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The preparation, crystal structures and some properties of californium oxysulfate and oxysulfide
J. inorg, nucl. Chem., 1974,Vol. 36, pp. 2023-2027. Pergamon Press. Printed in Great Britain
THE PREPARATION, CRYSTAL STRUCTURES AND SOME PROPERTIES OF CALIFORNIUM OXYSULFATE AND OXYSULFIDE* R. D. BAYBARZ,t J. A FAHEY:~ and R. G. HAIRE Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (Received 10 September 1973)
Abstract--Californium oxysulfate (Cf202804) has been prepared by calcination of Cf(lll)-loaded Dowcx resin beads or hydrated Cf2(SO4)3 in air at 700-800°C. At temperatures above 860°C, the oxysulfalc decomposed to the sesquioxide. Calcination of the hydrated californium sulfate or the californium oxysulfate salt in atmospheres containing hydrogen, or in vacuum, at 800°C produced the oxysulfide (Cf202S}. It was observed that the californium oxysulOde could be reoxidized to the oxysulfate by reheating the former product in air at 800°C. The decomposition of the oxysulfate and the oxysulfide to the sesquioxide by heating in air was found to be dependent on both the duration and the temperature of the calcination process. Examination of oxysulfate samples stored-at ambient temperatures as a function of time showed that self-irradiation initially causes a loss in crystallinity and subsequently a partial decomposition to the sesquioxide. Lattice parameters for the oxysulfate and oxysutfide were derived from X-ray data. The lattice constants for the orthorhombic oxysulfate are : a0 = 4.187 + 0-002/~, b o = 4.072 + 0.002 A and Co = 13-009 :_+_0-006A. The cell dimensions for the trigonal oxysulfide are: a o = 3.844 + 0.002 A and co 6-656 :_+ 0-004 A.
INTRODUCTION RF.SlN beads loaded with 249Cf(III) ions have been employed to study the Cf oxide system and to serve as intermediates for the subsequent synthesis of other Cf c o m p o u n d s [ l - 4 ] . Resin beads loaded with 252Cf have also been utilized in fabricating n e u t r o n sources[5]. By thermally d e c o m p o s i n g the Dowex-50-10aded resin beads (sulfonic acid type) in different atmospheres and at different temperatures, it is possible to prepare either the oxysulfate, the oxysulfide, or the sesquioxide of the metal cation. These c o m p o u n d s can also be formed by calcination of the hydrated metal sulfates. The particular products o b t a i n e d during the pyrolysis will depend on the atmosphere, temperature, a n d duration of the calcination process. This paper reports the p r e p a r a t i o n and characterization of the oxysulfate (Cf202SO4) and oxysulfide (Cf2O2S) of 249Cf. These products give additional
* Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. t A portion of this work was supported by the Alexander von Humboldt-Stiftung during the author's appointment at the European Institute for Transuranium Elements, Karlsruhe, West Germany. ++Present address: Bronx Community College, Bronx, New York.
evidence for the existence of two new series of actinide compounds, which are isostructural with the lanthanide compounds. The oxysulfides of plutonium[6] and the lanthanides[7] were characterized several years ago, but the oxysulfates of the lanthanides[8 101 and c u r i u m [ I l l have only recently been studied. For these two series of elements, all of the k n o w n oxysulfates exhibit an o r t h o r h o m b i c symmetry while the oxysulfides studied to date have trigonal symmetry at r o o m temperature.
EXPERIMENTAL Resin beads
The Dowex 50W-X4 resin beads were loaded to maximum uptake with 249Cf(1II) by placing the beads in a 0.1 M HCI solution of highly purified californium. The quantity of californium used was in excess of that calculated to fully load the beads. The size of the resin beads was selected such that the beads would contain 2-4/~g of californium when fully saturated. Techniques for purification of the californium have been described[5]. The purity of the californium used in this work was confirmed to be >_99.8 per cent by spark-source mass spectrometry. After being loaded, washed and dried, the resin beads were calcined in a platinum crucible in either air or 8 percent H 2 92 per cent N2 atmospheres, or in vacuum. On completion of the calcination process, the individual resin beads
2023
R. D. BAYBARZ,J. A. FAHEYand R. G. HAIRE
2024
were transferred to quartz capillaries; the capillaries were then evacuated and finally sealed. Resin beads containing Gd(lll) were also prepared by similar techniques. These beads were used for comparing their decomposition with that observed for the californium beads.
(o)Gd andCf hydrofed sulfo?es in oir. Cfz(S04)3
I20"/. " ~ ~ ~
~
Gdz(SO4~J ~ ~
Hydrated sulfate salts Hydrated samples of californium-249 sulfate were prepared from purified chloride solutions by fuming 1-mg quantities of the metal ion to dryness in a platinum crucible with 50-100#1 of Baker Ultex sulfuric acid. The resulting sulfate salt was taken up in 100-200 #1 of high-purity water and quantitatively transferred to a preweighed quartz cup. The solution was evaporated to dryness in the cup by a jet of argon at ambient temperature. The sample cup was then placed in position on a CAHN RG Electro-microthermobalance and purged with flowing argon until a constant weight had been obtained at room temperature. The samples were subsequently heated using a programmed heating rate of 2 deg/min in vacuum, 4 per cent H2-Ar, and air (flow rates approximately 30cm3/min). Temperature measurements were made using a Pt-10 per cent Pt-Rh thermocouple located 3 mm below the sample cup. Samples of hydrated gadolinium sulfate were prepared and thermally decomposed in a manner identical to that used for the californium salts. Decomposition of the gadolinium samples was studied for comparison with the de.composition of the californium samples.
