US2903351A - Thorium-beryllium alloys and method of producing same - Google Patents

Description

Sept. 8, 1959 F- H- SPEDDNG ETA'- 2,903,351

'I'HORIUM-BERYLLIUM ALLOYS AND METHOD OF PRODUCING SAME Filed April 1l. 1949 gl l I n u l g nl f a 5 4 a' ,amy

United States Patent O THORIUM-BERYLLIUM ALLGYS AND METHOD F PRODUCING SAME Frank H. Spedding and Harley A. Wilhelm, Ames, Iowa, and Wayne H. Keller, St. Louis, Mo., assignors to the United States of America as represented by the United States Atomic Energy Commission Application April 11, 1949, seria1No.s6,'/3s

9 Claims. (el. 7s1zz.7)

This application relates to the production of alloys from halides of the refractory metals, by which We intend to encompass all metals whose melting points are higher than 1600 C., and to the alloys produced thereby. The invention especially deals with alloys containing thorium, titanium, zirconium, and hafnium, the metals of group IVB of the periodic system.

This application is a continuation-impart of our copending application, Serial No. 695,299, tiled September 6, 1946, now U.S. Patent No. 2,782,116, granted on February 19, 1957.

The production of thorium has been proposed by reaction of the oxide, chloride or other compound of the desired metal with sodium metal. However, it has been found that such processes result in the production of the metal in a linely divided or pulverulent state, frequently in low yield, and in most cases the metal produced, whether in massive form or powdered state, has been contaminated with numerous impurities, particularly with the oxide of the metal undergoing preparation. Such mpurities are very disadvantageous for the production of alloys because the mechanical properties of the nal product are greatly impaired thereby.

The present invention provides a novel process whereby the metals herein contemplated may be produced and alloyed in situ and obtained in massive form (as relatively large aggregates) substantially free from impurities, particularly the oxide of the metal to be produced. In performance of the process, a reducing metal of the group consisting of alkali metals and alkaline earth metals such as sodium, potassium, lithium, calcium, barium, strontium or magnesium (usually in an excess of to l0 percent or more of the theoretical quantity required), is reacted with a iluoride of the refractory metal to be alloyed. Various metals which are below the refractory metal in the electromotive series may be simultaneously reduced by this process, together with the refractory metal, from their halides, whereby corresponding alloys are obtained. The halides of the metals of groups IIA, IIB, IIIA, IVA, and VA are suitable for co-reduction with the abovenamed refractory metals of group IVB of the periodic system.

We have found that such a process should be conducted at a temperature above the melting point of the metals being prepared or at least at a temperature suiciently high to form a molten metal phase and to maintain the resulting reaction mass in molten state for a time sutlicient to permit separation of a molten pool of metal from the resulting slag, which comprises the uoride of the reducing metal. This pool of molten metal may be withdrawn While the metals remain in molten state, or the pool may be allowed to solidify and be separated from the slag thereafter. Calcium and magnesium and similar alkaline earth metals are especially useful as reducing metals in this process.

The development of sufficient heat in the reaction mixture to establish the reaction temperature and to maintain the reaction mass in molten state until separation of the phase into layers has been secured, is important since, if the temperature is not high enough, the reaction will be incomplete and recovery of metal poor. With certain fluorides of metals which melt at lower temperatures and certain reducing metals, such as calcium, suthcient heat may be developed by the exothermic reaction to effect this desired result, provided proper precautions are taken to prevent loss of heat through the walls of the reactor and also provided that suicient reaction mixture is used in the reactor. On the other hand, special precautions must be resorted to in order to establish and maintain the required temperature for production of the refractory-type metals and alloys herein desired to be produced since they melt at temperatures up to l600 to l800 C.

