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Vol. 18, No. 2
Metallic Uranium'sz Production of the Pure Fused Metal b y Reduction of Uranium Chloride b y Calcium in a High Vacuum By J. F. Goggin, J. J. Cronin, H. C. Fogg, and C. James UNIVBRSITY OF Nsw HAMPSHIRE, DURHAM, N. H.
T
HE conflicting statements concerning so many of the metals indicate that there is much need for research in this direction. An examination of the literature reveals the fact that many of these elements are extremely active, combining readily with gases and reducing most refractories with which they come in contact. It is therefore necessary, when preparing an active metal, to use pure materials, a high vacuum, a powerful reducing agent, and the most stable refractory obtainable. Great care must be used in selecting the refractory, since any reducible impurity contained therein is almost certain to contaminate the product. Purification of Uranium Oxide
High-grade commercial uranium oxide was dissolved in nitric acid, the solution diluted, filtered, and evaporated to crystallization. The mother liquor was poured off and the crystals were dried in a centrifuge. These crystals were recrystallized and centrifuged several times. The mother liquors were submitted to fractional crystallization in order to obtain most of the uranium in the form of pure uranyl nitrate. These crystals were dissolved in water, precipitated by ammonium hydroxide, filtered, washed, and ignited. Reduction of Uranium Oxide by Metallic Calcium
This method, which has been recommended by various writers, was tried out under varying conditions. Since uranium metal, especially in the powdered form, rapidly combines with nearly all gases, it was necessary to carry out the reduction in a high vacuum. For this purpose the apparatus
_ _ _ _ _ _ J'
I _y- - l_ _(_ = J Figure 1
shown in Figure 1 was employed. A shows the apparatus complete with the reduction chamber in place. It consisted of a piece of large bore iron pipe (about 4 feet long) closed at one end with a welded plug. The other end was threaded and fitted with a regular pipe cap, drilled through, and tapped to take a short length of S/s-inch pipe, which was smoothly tapered to permit easy attachment of the vacuum pump. B and C-C' show two types of reduction chambers. The e s t , used only in the preliminary work and adapted only to the reduction of the oxide, was made of a short piece (6 to 12 inches long) of iron pipe with both ends threaded and closed with pipe caps. This type was found to be unsatisfactory because the calcium vapor escaped rapidly through the caps. Form C-C', which may be used in reducing either the oxide or chloride, was made of Shelby steel tubing. TightOctober 19, 1925. portion of this work was offered in partial fulfilment of the requirements for the degree of M. S. a t the University of New Hampshire. 1 Received
1A
fitting steel plates were used to close the smoothed ends of the tube. The plates projected slightly into the inside of the tube and were fastened in place by means of eight or ten small cap screws. Chambers made in this manner were sufficiently tight to prevent the escape of any appreciable quantity of calcium vapor. Pure uranium oxide was mixed with a little more than the theoretical amount of calcium shavings and placed in the reduction chamber. The latter was then put in the vacuum chamber and, after replacing the cap, the whole was connected with the pump and evacuated. Considerable time was allowed to elapse after the manometer ceased to show any change before heating was commenced. With the pump running, the end of the tube containing the reduction chamber was kept above a bright red heat by means of a powerful kerosene oil burner for 45 minutes, the highest temperature attained being around 1000" C. The apparatus was allowed to cool overnight, filled with dry carbon dioxide, opened, and the reduction chamber quickly transferred to a vessel containing alcohol. The contents were then slowly transferred to an ice-cold solution of ammonium chloride. After the solution had been changed several times, it was replaced by water, and the latter by alcohol. The powdered metal was next treated with alcohol containing hydrochloric acid to remove any calcium, uranium hydroxide, etc., and finally washed with pure alcohol. The product obtained by this method consisted of a slightly brownish powder mixed with small globules very similar to that described by several previous workers. The results of an analysis showed the presence of both oxygen and iron. Since the calcium used for the reduction carried only a minute amount of iron, it was evident that the remainder came from the reduction chamber. Owing to the great activity of the finely divided metal, it was decided to search for a method which would yield a fused product at the moment of reduction. It was recognized at this stage that two vital points had to be considered: first, the necessity of a reducing agent with a great affinity for oxygen; second, that the reduced metal must be kept from coming in contact with any iron. Unfortunately, the calcium oxide produced in the reduction of a metallic oxide by calcium is infusible, and prevents the globules of metal from uniting, even if the temperature of reduction is higher than the melting point of the desired metal. Since sodium and calcium chlorides are readily fusible, it seemed that the reduction of anhydrous uranium chloride by one of these metals deserved consideration. Calcium metal appeared to be the more satisfactory of the two, since it has a very much greater affinity for oxygen, which is certain to be taken up in the form of moisture during the manipulation of the anhydrous uranium chloride. Preparation of Anhydrous Uranium Chloride
The simplest method for the preparation of this compound is to allow chlorine and sulfur chloride to act upon the heated oxide. The essential parts of the apparatus (Figure 2) consisted of two quartz tubes, B and C, approximately 2.5 feet long by 2 inches internal diameter. These were con-
