UNITED STATES PATENT of FICE 2,477,924 METHOD of PREPARING URANUM TROXDE Sherman M

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Patented Aug. 2, 1949 2,477,924 UNITED STATES PATENT of FICE 2,477,924 METHOD OF PREPARING URANUM TROXDE Sherman M. Fried, Chicago, Ill., and Norman R. Davidson, Sierra Madre, Calif., assignors to the United States of America, as represented by the United States Atomic Energy Commission No Drawing. Application January 15, 1948, Serial No. 2,558 4 Claims. (C. 23-4.5) 2 This invention relates to the preparation of heating at temperatures between 450-750° C. in oxides of uranium in crystalline form, and more the presence of oxygen under a pressure varying particularly relates to the preparation of higher from 20-150 atmospheres. " . Oxides of uranium from lower oxides of uranium. In a further embodiment of this invention a The crystalline oxides of uranium and espe lower oxide of uranium, such as uranyl uranate cially the crystalline trioxide of uranium are (U3O8) in either amorphous or crystalline form compounds particularly well suited to processes is converted to the higher oxide (UO3) in Crystal for the production of uranium pentachloride. line form by heating within the same tempera Since preparation of uranium trioxide by a proc ture range and subjecting to oxygen under the eSS Such as the thermal decomposition of hydrat 10 same pressure conditions as previously set forth eduranyl peroxide usually produces uranium tri herein. It is apparent from the data listed in Oxide in an amorphous form, a process for the the table that the time required for conversion of production of crystalline uranium trioxide is par uranyl uranate (U3O3) to the higher oxide (UO3) ticularly advantageous. varies from 12-112 hours depending upon the It is thus an object of this invention to pro 5 pressures and temperatures to which the system wide a method whereby an amorphous oxide of is subjected. uranium can be converted to crystalline form. In a further embodiment of this invention the It is a further object of this invention to pro crystalline form of uranium oxide is prepared wide a method whereby a lower oxide of uranium more rapidly by treating an amorphous uranium can be converted to a higher oxide. 20 oxide with oxygen under superatmospheric pres A further object of this invention is to provide sures ranging between 60-150 atmospheres at a a method whereby a lower oxide of uranium in temperature from 700-750° C. for periods as short the amorphous phase can be converted to a as 1A-2 hours. It is apparent from the data set higher oxide in the crystalline form. forth hereafter that the temperatures and pres . Other objects and advantages will become ap 25 sures necessary for conversion of the amorphous parent upon further examination of this specifi oxide and the lower oxide to the higher oxide in cation. crystalline form vary directly with each other In accordance with the process of this inven and inversely with the duration of treatment of tion an amorphous oxide of uranium is convert the starting material. This is further illustrated ed to uranium oxide in crystalline form by sub 30 by the reaction wherein uranyl uranate (U3O8) is jecting the amorphous uranium oxide to superat converted to the hexagonal uranium trioxide InoSpheric pressures of Oxygen at an elevated (UO3) in 100% yield by treatment of either the temperature. The amorphous oxide of uranium amorphous or crystalline uranyl uranate (U3O8) is heated at temperatures between 450-750° C. With oxygen under a pressure from 60-150 at under Oxygen pressures varying from 20-150 at 35 mospheres at a temperature from 700-750° C. for mospheres. The crystalline product thus formed periods as short as 1%-2 hours. is characterized by its color as well as the crystal The temperature and pressure conditions used lattice constants and crystalline form. in Several experiments, wherein amorphous ox In One embodiment of this invention amor ides of uranium are converted to crystalline phous uranium trioxide (UO3) is converted to 40 uranium trioxide, are set forth in the following the crystalline form of the same compound by table. -

Formula of Formula of Substance Oxygen Phases Present in prod product Calc'd product Calc'd treated Tep. y Pressure Time uct (by X-ray Analysis) from Oxygen fron Ignition Uptake to U3O8

Aim. Hrs. 28 12 hexag------aum ------500 28 36 hexag.phase II------

