Materials Transactions, Vol. 51, No. 6 (2010) pp. 1102 to 1108
#2010 The Japan Institute of Metals
Production of Metallic Vanadium by Preform Reduction Process
Akihiko Miyauchi1; * and Toru H. Okabe2
1
2
Department of Materials Engineering, Graduate School of Engineering, the University of Tokyo, Tokyo 113-8656, Japan
Institute of Industrial Science, the University of Tokyo, Tokyo 153-8505, Japan
A fundamental study was conducted on a new process for producing vanadium (V) metal by the preform reduction process (PRP) based on
metallothermic reduction of vanadium pentoxide (V2 O5 ). Feed preforms with good mechanical strength even at elevated temperatures were
prepared by adding either CaO or MgO to V2 O5 feed powder because V2 O5 has a low melting point of 963 K; thus complex oxides (Cax Vy Oz ,
Mgx Vy Oz ) with high melting point at more than 1273 K were obtained. Reduction experiments were conducted by using either Ca or Mg vapor
at 1273 K for 6 h. V metal with a purity of more than 99% was successfully obtained when using Mg as a reductant. The feasibility of producing
V metal by the PRP will be discussed on the basis of fundamental experiments. [doi:10.2320/matertrans.M2010027]
(Received January 26, 2010; Accepted March 16, 2010; Published April 28, 2010)
Keywords: vanadium, reduction process, metallothermic reduction
1.
Introduction
Vanadium (V) is a transition-metal element with an atomic
number of 23. V metal is the 20th most abundant element
among all elements in the earth’s crust. The abundance of V
metal is 120 ppm in the earth’s crust, which is significantly
larger than the well-used common metals such as nickel (Ni,
84 ppm, 23rd rank) and copper (Cu, 60 ppm, 26th rank).1,2)
However, V metal belongs to a set of less common metals or
‘‘rare metals’’ since the production volume of V metal was
only 58 kt in 2007 and is far smaller as compared to that of
common metals.3) The small production volume of V metal is
partly due to its low concentration in the ore and uneven
distribution of its minerals. The principal V metal minerals
such as titanomagnetite contain only 1–2 mass% of V2 O5 .4)
The majority of the mineral resources are distributed in three
countries: China, Russia, and South Africa.
V metal and its alloys are mainly used as additive elements
(alloying elements) or as catalysts. In Japan, more than 85%
of V metal is used as an additive in steel products for
improving their tensile strength and heat resistance.5) Special
steel containing V metal is applied in bridges, industrial
tools, etc. In the field of chemical industries, V compounds
are utilized as a desulfurization catalyst in sulfuric acid
production processes. Furthermore, vanadium-titanium (VTi) alloys are now attracting considerable attention as new
electrode materials in hydrogen storage batteries, because V
has high hydrogen storage capacity at ambient temperature
and moderate pressure.6–8) Considering the expanding market
for hydrogen storage batteries, the demand for V-Ti alloys
may be expected to increase in the future.
Currently, V feed for smelting V metal is produced in the
form of its oxide (V2 O5 ) as a byproduct of steel slag or as a
residue of oil, and these V2 O5 feeds are mostly used as a
starting material for V products. V metal is commercially
produced by the aluminothermic reduction (ATR) of
V2 O5 .9,10) Although this process is simple and economical,
the product is not a high-purity V metal; it is a vanadiumaluminum (V-Al) alloy containing 20 mass% of aluminum
*Graduate
Student, the University of Tokyo
(Al). In order to produce high-purity V metal, multiple
melting steps by using an electron beam melting process are
necessary for removing the Al. For this reason, the ATR
process is not a suitable production process of high-purity V
metal. In the past, some researchers attempted to develop
an alternative to the ATR process for producing V metal.
Metallic V with more than 99% purity was first produced
through calciothermic reduction by Marden and Rich.11)
They used a mixture of V2 O5 , Ca and CaCl2 at 1173–1223 K.
