US2920021A - Processes and anodes for the electrolytic extraction of the metals ti, v, cr, zr, nb, mo, hf, ta and w from their carbides - Google Patents

Description

Jan. 5, 1960 H. F. e. UELTZ 2,920,021

PROCESSES AND ANODES FOR THE ELECTROLYTIC EXTRACTION OF THE METALS '1.,V,"C ,Z ,N ,M.,,H ,T AND W FROM THEIR CARBIDES Filed July 2, 1957 United States Patent PROCESSES AND ANODES FOR THE ELECTRO- LYTIC EXTRACTION OF THE METALS Ti, V, Cr, z gg, Mo, Hf, Ta AND W FROM THEIR CAR- Herbert F. G. Ueltz, Shrewsbury, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application July 2, 1957, Serial No. 669,478

9 Claims. (Cl. 204-64) The invention relates to processes and anodes for the electrolytic extraction of the metals Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W from their carbides.

One object of the invention is, in extraction of these metals as indicated, to avoid contamination of the extracted metal with carbon. Another object is to provide an anode that can be economically and easily made. Another object is to provide processes and anodes permitting the extraction of a large percentage of the metals from their carbides.

Another object is to provide a coherent anode that leaves a carbon skeleton intact after extraction of the refractory metal content. Another object is to provide an electrolytically permeable anode. Another object is to provide an anode of adequate strength for handling. Another object is to provide a process for anode manufacture that can be carried out in simple equipment. Another object is to provide a mix which can be easily molded into various shapes desired for anodes. Another object is to provide an anode that can be made coherent by firing at a low temperature. Another object is to provide an anode in porous coherent form suited for use in an electrolytic process for the extraction of refractory metalfrom its carbide in a fused salt bath medium consisting essentially of halide of alkali and alkaline earth metals and operated under an inert atmosphere. Another object is to provide an anode containing added bonding material that unites granular refractory metal carbide into an integral permeable structure having an electrical conductivity and other properties satisfactory for economical use in a fused salt bath. Another object is to produce an electrically conductive consumable anode of special characteristics so that the refractory metal component of its carbide content is structurally decomposable and extractable electrolytically under conditions that leave carbon and bonding constituents structurally non-decomposable.

Other objects will be in part obvious or in part pointed out hereinafter.

The accompanying drawing is a vertical axial sectional view of electrolytic apparatus for practicing the processes and in which can be used the anodes of the invention.

The metals titanium, zirconium and hafnium are in the fourth group of the periodic system, the metals vanadium, niobium andtantalum are in the fifth group of the periodic system, and the metals chromium, molybdenum and Wolfram (tungsten) are in the sixth group thereof. Their atomic numbers are Ti 22, V 23, Cr 24; Zr 40, Nb 41, Mo 42; and Hf 72, Ta 73, W 74. It will be seen, therefore, that they are closely related. They are all of them refractory and are called transition metals. Their oxides and their carbides are hard and refractory, and their carbides are good electrical conductors. Chemically they react similarly with many compounds. Their borides have similar properties. Hafnium compounds are usually found in zirconium ores. Each of these metals can be extracted from its carbide in a fused salt bath by electrolysis. These nine metals can be col- 2,920,021 Patented Jan. 5, 1960 the melting points of these carbides are shown in the following table.

TABLE I Melting Carbide Formula Point,

Degrees Titanium Carbide..- TiC 3,140:|: Vanadium Carbide... VO 2,810 Trichromium dicarbide OraCi 1,890 Pentaehromium dicarbide CrsCg 1, 665 Zirconium Carbide ZrC 3,500 NbO ca 3,900 M00 ,690 M0 0 2,680 Hi0 3,887 TaO 3,880 WO 2,870i50 Diwolfram Carbide W2C 2,8

Where there are two carbides, either carbide or mixture of the two carbides can be used in this invention and such mixtures are to be deemed to be included in the claims. Furthermore zirconium carbide usually contains a minor percentage of hafnium carbide and such mixture is to be deemed to be included as well as hafnium free zirconium carbide and zirconium free hafnium carbide.

