US2831802A - Production of subdivided metals - Google Patents

Description

PRODUCTION OF SUBDIVIDED METALS Ben E. Raney, Linton, Ind., assignor to Chicago Development Corporation, Riverdale, Md.

No Drawing. Application November 14, 1951 Serial No. 256,385

3 Claims. (Cl. 204-) This invention relates to the production of heavy metals in subdivided form. It relates particularly to processes for the reduction of heavy metal compounds to metallic particles by reacting these compounds with solutions of alkali or alkaline earth metals in fused chlorides of those metals. I have found that such reduction is more rapid than reduction by alkali or alkaline earth metals in other forms such as massive or vapor states. It also produces the heavy metals in the form of characteristic particles depending on the compound reduced. If the compound is solid and insoluble inthe molten chlorides, the metal particles are pseudomorphic after the compound. If the compound is soluble in the melt, the metal particles will be filamentary.

By heavy metals, I mean to refer in this specification to the metals in subgroup A of group IV, i. e., the metals of the titanium group of the periodic system, titanium, zirconium, and hafnium. For convenience, I will refer to the alkali and alkaline earth metals as alkalinous metals.

To carry out my invention the chlorides are fused and saturated with alkali or alkaline earth metal, the solution of the metal in the absence of undissolved metal is reacted with the heavy metal. compound to be reduced. The heavy metal compound must not, however, be introduced at a greater rate than the fused salt solution is replenished with alkalinous metal.

This is conveniently done by introducing the alkalinous metal into the stirred bath only as rapidly as it is dissolved and introducing the heavy metal compound in disperse form at the same rate in another portion of the bath.

I have found that in order to dissolve the alkalinous metal in the fused chlorides they must be substantially free from dissolved oxide, The process of my invention is inoperative if there is a substantial amount of oxide dissolved in the bath. The amount of dissolved oxide in fused commercial salts is too great. Several means of deoxidizing the bath are set forth in a later section. In certain instances, the subdivided metal to be produced may deoxidize the bath. This, however, is undesirable as the subdivided metal. will be contaminated with oxide which is not readily separated. My invention, therefore, contemplates a bath which is deoxidized in some manner so that the products of deoxidization may be readily separated from the subdivided metal.

In my co-pending application, Serial Number 152,175, filed March 27, 1950, and my co-pending application, Serial Number 230,336, filed June 7, 1951, now abandoned, I have disclosed the preparation of titanium powder. The methods disclosed in these applications diifer from the present method in many important respects although a superficial similarity exists. In the methods of these applications no provision is made for deoxidization of the bath or for the conditions necessary to obtain a solution of the alkalinous metal in the fused salt.

The heavy metal compound may be a chloride or oxide. The compound to be reduced and the alkalinous metal must be so selected that their reaction at the temperature of the fusedbath has a negative free energy. Data for Patented Apr. 22, 1958 ascertaining this point will be found in the literature (see U. S. Bureau of Standards Circular No. 500, February 1, 1952) and for purposes of applying it tothe present invention, the activity of the alkalinous metal. in solution may be considered unity.

A preferred form of carryingout my invention consists in the reduction of heavy metal chlorides or oxides to finely divided metal by bringing them into the solution of alkalinous metal in fused chloride produced by electrolysis of oxide free alkali andalkaline earth metal chlorides, at a place away from the cathode and at a suitable rate so that the alkalinous metal solution is always in excess, but no undissolved alkalinous metal is present at the place of reaction.

The anode in this embodiment of my process may be graphite in which case chlorine is evolved and removed from the cell by suitable means. It is frequently convenient however, to provide the heavy metal compounds to be reduced by anodic reaction. In the simplest instance, these compounds may be merely the chlorides of the anode metal or metals. The anode may advantageously be made, however, of partially reduced metal in which case, oxides and chlorides are provided by the anode. It is necessary that there be enough metal in such partially reduced material that the anode be conducting. Other conducting heavy metal compounds which form chlorides when used as anodes in the molten chloride bath may be used as anodes.

Anodes which react with chlorine to form chlorides such as mixtures of the heavy metal oxides and carbon may also be used.

