Reactions of antimony compounds with fluorine gas by thermogravimetric and differential thermal analyses and X-ray diffraction analysis

Article abstract of DOI:10.1016/j.jfluchem.2018.07.009

Antimony is one of the key fission products in the reprocessing of spent nuclear fuel by the fluoride volatility method because of the high volatility of antimony fluorides. Since the fluorination reaction of antimony compounds is not well understood, the reaction behavior of antimony compounds with F₂ was investigated by thermogravimetric and differential thermal analyses and X-ray diffraction analysis in this study. The target antimony compounds were antimony metal, SbF₃, Sb₂O₃, Sb₂O₄, and Sb₂O₅. The fluorination reaction of antimony metal started at 150 °C, and the fluorination product was SbF₃. SbF₃ volatilized completely by the reaction with F₂ above 190 °C; it was considered that volatile SbF₅ was formed by the reaction with F₂. In the series of fluorination of the antimony oxides, Sb₂O₃, Sb₂O₄, and Sb₂O₅, they started to react with F₂ and volatilize at 330 °C as SbF₅. During the fluorination of Sb₂O₃, Sb₂O₄ was formed temporarily in the course of the reaction. Oxygen released from the fluorination reaction of a part of Sb₂O₃ would oxidize remained Sb₂O₃ to Sb₂O₄. The reaction mechanism for the fluorination of antimony compounds obtained in this study is applicable to evaluate the transfer of antimony in the reprocessing process of the fluoride volatility method.

Full text of DOI:10.1016/j.jfluchem.2018.07.009

Journal of Fluorine Chemistry 214 (2018) 1–7
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Reactions of antimony compounds with fluorine gas by thermogravimetric
and differential thermal analyses and X-ray diffraction analysis
Daisuke Watanabea,b,⁎, Daisuke Akiyama , Nobuaki Satoa
a
a
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, Japan
Center for Technology Innovation – Energy, Research & Development Group, Hitachi, Ltd. 7-2-1, Omika-cho, Hitachi-shi, Ibaraki-ken 319-1221, Japan
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Reprocessing
Fluoride volatility method
Fluorination
Fission product
Antimony
Antimony is one of the key fission products in the reprocessing of spent nuclear fuel by the fluoride volatility
method because of the high volatility of antimony fluorides. Since the fluorination reaction of antimony com-
pounds is not well understood, the reaction behavior of antimony compounds with F
thermogravimetric and differential thermal analyses and X-ray diffraction analysis in this study. The target
antimony compounds were antimony metal, SbF , Sb , Sb , and Sb . The fluorination reaction of anti-
mony metal started at 150 °C, and the fluorination product was SbF . SbF volatilized completely by the reaction
with F above 190 °C; it was considered that volatile SbF was formed by the reaction with F . In the series of
fluorination of the antimony oxides, Sb , Sb , and Sb , they started to react with F and volatilize at
30 °C as SbF . During the fluorination of Sb , Sb was formed temporarily in the course of the reaction.
Oxygen released from the fluorination reaction of a part of Sb would oxidize remained Sb to Sb . The
2
was investigated by
3
2
O
3
2
O
4
2 5
O
3
3
2
5
2
2
O
3
2
O
4
2
O
5
2
3
5
2
O
3
2 4
O
2
O
3
2
O
3
2 4
O
reaction mechanism for the fluorination of antimony compounds obtained in this study is applicable to evaluate
the transfer of antimony in the reprocessing process of the fluoride volatility method.
1. Introduction
converted to oxide forms by a steam oxidation method [6,7], and finally
disposed as vitrified waste.
The fluoride volatility method is one of the promising reprocessing
Antimony is one of the FPs contained in spent nuclear fuel. A re-
ported amount of antimony in the spent fuel is 13.6 g/tHM [12]. An-
methods of spent nuclear fuel. It was developed by several research
groups [1–7], and recently its application to the fuel debris produced by
the severe reactor accident has been investigated after the Fukushima
Daiichi NPP accident [8]. In the fluoride volatility method, the spent
timony forms volatile fluorides such as SbF
100 kPa at 142.7 °C [1]. Therefore, antimony may volatilize in the
fluoride volatility method if SbF is formed by the fluorination reaction.