X-ray analysis Examination of lanthanide products prepared by decomposing either resin beads containing a metal cation or the hydrated sulfate salts showed that comparable results were obtained from each type of material under the same experimental conditions. Because of the scarcity of the californium isotope, X-ray examination of the californium products was limited to those obtained via the resin bead technique. The samples were examined by X-ray powder diffraction techniques that have been previously described[3]. Line positions on the films were read by two independent observers and their results averaged. The lattice constants were refined by the LCR-2 program[12], and theoretical line intensities were calculated with the aid of the POWD program [ 13], with no corrections being made for absorption or thermal motion. The error limits reported are the standard deviation. RESULTS AND DISCUSSION
Californium oxysulfate The oxysulfate of 249Cf (Cf202SO4) was prepared by calcining either the hydrous sulfate of californium or resin beads loaded with californium, in air at 700800°C. F r o m the thermal decomposition curve of the hydrated californium salt (Fig. la), it can be seen that the anhydrous sulfate obtained during the calcination is stable in air to approximately 600°C before it decomposes to the oxysulfate. The oxysulfate begins to decompose to the sesquioxide at temperatures above 860°C in air. Since chemical analyses of the californium sulfate
Cfz03 Gd202SO4
( b }Gd ond Cf hydrated sulfotes in H2-Ar
~
~
cf2o2s
o
GdzOaS
.$ { c)Gd oxysulfote in H2-Ar
GOzO Sq , I0%
~ . (dl Gd oxysulfote in oir
Gd202S
Gd202sq,
110% GdzO2S 110% i 0
a
GdzO2S
i 200
i
i i i i 400 600 Te mperQture,
i 800 *C
i
i 1(300
,C~la03 1200
Fig. 1. Thermal decomposition of Gd and Cf compounds.
salts could not be performed, their decomposition was compared to the decomposition of 1-mg quantities of gadolinium sulfates prepared in an identical fashion. F r o m Fig. l(a), it can be seen that the califomium and gadolinium salts decompose in air in a similar manner, with the exception that the californium compounds are formed at slightly lower temperatures than the corresponding gadolinium products. The water of hydration for both the gadolinium and the californium salts was calculated from the weight losses, and the data indicated that the starting materials had empirical formulas of Cf2(SO4)3.12H20 and Gd2(SO4)3.12H20. The number of water molecules for the gadolinium preparation is higher than previously reported by Wendlandt, who found an octahydrate[14]. The difference is undoubtedly due to the method of preparation since, in Wendlandt's work, the sulfates were washed with alcohol and then air dried. Thus, in our preparations excess water was apparently retained by the starting material. F r o m these results it can be concluded that californium and gadolinium will form the same hydrate under a given set of conditions. The decomposition of Gd-loaded resin beads was examined so that it could be compared with the decomposition of the hydrous sulfate salt. The decomposition of the Gd-loaded resin beads was found to be very similar to that of Nd- and Cm-loaded resin beads[10, 11]. After the carbon matrix of the Gd-loaded
Californium oxysulfate and oxysulfide beads h a d been removed by calcination in air, the oxysulfate o b t a i n e d was identical to the oxysulfate that was formed by partially decomposing the hydrated sulfate salt in air. Since the decomposition processes are kinetically controlled, the reactions are dependent on b o t h the time a n d the temperature of the calcination process. X-ray examination of californium resin beads heated to 650°C in air indicated that the product was pred o m i n a n t l y the oxysulfate, but several additional lines were observed which were due to small a m o u n t s of residual a n h y d r o u s sulfate. Heating the samples to approximately 800°C in air for approximately 8 hr yielded a single, highly-crystalline oxysulfate product. However, samples heated for longer periods (24hr) under these conditions were partially decomposed to sesquioxide, a n d these samples contained several of the stronger b.c.c. Cf203diffraction lines in addition to the lines assigned to the o r t h o r h o m b i c oxysulfate structure. To completely convert the californium oxysulfate bead to the sesquioxide required several days under the above conditions; however, at temperatures above 1000°C, the decomposition was rapid. Analysis of X-ray data showed only the C f 2 0 3 diffraction lines for samples heated at 1000°C for several hours, or for samples calcined at 1150°C for 5 min. The o r t h o r h o m b i c lattice parameters for Cf oxysulfate determined from powder diffraction data are: a o = 4.187 + 0-002/~, b0 = 4.072 _ 0-002/~, a n d Co = 13-009 _+ 0.006/~. A line list and the indexing of one sample are given in Table 1. The calculated intensities were obtained by assigning only the atomic positions of californium, using coordinates of two californium atoms at (0,0, Z) where Z = +~, one californium a t o m at (½, ½, ½), and one californium atom at (0,0,0). These intensities agreed well with the experimental californium data. In addition, a calculation of intensities for the isostructural L a 2 0 2 S O 4 compound, using the same coordinates listed above for the l a n t h a n u m atoms, was in excellent agreement with our experimental data for La2OESO 4. Ballestracci et al.