I am familiar with the reduction of metal compounds by adding them to alkalinous metals in the presence of fused salts. Such procedure is not in any way equivalent to my invention. When the compound. to be reduced comes in contact with the alkalinous metal in the mass, there is no solution of the alkalinous metalin the fused chloride. The compound is imperfectly reduced and the resulting metal is usually globular or sponge-like and not in discrete particles in the form described for my invention.

I am also familiar with the known art of producing subdivided metals by the electrolysis of molten electrolytes containing salts of these metals in solution. Such procedure is well known, for example, for the production of powdered iron. In such processes, the metal is deposited in idiomorphic crystals which may form nodular aggregates, but not as pseudomorphs or filaments as in my process.

I am also familiar with the deposition of metals like titanium, zirconium, and tantalum from the fluotitanates, fluozirconates and fluotantalates respectively in which the metal is also formed at the cathode.

I am also familiar with attempts to reduce compounds insoluble in molten electrolytic baths by introducing them at the cathode and bringing about a reaction with the alkali or alkaline earth metal formed. An example of this procedure is found in British Patent 1,759 of 1904 issued to Borchers et al. In this instance, titanium dioxide is introduced in excess at a cathode in a bath containing calcium, chloride and the titanium dioxide is in some measure reduced by the calcium formed.

This procedure is unsatisfactory because the compound to be reduced being present in excess is not completely reduced. Furthermore, and this is an important distinction of the prior art from my process, reduction in the processes of the art is brought about by discrete masses of the metal which is less effective than reduction by a solution of the metal in the fused chloride. It will beseen that if there is any reducible heavy metal compound at the cathode, there will be no opportunity for the formation of the solution of the alkalinous metal in the salt bath which electrostatic methods.

solution is essential to my invention. Accordingly, it is 'oftheessence ofmy'invention that the heavy metal compound to be reduced be introduced in disperse form at a place away from the cathode and at a rate no greater than it is reduced to metal.

' chlorides, but that TiO 'and ZrO are not reduced by Na 'or K, butare reduced by Ca. Hence if it is desired to reduce TiO 'or ZrO to metal by my process, the electrolyte should contain CaCI It will be noted further that when reduction of chlorides is carried out, the bath is simply replenished in its alkali or alkaline earth chloride content. However, when heavy metal oxides are reduced, an oxide of an alkali or alkaline earth metal is formed. When this is an alkali I metal oxide, it must not be allowed to accumulate in the bath in substantial concentration as it will react with and oxidize the subdivided metal. The bath must be frequently changed and deoxidized by methods which will be described in detail hereinafter. If the reduction is by an alkaline earth metal then the reduced metal will be contaminated with insoluble oxide of that metal and separation must be subsequently made.

The shape and form of the metal formed by my process is important because in the production of pure metals, I may make use of this shape factor to separate the reduced metal from anode fragments of the original metal I and from non-metallic anode slime or other non-metallic materials. The methods of separation of solids based on shape factorsare well known and include gravity and For example, the bundles which form from the filamentary particles are easily washed over the riflles of a shaking table, whereas the more symmetrical particles fall into the riffles of the table.

In other cases, the pseudomorphic particlesof metals may be of other shapes but always difierent from the anode fragments and slimes. metal particles from theanode fragments and slime may be made by other processes such as flotation in which size, shape, and surface condition are all factors.

The conditions of electrolysis are not particularly critical. Current densities at the anode may be 1005,000

amperes per square foot, cathode current density may be l00l,000 amperes per square foot. The anode may be of the impure metal it is desired to produce in pure subdivided form. The cathode may be any unattacked metal or carbon. When the anode is of the impure metal it is desired to produce, the cathode may be the same metal and the current may be from time to time reversed in order to produce subdivided metal from both electrodes.

, In this case the vessel holding the bath may be any unattacked metal or ceramic. When using a carbon anode, the cathode may conveniently be the metal vessel which contains the salt.

My methodfor the production of pure metals in solid subdivided form is applicable to those metals which are practically .advanta.geous not molten at the necessary temperatures of operation,

minimum about 450 C., and which do not alloy with the alkali or alkaline earth metals used and which meet the requirements previously set forth concerning the free energy of their compounds.