In accordance with this invention, it has been found that all, or a substantial portion of, the necessary heat required to ensure layer separation is developed internally by the simultaneous reaction involving co-reduction of said above-mentioned other metal halides in the reaction mixture of the refractory metal fluoride and the reducing metal. 'This second reaction is thermodynamically capable of developing a temperature higher than can be developed by the reaction of the reducing metal with the rcfractory metal fluoride alone. For example, an additional halide of another metal which, in the electromotive series, is below the reducing metal and below the refractory metal being produced, may be added to the reaction mixture, and the amount of reducing metal (calcium, magnesium, sodium, etc.) is increased accordingly. By this process, heat evolved from the second reaction aids in the establishment of the temperature required, and/ or the presence of said second reactants or reaction products lowers the melting point of the metals and/ or slag so that the layer separation may be secured. A particularly advantageous result may be obtained by the reduction of a mixture of the refractory metal liuoride and a chloride of the other metal, since in such a case the reaction heat is noticeably increased and, in addition, the fluidity of the resulting chloride-uoride slag and/or the melting point thereof is sufficiently low to permit very efficient separation of the alloy formed therefrom so that the resulting alloy is secured in high yield and good purity.

Alloys of thorium-beryllium, thorium-aluminum, thorium-zinc, thorium-bismuth, for instance, may be produced in this manner. The relative proportions of refractory metals to other metal may be adjusted within comparatively wide limits in accordance with results desired. Where the metal which is coproduced with the refractory metal is extremely light as in the case of beryllium, the quantity used of said other metal halide should be balanced if possible so as to avoid production of a metallic mixture having approximately the same density as the slag.

In conducting the reaction, we have found that it is desirable to establish a superatmospheric pressure upon the reaction mixture while the reaction is proceeding in order to maintain the reducing metal more or less uniformly dispersed throughout the reaction mass and thereby to ensure production of the resulting alloy in comparatively high yield. Where an alloy of high purity is desired, the pressure may be released after substantial reaction has occurred and many of the impurities can then be distilled from the molten metal. Alternatively, the molten metals may be allowed to solidify and subseifquently may be remelted and impurities distilled thererom.

Particularly advantageous results may be secured if the reaction is conducted n an elongated reactor of each height that the resulting molten pool of metal will have a minimum surface area in order to minimize loss of heat and premature solidification of the metal.

The reactor is usually constructed of iron or steel. The problem of securing a satisfactory lining is of paramount importance. The metals undergoing reduction as herein contemplated in general alloy readily with iron or steel. Should the lining become defective during the operation, metallic thorium or similar metal tends to flow through the defect to the metal wall of the reactor and to penetrate the wall, thus creating an exceedingly hazardous condition due to the fact that the molten metal flowing through the opening created in the wall reacts violently with the air.

The problem of securing suitable linings for bombs or other reactors used in this process has been rather complex. Silicates have been found to be unsuitable because the reducing metals tend to react therewith and to contaminate the metal produced. Applicants have found it especially advantageous to use a reactor which is provided with a lining or interior surface comprising a refractory compound, preferably lan oxide, of a metal above the metal undergoing reduction in the electromotive series which is preferably less volatile than the metal being produced. Alkaline earth metal oxides are particularly valuable for this purpose.

The lining may be deposited upon the walls of the reactor by any convenient means. In accordance with one process described in a co-pending application of Harley A. Wilhelm, Serial No. 567,284, filed December 8, 1944, now U.S. Patent No. 2,785,064, granted on March 12, 1957, an elongated cylindrical bomb provided with a centrally disposed mandrel of the size required for the reaction zone is filled with finely powdered anhydrous magnesium oxide, dolomitic oxide, calcium oxide or similar oxide, 'and the bomb is subjected to a rapid jolting action whereby the powder becomes compacted into an inherent well-bonded lining. Thereupon the mandrel is removed and the bomb is ready for use. Details on the construction of the reactor suitable for the process of our invention are fully described and illustrated in said application of Harley A. Wilhelm, Serial No. 567,284.

As previously noted, the process may be effectively conducted in an elongated reactor having a length at least three times its width or diameter, since the use of such a reactor permits ready establishment of a slagged metal pool of minimum surface area. A cylindrical pipe or shell provided with closed top and bottom ends is suitable. These closed ends may be sealed if desired. In general, where a highly volatile reducing metal, such as magnesium or sodium, is used, it is found preferable to mount the top or covering end upon the cylinder in a manner such that a minor amount of leakage of gas can take place so that the pressure in the reactor during the reaction does not become excessive, being in such a case, below the autogenous pressure of the system and rarely above a few hundred lbs./sq. in. and frequently below about 100 lbs./ sq. in. The amount of leakage permitted, however, should not be so great as to prevent establishment of a superatmospheric pressure within the reactor by the reactants. A tlange cover fitted to the top end of the reactor without a gasket provides a sufficiently loose fit.

