of this inventioncomprises specific non-ionic wetting agents alone or in admixture with certain alkyl aromatic sulfonates to be detailed more fully hereinafter. The non-ionic wetting agents or surfactants are selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from about 1,300 to 1,800, (2) a cogeneric mixture of conjugated polyoxypropylenepolyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of a reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight 'of the polyoxypropylene polymer in the mixture is within the range of from about 1,500 to 1,800, as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to by weight of the mixture, and (3) mixtures of (1) and (2).

Nonionic Wetting agent (2) above can be represented by the structural formula prevent or minimize effectively the 3 wherein Y represents an integer sufi'icient to provide a molecular weight of polyoxypropylene of from 1500 to 1800, and X and Z are in integers the total of which is sufiicient to provide oxyethylene groups in an amount equal to from about 80% to 95% by Weight of the total weight of the molecule.

Compounds of the types above described under (2) are available commercially under the proprietary designation Pluronic.

It has been determined also, according to the present invention, that substantial reduction of the undesired chromic acid spray can be accomplished by adding to the bath an admixture of from to 90 parts by weight of the above enumerated nonionic wetting agents (1), (2), and (3) and from 90 to 10 parts by weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group.

While the specific nonionic wetting agents (1), (2), and (3) enumerated above are effective in reducing substantially the chromic acid spray, it is preferred to employ the admixture as set forth hereinbelow as it is even more eifective. The preferred admixture will comprise from 40 to 60 parts by Weight of nonionic wet-ting agent (1), (2), or (3) and fiom 60 to 40 parts by weight of alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group.

Alkyl aromatic sulfonic acid compounds of the benzene series containing at least 7 carbon atoms in an alkyl group can be represented by the formula in which X represents hydrogen; a hydroxyl group; a lower alkyl group such as methyl, ethyl, propyl, isopropyl, and n-butyl; analkoxy group such as methoxy, ethoxy, benzyloxy and the like; an aryloxy group such as phenoxy and methylphenoxy; or a carboxyl group. R represents an alkyl hydrocarbon radical (saturated or unsaturated) containing 7 or more (preferably 10 to 19) carbon atoms, and M represents hydrogen or a metal, or an ammonium or an organic ammonium radical. For convenience this'class of compounds will be referred to hereinafter as alkyl aromatic sulfonates of the benzene series.

Reference is made to US. Patent 2,195,409 for a more detailed description of alkyl aromatic sulfonates of the benzene series, specific examples thereof, and methods of preparing the same.

The following specific example is given by way of illustration. All parts are by weight unless otherwise designated.

Example III One hundred parts of commercial lauryl alcohol (obtained by hydrogenation of fatty acids from cocoanut oil), 100 parts of phenol, and 100 parts of anhydrous zinc chloride are mixed and refluxed at 190 C. to 200 C. with agitation for about 16 hours. The condensation product is washed with water until substantially free of water-soluble products, and the resulting oil is fractionally distilled in vacuo. The fraction of the distillate collected as a faint yellow to water-white oil between 210 C. to 230 C. at 13 mm. mercury pressure consists mainly of lauryl phenols of which the probable formula of the main constituent is are added to 270 parts of the resulting oil which is held at a temperature below 10 C., then sulfonation is continued at room temperature for 2 hours. The sulfonation mixture is drowned in four times its weight of a mixture of ice and water and a solution of sodium hydroxide is added while keeping the temperature below 35 C. until the product is neutral (pI-l=7.0). The neutralized solution is evaporated to dryness to provide an alkyl aromatic sulfonate of the benzene series suitable for use in this invention.

The amount of stable additive composition of this invention that is added to the chromium electroplating bath will be sufficient to provide a bath surface tension of at least 55 dynes per cm. at 25 C. It has been determined that the stable additive composition of this invention, Whether it comprise the above defined nonionic wet-ting agents alone or the nonionic wetting agents in admixture with the alkyl aromatic sulfonates of the benzene series, can be added in amount of from about .015 to .40 ounce per gallon of electrolyte. It is within the skill of those versed in the art to determine the amount of additive composition'required to provide a bath surface tension of at least 55 dynes per cm. at 25 C., or at least an amount sufficient to retard substantially the liberation of chromic acid fumes or spray from the bath.

