US2636856A

US2636856A - Electrode for electrochemical oxidation

Info

Publication number: US2636856A
Application number: US35878A
Authority: US
Inventors: Alfred M Suggs; Reginald S Dean
Original assignee: PR Mallory and Co Inc
Current assignee: Duracell Inc USA
Priority date: 1948-06-29
Filing date: 1948-06-29
Publication date: 1953-04-28
Anticipated expiration: 1970-04-28

Description

prll 28, 1953 A. M. SUGGS ET AL 2,636,856

ELEOTRODE FOR ELEOTROOHEMIOAL OXIDATION Filed .June 29, 194e T/TH/v/c/M Patented Apr. 28, 1953 @FFE ELECTRODE FOR ELECTROCHEMICAL OXIDATION poration of Delaware Application J une 29, 1948, Serial No. 35,878

1 Claim. (Cl. 2041-290) This invention relates to materials containing titanium and carbon, and, more particularly, to materials containing titanium carbide and at least one of the elementary constituents thereof.

It is an object of the present invention to provide shaped bodies including titanium carbide and at least one of the elements of carbon and titanium in a stratified or interspersed arrangement, said bodies being characterized by high resistance to heat and to various chemical influences.

It is another object of the present invention to provide electrically conducting bodies and electrodes of improved character comprising titanium carbide interspersed with or bonded to titanium, graphite, or both, for the purpose of electrolytic and primary cells, space discharge devices, such as particularly vacuum tubes, pressure applying and sliding electrical contacts, and the like.

' It is a further object of the invention to provide an improved electrode for electrolytic cells, particularly useful in electrolytic cells for producing electrolytic manganese dioxide from manganese sulphate solutions containing sulphuric acid, the

said electrode comprising a layer of metallic titanium coated on both faces thereof with a layer of titanium carbide.

It is also within the contemplation 0f the present invention to provide an electrode of novel and improved character comprising a shaped porous body of graphite which is substantially fully impregnated with titanium carbide.

The invention also contemplates various methods of making titanium and carbon compositions of the described character on a practical and industrial scale at a low cost.

Other and further objects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, in which Figure l is a longitudinal sectional view of a composite body embodying the invention and comprising titanium, titanium carbide and carbon layers;

Figure 2 is a similar view of a composition ccmprising a porous layer of carbon or graphite impregnated with titanium carbide;

Figure 3 is a sectional view of an electrode including a layer or core of metallic titanium coated with a layer of titanium carbide;

Figure 4 is a sectional view of an electrode comprising carbon and titanium layers the boundary surface of carbon and titanium being characterized by the presence of titanium carbide which also impregnated the remainder of the carbon layer;

Figure 5 is a vertical sectional view, somewhat diagrammatic and fragmentary in character, of an apparatus for carrying a preferred method of the present invention into practice;

Figure 6 is a vertical sectional view of graphite mold with a body of metallic titanium cast into a cavity thereof;

Figure l is a similar View of the mold shown in Figure 6 after its portions unimpregnated with titanium carbide have been removed;

Figure 8 is a vertical sectional view of a cylindrical Crucible, the side and bottom walls of which are fully impregnated with titanium carbide; and

Figure 9 is a similar view of the crueible shown in Figure 8 after its bottom portion has been cut off to provide a hollow cylindrical electrode shell.

As is known, when carbon, preferably in the form of graphite, is heated with molten titanium, titanium carbide, TiC, is formed at the surface of contact. It has now been discovered that when such contact is carried out in an inert atmosphere, or in vacuum, the molten titanium wets the graphite and impregnates it to a considerable depth, completely lling the pores thereof. In this way there is formed, on cooling, a novel composition or composite body which comprises a layer of metallic titanium, a layer of titanium carbide which extends continuously into the pores of a graphite layer and firmly attaches the impregnated graphite layer to the titanium layer, and finally a layer of unimpregnated graphite.

