US2956935A

US2956935A - Chromium plating

Info

Publication number: US2956935A
Application number: US698062A
Authority: US
Inventors: Passal Frank
Original assignee: Metal and Thermit Corp
Current assignee: Primerica Inc
Priority date: 1957-10-08
Filing date: 1957-11-22
Publication date: 1960-10-18
Anticipated expiration: 1977-10-18

Description

nited States Patent 'ice CHROMIUM PLATING Frank Passal, Detroit, Mich., assignor to Metal & Thermit Corporation, Woodbridge Township, N.J., a corporation of New Jersey No Drawing. Filed Nov. 22, 1957, Ser. No. 698,062

15 Claims. (Cl. 20451) ing spray and mist, it is necessary to design special equipment and to provide large ventilation capacity. This corrosive spray and mist is caused by the formation of gas bubbles at the electrodes (oxygen at the anodes and hydrogen at the cathodes). These bubbles are relatively large and when they break at the surface, the electrolyte spatters into very fine droplets which become airborne.

Certain additives having strong wetting characteristics. are, and have been, used to reduce mist and spray. How-- ever, none of the additives now known are completely successful from a commercial viewpoint. Some are useful for very short periods of time but then rapidly decompose in the highly oxidizing chromic acid baths. Others, although effective in preventing spray and mist, are strongly adsorbed on the cathodes resulting in electrodeposits that have poor adhesion and that are pitted.

The most successful additives are the fiuorinated long chain hydrocarbons which are very expensive. I

It is an objective of this invention to provide a process for electroplating chromium from chromic acid baths with concomitant production of a minimum of spray and mist.

It is another object of this invention to provide a composition of matter which when incorporated in chromic acid baths minimizes the production of spray and mist during electrodeposition.

The invention also contemplates the use of chromic acid baths from which chromium may be electrode posited with a minimum of mist and spray at the surface.

I have now discovered that when chromium is electrodeposited from a chromic acid bath in which is incorporated a small but effective amount of a sulfonated alkyl diphenyl oxide, the electrodeposition is carried out,

wherein R is an alkyl group having from 6 to 18 carbon atoms in the chain and X is a catio'maiid it has-a value 'of octadecyl groups.

phenyl oxide and didodecyl diphenyl oxide.

0 or 1. The cation, X, is selected from hydrogen, ammonium and metals, and excludes metalloids which are converted in the chromic acid bath to acid radical anions which have a deleterious effect on the bath or on the electrodeposited chromium.

barium, magnesium, nickel, iron, and copper. The preferred compounds are the sulfonated salts of sodium,

potassium, lithium or ammonium. The operative alkyl.

groups, R, includes the hexyl, octyl, nonyl, dodecyl and The octyl, nonyl and dodecyl groups are preferred. Chromic acid baths are highly acid .and

strongly ionizing in nature. The sulfonated alkyl diphenyl oxide in the bath is believed to exist in the formv of the acid radical, having the formula:

Ru 1. B

so.- o:-

' The sulfonated alkyldipenhyl oxide as produced and utilized is a mixture of. the various substituted products. The sulfonic acid salt'group is believed primarily substituted in the position ortho to the oxygen-substituted carbon, whereas the alkyl chain is primarily substituted in the para position. The additive as commercially pro' duced and utilized may also be a mixture of monoand dialkyl substituted products.- A preferred additive is a mixture of the disulfonated salts of monododecyl dium and dipotassium salts are preferred.

' bath.

It have discovered that when as little as 0.005 g./l. (gram per liter) of sulfonated alkyl diphenyl oxide is added to a chromic acid bath in the chromium plating. process, the'amount of mist and spray is very substan-" tially 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 up," to which drag-out contributes. 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 and by the actual construction of the plating tanks. Baths containing this additive have 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 aifect the thickness of the foam blanket for a given volume of It is not contemplated that more than about 5 g./l. of the additive will be used. I prefer to use baths which contain about 0.01 g./l. and 0.25 g./l. in the bath.