The non-ionic wetting agents alone provide for substantial reduction of the surface tension of the chromium electroplating bath and is satisfactory for most baths. However, for baths of higher chromic acid concentration it is preferred to employ the admixture of non-ionic wetting agent acid alkyl aromatic sulfonates as above defined as the surface tension of the bath is more elfectively controlled thereby eliminating substantially any undesired chromic acid spray.

The examples that follow are illustrative of this invention.

Example IV To a chromic acid bath containing 54 ounces of CrO; per gallon of aqueous solution and a ratio of HSO :CrO within the range of 1:100 there is added .20 ounce per gallon of a non-ionic wetting agent consisting of a cogeneric mixture of conjugated poloxypropylene-polyoxyethylene compounds containing in their structure cxyproylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atorns, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymer in the mixture is about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute about by weight of the mixture. During operation of this bath, substantially no chromic acid spray or mist is noted.

Example V Achromium plating bath is prepared as described in Example IV above except that 40 ounces of CrO are employed per gallon of solution and .20 ounce per gallon of a polymer of ethylene oxide having a molecular weight of about 1500. Excellent results are obtained in plating various types of objects in this bath and there is substantially no chromic acid spray or mist noted.

To the chromium plating bath of Example II there is added about .30 ounce per gallon of a stable additive composition consisting of, by weight, 5 0 parts of the nonionic Wetting agent used in Example IV and 50 parts of the alkyl aromatic sulfonate of the benzene series of Example III. Good plating results are obtained and no objectionable chromic acid spray is noted.

The operating conditions for the bath of this invention are the same as those employed for the baths without the addition of the stable additive composition of this invention. Thus, operating temperatures of from about C. to 160 C. can be employed, and current densities of from about 100 to 500 amperes per square foot are satisfactory.

A significant reduction in the spray and mist formed during electrodeposition of chromium from aqueous acidic hexavalent chromium baths is apparent when the additive composition of this invention is employed. Further the additive compositions of this invention are very stable. That is they do not decompose in the chromium bath and lose their effectiveness.

It is to be understood that the above description of this invention is illustrative only and not in limitation thereof. F

We claim as our invention:

1. A chromic acid plating bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing a non-ionic wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containa ing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of a reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxye'thylene chains, the average molecular weight of the polyoxypropylene polymer in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by Weight of the mixture, and (3) mixtures of (l) and (2), said non-ionic Wetting agent being present in an amount sufiicient to retard substantially the liberation of chromic acid fumes from said bath.

2. A chromic acid plating bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing a stable additive composition comprising (A) from to 90 parts by Weight of a non-ionic Wetting agent selected from the group consisting of (l) polymers of ethylene oxide having an average molecular weight of from 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxy-propylene polymer, the oxyethylene groups are attached to the polyox-ypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymer in the mixture being from about 1500 to 1800 as determined by hydroxyl number,

and the oxyethylene groups present constitute from about 80% to 95% by Weight of the mixture and (3) mixtures of (1) and (2), and (B) from 90 parts to 10 parts by Weight of an alkyl aromatic sulfonic acid comwund of the benzene series containing at least 7 carbon atoms in an 1 alkyl group, said stable additive composition being present in an amount sufiicient to retard substantially the liberation of chromic acid fumes from said bath.

3. A chromic acid plating bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing a stable additive composition comprising (A) from 40 to 60' parts by Weight of a non-ionic lwetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular Weight of from 1300 to 1800', (2) a cogeneric mixture of conjugated polyoxyproplyene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxy-propylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular Weight of the polyoxypropylene polymer in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about to 95 by weight of the mixture, and (3) mixtures of (l) and (2), and (B) from 60 parts to 40 parts by weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group, said stable additive composition being present in an amount suflicient to retard substantially the liberation of chromic acid fumes from said bath.

