US3841978A - Method of treating a titanium anode - Google Patents

Abstract

1. A METHOD FOR THE ELECTRODEPOSITION OF MANGANESE DIOXIDE WHICH COMPRISES: PRETREATING A TITANIUM ANODE BY PROVIDING AN AQUEOUS ELECTROLYTE CONTAINING AT LEAST 25 GM./L. FLUORIDE IONS AND FROM ABOUT 800 TO 1200 GM./L. OF AT LEAST ONE OTHER COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID, ETHYLENE GLYCOL AND A MIXTURE OF NITRIC ACID AND PHOSPHORIC ACID; PLACING SAID TITANIC ANODE IN CONTACT WITH SAID ELECTROLYTE; PLACING A CATHODE IN CONTACT WITH SAID ELECTROLYTE; ELECTROLYZING SAID ELECTROLYTE AT AN ANODIC CURRENT DENSITY OF AT LEAST 10 AMPS/FT,2; PLACING THE TREATED TITANIUM ANODE IN AN ELECTROLYTIC CELL FOR THE ELECTRODEPOSITION OF MANGANESE, SAID CELL CONTAINING AN ELECTROLYTE COMPRISING AN AQUEOUS SOLUTIONS OF MANGANOUS ION IN A CONCENTRATION OF FROM ABOUT 15 TO 50 GM./L. AND FROM ABOUT 10 TO 25 GM./L. SULFURIC ACID, EFFECTING THE ELECTRODEPOSITION OF MANGANESE DIOXIDE ON THE ANODE AT AN ANODIC CURRENT DENSITY OF FROM ABOUT 8 TO 25 AMP/FT.2 AND RECOVERING SAID ELECTRODEPOSITED MANGANESE DIOXIDE.

Description

United States Patent O 3,841,978 METHOD OF TREATING A TITANIUM ANODE San-Chang Lai, Edmond, Okla., assignor t Kerr-McGee Chemical Corp., Oklahoma City, Okla. No Drawing. Filed Dec. 11, 1972, Ser. No. 313,851 Int. Cl. C01b 13/14 U.S. Cl. 20429 3 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method of treating a titanium anode. Broadly, the method comprises anodically treating the titanium anode in an electrolyte containing fluoride ions.

BACKGROUND OF THE INVENTION It is known to produce electrolytic manganese dioxide from an electrolyte comprising a manganese sulfatesulfuric acid solution. The manganese dioxide is deposited on the anode under carefully controlled conditions of electrolysis to produce a deposit having certain desired properties. The manganese dioxide so produced is recovered and used, for example, as a depolarizer for batteries.

When graphite is used, as the anode in such an electrodeposition process the current efliciency generally is limited to less than about 90%. Further, the manganese dioxide is strongly attached to the graphite surface and subsequent removal of the manganese dioxide also results in removal of particles of graphite, which necessarily contaminate the manganese dioxide. Moreover, it is diflicult to remove the deposited manganese dioxide without damaging the graphite anode.

Certain other materials also have been suggested for use as anodes in the electrodeposition of manganese dioxide, such as, for example, platinum, platinum plated titanium and other noble metals and their oxides. The cost of such anodes is too high for an economical commercial operation.

In U.S. Pat. No. 2,608,531 there is suggested a process for preparing electrolytic manganese dioxide using a particular type of titanium anode. Specifically, the patent discloses an anode consisting essentially of titanium particles compacted into a coherent but incompletely consolidated porous mass. However, such an anode is weak in mechanical characteristics and subject to breakage.

More recently, in U.S. 3,436,323 it is suggested that the disadvantages of a compacted titanium anode can be overcome by using an anode having a finely and sharply indented aventurine surface. Such surface preferably is obtained by sand blasting the surface of the anode. It has been found, however, when using such an anode, that an anodic current density in excess of about 9 amps per square foot results in passivation of the titanium anode surface.

Passivation is indicated by an increase in the electrical resistance of the anode. An increase in resistance necessarily requires an increase in the voltage applied to the anode to maintain a constant current density and also results in a corresponding increase in power consumption.

Titanium is substantially impervious to most corrosive environments (such as electrolytes), however, its susceptibility to passivation has limited its acceptance as a suitable anode material. Obviously, therefore, there is need for a method of treating titanium to reduce its susceptibility to passivation.