5
which vapor pressure is
5
nuclear fuel is reacted with fluorinating agent such as F
2
, NF
3
, ClF
3
, and
Because of this reason, antimony is considered as an important element
for the fluoride volatility method. Kleykamp [13] reported that anti-
mony was contained as metallic precipitate in spent nuclear fuel.
However, in the case of spent high burn-up nuclear fuel, antimony
metal may be oxidized to oxide form because of high oxygen potential
in the spent nuclear fuel. Therefore, it was considered that fluorination
reaction should be clarified for antimony metal and oxides.
BrF [9,10]. The elements in the spent nuclear fuel are separated into
5
several elemental groups depending on the difference in vapor pressure
of the fluorinated products. For example, uranium and plutonium is
fluorinated to UF
unstable and gradually decompose to PuF
hand, fluorinated fission products (FPs) such as SrF
vapor pressure, therefore, these are recovered as solid components and
separated from UF gas. Although, some FPs forms volatile fluorides
and co-volatilized with UF gas. For this reason, some separation
methods such as a distillation method and an adsorption method are
also developed for the separation of FPs from UF gas [1–7]. In order to
6
and PuF
6
gases; however, PuF
solid [11]. On the other
and LaF have low
6
is thermodynamically
4
2
3
Colbin [14] summarized information about some species of anti-
mony compounds and fluorination reactions. It is reported that anti-
6
6
mony metal is fluorinated to SbF
Sb is fluorinated to SbF by the reaction with the mixed gas of F
and N (4:1). However, the reaction temperatures of these reactions
were not reported. On the other hand, Komura et al. [15] reported that
UO was fluorinated by F to UF via UO 2. This fluorination reaction
was considered as an example of fluorination reaction of oxide material.
3 5 2
and SbF by the reaction with F , and
2
O
3
5
2
6
2
design the process of the fluoride volatility method, the transfer of FPs
should be clarified. Therefore, it is important to understand the fluor-
ination behaviors of FPs. Incidentally, the fluorinated FPs can be
2
2
6
2
F
⁎
Corresponding author.
E-mail address: daisuke.watanabe.kp@hitachi.com (D. Watanabe).
https://doi.org/10.1016/j.jfluchem.2018.07.009
Received 22 May 2018; Received in revised form 20 July 2018; Accepted 20 July 2018
Available online 21 July 2018
0022-1139/ © 2018 Elsevier B.V. All rights reserved.

D. Watanabe et al.
Journal of Fluorine Chemistry 214 (2018) 1–7
Based on this example, oxyfluoride may formed as intermediate product
in the fluorination reaction of oxide material. Colbin [14] suggested
antimony oxyfluorides such as SbOF, SbO F, and SbOF . Therefore, the
2 3
fluorination reaction of antimony oxides should be investigated taking
into account oxyfluoride formation. However, to the best of the authors’
knowledge no reports have been published about the reaction path.
Therefore, the reaction temperature and the reaction path of the
fluorination reaction of antimony compounds should be evaluated for
understanding the behavior of antimony in the fluoride volatility
method.
In this research, the reaction temperature and the reaction path of
the fluorination reaction were experimentally studied for some species
of antimony compounds. Thermogravimetric analysis (TG) and differ-
ential thermal analysis (DTA) using a thermogravimeter-differential
thermal analyzer and X-ray diffraction analysis (XRD) were carried out.
Oxide and metal forms are applied for nuclear fuel; therefore, antimony
2 3 2 4 2 5
metal and the antimony oxides, Sb O , Sb O , and Sb O , were used as
target compounds for fluorination. Additionally, in order to well un-
derstand the fluorination reaction of the antimony compounds, fluor-
ination of SbF
. Results and discussion
Results of fluorination experiment are shown in Section 2.1 for each
3
, a fluorination intermediate, was also investigated.
2
antimony compounds. Next, results of thermodynamic consideration on
related reaction are shown in Section 2.2. Finally, based on the results
shown in Sections 2.1 and 2.2, fluorination reaction was discussed in
Section 2.3 for each antimony compounds.
2
2
.1. Results of fluorination experiment of antimony compounds
Fig. 1. TG-DTA curves of the fluorination experiment of antimony metal at
three heating rates: (a) 10 °C/min, (b) 5 °C/min, and (c) 2 °C/min.
