US2754347A - Apparatus for refining rare refractory metals - Google Patents

Description

July 10, 1956 D. WROUGHTON ET AL 2,754,347

APPARATUS FOR REFINING RARE REFRACTORY METALS 2 Sheets-Sneet l Filed April 28, 1944 I I .I

July 10, 1956 D. WROUGHTON ET AL APPARATUS FOR REFINING RARE REFRACTORY METALS Filed April 28, 1944 2 Sheets-Sheet 2 aM/fam ATTORNEY Donald Wrougllton, Verona, and John W. Marden, East Orange, N. J., assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Applicaiion April 2s, 1944, serial No. 533,240

2 Claims. (ci. 13-33) This invention relates to apparatus for refining a rare refractory metal such as uranium and more particularly to apparatus for melting and casting such a metal in coalescent form.

in a copending application of William C. Lilliendahl et al., Serial No. 478,270, filed March 6, 1943, now Letters Patent No. 2,690,421, issued September 28, 1954, a method is described whereby uranium may be prepared in the form of a compressed coherent powder. Briefly, the method thereof includes the electrolysis of potassium uranous fluoride, KUFs, uranium tetrachloride, UC14, or uranium tetrafluoride, UF4, in a fused salt bath of sodium and calcium chlorides in which uranium is deposited on the cathode in the form of a powder, the separation of the powder from soluble impurities by grinding and washing with water and acid, and finally the compression of the uranium powder into a slug or button while protecting it from oxidation. By heating said uranium button to sintering temperature in a high vacuum as described in United States Letters Patent No. 1,814,719 to J. W. Marden et al., many vaporizable impurities may be eliminated from the button, but non-vaporizable impurities remain in the sintered mass. Such impurities cannot be tolerated in certain uses of uranium. In a copending application of George Meister, Serial No. 525,601 filed March 8, 1944, methods are described for rening and purifying uranium powder produced by electrolysis or produced by other reduction processes. Briey, the methods thereof include the melting of such uranium in a fused salt bath in air, vacuum or inert gases to remove oxides, salts and any other impurities to obtain uranium in a substantially pure coalescent form. The present invention relates to improvements in apparatus for refining and purifying rare refractory metals in accordance with the methods set forth in said copending Meister application.

The present invention provides apparatus for melting and fusing a rare refractory metal such as uranium to free it from vaporizable impurities, salts, and slags, to produce substantially pure metal in coalescent form which may be cast in any desired shape or form. The apparatus disclosed herein may be used in air without requiring the presence of inert gases or vacuum conditions, and may be constructed from easily obtainable materials, including carbon or graphite, at relatively low cost.

t is the general object of this invention to provide apparatus for refining and purifying a rare refractory metal such as uranium, whereby the impurities are separated from the metal while fusing the metal.

1t is an object of this invention to provide apparatus for fusing impure uranium powder to obtain uranium in coalescent form.

It is another object of this invention to provide ap-v paratus suitable for purifying and fusing uranium or the like in a fused salt bath.

It is still another object of this invention to provide an apparatus for refining impure uranium or the like at temperatures above the melting point` thereof.

2,754,347 Patented July 10, 1956 Other objects and advantages of the invention will be readily apparent to those skilled in the art from the following description of preferred embodiments of apparatus illustrated in the accompanying drawings, in which:

Fig. 1 is an elevational view in section of a preferred form of purifying and fusing apparatus. Figs. 2, 3, 4 and 5 are elevational views in section of modified crucibles suitable for use in the apparatus of Fig. l. Fig. 6 is an elevational view in section of a modified form of purifying and casting apparatus. Fig. 7 is an elevational View in section taken on line 7--7 of Fig. 8 of a furnace for use with crucibles of the types shown in Figs. 2, 3, 4 and 5. Fig. 8 is a plan view in section taken on line 8 8 of the apparatus shown in Fig. 7.

Referring to Fig. 1 of the drawings, a melting crucible is indicated by the numeral 10. The crucible 10 is contained within a furnace having a base 11, a tubular member 12, an upper member 13, and a cover 14. A supporting member 1S, cylindrical in shape, may be provided between the base 11 and the bottom of the crucible 10 to support the crucible. Heat insulating material 16 is also placed in the space between crucible 10 and base 11. A high-frequency induction coil 17 having electrical leads 17a and 17]) surrounds the cylindrical member 12 for heating the contents of the crucible 10.