28 30 3: ...... 30 530-560 30 700 150 750 70 a The UO3 was prepared by heating UO4.2HO to 400° C. b. UO3 actually lost 0.254% in weight under these conditions, probably because of moisture or oxides of nitrogen present in the original compound. If this weight loss is assumed to be due to moisture, the calculated composition of the starting material was UO3.O.4EO. q. The packing density of this material was measured as 3.88. 2,477,924 3 4. In the above table, the substance referred to Referred to the larger cell, the positions of as “phase II' is described as having a red color the uranium atoms become: which is identified as a hydrated form of uranium trioxide and is less stable than that phase identi 2U in (0 00) (A. A 0) fied as phase III, which is a yellow crystalline 5 4U in c (0% 0), h (A 60) material having the same lattice dimensions and - ..It has been observed that there is a strong hexagonal crystal structure as set forth herein similarity between the X-ray diffraction pattern for anhydrous uranium trioxide. obtained for the crystalline uranyl uranate, The apparatus for heating uranium oxides U3O8, and the crystalline trioxide. under Superatmospheric pressures of oxygen lo The U3O8-structure is obtained from the UO3 consists of a heavy-walled glass tube (I.D. 4 mm., . structure by means of slight changes. This is O. D. 12 mm.) to which a short length of 1 mm. shown by referring the UO3-structure to Ortho capillary is sealed. The tube is attached to a hexagonal axes and choosing the a2 axis three vacuum apparatus and pure dry Oxygen is con times longer than required. The cell so obtained densed in the small capillary to a measured has dimensions: length which determines the pressure in the a1=6.86 A. bomb when it is sealed off at the proper point. a2=11.89 A. The pressures quoted in the various experiments - aga-4.16 A. were calculated from the measured length of and the coordinates for the uranium atoms are liquid oxygen, assuming that the gas obeyed the exactly the same as given for U3O8 above. The perfect gas laws even at high pressures. AS a . oxygen positions in the two structures must be safety precaution the glass bomb was placed in very similar also, the important difference being side a steel jacket fitted with plugs and the entire that there are no uranyl oxygens at (0 0 /2) assembly was heated in a tube furnace. (A. A. A.) in the U3O8 structure so that the Annealed Pyrex bombs could usually withstand uranium atoms at (0 00) (42 A. 0) are to be re pressures of 30 atmospheres at 500° C. For ex garded as U+4 atoms. periments at higher pressures and temperatures The examples following are illustrative for the quartz bombs were used. A quartz bomb of 3 mm. process of this invention but are not to be con strued as a limitation upon the appended claims. I. D. and 10 mm. O. D. withstood 70 atmospheres 30 oxygen pressure at 750. C., while a quartz cap ExAMPLE I illary bomb 1 mm. I. D. and 10 mm. O. D. with A sample of amorphous uranium trioxide stood a pressure of 150 atmospheres at 700° C. (UO3), prepared by the thermal (at 350 to 400 The identification of the uranium trioxide pro C.) decomposition of hydrated uranyl peroxide, duced by the process of this invention is based 35 (UO4.2H2O), was heated from 450 to 500° C. for on the observed color and the X-ray diffraction 12 hours in 28 atmospheres of oxygen distilled pattern. - - from liquid oxygen. The amorphous uranium Uranium trioxide- is hexagonal. The unit cell trioxide, which was originally colored bright contains one molecule and has the lattice dimen orange became somewhat paler after this treat sions: 4) ment, and X-ray examination of the product a1=3.963+.004 A. showed that the crystal structure was hexagonal a 3-4,160.008 A. and the lattice dimensions were the same as those listed previously for crystalline uranium The calculated density is p=8.34. trioxide (UO3). The Space group is C3m and the atomic posi 45 EXAMPLE II tions are: 1. U in (0 0 0), 1. Or in (0.0 A), 2 Orr . . A sample of uranyl uranate that had been in - (4 % u) with ua-0.17. ignited in air at 800° C. was treated with oxygen ... Each uranium atom is bonded to two oxygens - at a pressure of 28 atmospheres for 36 hours at of the first kind with U-OI=2.08 A, and to six 500° C. The color of the solid changed from Oxygens of the second kind with U-OII-2.39 A. 50 black to deep red and X-ray analysis of the prod ... The OI-atoms should be regarded as uranyl uct indicated the presence of two phases: namely oxygens, although there are no (UO2) +2 groups hexagonal uranium trioxide (phase I) which is - in the structure. Instead there are endless isomorphous with the form obtained in Example 'uranyl chains'-O-U-Or-U-O-U- along I, and a new phase (phase II), which is colored the as axis. 55 red. The formula of the hexagonal product The uranyl uranate is orthorhombic with lat formed (phase I), as calculated from the weight tice dimensions as follows: difference measured with reference to the uptake of oxygen, is UO2.97. - - d1-670 A second sample of uranyl uranate (U3O8) was d2=3.98. 