1-s2.0-S0013468614019264

7252019 1-s20-S0013468614019264

httpslidepdfcomreaderfull1-s20-s0013468614019264 19

Electrochemical

behaviors of

Dy(III)

and

its

co-reduction

with

Al(III)

inmolten

LiCl-KCl salts

Ling-Ling Su ab Kui Liu b Ya-Lan Liu b Lu Wang b L i-Yong Yuan b Lin Wang b Zi-Jie LibXiu-Liang Zhao a Zhi-Fang Chaibc Wei-Qun Shiba School of Nuclear Science and Technology University of South China HengYang 421000 ChinabKey Laboratory of Nuclear Radiation and Nuclear Energy Technology Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 Chinac School of Radiological amp Interdisciplinary Sciences Soochow University Suzhou 215123 China

A R T I C L E I N F O

Article history

Received 15 July 2014

Received

in

revised

form

17

September

2014

Accepted 19 September 2014

Available online 22 September 2014

Keywords

molten chlorides

dysprosium

AlCl3intermetallic compounds

co-reduction

A B S T R A C T

In thiswork theelectrochemicalbehaviors ofDy(III) and itsco-reductionwithAl(III) onan inert tungsten

electrode was investigated in LiCl-KCl molten salts at the temperature of 773K by using cyclic

voltammetry (CV) chronopotentiometry (CP) and square wave voltammetry (SWV) techniques The

results showed that the reduction of Dy(III) ions in LiCl-KCl salts is a reversible diffusion controlled

process through a one-step reaction Dy(III) + 3e$ Dy(0) The diffusion coef 1047297cient of Dy(III) ions was

calculated byboth theCV andCPmethods Furthermorethe co-reductionof Al(III) andDy(III) ionson the

inert tungstenelectrodeallowsDy(III) ions tobe reduced at amore positivepotentialthroughforming Al-

Dyalloys Theconcentration ratioofAl(III) cationsto Dy(III) cations hasa large impacton theformationof

Al-Dy alloys In a Dy(III) ion rich system three signals attributed to the formation of Al-Dy intermetallic

compounds were observed in CV and SWV analyses while only two signals corresponding to Al-Dy

intermetallic compoundswere observed in the Dy(III) ion poor system Potentiostatic and galvanostatic

electrolyses performed on an aluminum electrode identi1047297ed the co-reduction by the formation of one

(Al3Dy) and two Al-Dy alloys

(Al3Dy AlDy) respectively Finally the electrolysis products were

characterized by the Scanning ElectronMicroscopy (SEM) coupled with EnergyDispersive Spectroscopy

(EDS) and X-ray diffraction (XRD) analysesatilde

2014 Elsevier Ltd All rights reserved

1 Introduction

Partitioning and Transmutation (PampT) is universally accepted to

be one of the key-steps in any future sustainable nuclear fuel

cycles in which high ef 1047297cient separations of actinides (An) and

lanthanides (Ln) are generally expected [1] Ln could account for as

much as 25 in weight of the whole 1047297ssion products (FP) [2] and

the strong neutron absorption cross sections of Ln would largely

pull down the transmutation ef 1047297ciency [3] However the

physicochemical properties of Ln and An are very similar and

make the separation of An from Ln extremely challenging [4]

The traditional pyrochemical electrore1047297ning process based on

chloride or

1047298uoride molten salts has been regarded to be a

promising alternative for future spent nuclear fuel cycle [5ndash7] The

simple inorganic molten ionic solvents are immune to radiation

damage and transparent to neutrons In a typical electrore1047297ning

process a solid stainless steel cathode and a liquid Cd cathode were

used to achieve the recovery of uranium and transuranium

elements respectively One of drawbacks of using this liquid Cd

cathode is that the content of Ln in deposited products is relatively

high compared to traditional solvent extraction based processes

which restrains the propagation of the process in industrial scale

As for the ef 1047297cient separation of An from Ln active solid

aluminium cathode seems to be a promising alternative It has

been found that the disparity of the deposition potential between

An and Ln is larger on the solid aluminium cathode than that on

other metal electrodes due to the formation of Al-An alloys [78] In

previous works a relatively high separation ef 1047297ciency of An over

Ln [7910] and excellent extraction and recovery of An [91112]

have been identi1047297ed possible on an Al cathode To establish a

reliable Al cathode based electrochemical pyrochemical process it

is still quite necessary to investigate the electrochemical proper-

ties of representative Ln in AlCl3 contaning melts Actually we have

successfully used solid Al cathodes to extract some Ln elements

from melts by forming Al-Ln intermetallic compounds [13ndash16]