4. The method of chromium plating which comprises electrodepositing chromium from a chromic acid plating bath comprising a non-ionic Wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containinga plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular Weight of the polyoxypropylene polymers in the mixture is from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by Weight of the mixture, and (3) mixtures of (1) and (2), said nonionic wetting agent being present in an amount sufiicient to retard substantially the liberation of chromic acid fumes from said bath.

5. The method of chromium plating which comprises electrodepositing chromium from a chromic acid plating bath comprising a stable additive composition comprising (A) from 10 to parts by weight of a non-ionic wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular Weight of from about 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of a reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular Weight of the polyoxypropylene polymer in the mixture being Within the range of from about 1500 to 1800 as deter-, mined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to by Weight of the mixture, and (3) mixtures of (1) and (2), and (B) from 90 parts to 10 parts by :weight of an alkyl aro matic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an 'alkyl group, said 'stable additive composition being present in an amount suflicient to retard substantially the liberation of chromic acid fumes from said bath.

6. The method of chromium plating Which comprises electrodepositing chromium from a chromic acid plating bath comprising a stable additive composition comprising (A) from 40 to 60 parts by weight of a non-ionic Wetting agent selected from the group consisting or" (1) polymers of ethylene oxide having an average molecular weight of from about 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of a reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymer in the mixture being Within the range of from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by weight of the mixture, and (3) mixtures of (1) and (2), and (B) from 60 parts to 40 parts by weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group, said stable additive composition being present in an amount suificient to retard substantially the liberation of chrorric acid fumes from said bath.

7. A chromic acid plating bath for the electro-deposition of chromium comprising an aqueous solution of from about 33 ounces to 54 ounces per gallon of CrO an amount of H 80, suflicient to provide a weight ratio of H SO :CrO of 1:250 to 1:60 and a quantity of non ionic Wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from about 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compound containing in their structure oxypropylene groups, oxyethylenegroups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compound being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of a reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular Weight of the polyoxypropylene polymers in the mixture is from about :1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by weight of the mixture, and (3) mixtures of (1) and (2) said non-ionic Wetting agent being present in an amount sufiicient to retard substantially the liberation of chromic acid fumes from said bath.

8. A chromic acid plating bath for the electrodeposition of chromium comprising an aqueous solution of from about 33 ounces to 54 ounces per gallon of CrO an amount of H 50 sufiicient to provide a ratio of H SO :CrO of 1:250 to 1:60 and a quantity of a stable additive composition comprising (A) from 10 to 90 parts by weight of non-ionic wetting agent selected from the group consisting of (l) polymers of ethylene oxide having an average molecular Weight of from about 1300 to 1 800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compound being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are atattached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymers in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by weight of the mixture, and (3) mixtures of (l) and (2), and (B) from 90 parts to 10 parts by Weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group said stable additive composition being present in an amount suflicient to retard substantially the liberation of chromic acid fumes and spray from said bath.

9. A chromic acid plating bath for the electrodeposition of chromium comprising an aqueous solution of from about 33 ounces to 54 ounces per gallon of C10 an amount of H 80 suificient to provide a ratio of H SO :CrO of 1:250 to 1:60 and a quantity of a stable additive composition comprising (A) from 40 to 60 parts by weight of a non-ionic Wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular Weight of from about 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compound being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are, attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymers in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by Weight of the mixture, and (3) mixtures of (1) and (2), and (B) from 60 parts to 40 parts by weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group said stable additive composition present in an amount suflicient to retard substantially the liberation of chromic acid fumes and spray from said bath.