60 heated for a total of 112 hours at a temperature a3=4.14 between 530 and 560° C. with oxygen at a pres sure of 30 atmospheres. The product consisted - and two uranium atoms per cell at (0 0 0) of two phases visible to the naked eye which (%. 20). Since there are 5% oxygens in this could be separated mechanically. One phase cell and weak lines were observed in long ex 65 was colored yellow and gave a pattern identical - posire patterns, we have concluded that the true with that of uranium trioxide prepared by the unit cell of uranyl uranate is more accurately ignition of the hydrated uranyl nitrate, - represented by a tripling of the a2 axis. The true. unit cell thus contains six uranium atoms and 16 Oxygen atoms, and the lattice constants are as 70 The formula of the product, as calculated from the oxygen uptake, is UO2.997. follows: - - - A 0.07267 g. sample of this product was ignited a=6.70 at 900.C. and thus converted to uranyl uranate d2=11.94 (0.07136 g.). The formula of the product formed a3=4.14 75 by the oxidation of uranyl uranate was calcu 2,477,924 5 6 lated from the weight loss (0.00131 g. equivalent oxygen at 1 atmosphere pressure at 650-675 C. to 1.804%) on ignition, to be UO2.2991. the weight loss was 0.06% and there was no A sample of uranyl uranate heated at 700° C. change in appearance. Upon ignition in air at for two hours with oxygen at a pressure of 150 850 C., the weight loss was 1.67% and the prod atmospheres produced uranium trioxide in the uct was uranyl uranate. The Sample consisted yellow crystalline phase (III). of 87% of the anhydrous yellow uranium trioxide after treatment at 650-675 C. EXAMPLE III The foregoing descriptions comprise the pre Uranyl uranate heated to 750° C. for one ferred embodiments of this invention. However, and one-half hours in the presence of 62-70 at O many alternations and changes may be made mospheres of oxygen likewise formed the yellow therein without departing from the spirit and crystalline phase, whose formula, as calculated scope of this invention as set forth in the ap from the oxygen uptake, Was determined as pended claims, which are intended to cover as UO2.993 and, as calculated by the ignition to broadly as possible in view of the prior art, all uranyl uranate, was UO3.01. In all cases where 5 features of novelty taken singly and/or in com uranyl uranate is ignited in oxygen at high pres bination. Sures to form uranium trioxide the Crystal struc What is claimed is: ture of the product is that of anhydrous uranium 1. A process for the preparation of uranium trioxide rather than that of a hydrate. trioxide in crystalline form, comprising heating The yellow crystalline phase of uranium tri an amorphous oxide of uranium at a temperature oxide (phase III) is stable for several hours in the 20 between 450-750 C. in the presence of between presence of 1 atmosphere oxygen at 700° C. but 20-150 atmospheres pressure of oxygen. at 800° C. is decomposed to uranyl uranate in 2. A process for the preparation of a crystal contrast to the amorphous uranium trioxide line uranium oxide, comprising heating uranyl which decomposes to UO2.959 at 620 C. and to uranate at a temperature between 450-750° C. UO2.82 at 625-630 C. 25 in contact with oxygen, said oxygen being pres The X-ray diffraction patterns for UO2.959 and ent at pressures between 20-150 atmospheres. UO2.82 are both identical having the following lat 3. A process for the preparation of a crystal tice dimensions: line uranium oxide, comprising heating uranyl uranate at a temperature between 700-750° C. diss6.90+0.02 A. 30 in contact with oxygen, said oxygen being under a2=3.910.02 A. a pressure between 60-150 atmospheres. a3=4.15-0.02 A. 4. A process for the preparation of crystal EXAMPLE IV line uranium trioxide, comprising heating amor Ignition of (hydrated) uranium trioacide 35 pholls uranium trioxide at a temperature be tWeen 450-750° C. in contact with between 2n A brick red colored sample of uranium trioxide 150 atmospheres pressure of oxygen. having a bulk density of 4.5 was heated at 600° C. for one-half hour with oxygen at One atmos SHERMAN M. FRIED. phere pressure. The sample decreased in weight NORMAN R. DAVIDSON. by 0.92% and microScopic examination revealed 40 the presence of two phases, one yellow and the REFERENCES CREO other dark green. The phases could be partially The following references are of record in the Separated by mechanical method and were re file of this patent: Spectively identified by X-ray analysis as ura Hopkins, Chapters in the Chemistry of the Less nium trioxide and uranyl uranate, the former 45 Familiar Elements, vol. II, chap. 18, Uranium, being isomorphous with the hexagonal uranium pages 11 and 12. Pub. in 1940 by Stipes Pub trioxide. On heating the brick red sample in lishing Co., Chicago, Illinois.