Electrolytic preparation and characterization of VCr alloys in molten salt from vanadium slag

Article abstract of DOI:10.1016/j.jallcom.2019.06.366

Vanadium slag contains several critical elements like V, Ti, Cr, Fe and Mn. In our previous work, V and Cr have been enriched by selective chlorination, increasing from 10.05% to 14.95% and 5.84%–8.69% separately. V and Cr still maintain the trivalence state in molten salt. In the current work, the electrodeposition behaviors of V³⁺ and Cr³⁺ in NaCl–KCl molten salt at 800 °C were investigated using cyclic voltammetry (CV) and square wave voltammetry (SWV) with a tungsten electrode. It was found that the reduction processes of V³⁺ and Cr³⁺ consist of two steps, M³⁺/M²⁺, M²⁺/M. The diffusion coefficients of V³⁺ and Cr³⁺ in NaCl–KCl molten salt were measured by CV. The effect of VCl₃/CrCl₃ mass ratio on VCr alloy was investigated by a two-electrode under constant voltage. Pure Cr can be obtained at 2.8 V in the NaCl–KCl molten salt, while VCr alloy (3.71 mass % V-94.28 mass% Cr-2.01 mass % O) was obtained when electrolysis voltage was controlled to 2.8 V at 800 °C. The composition of VCr alloy can be designed by changing the molten salt composition. This method can be applied for direct preparation of VCr alloy from vanadium slag, thus offering the use of low cost raw materials with direct environmental benefits.

Full text of DOI:10.1016/j.jallcom.2019.06.366

Journal of Alloys and Compounds 803 (2019) 875e881
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Electrolytic preparation and characterization of VCr alloys in molten
salt from vanadium slag
,
, c,
Shiyuan Liu a b, Lijun Wang a *, Kuo-chih Chou d, Ramachandran Vasant Kumar c
a Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing, 100083, China
b National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences,
Beijing, 100190, China
c Department of Material Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, CB3 0FS, UK
d State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, 100083, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Vanadium slag contains several critical elements like V, Ti, Cr, Fe and Mn. In our previous work, V and Cr
have been enriched by selective chlorination, increasing from 10.05% to 14.95% and 5.84%e8.69% sepa-
rately. V and Cr still maintain the trivalence state in molten salt. In the current work, the electrodepo-
sition behaviors of V3þ and Cr3þ in NaCleKCl molten salt at 800 ꢀC were investigated using cyclic
voltammetry (CV) and square wave voltammetry (SWV) with a tungsten electrode. It was found that the
reduction processes of V3þ and Cr3þ consist of two steps, M3þ/M2þ, M2þ/M. The diffusion coefficients of
V3þ and Cr3þ in NaCleKCl molten salt were measured by CV. The effect of VCl3/CrCl3 mass ratio on VCr
alloy was investigated by a two-electrode under constant voltage. Pure Cr can be obtained at 2.8 V in the
NaCleKCl molten salt, while VCr alloy (3.71 mass % V-94.28 mass% Cr-2.01 mass % O) was obtained when
electrolysis voltage was controlled to 2.8 V at 800 ꢀC. The composition of VCr alloy can be designed by
changing the molten salt composition. This method can be applied for direct preparation of VCr alloy
from vanadium slag, thus offering the use of low cost raw materials with direct environmental benefits.
© 2019 Published by Elsevier B.V.
Received 17 March 2019
Received in revised form
19 June 2019
Accepted 28 June 2019
Available online 29 June 2019
Keywords:
VCr alloy
Electrodeposition
NaCleKCleVCl3eCrCl3 molten salt
1. Introduction
Vanadium slag generated from V-bearing titanomagnetite
semlting, thus, it has been regarded as one of valuable sources due
Vanadium is a very important element. Vanadium in the form of
oxides such as VO2 can be applied to thin films and nanowire [1].