.1.1. Results of fluorination experiment of antimony metal
The TG-DTA curves of the fluorination experiment of antimony
metal are shown in Fig. 1. The temperature was heated from room
temperature to 500 °C. The heating rates for Fig. 1(a)–(c) were 10, 5,
and 2 °C/min, respectively. In order to investigate the effect of heating
rate on fluorination reaction, the fluorination experiment was carried
out at three heating rates. The mass change (ΔM) of antimony com-
pound obtained by TG is shown as solid lines in Fig. 1. The heat transfer
obtained by DTA is shown as dashed lines; upper signal corresponds to
the exothermic reaction. The sharp exothermic rising below 100 °C is
attributed to the surface fluorination of sample pan made of nickel
alloy.
A slight weight increase around 200 °C was observed followed by
the rapid weight decrease with several exothermic peaks in Fig. 1(a).
This indicates that antimony metal reacted with F
antimony metal was temporarily converted to heavier compounds by
reaction with F around 200 °C, and finally volatilized by further
fluorination. All of the antimony metal was volatilized in Fig. 1(b) and
c), but about 40% of the solid material remained in Fig. 1(a). At slower
2
exothermically, and
2
(
heating rate, the F
longer. Since the F
2
feed time per unit temperature increase became
feed time after start of fluorination reaction was
2
enough in the experiment at heating rate of 5 and 2 °C/min, all of the
antimony metal was volatilized in Fig. 1(b) and (c). On the other hand,
a continuous exothermic peak was observed in Fig. 1(a) and (b), but
two exothermic peaks clearly separated with each other were observed
in Fig. (c). When the heating rate was fast compered to reaction rate,
temperature increased before the reaction was finished. Therefore,
heating rate affected shift of TG-DTA curve and peak separation, and
heating rates of 10 and 5 °C/min would be too fast to observe two
exothermic peaks separately. These two exothermic peaks indicated
that the fluorination reaction of antimony metal proceeded by at least
two steps; based on Fig. 1(c), these were exothermic reaction with mass
increase at 150 °C and exothermic reaction with mass decrease at
Fig. 2. XRD patterns of the residue for the fluorination experiment of antimony
metal.
(a) product after fluorination at 500 °C and (b) product after fluorination at
170 °C.
In order to investigate the fluorination reaction, XRD analysis of
fluorination products was carried out. Additional fluorination experi-
ments were carried out to prepare the residue of fluorination reaction.
Fig. 2(a) shows XRD pattern of the residue obtained by the fluorination
experiment; the temperature was raised from room temperature to
500 °C with the heating rate of 10 °C/min. The residue was identified as
antimony metal. In this figure, broad peaks corresponding to polyimide
film also appeared in the 2θ range from 20 to 28 degrees. In order to
190 °C. Additionally, ΔM decreased by about 10% around 330 °C in Fig.
(
c), therefore, the other reaction was considered to be occurred.
2

D. Watanabe et al.
Journal of Fluorine Chemistry 214 (2018) 1–7
280 °C. Melting point of SbF
3
is 287 °C [14], and the vapor pressure of
SbF
3
was 0.5 kPa at 200 °C and 23.3 kPa at 287 °C [14]. Because of this
, it was considered that SbF started to volatilize
at 200 °C and completely volatilized by 280 °C in Ar flow condition. On
the other hand, in F , exothermic peaks were observed and SbF vola-
tilized completely as shown in Fig. 3. These results indicate that SbF
reacted with F exothermically. On the other hand, DTA curves in Fig. 3
vapor pressure of SbF
3
3
2
3
3
2
were very complicated. As same as the fluorination experiment of an-
timony metal, a continuous exothermic peak was separated by slowing
down the heating rate. For example, the shoulder of the exothermic
peak around 150 °C in Fig. 3(a) was clearly separated at 150 °C in
Fig. 3(b) at a heating rate of 5 °C/min. Since ΔM started to decrease
with the exothermic peaks around 200 °C in Fig. 3, it was considered
that this reaction was main fluorination reaction of SbF . Additional ΔM
3
decrease was observed above 330 °C in Fig. 3 as with the fluorination
experiment of antimony metal.