[8] have also reported t h a t the L a 2 0 2 S O 4 structure is o r t h o r h o m b i c . Several of the oxysulfate samples were examined as a function of time to ascertain the effects of damage due to self-irradiation. A similar investigation has been reported for curium oxysulfate[ll], in which it was observed that the samples exhibited a loss of crystallinity after approximately 3 days. The californium oxysulfate preparations were found to become amorphous after approximately 30 days as the result of self-irradiation; however, the oxysulfate structure could be restored by annealing at 500°C. After extended periods of time ( > 90 days), X-ray films made of the californium oxysulfate samples showed lines attributed to the b.c.c. Cf203 a n d indicated t h a t a radiationinduced decomposition of the oxysulfate h a d taken place. The lattice expansion or swelling of the californium oxysulfate due to self-irradiation was less p r o n o u n c e d t h a n was observed for the corresponding
2025
Table 1. Line list and indexing for orthorhombic C f 2 0 2 S Q 20 h . 0 1 0 1 0 1 1 1 1 0 2 0 2 2 1 1 2 1 2 1 2 2 1 3 1 2 2 1 3 2 1 4 2 4 3 4
Intensity
k
1 Observed Calculated* Observedt Calculated:~ . . . . . . . . . . . . . . . . 0 2 13.62 13.62 M 18.9 0 1 22.22 22.30 W 12-5 1 1 22-82 22.88 W 11.8 0 3 29.64 29.66 S 100.0 1 3 30.24 30.10 S96.3 1 0 30.64 30.62 S92-1 1 2 33-64 33.64 w 90 0 5 40-84 40.84 F 2.7 1 4 41.56 5.2 0 6 41-64 41.64 W 20.5 0 0 43.24 43.22 F+ 18.5 2 0 44.64 44.50 W17.0 0 2 45.44 45.52 T 2.6 1 1 49.46 49.46 T 3,2 2 1 50.46 50.32 T 3.4 1 6 52.46 52.58 M 42.3 I 3 53.66 53-56 M 40.0 2 3 54.46 54.38 M 38-3 0 6 61-46 61-58 F 13.2 2 5 62.06 61.96 T 2.9 2 0 63-86 63.76 F 11.9 2 2 65.48 65.54 T 3-5 0 9 68.68 68.70 W19.3 I 0 71.28 71.46 F 8.7 3 0 73.28 73.32 F 8.1 2 6 79.08 79.08 F 13.5 1 9 85.10 84.94 F 11.6 2 9 85.70 85.60 F 11.4 2 3 87.70 87.72 F 10.9 3 3 88.70 88.82 T 10.7 I 12 98-50 98.66 T 9.4 1 3 102.72 102-68 F t).3 0 12 106.52 106.40 T 4.6 0 6 109.72 109.74 T 4.6 3 4 111.52 111-56 T 3-4 ! 7 120.14 120.04 T ~.6
* Calculated using a 0 = 4.1869 A, b 0 = 4.0723 A and % = 13.0095 A, with 2(~} = 1.54178 A. +Estimated relative intensities on the basis of strong (S), medium [M), weak (W), faint (F) and trace {T). ++Calculated using the POWD intensity program scaled so that the 103 line had 1 = 100, with no temperature or absorption corrections. Based on orthorhombic synlmetry using the metal positions as noted in the paper curium c o m p o u n d [ l l], due to the lower specific activity of the 2a'9Cf isotope as c o m p a r e d with that of 244Cm.
Californium oxysulfide Californium oxysulfide was obtained by thermally decomposing the hydrated californium sulfate salt or californium oxysulfate in H2-containing atmospheres or in v a c u u m (1 x l0 -6 ram). The decomposition of gadolinium and californium hydrated sulfates in 4 per cent H 2 - A r atmospheres is s h o w n in Fig. l(b). The decomposition curves obtained in v a c u u m were very
R. D. BAYBARZ,J. A. FAHEYand R. G. HAIRE
2026
similar to those obtained in H 2 - A r atmospheres. F r o m the figure it can be seen that the above decompositions differ from the decompositions in air in that the sulfate is reduced to the oxysulfide in essentially a single step which occurs at a lower temperature. The oxysulfides show no further decomposition up to the maximum temperature used in the experiments. Calcination of californium oxysulfate derived from the resin beads in either 8 per cent H2-N2 atmospheres or in vacuum provided samples of californium oxy-
Table 2. Line list and hexagonal indexing for Cf202S 20
Intensity
h k
l Observed Calculated* Observedt Calculated:~
1 0 1 1 1 1 1 2 1 0 2 2 1 1 2 0 2 1 2 1 2 2 3 2 1 3 0 3 2 3 2 3 2 l 3 3 1 4 2 4 3 1
0 2 0 2 0 1 3 0 2 4 1 2 4 3 3 5 0 4 1 5 2 4 1 3 5 2 6 0 2 4 6 1 5 7 3 5 7 1 7 2 4 8
0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 0 I 1 1 0 1 0 0 1 I 0 1 1 2 0 0 1 1 0 1 0 1 0 0 0 1 0
26.82 30.04 38.24 47-32 49.24 55.06 56.86 62.46 63.86 70.88 75-48 77.08 81.88 89.60 94.30 113.32 114.90 129-74 137.90 145.50
26-78 26.78 30.02 38.24 47.30 49.36 49.36 55-18 55.18 55.20 57.04 62.38 62.40 64.10 70.76 70.78 75.58 75-58 77.16 77.18 81.84 81.86 89.56 89.56 89.58 94.18 94.20 113.24 113.24 113.24 113.26 114.94 114-94 114-94 129-52 129.52 129.52 138.00 138-06 145.44 145.46 145-52
W S W M W W WF+ F T T W F F T F F T T T
21-2 21.9 100.0 30.9 27.8 1.9 22.3 3-1 19.2 1.4 17.5 7.7 10.6 11.2 7-1 1.7 2-5 3-5 15.8 4-1 7-6 5.3 0.4 8.2 6-2 5.1 6.0 1.5 4.8 2.2 5.7 10-0 5-3 1.4 8.7 6.6 8.7 7.1 2-3 4.9 13.6 8-8
* Calculated using a 0 = 3-8436/~ and co = 6.6557/~, with 2(~) = 1.54178,~. t Estimated relative intensities on the basis of strong (S), medium (M), weak (W), faint (F) and trace (T). :~Calculated using the POWD intensity program scaled such that the 101 line had I = 100, with no temperature or absorption corrections. Based on the trigonal space group P3m using the atomic position listed in the text.