The reactants should be anhydrous and substantially free from oxygen. The reactants should be thoroughly mixed prior to introduction, and, in order to secure satisfactory mixing, the reducing metal should be nely divided (generally `about -10 to -50 mesh). In most cases the fluoride undergoing reduction may be much iiner, its particle size usually being -100 mesh. Sufticient reaction mixture is used substantially to till the reactor.

Following charge of the reaction mixture into the lined reactor, a cover of the lining material s provided, and the reactor is closed. The reaction is initiated by preheating until the reaction mixture or a portion of it or one or more of the components thereof has been heated to the temperature at. which reaction will take place 4 (about 400 to 600 C. or higher), or, where preheating is unnecessary, the reaction may be initiated by means of an electrical fuse. This fuse may comprise a short length of resistance wire attached to a suitable source of electrical power and functions by heating a localized portion of the mixture to the temperature at which reaction initiates (usually about 400 to 600 C.).

After reaction has been initiated, substantial pressure develops within the system due to vaporization of the reducing metal or halide and due to the fact that escape of the metal or vaporized halide is prevented or substantially minimized. 'I'he pressure developed in general exceeds 0.5 to 3 atmospheres gauge and in some cases is of the order of 75 to 100 lbs/sq. in. gauge or higher it serves to maintain the reducing metal more or less uniformly dispersed throughout the reaction mixture as reaction proceeds. This facilitates substantially complete reaction of the halide salts and also tends to prevent reversal of the reaction at the elevated temperature due to back reaction of the resulting metal with the slag or the calcium oxide or other oxide of the liner. Moreover, the pressure prevents or minimizes inleakage of air or moisture into the reactor.

When a bomb or reactor of elongated construction as herein described is used, particularly advantageous results accrue due to the fact that the reaction may be initiated in one end of the bomb by heating or otherwise and that thereby a temperature dierential may be established in which one end is above the boiling point of the reducing metal and the other end of the reactor is below the boiling point of the metal phase produced and frequently at a temperature several hundred degrees below that of the opposed end. This is found to be advantageous, since it effectively minimizes establishment of excessive pressures in the reactor. Furthermore, after reaction is over or begins to subside and cooling of the reactor begins to occur, distillation of the reducing metal from the molten mass takes place, and this metal condenses in the cooler end of the bomb. Thus, the temperature differential established permits substantial puriiication of the metal by removal of reducing metal, halides and other impurities as the metal is being cooled to the solid state.

After the reaction is completed, the molten mass is maintained in the molten state until the alloy has substantially completely separated from the slag. Usually this requires one or several minutes. Thereafter the alloy may be allowed to solidify into a solid ingot, or it may be withdrawn from the reactor in the molten state.

The resulting alloy is comparatively free from impurities although it may contain small amounts, for example one or several percent, of magnesium, calcium, or other reducing metal which has been used to effect the reaction, and it also may be contaminated with the addedmetal halide or its reaction product. For example, when thorium iluoride and zinc chloride are coreduced, the resulting product will be a mixture of alloy of thorium and zinc, and similar results are secured when halides of metals other than zinc are used in conjunction in the process herein contemplated. Further impurities may be present due to the use of reactants which are impure, and, in addition, some thorium or other refractory metal oxide may be present due to partial reaction of the refractory metal with the lining and/or due to the presence of a residual amount of water n the mixture or reactor lining.

As previously stated, a substantial purification of the alloy may be secured by heating it in vacuo at a temperature at which it is molten. In order to secure a satisfactory purification and prevent further oxidation or contamination of the metal, this treatment is preferably conducted in a closed crucible or melting chamber constructed of graphite or similar inert material, and the absolute pressure established within the crucible is generally below about 1 to 2 mm. of mercury and frequently of the order of 100 to 200 microns. Impurities such as magnesium, calcium, or other alkaline earth metal, sodium, potassium or other alkali metal, boron, silicon, cadmium, or other metals, phosphorus, sulfur, and halogens are removed to a very substantial degree by this process. The temperature of melting usually is 100 or 200 above the melting point of the alloy undergoing purification treatment but below the boiling point of such metal.