10. A stable additive composition for addition to chromic acid plating baths whereby the liberation of chromic acid fumes from said baths during use is retarded substantially comprising (A) from 10 to 90 parts by weight of a non-ionic Wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from 1300 to 1800, (12) a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular weight of the polyoxypropylene polymer in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present constitute from about 80% to 95% by Weight of themixture, and (3) mixtures of (1) and (2), and (B) from parts to 10 parts by weight of an alkyl aromatic sulfonic acid compound of the benzene series containing at least 7 carbon atoms in an alkyl group, said stable additive composition being present in an amount sufficient to retard sub- 1itantially the liberation of chromic acid fumes from said ath.

11. A stable additive composition for addition to chromic acid plating baths whereby the liberation of chromic acid fumes from said baths during use is retarded substantially comprising (A) from 40 to 60 parts by weight of a non-ionic Wetting agent selected from the group consisting of (1) polymers of ethylene oxide having an average molecular weight of from 1300 to 1800, (2) a cogeneric mixture of conjugated polyoxypropylenepolyoxyethylene compounds containing in their structure oxypropylene groups, oxyethylene groups and an organic radical derived from an organic compound containing a plurality of reactive hydrogen atoms, the compounds being characterized in that all of the oxypropylene groups are present in polyoxypropylene chains that are attached to the organic radical at the site of the reactive hydrogen atom to thereby constitute a polyoxypropylene polymer, the oxyethylene groups are attached to the polyoxypropylene polymer in polyoxyethylene chains, the average molecular Weight of the polyoxypropylene polymer in the mixture being from about 1500 to 1800 as determined by hydroxyl number, and the oxyethylene groups present References Cited in the file of this patent UNITED STATES PATENTS 2,115,192 Bruson Apr. 26, 1938 2,195,409 Flett Apr. 2, 1940 2,213,477 Steindorfi et al Sept. 3, 1940 2,655,471 Chester Oct. 13, 1953 OTHER REFERENCES Pluronics, Wyandotte Chemical Corp., 9 pages, received in Patent Oflice J an. 7, 1957.

Claims

1. A CHROMAIC ACID PLATING BATH FOR THE ELECTRODEPOSITION OF CHROMIUM COMPRISING AN AQUEOUS ACIDIC HEXAVALENT CHROMIUM SOLUTION CONTAINING A NON-IONIC WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF (1) POLYMERS OF ETHYLENE OXIDE HAVING AN AVERAGE MOLECULAR WEIGHT OF FROM 1300 TO 1800, (2) A COGENERIC MIXTURE OF CONJUGATED POLYOXYPROPYLENE-PROLYOXYETHYLENE COMPOUNDS CONTAINING IN THEIR STRUCTURE OXYPROPYLENE GROUPS, OXYETHYLENE GROUPS AND AN ORGANIC RADICAL DERIVED FROM AN ORGANIC COMPOUND CONTAINING A PLURALITY OF REACTIVE HYDROGEN ATOMS, THE COMPOUNDS BEING CHARATERIZED IN THAT ALL OF THE OXYPROPYLENE GROUPS ARE PRESENT IN PLOYOXYPROPYLENE CHAINS THAT ARE ATTACHED TO THE ORGANIC RADICAL AT THE SITE OF A REACTIVE HYDROGEN ATOM TO THEREBY CONSTITUTE A POLYOXYPROPYLENE POLYMER, THE OXYETHYLENE GROUPS ARE ATTACHED TO THE POLYOXYPROPYLENE POLYMER IN POLYOXYETHYLENE CHAINS THE AVERAGE MOLECULAR WEIGHT OF THE POLYOXYPROPYLENE POLYMER IN THE MIXTURE BEING FROM ABOUT 1500 TO 1800 AS DETERMINED BY HYDROXYL NUMBER, AND THE OXYETHYLENE GROUPS PRESENT CONSTITUTE FROM ABOUT 80% 95% BY WEIGHT OF THE MIXTURE, AND (3) MIXTURES OF (1) AND (2) SAID NON-IONIC WETTING AGENT BEING PRESENT IN AN AMOUNT SUFFICIENT TO RETARD SUBSTANTIALLY THE LIBERATION OF CHROMIC ACID FUMES FROM SAID BATH.