SUMMARY OF THE INVENTION A method now has been discovered of treating titanium whereby it is suitable for use as an anode, for example, in the electrodeposition of manganese dioxide. In accordance with the present method the titanium to be treated is placed in an electrolyte comprising an aqueous solution containing fluoride ions and at least one compound selected from the group consisting of ethylene glycol, acetic acid and a mixture of phosphoric acid and nitric acid. Thereafter, the titanium is anodically treated at an anodic current density of at least 10 amps per square foot. It has been found that titanium treated in accordance with the present method can be used as an anode in the electrodeposition of manganese dioxide at current densities of up to about 30 amps per square foot. Further, after repeated electrodepositing and stripping, the surface does not passivate or show any evidence of corrosion.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the present invention the titanium to be treated is made the anode of an electrolytic cell which also contains a suitable cathode. The cathode material is not critical and suitable materials include copper, nickel, mild steel, stainless steel, graphite, carbon and the like.

The cell contains an electrolyte comprising an aqueous solution of fluoride ions and at least one compound selected from the group consisting of ethylene glycol, acetic acid and a mixture of phosphoric acid and nitric acid.

The term titanium as used herein includes not only titanium but its alloys such as, for example, Ti-13V-11Cr- 3A1, Ti-6Al-6V-2Sn and Ti-8Al-lMo-1V. Also contemplated herein are metals selected from the group consisting of tantalum, zirconium, niobium, hafnium and their alloys.

The titanium may be in any form such as, for example, bar, plate, flat sheet, sheets of expanded metal and the like. A preferred form for subsequent use in the electrodeposition of manganese dioxide is disclosed in U.S. Pat. No. 3,654,102.

The composition of the electrolyte is critical. The concentration of fluoride ion in the electrolyte must be at least about 25 grams per liter of electrolyte. Generally, it is desirable that the fluoride ion concentration be maintained within a range of from about 55 to 75 grams per liter. Particularly good results have been obtained with a fluoride concentration of about grams per liter.

The source of fluoride ion is not critical. The fluoride may be introduced into the electrolyte in the form of an aqueous solution of hydrofluoric acid, by bubbling fluorine gas through the electrolyte and the like. Other sources of fluoride ion include sodium fluoride, potassium fluoride, magnesium fluoride, Zinc fluoride, trifluoacetic acid and other inorganic and organic fluoride compounds. Generally, it is preferred to use an aqueous solution of hydrofluoric acid as the source of fluoride ion.

Further, the electrolyte also must contain at least one other compound, either acetic acid, ethylene glycol or a mixture of phosphoric and nitric acid. Such other compound should be present in an amount within the range of from about 700 to 1,300 grams per liter of electrolyte and preferably within the range of from about 800 to 1,200 grams per liter. The optimum concentration will depend, among other things, on the particular compound selected. When using ethylene glycol or acetic acid, it generally is preferred to maintain a concentration of from about 850 to 1,000 grams per liter.

When using a mixture of phosphoric and nitric acid, however, it is advantageous to maintain the concentration within the range of from about 8001,200 grams per liter and preferably within the range of from about 9001,100 grams per liter. Further, when the other compound is a mixture of phosphoric and nitric acid, the weight ratio of phosphoric to nitric acid should be within the range of 5:1 to 2:3 and preferably within the range of from 3:1 to 3:2.

The actual part played by the fluoride and the other compound in this treating method is not fully understood and the inventor does not wish to be bound by any particular theory. However, it has been found that when titanium is treated in accordance with the present method, it may be used in a manganese dioxide electrodeposition process at higher current densities and for longer periods of time, without passivation occurring, than would otherwise be possible.

The titanium, after being placed in the electrolyte, is treated at an anodic current density of at least about amps/ftF. At lower current densities substantially no beneficial effect is obtained. The upper current density limit is primarily a function of the composition of the electrolyte. If too high a current density is applied the titanium will, of course, passivate; preventing elfective treatment. The optimum current density for treatment with a specific electrolyte composition is readily determinable experimentally. Generally, the anodic current density is within the range of from about 10 amp/ft. to 30 amp/ft. and preferably within the range of from about to 25 amp/ ft.

The treatment time generally is within the range of from about 2 minutes to about 30 minutes. As those versed in the art will appreciate, the treatment time will be a function of the current density applied during treatment. More particularly, with a given electrolyte, a low current density will require more time for an effective treatment than a higher current density. During the treatment a gray film forms on the surface of the anode. If the treatment is continued for an excessive length of time the film will begin to peel or flake olf the anode.

Temperature does not appear to be a critical parameter in the treatment method of the present invention. Indeed, within a temperature range of from about C. to about 50 C. substantially no dilference in the efiicacy of the invention is observed.

After the titanium has been treated in accordance with the present method, it then is removed from the electrolytic cell and preferably washed with water prior to its use in an electrolytic cell. Titanium treated in accordance with the present invention is particularly useful in the electrodeposition of manganese dioxide.