After impurities have been distilled from the molten mass, the molten metal may be drained from the crucible and cast into suitable ingots. A further puriiication of this metal is thus secured, since the non-volatile impurities, including oxides, tend to form a scum or film, particularly where the temperature of melting is maintained below the melting point of the respective oxides of the metals undergoing treatment. In such a case the oxides remain essentially solid or semi-solid, and the metal flows from' the oxide which in turn tends to adhere to the walls of the crucible or at least to separate substantially from the metal.

The following examples are illustrative.

Example I duced:

Lbs. Thorium uoride 17.05 Zinc chloride 3.77 Calcium 6.65

The charge was weighed and mixed in a dry room, precautions being taken to prevent absorption of an appreciable amount of moisture by the zinc chloride. A layer of dry calcium oxide was packed on top of the charge and the top flange was bolted on. The bomb was inserted in a gas burner furnace, leaving the end which had the ilanged cover exposed to the atmosphere. The temperature of the furnace was 1160 F. and the reaction initiated in fourteen and one-half minutes. The top of the reactor was at a temperature several hundred degrees below that of the central portion. Several minutes after the reaction initiated, the bomb was removed from the furnace and cooled with a water spray. The top flange was removed, and an ingot weighing about 13 lbs. and having the following analysis was obtained:

The process described in Example I was repeated using a sintered calcium oxide crucible in an iron bomb 2.5" by 12" and using the following charge:

G. Thorium uoride 250 Beryllium uoride Iodine 205 Calcium 121 The bomb was heated to 656 C. and the reaction initiated at this temperature. After cooling, a thoriumberyllium alloy which was quite malleable and quite resistant to corrosion was secured in the form of a massive ingot. k

Example III The process of Example 1I was repeated using the following charge:

A thorium-beryllium alloy was secured containing about 17% by weight beryllium and 83% by weight thorium. The product produced was hard and quite resistant to corrosion.

By the process of the invention, thorium-beryllium alloys may be prepared which have the two components in any ratio possible. As little as 0.5% beryllium, or even less, causes a reduction of the melting point of thorium by as much as 500 C. These alloys having a low beryllium content are easy to cast, and they are considerably more resistant to corrosion than pure thorium.

The -attached drawing contains curves in which the corrosion resistance to air at various temperatures of a 2% beryllium-thorium alloy is compared, by way of example, with that of pure thorium. It will be readily seen how favorable an effect the addition of 2% beryllium has on the corrosion resistance.

Another interesting alloy of the numerous ones produced by the process of our invention is that containingA 94% by weight of beryllium and 6% by weight of thorium. This alloy crystallizes in the cubic system. It has a highly increased degree of malleability as compared with that of pure bryllium.

Example IV The process of Example III was lrepeated using a mixture of bismuth and thorium uoride in the proportion of 1 mole Th1-l,b to 1/3 mole BiF3 to 3 moles calcium metal. Thorium-bismuth alloy separated and was recovered.

The invention is particularly concerned with, and has been described with particular reference to, the production of thorium Ialloys. However, the principles herein disclosed may be applied to the production of other alloys of the refractory metals. For example, liuorides of other high-melting metals such as hafnium, chromium, titanium, zirconium, tungsten, tantalum, or similar metals of the group IVB, group VB and group VIB, which melt at 1600 to 1800 C. or above, may be reduced with zinc chloride, cadmium chloride, or similar chloride or other halide of a B group metal as above-listed.