sulfide for X-ray analysis. To obtain good diffraction patterns of californium oxysulfide, the oxysulfate beads were heated 6-8 hr at 800°C in 8 per cent H 2 - N 2 or in vacuum. Examination of oxysulfate samples heated for shorter periods indicated that the reduction to the oxysulfide proceeded more rapidly in the 8 per cent H2-N2 atmospheres than in vacuum. Analysis of the X-ray data showed that the californium oxysulfide had a trigonal structure, based on the analogy with the reported lanthanide oxysulfides[7]. The lattice parameters for californium oxysulfide are: ao = 3.844 + 0.002 A and c o = 6.656 + 0.004 A. A line list and the indexing are given in Table 2. The line intensities were calculated for the P'Jm space group with two californium atoms at +(13, 23, 0.28), one sulfur atom at (0, 0, 0), and two oxygen atoms at _+(~3,I, 0.64). These assignments gave calculated intensities which agreed with the observed intensities. During the course of this work it was observed that californium oxysulfide could be reoxidized to the oxysulfate by reheating the former product in air up to 800°C, and at the expense of losing some of the sulfur content. Heating californium oxysulfide beads under these conditions gave a product which X-ray analysis showed to be californium oxysulfate along with a significant amount of Cf203. When this material was treated through a second reduction-oxidation cycle in 8 per cent H2-N2 and then air at 900°C, the resulting product gave only a b.c.c. Cf203 diffraction pattern. This behavior is in accord with the decomposition curve for californium oxysulfate shown in Fig. l(a), where the oxysulfate decomposition to the oxide is shown to begin at approximately 860°C. The lattice parameter for the b.c.c. Cf20 3 product obtained after heating the oxysulfide in air at 900°C was 10.808 + 0.003 A, which is characteristic of slightly-oxidized Cf20313 ]. Subsequent treatment of this oxide with 8 per cent H 2 - N z yielded a Cf20 3 p r o d u c t having a lattice parameter of 10.829 __+ 0-003A. The two oxide lattice parameters are in accord with previously determined parameters for the sesquioxide[3] and indicate that no appreciable quantity of sulfur remained in the sample. The interconversion of gadolinium oxysulfide-oxysulfate products by using oxidizing and reducing atmospheres was examined in the thermobalance. The oxysulfate of gadolinium was first prepared by heating the hydrated sulfate salt in air at 850°C for approximately 3 hr. After being cooled to room temperature, the oxysulfate was reduced to the oxysulfide by heating in a 4 per cent H 2 - A r atmosphere (Fig. lc). The resulting oxysulfide was cooled to room temperature and then reheated in air to 1200°C. During this reheating step, the oxysulfide was oxidized to the oxysulfate, with the latter decomposing to the sesquioxide at higher temperatures (Fig. ld). It appears that these reactions and their products could be controlled by careful attention to experimental conditions. It was found that the temperature observed for the reduction of G d oxysulfate to the oxysulfide was very similar to that for
Californium oxysulfate and oxysulfide the oxidation of Gd oxysulfide to oxysulfate. Thus, in the oxidation of californium oxysulfide beads in air, as discussed above, it is possible that lower temperatures (approximately 650°C) may have prevented the formation of Cf203.
2027
AC Th PO U Np ~ AmCrn BI( Cf Es FmMdNo Lw
M202S04
Cell volumes o f the oxysulfides and oxysulfates
In a recent paper, Hale and Moseley[l 1] derived an empirical equation relating the volume of the lanthanide oxysulfate cell to the radius of the trivalent metal ion. Applying their equation to the measured cell volume of C f 2 0 2 S 0 4 , one derives a value of 0.942A for the radius of Cf 3+. This value is identical to that obtained from the b.c.c. Cf203[15]. This fact, along with the lattice parameters, axial ratios, cell volume, and observed intensities, indicates that Cf202SO,, is isostructural with the lanthanide oxysulfates. A comparison of the samarium oxysulfide X-ray data reported by Eick[7] with our X-ray data for californium oxysulfide and the agreement of the calculated and observed diffraction lines and intensities indicates that californium oxysulfide is isostructural with the lanthanide oxysulfide series. The cell w)lumes of the lanthanide and kno~n actinide oxysulfates and oxysulfides are plotted in Fig. 2. The figure suggests the existence of two new series of compounds for the actinides. Unfortunately, only the oxysulfates for c u r i u m [ I l l and californium and the oxysulfides for plutonium[6] and californium are known at the present time, but it appears likely that both compounds exist for the other trivalent transplutonium elements• Experimental work is presently being done to prepare these compounds for the missing actinide members. The results of this work will be published in a subsequent paper. Ackmm'ledgements The helpful suggestions ofJ. G. White. Fordham University, and the computer time provided b', Fordham University are gratefully acknowledged by J. A. Fahey.
REFERENCES
I. J. L. Green and B. B. Cunningham, lnorg, nut~. Chem. Lett. 3, 343 (1967). 2..I.C. Copeland and B. B. Cunninghan3, J. im,'g, m.'l. Chcnl. 31. 733 (1969). 3. R. D. Baybarz, R. G. tlaire and J. A. Fahe~, J. mote. nut/. Chem. 34, 557 ( 19721.
J 210
IOOF
~J
••,"
75~
- - L_anthandle .... Achnides LIO Ce Pr Nd Pm SmEu Gld T ~ D y ~ _ E r L~ T
Y~ Lu......
Fig. 2. Cell volumes of the lanthanide and known aclinide oxysulfates and oxysulfides.
4. J. R. Peterson and R. D. Baybarz. ln,r~ m,/. (hem. Len. 8, 423 (1972). 5. R. D. Baybarz, J. B. Knauer and P. B. Orr, USAE(" Rep. ORNL-467L 1973. 6. W. H. Zachariasen, Acta crystallogr. 2, 60 (1949). 7. H. A. Eick, J. Am. chem. Soc. 80, 43 (1958). 8. R. Ballestracci and J. Mareschal. ,~latcr R~'~ Bull 2, 993 (1967). 9. M. W. Nathansand W. W. Wcndlandt..l m,,rm m./. ('hem. 24. 869 (1962). 10. W. H. ttale. Jr., J. morg. m./. Chcnt. 33• 1227 I t9711 11. W. H. tlale, Jr. and W. C. Mosley. ,/. nzor~,,, m . / . (']mm. 35, 165 (1973). 12. D. E. Williams, Ames Lab. Rcp. IS-1(152, It)64 13. D. K. Smith, Univ•Calif. Lawrence Radiat l.ab, Rep, UCRL-7196, 1963. 14. W. W. Wendlandt, J. inorg, mwt. Chem. 7.51 ~1958i. 15. R. G. ttaire and R. D. Baybarz, J, im,'e, m~/. ('hem. 35. 489 (1973).