Vanadium is also important alloying element. VCr alloy is widely
used as a hydrogen storage material and as a fusion reactor material
[2]. In the production process of VCr alloy, the traditional method
proposed is to convert V2O5 to the VCl5 and reduce VCl5 to V
metallothermically by Mg. Metallic Cr is obtained from Cr2O3 by
electrolysis or by metallothermic reduction by Si or Al. In subse-
quent steps, V and Cr are arc-melted over several times under an
argon atmosphere and then the cast metal is pulverized. This
process is highly energy-intensive and the required raw materials
are high-cost pure substances [3,4]. Using ore and slag to prepare
VCr alloy can reduce raw material costs. Such an approach can be
considered as economically viable.
to several valuable elements inside, with an approximate compo-
sition of 13e19 mass% V2O3 and 1e5 mass% Cr2O3. Currently, in
order to recover V and Cr from vanadium slag, the traditional
methods convert insoluble V3þ or Cr3þ from slag to water-soluble
V5þ or Cr6þ under oxidizing conditions [5e7]. The hazardous V5þ
and Cr6þ may have the greatly potential to threaten the environ-
ment [8,9].
In order to effectively recover and utilize vanadium slag avail-
able in significant quantities in China, a novel process for selective
extraction of iron and manganese by NH4Cl chlorination was pro-
posed in the present laboratory [10]. The enrichment ratio of V and
Cr was obtained as 48% [11]. V and Cr elements in the enriched
vanadium slag after AlCl3 chlorination are presented in the form of
VCl3 and CrCl3 in molten salt. VCr alloy can be obtained by molten
salt electrolysis from the VCl3 and CrCl3 molten salt.
With respect to the electrochemical behavior of vanadium ions
in molten salt, most of them are studied in LiCleKCleTiCl2 system,
CaCl2eNaCleVCl2 and LiCleKCl system [12e14]. The electro-
chemical behavior of Cr2þ and Cr3þ in NaCleKCl were investigated
* Corresponding author. Collaborative Innovation Center of Steel Technology,
University of Science and Technology Beijing, Beijing, 100083, China.
E-mail address: lijunwang@ustb.edu.cn (L. Wang).
https://doi.org/10.1016/j.jallcom.2019.06.366
0925-8388/© 2019 Published by Elsevier B.V.

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S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
[15,16]. However, the NaCleKCleVCl3eCrCl3 system is not reported.
Meanwhile, the CV and SWV study of and Cr in the
3. Results and discussion
V
NaCleKCleVCl3eCrCl3 systems are important to understand the
electrochemical reactions in the salt phase and industrial electrol-
ysis processes.
3.1. Electrolysis of V in NaCleKCleVCl3 molten salt system
The dotted line in Fig. 1 is the CV of the blank NaCleKCl molten
salt at a scan rate of 200 mV/s. It can be seen from the dotted line in
Fig. 1 that there is no oxidation and redox peak from 0 V to ꢁ1.8 V,
In this work, the original oxidation states of elements V and Cr are
V3þ and Cr3þ. The trivalent V and Cr are reduced to alloy in one single
step at relatively low temperatures. It is found that VCl3/CrCl3 mass
ratios have a significant effect on the preparation of VCr alloy. In the
present work, chromium-based alloys of low-oxygen content were
successfully synthesized. This method can be applied for direct
preparation of VCr alloy from vanadium slag, thus offering the use of
low cost raw materials with direct environmental benefits.
and only
a pair of reduction and oxidation peaks appear
between ꢁ1.8 V and ꢁ2.4 V. The reduction peak and oxidation peak
from the dotted line in Fig. 1 are attributed to reduction of Naþ and
oxidation of Na at the W electrode, respectively. In addition to the
redox peaks of sodium, there are no other redox peaks between 0 V
and ꢁ2.4 V.
In order to understand the mechanism of V3þ ion reduction, CV
of NaCleKCleVCl3 system are investigated and the results were
shown in Fig. 2(a). It can be seen that two groups of signals are
observed. The cathodic peaks (A and B) currents remarkably in-
crease while the cathodic peaks (A and B) potentials clearly shift
negatively with increasing scan rate.
2. Experimental section
2.1. Materials
In each experiment, the solid reagents of NaCl, KCl, VCl3 and
CrCl3 used were of analytical grade. NaCl and KCl were dried at
200 ꢀC. The Ag/AgCl electrode was used as the reference electrode
(RE), which was assembled by NaCleKCleAgCl (2 mol%) molten
salts and a half-open alumina tube (6 mm diameter). The silver
wire (1 mm diameter) was inserted into the molten salt. The open
end of alumina tube was sealed to prevent gas exchange. A tungsten
wire (1 mm diameter) was used as the working electrode (WE). The
graphite rode with the diameter of 6 mm was used as the counter
electrodes (CE).
