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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
-.
..
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. --
-
......
...
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.
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-
This paper was submitted for publication
in the open literature at least 6 months
prior to the issuance date of this Micro-
card. Since the U.S.A.E.C. has no evi-
dence that it has been published, the pa-
per is being distributed in Microcard
form as a preprint.
-
-
-
-
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LEGAL NOTICE
This report was prepared as an account of
Government sponsored work. Neither the
United States, nor the Commission, nor any
person acting on behalf of the Commission:
A. Makes any warranty or representa-
tion, expressed or implied, with respect to
the accuracy, completeness, or usefulness
of the information contained in this report,
or that the use of any information, appa-
ratus, method, or process disclosed in this
report may not infringe privately owned
rights; or
B. Assumes any liabilities with respect
to the use of, or for damages resulting from
the use of any information, apparatus,
method, or process disclosed in this report.
As used in the above, “person acting on
behalf of the Commission” includes any em-
ployee or contractor of the Commission, or
employee of such contractor, to the extent
that such employee or contractor of the
Commission, or employee of such contractor
prepares, disseminates, or provides access
to, any information pursuant to his employ-
ment or contract with the Commission, o
his employment with such contractor.
.:.,::in
.
.
s.
.
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.
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ORNI P 491
DTIE-P
KILPASY" FOR D E
V
Z 5.1-CE35TFISA:
į OCT 8 1999
Contribution from the
MASTER
Chemistry Division, Oak Ridge National Laboratory
pistoolid
and the
Department of Chemistry, University of Tennessee
....NOF-FOR PUBLIC RELEASE - OFFICIA
...DISTRIBUTION' MAY BE MADE OFFICIAL
REQUESTS. MAYBEL FILLEORETIS
SOME FLUORINE COMPOUNDS OF RHENIUM CONTAINS NOTHING OF PATENT, INTEREST
...PROCEDURES ON.FILE IN RECEIVING.COM
AND TECHNETIUM 2
... SECTION.
..
.
I
ori
Miil.
.................en sen1.*'."
:(1) Research sponsored by the U. S. Atomic Energy Commission
under contract with the Union Carbide Corporation.
(2) A more detailed account of this work is given in a thesis by
David E. LaValle submitted in partial fulfillment of the
requirements of the degree of Master of Science, University of
Tennessee, December, 1963.
By D. E. LaValle, R. M. Steele, and Wm. T. Smith Jr.
ABSTRACT
The compound potassium hexafluororhenate(IV),
KąReFo, previously reported to exist in several forms,
was prepared in its pure state and was characterized.
form as a preprint.
per is being distributed in Microcard
dence that it has been published, the pa-
card. Since the U.S.A.E.C. has no evi-
prior to the issuance date of this Micro-
in the open Literature at least
This paper was submitted for publication
honths

шор Рохо плод и реда са
The corresponding technetium compound, K2TcF6, was
I.
w
wie
A
B. f
C
potnately owned shta; or
of way laformation,
inem, or Mapy
daembonetes, or mobile scouto, my normation pe
A. Maka mynuty or top
wel wploys or outractor of the Content, or aylyn o mal outractor paper,
nd be the mone, "parte acting a ball of the Count
ployee or contractor of the Commission, or employen et much contractor, to the extent that
alay batarration, apparatu, method, or pracow discloved in the repat.
any liabilities with soupect to the w
with me contract.
• tacy, completeness, a watains of the ta formation cound te this report, or that the we
menta, method, or process declined to the report may not intring
Hamo, mor the Coualor, or my person sety a bola de Cotostat:
u
tation, pruund or implied, vid repect to the accu-
pley
of, or for dengue rosing from the
" tached
i '
er omtrent
- -
also prepared. The new compound rhenium nitrogen
LEGAL NOTICE -
.
fluoride, ReNF, and also a possible technetium analog:
were obtained. A method was developed for the
.
-
..
..
.
.
..
раа ч зах им рамото
preparation of previously known but not well characterized r
rhenium tetrafluoride, ReF4; some properties of the
.
.
..
..