THE PREPARATION, CRYSTAL STRUCTURES AND SOME PROPERTIES OF CALIFORNIUM OXYSULFATE AND OXYSULFIDE* R. D. BAYBARZ,t J. A FAHEY:~ and R. G. HAIRE Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (Received 10 September 1973)
Abstract--Californium oxysulfate (Cf202804) has been prepared by calcination of Cf(lll)-loaded Dowcx resin beads or hydrated Cf2(SO4)3 in air at 700-800°C. At temperatures above 860°C, the oxysulfalc decomposed to the sesquioxide. Calcination of the hydrated californium sulfate or the californium oxysulfate salt in atmospheres containing hydrogen, or in vacuum, at 800°C produced the oxysulfide (Cf202S}. It was observed that the californium oxysulOde could be reoxidized to the oxysulfate by reheating the former product in air at 800°C. The decomposition of the oxysulfate and the oxysulfide to the sesquioxide by heating in air was found to be dependent on both the duration and the temperature of the calcination process. Examination of oxysulfate samples stored-at ambient temperatures as a function of time showed that self-irradiation initially causes a loss in crystallinity and subsequently a partial decomposition to the sesquioxide. Lattice parameters for the oxysulfate and oxysutfide were derived from X-ray data. The lattice constants for the orthorhombic oxysulfate are : a0 = 4.187 + 0-002/~, b o = 4.072 + 0.002 A and Co = 13-009 :_+_0-006A. The cell dimensions for the trigonal oxysulfide are: a o = 3.844 + 0.002 A and co 6-656 :_+ 0-004 A.
INTRODUCTION RF.SlN beads loaded with 249Cf(III) ions have been employed to study the Cf oxide system and to serve as intermediates for the subsequent synthesis of other Cf c o m p o u n d s [ l - 4 ] . Resin beads loaded with 252Cf have also been utilized in fabricating n e u t r o n sources[5]. By thermally d e c o m p o s i n g the Dowex-50-10aded resin beads (sulfonic acid type) in different atmospheres and at different temperatures, it is possible to prepare either the oxysulfate, the oxysulfide, or the sesquioxide of the metal cation. These c o m p o u n d s can also be formed by calcination of the hydrated metal sulfates. The particular products o b t a i n e d during the pyrolysis will depend on the atmosphere, temperature, a n d duration of the calcination process. This paper reports the p r e p a r a t i o n and characterization of the oxysulfate (Cf202SO4) and oxysulfide (Cf2O2S) of 249Cf. These products give additional
* Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. t A portion of this work was supported by the Alexander von Humboldt-Stiftung during the author's appointment at the European Institute for Transuranium Elements, Karlsruhe, West Germany. ++Present address: Bronx Community College, Bronx, New York.
evidence for the existence of two new series of actinide compounds, which are isostructural with the lanthanide compounds. The oxysulfides of plutonium[6] and the lanthanides[7] were characterized several years ago, but the oxysulfates of the lanthanides[8 101 and c u r i u m [ I l l have only recently been studied. For these two series of elements, all of the k n o w n oxysulfates exhibit an o r t h o r h o m b i c symmetry while the oxysulfides studied to date have trigonal symmetry at r o o m temperature.
EXPERIMENTAL Resin beads
The Dowex 50W-X4 resin beads were loaded to maximum uptake with 249Cf(1II) by placing the beads in a 0.1 M HCI solution of highly purified californium. The quantity of californium used was in excess of that calculated to fully load the beads. The size of the resin beads was selected such that the beads would contain 2-4/~g of californium when fully saturated. Techniques for purification of the californium have been described[5]. The purity of the californium used in this work was confirmed to be >_99.8 per cent by spark-source mass spectrometry. After being loaded, washed and dried, the resin beads were calcined in a platinum crucible in either air or 8 percent H 2 92 per cent N2 atmospheres, or in vacuum. On completion of the calcination process, the individual resin beads
2023
R. D. BAYBARZ,J. A. FAHEYand R. G. HAIRE
2024
were transferred to quartz capillaries; the capillaries were then evacuated and finally sealed. Resin beads containing Gd(lll) were also prepared by similar techniques. These beads were used for comparing their decomposition with that observed for the californium beads.
(o)Gd andCf hydrofed sulfo?es in oir. Cfz(S04)3
I20"/. " ~ ~ ~
~
Gdz(SO4~J ~ ~
Hydrated sulfate salts Hydrated samples of californium-249 sulfate were prepared from purified chloride solutions by fuming 1-mg quantities of the metal ion to dryness in a platinum crucible with 50-100#1 of Baker Ultex sulfuric acid. The resulting sulfate salt was taken up in 100-200 #1 of high-purity water and quantitatively transferred to a preweighed quartz cup. The solution was evaporated to dryness in the cup by a jet of argon at ambient temperature. The sample cup was then placed in position on a CAHN RG Electro-microthermobalance and purged with flowing argon until a constant weight had been obtained at room temperature. The samples were subsequently heated using a programmed heating rate of 2 deg/min in vacuum, 4 per cent H2-Ar, and air (flow rates approximately 30cm3/min). Temperature measurements were made using a Pt-10 per cent Pt-Rh thermocouple located 3 mm below the sample cup. Samples of hydrated gadolinium sulfate were prepared and thermally decomposed in a manner identical to that used for the californium salts. Decomposition of the gadolinium samples was studied for comparison with the de.composition of the californium samples.