The materials used in both the crucible and furnace construction must be carefully selected because of the relatively high temperatures encountered and because of the nature of the substances treated within the crucible. The crucible 10 may be made of carbon or graphite, the latter being preferred. The base 11 and member 12 may be of Transite, or of similar heat resisting material. The cylindrical member 12 should be of material resistant to high temperatures, such as alundum or silica. The cover plate 14 should also be of refractory material, and the material 16 under the crucible should be heat insulating, such as asbestos, Silo-cel, or the like. The high frequency oscillator coil 17 may be of any well known type, air or water cooled if desired, and may be replaced by glow bars or resistance heating units, as will be apparent to those skilled in the art.

The mode of operation of the apparatus of Fig. 1 for refining uranium may be as described in the methods disclosed in the above-mentioned copending application of Meister, Serial No. 525,601. The crucible 10, which may be of any desired size, for example, 2% to 10 inches in diameter and 5 to 30 inches deep, is partially filled with salts suitable for the melting bath. Various salts such as sodium chloride, NaCl, calcium chloride, CaClz, barium chloride, BaClz, sodium fiuoride, NaF, calcium uoride, CaFz, barium fluoride, BaF2, magnesium fluoride, MgFz, potassium acid fluoride, KHFz, alone or in cornbination, and also these salts together with small percentages of uranium, tetrafiuoride, UF4, may be used. Other salts such as phosphates, borates, hydroxides, and the like may also be satisfactory. The salts in the crucible are heated and fused by means of the coil 17, glow bars, resistance heating elements, or the like. When the salt bath is fused and at a temperature of the order of 1000 to 1100 C., electrolytically deposited uranim, or impure uranium produced by other methods, is fed into the salt bath contained in the crucible 10. The bath temperature may then be raised, by means of coil 17, to bring the temperature of the charge to about 1200 C., at which point it is maintained for about ten minutes while the charge is stirred with a carbon rod. During this time, the uranium in the charge is fused and coalesces as substantially pure liquid in the bottom of crucible 10, as indicated by the numeral 18 in Fig. l. Some of the impurities present in the uranium charge are apparently converted to volatilizable halides which are emitted from the bath. Other impurities appear to collect as a slag 19 above the molten uranium y18. The salt bath appar.- ently collects at the upper portion of the contents of the Crucible as a salt layer 20.

After the fusing and refining of the uranium charge has taken place substantially as described above, the pure coalescent uranium may be recovered by allowing the apparatus to Cool and the Crucible contents to solidify. The salt and slag layers effectively prevent oxidation of the uranium being treated. After the Crucible contents have solidified, the Crucible may be broken apart and the uranium slug recovered from the bottom of the Crucible.V

In the event that crucibles having a bottom tap or a pour,- ing lip are used, as will be described hereinafter, the molten uranium in the bottom of the Crucible may be run into a suitable mold for casting in a desired shape without solidifying in the Crucible itself.

Referring again to the accompanying drawings, modied forms of melting Crucibles are illustrated in Figs. 2, 3, 4 and 5. The Crucible 2l of Fig. 2 is provided with a bottom tap or opening normally Closed by a plug 22 integral with or carried by a rod actuator 23. An inclined insert Z4 may be provided in the bottom of the Crucible 2l to Cause the melted metal to flow to the bottom tap when the plug 22 is raised by the rod 23. The insert 24 should be secured in the bottom of the Crucible by tight lit or by a dowel or the like. The Crucible 2l, plug 22, rod 7,3, and insert 24 are preferably made from graphite, or from other refractory materialsrinert to the salt bath and rare refractory metals such as uranium at high temperatures. Vl/hen using the Crucible 2l, the furnace of Fig. 1 may be modified, for example, as shown in Fig. 7 described hereinafter, to receive a suitable mold located below the tap closed by plug 22. Y

The Crucible 2:3, shown in Fig. 3, has a modified bottom surface provided by a tapered portion 26. The tapered bottom portion 26 of Crucible 25 provides a small volume space facilitating the fusing and Coalescing of the molten metal as the metal settles to the bottoni of the fused salt bath contained in the Crucible. Crucible 25 is preferably formed of graphite.

ln the Fig. 4 embodiment, the Crucible 27 is similar to Crucible 10 of Fig. 1, and is provided with a cupped insert 28, also of graphite, suitably secured in the bottom of the Crucible. The insert 2b has a small area recess 29 with tapered edges to provide a pool of cross sectional area less than the cross sectional area of the interior of the Crucible 27 to assist in the collecting and coalescing of the molten metal.