More particularly, the treated titanium is used as the anode in an electrolytic cell for the electrodeposition of manganese dioxide. The cell contains an electrolyte comprising an aqueous solution containing manganous ion in a concentration of from about 15 to 50 grams per liter and from about 10 to grams per liter sulfuric acid. The electrolyte temperature is maintained within a range of from about 90 to 98 C. When the titanium anode has been treated in accordance with the method of the instant invention it is possible to operate the cell at an anodic current density of from about 8 to 25 amp/ft. or even higher. Generally, it is preferred to maintain the anodic current density Within the range of from about 12 to 20 amp/ftfi.

The following examples are set forth for the purpose of illustration only and are not to be construed as limiting the scope of this invention.

EXAMPLE I An untreated strip of titanium is obtained and placed in an electrolytic cell as the anode. The electrolyte in the cell comprises 800 ml./l. H PO (85%), 150 ml./l. HNO (71%) and 50 ml./l. (49%). An electric current is caused to flow through the titanium anode in an amount suflicient to provide an anodic current density of about 20' amp./ ft. for two minutes. The treated titanium then is removed and rinsed with water.

The treated titanium then is used as the anode in a manganese dioxide electrodeposition process. During electrodeposition of manganese dioxide on the anode, the initial concentration of manganous ion (Mn++) and H 80 in the electrolytfi is about 20 g./l. and 15 g./l. respectively.

The initial cell voltage to maintain an anodic current density of 16 amp/ft. is about 2.0 volts. Manganese dioxide is electrodeposited on the anode for about 96 hours. During the electrodeposition the concentration of manganous ion and H SO is maintained within the range of about 19 to 24 g./l. and 15 to 26 g./l. respectively. At the end of that time the cell voltage required to maintain the current density at 16 amp/ft. is only 2.5 volts. Thus after 96 hours of operation the cell voltage has increased only 0.5 volts. When the foregoing process is repeated using an untreated titanium anode, the cell voltage increases 3.8 volts after 96 hours.

This example clearly demonstrates the eflicacy of the present invention when the treating electrolyte comprises an aqueous solution of fluoride ions and a mixture of nitric and phosphoric acid.

EXAMPLE )1 An untreated strip of titanium is obtained and placed in an electrolytic cell as the anode. The electrolyte in the cell comprises 820 ml./l. ethylene glycol, 60 ml./l. H 0 and 120 ml./l. HF (49%). An electric current is caused to flow through the titanium anode in an amount suflicient to provide an anodic current density of about 20 amp/ft. for three minutes. The treated titanium then is removed and rinsed with water.

The treated titanium then is used as the anode in a manganese dioxide electrodeposition process. During electrodeposition of manganese dioxide on the anode, the concentration of manganous ion (Mn++) and H in the electrolyte is maintained at about 25 g./l. and 20 g./1. respectively. The initial cell voltage to maintain an anodic current density of 16 amp/ft. is about 1.8 volts. After 24 hours of electrodeposition the anodic current density is increased to 20 amp/ft? and the electrodeposition continued for an additional 66 hours.

Manganese dioxide is electrodeposited on the anode for a total time of hours. At the end of that time the cell voltage necessary to maintain the 20 amp/ft. current density is only about 2.25 volts. Thus after 90 hours of operation the cell voltage has increased only about 0.45 volts. When the foregoing process is repeated using an untreated titanium anode, the cell voltage increases 6 volts after an hour, indicating passivation of the untreated titanium anode.

This example clearly demonstrates the efficacy of the present invention when the treating electrolyte comprises an aqueous solution of fluoride ions and an ethylene glycol.

EXAMPLE III Two untreated strips of titanium are obtained and placed in an electrolytic cell as anodes. The electrolyte in the cell comprises 888 ml./l. glacial acetic acid and 112 ml./l. HF (49%). An electric current is caused to flow through the titanium anodes in an amount sufiicient to provide an anodic current density of about 16 amp/ft After about ten minutes one of the treated titanium strips (designated A) is removed and rinsed with water. After an additional 10 minutes the other titanium strip (designated B) is removed and rinsed with water.

The treated titanium strips A and B then are used as anodes in a manganese dioxide electrodeposition process. During electrodeposition of manganese dioxide on the anode, the concentration of manganeous ion (Mn++) and H 80 in the electrolyte is maintained at about 25 gm./l. and 20 gm./l. respectively. The initial cell voltage to maintalil an anodic current densty of about 20 amp/ft. is 1.8 v0 ts.