The sulfonated alkyl diphenyl oxides are solid materials and are preferably added to the bath in the form of an aqueous solution. When such solutions are stored,

producea minimum of spray and mi stduring the electro 1 depositionof chromium. a H v It has been found that the sulfonated alkyl diphenyl oxides are efiective in reducing spray and mist. in the; various types of chromic acid baths. The se include.

baths containing sulfate catalyst, :and also those containing mixed catalysts. It iselfective in low conceni atentecl oct. 18, 1960 Illustrative metals includesodium, potassium, lithium, trivalent chromium, calcium,

The disodi tration baths, such as those containing 180 to 250 g./l. of chromic acid, as well as medium and high concentration baths containing as much as 550 to 600 g./l. of chromic acid. These baths are operated under conventional process conditions. The chromium electroplating baths referred to herein are the conventional hexavaient chromium baths comprised largely of chromic acid. Although these baths are commonly referred to as being formed from chromic acid, they are more correctly noted as being formed from chromic anhydride or equivalent material.

For the purpose of further illustrating the advantages of the present invention, the following illustrative examples are included:

Chromium electrodeposition was carried out in a standard cell by electrolysis using insoluble lead anodes and plating on the cathode. Standard conditions were used unless otherwise specified.

CrO g./l.. 250 50.; (as Na SO g./l 2.5 The sodium salt of sulfonated dodecyl diphenyl oxide g./l 0.25 Temperature F..- 110 C.D.1 a.s.i.

CrO g./l 325 S g./l 3.25 The sodium salt of sulfonated dodecyl diphenyl oxide g./l 1.0 Temperature F..- 120 C.D.--1.5 a.s.i.

CrO g/l 400 S0 g./l 4.0 The sodium salt of sulfonated dodecyl diphenyl oxide g./l 5.0 Temperature F..- 105 C.D.0.75 a.s.i.

CrO g./l 250 S0, g./l 2.5 The sodium salt of sulfonated dodecyl diphenyl oxide g./l 0.5 Temperature F 130 C.D.2.5 a.s.i.

CrO g./l 400 K SiF In excess of saturation SrSO, In excess of saturation C.D.-1 a.s.i.

The sodium salt of sulfonated dodecyl diphenyl oxide (a) 2 g./l "Temperature, F- 110 (b) 0.25 g./l do 110 (c) 0.25 g./l dd 130 (d) 0.025 g./l. do 110 (e) 0.025 g./] do- 130 010 g./l 250 K SiF In excess of saturation SrSO In excess of saturation Kgcl'zoq g./l 10 SrCrO g./l 5 C.D.- --1 a.s.i.

The sodium salt of sulfonated dodecyl diphenyl oxide (a) 1 g./l Temperature, F-.. 130 (b) 0.25g./1 do (c) 0.25 g./l. do.. 130 (d) 0.025 g./l do.. 110 (e) 0.025 g./l do 130 (f) 0.01 g./l do The additive used in the noted tests was a mixture of the disddium salts of monododecyl diphenyl oxide disulfonate and didodecyl diphenyl oxide disulfonate (4:1 ratio). The potassium salts are as effective, as are the homologous alkyl substituted compounds.

The baths made up and operated as specified in the examples have relatively thin stable foam blankets at the surface and exhibit a substantial reduction of the amount of mist and spray when compared to similar baths used as controls. Service tats illustrated that the baths were etfective for relatively long periods of time with out replenishment and that the baths could be maintained in excellent condition by periodic additions of the additive. An unusual feature of the baths containing very small amounts of the sulfonated alkyl diphenyl oxides is that they effectively operate with a minimum of spray and mist and yet, many of the baths have such a small concentration of the additive that there is little discernable lowering of surface tension. Life tests run over relatively long periods of time did not indicate any buildup of harmful decomposition products.