2
.1.3. Results of fluorination experiment of Sb
Next, the results of fluorination experiment were shown for anti-
mony oxides. First, the result of fluorination experiment was shown for
Sb due to its simplest fluorination reaction. The TG-DTA curves of
fluorination experiment of Sb are shown in Fig. 5. Heating rates for
2 5
O
2 5
O
2 5
O
Fig. 5(a) and (b) was 10 and 5 °C/min, respectively. As shown Fig. 5,
ΔM decreased with the exothermic reaction above 330 °C. Therefore, it
2 5 2
was clarified that Sb O reacted with F above 330 °C. Since the shapes
of TG-DTA curves in Fig. 5(a) and (b) was resembled each other, the
fluorination reaction would not be affected by the heating rate.
2 5
When the residue of the fluorination experiment of Sb O heated up
to 500 °C with the 10 °C/min of heating rate was investigated by XRD
analysis, no XRD peak was observed. As the result, it is clarified that the
residue was changed from the starting material of Sb
not be identified. The physical appearance of residue was white powder
which resembled the starting material of Sb
2 5
O , but it could
3
Fig. 3. TG-DTA curves of the fluorination experiment of SbF at three heating
rates: (a) 10 °C/min, (b) 5 °C/min, and (c) 2 °C/min.
2 5
O .
identify the product of the first exothermic reaction in Fig. 1(c), the
residue was obtained by the fluorination experiment; the temperature
was increased from room temperature to 170 °C with the heating rate of
2
.1.4. Results of fluorination experiment of Sb
The TG-DTA curves of fluorination experiment of Sb
2 4
O
2 4
O are shown
in Fig. 6. The heating rates for Fig. 6(a) and (b) was 10 and 5 °C/min,
respectively. As shown in Fig. 6, the exothermic reaction started at
3
of exothermic peak was observed at about 430 °C. The temperature of
exothermic peak around 430 °C was slightly shifted to higher
1
0 °C/min followed by keeping at 170 °C for 30 min. Fig. 2(b) shows the
XRD pattern of the residue obtained by this fluorination experiment.
That material was identified as a mixture of antimony metal and SbF
30 °C, and the ΔM decreased with the exothermic reaction. The change
3
.
2
.1.2. Results of fluorination experiment of SbF
In order to further investigate the fluorination reaction of antimony
metal, the fluorination experiment of SbF , which was the intermediate
fluorination product of antimony metal, was carried out. The TG-DTA
curves of fluorination experiment of SbF are shown in Fig. 3. Heating
rates for Fig. 1 (a)–(c) was 10, 5, and 2 °C/min, respectively. In order to
compare the reaction with F , the TG-DTA curve of the heating ex-
periment of SbF at Ar atmosphere is also shown in Fig. 4.
As shown in Fig. 4, SbF started to volatilize at 200 °C in Ar with an
endothermic reaction and the volatilization of SbF was completed by
3
3
3
2
3
3
3
Fig. 4. TG-DTA curves of the heating experiment of SbF
3
in Ar atmosphere at
2 5
Fig. 5. TG-DTA curves of the fluorination experiment of Sb O at two heating
heating rate of 10 °C/min.
rates: (a) 10 °C/min and (b) 5 °C/min.
3

D. Watanabe et al.
Journal of Fluorine Chemistry 214 (2018) 1–7
2 4
Fig. 6. TG-DTA curves of the fluorination experiment of Sb O at two heating
rates: (a) 10 °C/min and (b) 5 °C/min.
temperature with increasing heating rate, therefore, reaction rate
would be slow compared with heating rate. However, since the shape of
TG-DTA curves in Fig. 6(a) and (b) was resembled each other, the
fluorination reaction would not be affected by the heating rate.
The residue of the fluorination experiment heated to 500 °C with the
heating rate of 10 °C/min was identified as Sb
2
O
4
by XRD analysis. It
indicated that Sb
fluoride.
2
O
4
was directly fluorinated to volatile antimony
2 3
Fig. 7. TG-DTA curves of the fluorination experiment of Sb O at three heating
rates: (a) 10 °C/min, (b) 5 °C/min, and (c) 2 °C/min.