.......
compound were determined.
...
.
.
..
Since Puff and Kwasnik
reported the preparation of potassium
(3) O. Ruff and W. Kwasnik, 2. Anorg. Allgem. Chem., 212, 65(1934).
. -
.
.
-..
.
hexafluororhenate(IV), KaReF6, as a green compound, uncertainty .
has existed as to the color of the pure form of this substance.
Feacock* described it as a white compound, and Weise as a substance
.
.
in
.
(4) R. D. Peacock, Chem. Ind. (London), 1453(1955).
(5) E. Weise, 2. Anorg. Allgem Chem., 283, 377(1956).
existing in both a white and a pink form.
The present study was an attempt to eliminate this ambiguity
and to prepare the technetium analog, KąReFg. From the potassium
complexes the corresponding ammonium compounds were to be prepared.
*.
-
.
-
-
and decomposed thermally to yield lower fluorides of rhenium and
-
...
-
.
..
technetium. Alternatively, the reduction of rhenium hexafluoride
.
.
..
was to be investigated as a means of producing lower fluorides of
...
rhenium.
.
;'
,
N
RESULTS
=
N
A
Potassium Hexafluororhenate(IV).-Ruff and Kwasnik reported
that the green salt K ReFo was the product of a preparation in an
YRYm
other halogen complexes. 6 17 18 Peacocks reported his white salt as
(6) E. Enk, Bel., 4, 791(1931).
(7) F. Krause and H. Steinfeld, Ibid., 64, 7952(1931),
(8) H. V. A. Briscoe, P. L. Robinson, and A. I. Rudge, J. Chem. Soc.,
3218(1931).
rin
-
(9) R. D. Peacock, Ibid., 1291(1956).
WANTv
'
'
"
.
-3-
the product of ihe fusion of ammonium he:calodorhenate(IV), (NH4)2Reis,
in potassium bifluoride, KHF2, at 250°.
Numerous attempts in this laboratory to produce the green and
white forms of the complex by the methods described were unavailing.
Variations of the fusion method, such as protection of the melts by
inert gas, adiition of gaseous hydrogen fluoride during fusion,
rigorous predrying of the KHF2 by electrolysis, and extractions of
the melts with water, acids, or anhydrous methanol in a Soxhlet
extractor under inert gas, failed to produce anticipated results.
Whenever KaReFe was obtained, it was the pirik form described by
Weise.
Weises reported obtaining the white salt both by treating the
pink form with gaseous HF at 450° for prolonged periods and by
recrystallizing the pink form from 40% HF. These transfornations
could not be duplicated in our laboratory. Instead, it was found
that treatment with HF (gaseous or aqueous) Jestroys the compound,
the products depending on whether air is available to the reactants
or is excluded. From dilute HF (up to 5%), pink K Refo recrystallizes
unchanged. In stronger solutions of HF the color of the solution
changes to yellow, green, and finally black. The product isolated
from the yellow solution was indicated by X-ray diffraction analysis
to be 90 to 95% K ReFg and the remaining 5 to 10% to be an unknown
phase. The green solution yielded a product that consisted of about
90% K2ReFe, some KRe04, and an unknown phase; the black solution
yielded a product. composed about equally of these three constituents.
However, when a solution (pink) of KaReFg in 40% HF was evaporated to
-4-
dryness in an inert atmosphere, the end product was a black substance
whose X-ray pattern was that of K ReF8 plus some additional lines.
When gaseous HF was passed over pink KeReFg for 10 br., an olive-drab
product was obtained that did not change color under six additional
hours of treatment. The X-ray pattern showed lines characteristic
of K2ReFo and some additional lines.
The action of HF was best illustrated by an experiment made by
means of a modification of the fusion method. A mixture of potassium
perrhenate, KRe04, (2 8.) and potassium iodide, KI, (7 8.) was added
to molten KHF2 (40 g.). NO apparent reaction occurred, even when the
mixture was heated to 800°. However, when the melt was cooled and
5 ml of water was added, followed by reheating, iodine was evolved.