The chromium deposits produced under standard conditions were bright and meet the usual commercial standards. The sulfonated alkyl diphenyl oxides are compatible in the baths with the other usual bath components and additives, including other additives used as antimisting agents. Pilot plant studies of baths containing the sulfonated aikyl diphenyl oxides disclose that over a period of time substantially less chromic acid had to be replaced in the bath. This is attributable to the decrease in spray and mist, both of which contribute to large chromic acid losses in baths without an anti-misting additive. In light of the foregoing description, the following is claimed:

1. An improved bath for the electrodeposition of chromium comprising an aqueous acid chromium plating solution and as an anti-misting additive, a small amount sufiicien t to substantially decrease mist in said bath of a disulfonated alkyl diphenyl oxide.

2. An improved bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and as an anti-misting additive, at least 0.005 g./l. of at least one compound having the general formula Rn R wherein R is an alkyl group having 6 to 18 carbon atoms, and n is an integer having a value from 0 to 1.

3. A bath as set forth in claim No. 2, containing between 0.1 g./l. and 0.25 g./l. of the additive.

4. A bath as set forth in claim No. 3 in which R is selected from the class consisting of octyl, nonyl and dodecytl.

5. A bath as set fonth in claim No. 2 in which the anti-misting additive is added in the form, of the disod-ium salt of disulfonated monododecyl diphenyl oxide.

6. A bath as set forth in claim No. 2, in which the anti-misting additive is added in the form of the potassium salt of disulfonated monododecyl diphenyl oxide.

7. A bath as set forth in claim No. 2, in which R is an octyl group.

8. A bath as set forth in claim No. 2, in which R is a nonyl group.

1 a la cces iq s e qs sp itias ih 'Q llill l nata with a minimum of spray and mist the improvement which comprises electroplating chromium from an aqueous chromic acid bath to which has been added a small amount sufl'icient to substantially decrease mist in said bath of disulfonated alkyl diphenyl oxide.

10. In a process for eleotrodepo-siting chromium metal with a minimum of spray and mist the improvement which comprises electroplating chromium from an aqueous chromic acid bath to which has been added at least 0.005 g./l. of at least one compound having the general formula wherein R is an alkyl group having 6 to 18 carbon atoms, 11 is an integer having a value from 0 to 1, and X is a cation selected from the class consisting of hydrogen, ammonium, and a metal.

11. A liquid anti-misting additive for minimizing the formation of mist and spray from aqueous chromic acid baths during electrolysis comprising an aqueous solution of a disulfonated alkyl diphenyl oxide stabilized to prevent mold formation with an alkali salt of a chromic acid selected from the class consisting of chromic and dichromic acids in suflicient amount to effect said stabilization.

12. A liquid anti-misting additive for minimizing the formation of mist and spray from aqueous chromic acid baths during electrolysis comprising an aqueous solution of at least one compound having the general formula in which R is a dodecyl group, n is an integer having a value from 0 to 1, and X is sodium, stabilized to prevent mold formation with an alkali metal chromate in suflicient amount to elfect said stabilization.

14. The composition of matter of claim No. 13 in which the alkyl diphenyl oxide additive comprises a mixture of the disodium salt of monododecyl diphenyl oxide disulfonate and didodecyl diphenyl oxide disulfonate in a ratio of about 4 to 1.

15. An improved bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and, as an anti-misting additive, a small amount sutficient to substantially decrease mist in said bath of octadecyldiphenyl oxide sulfonate.

Brown June 12, 1956 p

Claims

2. AN IMPROVED BATH FOR THE ELECTRODEPOSITION OF CHROMIUM COMPRISING AN AQUEOUS CHROMIC ACID CHROMIUM PLATING SOLUTION AND AS AN ANTI-MISTING ADDITIVE, AT LEAST 0.005 G./L. OF AT LEAST ONE COMPOUND HAVING THE GENERAL FORMULA