US2913377A - Aqueous electrolytic process - Google Patents

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United States Patent AQUEOUS ELECTROLYTIC PROCESSES Henry Brown, Huntington Woods, Mich., assignor to The Udylite Research Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application June 11, 1956 Serial No. 590,389

6 Claims. 01. 2 04--ss This invention relates to the prevention of mist and spray by the use of a surface-active fluorocarbon sulfonic acid dissolved in the aqueous acidic solutions of certain electrolytic processes employing insoluble or highly polarized anodes at which gases such as oxygen, ozone or chlorine are evolving.

It is well-known that ordinary surface-active agents can prevent the mist and spray which is evolved by gases that are liberated in aqueous electrolytic processes. The surface-active agents accomplish this by lowering the surface tension of the aqueous electrolyte and by forming a foam blanket with the evolved gases which can greatly minimize mist and spray. Thus, ordinary surface-active agents are used, for example, in alkaline electrolytic cleaners, and also in non-electrolytic processes such as acid dips and metal pickling operations for the prevention of mist and spray from evolved hydrogen. However, in aqueous acidic electrolytic processes involving the use of insoluble or highly polarized anodes, ordinary surface-active agents (which have in common one or more hydrocarbon chains) are oxidized quite rapidly at the insoluble or highly polarized anodes, and it is difficult to control and maintain the proper concentrations of surface-active agents for suppression of mist and spray. Furthermore, in the case of acidic electrolytes employing insoluble or highly polarized anodes, the oxidized and hydrolyzed products resulting from the degradation of ordinary surface-active agents may cause harmful results on the insoluble or highly polarized anode (for example, cause excessive attack of lead anodes if acetic acid is one of the oxidation byproducts) or cause a harmful effect on cathodically deposited metals such as pitted zinc plate from acidic zinc sulfate solutions or pitted chromium cathodes from chrome-alum solutions in case the oxidation residues of the surface-active compound are oily or grease-like.

It has been found that surface-active fluorocarbon sulfonic acids as exemplified in Table I containing 6 to carbon atoms inclusive (preferably 8 carbon atoms) are not oxidized at insoluble or highly polarized anodes in aqueous electrolytic processes even though current densities of over 1,000 amperes per square foot are employed, but instead are completely stable to the powerful oxidizing conditions existing at such insoluble type anodes as, lead and lead alloys (lead-antimony, lead-tin, tellurium lead, lead-silver), graphite, silver, silver alloys, copper alloys, magnetite and silicon containing anodes, and independent of whether lead dioxide, manganese dioxide, peroxides, chlorine, chlorates, persulfates, oxygen or ozone are being formed at the insoluble or highly polarized anodes. Furthermore, these fluorocarbon sulfonic acids of Table I are stable to the reducing conditions existing at cathodes whether the electrolyte is an alkaline, neutral or acidic sulfate or chloride solution.

' The compounds of Table I show exceptional surfaceactivity (they are capable of lowering the surface tension of aqueous electrolytes down to 20-25 dynes/cm.) and arecapableof forming thin foam blankets with'the I from the completely successful minimization or preven 2,913,377 Patented Nov. 17, 1959 bubbles of evolved gases, preventing or greatly minimizing the formation of mist and spray from electrolytic processes employing insoluble or highly polarizedfanodes. Thus, with the very stable compounds of Table I it is very easy to control the mist and spray evolving from. electrolytic processes employing insoluble type anodesat the cathodes at a rate to exceed 2% of the atmosphere when the danger of explosion would be present, the ventilators and baffles are kept free from accumulation of sprayed and dried electrolyte and the need for washers in the ventilating system is eliminated. Apart tion of mist and spray in aqueous electrolytic processes using insoluble anodes accomplished by the compounds of Table I, there is an improvement in the smoothness of metal plate obtained in the presence of the compounds of Table I in certain aqueous electrowinning processes (for Zn, Cd, Mn and Cu from sulfate electrolytes). This is especially noticeable in the more dilute solutions and also where there is a tendency for fine particles and bubbles to stick to the cathodes. The compounds of Table I tend to greatly decrease the contact angle of the bubbles adhering to the cathode and the bubbles do not grow large but readily detach from the cathode surface as very fine bubbles. The compounds of Table I tend to concentrate at interfaces such as the electrode surfaces and apparently in this way aid in obtaining smoother and more fine-grained plate, which are very desirable characteristics in plating thick cathode sheets as in electrowinning. The compounds of Table I do not appear to plate out to any noticeable extent and electrodeposits (Zn, Cd, Mn, and Cr plated from theirsulfate salts) are found not to contain any sulfur contributed by the surface-active agent, unlike the case often found with ordinary sulfonic surface-active compounds.

