US2750335A - Chromium electrodeposition - Google Patents

Description

Patented June 12, 1956 CHROMIUM ELECTRODEPOSITION Henry Brown, Huntington Woods, and Donald R. Millage,

St. Clair Shores, Mich., assignors to The Udylite Research Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application July 17, 1953, Serial No. 368,836

5 Claims. (Cl. 20451) Well known, with the evolution of relatively large quantities of hydrogen at the cathode and of oxygen and ozone at the insoluble anodes. The undesirable spray and mist of chromic acid results from the violent bursting of the multitudinous gas bubbles of high surface energy which are released by the electrolysis. The spray and mist resulting from this bubblebursting is of considerable volume because of the high current densities used in the plating, the low efliciency of chromium deposition and the use of insoluble anodes. Due to the corrosiveness and high toxicity to the workers of this spray and mist and its Well known deleterious contaminating eifect on other plating baths such as nickel, copper, cadmium and zinc, it is necessary in large scale production to employ powerful ventilation to continuously remove the same as it is formed. For example, to carry away the mist formed in a 2,000 gallon tank installation requires an exhaust of as much as 10,000 cubic feet per minute to enable safe continuous production. The use of powerful ventilation is expensive not only from the standpoint of the initial installation cost and upkeep maintenance, but also because of the abstraction of the heated air in winter. Moreover, not all of the spray and mist is removed from the area of the plating tank even when powerful ventilation is employed and this is especially true on wide plating tanks. In the usual installation, a certain amount of chromic acid mist does contaminate the air, especially when stray air currents pass over the tank during electrodeposition. From the standpoint of toxicity, the maximum safe concentration of chromium trioxide is now considered to be 0.1 milligram per cubic meter of inhaled air. In addition to the disadvantages connected with adequate ventilation, there is the further disadvantage of the loss of chromic acid in the exhausted air which may amount to about 30% of the chromic acid which is used in the electrodeposition. The amount of chromic acid thus exhausted, together with that which is carried out on the surface of the articles themselves,

actually represents more chromic acid than that which is used up in the formation of the chromium coating.

The problems arising as the result of the formation of chromic acid spray and mist in commercial chromium plating, were recognized almost from the very inception of chromium plating and various attempts have been made to prevent or to greatly minimize the formation of this spray and mist. As examples of attempted solutions, it has been suggested to form blankets on the surface of the bath by the use of various oils, floating objects such as plastic pieces, and various wetting agents especially non-ionic wetting agents. None of these attempts have been found to be eminently satisfactory, and all have left much to be desired. For example, nonionic wetting agents are rapidly oxidized at the anode, and floating plastic pieces are too readily displaced when articles are placed in and taken out of the bath. Heretofore, no ordinary compound which is soluble in a conventional aqueous acidic hexavalent chromium bath has been found that will prevent or efiectively minimize the formation of spray and mist and yet be stable to the extremely powerful oxidizing conditions existing at the insoluble anodes during the electrodeposition of chromium from such baths.

It is, therefore, the principal object of the invention to provide a stable additive for an acidic hexavalent chromium bath which greatly minimizes the formation of spray and mist during electrolysis of such baths with insoluble or highly polarized anodes.

Another important object of this invention is to provide improved acidic hexavalent chromium baths and a method for chromium plating which substantially elimis nates the necessity for the use of expensive ventilating procedures currently employed.

Another object is to provide an additive for an aqueous acidic hexavalent chromium bath which is capable of producing chromium deposits of increased brightness which persists with increasing thickness of the deposits.

It has now been found that these and related objects are accomplished when certain cationic surface-active compounds characterized as 1,1 dihydro fluorocarbon amines or their salts are added to aqueous acidic hexavalent chromium baths of the type conventionally used in chromium electroplating.