Corresponding author Tel +86 010 88233968 fax +86 010 88235294

E-mail addresses shiwqihepaccn (W-Q Shi) 13974753181163com

(X-L Zhao)

httpdxdoiorg101016jelectacta201409095

0013-4686atilde 2014 Elsevier Ltd All rights reserved

Electrochimica Acta 147 (2014) 87ndash95

Contents

lists

available

at

ScienceDirect

Electrochimica

Acta

journa l h omepage wwwe lseviercomloca te e le cta cta

7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264


Actually this method has been con1047297rmed in the LiCl-KCl melt

for the preparation of other Ln and An [1012ndash1623] chloridesIn the electrolytic process anhydrous Dy2O3 and AlCl3 (both AR

grade) powders were directly added to the LiCl-KCl melt In LiCl-

KCl melt with the working temperature of 773 K AlCl3 can be easily

gasi1047297ed and turn into Al2Cl6 part of them reacts with Dy2O3 to

release Dy(III) ions This reaction can be represented as

Dy2O3 (s) + Al2Cl6 (g) == Al2O3 (s) + 2 DyCl3 (l) (2)

From the thermodynamic data [29] the change of Gibbs energy

of this reaction at 773 K is calculated to be -90345 kJ mol1 It

reveals that reaction (2) could proceed forward at our experimen-

tal temperature In this work we 1047297rstly explored the electrochem-

ical behaviors of dysprosium on an inert tungsten electrode hence

after the complete chlorination of Dy2O3 the LiCl-KCl-DyCl3 melt

was puri1047297ed completely out of AlCl3 by bubbling dry argon

continuously until the ICP-MS analysis of the taken melt sample

shows no remnant Al(III) ion The concentration of Dy(III) ions in

the LiCl-KCl-DyCl3 melt was measured at the same time Then the

co-reduction process of Dy(III) and Al(III) were investigated by

increasing the content of AlCl3 in the melts However owing to the

volatility of AlCl3 the concentration of AlCl3 we present below is

the initial fractions when AlCl3 were added into the melts

23 Electrochemical electrodes and characterization of cathodic

deposits

A custom-built quartz structure was used to position all of the

electrodes and the thermocouple in molten salt A silver wire (d

= 1 mm 9999) dipped into the solution of AgCl (1 wt) in LiCl-

KCl melts contained in a Pyrex tube was used as the reference

electrode All potentials were referred to the Ag+Ag couple As for

the counter electrode a 6 mm graphite rod was used The working

electrode consisted of 1 mm tungsten (W)wire with the lower end

polished by SiC paper Before each measurement the working

electrode was cleaned by galvanostatic anodic polarization The

active electrode surface area was calculated after each experiment

by

measuring

the

immersion

depth

of

the

electrode

in

the

moltensalts As to the electrolysis process an aluminum plate (Alfa

99999) with thick to be 2 mm was used as cathode After

electrolysis the aluminum electrode was abraded and polished by

SiC paper followed by ultrasonic cleaning in ethylene glycol and

ethanol (Sinopharm 998) in an ultrasonic bath for 15 min and

stored in the glove box before analysis

3

Results

and

discussion

31 Electrochemical behavior of Dysprosium Ions on the Tungsten

Electrode

311 Cyclic Voltammetry

In

the

present

work

investigations

of

dysprosium

began

withCV measurements to establish the nature of the system and the

reversibility of the observed reactions The typical CV curve of the

pure LiCl-KCl melts is shown in Fig 1 (dotted curve) The

electrochemical window offered by the LiCl-KCl melts have been

reported to be limited between the reduction of lithium ions

(peak L c) and the anodic release of chlorine [1217] The fact that

there is no other additional peak in its electrochemical window

identi1047297es the applicability of the LiCl-KCl melts for our inves-

tigations

Fig 1 also shows the typical CV of LiCl-KCl-DyCl3 (373 105

mol cm3) mixture with the scan rate of 01Vs1 on a W working

electrode at the temperature of 773 K The signals EaEc were

observed in the voltammogram with the reduction peak (Ec) at

-204

V

and

the

corresponding

anodic

peak

(Ea)

at

-184

V

respectively The reduction (Ec) occurs in a single sharp peak

mode with a gradual decay manifesting the deposition of an

insoluble phase [3031] The reverse anodic scan shows an

oxidation peak (Ea) with much higher amplitude than the

reduction peak due to the availability of the deposited metal for

the re-oxidation According to the previous works of Zhang et al

[22] Chang et al [18] and Konishi et al [19] peaks Ea and Ec had

been ascribed to the deposition and dissolution of Dy metal It is

possible that dysprosium metal would be deposited in a single

direct step by direct reduction of Dy(III) ion into Dy(0)

