Barium polyuranates

Barium polyuranates

J. lnorg. Nucl. Chem., 1964, Vol. 26, pp. 1847 to 1851. Pergamon Press Ltd. Printed in Northern Ireland BARIUM POLYURANATES J. G. ALLPRESS Division o...

232KB Sizes 3 Downloads 16 Views

J. lnorg. Nucl. Chem., 1964, Vol. 26, pp. 1847 to 1851. Pergamon Press Ltd. Printed in Northern Ireland

BARIUM POLYURANATES J. G. ALLPRESS Division of Tribophysics, Commonwealth Scientific and Industrial Research Organization, University of Melbourne (Received 1 April 1964) Abstract--The compounds Ba2U3Oll and BaU207 have been prepared by solid state reactions of U~O8 with BaCI2 and BaUO4. The X-ray powder data, infra-red spectra and thermal stability of these compounds are reported. Both compounds are also formed, together with a possible new form of UOa, during the decomposition of barium uranyl acetate. OF the phases which occur in the Ba ' r - U v l - O system, only BaUO4 IlI a n d Ba3UO6 ¢2) are well characterized. Attempts to prepare Ba2UO 5 have n o t been successful, ¢3~ a n d the existence of u r a n i u m - r i c h phases is in doubt. Thus HOEKSTRA and KATZC4) failed to o b t a i n a single phase B a U 2 0 v by d e c o m p o s i n g b a r i u m u r a n y l acetate, but more recent R u s s i a n work ¢'~) indicates that BaUzO 7 does exist, a n d that a phase of variable c o m p o s i t i o n BaO(2 - - x)UO~, x = 0.2-0.5 is also stable. This note describes an a t t e m p t to prepare a n d identify the stable phases with atomic p r o p o r t i o n s B a / U < 1. Identification of phases Ten mixtures of barium chloride (A.R. grade) and UaOs (from pure uranyl acetate or nitrate, by ignition) having atomic proportions Ba/U ranging from 0'36 to 1'00 were prepared by weighing and grinding. These mixtures were reacted in the solid state by heating in air at 900°C for six weeks, and were removed and reground several times during this period. The products varied in colour from pure yellow at Ba/U = 1 through orange to dirty brown at Ba/U == 0.36. The coloured phases were all soluble in dilute hydrochloric acid, indicating that they contained uranium in the fully oxidized hexavalent state. A black, insoluble residue (later found to be UaOs) was present in some cases, but its amount was only significant for the preparations where Ba/U was less than 0.5. A portion of the diffraction pattern of each product was recorded with a Phillips PWl051 diffractometer. A comparison of these data indicated that two new phases, as well as BaUO4 and U3Os, could be recognized. Their characteristic X-ray reflexions were strongest at the compositions Ba]U =. 0.63-0.69 and at Ba/U = 0.50, indicating that the two phases were probably Ba2U30~, and BaU20¢, where the composition is derived from the Ba/U ratio and the valency of uranium. To confirm these compositions, the following reactions were carried out at 900°C. 6BaUO4 ÷ U3Os 3BaUO4 + U~Oa

air

air

> 3Ba2UaO,~ > 3BaUdOT.

The products were substantially pure, but each contained small amounts (estimated from the X-ray data to be <5 per cent) of the other and of either BaUO4 or UaOs. This is probably a result of the ~ S. SAMSONand L. G. SILL~N,Arkiv. Kemi Mineral. Geol. A 25, No. 21 (1947). ,2~ W. RODORrVand F. PFITZER,I . Naturforsch. 9 b, 568 (1954). ea~J. O. SAWYER,J. lnorff. Nuel. Chem. 25, 899 (1963). ~4~H. R. HOEKSTRAand J. J. KATZ,J. Amer. Chem. Soc. 74, 1683 (1952). (51 E. A . IPPOLITOVA, YU. P. SIMANOV, L. M . KOVBA, G . P. POLONINA a n d I. A . BEREZNIKOVA, Radiokhimiya 1,660 (1959). 1847

1848

J . G . ALLPRESS

difficulty of obtaining a complete reaction in the solid state, and it introduces a slight uncertainty as to the exact composition of these phases. There was no evidence of any phase with Ba/U < 0'5. All mixtures in this range of composition produced BaU207 and UzOs when heated. Thus the existence of the compound BaO(2 -}- x)UO3 tS~ where x = 0'2-0"5, is not confirmed.