X-ray analysis Examination of lanthanide products prepared by decomposing either resin beads containing a metal cation or the hydrated sulfate salts showed that comparable results were obtained from each type of material under the same experimental conditions. Because of the scarcity of the californium isotope, X-ray examination of the californium products was limited to those obtained via the resin bead technique. The samples were examined by X-ray powder diffraction techniques that have been previously described[3]. Line positions on the films were read by two independent observers and their results averaged. The lattice constants were refined by the LCR-2 program[12], and theoretical line intensities were calculated with the aid of the POWD program [ 13], with no corrections being made for absorption or thermal motion. The error limits reported are the standard deviation. RESULTS AND DISCUSSION
Californium oxysulfate The oxysulfate of 249Cf (Cf202SO4) was prepared by calcining either the hydrous sulfate of californium or resin beads loaded with californium, in air at 700800°C. F r o m the thermal decomposition curve of the hydrated californium salt (Fig. la), it can be seen that the anhydrous sulfate obtained during the calcination is stable in air to approximately 600°C before it decomposes to the oxysulfate. The oxysulfate begins to decompose to the sesquioxide at temperatures above 860°C in air. Since chemical analyses of the californium sulfate
Cfz03 Gd202SO4
( b }Gd ond Cf hydrated sulfotes in H2-Ar
~
~
cf2o2s
o
GdzOaS
.$ { c)Gd oxysulfote in H2-Ar
GOzO Sq , I0%
~ . (dl Gd oxysulfote in oir
Gd202S
Gd202sq,
110% GdzO2S 110% i 0
a
GdzO2S
i 200
i
i i i i 400 600 Te mperQture,
i 800 *C
i
i 1(300
,C~la03 1200
Fig. 1. Thermal decomposition of Gd and Cf compounds.
salts could not be performed, their decomposition was compared to the decomposition of 1-mg quantities of gadolinium sulfates prepared in an identical fashion. F r o m Fig. l(a), it can be seen that the califomium and gadolinium salts decompose in air in a similar manner, with the exception that the californium compounds are formed at slightly lower temperatures than the corresponding gadolinium products. The water of hydration for both the gadolinium and the californium salts was calculated from the weight losses, and the data indicated that the starting materials had empirical formulas of Cf2(SO4)3.12H20 and Gd2(SO4)3.12H20. The number of water molecules for the gadolinium preparation is higher than previously reported by Wendlandt, who found an octahydrate[14]. The difference is undoubtedly due to the method of preparation since, in Wendlandt's work, the sulfates were washed with alcohol and then air dried. Thus, in our preparations excess water was apparently retained by the starting material. F r o m these results it can be concluded that californium and gadolinium will form the same hydrate under a given set of conditions. The decomposition of Gd-loaded resin beads was examined so that it could be compared with the decomposition of the hydrous sulfate salt. The decomposition of the Gd-loaded resin beads was found to be very similar to that of Nd- and Cm-loaded resin beads[10, 11]. After the carbon matrix of the Gd-loaded
Californium oxysulfate and oxysulfide beads h a d been removed by calcination in air, the oxysulfate o b t a i n e d was identical to the oxysulfate that was formed by partially decomposing the hydrated sulfate salt in air. Since the decomposition processes are kinetically controlled, the reactions are dependent on b o t h the time a n d the temperature of the calcination process. X-ray examination of californium resin beads heated to 650°C in air indicated that the product was pred o m i n a n t l y the oxysulfate, but several additional lines were observed which were due to small a m o u n t s of residual a n h y d r o u s sulfate. Heating the samples to approximately 800°C in air for approximately 8 hr yielded a single, highly-crystalline oxysulfate product. However, samples heated for longer periods (24hr) under these conditions were partially decomposed to sesquioxide, a n d these samples contained several of the stronger b.c.c. Cf203diffraction lines in addition to the lines assigned to the o r t h o r h o m b i c oxysulfate structure. To completely convert the californium oxysulfate bead to the sesquioxide required several days under the above conditions; however, at temperatures above 1000°C, the decomposition was rapid. Analysis of X-ray data showed only the C f 2 0 3 diffraction lines for samples heated at 1000°C for several hours, or for samples calcined at 1150°C for 5 min. The o r t h o r h o m b i c lattice parameters for Cf oxysulfate determined from powder diffraction data are: a o = 4.187 + 0-002/~, b0 = 4.072 _ 0-002/~, a n d Co = 13-009 _+ 0.006/~. A line list and the indexing of one sample are given in Table 1. The calculated intensities were obtained by assigning only the atomic positions of californium, using coordinates of two californium atoms at (0,0, Z) where Z = +~, one californium a t o m at (½, ½, ½), and one californium atom at (0,0,0). These intensities agreed well with the experimental californium data. In addition, a calculation of intensities for the isostructural L a 2 0 2 S O 4 compound, using the same coordinates listed above for the l a n t h a n u m atoms, was in excellent agreement with our experimental data for La2OESO 4. Ballestracci et al.