McKechenie and Seybolt proposed another reaction based on
calciothermic reduction with a small amount of flux such
as CaI2 .12) Gregory researched calciothermic reduction of
V2 O3 .13) In order to eliminate oxygen contamination,
chloride metallurgy for producing high purity V metal was
investigated by Campbell et al.14) Preparation of high-purity
V by the Van Arkel-de Boer process (Iodide disproportionaton process) was studied by Carlson et al.15,16) However, an
effective production process suitable for commercial mass
production has not been established at this stage. Therefore,
the development of a simple and efficient production process
of high-purity V metal is strongly required. In the recent
years, Suzuki et al. investigated electrochemical reduction of
V2 O5 or V2 O3 in molten CaCl2 for producing high purity V
metal and its alloys,17–19) as well as calciothermic reduction
of V2 O5 and TiO2 for producing V-Ti alloys.20) With these
backgrounds, the present study aims to develop a new process
for the effective production of V metal from its oxide by
utilizing a simple metallothermic reduction.
2.
Preform Reduction Process (PRP)
As an effective production process of high-purity V metal
from V2 O5 , we selected the preform reduction process
(PRP).21–23) Feed preforms are prepared by mixing a starting
material oxide feed, flux, and binder solution. After drying,
the preforms have sufficient mechanical strength to stand
alone. By utilizing the features of the mechanical structure of
the feed preforms, contamination from the reduction container can be prevented. In the PRP, the oxide in the preforms is
directly reduced to metal by reductant vapor. After reduction,
the produced metal is recovered by leaching. The advantages
Production of Metallic Vanadium by Preform Reduction Process
Temperature, T / K
0
2000
-200
3/2 Fe +
-400
+
4/5 V
-600
O2 = 1/2
Vapor pressure of element i, log pi / atm
Standard Gibbs energy of formation, ∆G°f / kJ mol -1
Reduction temperature
Fe 3O4
/5 V 2O 5
O2 = 2
= TiO2
Ti + O 2
l O3
2/3 A 2
=
O
l+ 2
4/3 A
-800
-1000
2 CaO
O2 =
+
a
2C
gO
=2M
O
2
+
g
-1200
2M
-1400
300
500
700
900
1100 1300
1000
500
P °Mg = 0.458 atm
at 1273 K
-2
P °Ca = 0.018 atm
at 1273 K
Mg
-4
Al
Ca
Fe
-6
Ti
-8
-10
V
0.5
Temperature, T / K
Fig. 1
1103
1.0
1.5
2.0
Reciprocal temperature, 1000 T -1 / K-1
Ellingham diagram of some selected oxides.24)
Fig. 2 Vapor pressure of some selected elements as a function of reciprocal
temperature.24)
of this process are its effective control of purity and
morphology and its ability to flexibly scale the reduction
process. Contamination into the product can be easily
avoided because the feed material in the self-supporting
preform does not have physical contact with the reaction
container or the reductant. Highly flexible scalability is
achieved as it is possible to simultaneously treat multiple
pieces of preforms in a single reduction chamber. Furthermore, the amount of molten salt (or flux) used in this process
is smaller than that used in other processes.
3.
atures at above melting point of V2 O5 . In order to solve this
problem, V2 O5 was mixed with flux such as magnesium
oxide (MgO) or calcium oxide (CaO) and calcined to
synthesize complex vanadium oxides. In Fig. 3, equilibrium
phase diagrams of V2 O5 -MgO and V2 O5 -CaO quasi binary
systems are shown.26,27) It is expected that Mg2 V2 O7 and
Ca2 V2 O7 maintain enough mechanical strength even at the
reduction temperature (Tred. ¼ 1273 K) because these compounds have high melting points.
Thermodynamic Analysis
4.