Broadly the amines which are suitable for the purposes of this invention comprise the primary, secondary, tertiary and quaternary 1,1 dihydro fluorocarbon amines containing a saturated fluorocarbon chain of from 3 to 7 carbon atoms, and the salts of the primary, secondary and tertiary amines. Preferred salts are the chromic acid or dichromate salts. Typical examples of these 1,1 dihydro fluorocarbon amines and the optimum concentrations for use in otherwise conventional hexavalent chromium baths are given in Table I. It is to be understood that the proportions set forth in Table I represent only the optimum concentrations, and that benefit is received with somewhat lower concentrations and that concentrations up to saturation may be used with good results. Preferably quantities approaching saturation should be employed for maximum reduction of spray and maximum brightness of plate. I

TABEE I 1,1 Dihydro fluorocarbon Amines grams/liter (1) CF3(CFz)2OHzNH1 4-12 (2) OF3 CF2 4CH2NHZ 0. 5-3

(3) CF (CFg) CHgNHg 0. 3-1. 5

H (4) CF (CF;) 4CH7N/ 0. 5-2

Y on; G fi zlr fiz -12 (6) v. 'C'EflQEflziQHzN (l.5 2

CHzCH;

(7). i -GEa(CFz]oQE-2N C a 0. 05-0v 5 CHQC'OOH (8) CFflcFzliCHzN cfia 0. 1 05 Br 0H:

CH; (9).. ..i QEKCEQQCHINZCHI -O.1-1.-5

CH: ongs-o.

no) cardamom-1f a o;1-.1

(11), G a'(CEi)z'CHzN-QHs 0. 5-4

1i mm The 1,1 dihydrofluorocarbon amines of Table I can he represented 'by-th e general formula:

where n..- 2.6 and R1, R2 and R3 are hydrogen or carbonatoms carrying hydrogen, and the sum of the carbon atoms of'R1-l-R2+R3 being not more than six, and X 'is an anion. Preferably Xis sulfate, acid sulfate, methiosulfate, Qfiuoride or dichromate.

The surface-active cationic portion of the compounds is the dominant portion in the accomplishment of the invention, and the anionic portion is usually dichromate or chromate once the compound is dissolved in the acidic hexavalent chromium baths. It is to be understood that the basic l,1 dihydro fluorocarbon amine ,(that is, the amine without the dotted line attachments to N of R3 and X may be the form in which ,thematerial is added tothe bath. For example, 71,1 dihydro perfluorohexylamineirnay be addedas such. However, oncedissolved in theacidic bath, {it formsia salt with the chromicacid ,or .dichromates of the bath. Thissalt formation with the primary amin is also true, of course, with the secondary and tertiary amines.

The presence in the chromium plating baths .of halide ions other than fluoride, are not in g,eneral as desirable as ,dichromate, chromate or sulfate, acidsulfate ,or methiosulfate. Also the presence of organic acids such as formic, acetic, etc. are not generally desirable when insoluble 4 lead or lead-alloy anodes are used because of their anodic attack on these anodes.

The additives of this invention can be made from fluorocarbon carboxylic acids made by the process as disclosed in U. S. Patent 2,519,983. With such carboxylic acids, amides or nitriles as starting compounds, the various members listed in Table I may be synthesized by conventional methods employed in organic chemistry.

In addition to greatly reducing the formation of spray and mist, the incorporation of the 1,1 dihydro fluorocarbon amine compounds of this invention, for example, 1,1 dihydro perfluorohexylamine in conventional hexavalent chromimum plating baths has been found to enable the plating of thicker bright chromium deposits over a bright surface before dulling of the chromium sets in. This advantage has been found'to exist in comparison to a conventional hexavalent chromium plating bath or a conventional hexavalent chromium plating bath whichhas been modified .by the incorporation of a fluorocarbon sulfonic compound. This can'be readily seen in .chromium plates of 0.05 to .1 mil thickness. The thicker chromium plate increases the corrosion protection of nickel, or of nickel, nickel-cobalt, nickel-iron covered ferrous surfaces by decreasing -the porosity of the chromium plate. For example, steel that is plated with 11.5 mils of bright nickel and over-laid with 0:08 to-0.12 mils of chromium, provides greatly superior corrosion protection in industrial atmospheres than is aiforded when the over-layer of chromium has a conventional thickness of only .01-.03 mil.

"With the 1,1 dihydro fluorocarbon amines, no excessive trivalent chromium ions are formed in the cathodic processes.