[8] have also reported t h a t the L a 2 0 2 S O 4 structure is o r t h o r h o m b i c . Several of the oxysulfate samples were examined as a function of time to ascertain the effects of damage due to self-irradiation. A similar investigation has been reported for curium oxysulfate[ll], in which it was observed that the samples exhibited a loss of crystallinity after approximately 3 days. The californium oxysulfate preparations were found to become amorphous after approximately 30 days as the result of self-irradiation; however, the oxysulfate structure could be restored by annealing at 500°C. After extended periods of time ( > 90 days), X-ray films made of the californium oxysulfate samples showed lines attributed to the b.c.c. Cf203 a n d indicated t h a t a radiationinduced decomposition of the oxysulfate h a d taken place. The lattice expansion or swelling of the californium oxysulfate due to self-irradiation was less p r o n o u n c e d t h a n was observed for the corresponding
2025
Table 1. Line list and indexing for orthorhombic C f 2 0 2 S Q 20 h . 0 1 0 1 0 1 1 1 1 0 2 0 2 2 1 1 2 1 2 1 2 2 1 3 1 2 2 1 3 2 1 4 2 4 3 4
Intensity
k
1 Observed Calculated* Observedt Calculated:~ . . . . . . . . . . . . . . . . 0 2 13.62 13.62 M 18.9 0 1 22.22 22.30 W 12-5 1 1 22-82 22.88 W 11.8 0 3 29.64 29.66 S 100.0 1 3 30.24 30.10 S96.3 1 0 30.64 30.62 S92-1 1 2 33-64 33.64 w 90 0 5 40-84 40.84 F 2.7 1 4 41.56 5.2 0 6 41-64 41.64 W 20.5 0 0 43.24 43.22 F+ 18.5 2 0 44.64 44.50 W17.0 0 2 45.44 45.52 T 2.6 1 1 49.46 49.46 T 3,2 2 1 50.46 50.32 T 3.4 1 6 52.46 52.58 M 42.3 I 3 53.66 53-56 M 40.0 2 3 54.46 54.38 M 38-3 0 6 61-46 61-58 F 13.2 2 5 62.06 61.96 T 2.9 2 0 63-86 63.76 F 11.9 2 2 65.48 65.54 T 3-5 0 9 68.68 68.70 W19.3 I 0 71.28 71.46 F 8.7 3 0 73.28 73.32 F 8.1 2 6 79.08 79.08 F 13.5 1 9 85.10 84.94 F 11.6 2 9 85.70 85.60 F 11.4 2 3 87.70 87.72 F 10.9 3 3 88.70 88.82 T 10.7 I 12 98-50 98.66 T 9.4 1 3 102.72 102-68 F t).3 0 12 106.52 106.40 T 4.6 0 6 109.72 109.74 T 4.6 3 4 111.52 111-56 T 3-4 ! 7 120.14 120.04 T ~.6
* Calculated using a 0 = 4.1869 A, b 0 = 4.0723 A and % = 13.0095 A, with 2(~} = 1.54178 A. +Estimated relative intensities on the basis of strong (S), medium [M), weak (W), faint (F) and trace {T). ++Calculated using the POWD intensity program scaled so that the 103 line had 1 = 100, with no temperature or absorption corrections. Based on orthorhombic synlmetry using the metal positions as noted in the paper curium c o m p o u n d [ l l], due to the lower specific activity of the 2a'9Cf isotope as c o m p a r e d with that of 244Cm.
Californium oxysulfide Californium oxysulfide was obtained by thermally decomposing the hydrated californium sulfate salt or californium oxysulfate in H2-containing atmospheres or in v a c u u m (1 x l0 -6 ram). The decomposition of gadolinium and californium hydrated sulfates in 4 per cent H 2 - A r atmospheres is s h o w n in Fig. l(b). The decomposition curves obtained in v a c u u m were very
R. D. BAYBARZ,J. A. FAHEYand R. G. HAIRE
2026
similar to those obtained in H 2 - A r atmospheres. F r o m the figure it can be seen that the above decompositions differ from the decompositions in air in that the sulfate is reduced to the oxysulfide in essentially a single step which occurs at a lower temperature. The oxysulfides show no further decomposition up to the maximum temperature used in the experiments. Calcination of californium oxysulfate derived from the resin beads in either 8 per cent H2-N2 atmospheres or in vacuum provided samples of californium oxy-
Table 2. Line list and hexagonal indexing for Cf202S 20
Intensity
h k
l Observed Calculated* Observedt Calculated:~
1 0 1 1 1 1 1 2 1 0 2 2 1 1 2 0 2 1 2 1 2 2 3 2 1 3 0 3 2 3 2 3 2 l 3 3 1 4 2 4 3 1
0 2 0 2 0 1 3 0 2 4 1 2 4 3 3 5 0 4 1 5 2 4 1 3 5 2 6 0 2 4 6 1 5 7 3 5 7 1 7 2 4 8
0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 0 I 1 1 0 1 0 0 1 I 0 1 1 2 0 0 1 1 0 1 0 1 0 0 0 1 0
26.82 30.04 38.24 47-32 49.24 55.06 56.86 62.46 63.86 70.88 75-48 77.08 81.88 89.60 94.30 113.32 114.90 129-74 137.90 145.50
26-78 26.78 30.02 38.24 47.30 49.36 49.36 55-18 55.18 55.20 57.04 62.38 62.40 64.10 70.76 70.78 75.58 75-58 77.16 77.18 81.84 81.86 89.56 89.56 89.58 94.18 94.20 113.24 113.24 113.24 113.26 114.94 114-94 114-94 129-52 129.52 129.52 138.00 138-06 145.44 145.46 145-52
W S W M W W WF+ F T T W F F T F F T T T
21-2 21.9 100.0 30.9 27.8 1.9 22.3 3-1 19.2 1.4 17.5 7.7 10.6 11.2 7-1 1.7 2-5 3-5 15.8 4-1 7-6 5.3 0.4 8.2 6-2 5.1 6.0 1.5 4.8 2.2 5.7 10-0 5-3 1.4 8.7 6.6 8.7 7.1 2-3 4.9 13.6 8-8
* Calculated using a 0 = 3-8436/~ and co = 6.6557/~, with 2(~) = 1.54178,~. t Estimated relative intensities on the basis of strong (S), medium (M), weak (W), faint (F) and trace (T). :~Calculated using the POWD intensity program scaled such that the 101 line had I = 100, with no temperature or absorption corrections. Based on the trigonal space group P3m using the atomic position listed in the text.