A reductant suitable for the PRP and the optimum
reduction temperature were studied from the thermodynamic
view-point. Calcium (Ca) or magnesium (Mg) was selected
as a suitable reductant for the V2 O5 reduction by considering
the Gibbs energies for the formation of oxides shown in
Fig. 1.24) For reducing V2 O5 by the PRP, the reductant metal
has to be supplied in a vapor form. The vapor pressure of
some selected elements as a function of temperature is
illustrated in Fig. 2.24) In order to have an efficient supply of a
reducing agent in the gas phase, it is desirable that the vapor
pressure of the reducing agent is higher than 104 atm at the
reduction temperature.25) In this study, 1273 K was selected
as the reduction temperature because their vapor pressures
are higher than 103 atm, which is high enough for sufficient
gas supply of the reducing agents.
The melting point of V2 O5 is 963 K, which is lower than
the reduction temperature. This low melting point causes
difficulty in the fabrication of a suitable feed preform for the
PRP. The preforms fabricated only from V2 O5 and a binder
cannot retain their mechanical shapes at elevated temper-
Experimental
A flowchart of the production of V metal by the PRP
employed in this study is shown in Fig. 4. The PRP of V2 O5
using Ca or Mg vapor as a reductant consisted of four major
steps: preform fabrication, calcination, reduction by reductant vapor, and sample recovery by acid leaching. Firstly, the
feed preform was fabricated from a slurry made of V2 O5
powder (99.9% purity), CaO or MgO powder as a flux, and a
collodion solution (5 mass% nitrocellulose in ethanol and
ether) as a binder. The experimental conditions for preparing
the feed preform using the Ca or Mg vapor were determined.
The viscosity of the slurry was controlled by varying the
amount of the flux and binder. The cationic molar ratio,
RCat./V , listed in Table 1 is defined as RCat./V ¼ NCat. =NV ,
where NCat. and NV are the mole amounts of the cation in
the flux and V, respectively. Plate-shaped preforms with a
thickness of 3–10 mm were prepared by casting the obtained slurry into a stainless steel mold. Secondly, the cast
preforms were heated and calcined in air for 2 h at calcined
temperatures.
1104
A. Miyauchi and T. H. Okabe
Table 1
Experimental conditions for the preparation of feed preforms.
Mass of sample, wi /g
Cationic
molar ratio,
RCat./V 2
Calcined
temperature,
Tcal. /K
Calcined
time,
t00 cal. /h
Note
(Corresponding figures)
CaO
Binder
Collodion1
1.19
—
4.02
1.0
1173
2
Fig. 6(a)
1.79
—
4.56
1.5
1173
2
2.68
—
1.67
4.66
1.0
1173
2
2.68
—
2.48
5.25
1.5
1173
2
A-5
2.68
1.19
—
4.09
1.0
873 ! 1173
2
A-6
2.68
1.79
—
4.60
1.5
873 ! 1173
2
A-7
2.68
—
1.67
4.76
1.0
873 ! 1173
2
A-8
2.68
—
2.48
5.29
1.5
873 ! 1173
2
Exp.
no.
Flux
Feed
V2 O5
MgO
A-1
2.68
A-2
2.68
A-3
A-4
1
2
Fig. 6(b), Fig. 7(a) (c), Fig. 8
Fig. 7(b) (d), Fig. 9
Collodion solution (5 mass% nitrocellulose in ethanol and ether) was used.
RCat./V ¼ xCat. =xV , xcat. : mole amounts of cations in flux, xV : mole amounts of vanadium.