The Crucible 3o, shown in Fig. 5, is provided with a rotatable closure plug 3l positioned in the bottom tap or opening to Control the tapping of molten metal through a Crucible passage 32. The inner bottom portion of the Crucible 35; may 'oe tapered as shown, similar to the Fig. 3 construction. Means such as the bar 33 may be provided for turning the plug 3l from a closed position to the open position illustrated. A suitable mold may be positioned below the passage 32 for casting the moltenV uranium, as mentioned in Connection with the description of the Fig. 2 construction.

The modified apparatus shown in Fig. 6 includes a Crucible 35 positioned in a tubular member of refractory material. The member 36 is provided with a base plate 3'7 and an upper support plate 38, the latter being connected to a fixed pivot 39 whereby the furnace and Crucible may be tilted. insulating material i9 is positioned below the Crucible 35, and heating means, such as the oscillator coil 4l surrounds the member 36. YA refractory cover plate 42 may be used to close the upper end of member 35. A graphite pouring tube 43 is secured to the upper end of Crucible 35' and extends outwardly therefrom at approximately right angles to the axis of the Crucible. A lip i4 may be provided on the upper end of Crucible 35 to avoid spilling the fused "salt bath from the Crucible when the apparatus is tilted to. pourV molten 'niiet-al from"'tlf'bath.` HAu refractory is provided to receive the molten metal from the pouring tube 43, and may be supported in a refractory cup 46 positioned on a support 47. A rigid support 4S is provided to engage the base plate 37 for supporting the fur nace in the upright position illustrated.

The mode of operation of the apparatus of Fig. 6 is generally similar to the operation of the apparatus of Fig. l, in that the Crucible 35 is partially filled with salts suitable for the melting bath. The salts in Crucible 35 are heated and fused by means of the coil lil, glow bars, resistance units, or the like. When the fused salt bath temperature is of the order of 1100" C., the impure rare refractory metal such as uranium is fed into the bath and stirred if necessary while the temperature is increased and maintained at about 1200 C. The substantially puren metal collected in the bottomn of nthe Crucible 35 is recovered by tilting the furnace about pivot 3Q until the Crucible Contents run out through the pouring tube i3 into the mold 45. Since the mold 45 is smaller in size than the Crucible 35, the fused salt bath and slag may overrun the top of the mold 45 and be Collected inthe Vsurrounding cup 46 for further use. After the pouring and Casting operation, the furnace is tilted back to the upright position illustrated, against the support stop 48, and is ready for another Charge of salt and metal.

The apparatus shown in Figs. 7 and 8 provides a furnace heated by glow bars 5t) in place of high frequency oscillator coils. A graphite Crucible 5l is positioned within the tubular member 52 of refractory material. Insulating material 53 may be provided within the furnace casing 54 and below the Crucible 51. Where the Crucible 51 is similar to that described in connection with Figs. 2 and 5, a mold 5S.supported by a member 56 is postioned below the Crucible tap. A graphite tube 57 is secured to the upper end of the Crucible 51 and extends outwardly beyond the furnace Casing. The tubular member 52 may be provided with a projecting sleeve 58 of similar material surrounding the tube 57. The graphite tube 57 serves to carry olf excess fused salts from the Crucible 51 in the event that the addition of metal to the fused salt bath raises'the bathlevel so high as to tend to overflow the Crucible. The glow bars'Stl may be Connected to a suitlable source of electric current as is well known in the .heating art.

The mode of operation of the apparatus of Figs. 7 and 18 is similar to the operation of the apparatus of Fig. l.

The excess of fused saltsthat may be present, when impure uranium is added to the Crucible 51, overflows through the tube 57 and may be Collected for further use. After the metal has been refined in a fused salt bath contained in Crucible 51, the molten metal may be drawn off through the bottom tap of Crucible 51 into a mold 55. The Crucibles of Figs. l, 2, 3, 4 and 5 may be substituted for the Crucible 51 in the glow bar heated furnace of Fig. 7 by slight adaptations that will be readily apparent.