In accordance with my invention, a refractory metalof one of groups :IV, V and V1 is extracted from its carbide (including the extraction of zirconium with hafnium from zirconium carbide containing hafnium carbide) in an electrolytic process with the carbide as the anode in contact with a fused salt bath of halideof metal selected from the group consisting of the alkali metals and the alkaline earth metals and mixtures thereof, using any suitable conductor as the cathode which is also in contact with the fused salt bath. An inert atmosphere is maintained over the molten salt protecting the anode and the cathode. Any one of argon, krypton, neon, helium or xenon can be used, but I prefer argon because of its high density and moderate cost.

One apparatus, and the best one now known to me, in which the process of this invention can be carried out is illustrated in the drawing. A refractory box 1 consisting of a sheet steel cylinder 2, to the bottom of which is welded a bottom plate 3 and having a top plate 4 secured thereto by bolts 5 is filled with refractory brick. The box 1 is shown as supported by legs 8. Through a space 10 in the brick extend resistor bars 11 made of silicon carbide of a type now well known, these bars having so called cold ends 12 as such bars practically always do. The cold ends 12 extend through alumina sleeves 15 that extend through the top plate 4 and the brick to receive the upper cold ends 12 and through the brickand the bottom plate 3 to receive the lower cold ends 12. The lower cold ends 12 are supported by refractory blocks 16 which rest upon the lower horizontal portions of Z shaped irons 17 the upper horizontal portions of which are welded to the bottom plate 3. Electrical connections are made to the cold ends 12, but these are well known and are not shown. By energizing the bars 11 the temperature in the cell 20 can be brought to the desired level.

The cell 20 is made of steel. It has a hollow flange 21 through which cooling water is pumped by means of connections 22 and 23. It is bolted by means of bolts 24 to a head plate 25 having a hollow upward extention 26 through which water is pumped by means of connections 27 and 28. The head plate 25 is sealed to the flange 21 by means of a ring 30 between these parts. The ring 30 is made of chlorinated butadiene.

The extention 26 has a flange 35 which is bolted by means of bolts 36 to a flange 37 on the bottom of a pipe shaped valve body 40 transversed by a vacuum seal valve apparatus 41 which can be operated to seal off the space below it. This valve apparatus 41 is not shown in detail as it belongs in another art and any good one can be used.

Extending upwardly from the valve body 49 is a water cooled pipe 50. This is provided to allow the top of the apparatus to become relatively cool. This pipe 50 has a bottom flange 51 and a top flange 52, and from the bottom of the former to the top of the latter the pipe 50 is two feet high. The flange 51 is bolted to an upper flange 53 provided on the top of the valve body 40 by means of bolts 55. The flange 52 is bolted to a plate 57 by means of bolts 58. The plate 53 has a central hole 60 and above this central hole 66 is a rubber sealing tube 61 the lower part of which is reinforced with a steel sleeve 62. The rubber sealing tube 61 is held down onto the plate 57 by means of a laminated cloth and phenolic resin plate 65 having a hole 66 therethrough, hold down bolts 67 extending between the plate 57 and the plate 65 being provided to hold these plates together.

The water cooled pipe 50 is cooled by a water chamber 70 welded thereto and connections 71 and 72 to circulate the water. A gasket 73 is provided between the flanges 57 and 53 and a sealing ring 74 is provided between the flanges 57 and 52, both of these being made of chlorinated butadiene. It is'important to keep the system free of air, that is to exhaust the air before starting the electrolysis and to remove any contaminating atmosphere which may be generated during the electrolysis. To that end I pump through the system argon or other inert gas by way preferably of an upper pipe 80 exhausting the gas through a lower pipe 81, the former for example extending into the top of the pipe 50 and the latter into the flange 25 and connected to a bore 82 extending to the inside of the extension 26. l find it is preferable to have the argon entrance above the argon exit to drive salt vapor downwardly to keep it from plugging the upper part of the apparatus; The system should be flushed with argon before starting electrolysis desirably for about twenty-four hours. Argon is pumped all of the time during electrolysis (but could be interrupted for short periods). In an apparatus of this size a flow of argon of two cubic feet per hour is satisfactory.