Flux
(a)
1100
1074°C
V2O5
Binder
Mixing / casting
Mg3(VO4)2 + L
Reduction temp. in this study (1273 K)
Preform fabrication
Feed preform
Mg2V2O7 + Mg3V2O8
Mg2V2O7 + L
V2O5 + L
670°C
MgV2O6 + L
Mg2V6O17 + L
V2O5 + Mg2V6O17
500
0
V2O5
20
Mg2V2O7
MgV2O6
604°C
40
Calcination
Reductant (Ca or Mg)
50% CH3COOH aq.,
20% HCl aq.,
Distilled water,
Isopropanol,
Acetone
Leaching
L
S
Waste
solution
Vacuum drying
80
(MgO)
60
Reduction
Reduced preform
MgV2O6 +
640°C
Mg2V2O7
700
742°C
Mg3V2O8
L
Mg3V2O8 + MgO
900
Mg2V6O17
Temperature, T’ / °C
980°C
MgO content, x MgO (mol%)
V metal powder
Fig. 4
Flowchart of the production of V metal by PRP in this study.
(b)
1380°C
1200
Reduction temp. in this study (1273 K)
800
778°C
0
V2O5
20
40
CaV2O6
618°C
600
1015°C
Ca3V2O8
1000
L
Ca2V2O7
Temperature, T’ / °C
1400
60
(CaO)
CaO content, x CaO (mol%)
Fig. 3 Equilibrium phase diagram of (a) V2 O5 -MgO quasi-binary system,26) (b) V2 O5 -CaO quasi-binary system.27)
Figure 5(a) is a schematic illustration of the experimental
apparatus used for the calcination step. In this calcination
step, the binder and water in the feed preforms were removed,
and an adequate amount of mechanical strength was further
granted to the preforms. Then, the calcined preforms were
installed in a reaction vessel and reduced by the Ca or Mg
vapor in the reduction step. Figure 5(b) is a schematic
illustration of the experimental apparatus used for producing
V metal by the PRP. Four pieces of the calcined preforms
(4–6 g each) containing vanadium oxides were placed in a
thick-walled stainless steel vessel, and the reductant solid
was placed at the bottom of the vessel. Two times excess
stoichiometric amount of reductant (Ca or Mg) was used in
the reduction experiment (see RR values in Table 2). The
reductant solid was physically isolated from the feed preform, and the reductant vapor was supplied to the feed
preform. Sponge titanium was also placed at the bottom of
the vessel for gettering the nitrogen gas in the system.
After being sealed by tungsten inert gas (TIG) welding, the
Production of Metallic Vanadium by Preform Reduction Process
1105
Table 2 Experimental conditions for the reduction experiments, and representative analytical results of vanadium powder obtained after
reduction.
Exp.
no.
Flux
Reductant
Composition of vanadium powder
Mass of samples, wi /g
Cationic
molar
ratio,
RCat./V 1
Excess
reductant
ratio,
RR 2
Reduction
temperature,
Tred. /K
Reduction
time,
t00 red. /h
1.5
1.5
2.0
2.0
1273
1273
6
6
obtained after reduction, Ci 3 /mass%
Calcined
preform,
wcal. /g
Reductant,
wR /g
CV
CMg
CCa
CFe
CCr
3.937
3.670
3.345
4.906
99.7
86.0
0.2
2.4
—
10.6
0.01
0.3
0.03
0.5
A-6-1
A-6-2
MgO
MgO
Mg
Ca
A-8-1
CaO
Mg
1.5
2.0
1273
6
3.474
2.573
85.4
—
13.0
0.2
0.4
A-8-2
CaO
Ca
1.5
2.0
1273
6
3.604
3.976
79.0
—
20.4
0.1
0.4
1
RCat./V ¼ xCat. =xV , xcat. : mole amounts of cations in flux, xV : mole amounts of vanadium
Excess reductant ratio: RR ¼ wR =wR,theo. , wR,theo. : stoichiometic mass of reductant necessary for reduction.
3
Determined by XRF; value excludes carbon and gaseous elements.
2
(a)
Alumina tube
Ceramics chamber
ature. It was then successively rinsed with distilled water,
alcohol, and acetone, followed by drying in vacuum. The
phases in the sample were identified using X-ray diffraction
analysis (XRD; Rigaku, Rint 2000, Cu–K line). The
composition of the sample was determined by X-ray
fluorescence spectrometry (XRF; JEOL Ltd., JSX-3210).