2.1.5. Results of fluorination experiment of Sb
2 3
O
Finally, the result of fluorination experiment was shown for Sb
2 3
O
which has the lowest valence state of antimony among the antimony
oxides used in this study. The TG-DTA curves of fluorination experi-
2 3
ment of Sb O are shown in Fig. 7. Heating rates for Fig. 7(a)–(c) was
10, 5, and 2 °C/min, respectively. As shown in Fig. 7, an initial sharp
exothermic peak was observed around 330 °C independent of heating
rate, and ΔM started to decrease. After that, ΔM continued to decrease
2 3
with the broad exothermic curve. Therefore, it is clarified that Sb O
reacted with F
min of heating rate (Fig. 7(c)), all of the Sb
2
above 330 °C by two step reactions. In the case of 2 °C/
was volatilized. On the
2 3
O
other hand, some amount of material remained after the fluorination
experiment in the case of 10 and 5 °C/min. It would be caused by dif-
ference of the F feed time in each experiment; this effect was men-
2
tioned in Section 2.1.1 in detail. Since the shape of TG-DTA curves in
Fig. 7(a), (b), and (c) was resembled each other, the fluorination re-
action would not be affected by the heating rate.
The residue after the fluorination of Sb
a heating rate of 10 °C/min was identified as Sb
indicated that Sb was converted to Sb
fluorination reaction.
2
O
3
heated up to 500 °C with
by XRD analysis. It
2 4
O in the course of the
2 4
O
2
O
3
Fig. 8. Gibbs free energy of the reaction of antimony compounds.
2.2. Thermodynamic consideration of fluorination of antimony compounds
Fluorination reactions of antimony metal and Sb
ΔG value in the temperature range as given in Fig. 8. In room tem-
perature, ΔG of the fluorination reaction forming SbOF from Sb was
negative, however, ΔG of the fluorination reaction forming SbF from
SbOF also was negative. Therefore, if SbOF was formed by the fluor-
ination reaction, it would be further fluorinated to SbF . As mentioned
in Section 2.1.5, Sb was formed in the fluorination experiment of
Sb . It was indicated in Fig. 8 that Sb would be oxidized to Sb
by the reaction with O
2 3
O were negative
In this section, thermodynamic consideration was examined for
related reaction of fluorination reaction of antimony compounds. The
Gibbs free energy (ΔG) for the related reactions were evaluated by the
calculation using the thermodynamic data base [16] and using the
thermodynamic properties which Wagman et al. [17] suggested. The
results of thermodynamic consideration are shown in Fig. 8. Since the
2 3
O
3
3
2 4
O
data of SbF
5
and oxyfluorides except for SbOF were missing, the related
2
O
3
2
O
3
2 4
O
reactions were not given in Fig. 8.
2
.
4

D. Watanabe et al.
Journal of Fluorine Chemistry 214 (2018) 1–7
2
2
.3. Fluorination reaction of antimony compounds
decrease of ΔM was observed above 190 °C especially; decrease of ΔM
seemed to be delayed from start of the exothermic reaction. Therefore,
.3.1. Fluorination reaction of antimony metal
it was considered as main fluorination reaction of SbF
3
, which was
As mentioned in Section 2.1.1, three reactions were observed in the
given as reaction (2), was exothermic peaks above 190 °C.
TG-DTA curves shown in Fig. 1; exothermic reaction with mass increase
at 150 °C, exothermic reaction with mass decrease at 190 °C, and re-
action with slight mass decrease at 330 °C. These reactions were clearly
observed in Fig. 1(c) because the fluorination reactions could be se-
parately observed at slow heating rate. And as shown in Fig. 2, the
residue of fluorination reaction at 500 °C was antimony metal, and that
The shoulder of the exothermic peak at 150 °C in Fig. 3(a) and the
exothermic peak at 150 °C in Fig. 3(b) was observed with or without
slightly mass increase; this exothermic peak was obscure for Fig. 3(c).
Colbin [14] suggested some addition compounds consisted by SbF
SbF . Since the change of ΔM was small, exothermic reaction may
fluorination reaction to produce such addition compounds.
3
and
5
at 170 °C was antimony metal and SbF
confirmed that fluorination reaction of antimony metal at 150 °C and
3
. Based on these result, it is
In main fluorination reaction above 190 °C, two or three exothermic
peaks was observed in Fig. 3 (c). Since the heat production was large in
the fluorination reaction because the valence state of antimony was
oxidized to pentavalent from trivalent, the temperature may be in-
creased locally by heat production of the fluorination reaction as same
as the fluorination reaction of antimony metal. In such condition,
1
90 °C were described by reactions (1) and (2).