A composite body of the described character is illustrated in Figure 1 of the drawing wherein reference numeral I0 denotes the layer of titanium, and Il is the layer of titanium carbide which extends continuously into the pores of the adjoining graphite layer l2, the further removed portions of which are unimpregnated and free from titanium carbide. This composition or composite body embodies the principles of the invention in their broadest aspects and is the basic material of the present invention. It is capable of various modifications and is adapted to many different practical applications, depending on the relative thickness of the various layers, some of which may be completely absent. For example, a graphite or carbon layer or body impregnated with titanium carbide, such as is shown at Ill in Figure 2, has greatly increased mechanical strength, decreased porosity and increased resistance to oxidation. Articles or structural parts made from graphite impregnated with titanium carbide in the described manner are highly resistant to attack by combustion gases at temperatures up to 2200 F. and may be used for apparatus exposed to such temperatures.

According to a modification of the invention, a composite body of the described general character is formed by melting titanium in contact with dense graphite in vacuum and allowing the contact to persist for only a few minutes. There-is obtained a composite body of the type shown in Figure 1 and the impregnated (and unimpregnated) 'graphite may be removed by making the said body an anode in dilute sulphuric acid bath, and passing a current in excess of 50 .amperes per square foot anode surface through said bath. In this way, the graphite is removed from the surface of the composite body and the result is a layer of titanium completely covered with a roughened surface of titanium carbide. In preparing this composite material, the titanium is preferably melted between two graphite layers so that both sides of the titanium layer will be completely covered with titanium carbide. Thetita- -nium layer may be quite thin, as molten titanium wetsA graphite and will be. drawn by capillarity into the smallest crevices. Titanium melted in a graphite Crucible has been found to ow upward into spaces between hot graphite plates several inches high and 12 thick.

A composite body of the described character and comprising a layer or core l5 of titanium and titanium carbide la covering the surface thereof is. shown in Figure 3. of the drawing. This material has. outstanding properties asv an anode for electrochemical oxidation. An electrode of titanium coated with titanium carbide in the described manner shows none of the tendency to form anodic ilms characteristic of titanium. It is. unattacked by sulphuric acid or sulphates when used as. an anode and by concentrated hydrochloric acid, unless; theanode current density exceeds 100 amperes per square: foot. l

The.. titanium carbide coated titanium electrodes of the invention have been found particularly useful inmaking eleetrolytic manganese dioxide from. manganese sulphate solutions containing sulphuric acid. Heretofore, graphite electrodes were employed for this purpose. but their use. restricted .the acidity and thecurrent density that could be used While it was known .that both the processv and .the product could be .improved by using platinum anodes, the :cost of such. anodes was. prohibitive. The anodes'of. the

"present, invention have been found to be in every .way equivalent. tov platinum anodes for this purpose.

According to another modified' embodiment of the invention, the. composite body comprising titanium., titanium carbide, graphite. impregnated with titanium carbide andunimpregnatedl or .excess graphite is, subjected to a. treatment removing the excess graphite thereby providing an electrode having a. surface. composed of graph- .ite that is. fully impregnated with titanium carmay be. used Aas, thev positiveelectrode of a primarycell, such as a conventional LeClanche, cell and. provides4 important advantages, such as a substantial increase inthe electromotive force ofi the cell.. Thus, While with a conventional carbon electrode the electromotive. force, of the cell moval of the unimpregnated or excess graphite' from the titanium-titanium carbide-graphite composition byv mild abrasion. Although the resistance to abrasion increases sharply as the impregnated portion of the graphite is reached, the low friction characteristic of a graphite surface is ina great measure retained. A fixed contact the. titanium of high electrical conductivity to the titanium impregnated graphite canbe madeby melting or spraying copper onone surface i',hereof.- y

I Titanium-impregnated carbon or graphite anodes of the described character are useful in space discharge. of all types, such as in gas and .high vacuum tubes, including reetifying tubes.

In order that those skilled in the art may have a better understanding of the invention, the following illustrative example may be given of the preferred method of preparing the titaniumtitanium carbide-graphite composition whichy is the basic material contemplated by the. present invention.