Heating element
Thermocouple
Alumina crucible
Feed preform
(b)
TIG weld
Stainless steel cover
Stainless steel
reaction vessel
Feed preform
(V2O5 + flux)
Stainless steel plate
Reductant (Ca or Mg)
Ti sponge getter
Fig. 5 Schematic illustration of the experimental setup for (a) the
calcination experiment, (b) the reduction experiment.
steel reaction vessel was then heated in an electric furnace
maintained at a constant temperature of 1273 K for 6 h; the
preforms reacted with the reductant vapor.
After 6 h of reaction, the reaction vessel was removed from
the furnace and was quenched in water. Finally, the preforms
in the container were mechanically recovered at room
temperature by opening the sealed vessel with a lathe. The
product in the preforms obtained after the reduction experiment was recovered by leaching the preforms with an acid,
i.e. by dissolving the reaction product (CaO/MgO), flux,
and excess reductant in an acetic acid solution. The obtained
product was rinsed with hydrochloric acid at room temper-
5.
Results and Discussion
5.1 Calcination process
The plate-shaped preform was fabricated by casting feed
slurry prepared by mixing V2 O5 , flux, and the collodion
solution. The size of the preform was 50 20 4 mm, and
it was beige in color. Figure 6 shows representative photographs of the obtained samples after calcination experiment.
As shown in Fig. 6(a), samples (Exp. A-1-Exp. A-4) did not
sustain their original shapes, after the calcination process at a
constant temperature of 1173 K for 2 h because of melting
V2 O5 in the feed preforms immediately after starting
calcination procedure. Samples with a cationic molar ratio
of RCat./V ¼ 1:5 (Exp. A-6 and Exp. A-8) maintained their
original shape (see Fig. 6(b)), after the calcination step at
temperatures ranging from 873 K to 1173 K in 2 h. In
contrast, other samples with RCat./V ¼ 1:0 (Exp. A-5 and
Exp. A-7) did not retain their original shapes since they lost
their mechanical strengths due to the melting of V2 O5 .
The preforms which retained their shapes were successfully
produced in the calcination process by adjusting both the
amount of flux and the calcination temperature. Figure 7
presents the appearance and X-ray diffraction patterns of
the samples (Exp. A-6 and Exp. A-8) obtained after the
calcination process. The shape and color of the preform were
retained after performing calcination at temperatures rising
from 873 K to 1173 K in 2 h. By the reaction between V2 O5
and the flux, Mg2 V2 O7 or Ca2 V2 O7 were formed in the
obtained preforms. Although the melting point of Mg2 V2 O7
is slightly lower than 1273 K (see Fig. 3), the preforms
demonstrated sufficient mechanical strength even at elevated
temperatures. This is probably because MgO and Mg3 V2 O8
in the preforms contribute to maintaining the shape of
preforms, and Mg2 V2 O7 is reduced to V metal or suboxides
before melting the parts of preforms. The detail reason is
under investigation.
1106
A. Miyauchi and T. H. Okabe
(a) Melted preform
(a) Exp. A-6 (Flux: MgO, aR Cat. / V = 1.5)
(b) Exp. A-8 (Flux: CaO, aR Cat. / V = 1.5)
(b) Solid preform
(c) Exp. A-6 (Flux: MgO, aR Cat. / V = 1.5)
Intensity, I (a.u.)
MgO
20
JCPDS # 77-2364
Mg2V2O7 JCPDS # 70-1163
30
40
50
60
Angle, 2 θ (degree)
70
80
(d) Exp. A-8 (Flux: CaO, aR Cat. / V = 1.5)
5.2
Magnesiothermic reduction (Exp. A-6-1 and Exp. A8-1, reductant: Mg)
Figure 8 illustrates the appearance and the representative
XRD patterns of the samples with MgO flux obtained after
each step in Exp. A-6-1, and the experimental conditions for
reduction experiments are presented in Table 2. The color
of the preform changed to a jet-black color after the PRP
by Mg vapor at 1273 K for 6 h (Fig. 8(a)), and the shape of
the preform was slightly deformed. However, it was easy to
recover the preform from the reaction vessel because it was
physically isolated from the vessel even after reduction.