/3Sb + F → 2/3SbF
+ F → SbF
As shown in Fig. 3, the fluorination reaction of SbF
2
2
3
(1)
(2)
SbF
3
2
5
3 3 5
fluorination of SbF and volatilization of SbF and SbF would be
3
with drastic
concurrently occurred; it meant that some phenomena were con-
currently occurred. Because of these phenomena, it may be considered
that some sharp exothermic peaks were found above 190 °C in Fig. 3.
Additionally, decrease of ΔM was delayed from start of the exothermic
reaction around 190 °C, this may be caused by balancing of volatiliza-
decrease of ΔM was observed at 190 °C which was same temperature of
second exothermic reaction shown in Fig. 1(c). This result would be
support the idea that the exothermic reaction at 190 °C in Fig. 1 was
reaction (2).
−1
The vapor pressure of SbF
50 °C by the calculation using a thermodynamic data base [16], and
that of SbF has been reported as 100 kPa at 142.7 °C [1]. Namely, SbF
has low volatility at 150 °C, and SbF has high volatility at that tem-
perature. And in 150 °C, SbF did not volatilize as shown in Fig. 4.
Therefore, the temporary increase of ΔM at 150 °C in Fig. 1(c) would be
caused by the formation of SbF . Then, ΔM should be +47% when
reaction (1) completed without volatilization of SbF . However, ΔM
3
was evaluated as about 10
kPa at
5
tion of SbF and formation of addition compounds, which was men-
tioned in previous paragraph.
1
5
3
As same as the case of antimony metal, ΔM seemed to decrease
slightly over 330 °C in Fig. 3. It would be caused by fluorination reac-
tion of few amount of antimony oxide. And, in TG-DTA curves in Fig. 3,
exothermic peaks were not separately observed each other at high
heating rate, however, the shape of TG-DTA curves were seemed to be
resembled. It is considered that heating rate would not affect to the
5
3
3
3
was +13% as maximum in Fig. 1(c). From this view point, in Fig. 1(c),
metal antimony would be remained at 180 °C which was finish tem-
perature of initial fluorination reaction. On the other hand, ΔM started
3
fluorination reaction of SbF .
2
.3.3. Fluorination reaction of Sb
Sb was volatilized by the fluorination reaction above 330 °C as
shown in Fig. 5. Since antimony is pentavalent in Sb , antimony
2 5
O
to decrease above 180 °C in Fig. 1(c). At 180 °C, vapor pressure of SbF
3
2 5
O
3
was 0.2 kPa [16], and SbF did not volatilize as shown in Fig. 4. Since
2 5
O
fluorination reaction was large exothermic reaction, temperature of
local place such as the interface of gas-solid reaction may be increased
over 180 °C in this experiment. Because of this reason, antimony metal
cannot be further oxidized to a higher valence state even by the
fluorination reaction. Reduction of antimony also cannot occur by the
fluorination reaction. Therefore, the fluorination reaction is considered
as reaction (3).
started to volatilize at 180 °C as SbF
SbF started above 190 °C, decrease of ΔM stopped from 190 °C to
20 °C in Fig. 1(c). As mentioned in more detail section 2.3.2, it would
be caused by balancing of volatilization of SbF and formation of ad-
, which was suggested by
3 5
or SbF . After the fluorination of
3
2
1/5Sb
2
O
5
+ F
2
→ 2/5SbF
5
+ 1/2O
2
(3)
5
dition compounds consisted by SbF
Colbin [14].
3 5
and SbF
As mentioned in section 1, formation of oxyfluoride should be in-
vestigated for the fluorination reaction of oxide materials. Colbin [14]
suggested antimony oxyfluorides such as SbO F, and SbOF . The de-
In the XRD pattern of residue of fluorination reaction of antimony
metal at 500 °C shown in Fig. 2(a), only antimony metal peaks were
2
3
composition reactions of antimony oxyfluorides were suggested as re-
actions (4) and (5) [14].
detected. SbF
dicates that metal antimony would be fluorinated to SbF
90 °C. Therefore, it was considered that SbF peaks were not detected
3
was fluorinated to volatile SbF
5
above 190 °C. It in-
5
directly above
5
SbO
2
F → 2Sb
2
O
4
+ SbF
5
5
+ O
2
(4)
(5)
1
3
and only antimony metal peaks were detected in the XRD pattern of
Fig. 2(a).