The linear dependence of Ip on v1/2 (v is the scan rate and Ip is
the cathodic peak currents (IA and IB)) is shown in Fig. 2(b), sug-
gesting that the reduction of V3þ ions on the W electrode are
controlled by the V3þ ions diffusion from molten salt to the elec-
trode surface.
Fig. 2(c) indicates variation of the cathdoic peak potential with
the logarithm of the sweep rate. The cathodic peak potentials
measured under increasing sweep rates shift towards a more
negative value. Meanwhile, the cathodic peak potential vs. the
logarithm of the sweep rate is found to be linear. The anodic peak
2.2. Experimental procedure
and the cathodic peak currents corresponding to V3þ/V2þ and V2þ
/
V couples electron transfer steps can be clearly observed in Fig. 2 (a)
and be regarded as quasi-reversible.
2.2.1. Electrochemical experiments
A tungsten wire (1 mm diameter) as the working electrode was
held 1 cm in the molten salt. CV and SWV were carried out using a
PAPSTAT 2273 electrochemical workstation and were used to
explore the electrochemical properties of VCl3 and CrCl3 in the
molten salt system.
The diffusion coefficient can be calculated by the following
equation when both the reactant and product are soluble [17]:
3
2
3
2
Ip ¼ 0:4463n F AðRTÞꢁ1=2D1=2C0v1=2
(1)
Where F is the Faraday constant, n is the number of exchanged
electrons, Ip is the peak current (A), T is the temperature in K, R is
the ideal gas constant (Jꢂmolꢁ1Kꢁ1), C0 is the concentration of VCl3
in the NaCleKCl molten salt, D is the diffusion coefficient of V3þ, A is
the surface area of W working electrode in cm2, and v is the scan
rate in V/s. The diffusion coefficient of V3þ is calculated as
2.2.2. Preparation and characterization of cathodic deposits
A near eutectic mixture of 40.4 g of NaCl and 50.4 g of KCl were
mixed evenly with pre-specified weighed amounts of VCl3 and
CrCl3. The alumina crucible containing the sample was placed in a
shaft furnace and subjected to vacuum for 15min. The samples
were heated to the 200 ꢀC by SiC rod heating furnace and held for
24 h to drive off moisture and other volatiles, after which the
samples were heated to 800 ꢀC under a flow of high purity grade
argon. In order to further purify the molten salt, a voltage lower
than a decomposition voltage of molten salt is applied to electrol-
ysis for a period of time before the electrochemical test and elec-
trolysis. V and Cr electrolysis were carried out in the two-electrode
cell at constant potential. After electrolysis, the W and graphite
electrodes were pulled out from the molten salt, held 10 cm above
the salt and cooled to room temperature under the protection of
argon gas. The deposited product was found attaching to the sur-
face of the W electrode. And then the products were obtained by
washing with deionized water and drying. The main crystalline
phase of deposited product was analyzed using X-ray diffraction
8.72✕10ꢁ5 cm2sꢁ1, which is close to the values (8.22✕10ꢁ5 cm2sꢁ1
)
reported by Polovov [18].
(XRD) with a Cu K
a radiation source. The morphology and
elemental contents of the products were observed by SEM (Zeiss
Ultra 55) and EDS. The V and Cr contents of the products were
analyzed by the using ICP-AES. The content of oxygen in VeCr alloy
was determined by the LECO TCH600 (The instrument LECO TCH
600 is mainly used for the measurement of medium and micro-
level oxygen, hydrogen and nitrogen in steel, nonferrous metals,
alloy, special metals, etc.).
Fig. 1. The CV of blank NaCleKCl molten salt.

S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
877
Fig. 3. SWV of NaCleKCleVCl3 (1.6 wt %) melts. Working electrode: tungsten. Step
potential: 3 mV. Scan rate: 200 mV/s; Temperature: 800 ꢀC.