These results indicate that this PRP is suitable for avoiding
contamination from the reaction vessel. During the leaching
step in the acetic acid solution, the original shape of the
preform was lost and a powder with a grayish black color
was obtained without pulverizing the reduced preform
(Fig. 8(b)). Figure 8(c) presents an XRD pattern of the
preform after reduction at 1273 K for 6 h. All the complex
oxides were reduced to V metal by the Mg vapor. The
morphology of the sample was sponge like metal powder. A
summary of the analytical results of the obtained V powder
CaO
Intensity, I (a.u.)
Fig. 6 Photograph of the obtained samples in the alumina crucible after the
calcination experiment, (a) Exp. A-1 (Flux: MgO, RCat./V ¼ 1:0, Tcal. ¼
1173 K), (b) Exp. A-6 (Flux: MgO, RCat./V ¼ 1:5, Tcal. ¼ 873 ! 1173 K).
20
JCPDS # 77-2010
Ca2V2O7 JCPDS # 72-2312
30
40
50
60
Angle, 2 θ (degree)
70
80
Fig. 7 The obtained sample after the calcination process. (a RCat./V ¼
xCat. =xV , xcat. : mole amounts of cations in flux, xV : mole amounts of
vanadium.) (a) Photograph of the preform (Exp. A-6, Flux: MgO,
RCat./V ¼ 1:5, Tcal. ¼ 873 ! 1173 K), (b) Photograph of the preform
(Exp. A-8, Flux: CaO, RCat./V ¼ 1:5, Tcal. ¼ 873 ! 1173 K), (c) X-ray
diffraction pattern of the sample (Exp. A-6), (d) X-ray diffraction pattern
of the sample (Exp. A-8).
after reduction as well as of other samples is listed in Table 2.
The XRF analysis revealed the purity of the obtained
vanadium powder to be 99.7 mass% V, 0.2 mass% Mg, and
0.03 mass% Cr (Exp. A-6-1). In contrast, the preform with
CaO flux (Exp. A-8-1) was not completely reduced to V
metal. The XRD analysis revealed that the black powder
obtained after leaching process consisted of V metal and
CaV2 O4 . This is probably because the calcium complex
Production of Metallic Vanadium by Preform Reduction Process
(a) After reduction
(a) After reduction
(b) After leaching
(b) After leaching
(c) After reduction
(c) After reduction
30
40
Intensity, I (a.u.)
JCPDS # 77-2364
50
60
70
Angle, 2 θ (degree)
80
30
JCPDS # 77-2010
CaV2O4 JCPDS # 74-1359
40
50
60
Angle, 2 θ (degree)
70
80
(d) After leaching
V
40
CaO
JCPDS # 22-1058
Intensity, I (a.u.)
MgO :
(d) After leaching
30
:
:
JCPDS # 22-1058
50
60
70
Angle, 2 θ (degree)
CaV2O4 JCPDS # 74-1359
Intensity, I (a.u.)
Intensity, I (a.u.)
V
1107
80
30
40
50
60
Angle, 2 θ (degree)
70
80
Fig. 8 Photograph and XRD pattern of the obtained sample (Exp. A-6-1),
(a) and (c): After the reduction process (R: Mg, Flux: MgO, Tred. ¼
1273 K, t00 red. ¼ 6 h), (b) and (d): After the leaching process (50%
CH3 COOH aq. (t00 lea. ¼ 12 h), 20% HCl aq. (t00 lea. ¼ 1 h)).