The process is applicable to mixtures of compounds of several metals. Such mixtures of compounds can be sup plied in various ways, but conveniently from an alloy anode. ,Suc'h mixtures of compounds are reduced to dis- Separation of the newly formed cret e unalloyed particles of the metals. Such mixtures of 7 5 from the metals.

metal particles can be separated by mechanical or chemical means.

As previously mentioned, the oxygen content of the bath must be kept low to obtain metals relatively free of oxygen. This may be accomplished by using a very large amount of oxygen-free molten chlorides with relation to the metal deposited and removing the oxygen from the chlorides before recirculating them in the system. The oxygen can be removed from molten chlorides by passing hydrochloric acid gas through them or by treating them with calcium metal. This method involves the separation of the metals from the salts before the latter can be deoxidized. This may be done by solution of the salts in Water, or by separating the molten salts mechanically Gravity or hot pressing may be em- :loyed. I prefer, however, to deoxidize the molten salts vithout separating them from the subdivided metal. I accomplish this in one of I several ways. In one example I react the salt with incandescent carbon. The reaction of K 0, for example, with incandescent carbon is as follows:

The incandescent carbon is maintained in a limited zone of the salt bath for example an electrically heated graphite spiral. The potassium vaporized at the graphite is condensed in the bath away from the spiral, while the COescapes. In some cases a small amount of carbide metal may be formed by reaction of the incandescent carbon with the subdivided metal. This adheres to the spiral. The amount of carbide formed is small compared to the carbon monoxide because the oxygen being in solution has much higher mobility and difiuses from throughout the bath to react while only a local zone of subdivided metal reacts.

In another method of deoxidizing the salt bath, I use 1 heated filament of metallic iron. This reacts with the alkali metal oxide in accordance with the reaction:

'there may be some reaction of the subdivided metal and the Fe O to produce oxidic compound which, however,

, adhere to the iron filament and do not contaminate the remaining subdivided metal.

Other reactions may be employed in which the oxygen of the bath is removed by a reaction which depends on its mobility and hence the product is concentrated locally, and there is a minimum of reaction with the subdivided metal.

I prefer to use in my process the lowest melting mix ture of alkali and alkaline earth metal chlorides which is consistent with the free energy requirements for reduction which have been set forth. In order to reduce oxides, I prefer to have at least one alkaline earth chloride present since the negative free energy of reduction of heavy metal oxides by the alkaline earth metals is greater than for the alkali metals. In fact, several metals which are utilized for the practice of my invention as titanium and zirconium are not reduced from their oxides by sodium and potassium.

I have described my invention with the use of chlorides of the alkali or alkaline earth metals because they are taminating the metals produced. Such additions to the chloride bath are encompassed within my invention.

Having now described my process, I will illustrate it Bromides or mixtures of s by examples. In these examples all proportions not otherwise defined are on a weight basis.

Example I I make a fused bath of oxygen-free calcium and sodium chlorides in the proportion 66% CaCl 34% NaCl. I heat this bath in a ceramic pot to 750 C. at which temperature it is fused. I introduce into this bath metallic sodium in the form of a ribbon near one side of the pot. The metallic sodium reacts to form metallic calcium which dissolves in the bath. I introduce titanium dioxide in finely divided form at the other side of the pot, being sure that the rate of introduction of the sodium on the one hand and the Ti on the other are equivalent. Metallic titanium particles are formed in the bath. These particles are pseudomorphic after the titanium dioxide.

Example [I I take a molten bath of 67% calcium chloride, 33% sodium chloride. This bath is held in a ceramic container holding 150 lbs. of molten salt and provided with two graphite electrodes, immersed to the extent of 1 square foot in the chloride bath. An atmosphere of argon is maintained. One of these electrodes which is used as the anode is provided with a ceramic skirt dipping into the salt bath so that chlorine may beconducted fro it. I hold his bath at a temperature of 750 C. and pass a unidirectional current through it at a current density of 2,000 amperes per square foot and 6 volts. I prepare in a separate container a similar fused bath and stir into it 10% by weight of titanium dioxide. I cast this melt in the form of rods. The ceramic container of the electrolytic bath is provided with a cover and an atmosphere of argon maintained over it. The rods containing titanium dioxide are fed into the melt at a point equidistant between the electrodes. The rate of feeding titanium dioxide is adjusted so that 1,500 grams is fed into the pot in an hour. This is electrochemically equivalent to the calcium ion discharged at the cathode. When about 10,000 grams of titanium dioxide have been fed into the electrolytic vessel, the electrolysis is discontinued, the salt removed from the pot and solidified in an inert atmosphere. Titanium metal particles pseudomorphic after the titanium dioxide used are distributed through the salt. The salt is then broken up and treated with dilute hydrochloric acid "to dissolve the salts and the calcium oxide. The titanium particles are separated from the solution and washed with Water. They are found to have a purity of 99.8% titanium.