Surface-active fluorocarbon carboxylic acids which were also found to be stable to the powerful oxidation conditions existing at insoluble anodes such as lead or lead-alloy anodes in aqueous acidic electrolytes, and which also lower the surface tension of the electrolyte solutions to low values, were, however, of little value in preventing mist and spray during electrolysis even though the most surface-active example, perfluoro-octanoic acid was used as well as the six-carbon compound. Also, no improvements were found if chlorine atoms were partially substituted for fluorine atoms, as for example,

one chlorine atom present to every three fluorine atoms, with the chlorine atom on every other carbon atom.

Table I to be used in the aqueous electrolytic processes are from about 0.003 gram/liter for the more active compounds to about 6 grams per liter for least active:

examples. In general, Examples 3, 6 and Sam preferred since smaller concentrations may be used etfec tively and for higher temperature baths (over about 50 C.) Example 3 is preferredas it maintains a thin foam blanket with the least concentration most readily at high- 3 er tempeiatiiresi However-"where very low foaming is required, Examples Sand 6a'r'epreferred. In the compounds of Table I, about three hydrogen atoms may be substituted for fluorine atoms, or about one hydrogen or One -(:lilbfin "aibfn cid'b'jfdschfbll' every other carbon atom carrying fluorine and actually "two hydroge'ns or chlorine 'ammscan be ptes'e'nto1'1 the same carbon atom when adjacent to acarbon atom" carrying at least two fluorine'atoms; withoufseriously decreasing the effectiveness or the stability of the compounds of Table-1.. In general, the preferred'compounds' are thus, the compounds ofTable I, from the standpoint oPefi'ectiveness and stability. v

' TABLEI Gone. in baths grams/liter (1;; Perfluoro phexsgl -sull'onlc aeid... (2 Perfluoro n-heptyl sultonie acid (3) Perfluorb n-oct'yl sulfonic acid (CFACFMCFgSOgH).

(4;; Perfluoro n-decylsulmnieamdn (6 Perfluoro p-methyl cyelohexyl sulfonic acid (6) Perfluorop'ethylcyclohexyl sulfonieaeid (O5FS0'=H)-..- 0.1-4

(7; Periiuoro eycloliexyl w-methyl sultonie acid (8 Perfluoro cyclohexyl w-ethyl sulfonic acid (@GFiCFsSOiH): 0.1-4

To illustratethe scop'e'and'utility of'the compounds of this invention, the following examples? of. electrowinning baths are given'in'Exainples'l, 2, 3, 4 and 5. In Examples 6A" and 6B, the'use ofthe'com'pounds' ofTable I are illustratediin aluminum anodizing baths.

Example I- Aqueous acid zinc Cathode current-densities of 5 to over 1,000 amperes/ sq. ft. depending on the acidity of the bath andthe degree of agitation.

Example 2- A'queous acid'cad'mium' sulfate baths with lead or lead alloy anodes."

' Grams/liter Cdso so- 300 HQSO}, 5- 100 Compound 3 of Table'f .Q. 0.003-0.02 pH=*2;5to'0ll'.

Cathode current densities of. 5 to 500. amperes/sq. ft.

Example '3 Aqueous acid copper sulfate baths lead or lead alloy anodes.

Grams/liter Cuso' 25-300 H 50; 5-100 Compounddof'lable I 0.1- 2 pI-I=3L5 t 0.1.

Cathode-current densities of -300 amperes/sq. it.

I Example'4 Aqueous manganous sulfate. baths. with lead or lead alloy anodes, and the anode; compartment separated. by

a-porous-diaphragm from thecathode' department. The anode'compartmentis kept acidic.

Grams/liter MnSO, 25- 200 (NI -I SO 25- 200 Compound 3zof-'Tab1e.I 0005-004 4 v Cathode current densities of 5-100 amperes/ sq. ft.

Example 5 Aqueous acidic cbromic sulfate baths with lead or lead alloy anodes, and the anode compartment separated by a porous diaphragm (e.g. Vinyon cloth) from the cathode compartment.

Grams/liter Cr (SO 25-200 (NI-10580 2s-'200 Compound 6 of Table'I 0.1- 3

Example v6 In the anodizing. of aluminum where the aluminum,

represents a highly polarized anode.

(A) Chromic. acid process.-CrO at 5 to 10% strength. Temperature=32 F. to 100 F., With voltages as high as 40 volts. Concentration of compound 6 of Table fat 0.1 to 2 g./l., or compound 3 of Table I at 0.01 to 0.1.g./l.

(B) Sulfuric acid process-H 50 at 10-25% by weight. Temperature=32 F. to F., with voltages as high as 40 volts. Concentration of compound 6 of Table I at 0.1 to 2 g./l., or compound 3 of TableI at.