25
After extraction of the cooled flux with water and the usual
purification procedure (see Experimental), pink KąReFo was obtained.
However, when the experiment was repeated with the sole change of
adding 5 ml of 48% HF instead of water, a slight initial reaction
occurred which soon ceased; the product ultimately extracted from
the flux was predominantly KRe04.
Best results for the preparation of pure K ReFo (pink) were
obtained by fusing either the corresponding chloro or bromo complex
in KHF2 and gradually raising the temperature to 700°. Elemental
analysis of the resultant pink salt indicated 20.7% K (calcd., 20.7%),
49.5% Re (calcd., 49.2%), 30.1% F (calcd., 30.1%). The tetragonal
unit cell of parameters a = 5.86 Å and 9 = 4.60 Å is in accord with
the X-ray data of Peacock and of Weise.5 Infrared analysis of
the solid material gave no evidence of hydroxyl groups, which had
been suggested as a possible source of the pink color. -
.
r
.
-5-
The rate of hydrolysis of K ReF8 as measured on a Cary
spectrophotometer by following the increase of perrhenate ion in
solution was 0.17 and 6.2%/day at 25° and 60°, respectively. The
solubility of the salt in water(25°) is about 28/100 ml.
Potassium Ilexafluorotechnetate (IV).-Potassium hexafluorotech-
netate(IV), K2TcFe, was prepared by fusion of the corresponding :
chloro complex and is comparable with the compound described by
Schwochau and Herr;10 the unit cell was tetragonal,and the
(10) K. Schwochau and W. Herr, Angew. Chem., 75, 95 (1963).
parameters were a = 5.18 Å and = 4.64 Å . It is pale lavender
and its solubility (25) is about 1.5 g./100 ml. The rate of
hydrolysis is 0.015 and 1.6%/day at 25° and 60, respectively.
Rhenium Nitrogen Fluoride.--Ammonium hexafluororhenate(IV),
(NH4)2ReF6, prepared from the corresponding potassium salt by an
ion-exchange procedure, was shown by thermogravimetric analysis
to decompose in argon at 300°. A thermal decomposition of (NH4)2ReF6
at this temperature in gaseous HF resulted in a mixture of
,
A
unidentified phases, but decomposition in vacuo or in argon gave
a black residue; X-ray analysis showed that about 97% of the residue
was a single phase. The powder-diffraction data indicated that the
highest degree of symmetry which satisfied all the diffraction maxima
of the Debye-Scherrer pattern was a tetragonal unit cell having the
parameters a = 5.88 X and = 13.00 X: . These data, as well as those for other
compounds discussed, are given in Table I. Elemental analysis
(Table I)
.
S
.
D
.
-6-
TABLE I
X-Ray Powder Diffraction Data
Compound
hkl
sobgÅ
Scale' Å
RENAD
101
5.360
5.334
3.492
(112
53.503
73.:88
2203
.004
3.240
3.250
200
2.938
2.576
105
2.366
2.240
2.940
52.578
(2.561
2.378
2.248
52.180
12.166
2.079
213
*********** 7o
2.174
5204
2006
220
2.073
301
1.932
1.938
116
1.914
1.842
1.921
(1.849
1.841
1.771
(1.751
(1.744
207
1.764
1.748
5224
3.14
1.614
1.614
305
1.561
1.524
323
1.565
1.526
(1.517
21.513
$217
1.513
218
•7-
TABIE I (continued)
Compound
dob» À
a calce
Å
1.47o
1.47o
W+
411
1.419
1.418
M+
316
1.11
，
-
325
1.409
1,581
1.554
M-
--
-
•.
1.581
1.356
1.554
，
༼552
M+
- ་
•
བ
-...
•
ས
• :
07
1.347
1.548
• • •
•
-
-.. -
1.359
•.
40
1.315
+
228
NE
219
1.359
1.315
1.28o
1.265
1.219
5.2oo
4.791
M-
424
TONAS
# | ༔ ༔ བྷ R , དྷཝཱ ༔ སྤྱི ཙྪཱ དྷཱ ཙྪཱ ཉྙོ ཝཾ ཡྻོ ཙྩོ | ཙྩཾ ཡྻོ ཙྩོ དནྟི |
1.28o
1.266.