February, 1926
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
nected by a short piece of similar tubing which fitted loosely inside, the joint being made tight with a turn of asbestos paper (previously ignited) and alundum cement. The tube C, containing the charge of uranium oxide, usually from 800 to 1000 grams, was placed in the furnace D. This fur-
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which were covered with a bright shining alloy of uranium and iron. Although the product was useless, it showed two things clearly: first, that the temperature of the reaction was sufficiently high to produce the metal in a fused condition; and second, that a lining to protect the metal from iron was necessary. The next reduction, therefore, was carried out with this last point in view. The reduction chamber was of the type used above, except that it was much larger and fitted with an alundum crucible closed by a cover of the same material. Owing to the intended increase in the quantity of material undergoing reduction, i t became necessary to change the type of apparatus and the method of heating. After a p proximately twice the quantities of uranium chloride and
-----
Figure 2
nace was simply a piece of magnesia pipe covering closed at the ends by pieces of asbestos board, a, through which holes were cut to allow the silica tube to extend. Heat was supplied by four powerful blast lamps, whose flames were directed through the openings, b, cut through the wall of the furnace. The burnt gases passed out the series of small openings, c, through the top of the furnace. Such a furnace allowed a high temperature to be obtained in a few minutes, and although the furnace body was good for only six or seven runs, it could be cheaply and quickly replaced. When a temperature of 900" C. or more had been reached, chlorine from the cylinder was passed through the wash bottle K containing concentrated sulfuric acid to indicate flow, and through a drying tower, G, connected to a safety trap, H . From the tower the chlorine passed into the quartz tube, E , where it mixed with the sulfur chloride coming from the dropping funnel, F. The tube E projected slightly into the high-temperature tube, C, where the heat caused rapid volatilization of the sulfur chloride. The uranium chloride formed in C was condensed in B. The sulfur dioxide, the excess of chlorine, and any undecomposed sulfur chloride passed into the trap A and thence to the hood. Using the apparatus fitted with tubes of the dimensions given, a t least a kilogram of the chloride could be prepared in an hour and a half.
calcium were placed in the alundum crucible, the crucible was put in the nichrome-wound reduction bomb. This was then placed in the vacuum chamber (Figure 3), which consisted of a steel cylinder approximately 18 inches high and 14 inches in diameter with a welded bottom and a flanged top to which the cover was tightly fitted by means of a gasket and bolts. The connections for electrically heating the bomb were led out through openings A , while the opening B was connected to two Hyvac pumps. I n order to watch the heating and to determine when the reduction took place, a thermocouple was introduced through the opening C. To prevent excess radiation an ignited asbestos lining, D, around
Reduction of Uranium Chloride by Calcium
About 400 grams of uranium chloride prepared in this manner were mixed with a 10 per cent excess of calcium shavings and placed in the reduction chamber (C, Figure 11. This was then placed in the vacuum chamber, and the reaction carried out in the manner described for the reduction of the oxide, the only difference being that the tube was kept in a vertical instead of a horizontal position. Upon opening the reduction chamber, it was seen that a violent action had taken place and the whole mass had fused and run to the bottom. A stream of cold water was allowed to run into the vessel until the slag of calcium chloride had been removed, when the uranium was left in the form of a fused mass. This was carefully detached and examined. The product was found to be much contaminated with iron from the walls of the chamber,
Figure 3
the sides and bottom and an asbestos disk, E , over the top of the bomb were used. After the cover had been bolted down, connections made, and a vacuum established, the heating current was turned on and the pyrometer readings were noted a t equal intervals. When the reduction took place a sharp increase in temperature was observed. After 12 to 24 hours the vessel was opened
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and a stream of water run into the crucible to remove the soluble slag. It was found that the uranium had fused into one mass, which was somewhat brittle and hard and not easily worked. A careful analysis made by the highly trained chemists of a reputable company gave the following results: Uranium Iron Carbon Oxygen
Silicon Calcium Aluminium
99.31 0.57 0.09 0.03
None None Trace
This analysis showed the presence of iron and carbon in objectionable quantities. An examination of the products used indicated that cab cium was the source of these impurities. Therefore, to elim-
Vol. 18, No. 2
inate these substances, the calcium was carefully sublimed before using. While the sublimed calcium itself gave practically no test for iron, the residue contained much iron and carbide. A similar reduction to the one last described was made using sublimed calcium, with the result that a mass of uranium weighing 1500 grams was obtained. I n general, the product resembled the first one except that the ingot possessed a convex surface, was very silvery, and clean, and showed fine crystalline markings. A careful determination showed the iron content to be less than 0.01 per cent. This same process has been applied with success to the preparation of zirconium, beryllium, and thorium, and plans are being made to test it on vanadium, hafnium, etc.