The diffusion coefficient could be calculated by the following
equation when the product is insoluble [19]:
3
2
3
2
Ip ¼ 0:61n F AðRTÞꢁ1=2D1=2C0v1=2
(2)
Where F is the Faraday constant, n is the number of exchanged
electrons, Ip is the peak current (A), T is the temperature in K, R is
the ideal gas constant (Jꢂmolꢁ1Kꢁ1), C0 is the concentration of VCl2
in the NaCleKCl molten salt, D is the diffusion coefficient of Cr2þ, A
is the surface area of W working electrode in cm2, and v is the scan
rate in V/s. Assuming that all of the V3þ are converted to V2þ, the
minimum diffusion coefficient of V2þ is calculated as 3.49✕10ꢁ6
cm2sꢁ1
.
SWV, as a sensitive transient method, was employed to inves-
tigate the electrochemical behavior of V ions in the NaCleKCl melt.
Fig. 3 shows the results obtained on the tungsten electrode at a step
potential of 3 mV and scan rates of 200 mV/s in the NaCleKCleVCl3
(1.6 wt%) melts at 800 ꢀC. It can be seen from Fig. 3 that two large
signals appear at ꢁ0.3987 V and ꢁ1.1222 V. The number of the
corresponding exchanged electrons can be calculated according to
the following equation [20]:
W1=2 ¼ 3:52RT=nF
(3)
where W1=2 is the width of the half peak, R is the gas constant, T is
absolute temperature (K), F is the Faraday constant, and n is the
number of exchanged electrons.
The computed values of nA and nB are 1.07 at ꢁ0.3987 V and
1.7 at ꢁ1.1222 V. Thus, it can be concluded that peaks A and B
correspond to the V3þ/V2þ and V2þ/V couples. The two-step
transfer electron number is 2.77. It can also be seen from the
SWV that the V3þ/V2þ and V2þ/V couples electron transfer steps
could be regarded as quasi-reversible at 800 ꢀC.
3.2. Electrolysis of Cr in NaCleKCleCrCl3 molten salt system
Fig. 2. (a) CV of VCl3 (1.6 wt %) -NaCl-KCl melt on W working electrode at 800 ꢀC; scan
rate 0.1e1 Vꢂsꢁ1. (b) variation in the cathodic peak currents with the square root of the
sweep rate (c) variation in cathodic peak potentials with the logarithm of the sweep
rate.
The CV results of NaCleKCleCrCl3 system are shown in Fig. 4(a).
When the voltage is scanned in the negative direction, three
cathodic peaks (A, B and C) are observed at 800 ꢀC. The cathodic
peaks (A and B) are attributed to reduction of Cr3þ at the W elec-
trode. The cathodic peaks (C) appeared in CV, which may be

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S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
suggests that reduction reaction of Cr ions on the W electrode are
controlled by the Cr ions diffusion from molten salt to electrode
surface [16,17,22].
Fig. 4(c) displays variation of the cathodic peaks potential with
the logarithm of the sweep rate. The cathodic peaks potential
measured under different scan rates shift towards a more negative
value with increasing sweep rates. Meanwhile, the cathodic peaks
potential vs. the logarithm of the sweep rate is linear. The anodic
peak and cathodic peak clearly observed in Fig. 4(a) are associated
with the electron transfer steps of Cr3þ/Cr2þ and Cr2þ/Cr couples,
which can be regarded as quasi-reversible. The diffusion coefficient
of Cr3þ is calculated as 26.5✕10ꢁ5 cm2sꢁ1, which is larger than the
values (6.5✕10ꢁ5 cm2sꢁ1) reported by Ge et al. [16]. The main
reason for the large data deviation is that the understanding of
three peaks of chromium ions is different. Ge et al. attribute the C
peak to the reduction peak of the Cr3þ/Cr2þ and the A peak to the
peak of impurity oxygen ion in the molten salt. However, the source
of the oxygen ion is not explained in detail. In the present work, the
C-peak was interpreted as corresponding to CreW peak, which is in
accordance with the literature [21]. Assuming that all of the Cr3þ in
the NaCleKCleCrCl3 are converted to Cr2þ, the minimum diffusion
coefficient of Cr2þ is calculated as 8.50✕10ꢁ6 cm2sꢁ1
.