Fig. 9 Photograph and XRD pattern of the obtained sample (Exp. A-8-2),
(a) and (c): After the reduction process, (R: Ca, Flux: CaO, Tred. ¼ 1273 K,
t00 red. ¼ 6 h), (b) and (d): After the leaching process (50% CH3 COOH aq.
(t00 lea. ¼ 12 h), 20% HCl aq. (t00 lea. ¼ 1 h)).
oxides (i.e. CaV2 O4 ) formed in the preform are chemically
stable and it becomes difficult to reduce by Mg vapor. The
details are unclear at this stage.
leaching. All of Ca2 V2 O7 was reduced to CaV2 O4 with the
Ca vapor after reduction, that is, the oxidation state of V
changed from +v to +iii. However, metallic V was not
produced in the experimental conditions employed in this
study. In the same way, V metal was not produced in Exp. A6-2, in which MgO was used as a flux; rough black powder
obtained after leaching was identified as Mg1:5 VO4 (i.e.
Mg3 V2 O8 ) by XRD analysis. The XRF analysis revealed the
purity of the obtained powder in the Exp. A-8-2 and Exp. A6-2 to be higher than 85 mass% V. It is assumed that a part of
5.3
Calciothermic reduction (Exp. A-6-2 and Exp. A8-2, reductant: Ca)
Figure 9 presents the appearance and the representative
XRD patterns of the samples obtained after each step in
Exp. A-8-2 with CaO flux. When Ca was employed as the
reductant, black solid in the form of flake was obtained after
1108
A. Miyauchi and T. H. Okabe
the surface of the obtained powder was reduced to metallic V.
At this stage, the reason for the unsuccessful results of
calciothermic reduction is not clear. The difference between
the results obtained using the Mg and Ca reductants are
probably due to the difference in their vapor pressures. The
vapor pressure of Mg (0.458 atm) is 26 times larger than that
of Ca (0.018 atm) at 1273 K. In fact, the amount of Ca
reductant remained in the crucible after the reduction was
larger than that of Mg. From a thermodynamic view-point
(see Fig. 1), Ca is a more favorable and strong reductant
compared to Mg. Therefore, certain kinetic reasons may have
hindered the calciothermic reduction of vanadium oxides
under PRP employed in this study, e.g., the slow diffusion of
Ca in the CaO byproduct formed at the surface of the
reduction product, and/or formation of compounds acting as
a kinetic barrier.
6.
Conclusion
In order to develop a new reduction process for producing
fine vanadium powder using the metallothermic reduction,
the preform reduction process (PRP) has been applied.
Slurries obtained by mixing V2 O5 powder, a flux (e.g. MgO,
CaO) and a binder (e.g. collodion), were cast into molds and
then dried to obtain the preforms. Before the reduction
process, fabricated preforms with RCat./V ¼ 1:5 were calcined
by heating from 873 to 1173 K in 2 h in order to produce
the preforms with good mechanical strength at elevated
temperatures. The sintered solid preforms containing to
complex oxides (Mgx Vy Oz , Cax Vy Oz ) were then reacted
with Ca or Mg vapor at a constant temperature of 1273 K for
6 h. When Mg vapor was used as a reductant, pure vanadium
powder of more than 99 mass% purity was obtained after
leaching process. The PRP was thus demonstrated to be
suitable for producing a fine, homogeneous metallic vanadium powder.
Acknowledgements
The authors are grateful to Profs. M. Maeda, S.
Yamaguchi, Y. Mitsuda, and K. Morita of The University
of Tokyo for their generous support and valuable discussions,
and Messrs. K. Tomoda and Y. Watanabe of the Nippon
Catalyst Cycle Co. Ltd. for providing valuable technical
information. We would specially like to thank Dr. K. Yasuda
and Mr. K. Yanada for their useful discussions. Thanks are
also due to Mr. T. Oi for providing technical assistance in
producing the metal powder.
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