sulfide for X-ray analysis. To obtain good diffraction patterns of californium oxysulfide, the oxysulfate beads were heated 6-8 hr at 800°C in 8 per cent H 2 - N 2 or in vacuum. Examination of oxysulfate samples heated for shorter periods indicated that the reduction to the oxysulfide proceeded more rapidly in the 8 per cent H2-N2 atmospheres than in vacuum. Analysis of the X-ray data showed that the californium oxysulfide had a trigonal structure, based on the analogy with the reported lanthanide oxysulfides[7]. The lattice parameters for californium oxysulfide are: ao = 3.844 + 0.002 A and c o = 6.656 + 0.004 A. A line list and the indexing are given in Table 2. The line intensities were calculated for the P'Jm space group with two californium atoms at +(13, 23, 0.28), one sulfur atom at (0, 0, 0), and two oxygen atoms at _+(~3,I, 0.64). These assignments gave calculated intensities which agreed with the observed intensities. During the course of this work it was observed that californium oxysulfide could be reoxidized to the oxysulfate by reheating the former product in air up to 800°C, and at the expense of losing some of the sulfur content. Heating californium oxysulfide beads under these conditions gave a product which X-ray analysis showed to be californium oxysulfate along with a significant amount of Cf203. When this material was treated through a second reduction-oxidation cycle in 8 per cent H2-N2 and then air at 900°C, the resulting product gave only a b.c.c. Cf203 diffraction pattern. This behavior is in accord with the decomposition curve for californium oxysulfate shown in Fig. l(a), where the oxysulfate decomposition to the oxide is shown to begin at approximately 860°C. The lattice parameter for the b.c.c. Cf20 3 product obtained after heating the oxysulfide in air at 900°C was 10.808 + 0.003 A, which is characteristic of slightly-oxidized Cf20313 ]. Subsequent treatment of this oxide with 8 per cent H 2 - N z yielded a Cf20 3 p r o d u c t having a lattice parameter of 10.829 __+ 0-003A. The two oxide lattice parameters are in accord with previously determined parameters for the sesquioxide[3] and indicate that no appreciable quantity of sulfur remained in the sample. The interconversion of gadolinium oxysulfide-oxysulfate products by using oxidizing and reducing atmospheres was examined in the thermobalance. The oxysulfate of gadolinium was first prepared by heating the hydrated sulfate salt in air at 850°C for approximately 3 hr. After being cooled to room temperature, the oxysulfate was reduced to the oxysulfide by heating in a 4 per cent H 2 - A r atmosphere (Fig. lc). The resulting oxysulfide was cooled to room temperature and then reheated in air to 1200°C. During this reheating step, the oxysulfide was oxidized to the oxysulfate, with the latter decomposing to the sesquioxide at higher temperatures (Fig. ld). It appears that these reactions and their products could be controlled by careful attention to experimental conditions. It was found that the temperature observed for the reduction of G d oxysulfate to the oxysulfide was very similar to that for
Californium oxysulfate and oxysulfide the oxidation of Gd oxysulfide to oxysulfate. Thus, in the oxidation of californium oxysulfide beads in air, as discussed above, it is possible that lower temperatures (approximately 650°C) may have prevented the formation of Cf203.
2027
AC Th PO U Np ~ AmCrn BI( Cf Es FmMdNo Lw
M202S04
Cell volumes o f the oxysulfides and oxysulfates
In a recent paper, Hale and Moseley[l 1] derived an empirical equation relating the volume of the lanthanide oxysulfate cell to the radius of the trivalent metal ion. Applying their equation to the measured cell volume of C f 2 0 2 S 0 4 , one derives a value of 0.942A for the radius of Cf 3+. This value is identical to that obtained from the b.c.c. Cf203[15]. This fact, along with the lattice parameters, axial ratios, cell volume, and observed intensities, indicates that Cf202SO,, is isostructural with the lanthanide oxysulfates. A comparison of the samarium oxysulfide X-ray data reported by Eick[7] with our X-ray data for californium oxysulfide and the agreement of the calculated and observed diffraction lines and intensities indicates that californium oxysulfide is isostructural with the lanthanide oxysulfide series. The cell w)lumes of the lanthanide and kno~n actinide oxysulfates and oxysulfides are plotted in Fig. 2. The figure suggests the existence of two new series of compounds for the actinides. Unfortunately, only the oxysulfates for c u r i u m [ I l l and californium and the oxysulfides for plutonium[6] and californium are known at the present time, but it appears likely that both compounds exist for the other trivalent transplutonium elements• Experimental work is presently being done to prepare these compounds for the missing actinide members. The results of this work will be published in a subsequent paper. Ackmm'ledgements The helpful suggestions ofJ. G. White. Fordham University, and the computer time provided b', Fordham University are gratefully acknowledged by J. A. Fahey.
REFERENCES
I. J. L. Green and B. B. Cunningham, lnorg, nut~. Chem. Lett. 3, 343 (1967). 2..I.C. Copeland and B. B. Cunninghan3, J. im,'g, m.'l. Chcnl. 31. 733 (1969). 3. R. D. Baybarz, R. G. tlaire and J. A. Fahe~, J. mote. nut/. Chem. 34, 557 ( 19721.
J 210
IOOF
~J
••,"
75~
- - L_anthandle .... Achnides LIO Ce Pr Nd Pm SmEu Gld T ~ D y ~ _ E r L~ T
Y~ Lu......
Fig. 2. Cell volumes of the lanthanide and known aclinide oxysulfates and oxysulfides.
4. J. R. Peterson and R. D. Baybarz. ln,r~ m,/. (hem. Len. 8, 423 (1972). 5. R. D. Baybarz, J. B. Knauer and P. B. Orr, USAE(" Rep. ORNL-467L 1973. 6. W. H. Zachariasen, Acta crystallogr. 2, 60 (1949). 7. H. A. Eick, J. Am. chem. Soc. 80, 43 (1958). 8. R. Ballestracci and J. Mareschal. ,~latcr R~'~ Bull 2, 993 (1967). 9. M. W. Nathansand W. W. Wcndlandt..l m,,rm m./. ('hem. 24. 869 (1962). 10. W. H. ttale. Jr., J. morg. m./. Chcnt. 33• 1227 I t9711 11. W. H. tlale, Jr. and W. C. Mosley. ,/. nzor~,,, m . / . (']mm. 35, 165 (1973). 12. D. E. Williams, Ames Lab. Rcp. IS-1(152, It)64 13. D. K. Smith, Univ•Calif. Lawrence Radiat l.ab, Rep, UCRL-7196, 1963. 14. W. W. Wendlandt, J. inorg, mwt. Chem. 7.51 ~1958i. 15. R. G. ttaire and R. D. Baybarz, J, im,'e, m~/. ('hem. 35. 489 (1973).