0.01 to 0.1 g./l.

The compounds of Table I also give excellent resultsv when aqueous oxalic acid solutions and when aqueous phosphoric acid solutions are used as the anodizing baths. In anodizing aluminum in warm or hot baths, e.g. 200 F. or up to boiling, compound 3 of Table I (perfiuoro n-octyl-l-sulfonic acid) is the preferred compound to use, andmay. be used in a concentration of about 0.01 to 0.2 gram/liter, because it tends to form the most stable thin foam blanket at these higher temperatures. In colder baths the use of compound 6 of Table I at concentrations of about 0.3 to 2 grams/liter is generally preferred as itdoes not tend to over-foam. However,

if the baths are to be discarded often then compound 3 of TableI is preferred since it is used in the lowest con-- centrations.

Not only are the compounds of, Table I highly suitable for the elcctrowinning or electroplating of the metals.

given in the above Examples 1-5 inclusive, when insoluble or highly polarized anodes are used, but also in the electrolytic processes for the preparation of manganese dioxide, andin the electrolytic process for the formation of lead dioxide positive plates, and spongy lead (from lead oxide) negative plates of lead storage batteries. The compounds of Table I are compatible with the lignin and lignin sulfonate used in the negative plates. Furthermore, in the chlor-alkali electrolytic cells for the production of chlorine from sodium or potassium chloride, the.

compounds of Table I are completely stable to the oxidizing and reducing conditions.

In general, the compounds of Table I cause the quick detachment of the bubbles of gases released during,

electrolysis, thus only small bubbles formand because the compounds ofv Table I are stable to the oxidizing conditions at the insoluble anodes, their effect is uniform and consistent without harmful side reactions. In general, the concentrations of the. compounds of Table I cambe; used: up; tosaturationinthebaths, though 11011331.

ly only 0.005 to 0.1 g./l. is the concentration needed for compound 3 and 0.1 to 3 g./l. for compound 6 of Table I with compound 3 preferred for the hotter baths and compound 6 for the cooler baths, or where the thinnest foam blanket is required, or where actually no foam blanket is desired with the reduction of mist and spray. To get as complete suppression of mist and spray as possible, a foam blanket must be formed.

The perfluoroalkane sulfonic acids of this invention may be used in form of salts, for example, sodium or potassium salts, also they may be characterized or defined as fiuoroalkane sulfonic acids or sulfonates of six to ten carbon atoms inclusive, in Which the fluorine atoms exceed the number of chlorine or hydrogen atoms that may be present in the fluorocarbon chain.

What is claimed is:

1. In an anodizing process employing essentially insoluble anodes selected from the group consisting of aluminum, manganese and lead and an aqueous solution of an acid selected from the group consisting of sulfuric, phosphoric, and oxalic acids, the improvement comprising minimizing the formation of spray and mist during anodizing by incorporating in said aqueous electrolyte a perfluoro-alkane sulfonic acid of 6-10 carbon atoms inclusive in a quantity to produce therein a concentration of about 0.003 to 6 grams/ liter.

2. A process in accordance with claim 1 wherein the process is anodizing aluminum in an aqueous sulfuric acid solution.

3. A process in accordance with claim 1 wherein the process is anodizing aluminum in an aqueous phosphoric acid solution.

4. A process in accordance with claim 1 wherein the process is anodizing aluminum in an aqueous oxalic acid solution.

5. A process in accordance With claim 1 wherein said perfluoro-alkane sulfonic acid is perfluoro n-octyl-l-sulfonic acid and is present in a concentration of about 0.003 gram/liter to about 0.5 gram/liter.

6. A process in accordance with claim 1 wherein the said perfiuoro-alkane sulfonic acid is perfiuoro p-ethyl cyclohexyl sulfonic acid and is present in an amount of about 0.3 to about 2 grams/liter.

References Cited in the file of this patent UNITED STATES PATENTS 2,750,334 Brown June 12, 1956

Claims (1)

1. IN AN ANODIZING PROCESS EMPLOYING ESSENTIALLY INSOLUBLE ANODES SELECTED FROM THE GROUP CONSISTNG OF ALUMINUM, MANGANESE AND LEAD AND AN AQUEOUS SOLUTION OF AN ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC, PHOSPHORIC, AND OXALIC ACIDS, THE IMPROVEMENT COMPRISING MINIMIZING THE FORMATION OF SPRAY AND MIST DURING ANODIZING BY INCORPORATING IN SAID AQUEOUS ELECTRODYTE A PERFLUORO-ALKANE SULFONIC ACID OF 6-10 CARBON ATOMS INCLUSIVE IN A QUANTITY OF PRODUCE THEREIN A CONCENTRATION OF ABOUT 0.003 TO 6 GRAMS/LITER.