Referring now .more particularly to-Figure 5 of the drawing, reference, numeral 2B denotes a vacuum, melting furnace which is electrically heated by a heater element in the form ofla split graphite. cylinder 2| surroundingv graphite crucible 2li. andis connectedto a vacuum pump (not shown) through a conduit 221. Metallic Ytitanium in the. form of chipspreparedv by thev accordingly made. of graphite: 'and lis heated' to a. temperature determined by the extent of inipregnation of thev graphite desired.y The higher the temperature ofthe mold, the greater willy be .the impregnation. In thez simplest case, the mold may take the forrnofathin slitin agi-aphite block, as is shown at 21 in Figure 5. When 28 has been cast in this slit, the excess graphite beyond the zone of impregnation may be removedv mechanically' and the resulting strip of titanium coated onall sides with titanium carbide and graphite impregnated with vtitanium carbideis ready for further treatment to produce a positive electrode of a primary'ce'll or for removal of the graphite to form an anode for an electrolytic manganese dioxide cell.v

This procedure for producing the composite bodies of the invention is further illustrated in Figure. 6 in which 26 is a block ofgraphitewith a slit 21 therein constituting a mold and 28: is the consolidatedbody of" titanium. in said slit. Upon removal of the excess` graphite along dotted -

lines

29 and 30, the composite body shown-in Figure '7 isv obtained, comprising layers ofjme- Atallic titanium 28,. titanium carbide.3 and graphite impregnated with titanium carbide 32. This composite body may then be subjected to one of the further treatments disclosed more fully in the foregoing.

When it is desired to prepare only graphite impregnated with titanium carbide, a simple and inexpensive procedure is to melt titanium in a graphite crucible in a vacuum melting furnace and rely on the impregnation of the walls of such crucible when the titanium is melted. Thus, in a practical case, a generally cylindrical graphite crucible was provided having a diameter of 11/2". a height of 3" and a wall thickness of 1A, with a small aperture in the bottom thereof. Titanium was melted in this crucible and allowed to flow into a mold, much in the same way as this is illustrated in Figure 5. The crucible walls were found to be uniformly and completely impregnated with titanium carbide. A cylindrical electrode suitable for a primary cell was made by removing the lower portion of the crucible.

This method is further illustrated in Figures 8 and 9. Figure 8 is a vertical sectional view of the carbide-impregnated graphite crucible 24 with a small aperture 25 in the bottom thereof. Upon cutting off the bottom portion of the crucible along dotted line 34, the carbide-impregnated graphite electrode shown in Figure 9 in the form of a cylindrical shell is obtained.

While the methods of manufacture described in the foregoing are the preferred ones, other methods have been used with success in producing the compositions of the invention. Thus, powdered titanium can be mixed with powdered carbon and the mixture compacted by pressure and heated to a temperature from 1500 C. to 2000o C. to form a carbon-titanium carbide mixture which can be used for the purposes described in this application. Likewise, metallic titanium can be heated in contact with carbon to a temperature just below the melting point of titanium to form a layer of titanium carbide on metallic titanium and the composition so formed can be used for the purposes herein described.

It has been found that for the purposes of the invention alloys of titanium containing at least 90% titanium can be used in place of pure titanium. Such alloys may in fact be advantageous because of their lower melting point. Ex-

amples of alloying constituents which may be used are iron, cobalt, nickel, chromium, manganese, molybdenum, tungsten, aluminum, beryllium and zirconium. The amounts of oxygen, nitrogen or carbon introduced into the titanium or its alloys by the heating step of this invention do not change the properties of the composition produced.

While the present invention, as to its objects and advantages, has been described herein as oarried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claim.

What is claimed is:

An electrode for use in electrochemical oxidation apparatus adapted to convert electrolytic manganese dioxide from manganese sulphate solutions containing sulphuric acid, said electrode being fabricated of the elements titanium, titanium carbide and carbon, said titanium forming a central core for said electrode, the outside sui'- face of said core being attached to an exposed carbon layer impregnated with titanium carbide throughout, the percentage of carbon in said layer increasing in extent from the titanium core toward the surface of said impregnated layer, said electrode being characterized as capable of handling current densities of up to amperes per square foot and resisting attack by sulphuric acid and sulphates.

ALFRED M. SUGGS. REGINALD S. DEAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 779,733 Price Jan. 10, 1905 1,082,978 Steinmetz Dec. 30, 1913 1,098,794 Fleming June 2, 1914 1,156,696 Krueger Oct. l2, 1915 1,547,539 Antropoff July 28, 1925 1,601,036 Nyberg Sept. 28, 1926 1,776,053 Voigtlander Sept. 16, 1930 1,996,643 De Pree Apr. 2, 1935 2,206,395 Gertler July 2, 1940 2,453,896 Dean Nov. 16, 1948