Properties of Ba2UzOal and B a U 2 0 7. Physical appearance. Ba2UaOal is a bright orange microcrystalline powder. B a U 2 0 7 is a mustard yellow microcrystalline powder. X-ray data (CuK~ radiation). B a 2 U a O u - - t h e relevant data are given in Table 1. TABLE 1.--POWDER DIFFRACTION DATA FOR

Ba2UaOll

Intensity

sin 2 0 × lOobs

36 19 5 4 3 100 27 88 4 12 7 4 4 6 5 18 19

135 155 361 398 441 543 559 588 714 766 820 894 903 1153 1427 1581 1713

* The reflexions, particularly those of low intensity, were poorly defined. B a U 2 0 7 - - t h e data for this c o m p o u n d (Table 2) have been successfully interpreted in terms o f a tetragonal unit cell, whose dimensions are a = 7.128 ± 0.005 A, c : 11"95 ± 0"01 A. The reflexions are limited to those for which h + k + l : 2n, indicating that the unit cell is body-centred. The density, measured pycnometrically, was 7.2 40.2 g cm -3 and does not agree well with the calculated value o f 7.93 g cm -3 for Z = 4. Discrepancies o f similar magnitude have been observed for other uranates/3"0~ Thermalstability. Ba2U30 n darkens in colour on heating in air, but apart from this it appears to be stable up to at least 1500°C. The c o l o u r change is similar to, but not as p r o n o u n c e d as, that observed on heating calcium uranate, CaUOa, where it is accompanied by a loss o f oxygen. ~7~ B a U 2 0 7 also apparently loses oxygen on heating, and changes colour from yellow t h r o u g h orange to b r o w n as the temperature is raised. A t 1100-1200°C, it teJ L. M. KOVBA,E. A. IPPOLITOVA,YU. P. SIMANOVand V. I. SFITSYN,Dokl. Akad. Nauk S.S.S.R. 120, 1042 (1958). tT~j. S. Ar,rDERSON,Bull. Soc. Chim. 20, 781 (1953).

Barium polyuranates

1849

decomposes rapidly into two phases which were identified by X-ray diffraction as Ba2U3Ola and UaOs, i.e. 2BaU207 ll°°°c Ba2UaO1, + 1U308. air

Infra-red spectra. The infra-red spectra of these compounds, as well as that of BaUO4, were recorded with a Perkin Elmer Model 112 spectrophotometer, using the TABLE 2.--POWDER D I F F R A C T I O N D A T A a = 7"128 :k 0"005/~, c = 11 '95

Intensity

sin ~ 0 × 104obs

hkl

35 12 5 52 90 100 15 5 9 5 11 14 4 12 19 30 4 2 14 4 16 3

158.9 400.7 468-1 491.0 629-0 635-2 665-5 935.0 958-6 1095 1134 1158 1335 1426 1562 1601 1625 1733 1870 1892 1969 2034

101 112 200 103 211 202 004 220 213 301 204 105 312 303 321 224 215 116 400 323 206 411 402 305 413 422 404 325 217 316 008

6 9 20 6 2 9 7

2094 2364 2510 2537 2559 2624 2666

BaU207 0"01 ,~,

FOR

4 sin s 0 × 10ealo

158-6 400.3 467-9 491.4 626.5 634-3 665.6 935'8 959-3 1094 1134 1157 1336 1427 1562 1601 1625 1732 1872 1895 1966 2031 2038 2093 2363 2506 2537 2561 2623 2667 2662

potassium chloride disc method (s) of sample preparation. The region from 3000 to 700 cm. -1 was scanned, and the absorptions were found only below 1000 cm.- 1. The results are given in Table 3 and Fig. 1. No attempt has been made to analyse the spectra in detail, but it is very likely that the absorptions in this region arise from the vibrations of uranyl groups. The asymmetric stretching frequency of the uranyl group in most uranyl salts lies in the range 850-1000 cm -1, and the symmetric stretching frequency occurs at 800-900 c m - 1 . (9) Both these vibrations are likely to be modified considerably in the uranates, where there may be strong interactions with vibrations of (~) U. SCHIEDT a n d H. RrIEINWEIN, Z. Naturforsch. 7 b, 270 (1952). (9) L. H. JONES, Spectrochimiea Acta 10, 395 (1958). 6

1850

J . G . ALLPRESS TABLE 3.--INFRA-RED SPECTRA Compound

Absorptions (cm- t )

BaUO4 Ba~UaOll BaU207 (UO3)*

772 830 765 929

s s s s

729 s 760 s vb

684 s

853 m

802 s

753 s

s, strong m, medium vb, very broad * Spectrum extracted from that of a mixture with Ba2UsOll (Fig. ld). The frequency 753 cm -t may be in error for this reason.

the other oxygen atoms close to the uranium atom. Apart from the question of the interpretation of these spectra, they provide a convenient means of identification, and are included in this report for this reason.