1.219
5.18o
4.7o
3.515
2.991
ooo1.
201:1
3.502
2.985
བྷ་ཝ༧ས་པ ་ ཐམསཨ ཨམ་
1120
121
2.5ཅར
2.557
༦
.
o21
2.278
;:x;
3
2•279
2.23o
2,173
་ཆབn
1012
2.174
M+
1.959
:་:
-2
t
- : ༌༌ -
1122
2131
1.871
1.815
1.768
1.788
1.957
1.87o
1.812
1.758
1.77. ་
:་:::
:་
，
1.6sod
:་:༌
:
---..-...
TABLE I (continued)
Compound
hls?
obs, À
calc, À
2132
1.519
1.516
1.495
2.497.
2250
3110
1.435
1.436
1.409
1223
1.407
1.. 377
1.376
2023
1.361
7.080
Refde
110
112
5.340
003
400
5.040
103
4.745
210
4.484
2202
4.291
(113
1.359
7.160
(5.330
15.315
5.038
4.704
4.527
54.276
24.268
53.988
(2.939
(3.303
23.265
53.201
73.191
13.133
13.109
2.849
root
3.952
2212
3.278
3301
1222
3.198
(310
2005
3.121
2.876
2.607
2.529
2.608
2.386
2.530
(2.386
2.383
(2.381
TABLE I (continued)
Compound hki
a obce Å
Scale' À
324
2.298
,
M
331
216
1 UU 91 *
007
2.270
420
(2.295
{2.297
(2.292
82.279
2.264
2.177
2.180
2.047
(1.994
31.985
| * *izi
422
2.186
325
2.180
334
2.047
1.989
008
510
(405
(1.983
Relative intensity: S = strong, M = medium, w = weak.
Pcr ka radiation, 1 = 2.909 A.
Ccu ka radiation, 1 = 1.5418 A.
Not explained by unit cell.
.
.
-
-iii-.
indicated 83.5% Re, 6.3% N, and 8.39 F. The calculated composition :
of the hypothetical compound rhenium nitrogen fluoride, ReNF, is:
Re, 85.0%; N, 6.4%; and F, 8.7%. The residues from several
decompositions were weighed and gave the values 65.9, 65.2, and 64.4%.
of original weight (calcd. ReNF, 65.28).
The range of stability of ReNF is not great. Thermogravimetric
analysis indicated that it decomposes at 500°. A slight inflection
in the thermolysis curve at 900° suggests that a small amount of
material decomposes; possibly the material is rhenium nitride (RezN). 11
(11) H. Hahn and A. Konrad, z. Anorg. Allgem. Chem., 264, 174 (1951).
Technetium Nitrogen Fluoride.Similar experiments were performed
with ammonium hexafluorotechnetate(IV), (NH4)2TcFe, but the amounts
of material were too limited for adequate elemental analysis. The
residue after decomposition of (NH4)2TcF8 in argon at 300° was 53.5%
of the original weight (calcd. for TCNF, 53.0%; for TcF2, 55.0%).
The residue was reduced to technetium metal in hydrogen at 500°.
The loss in weight was 25.5%. The calculated loss for TCNF 18 25.096;
for TcFa, 27.7%. Surprisingly, however, a hexagonal unit cell 18
postulated from the powder-diffraction data, the parameters bring
a = 5.98 A and < = 4.80 Å (Table 1).
Rhenium Tetrafluoride. - Rhenium tetrafluoride, ReF4, was reported
by Hargreaves and Peacock12 as a product of the pyrolysis of rhenium
(12) G. B. Hargreaves and R. D. Peacock, J. Chem. Soc., 1099 (1960).
-
pentafluoride, ReFs, and was observed by Malm and Selig?3 to occur
..
.
..
(13) J. G. Malm and H. Selig., J. Inorg. Nucl. Chem., 20. 189 (1961).