The substantially pure coalescent uranium resulting from the refining of impure uranium in the above-described apparatus may give a recovery of 86% of the theoretical uranium content of the uranium salts charged into the electrolysis bath of the process of the previously mentioned Copending William C. Lilliendahl et al. application. The yieldV is found to be equal or better than that attained by subjecting electrolytically deposited uranium powder to the usual'washing, grinding and sintering procedure. The apparatus herein disclosed offers less opportunity for Contamination of the uranium than is present in the washing and grinding procedure. Electrode deposits of uranium powder may be quickly and efficiently refined and molded to produce a coalescent substantially pure uranium which is suitable for many Commercial uses without furtherY refining. The Crucible constructions shown and described have been found to be economical A and to facilitate the continuous operation o f the refining furnace. The Crpcibles may A be readily withdrawn from the furnace and another Crucible and charge inserted for continued refining operations. The novel Crucible shapes disclosed aid in the collection of Coalescent uranium metal in the bottom of the Crucible under a protecting blanket of slag and fused salts. The use of a vacuum or a circulated inert gas around the furnaces shown is not necessary since the fused salt bath protects the molten uranium from contact with air or other contaminating substances. However, the evolved volatile impurities given oif from the refining crucibles may be withdrawn by a vacuum or may be swept away by an inert gas if desired. Recovery of the dense Coalescent body of uranium metal may be made by breaking open the Cool crucible or by casting the uranium in a suitable mold, as described hereinbefore. Although the furnace has been shown heated by either high frequency induction or by glow bars, various other methods of heating will be readily apparent. Among these would be heating by passing a heavy alternating current between the Crucible and a central carbon rod inserted into the fused salt bath. Even with the tapping or casting operation taking place in air, coalescent metal bodies of high purity and density are attained. The slag layer removed from the refining Crucible may be returned to the electrolysis furnace for still further economy.

Although only preferred apparatus and embodiments thereof have been described, it will be understood that numerous variations and modifications may be made without departing from the spirit and scope of our invention as defined inthe appended claims.

We claim:

1. In apparatus for refining uranium or the like in a fused salt bath, a graphite Crucible and a graphite insert in the bottom of said Crucible, said insert having a sloping upper surface providing a pool of cross sectional area less than the cross sectional area of said Crucible for the collection of Coalescent uranium or the like under a fused salt bath contained in said Crucible.

2. Apparatus for refining uranium that includes an insulating base, a tubular member of refractory material supported on said base, a removable Cover supported on said tubular member and defining therewith a furnace chamber, a refractory Crucible removably positioned within said furnace chamber, said Crucible having a tap at the bottom thereof and an insert having an inclined upper surface to provide a pool draining toward said tap, means insertable in said Crucible for opening and closing said tap, a passageway extending through the furnace chamber and associated with the tap whereby material may be removed from the Crucible, heat insulating means intermediate t'he Crucible and base member, and means surrounding the tubular member for electrically heating said Crucible.

References Cited in the file of this patent UNITED STATES PATENTS 243,788 Pedder July 5, 1881 1,112,993 Dunton Oct. 6, 1914 1,372,676 De Bats Mar. 29, 1921 1,378,189 Northrup May 17, 1921 1,423,501 McClain July 18, 1922 1,466,739 Nakamura Sept. 4, 1923 2,027,065 Sadtler Jan. 7, 1936 FOREIGN PATENTS 361,607 Germany Mar. 7, 1922 524,198 Great Britain July 31, 1940

Claims (1)

1. IN APPARATUS FOR REFINING URANIUM OF THE LIKE IN A FUSED SALT BATH, A GRAPHINE CRUCIBLE AND A GRAPHITE INSERT IN THE BOTTOM OF SAID CRUCIBLE, SAID INSERT HAVING A SLOPING UPPER SURFACE PROVIDING A POOL OF CROSS SECTIONAL AREA LESS THAN THE CROSS SECTIONAL AREA FO SAID CRUCIBLE FOR THE COLLECTION OF COALESCENT URANIUM OR THE LIKE UNDER A FUSED SALT BATH CONTAINED IN SAID CRUCIBLE.

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