The decomposition of barium uranyl acetate HOEKSTRA and K A T Z (4) attempted to prepare BaU20 r by igniting the double acetate at 700°C. This experiment was repeated here, and also extended to higher temperatures. The double acetate Ba(UO2)2(OCOCHa)n-2H20 was prepared (4) by crystallization from a hot solution of uranyl acetate and barium acetate in 6M acetic acid. Ignition of this compound at temperatures between 500 and 700°C gave an orange product of overall composition B a U 2 0 7. The loss of weight on ignition was 32.02 per cent, compared with an expected loss of 32.05 per cent for decomposition to BaUzO 7. The X-ray diffraction pattern of the product showed that it was a mixture of Ba~U3Oll and a second unknown phase. BaU207 began to appear together with these two phases after ignition at 800°C. When the double acetate was heated briefly at 900-1000°C, a black component appeared, and the mixture consisted

(b)

r I

I

i

I

i

I

Cc)

1000

900

800

I000 700 FREQUENCY CM: I

900

800

700

FIG. 1.--Infra-red spectra (a) (b) (c) (d)

BaUO4 Ba2U3Oll BaU2Or Product of ignition of Ba(UO2)2(OCOCHz)6"2H20 at 700°C.

Barium polyuranates

1851

Of Ba2U3011 and U 3 0 s, together with a small a m o u n t o f B a U 2 0 7. Thus it is very probable that the u n k n o w n orange phase in the p r o d u c t of the 800°C ignition is a tbrm of UO a. The X-ray diffraction pattern of this c o m p o u n d (Table 4) consisted o f poorly defined reflexions, and was unlike that o f e-UO3, (~°1 v-UO3 I1~1 or rS-UO~. 1'21 lts infra-red spectrum (Table 3, Fig. 1) did not correspond to reported TABLE 4.--POWDER DIFFRACTION DATA FOR A POSSIBLE NEW FORM OF U O 3 EXTRACTED FROM DATA FOR THE MIXTURE OF B a o U 3 0 ~ @ U O 3

Intensity

sin 2 0 × 10~b~*

41 32 7 7 95 82 100 38 13 14 10 21 17 vb 19 10 13

127 329 405 435 503 511 637 657 1005 1022 1496 1539 1620-1680 2015 2O43 2073

* The reflexions were broad, hence the accuracy of these values is limited. spectra o f any form of UO3, (13'14) while its remarkable stability is also in contrast to the k n o w n forms of U O 3, which all decompose well below 800°C. Prolonged ignition o f the double acetate at 900°C eventually p r o d u c e d a g o o d sample of B a U 2 0 7 which was almost completely free of Ba2U30 n and U3Os, p r o b a b l y because of the very favourable conditions inherent in the use o f a decomposition reaction. The barium and uranium ions in the double acetate are evenly distributed at the atomic level, and the diffusion problems attending the earlier solid-solid reactions are greatly reduced. The decomposition reaction can be summarized as follows: 2Ba(UO2)2(OCOCHa)d2 H20

500-800~C

fast gIIO

Ba2U30 n + UO3

~}O(l°(" ~low

I

~100_1000oC

I



fast

B a U 2 0 7 .+-=----:~°°°c Ba2U301, + 1UzOs slow Acknowledgement--Part of this work was carried out in the Chemistry Department of the University of Melbourne, during the tenure of a C.S.I.R.O. post-graduate studentship.

(10) W. H. ZACHARIASEN,Acta Cryst. 1,265 (1948). ~1~ R. ENGMANNand P. M. de WOLFF,Acta Cryst. 16, 993 (1963). ~ E. WAIT,J. hwrg. Nucl. Chem. 1, 309 (1955). (lal H. R. HOEKSTRAand S. SIEGEL,J. Inorg. Nucl. Chem. 18, 154 (1961). ~1~ M. TsuBoi, M. TERADAand T. SHIMANOUCH~,J. Chem. Phys. 36, 1301 (1962).