Example III I take a molten electrolytic bath like that in Example II except that in place of the rods of fused salt containing dispersed titanium dioxide I add titanium tetrachloride by forcing the liquid TiCl under the fused salts between the electrodes. I add the titanium tetrachloride at the rate of 3,400 grams per hour, which is the electrochemical equivalent of the current passed if all the tetrachloride is reduced to metal. I introduce about 25,000 grams of tetrachloride. The molten salt is then filled with dispersed titanium particles which are filamentary. This filamentary form arises from the reduction, by the solution of calcium in the melt, of a titanium chloride solution being formed from the TiCl Example IV The current is 1,000 amperes which corresponds to 2,000 amperes per square foot on the anode and 200 amperes per square foot on the cathode, I introduce anhydrous zirconium-tetra-chloride into the bath between the electrodes. There are formed filamentary particles of zirconium in the fused bath. I continue the addition of finely divided zirconium chloride with stirring until the bath becomes too viscous to stir readily. I then discontinue the electrolysis and allow the bath to solidify. I remove the solidified bath from the pot, dissolve the salts in water and recover the subdivided metal.

Example V.

I make a fused bath of 67% KCl, 33% CaCl I place this bath in a ceramic pot and heat to 700 C.

In this bath, I place two electrodes of titanium which contains oxygen. I pass a unidirectional current at 2,500 amperes per square fot between the electrodes,

the direction of the current being periodically reversed. There is formed at the electrode which is the anode, titanium dichloride which is only slightly soluble in the bath. This titanium dichloride is reduced in situ to form filamentary particles by the calcium formed at the cathode and dissolved in the bath. The calcium chloride formed by this reduction replenishes the bath. The oxide which enters the bath from the anode is reduced by the calcium and the resulting calcium oxide is insoluble in the bath. I continue the electrolysis with periodic reversals of the current until both electrodes are consumed. I then allow the bath to solidify and dissolve the salts in dilute hydrochloric acid which also dissolves the calcium oxide formed. I recover the pure oxygenfree titanium as aggregates of filamentary particles. I find that this process is highly efficient electrically, there is produced almost exactly 24 grams of subdivided metal per ampere hour.

Example V] I take a ceramic chamber containing a fused bath of 65% KCl, 35% Cacl this chamber being divided by a partition well below the salt level. In one compartment of this chamber I place a graphite anode, in the other portion, I place briquets of TiO+carbon. I place two graphite electrodes with ceramic sleeves in contact at their lower end with a pile of the briquets and pass an alternating current through the two electrodes until the TiO+carbon briquets are heated to 800 C. I then connect the two graphite electrodes in contact with the TiO+carbon briquets up as an anode connection and pass a unidirectional current between the TiO+carbon briquets and the graphite anode. As a result of this electrolysis carbon monoxide is given off from the graphite and carbon briquets and metallic titanium is formed dispersed through the salt.

Example VII I take an iron pot containing about 50 lbs. of CaCl 65%, KCl-35%. I provide this pot with a cover through which an electrode of compact metal may be introduced. I heat the electrolytic bath to 750 C. and pass a unidirectional current of 1,500 amperes from the compact metal anode to the pot as cathode. The compact metal used is sintered thoriumv and has a surface exposed to the electrolyte of about 25 square inches and is lowered into the electrolyte as it is consumed. During the operation an atmosphere of argon is maintained above the fused salt. I continue the electrolysis with frequent stirring of the metal until 15 lbs. of the anode. metal is consumed. I then allow the fused bath to solidify, remove it from the pot, dissolve the salt in water and treat the recovered thorium powder with dilute hydrochloric acid to remove calcium oxide. The thorium recovered in this way is highly pure and in form of filamentary particles.