Fig. 5 shows the SWV results obtained on thetungstenelectrode at
a step potential of 3 mV and scan rates of 200 mV/s in the
NaCleKCleCrCl3 (1.6 wt%) melts at 800 ꢀC. It can be seen from Fig. 5
that three large cathodic signals have appeared at ꢁ0.3957 V, ꢁ
1.239 V, and ꢁ1.348 V. Peaks A and C correspond to the Cr3þ/Cr2þ and
Cr2þ/Crcouples. The cathodic peaks (B) appeared in CV, which may be
attributed to the formation of CreW alloy [21].
The Fig. 6 shows the effect of electrolysis time at 2.8 V and
800 ꢀC on current. The current declines from 3.17A to 2.04A when
the voltage of 2.8 V is applied in 0.2 min, suggesting electrolytic cell
has reached equilibrium. As the metal chromium deposits on the W
electrode surface, the effective electrode area of W cathode in-
creases. As the metal Cr deposits on the W electrode surface, the
effective electrode area of W cathode increases. The current in-
creases from 2.04A to 3.17 A with time up to 30 min, which can be
attributed to increase in the surface area of the W cathode. The
current decreases to 0.33A with time up to 105min, which was
related to decline concentration of Cr3þ. And then, the current
declines to a constant about 0.11 A with 105e166 min [23].
The XRD pattern in Fig. 7 indicates that the deposited product is
pure Cr. Meanwhile, the crystal Cr oriented in (200) face has a
Fig. 4. (a) CV of CrCl3 (1.6%)-NaCl-KCl melt on W working electrode at 800 ꢀC; scan
rate: 0.1e1 V/s (b) variation in the cathodic peak currents with the square root of the
scan rate, (c) variation in cathodic peak potentials with the logarithm of the scan rate.
attributed to the formation of CreW alloy [21]. The cathodic peak (A
and B) currents increase and the cathodic peak (A and B) potentials
clearly shift negatively with the increase of the scan rate.
The linear dependence of Ip on v1/2 (v is the scan rate and Ip is
the cathodic peaks current (IA and IB)) is shown in Fig. 4(b).
Meanwhile, Ip increases with v1/2. This behavior from Fig. 4(b)
Fig. 5. SWV of NaCleKCleCrCl3 (1.6 wt %) melts. Working electrode: tungsten. Step
potential: 3 mV. Scan rate: 200 mV/s; Temperature: 800 ꢀC.

S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
879
Fig. 9. SWV of NaCleKCleCrCl3 (1.91 wt%)-VCl3(1.91 wt %) melt. Working electrode:
Fig. 6. Effect of time on the current in electrolysis of molten salt (NaCleKCleCrCl3
tungsten. Step potential: 3 mV. Scan rate: 200 mV/s; Temperature: 800 ꢀC.
(7.60%), 800 ꢀC).
3.3. Electrochemical behaviors of CrCl3 and VCl3 in the NaCleKCl
molten salt
SWV was employed to investigate the electrochemical behav-
iors of V3þ and Cr3þ in the NaCleKCleCrCl3 (1.91 wt%)-VCl3 (1.91 wt
%) melts at 800 ꢀC and the results are in Fig. 9 obtained on the
tungsten electrode at a step potential of 3 mV and scan rates of
200 mV/s. It can be seen from Fig. 9 that four large cathodic signals
have appeared at ꢁ0.239 V, ꢁ0.418 V, ꢁ1.084 V, and ꢁ1.323 V, and
from Fig. 3 that the cathodic peak potential of V3þ/V2þ and V2þ/V
are ꢁ0.3987 V and ꢁ1.122 V, while the cathodic peak potential of
Cr3þ/Cr2þ and Cr2þ/Cr were ꢁ0.3957 V and ꢁ1.348 V (Fig. 5). Thus,
both Cr and V reduction takes place via two steps, and the peaks A,
B, C and D correspond to Cr3þ/Cr2þ, V3þ/V2þ, V2þ/V and Cr2þ/Cr
redox couples. It can be seen from Fig. 5 that Cr3þ is first reduced to
Cr2þ. The peak position of Cr3þ/Cr2þ is shifted in the positive di-
rection, arising from the presence of V3þ. The second reduction
peak is associated with V3þ reduction to V2þ. Due to the presence of
Cr2þ and Cr3þ, the peak position of V3þ/V2þ is negatively shifted.