The steel cell 2t) (an ordinary low carbon steel was used) was six inches inside diameter. The extension 26, made of the same steel, had an inside diameter of four inches and so did the valve body 40 and the pipe 50. All of these parts were made of the same steel except the body 40 which was made of aluminum. Dimensions of the apparatus not mentioned can be calculated closely by scaling the drawing relative to a dimension given. The cell 20 was Nichrome plated on the outside, by flame spraying.

Fitted into the cell 29 is a graphite crucible 90 and the drawing sufficiently shows its shape and position. Inside of the graphite crucible 90 is a. long sleeve made up of a series of anode rings 100 of metal carbide of Table I, bonded with pitch in the manner to be particularly described, this being a prime feature of this invention. It was easier to make short rings than a long sleeve and there is no difference between the two in operation. This invention is a process with the use of an anode bonded in accordance with the description and claims hereof, and is also an anode so bonded. So far as the invention is concerned the shape of the anode 100 may be varied within very wide limits and it doesnt have to be a sleeve in all cases although I would prefer it to be in that shape or in the shape of a cup. The anodes actually used consisted of six rings 100 each having an inside diameter of three and three-quarters inches, an outside diameter of four and nine-sixteenths inches and two inches high. It will be un- 4 derstood that the apparatus details are no part of the present invention which relates to a process and an anode, but to enable the invention to be practiced in the best mode I have described the best apparatus now known to me.

A long red shaped cathode 101 extends in an axial position relative to the cell 20 the crucible and the sleeve 1%, vertically from close to the bottom of the anode through the extension 26, through the valve body 40, through the valve mechanism 41 when the valve thereof is open, through the pipe 50, through the hole 69, through the rubber sealing tube 61 and through the hole 66, projecting a slight distance above the plate 65. There it is connected by a clamp to the negative side of a source of direct current electrical energy as indicated by the negative sign above its top. The cell 2% and therefore also, through the crucible 9d, the anode 1th) is connected by electrical connections to the other side of the circuit which is therefore a source of positive electricity as indicated by a positive sign close to the bottom of the bolt 24 that is shown; a convenient place to make the connection. But any way of connecting the anode 100 to the positive side of the source is satisfactory.

The cathode 101 was actually made of steel but other metals resistant to corrosion can be used, nickel being a good example. The cathode is withdrawn from time to time to collect metal deposited thereon. To do this it is first drawn upwardly through the sealing tube 61 until its bottom has cleared the valve mechanism 41. Then the valve is closed. After an interval of time usually about an hour to allow the cathode 1151 where the metal has collected thereon and said metal to cool down enough to avoid reaction with the air, the plate 65 is unbolted and lifted up and off the cathode 101, and then the cathode 1M with the deposit of metal is entirely removed from the system, ad the metal is scraped off and collected for further processing which need not be described herein. Briefly such processing involves dissolving off the salt clinging to the metal, pressing the sponge metal so clean of salt, melting it in a vacuum and casting ingots, or, in-

stead of melting and castingthe metal, it can be pressed and sintered to form articles.

While the bottom of the cathode 101 and the metal thereon is cooling in the valve body 4t and pipe 50, argon or other inert gas is pumped from the pipe 80 to an exhaust pipe 105 having a valve 106 so that it can be opened at this time and closed when the cathode 101 is down and the process is operating.

In the following examples of the manufacture of anodes for and of this invention different shapes and sizes are described as I have used several different sizes of apparatus differing also in details and the anodes were not in every case rings or sleeves. While all of the examples herein deal with titanium carbide, all of the other carbides can be used in like manner making allowance for they specific gravity thereof in each case.

Example I A mixture of 500 grams of soft coal tar pitch and 2270 grams of minus 100 mesh titanium carbide was blended in the following manner:

The pitch and titanium carbide were placed in a graphite mixing pot and heated over a hot plate until the pitch was fluid and the carbide was hot enough to maintain the pitch in fluid condition. The two were blended easily by mixing with a spatula to form a homogeneous. mixture. The hot mixture was placed into a cold enameled basin and allowed to cool to room temperature. This could be readily broken up and screened through a 6-mesh screen.