Effect of Sulfur in the Briquetting of Subbituminous Coal' By H. K. Benson, J. N. Borglin, and R. K. Rourke UNlVER5ITY
OF
WASHINGTON, SEATTLE, WASH.
MONG the subbituminous coals of the State of Washington are some that are more commonly designated as lignites owing to the property of "slacking" or disintegration by weathering. This characteristic has limited the commercial use of such coals and has stimulated experimental studies seeking modifications of structure tending toward greater permanency in form. I n this class is the coal mined at Tono, Washington. It is black in color, with a brown streak, is slightly banded in structure, and breaks with a conchoidal fracture. The proximate analysis of the coal is given in Table I.
A
Table I-Percentage
Composition of Tono Coal Laboratory sample Air-dry Pure coal air-dry Per cent Per cent Per cent
C A R SAMPLE'
As received Per cent Moisture 20.2 14.5 Volatiles 31.5 33.5 Fixed carbon 39.9 43.9 Ash 8.4 9.05 Sulfur 0.52 0.56 Nitrogen 1.06 1.14 B. t. U. 9280 9940 a U.S. Geol. Survey, Bull. 474, 75.
44:i) 56.0 0:?3 1.49 13,000
12.3 40.8 39.8 7.1 0.3 1.60 9650
I n a previous investigation2 it was found that the maximum yield of by-products was obtained upon distillation of a retort temperature of 380' C. Approximately 5.5 per cent of low-temperature tar, 54 per cent of solid residue, together with 4400 cubic feet of gas were obtained. The residual coal, aside from a slight silvery luster, was not changed in appearance. Its proximate analysis was as follows: Moisture Volatiles Fixed carbon Ash B. t. u.
Per cent 0.00
14.00
73.00
13.00
12,710
but its physical form was not more favorable for commercial purposes than that of the original coal. I n the present study an attempt was made in a preliminary way to modify the structure of Tono coal, so that its fuel values and its form and structure might alike enhance its commercial use. Attention was directed to the action of sulfur as a temporary intermediate agent in the coking of coal, and various mixtures of sulfur, asphaltic binder, and Tono coal were heated to 700'-950' C. for the purpose of forming a coke-like mass. Experimental The coal was ground to pass 20 mesh and then mixed with pulverized, crude sulfur in varying proportions. This mixture was then poured into molten asphalt obtained from a local briquetting plant, thoroughly stirred until a uniform plastic mass was obtained, and then compressed in a hydraulic press into briquets 3 cm. (1.25 inches) in diameter and 5 cm. (2 inches) long. The briquets were carbonized in cast-iron retorts for 8 hours at temperatures of 700" to 950" C . Some runs were allowed to cool in the retort while others were quenched with water.
Experiment I Run
Table 11-Sulfur and T o n o Coal Sulfur in Sulfur in mixture residue Per cent Per cent Temperatwe, 700' C.
1.95 4.75 8.52
9.10
REMARKS
3.57 6.80
The general effect of low-temperature distillation resulted in an increase of approximately one-third in heating value,
To ascertain the effect of the asphaltic binder, briquets containing 5, 10, 15, and 35 per cent, but no sulfur, were carbonized under the same conditions as above. The residue crumbled under pressure between the fingers.
1 Presented by H. K. Benson and J. N. Borglin before the joint session of the Division of Petroleum Chemistry and the Section of Gas and Fuel Chemistry a t the 70th Meeting of the American Chemical Society, Los Angeles, Calif., August 3 to 8, 1925. Benson and Davis, THISJOURNAL, 9, 946 (1917).
To ascertain the effect of briquetting, a batch was divided into two parts, one distilled unbriquetted and the other briquetted. (Table 111)
*
Experiment II