The third reduction peak is the peak of V2þ reduction to metallic V.
The peak position of V2þ/V is positively shifted, which is attributed
to the presence of Cr2þ and Cr3þ. The fourth peak is the peak of Cr2þ
reduction to Cr. Due to the presence of V2þ and V3þ, the peak po-
sition of Cr2þ/Crþ is positively shifted. The potential positive shift is
due to an increasing of activity of the formed metal ions [24]. It can
be also clearly seen from Fig. 9 that the peak potentials of V3þ and
Cr3þ are different.
Fig. 7. XRD patterns of the deposited product (NaCleKCleCrCl3(7.60%), 2.8 V, 800 ꢀC).
The reduction of V3þ and Cr3þ can be depicted as follows:
V
3þþ3e ¼ V
(4)
(5)
Cr3þþ3e ¼ Cr
According to the Nernst equation [25]:
RT aV3þ
EV3þ ¼ Eq
þ
ln
(6)
Fig. 8. SEM image of deposited product (NaCleKCleCrCl3 (7.60%), 2.8 V, 800 ꢀC).
V3þ=V
=V
nF
aV
Where aV3þ and aV are activity of V3þ and metal V, respectively. The
activity of metal vanadium is assumed to be 1. Peak potential of V3þ
can be shifted to more negative values from decreasing concen-
tration of V3þ. Thus, co-deposition of V3þ and Cr3þ can be achieved
by adjusting the concentration of V3þ and Cr3þ in the molten salt.
Based on the CV and SWV results, the co-deposition of V3þ and
preferentially growth orientation. The Fig. 8 presents the SEM
morphology of the Cr product. It can be seen that the Cr formed
exhibits a dendritic shape. The content of oxygen in Cr product was
determined by the LECO TCH600. The mass percentages of Cr and O
in the Cr product are 99.79% and 0.21% O, respectively.

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S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
Fig. 10. XRD patterns of the deposited product at different VCl3/CrCl3 mass ratio and
800 ꢀC for 130 min.
Cr3þ were performed in NaCleKCleVCl3eCrCl3 molten salt using a
two-electrode cell at different VCl3/CrCl3 mass ratio at 800 ꢀC.
Changes in the standard Gibbs free energy formation of VCl3 and
CrCl3 as a function of temperatures were calculated by the FactSage
6.4 program. According to Nernst equations, the theoretical
decomposition voltage of VCl3 and CrCl3 at 800 ꢀC are 1.18 V and
1.06 V, respectively. A higher cell voltage than the theoretical
decomposition voltage is necessary for electrolysis of VCl3 and
CrCl3, in order to overcome polarization at the electrodes with Cr
formation at a very slightly lower voltage.
The influence of VCl3/CrCl3 mass ratio on the formation of VeCr
alloy was investigated. The electrolysis of molten salt
(NaCleKCleCrCl3eVCl3) was performed at 800 ꢀC for an applied
potential of 2.8 V. The XRD pattern in Fig. 10 indicates that the
deposited product at VCl3/CrCl3 mass ratio of 2:1 consists of a phase
mixture of VCr alloy and V2O3. The deposited product at VCl3/CrCl3
mass ratio of 1:6 is made up of nearly pure Cr and V2O3, while at a
mass ratio of 1:9, nearly pure Cr single phase is formed. The Fig. 11
(a)-(c) presents the SEM morphology of the deposited product at
different VCl3/CrCl3 mass ratios. The EDS analyses of deposited
cathode products are shown at Table 1. It can be seen that the VCr
alloy and V2O3 at VCl3/CrCl3 mass ratio of 2:1 exhibits a granular
shape. Based on the XRD analysis, the particle 1 in Fig. 11(a) is VeCr
alloy and the particle 2 in Fig. 11(a) represents V2O3 and V. The
deposited product at VCl3/CrCl3 mass ratio of 1:6 and 1:9 in
Fig. 11(b)-(c) show two different morphological crystals, viz, a
granular shape and a floc. Compared with the oxygen content in the
granular shape, the oxygen content in the floc increases. Although
the deposited products have two different morphologies, the two
forms of products are both seen to be metallic chromium. In view of
the inaccuracy of the oxygen content in the sample by EDS, the
content of oxygen in Cr product at VCl3/CrCl3 mass ratio of 1:9 was
determined by the LECO TCH600. The mass percentages of V, Cr and
O in the Cr product are 3.71%, 94.28% and 2.01% O, respectively.