-1l-
during some of their reductions of ReFy to ReFo by rhenium metal.
This reduction was investigated further in this laboratory.
The compound keFe (with associated ReFr) and rhenium metal were
heated in sealed nickel tubes under various conditions of
temperature (usual maximum, 400º), lengtia of time, and ratio of
reactants. Some tubes were quenched in liquid nitrogen; others
were allowed to cool slowly. In one trial the reactants were heated
in a thick-walled (0.06 in.) nickel tube at 400° overnight and then
to 600° over a period of 2 hr. Only about 15% of the metal reacted.
The usual products besides unreacted materials were moderate
amounts (10 to 30%) of ReFs and traces of ReF4. In no case was a
fluoride lower than ReF4 observed. The residue after removal of
the volatile ingredients was always rhenium metal - by its color
and grain-size obviously unreacted material and unlike the black
powders resulting from disproportionation. A study was made to
establish the approximate conditions for producing the may.imum
amount of ReF4. Heating 8 g. of rhenium metal with a 100%; excess
of ReF6 (relative to the production of ReF4) in a nickel tube for
4 days at 400° and for an additional 20 hr. at 500°
resulted in the reaction of ^60% of the metal to produce mainly
ReFs from which by disproportionation (in a dry nitrogen atmosphere)
38. of ReF4 was obtained.
The optimum conditions for the production of ReFa, however,
were established in a procedure run at ordinary pressure. A nickel
reservior that contained ReFo was opened to an evacuated nickel tube
that contained 5 8. of finely divided rhenium metal at 550°.
-12-
Outside this hot zone the entire system was kept at ~40° to maintain
a pressure of ReFG near atmospheric in the system. After 10 days the
nickel tube was sealed, removed to an inert-atmosphere glove box,
and examined. Essentially the sole reduction product was ReFm,
which had deposited just beyond the hot zone in the nickel tube;
ReFs was present only in traces and farther away from the hot zone.
The 4 g. of ReF4 obtained represented a conversion of about 70%
of the ReFg.
When the ReF4 was purified by sublimation in vacuo (which begins
at 150° and is fairly rapid at 200°), some ReFg was obtained; a black
residue remained that was stable to 300'. X-ray diffraction analysis
indicated that the residue consisted of about equal parts of rhenium
metal and an unknown phase, which may have been a fluoride lower than
Ref:. An elemental. ana lysis of the sublimed ReF4 indicated: Re, 70.4%
(calcd. 71.0%); F, 28.6% (calcd. 29.0%). The X-ray power pattern
could be indexed on the basis of a unit cell of tetragonal symmetry
having parameters a = 10.12 Å and g = 15.95 Å (Table 1).
Rhenium tetrafluoride is a medium-to-dark blue substance and is
exceedingly sensitive to reaction with the atmosphere. It can be
kept in Teflon capsules with screw caps or in sealed glass tubes.
It dissolves rapidly in water, methanol, ethyl alcohol, and ether
to give intense-blue solutions. In water, immediate hydrolysis is
evident from the deposition of a black substance, but in methanol
the blue color of the solution persists for a short time. When a few
drops of 30% H202 is present in these solvents, the blue colors last
longer – in water up to half an hour, in methanol for several hours –
before black precipitates form.
-13-
Attempts were made to determine the nature of these solutions.
A methanol solution was evaporated to dryness under reduced pressure.
The X-ray pattern of the resultant black residue was similar to that
of ReF4 but with some differences. The product from a methanol
Bulution of ReFm that contained H202 gave a different X-ray pattern
that was not identified. In further experiments, solutions of
anhydrous KF and ReF4 in methanol (without H202) were mixed. In a
few minutes 4 bright-green precipitate deposited beneath a light
green supernatant solution. The precipitate was highly sensitive
to air (it turned black); therefore, in a succeeding attempt it
was filtered off under an inert gas. The green substance gave no
X-ray pattern; however, flame photometric analysis indicated a
potassium content of 19.8% compared with 20.7% calculated for KęReFe.
In another trial, the green precipitate was allowed to digest
overnight in a closed plastic bottle under argon. The precipitate,
which had become pale blue under a light-yellow supernatant solution,
contained only 10.4% potassium and produced a well-defined but
-
-
-
-
-
-
-
-
unidentified X-ray pattern.
In anothe. experiment, an intimate mixture of solid ReF4 and
solid KF (anhydrous, zone-refined) was prepared in the inert-atmosphere
glove box and was compressed in a small steel cylinder between two
.
.
*
close-fitting movable plungers. This apparatus was in turn sealed in
a nickel tube under argon and heated for 60 hr, at 250° and for an
o additional 4 br. at 300°. X-ray analysis showed that the dark
grayish-green product consisted of about equal parts of KeReFo and
an unknown phase. Icaching the dark material with methanol left a
*** tercintag
- 14-
violet water-soluble residue that formed a stable violet solution.
The violet solid contained 16.0% potassium.
EXPERIMENTAL
Materials.-The ordinary chemicals used were reagent grade.
Potassium perrhenate and ammonium perrhenate of >99% purity were
obtained from the University of Tennessee, and ammonium pertechnetate
..
..
.
"'..
..
-
.
was recrystallized from a slightly impure product obtained from the
Istopes Division of the Oak Ridge National Laboratory. The potassium
hexabromorhenate(IV), K ReBre, was prepared as described by Weises."
potassium hexachlorotechnetate(IV), KąTCC18, &ccording to Nelson,
Boyd, and Smith; 14 and (NH4)2Re Is as described by Peacock. -
(14) C. M. Nelson, G. E. Boyd, and W. T. Smith, Jr., J. Am. Chem. Soc.,
76, 348 (1954).
Rhenium metal was prepared by the reductijn of NH4RE04 in hydrogen. 15
(15) Rhenium metal obtained in this manner may contain a small amount
of rhenium nitride. In an experiment, Regn was prepared by heating
NH4ReO4 in a static atmosphere of hydrogen at 300° for two days. The
resulting metal was dissolved in 10% H202, and the insoluble nitride
was removed by filtration.
The HF, in small cylinders, was a product of the Matheson Company.
The fluorine was made available with its accessory apparatus in the
Fluorine Laboratory of the Chemical Technology Division of the Oak
Ridge National Laboratory.
i
=
-4
..
-
-
:
:
-
-
:
-
-
----------
-
.
.
4
-:-
--15-
Apparatus and Procedures.--Fluorocomplexes. Fusions were done
,
IN A 100-ml. platinum crucible provided with a cover.
The crucible
was heated in a small, electric crucible furnace just large enough
to accommodate it. The crucible was supported so that it projected
1/8 in. above the furnace to allow fumes to escape. A thermocouple
led from the furnace to an indicating and controlling Capacitrol.
Gaseous FF or argon, or both, could be admitted either to or under
the surface of the melt through 1/4-in. copper tuting that terminated
in a 6 in. length of 1/4-in. platinum tubing.
Fusions or evaporations in inert atmosphere were accomplished in
platinum boats fashioned from sheet platinum. The boats rested in a
nickel tube 40 in. long and 2 in. in diameter. The tube was closed
by removable flat plates (fitted with openings of 1/4-in. copper
tubing) bolted to flanged ends through Teflon O-rings and was heated
with a hinged-type tube furnace.
Filtrations were accomplished with a polyethylene Büchner type
funnel, holding ordinary filter paper, in a bell«jar arrangement so
that suction could be applied.
Fusions were made as follows. The halogen complexes were ground
in an inert-atmosphere glove box to pass a 200-mesh screen. A weight
of KHF2 was taken equal to ten times the weight of the complex, and
the KHF2 was melted. The complex was added to the melt a little at
a time and was allowed to dissolve. The crucible was covered, and
the temperature was raised slowly to 700° aver the course of an hour.
The trial was terminated either by placing the crucible in an
aluminum desiccator that contained sodium hydroxide pellets and
allowing it to cool or by quenching the crucible and its contents
UNCLASSIFIED
ORNL-OWG. 63-6738

FB1852=
16-
in liquid nitrogen and rapidly transferring it to the glove box,
where the contents were ground to pass a 100-mesh screen. The
ground material was removed from the box and was extracted with a
minimum of cold water in a 300-ml. platinum dish with magnetic stirring
by a Teflon-covered bar. The residue — whicla consisted principally
of KaKeFe (cr KTCFG), a small amount of KF, and some dark hydrolytic
products – was filtered off, treated with hot water, and warmed
gently for a few minutes to coagulate the black material. Removal
of this residue by filtration left a a pink solution, which was
concentrated to crystallization under an infrared lamp with magnetic
stirring. Very fine, semitransparent, pink leaflets of tetragonal
symmetry were obtained, usually in a yield of about 80%.
When the rapid recovery of products from solutions was required,
Os
precipitation was accomplished by pouring the solution into ten times
its volume of a 1:1 mixture of ether and alcohol.
The KąReFe was converted to (NH4)2ReF6 by passing the solution
of the potassium salt through a column of acid-form Dowex 50W-X8 and
neutralizing the resulting fluororhenic acid(IV), H ReFs, with NH4OH.
The (NH4)2ReFo was precipitated by the ether-alcohol procedure.
To convert KaTcFo to the ammonium salt, 2.5 g. of the potassium
compound was dissolved in a slurry of 6 g. of the resin 1. 20 ml. of
water contained in a beaker. The blurry was stirred for an hour, and
the solution was then passed through a small column that contained
5 g. of the resin. The resins in the beaker and column were rinsed
until the total volume of solution was 100 ml. Only a small portion
of the resultant solution of H2TcFe was neutralized to provide the
(NH.)>TCFA used in the decomposition experiments. -
-17-
Rhenium Tetrafluoride. First, rhenium hexafluoride was prepared
from the component elements by passing a mixture of fluorine and
helium, appropriate to controlling the reaction, through a nickel
tube that contained finely divided rhenium metal (no g.). The exit
of the nickel tube led through 3/8-'a. copper tubing to a flanged
nickel can (2-in. diameter, 5-in. deep). A cover ,fitted with two
Veeco type valves having Teflon seats, was held against the flange
of the can through a Teflon O-ring (A in Fig. 1).
(Figure 1)
The entrance to the can terminated at the cover, and the bottom
half of the can was cooled in an acetone-Dry Ice mixture during the
fluorination, while the cover was heated with heating tape to ~100°.
A thermocouple wired to the bottom of the reaction tube was useful
in indicating the incidence of rapid reaction, which sometimes occurred
at room temperature. The tube was brought to a final temperature of 300°.
After the valves were closed, the can was removed and attached
to the vacuum system shown in Fig. 1. A is the nickel can; B, Veeco
type valves; C, Kovar glass-to-metal seals; D, glass traps; E, nickel
pressure tube; I, Kerotest valves with Teflon seats; G, Vacuum-pressure
gage; H, thermocouple gage; I, soda-lime trap; J, outlets to mechanical
vacuum pumps; and K, inlet for nitrogen. All connections were of /-in.
copper tubing.
The nickel pressure tube (12-in. long, 1/2-in. diameter, 0.035-in.
wall thickness) flattened and welded at one end was charged with 2.5 g.
of rhenium metal (200-400 mesh), and was attached to the system. By
appropriate manipulation of valves and vacuum, the ReFs was transferred
ORNL-DWG. 63-6738
Fig. 1.-Vacuum system for transferring rhenium hexafluoride to nickel tubes.
-19-
to the first glass trap (cooled in acetonemDry Ice mixture), then
to the second trap (cooled in liquid nitrogen), and finally to the
nickel tube. Liquid nitrogen was maintained around the tube while
it was removed with the valve aütached, flattened, crimped, and welded.
As the tube returned to room temperature, a slight initial reaction
occurred, which warmed it to ~200°.
In typical runs, tubes that contained 2.5 g. of rhenlum metal
with about 8 g. of ReFo were heated from 6 to 24 hr. at temperatures
up to 400. The flattened ends were always bulged; the tubes
usually failed beyond 400°, because minute holes developed at the welds.