Manganese dioxide is electrodeposited on the anodes for a total time of 168 hours. At the end of that time the cell voltage necessary to maintain the 20 amp/ft. current density for strip A is about 3.4 volts and for strip B only about 2.8 volts. Thus after 168 hours of operation the cell voltage has increased only 1.6 and 1.0 volts for strips A and B respectively. When it is attempted to repeat the foregoing process using an untreated titanium anode, the cell voltage increases over volts after less than an hour.

This example clearly demonstrates the eflicacy of the present invention when the treating electrolyte comprises an aqueous solution of fluoride ions and acetic acid.

The foregoing description and examples are intended to be illustrative only and are not to be construed as limiting the scope of the invention; reference being had to the appended claims for such latter purpose.

What is claimed is:

1. A method for the electrodeposition of manganese dioxide which comprises:

pretreating a titanium anode by providing an aqueous electrolyte containing at least 25 gm./l. fluoride ions and from about 800 to 1200 gm./l. of at least one other compound selected from the group consisting of acetic acid, ethylene glycol and a mixture of nitric acid and phosphoric acid;

placing said titanium anode in contact with said electrolyte;

placing a cathode in contact with said electrolyte;

electrolyzing said electrolyte at an anodic current density of at least 10 amps/ftF; placing the treated titanium anode in an electrolytic cell for the electrodeposition of manganese, said cell containing an electrolyte comprising an aqueous solution of manganous ion in a concentration of from about to 50 gm./l. and from about 10 to 25 gm./l. sulfuric acid, etfecting the electrodeposition of manganese dioxide on the anode at an anodic current density of from about 8 to amp/ft. and recovering said electrodeposited manganese dioxide.

2. The method of claim 1 wherein the anodic current density during the treatment is maintained within the range of from about 10 amps/ft. to amps/ft 3. The method of claim 2 wherein the concentration of fluoride ions is maintained within a range of from about to gm./l.; the selected compound is acetic acid present in an amount within the range of from about 850 to 1000 gm./l. and said anodic current density during treatment is maintained within the range of from about 15 to 25 amps/ft References Cited UNITED STATES PATENTS 3,455,798 7/1969 Mehne et al. 20496 3,436,323 4/ 1969 Shimizv et al. 20496 3,616,279 10/1971 Kendall 20456 R FOREIGN PATENTS 23,813 8/1970 Japan 20496 OTHER REFERENCES Bureau of Mines Electrodeposition Cramer et 25 al., September 1967, pp. 4 and 50.

RICHARD L. ANDREWS, Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CURRECTION Patent No. 8.41 r 978 D t d October 15 1974 Inven San-Chenq'Lai It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 66, after "50 ml./l." please insert HF Column 4, line 68, "densty" should read density Signed and sealed this 3rd daydof December 1974.

(SEAL) Attest: v

McCOY M. GIBSON JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents ORM PO-1050 (10-69) I USCOMM DC 60376P69 it u,s. eovzmmsm Pmm'ms OFFICE: I969 o-ass-su

Claims (1)

1. A METHOD FOR THE ELECTRODEPOSITION OF MANGANESE DIOXIDE WHICH COMPRISES: PRETREATING A TITANIUM ANODE BY PROVIDING AN AQUEOUS ELECTROLYTE CONTAINING AT LEAST 25 GM./L. FLUORIDE IONS AND FROM ABOUT 800 TO 1200 GM./L. OF AT LEAST ONE OTHER COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID, ETHYLENE GLYCOL AND A MIXTURE OF NITRIC ACID AND PHOSPHORIC ACID; PLACING SAID TITANIC ANODE IN CONTACT WITH SAID ELECTROLYTE; PLACING A CATHODE IN CONTACT WITH SAID ELECTROLYTE; ELECTROLYZING SAID ELECTROLYTE AT AN ANODIC CURRENT DENSITY OF AT LEAST 10 AMPS/FT,2; PLACING THE TREATED TITANIUM ANODE IN AN ELECTROLYTIC CELL FOR THE ELECTRODEPOSITION OF MANGANESE, SAID CELL CONTAINING AN ELECTROLYTE COMPRISING AN AQUEOUS SOLUTIONS OF MANGANOUS ION IN A CONCENTRATION OF FROM ABOUT 15 TO 50 GM./L. AND FROM ABOUT 10 TO 25 GM./L. SULFURIC ACID, EFFECTING THE ELECTRODEPOSITION OF MANGANESE DIOXIDE ON THE ANODE AT AN ANODIC CURRENT DENSITY OF FROM ABOUT 8 TO 25 AMP/FT.2 AND RECOVERING SAID ELECTRODEPOSITED MANGANESE DIOXIDE.