Cr/V mass ratio in the VCr alloy are listed in Table 1. Fig.12 shows
the effect of varying CrCl3/VCl3 mass ratio on the resulting Cr/V
mass ratio values in the VCr alloy under the operating conditions of
800 ꢀC for 130 min. Cr/V mass ratio in the VCr alloy increased with
increasing CrCl3/VCl3 mass ratio. According to Fig. 12, different ra-
tios of V/Cr alloy can be obtained by controlling the CrCl3/VCl3 mass
ratio.
Fig. 11. SEM image of deposited product at 800 ꢀC for 130 min (a) VCl3/CrCl3 mass ratio
of 2:1, (b) VCl3/CrCl3 mass ratio of 1:6, (c) VCl3/CrCl3 mass ratio of 1:9.
In the present work, V2O3 detected in the deposited products is
mainly attributed to oxidation of metal vanadium obtained by
electrolysis. Similar results are reported in the literature [3,26].
4. Conclusions
The electrodeposition behaviors of V3þ and Cr3þ in NaCleKCl
molten salt at 800 ꢀC were investigated using CV and SWV with a
tungsten electrode. The reduction of V3þ ions to metal V was found

S. Liu et al. / Journal of Alloys and Compounds 803 (2019) 875e881
applications of vanadium dioxide, Mater. Today 21 (8) (2018) 875e896.
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EDS analysis of deposited product (in Fig. 11).
phase
EDS analysis of the deposited product [wt%]
V
Cr
O
a-1
a-2
b-1
b-2
c-1
c-2
50.79
88.61
3.93
8.66
3.68
4.79
45.43
0
95.10
85.24
93.42
90.08
3.78
11.39
0.97
6.10
2.90
5.13
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to take place in two steps corresponding to V3þ/V2þ and V2þ/V. The
reduction of Cr3þ ions to metal Cr similar involved redox steps of
Cr3þ/Cr2þ and Cr2þ/Cr. The electrochemical processes of V3þ and
Cr3þ were proved to be controlled by diffusion. The diffusion co-
efficients of V3þ and Cr3þ in NaCleKCl molten salt were 8.72✕10ꢁ5
cm2sꢁ1 and 26.5✕10ꢁ5 cm2sꢁ1. Based on the CV and SWV analysis,
electrodeposition of Cr was investigated by a two-electrode
arrangement under constant voltage, and pure Cr was obtained.
Meanwhile, the effect of VCl3/CrCl3 mass ratio on VCr alloy was
investigated by a two-electrode cell under constant voltage. It was
found that VCl3/CrCl3 mass ratio significantly affected the purity of
product. V2O3 detected in the deposited products is mainly attrib-
uted to oxidation of metal vanadium obtained by electrolysis. VCr
alloy (3.71 mass % V, 94.28 mass% Cr and 2.01 mass % O) was ob-
tained when electrolysis voltage was controlled at 2.8 V at 800 ꢀC.
Acknowledgments
[25] M. Li, Q.Q. Gu, W. Han, Y.D. Yan, M.L. Zhang, Y. Sun, W.Q. Shi, Electrode-
position of Tb on Mo and Al electrodes: thermodynamic properties of TbCl3
and TbAl2 in the LiCl-KCl eutectic melts, Electrochim. Acta 167 (2015)
139e146.
[26] L.Y. Liu, Y.D. Yan, W. Han, M.L. Zhang, L.Y. Yuan, R.S. Lin, G.A. Ye, H. He,
Z.F. Chai, W.Q. Shi, Electrochemical separation of Th from ThO2 and Eu2O3
assisted by AlCl3 in molten LiCleKCl, Electrochim. Acta 114 (2013)
180e188.
The authors are grateful for the financial support of this work
from the National Natural Science Foundation of China
(No.51474141, 51774027), and China Postdoctoral Science Founda-
tion (2019M650848).
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