In contrast to the relatively short chain fluorocarbon amines of this invention, ordinary amines such as n-octyl amine or -n-dimethy1 n-toctyl amine do not prevent spray or -mist,-and-it is necessary to use n-decyl amine or longer chain amines -to;prevent spray and mist from the acidic hexavalent chromium plating baths. However, these ordinary surface-active amines are rapidly oxidized anodically in an amount of about .1-1 gram/liter in about 4 hours, thus-destroying their surfaceeactive properties.

The examples given below set forth formulations of operative chromium plating baths useful for decorative or engineering purposes. It will be understood that other compounds covered by Formula Aand exemplified by the compounds of Table I maybe used in these typical formulations [in the "place of the particular examples given. Additionally, it is to 'be'understood that mixtures of the compounds 'of this invention may be employed as well as the single compounds.

Example I HO -2 50 grams/liter chromic acid '(CrOa) 1:53 grams/ liter S04 ion 2zgrams/iliter 1,1dihydroperfiuorohexyl amine (Example 2 of Table I) Temperature 20 -C.-30 C.

Cathode current density-l'OO- 3OO ;amps./ sq. ft. (approximately 1- 030 amps] sq. :dm.)

In the formulation of Example I, catalysts other than the sulfate ion may be employed, such for example as thefluoriideion'or the fluosilicate 'i'on'or mixtures thereof. The proportion of fluoride or fluosilicate ion employed is an amount 'which provides an equivalent catalytic effect :to that which :is provided by the l.53 grams/liter of the sulfite ion.

Example 11 200-400 vgrams/liter CrOs 2?4 grams/ liter .SOr anion 1 gram/liter 1,1 dihydro .perfiuorohexyl trimethyl amine methiosulfate (Example '9 of Table I Temperature 20 C.50 C.

Cathode current density'l50300 amps./ sq. ft.

What is claimed is:

1. A bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing a compound having the formula:

R1 C 1*;(0 FahcHalfi -Rz 1: \RI

where n=2 to 6, R1, R2, and R3 are selected from the group consisting of hydrogen and hydrocarbons, the sum of the carbon atoms of R1+R2+R3 being not more than 6, and X is an anion, said compound being present in sufficient amount to substantially decrease formation of spray and mist.

2. A bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about 0.05 gram per liter of a compound having the formula:

R1 C FKC FahCHzIYg-Rg X R;

where n=2 to 6, R1, R2, and R3 are selected from the group consisting of hydrogen and hydrocarbons, the sum of the carbon atoms of R1+Rz+Ra being not more than 6, and X is an anion.

3. In a process of electrodepositing chromium from aqueous acidic hexavalent chromium solutions, the improvement which consists in adding to the solution a compound having the formula:

R1 N IM HIIF Ra 5: R; where n=2 to 6, R1, R2, and R3 are selected from the group consisting of hydrogen and hydrocarbons, the sum 6 of the carbon atoms of R1+R2+R3 being not more than 6, and X is an anion, said compound being added in sufficient amount to substantially decrease formation of spray and mist.

4. A method of electrodepositing chromium which comprises the steps of adding to an aqueous acidic hexavalent chromium solution at least about 0.05 gram/liter of a compound having the formula:

R1 OFKCFflnCHflTR-Rz X R,

where n=2 to 6, R1, R2, and R3 are selected from the group consisting of hydrogen and hydrocarbons, the sum of the carbon atoms of R1+R2+R3 being not more than 6, and X is an anion, and electroplating chromium from the solution.

5. In a bath for the electrodeposition of chromium comprising an aqueous acidic solution of hexavalent chromium, an additive in an amount of at least about 0.05 gram/ liter, said additive consisting of a compound having the formula:

R1 CF;(GF:)CH2ITI\R2 it R;

where n=2 to 6, R1, R2, and R3 are selected from the group consisting of hydrogen and hydrocarbons, the sum of the carbon atoms of R1+Rz+R3 being not more than 6, and X is an anion.

Simons Aug. 22 ,l950 Chester Oct. 13, 1953

Claims (1)

1. A BATH FOR THE ELECTRODEPOSITION OF CHROMIUM COMPRISING AN AQUEOUS ACIDIC HEXAVALENT CHROMIUM SOLUTION CONTAINING A COMPOUND HAVING THE FORMULA: