Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture
The paper presents the results of investigations of the interaction of rare-earth fluorides with metallic sodium and zirconium in a molten sodium fluoride–zirconium fluoride mixture. The investigations have been carried out by differential thermal analysis (DTA), X-ray phase analysis (XPA), IR spect...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2005
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| Цитувати: | Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture / R.M. Savchuk, A.O. Omelchuk, N.M. Kompanichenko // Вопросы атомной науки и техники. — 2005. — № 4. — С. 120-125. — Бібліогр.: 16 назв. — англ. |
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Savchuk, R.M. Omelchuk, A.O. Kompanichenko, N.M. 2015-04-19T14:23:05Z 2015-04-19T14:23:05Z 2005 Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture / R.M. Savchuk, A.O. Omelchuk, N.M. Kompanichenko // Вопросы атомной науки и техники. — 2005. — № 4. — С. 120-125. — Бібліогр.: 16 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/80567 The paper presents the results of investigations of the interaction of rare-earth fluorides with metallic sodium and zirconium in a molten sodium fluoride–zirconium fluoride mixture. The investigations have been carried out by differential thermal analysis (DTA), X-ray phase analysis (XPA), IR spectroscopy, and chemical analysis. It has been shown that metallic sodium and zirconium reduce rare-earth fluoride in the temperature range were the constituents of reaction mixture are in solid phase to form compounds of zirconium in lower oxidation states and rare-earth metals. The dependence of the temperature at the commencement of exchange reactions on the chemical nature of rareearth halide has been established: increase in the melting point of rare-earth fluoride leads to a rise of initial interaction temperature. The degree of reduction of rare-earth fluorides by reducing metals depends on the ratio of the constituents of the original reaction mixture. Приведені результати досліджень взаємодії фторидів рідкісноземельних елементів (РЗЕ) з металічним натрієм та цирконієм у розплавленій суміші фторидів натрію та цирконію. Дослідження виконані методами диференційно-термічного (ДТА), рентгенофазового (РФА), ІЧ-спектроскопії та хімічного аналізів. Показано, що металічний натрій та цирконій відновлюють фториди РЗЕ в температурному інтервалі, коли складові компоненти реакційних сумішей перебувають в твердій фазі, з утворенням сполук цирконію нижчих ступенів окислення та рідкісноземельних металів. Виявлена залежність температури початку реакцій обміну від хімічної природи галогеніду РЗЕ: зростання температури плавлення фториду РЗЕ призводить до підвищення температури початку взаємодії. Ступінь відновлення фторидів РЗЕ металами- відновниками залежить від співвідношення компонентів у вихідній реакційній суміші. Приведены результаты исследований взаимодействия фторидов редкоземельных элементов (РЗЭ) с металлическим натрием и цирконием в расплавленной смеси фторидов натрия и циркония. Исследования выполнены методами диференциально-термического (ДТА), рентгенофазового (РФА), ИК-спектроскопии и химического анализов. Показано, что металлический натрий и цирконий восстанавливают фториды РЗЭ в температурном интервале, когда составные компоненты реакционных смесей находятся в твердом состоянии, с образованием соединений циркония низших степеней окисления и редкоземельных металлов. Установлена прямолинейная зависимость температуры начала реакций обмена от химической природы галогенида РЗЭ: увеличение температуры плавления фторида РЗЭ приводит к повышению температуры начала взаимодействия. Степень восстановления фторидов РЗЭ металлами-восстановителями зависит от соотношения компонентов в исходной реакционной смеси. The work was supported by STCU Project #294. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture Взаимодействие фторидов редкоземельных элементов с металлами в расплавленной смеси фторидов натрия и циркония Взаємодія фторидів рідкісноземельних елементів з металами в розплавленій суміші фторидів натрію та цирконію Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| spellingShingle |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture Savchuk, R.M. Omelchuk, A.O. Kompanichenko, N.M. |
| title_short |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| title_full |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| title_fullStr |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| title_full_unstemmed |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| title_sort |
interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture |
| author |
Savchuk, R.M. Omelchuk, A.O. Kompanichenko, N.M. |
| author_facet |
Savchuk, R.M. Omelchuk, A.O. Kompanichenko, N.M. |
| publishDate |
2005 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Взаимодействие фторидов редкоземельных элементов с металлами в расплавленной смеси фторидов натрия и циркония Взаємодія фторидів рідкісноземельних елементів з металами в розплавленій суміші фторидів натрію та цирконію |
| description |
The paper presents the results of investigations of the interaction of rare-earth fluorides with metallic sodium and zirconium in a molten sodium fluoride–zirconium fluoride mixture. The investigations have been carried out by differential thermal analysis (DTA), X-ray phase analysis (XPA), IR spectroscopy, and chemical analysis. It has been shown that metallic sodium and zirconium reduce rare-earth fluoride in the temperature range were the constituents of reaction mixture are in solid phase to form compounds of zirconium in lower oxidation states and rare-earth metals. The dependence of the temperature at the commencement of exchange reactions on the chemical nature of rareearth halide has been established: increase in the melting point of rare-earth fluoride leads to a rise of initial interaction temperature. The degree of reduction of rare-earth fluorides by reducing metals depends on the ratio of the constituents of the original reaction mixture.
Приведені результати досліджень взаємодії фторидів рідкісноземельних елементів (РЗЕ) з металічним натрієм та цирконієм у розплавленій суміші фторидів натрію та цирконію. Дослідження виконані методами диференційно-термічного (ДТА), рентгенофазового (РФА), ІЧ-спектроскопії та хімічного аналізів. Показано, що металічний натрій та цирконій відновлюють фториди РЗЕ в температурному інтервалі, коли складові компоненти реакційних сумішей перебувають в твердій фазі, з утворенням сполук цирконію нижчих ступенів окислення та рідкісноземельних металів. Виявлена залежність температури початку реакцій обміну від хімічної природи галогеніду РЗЕ: зростання температури плавлення фториду РЗЕ призводить до підвищення температури початку взаємодії. Ступінь відновлення фторидів РЗЕ металами- відновниками залежить від співвідношення компонентів у вихідній реакційній суміші.
Приведены результаты исследований взаимодействия фторидов редкоземельных элементов (РЗЭ) с металлическим натрием и цирконием в расплавленной смеси фторидов натрия и циркония. Исследования выполнены методами диференциально-термического (ДТА), рентгенофазового (РФА), ИК-спектроскопии и химического анализов. Показано, что металлический натрий и цирконий восстанавливают фториды РЗЭ в температурном интервале, когда составные компоненты реакционных смесей находятся в твердом состоянии, с образованием соединений циркония низших степеней окисления и редкоземельных металлов. Установлена прямолинейная зависимость температуры начала реакций обмена от химической природы галогенида РЗЭ: увеличение температуры плавления фторида РЗЭ приводит к повышению температуры начала взаимодействия. Степень восстановления фторидов РЗЭ металлами-восстановителями зависит от соотношения компонентов в исходной реакционной смеси.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/80567 |
| citation_txt |
Interaction of rare-earth fluorides with metals in a molten sodium fluoride-zirconium fluoride mixture / R.M. Savchuk, A.O. Omelchuk, N.M. Kompanichenko // Вопросы атомной науки и техники. — 2005. — № 4. — С. 120-125. — Бібліогр.: 16 назв. — англ. |
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INTERACTION OF RARE-EARTH FLUORIDES WITH METALS
IN A MOLTEN SODIUM FLUORIDE–ZIRCONIUM FLUORIDE MIX
TURE
R.M. Savchuk, A.O. Omelchuk, and N.M. Kompanichenko
V.I .Vernadkii Institute of General and Inorganic Chemistry
Ukrainian National Academy of Sciences
Prospect Palladina 32-34, 03680, Kyiv 142, Ukraine
e-mail: savchuk@ionc.kar.net
The paper presents the results of investigations of the interaction of rare-earth fluorides with metallic sodium and
zirconium in a molten sodium fluoride–zirconium fluoride mixture. The investigations have been carried out by dif
ferential thermal analysis (DTA), X-ray phase analysis (XPA), IR spectroscopy, and chemical analysis. It has been
shown that metallic sodium and zirconium reduce rare-earth fluoride in the temperature range were the constituents
of reaction mixture are in solid phase to form compounds of zirconium in lower oxidation states and rare-earth met
als. The dependence of the temperature at the commencement of exchange reactions on the chemical nature of rare-
earth halide has been established: increase in the melting point of rare-earth fluoride leads to a rise of initial interac
tion temperature. The degree of reduction of rare-earth fluorides by reducing metals depends on the ratio of the con
stituents of the original reaction mixture.
The research carried out in recent years showed that
one of the promising methods for the destruction of ra
dioactive wastes accumulated by operating nuclear pow
er stations and by the production of weapon plutonium
is the accelerator-driven transmutation of long-lived nu
clides, and that a suitable reaction medium is molten salt
compositions. According to the existing infrastructure
of a nuclear power system, spent fuel is fluorinated to
extract uranium [1], zirconium tetrafluoride, which is
part of fuel element jackets, forming the basis of fluori
nation products. If sodium fluoride is added to fluorina
tion products (ZrF4) in a 1:1 (mol) ratio, the composi
tion formed, NaF-ZrF4, will conform to the criteria for
choosing fuel mixtures for nuclear reactors and will be a
good carrier of nuclear transmutation products.
In the course of the operation of such reactors, a
continuous change of the fuel composition takes place,
which is caused by the accumulation of actinide trans
mutation products and structural material corrosion
products. Among them are rare-earth fluorides, isotopes
and fluorides of transition, alkaline, alkaline-earth ele
ments, etc [1-3]. Most of the isotopes formed have a
large thermal neutron capture cross-section, which in
fluences the neutron-energy balance of the reactor. Be
sides, fission products influence the corrosion resistance
of structural materials towards molten-salt fuel compo
sition.
Whereas the nuclear transmutations that are possible
to date are exhaustively studied in terms of theoretical
physics, the chemistry of molten salt blanket is at the
initial stage of investigation. There is no information on
the general laws governing chemical interaction in fuel
composition, on the effect of nuclear and chemical
transformations on structural materials, efficient meth
ods for the adjustment of the composition of fuel mix
tures, their utilization, and subsequent storage.
In view of this, the investigation of chemical pro
cesses occurring in melts, which form the basis of fuel
mixtures in reactors-transmuters, is topical and is of not
only scientific, but also practical interest.
This paper presents results of a study of the interac
tions that take place between nuclear transmutation
products (simulative objects: La, Pr, Nd, Gd, Dy, Yb
fluorides) and the metals that are part of the fuel ele
ment jacket, fuel mixture, and structural materials.
The investigations have been carried out by differen
tial thermal analysis (DTA), X-ray phase analysis
(XPA), chemical analysis, and IR spectroscopy. A ther
modynamic evaluation of the interaction of the compo
nents of a number of systems has been performed.
EXPERIMENTAL
The DTA was made on a Q-1500 derivatograph in
corundum (or alundum) crucibles for DTG investiga
tions under dry argon since the reducing metals (Zr, Na)
and rare-earth fluorides are oxidized by atmospheric
oxygen [4, 5]. The heating rate of the samples under in
vestigation was 5-10 deg/min. Aluminum oxide was
used as a standard. For a more reliable protection of
samples from air oxidation, they were coated with a
molten NaPO3-V2O5 mixture. According to the results of
Ref [6], the presence of a protective coating of the com
position (wt %) NaPO3 (75)–V2O5(25) does not interfere
in the identification of thermoeffects which are ob
served between the constituents of reaction mixtures;
moreover, this coating has good protective properties in
thermographic investigations.
The XPA was made on a DRON-UM diffractometer
with CuKα radiation by the powder method. The IR
spectra were recorded in a frequency range of 3800…
200 cm-1 by means of a Specord-80M device on pelleted
samples with potassium bromide. The concentration of
the metals in a lead-sodium alloy was determined by a
procedure described earlier [7].
__________________________________________________________________________________
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2005. №.4.
Серия: Физика радиационных повреждений и радиационное материаловедение (87), с. 120-125.
120
mailto:savchuk@ionc.kar.net
Analytically pure and extra pure reagents and sub
limed zirconium tetrafluoride of monoclinic system,
which was obtained by dehydration and simultaneous
fluorination of ZrF4·xHOH were used for the investiga
tions [8].
The interaction between rare-earth fluorides and re
ducing metals was investigated in a previously prepared
NaF (51 mol. %)–ZrF4 (49 mol. %) mixture. The rare-
earth fluoride content of this mixture was varied from 4
to 20 wt %; the ratio Zr:MF3 (mol %)(M=La, Yb) was
varied from 10:1 to 4:1, and the ratio Na:LaF3 was var
ied from 1:1 to 1:3. The samples were prepared by pro
cedures described earlier [7, 9].
The heating curves for a NaF (51 mol %)–ZrF4 (49
mol %) mixture exhibit only one thermoeffect at (525 ±
5)°C, which is characteristic of the melting of a eutectic
mixture in the NaF-ZrF4 system and is in satisfactory
agreement with literature data (Fig. 1) [10].
Fig. 1 Heating curve for the solvent melt NaF
(51 mol %)–ZrF4 (49 mol %)
It should be noted that alloys of the system NaF-
ZrF4 are characterized by supercooling. Indeed the cool
ing curves for a NaF (51 mol %)–ZrF4 (49 mol %) mix
ture exhibit an effect of solidification of sodium fluo
ride-zirconium fluoride melt at 490°C (Fig. 2).
Fig. 2. Cooling curve for the solvent melt NaF
(51 mol %)–ZrF4 (49 mol %)
This phenomenon may be accounted for by the for
mation of thermodynamically unstable phases and their
disordering. The results obtained agree with the data
presented in Ref [11], where it was shown that in the
NaF-ZrF4 system at a zirconium tetrafluoride concentra
tion of 40…60 mol %, the heating and cooling curves
exhibit only one thermoeffect, independent of interac
tion time and temperature, the melting temperature be
ing higher than the crystallization temperature. The
compounds that are formed by interaction have close
melting points and show polymorphous transformations
at 160 and 440°C.
A compound of the composition 7NaF·6ZrF4 has
been identified by an XPA (Fig. 3).
Fig. 3 Diffractogram of the NaF
(51 mol %)–ZrF4 (49 mol %) mixture
The results of the XPA of a NaF (51 mol %)–ZrF4
(49 mol %) mixture show that a fraction is formed at the
top of the melt; the fraction shows a texture, due to long
soaking, which is manifested in diffractograms by a
group of strong reflections from crystallographic plane
with d = 0.5077 nm. At the bottom of the melt is a frac
tion, whose basis is formed by a phase with fcc lattice
(a0 = 0.543 nm.).
When sodium was used as a reductant, a lead-sodi
um melt, synthesized by the electrochemical method,
was used to avoid strong interaction between rare-earth
fluorides and metallic sodium, which may give rise to
difficulties in the interpretation of DTG diagrams. The
concentration of the metals in the alloy synthesized was
determined by a procedure described earlier [7].
The NaF-ZrF4-LnF3-M systems, where M = Zr, Na,
were investigated on samples of 1.5…3.5 g mass.
Pounded mixtures were poured into a glassy carbon cru
cible, which was placed in a hermetically sealed metal
lic reactor (Fig. 4). The samples were first subjected to
vacuum degassing at 200 and 300°C and then heated
under dry oxygen-free argon. The temperature in inves
tigations did not exceed 600…650°C.
The rare-earth metal concentration in the salt phase
after the occurrence of exchange reaction was deter
mined by complexometric titration in the presence of
eriochrome black T and by gravimetric method by pre
cipitating the rare-earth metal with oxalic acid [12]. The
fluoride ion content of the reaction mixture was deter
mined by means of a fluorine-selective electrode [13],
__________________________________________________________________________________
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2005. №.4.
Серия: Физика радиационных повреждений и радиационное материаловедение (87), с. 120-125.
121
and sodium was determined by flame photometry. It
should be noted that the presence of zirconium and lead
interferes in the determination of the degree of reduction
of rare-earth fluorides in the systems under investiga
tion, therefore these metals were extracted from the
samples under analysis by procedures described earlier
[7, 9].
Fig. 4. Principal scheme of a reactor for the investiga
tion of the reduction of rare-earth fluorides by reducing
metals: (1) crucible, (2) sample under investigation, (3)
Pt-Rh thermoconple
RESULTS AND DISCUSSION
A characteristic of the interaction between rare-earth
fluorides and reducing metals is free Gibbs energy
(ΔG). The exchange reaction between the constituents
of the mixtures under investigation may be schematical
ly represented as follows:
6LnF3 + 7Zr → 2ZrF4 + 6Ln + 5ZrF2;
LnF3 + 3Na → Ln + 3NaF,
where Ln is rare-earth element. The calculations that
have been made on the basis of the data obtained in Ref
[14] give ground to consider the interaction between
rare-earth fluorides and reducing metals to be possible
on the whole since a noticeable decrease in the ΔG val
ue is observed.
Investigation of the NaF-ZrF4-LnF3-Zr system.
The reduction of lanthanum and ytterbium fluorides by
metallic zirconium in a molten sodium fluoride-zirconi
um fluoride mixture takes place in a temperature range
of 440…580°C, the rate of the exchange reaction de
pending on the fineness of reducing metal and being the
higher, the higher its fineness. The differential heating
curves exhibit a number of thermoeffects: endotherms
of the melting of NaPO3-V2O5 mixture (365 ± 5°C) and
the solvent melt NaF-ZrF4 (520 ± 5°C); an exotherm
with an initial interaction temperature of 440-460°C,
whose maximum is overlapped by the endotherm of the
melting of a eutectic sodium fluoride-zirconium fluoride
mixture. These exotherms and the thermoeffects at (460
± 5)°C and (490 ± 5)°C may be assigned to exchange
reactions between metallic zirconium and rare-earth flu
oride and zirconium tetrafluoride with the formation of
compounds of zirconium in lower-oxidation states and
rare-earth metal. Since the trend of the DTA and TG
curves for the samples under investigation is practically
the same, a typical DTA curve for the NaF-ZrF4-LaF3-
Zr system is shown in Fig. 5 as an example.
Fig. 5. Heating curve for a sample of the system NaF-
ZrF4-LaF3-Zr containing 10 wt.% LaF3
The results of an XPA of interaction products
showed that zirconium (IV) and (II) compounds:
Na2ZrF6, Na7Zr6F31, Na5Zr2F13, ZrF2; complicated com
pounds comprising rare-earth fluorides and sodium fluo
ride, and reduced lanthanides are present in the samples
under investigation. The unit cell parameters have been
calculated for the identified compounds by means of a
computer program; they are in satisfactory agreement
with those given in publications. It should be noted that
the parameters of the compound ZrF2, which crystallizes
in orthorhombic system with a = 0.40425 nm, b =
0.49537 nm, c = 0.65801 nm, have some deviations
from literature data (a = 0.409 nm, b = 0.491 nm, c =
0.656 nm), which may be due to the different stoichiom
etry of this compound (Table 1) [15, 16].
A fragment of diffractogram of the interaction prod
ucts of the system NaF-ZrF4-Zr
Experimental data Literature data
Sample ZrF2
d A° I/I0, % d A° I/I0, %
4,077 59 4.065 60
3,453 20 3.448 30
3,285 28 3.279 60
2,942 14 2.933 10
2,779 67 2.762 100
1,918 57 1.923 10
1,731 15 1.739 10
1,654 24 1.664 60
1,545 20 1.541 30
1,479 20 1.484 60
1,378 32 1.377 60
1,319 19 1.316 30
IR spectroscopic investigations of NaF-ZrF4 samples
showed the absorption bands to correspond to the vibra
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122
tion frequency range of (ZrF4)n groupings (n = 6…8).
The most intense absorption band at 490-500 cm-1 re
lates to Zr-F bridge bond stretching vibrations and that
at 580-590 cm-1 to Zr-F nonbridge bond stretching vi
brations; the medium-intensity bands in the range 270-
290 cm-1 relate to the bond deformation vibrations of
fluorozirconate groupings. The presence of Zr-F bridge
and nonbridge bonds in spectra indicates the complexes
formed to be unsymmetrical. The presence of com
pounds of zirconium in lower oxidation states in interac
tion products is also evidenced by IR spectra, which are
in satisfactory agreement with literature data (Fig. 6). It
should be noted that zirconium difluoride, which was
obtained at the stochiometric ratio of the ZrF4 and Zr
constituents in a potassium fluoride-lithium fluoride
melt (50 mol % KF), turned out to be X-ray amorphous,
therefore the authors identified it by IR spectroscopy
[16].
Fig. 6. IR spectra of products of interaction between
zirconium tetrafluoride and metallic zirconium in the
melts KF-LiF (a) [16] and NaF-ZrF4 at the ratio ZrF4 :
Zr = 3 : 1 (b)
Thus, the interaction in the system NaF-ZrF4-LnF3-
Zr (where Ln = La, Yb) may be represented by the fol
lowing equations:
4LaF3 + 3Zr → 4La + 3ZrF4 (1)
Zr + ZrF4 → 2ZrF2 (2)
2LaF3 + 3ZrF2 → 2La + 3ZrF4, (3)
i.e. exchange reaction (1) is paralleled by the interaction
of metallic zirconium with tetrafluoride to form zirconi
um difluoride (2), which then also takes part in the re
duction of rare-earth fluoride to metal (3).
Investigation of the system NaF-ZrF4-LnF3-Na.
According to the results of thermographic investigations
carried out, the interaction of rare-earth trifluoride with
lead-sodium alloy is characterized by a broad thermoef
fect in the temperature range 70…480°C. Endotherms
of the melting of intermetallic compounds of sodium
and lead of the compositions NaPb3 and Na5Pb2 have
been found on heating curves at 320 and 400°C. The in
teraction between rare-earth fluoride and metallic sodi
um begins in the solid phase since the beginning of the
exotherm on DTA curves is in the temperature range
70…90°C and reaches a maximum at (380 ± 5)°C.
The results of an XPA of the interaction products of
the system NaF-ZrF4-LaF3-Pb-Na showed that in the
samples under investigation there are complicated com
pounds comprising sodium and zirconium fluorides
(Na3ZrF7, Na2ZrF6) and ZrF2-x (1 > x > 0), which is
formed by interaction between metallic sodium and zir
conium tetrafluoride and crystallizes in orthorhombic
system, and metallic lanthanum of hexagonal system
(Fig. 7).
Fig. 7. Diffractogram of interaction products of a sam
ple of the system NaF-ZrF4-Pb-Na-LaF3
It should be borne in mind that along with the reduc
tion of rare-earth fluoride, the interaction of reducing
metal with zirconium tetrafluoride, which is part of the
solvent melt NaF-ZrF4, occurs. This is supported by the
results of an investigation of the system NaF-ZrF4-Pb-
Na at NaF-ZrF4: Na ratios of 1:1 to 3:1 (mol). The inter
action between the constituents of mixtures is character
ized by a broad exotherm with a maximum at (380 ± 5)°
C. A number of endotherms of the melting of the inter
metallic compounds NaPb3 and Na5Pb2 have been found
on DTA curves (Fig. 8, curve 1) at (380 ± 5)°C and (400
± 5)°C.
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123
Fig. 8. Heating (1) and cooling (2) curves for a sample
of the system NaF-ZrF4-Pb-Na
As a result of the investigations carried out it has
been found that metallic sodium reduces zirconium
tetrafluoride in the NaF-ZrF4 mixture to lower oxidation
states in the temperature range 70…500°C and increases
the melting point of the solvent melt to 730°C.
The character of the interaction of the components
of the systems under investigation in the case of cooling
differs greatly from that considered above. The DTA
curves exhibit in the temperature range 700…730°C
only a thermoeffect which corresponds to the endotherm
of the melting of sodium fluoride-zirconium fluoride
mixture (Fig. 8, curve 2).
The following compounds have been identified by
XPA among the interaction products of the NaF-ZrF4-
Pb-Na system: ZrF2, Na5Zr2F13, Na3ZrF7, Na2ZrF6. The
considerable increase in the melting point of sodium flu
oride - zirconium fluoride mixture (710°C) may be at
tributed to the formation at the peritectic point of the
compounds 5NaF·2ZrF4, which has a higher melting
point as compared with the main compound 7NaF6ZrF4
(520°C) of the original mixture.
The results of investigation of the interaction of rare-
earth fluoride with lead-sodium alloy showed that the
law governing reduction established manifests itself in
the case of change of the reducing metal. That is the in
teraction of metallic sodium with rare-earth trifluoride
and with the zirconium tetrafluoride of the solvent melt
takes place at the same time to form compounds of zir
conium in lower oxidation states and a rare-earth metal.
Thus, as a result of the research carried out, it has
been found that the interaction of zirconium and sodium
with rare-earth fluorides begins in the temperature range
where the constituents of reaction mixtures are in the
solid state. Zirconium (IV) and (II) compounds:
Na2ZrF6, Na5Zr2F13, ZrF2; complicated compounds com
prising rare-earth trifluoride and sodium fluoride (NaL
nF4), and reduced lanthanides have been identified in
the interaction products by physico-chemical methods
of analysis. It has been found that the degree of reduc
tion of rare-earth fluorides depends on sodium concen
tration in lead-sodium alloy. It has been found that at a
reducing metal concentration in the alloy of over 15 wt
%, practically complete reduction of rare-earth metal
from its fluoride takes place, whereas at even fourfold
excess of zirconium the degree of reduction of rare-
earth fluorides is no more than 33…35 wt %.
Comparison of the results of the work with the data,
obtained earlier, on the interaction of rare-earth fluo
rides with metallic zirconium and sodium in a molten
sodium fluoride-lithium fluoride mixture [7, 9] shows
that the change of the cationic composition of reaction
mixtures (NaF–LiF, NaF–ZrF4) influences the stepwise
character of exchange reactions between rare-earth fluo
rides and reducing metals. In the system NaF–ZrF4,
sodium and zirconium reduce not only rare-earth fluo
rides but also zirconium tetrafluoride. Compounds of
zirconium in lower oxidation states also show reducing
ability with respect to rare-earth fluorides.
An interaction takes place between rare-earth fluo
rides and sodium and lithium fluorides to form complex
compounds of the composition MLnF4 (where M = Li,
Na). Increase in the atomic number of rare-earth ele
ment does not affect the composition of these com
pounds.
ACKNOWLEDGEMENTS
The work was supported by STCU Project #294.
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ВЗАИМОДЕЙСТВИЕ ФТОРИДОВ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ С МЕТАЛЛАМИ
В РАСПЛАВЛЕННОЙ СМЕСИ ФТОРИДОВ НАТРИЯ И ЦИРКОНИЯ
Р.Н. Савчук, А.А. Омельчук, Н.М. Компаниченко
Приведены результаты исследований взаимодействия фторидов редкоземельных элементов (РЗЭ) с металлическим
натрием и цирконием в расплавленной смеси фторидов натрия и циркония. Исследования выполнены методами дифе
ренциально-термического (ДТА), рентгенофазового (РФА), ИК-спектроскопии и химического анализов. Показано, что
металлический натрий и цирконий восстанавливают фториды РЗЭ в температурном интервале, когда составные компо
ненты реакционных смесей находятся в твердом состоянии, с образованием соединений циркония низших степеней
окисления и редкоземельных металлов. Установлена прямолинейная зависимость температуры начала реакций обмена
от химической природы галогенида РЗЭ: увеличение температуры плавления фторида РЗЭ приводит к повышению тем
пературы начала взаимодействия. Степень восстановления фторидов РЗЭ металлами-восстановителями зависит от соот
ношения компонентов в исходной реакционной смеси.
ВЗАЄМОДІЯ ФТОРИДІВ РІДКІСНОЗЕМЕЛЬНИХЕЛЕМЕНТІВ З МЕТАЛАМИ
В РОЗПЛАВЛЕНІЙ СУМІШІ ФТОРИДІВ НАТРІЮ ТА ЦИРКОНІЮ
Р.М. Савчук, А.О. Омельчук, Н.М. Компаніченко
Приведені результати досліджень взаємодії фторидів рідкісноземельних елементів (РЗЕ) з металічним натрієм та ци
рконієм у розплавленій суміші фторидів натрію та цирконію. Дослідження виконані методами диференційно-термічного
(ДТА), рентгенофазового (РФА), ІЧ-спектроскопії та хімічного аналізів. Показано, що металічний натрій та цирконій
відновлюють фториди РЗЕ в температурному інтервалі, коли складові компоненти реакційних сумішей перебувають в
твердій фазі, з утворенням сполук цирконію нижчих ступенів окислення та рідкісноземельних металів. Виявлена залеж
ність температури початку реакцій обміну від хімічної природи галогеніду РЗЕ: зростання температури плавлення
фториду РЗЕ призводить до підвищення температури початку взаємодії. Ступінь відновлення фторидів РЗЕ металами-
відновниками залежить від співвідношення компонентів у вихідній реакційній суміші.
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