A graphite crucible of seven inches inside eight inches outside diameter was then lined with this mixture in the following manner:

The crucible was heated to about 60 C. by placing down with-a small airhammer and tamping bar. A tapered wooden arbor was then placed in the crucible with the small end down against the pitch bonded TiC 1n the bottom of the crucible. The granular mix was poured into the cavity between the arbor and the crucible a little at a time and tamped after each addition with the air hammer and tamping bar until the entire cavity was filled. The crucible was removed from the hot plate before tamping and placed back on periodically to keep it hot. The tapered arbor was removed by pulling out, leaving a well 9%" deep, 5" diameter at the bottom, and 6" diameter at the top. The inside height of the crucible was nine inches.

This pitch bonded TiC lined graphite crucible was placed in carbon black in an alumina cylinder, and covered with a graphite cover which had refractory tubes; an argon delivery tube and an exit tube for the argon and volatiles of the pitch. The crucible was then placed in an induction heating coil and the temperature inside was raised gradually to .1000 C. in two hours. The crucible was then removed and cleaned by blowing the loose carbon black out with a jet of air leaving a hard carbon bonded TiC lining in the graphite crucible. All this time the argon was flowed at the rate of about 3 cubic feet per hour. This completed the anode.

Example ll Carbon bonded anode rings of eight inches inside diameter for a large cell were prepared as follows:

A mixture of 61.5 pounds of minus 100 mesh titanium carbide and 10.9 pounds of powdered hard pitch was blended together at room temperature in a fiber drum on a roller mill. The powdered hard pitch has a melting point of 285-315 F. and is a coal tar pitch.

Four rings, 9%" OD. x 7% ID. x 5 /2" high and weighing 13.4 pounds per ring were pressed in a mold at three tons per square inch. These rings were stacked in a graphite crucible to form a 22 inch high tight fitting liner. The crucible was placed in the cell having a water cooled flange and a water cooled cover with a chlorinated butadiene ring seal between. The cell was placed in a furnace heated by resistor bars. The system was purged once with a vacuum and subsequently filled with argon gas which was flowed continuously during the baking at about 6 cubic inches per hour. The crucible and rings were then baked and the volatiles were distilled ofi by raising the temperature to 1000" C. The heating period was six hours.

The furnace was allowed to cool and the crucible was removed. The rings lost 7% by weight due to the loss of volatiles in the pitch. The rings formed a liner of fairly hard carbon bonded titanium carbide.

Example Ill Carbon bonded anode'rings of four inches inside diameter for the cell discribed were prepared as follows:

A mixture of 2526 grams of minus 100 mesh titanium carbide and 274 grams of powdered hard pitch was blended at room temperature as in Example II. Six rings 4%; OD. x 3% ID. x 2" high (approximately) were pressed at five tons per square inch. Each ring weighed 454 grams. The rings were then stacked in the graphite crucible 90 to form a tight fitting liner 11" high.

The crucible 90 was then purged of air by drawing a vacuum and the argon was connected and flowed at the rate of 2 cubic feet per hour. The volatiles were then baked off by raising the temperature gradually to 1000 C. This took about six hours including a one-hour soaking period at 1000" C. the argon being flowed at the same rate all of the time. The rings lost 3.2% by weight due to the loss of volatiles in the pitch. The resultant liner was hard carbon bonded titanium carbide. This example represents the best mode according to the invention.

The following are typical analyses of some of the-titanium carbidesv used in our electrolyses:

,Example I: No analysis made.

Example II: Titanium carbide (technical grade):

These materials were produced in an arc furnace. The iron was analyzed after an acid treatment of this material.

The following examples of cell operations are runs A and B for the anode of Example II, and runs C, D, E

and F for the anode of Example III. The salt in each case was, by weight, NaCl and 15 K TiF TABLE II Example II Example III A B O D E F .30 27 27 27 30 Current Density, amps/dm.