In Fig. 1(c), ΔM slightly decreased over 330 °C. As shown in
2
Figs. 5–7, antimony oxides started to react with F above 330 °C. The
XRD pattern of starting material of antimony metal indicated only an-
timony metal, however, the surface of starting material may be already
oxidized. Since the decrease of ΔM was slight at 330 °C in Fig. 1(c), it
was considered that the reaction would be fluorination reaction of
antimony oxide such as oxidized surface of antimony metal.
In TG-DTA curves in Fig. 1, exothermic peaks were not separately
observed each other at high heating rate, however, the shape of TG-
DTA curves were seemed to be resembled. It is considered that heating
rate would not affect to the fluorination reaction of antimony metal.
5SbOF
3
→ Sb
2
O
4
+ 3SbF
+ 1/2O
2
The reaction temperatures of reactions (4) and (5) were reported as
50 °C and 200 °C, respectively [14]. SbO F seemed to be relatively
stable at 330 °C which was the reaction temperature of the fluorination
3
2
of Sb
Sb
2
O
5
. Therefore, SbO
2
F was considered as a potential intermediate.
2
O
5
may be fluorinated to SbF
5
via SbO
2
F according to reactions (6)
and (7).
Sb + F
/2SbO F + F
2
O
5
2
→ 2SbO
2
F + 1/2O
2
(6)
(7)
1
2
2
5 2
→ 1/2SbF + 1/2O
However, the TG-DTA curve was looked as that Sb
by one step reaction. Therefore, if SbO F were formed by reaction (6),
SbO F would be immediately fluorinated to SbF by reaction (7).
The residue of fluorination reaction of Sb could not be identified.
The residue of fluorination experiment of Sb and Sb was oxide
compound, which was Sb
2 5
O was reacted
2
2
5
2
.3.2. Fluorination reaction of SbF
As shown in Fig. 3, several exothermic peaks were observed in the
TG-DTA curves. However, the exothermic reaction with drastic
3
2
O
5
2
O
3
2 4
O
2 4
O . Abe et al. [18] suggested amorphous
5

D. Watanabe et al.
Journal of Fluorine Chemistry 214 (2018) 1–7
Sb
2
O
5
. The residue of fluorination reaction of Sb
2
O
5
may be amorphous
the reaction. Sb
reacted with F
ever, Sb was formed temporarily in the course of the reaction.
Oxygen released from the fluorination reaction of a part of Sb would
oxidize remained Sb to Sb . Sb , reported as a mixture of tri-
valent and pentavalent antimony, reacted with F and volatilized above
30 °C. The product of the fluorination reactions of these antimony
2
O
5
reacted with F
2 2 3
and volatilized above 330 °C. Sb O
oxide such as amorphous Sb
2
O
5
.
2
and completely volatilized finally above 330 °C, how-
2 4
O
2 3
O
2
.3.4. Fluorination reaction of Sb
As shown in the TG-DTA curves in Fig. 6, Sb
above 330 °C. The residue of fluorination reaction was starting ma-
. It suggested that Sb was directly fluorinated to vo-
latile compound. On the other hand, Sb was reported as a mixture of
trivalent and pentavalent antimony [19]. It would suggest that Sb
was consisted by Sb and Sb . Therefore, it was considered that
Sb was fluorinated by reactions (3) and (8).
2 4
O
2
O
3
2
O
4
2 4
O
2 4
O started to react with
F
2
2
3
terial of Sb
2
O
4
2 4
O
5
oxides was considered as volatile SbF . Therefore, it was clarified that
2 4
O
antimony compounds reacted with fluorine and antimony would be
volatilized as SbF by the fluorination reaction.