7 Example VIII I take an apparatus and bath like that in Example II. I pass the chlorine from the anode over impure titanium and purify the TiCl obtained. I introduce this purified TiCl into the bath in accordance with Example III and obtain highly pure titanium powder.

Example IX I proceed as in Example VI. In this example the chloride of titanium formed at the anode rises with the melt due to the buoyant action of the evolved carbon monoxide, as it reaches a point above the partition it diffuses into the other compartment where it is reduced by the selution of calcium metal in the fused salt to form titanium particles. The anode slimes or frag- 11161 118 fall to the. bottom of the anode compartment. I now recover the salts from the two compartments in separate fractions. From the salt recovered from the cathode compartment I obtain particles of titanium free from anode fragments and slimes.

What is claimed is:

1. Process of producing a metal of the titanium group, which comprises bringing together in a reaction zone a chloride of a metal of the titanium group of the periodic system and a solution of at least one alkalinous metal in a fused bath consisting essentially of at least one alkalinous metal chloride, said fused bath being free from undissolved alkalinous metal, said reaction zone being initially devoid of undissolved alkalinous metal and of said titanium group metal chloride, and said titanium group metal chloride and said alkalinous metal solution being brought together in the reaction zone at the rate at which titanium group metal is produced thereby producing filamentary particles of titanium group metal.

2. Process as defined in claim 1, in which the titanium group metal is titanium.

3. Process of producing a metal of the titanium group of the periodic system, which comprises electrolyzing a fused bath consisting essentially of at least one alkalinous 7 metal chloride, in an electrolytic cell having a conductive anode containing a metal of said titanium group, to form at the cathode a solution of alkalinous metal in alkalinous metal chloride and at the anode a chloride of said titanium group metal, and bringing the anode and cathode products together in a reaction Zone free from undissolved alkalinous metal and at the rate the titanium group metal is produced thereby producing filamentary particles of titanium group metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,202,818" 'Edgecornb Oct;31, 191.6 1,355,368 Underwood Oct. 12, 1920 1,699,302 Mayer Ian. 15, 1929 1,704,256 Lorenz Mar. 5, 1929 2,134,457 Tainton Oct. 25, 1938 2,148,345 Freudenberg Feb. 21, 1939 2,274,699 Jacobs Mar. 3, 1942 2,302,604 Dolbear Nov. 17, 1942 2,391,903 Iohansson Jan. 1, 1946 2,413,411 Kroll Dec. 31, 1946 2,519,792 Rosen Aug. 22, 1 950 2,598,833 Renman June 3, 1952 FOREIGN PATENTS 13,759 Great Britain -a 1904 263,301 Germany Aug. 5, 1913 626,636 Great Britain July 19, 19.49 635,267 'Great Britain Apri. 5, 1950 637,714 Great Britain May 24, 1950 France Dec. "30, 1953 OTHER REFERENCES Treatise on Powder Metallurgy,. by Goetzel, vol. I.

(1949), pages 92 thru 97.

Claims (1)

1. PROCESS OF PRODUCING A METAL OF THE TITANIUM GROUP, WHICH COMPRISES BRINGING TOGETHER IN A REACTION ZONE A CHLORIDE OF METAL OF THE TITANIUM GROUP OF THE PERIODIC SYSTEM AND A SOLUTION OF AT LEAST ONE ALKALINOUS METAL IN A FUSED BATH CONSISTING ESSENTIALLY OF AT LEAST ONE ALKALINOUS METAL CHLORIDE, SAID FUSED BATH BEING FREE FROM UNDISSOLVED ALKALINOUS METAL, SAID REACTION ZONE BEING INITIALLY DEVOID OF UNDISSOLVED ALKALINOUS METAL AND OF SAID TITANIUM GROUP METAL CHLORIDE, AND SAID TITANIUM GROUP METAL CHLORIDE AND SAID ALKALINOUS METAL SOLUTION BEING BROUGHT TOGETHER IN THE REACTION ZONE AT THE RATE AT WHICH TITANIUM GROUP METAL IS PRODUCED THEREBY PRODUCING FILAMENTARY PARTICLES OF TITANIUM GROUP METAL.