The invention as herein described has been particularly concerned with the production of the metals from their uorides which have the general formula MFz where M is the metal concerned and x is a small whole number, usually being 2, 3, or 4, depending upon the respective valence of the metal. However, where the liuoride is highly volatile, as in the case of TiF4, it is desirable to avoid use of such a uoride because of the high pressures developed. In such a case more complex, less volatile fluorides, such as NazTiFG or KzTiF or the correspond ing zirconium compounds may be used. The process may be used in connection with the production of metals from other halides such as chlorides, bromides, or iodides of the above metals. At the same time, however, production of metal from these compounds may be disadvantageous in some cases due to the high pressures which may be developed in the reactor and also due to the hygroscopicity of the chlorides and similar halides. The hygroscopicity of some of these halides is particularly objectionable, because the water thus introduced reduces the yield of metal and makes the separation of the molten phases more diicult. In consequence, it is preferred to conduct the reactions herein contemplated using the fluoride. However, mixtures of uoride and chloride may be used as previously described, and in such a case increased fluidity in the slag permits a more complete recovery of the metals produced. Similar results may be secured by using other chloride-fluoride mixtures, or other mixtures of metal fluorides with metal halides. For example, a mixture of ThF4 and ThCl4, ThBr4, or ThI4 may be co-reduced. Likewise, a mixture of ThCl4 and ZnF2 may be reduced as herein contemplated. Moreover, halides of chromium, zirconium, etc., such as chromic chloride, chromic uoride, or other of the refractory metal halides may be reduced by this process. Where the simple halides are undesirable because of their high volatility, less volatile halides, such as NazTiF, K2TiF6, or Na2ZrP6 may be reduced by the present process.

While the invention is particularly concerned with the reduction of halides of refractory metals above-dened, it may be advantageously applied to reduction of metal halides generally. Thus, the co-reduction, by means of a metal higher in the electromotive series, of a fluoride of a metal lower in the series with another halide of the same or diierent metal, such yas the chloride thereof, is advantageous to form a more luid and/ or lower-melting slag which separates more readily from the molten metal formed. For example, beryllium iluoride may be co-reduced with lead chloride, zinc chloride or cadmium chloride by calcium or similar metal as herein contemplated.

Although the present invention has been described with particular reference to the specific details of certain embodiments thereof, it is not intended thereby that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

What is claimed is:

1. A binary thorium-beryllium alloy in which thorium is the predominant ingredient.

2. A binary-beryllium alloy in which beryllium is the predominant ingredient.

3. An alloy consisting of 83% by Weight of thorium and 17% by weight of beryllium.

4. A binary thorium-beryllium alloy containing approximately 0.5% beryllium.

5. A binary thorium-beryllium alloy containing approximately 2% beryllium.

6. An alloy consisting substantially of 94% beryllium and 6% thorium.

7. A method of preparing a thorium-beryllium alloy, comprising the steps of simultaneously reducing uoride of thorium and a halide of beryllium with a metal selected from the group consisting of alkali metals and alkaline earth metals at a temperature sufficiently high to form a molten alloy of said metals, and of maintaining said elevated temperature until separation of the alloy from a slag formed has taken place.

8. A method of preparing a thorium-beryllium alloy, comprising the steps of simultaneously reducing thorium uoride and beryllium fluoride with calcium at approximately 650 C., and of maintaining said temperature until the thorium-beryllium alloy has separated from a slag formed.

9. A binary thorium-beryllium alloy.

References Cited in the file of this patent UNITED STATES PATENTS 1,648,954 Marden Nov. 15, 1927 1,728,940 Marden Sept. 24, 1929 1,728,942 Marden Sept. 24, 1929 1,814,721 Marden July 14, 1931 2,025,614 Rohn Dec. 24, 1935 2,193,363 Adamoli Mar. 12, 1940 OTHER REFERENCES Hessenbruch: Nickel Alloys for Use as Pins in Artiiicial Teeth, Chemical Abstracts, vol. 35, p. 6922 (1941).

Baenziger et al.: U.S. Atomic Energy Commission Document No. ABCD-2506, The MBela Compounds; declassied Mar. 2, 1949, 4 pages.

Claims (2)

1. 7. A METHOD OF PREPARING A THORIUM-BERYLLIUM ALLOY COMPRISING THE STEPS OF SIMULTANEOUSLY REDUCING FLUORIDE OF THORIUM AND A HALIDE OF BERYLLIUM WITH A METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE EARTH AT A TEMPERATURE SUFFICIENTLY HIGH TO FORM A MOLTEN ALLOY OF SAID METALS, AND OF MAINTAINING SAID ELEVATED TEMPERATURE UNTIL SEPARATION OF THE
2. 9. A BINARY THORIUM-BERYLLIUM ALLOY.

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