Cathode t. 210 240 220 220 220 245 Current Amperes 800 800 300 300 300 300 Percent Titanium xtracted 7.5 72 4 8 19 33 Hardness, BEN 196 440 201 154 As the principal component of the salt for the fused salt bath I have used, besides sodium chloride, a eutectic mixture of 60 mols of lithium chloride and 40 mols of potassium chloride. Of the halogens, the chlorides will mostly be used because they are more readily available. The alkali metals are sodium, potassium, lithium, rubidium and cesium and halides of the latter two are rare. The alkaline earth metals are calcium, magnesium, barium and strontium and halides of all of them are reasonably available but the first two, especially their chlorides are cheaper. All kinds of mixtures of these halides can be used for the salt bath.

It is highly desirable to have halide of the metal being extracted in the fused salt bath, as this improves the process although metal can be extracted in its absence. However, too much of it seems to poison the process. The limits are wide and, in order to express a rule that applies to all of the cases, the percentage range is best stated as of the refractory metal in the form of halide. The range is from .1% to 15% of the refractory metal (being extracted) in the form of halide. The case of 15% by weight of potassium titanium fluoride, K TiF is 3% Ti which is well within this range.

By using an anode as defined herein the contamination of the extracted metal with carbon is avoided. Too much carbon raises the Brinell hardness, BHN. If the hardness is too high the metal is not as workable. In order to make good airframe parts the hardness of titanium should be in the lower ranges of those herein disclosed. For some uses harder metal is satisfactory.

If the anode is all carbide (and I have tried the process with such an anode) made simply by sintering the kind of carbide disclosed herein, the extraction of the metal leaves a carbon residue which crumbles. This carbon circulates in the salt bath due to the convection currents therein and contaminates the metal being extracted. But by bonding the carbide with baked pitch a carbon skeleton which does not crumble results. The carbide is bonded with carbon thereby, and the bond is essentially carbon, meaning that practically all of the pitch has been converted to carbon by the baking or firing. If this. is so the advantages of the invention are achieved.

Furthermore, an all-carbide anode must be sintered at very heigh temperature, usually in excess of 2000 C. in either inert gas or vacuum, and this procedure is much more expensive than the low temperature baing step of the present invention. Still another advantage of a baked pitch bonded anode over the sintered anode is its much greater open porosity, which permits molten electrolyte to penetrate the interior of the anode body and thereby allow most of the titanium to be anodically extracted. The sintered anodes had a porosity of only about 11%. The anodes of my example had porosities of 31%, Example I; 41%, Example 11; and 34%, Example III. A porosity of from 15% to 65% gives satisfactory results.

The objects of my invention can be achieved by providing an anode prepared in accordance with the examples and modifications of them. The granular metal carbide may vary in sizing from coarse lumps down to very fine powders. The carbon bond is developed from additional carbon derived from carbonaceous material, that is to say it is additional to the combined carbon of the metal carbide. The carbon of the bond is elemental carbon.

Pitch is a good source material for carbon bond, although other carbonaceous materials can be used. Baking or firing is a good way to eliminate volatiles and develop the carbon bond in situ, preferably in the absence of air. Argon is a good inert atmosphere to employ and helium can be used. Other inert gases can also be used. The product has the desired porous nature and permeability characteristics as well as adequate strength for handling.

But a bonding of the carbide with carbon can be achieved by using many other carbonaceous materials. Most of the resins, natural and synthetic can be used. Of the; former there is gutta-percha, rubber and shellac. The rubber should have little or no sulphur. Of the latter phenolic resin, the butadienes, styrene and methyl methacrylate can be used. Any used should consist essentially of carbon and volatiles, leaving only carbon. All including the pitches are organic.

Carbide of refractory metal of one of groups IV, V and VI bonded with carbon as herein disclosed is a good conductor but I do not have any figures of resistivity. In all cases, however, it is conductive enough to serve as an anode. Both components are conductive.