2 4
O
2
O
3
2 5
O
5
2 4
O
4. Experimental
1/5Sb + F → 2/5SbF + 3/10O
2
O
3
2
5
2
(8)
4.1. Materials
As shown in Fig. 7, the fluorination reaction of Sb
2
O
3
proceeded by
two step reactions; sharp exothermic reaction with ΔM decrease and
Antimony metal of 99.5% purity, SbF
purity was not provided) (all form Wako Pure Chemical Industries,
Ltd.), and Sb of 99.995% purity (Sigma-Aldrich Co., LLC) were used
as-received. Sb was obtained by the oxidation of Sb in air at
00 °C and its identity verified by XRD analysis. All of the antimony
compounds including antimony metal were fine powder. Analytical
grade 5% F -N gas (95.09% N and 4.91% F ) and 10% F -N (90.1%
and 9.9% F ) (Central Glass Co., Ltd.,) and argon gas of 99.9999%
purity (Nippon Sanso Co., Ltd.) were used as-received; the study was
started with 5% F -N but when it could not be obtained, 10% F -N
was used for the remaining experimental runs.
3 2 5
of 95% purity, Sb O (the
broad exothermic reaction with ΔM decrease. The sharp exothermic
2 5
reaction was not observed in the fluorination reaction of Sb O as
2 3
O
shown in Fig. 5. Therefore, sharp exothermic peak would be caused by
the change of the valence state of antimony. Because of this reason, the
change in the exothermic peak around 430 °C in the Fig. 6 was con-
sidered to be caused by the change of the valence state of antimony in
2
O
4
2 3
O
9
2
2
2
2
2
2
the Sb
exothermic peak at 330 °C observed in the fluorination reaction of
Sb (Fig. 7) was not observed in Fig. 6. When Sb was used as
starting material, it is considered that the fluorination of Sb started
started by
2 4
O from trivalent to pentavalent. On the other hand, the sharp
N
2
2
2
O
3
2 4
O
2
2
2
2
2 5
O
2 3
at 330 °C by reaction (3) first, and the fluorination of Sb O
reaction (8) later.
4.2. Thermogravimetric and differential thermal analyses
2
.3.5. Fluorination reaction of Sb
As mentioned in Section 2.1.5, Sb
2 3
O
The Rigaku TG-DTA system (Thermo plus 2) set in a high purity
argon atmosphere glove box was used. In order to prevent corrosion by
, nickel or nickel alloy was used in the TG-DTA system and the pan for
the TG-DTA. The amount of antimony compounds for an experimental
run was about 10 mg. The flow gas was a mixture of Ar (40 mL/min)
2 3 2
O reacted with F above 330 °C
by two step reactions shown in the TG-DTA curves in Fig. 7; sharp
exothermic reaction with ΔM decrease and broad exothermic reaction
with ΔM decrease. And, the residue of the fluorination reaction was
F
2
2 4 2 3
identified as Sb O by XRD analysis. Sb O was volatilized by the
and 5% F
-N (10 mL/min). F
method using Al adsorbent. Heating was carried out from room
temperature to 500 °C with heating rates of 2, 5, and 10 °C/min.
2
-N
2
(20 mL/min) or a mixture of Ar (50 mL/min) of and 10%
fluorination reaction as shown in Fig. 7, therefore, the fluorination
reaction was considered as reaction (8). SbOF and SbF would be po-
tential product of fluorination reaction, however, ΔG of fluorination
reaction of SbOF to SbF was negative as shown in Fig. 8 and SbF
should fluorinated to SbF above 190 °C as discussed in Sections 2.3.1
F
2
2
2
in off-gas was eliminated by an adsorption
3
2 3
O
3
3
5
4.3. X-ray diffraction analysis
and 2.3.2. Therefore, reaction (8) was considered as appropriate
fluorination reaction.
On the other hand, since Sb
oxidation reaction (9) also would be occurred concurrently.
The identification of the residue of the fluorination experiment was
2 4
O was formed in the experiment,
carried out by X-ray powder diffraction with the Rigaku X-ray dif-
fractometer (MiniFlex600). The sample material for XRD analysis was
covered as necessary by polyimide film to prevent exposure to air.
2
4
Sb
2
O
3
+ O
2
→ 2Sb
2
O
4
(9)
Reactions (8) and (9) are summarized as reaction (10).
References
/5Sb
2
O
3
+ F
2
→ 2/5SbF
5
+ 3/5Sb
2
O
4
(10)
[
[
[
[
[
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7