The tubes were quenched in liquid nitrogen, removed to the inert-
atmosphere glove box, opened at one end, and placed in a sublimination
tube (A in Fig. 2), which was temporarily stoppered. The tube was
(Figure 2)
attached to the vacuum system at joint E - the trap F having previous ly
been attached at G - and the whole system was flushed out with nitrogen,
which continued to emerge at E. After attachment, the system was
immediately evacuated. In Fig. 2, B is the nickel tube; C, furnace; :
D, side-bulb to receive ReFs; E, assembled O-ring joint (held together
by a ball-and-socket joint clamp); I, break-seal; and J, Kovar glass-
to-metal seal. The rubber O-ring in the joint E is coated with a
fluorinated lubricant. The products of the sublimations were: a
moderate amount of ReFo caught in the liquid-nitrogen trap along wit”.
a small amount of pale-blue rhenium oxytetrafluoride, Re0F4, 16 anú a
(16) G. H. Cady and G. B. Hargreaves, J. Chem. Soc., 2568 (1961).
ORNL-DWG. 63-6739
20-
Fig. 2.-Sublimation tube.
Varhi
Meyh
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yellow viscous liquid mixed with a green solid in the cool parts
of the sublimation tube. By heating the yellow liquid gently with
a burner, ReFo was evolved leaving behind ReFs. The ReF's was
sublimed into the small side bulb. Nitrogen was admitted to the
bulb, the bulb was heated, and more Refe was evolved leaving blue
ReF4 in the bulb to be sealed off.
The ReFo was salvaged by sealing off the trap at H, attaching
VO
the trap to the vacuum system through the break-seal I at J, and
subliming the ReFo into an evacuated nickel storage can fitted with
a valve (H in Fig. 3).
(Figure 3)
The arrangement for the preparation of ReF4 at atmospheric
pressure is shown in Fig. 3. The nickel reaction tube at B is enclosed
in furnace A. At C is a silver-soldered connection to copper tubing
I (for easy cutting in the glove box) provided with coils for air-cooling.
Kerotest valves are at G, and I leads to the vacuum system. Heating
tape surrounds the system from H to F. After the reaction has occurred,
the tube is filled with nitrogen, flattened between F and E, and severed.
Analysis.--Samples that contained the fluoride complex ion, ReF62",
were decomposed by fusion in sodium carbonate that contained a small
amount of sodium peroxide. Otherwise, alkaline hydrogen peroxide was
usually sufficient. Control determinations were done colorimetrically:
rhenium with a-furildioxime, fluorine with Thoron, 27 and potassium by
wer
U
.
(17) Eastman Chemical No. 6748; HOC10H4 (C03Na)2N:NC8H4AsO3H2 .
flame photometry. Characterization and final analyses were done
gravimetrically: potassium by precipitation as the tetraphenylborate,
rhenium as tetraphenylarsonium perrhenate, and fluorine as lead

UNCLASSIFIED
ORNL-DWG. 63-6739
J
I
ORNI-DWG. 63-6761
-22-
Fig. 3.- Arrangement for the preparation of rhenium tetrafluoride.
.
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chlorofluoride. The K2ReFe for infrared analysis was prepared in the
glove box by mixing 3 mg. of the solid with 500 mg. of "spectroscopic"
KBr and forming a pellet of the mixture.
Acknowledgements.--The authors express their appreciation: to
Dr. G. E. Boyd for his support of the work, to Drs. R. H. Busey and
H. Yakel for aid and advice, and to the Analytical Chemistry and
Chemical Technology Divisions for the use of physical facilities and
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-24-
LIST OF FIGURES
ORNL Drawing
Figure
Number
Caption
63-6738
w or
Vacuum system for transferring
rhenium hexafluoride to nickel
tubes.
Sublimation tube.
63-6739
63-6761
Arrangement for the preparation
of rhenium tetrafluoride.
UNCLASSIFIED
.DWG-اORN
63
-
6761
1 H
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