It Will thus be seen that there has been provided by this invention processes and anodes for the electrolytic extraction of the metals Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W from their carbides in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiments above set forth it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In an electrolytic process for extracting a refractory metal of one of groups I-V.., V" andVI in afuscdi salt bath:

consisting essentially of halide of metal selected; from: the groupv consisting of alkali and alkaline earth metals; and mixtures of such halides with from 1% to 15% of such refractory metal in the, form of halide, from; a, solidv consumable anode of carbide of metal being; extracted.- and on a cathode in said bath, whilev maintaining the. salt in the fused state under an inert atmosphere, by passing an electrolysing current through the fused salt bath between said anode and cathode, thus depositing; said metal in solid form on said cathode, and recovering the resultant solid cathodically deposited metal, the: improvement which consists in providing the anode in, porous unsintered coherent form carbon bonded primarily by means of elemental carbon additional to the carbon, of the carbide.

2. Process according to-claim 1 in which the refractory metal is titanium.

3. Process according to claim 1 in which the refractory metal is zirconium.

4. Process according to, claim 1 in which. the refractory: metal is niobium.

5. Process according to claim 1 in which the refractory metal is tantalum.

6. Process according to claim 1 in which the iefrac tory metal is vanadium.

7. Process according to claim. 1 in which the anode comprises the refractory metal carbide in granular form carbon bonded by the carbon produced in situ by baking organic matter.

8. Process according to claim 1 in which the anode comprises the refractory metal carbide in granular form carbon bonded by the carbon produced in situ by baking pitch.

9. In an electrolytic process for extracting a' refractorymetal of one of groups IV, V and VI comprising the steps of providing a fused salt bath consisting essentially of halide of metal selected from the group consisting of alkali and alkaline earth metals and mixtures of suchhalides with from 1% to 15% of such refractory metal in the form of halide, providing a solid consumable anode of carbide of metal being extracted and a cathode in electrical and chemical contact with said bath, maintaining the salt in the fused state under an inert atmosphere, passing an electrolyzing current through the fused salt bath between said said anode and cathode, depositing said metal in solid form on said cathode, and recovering the resultant solid cathodically deposited metal, the improvement which comprises using in the process a coherent, porous, unsintered consumable anode composed of granules of carbide of said refractory metal bonded primarily by additional carbon derived from carbonaceous material in situ by baking organic matter.

References Cited in the file of this patent UNITED STATES PATENTS.

Raynes et a1 Nov; 12, 1957 Washburn June 10, 1958 OTHER REFERENCES nix UNITED STATES PATlIN CERTIFICATE OF Patent No.u 2 92O O2I T OFFICE CORRECTION January 5 1960 Herbert F, G. Ueltz.

It is hereby certified 1;

r appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 2, line l8 Table I third column thereof "Zirconium Carbide for "Z JSOO read am 3 540 line 40 for "1%" read e .,l% line 46. second occurrence.

v opposite, column 8 a strike out said,,.

Signed and sealed this 23rd day of August 1 .460.

(SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. IN AN ELECTROLYTIC PROCESS FOR EXTRACTING A REFRACTORY METAL OF ONE OF GROUP IV, V AND VI IN A FUSED SALT BATH CONSISTING ESSENTIALLY OF HALIDE OF METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METALS AND MIXTURES OF SUCH HALIDES WITH FROM .1% TO 15% OF SUCH REFRACTORY METAL IN THE FORM OF HALIDE, FROM A SOLID CONSUMABLE ANODE OF CARBIDE OF METAL BEING EXTRACTED AND ON A CATHODE IN SAID BATH, WHILE MAINTAINING THE SALT IN THE FUSED STATE UNDER AN INERT ATMOSPHERE, BY PASSING AN ELECTROLYSING CURRENT THROUGH THE FUSED SALT BATH BETWEEN SAID ANODE AND CATHODE, THUS DEPOSITING SAID METAL IN SOLID FORM ON SAID CATHODE, AND RECOVERING THE RESULTANT SOLID CATHODICALLY DEPOSITED METAL, THE IMPROVEMENT WHICH CONSISTS IN PROVIDING THE ANODE IN POROUS UNSINTERED COHERENT FORM CARBON BONDED PRIMARILY BY MEANS OF ELEMENTAL CARBON ADDITIONAL TO THE CARBON OF THE CARBIDE.

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