Furthermore the reversibility of the reaction of deposition and

dissolution of Dy(III)Dy(0) was evaluated over a wide scan rate

range from 005 to 03 Vs1 As shown in Fig 2a the peak potential

shifts very slightly with the increasing scan rates Therefore the

reduction of Dy(III) to metal should be considered to be a reversible

process The Nernstian behavior of the reaction at low scan rates

can be further con1047297rmed by plotting the mid-peak potential as a

function of the scan rate As shown in Fig 2c the mid-peak

potential almost remains stable (-196 V) at the scan rates of 005

01 015 and 02 Vs1 In addition the plot of the cathodic peak

current versus the square root of the sweep rates shows a linear

relationship in Fig 2b indicating the process is a diffusion

controlled one Therefore it is plausible to use the Berzin-Delahay

equation [32] in this work for a soluble-insoluble couple accordingto the theory of linear sweep voltammetry

Ip= 0061(nF)32C0D12V12(RT)12S (3)

where n is the number of exchanged electrons F denotes the

Faraday constant (96500C mol1) Co represents the solute con-

centration (mol cm3) D corresponds the diffusion coef 1047297cient

(cm2 s1) v designates the potential scanning rate (V s1) T is the

absolute temperature (K) and S corresponds the electrode area

(cm2)

The measurement of the slope of the curve in Fig 2b yields the

following relation at T = 773 K and C0= 373 105mol cm3

I p

V 1=2 frac14 eth0068 000082THORNAS1=2V 1=2 (4)

Assuming n = 3 through the combination of Eqs (3) and (4) the

diffusion coef 1047297cient (D) of Dy(III) ions under this condition can be

calculated to be 510 106 cm2 s1

Fig 2 (a) CVs for 373 105molcm3DyCl3 in LiCl-KCl melts at various scan rates

Working electrode W (S068 cm2) Scan rates 005 01 015 02 025 and 03 Vs1

(b) Plot of the cathodic peak current as a function of the square root of the scan rate

(c) Mid-peak potential as a function of the scan rate The dashed curve represents

the

average

mid-peak

potential

(-196

V

vs

Ag

+

Ag)

L-L Su et al Electrochimica Acta 147 (2014) 87 ndash95 89

7252019 1-s20-S0013468614019264


In addition it can be found that there is always a fuzzy pre-

platform more anodic to the reduction peak Ec in Fig1 and 2which

is very drawn out at all scan rates in Fig 2 suggesting that this

process could not be diffusion controlled However there are still

some discrepancies about the ascription of this pre-platform

[172123] Ref [1723] ascribed it to the reduction of Dy(III) to Dy

(II) whereas Ref [21] held that the similar pre-platform before the

reduction of Dy(III) ions in LiF-CaF2 melt might be an adsorption

effect of Dy(III) ions to the surface of the working electrode

Combining the results of following SWV we prefer to supporting

the pre-platform is attributed to the adsorption effect of Dy(III)

ions to the surface of the W electrode

312 Chronopotentiometry

The electrochemical behavior of the redox couple Dy(III)Dy(0)

was also studied by CP technique Fig 3 shows the evolution of the

CPs of DyCl3 in LiCl-KCl melts with the applied current density from

-16 mA to -24 mA on a W electrode These curves exhibit a single

wave in the same potential range as that observed in the CV curves

and therefore should be associated with the reduction of Dy(III) ions

into metal In the CP technique transition time (t) means the time

necessary to observe the complete depletion of the electroactive

species (here the Dy(III) ion) resulting from the diffusion in the layer

of electrolyte at the electrode surface From Fig 3a it can be found

that t decreases with the increase of the applied current density In

addition the time-current relationship at a constant value in Fig 3b

proves

the

diffusion-controlled

process

of

Dy(III)

to Dy(0)

and

thevalidity of Sands law (Eq (5)) [32]

it 1=2 frac14 05nFSC ethpDTHORN1=2 (5)

where t is the transition time (s) i denotes the applied current (A)

We also assumed the number of exchanged electron n = 3 The

diffusion coef 1047297cient at T = 773 K and C = 346 105mol cm3 was


Table 1 gathered the diffusion coef 1047297cients of Dy(III) in LiCl-KCl

eutectic at 773 K Under the same conditions the diffusion

coef 1047297cient calculated by Ref [17] is approximately three times

higher than that measured by Ref [6] The diffusion coef 1047297cient of

Dy(III) ion in LiCl-KCl melts determined in this work was 51 106

cm2 s1 and 172 105 cm2 s1 using CV and CP techniques

respectively The complex chemical behaviors of Dy(III) ions in

LiCl-KCl melts differences in the principles of CV and CP

techniques [33] and imprecise measurement of the wetted length

of the working electrode could account for these discrepancies

Similar

phenomena

were

observed

in

the

case

of

cerium

anduranium in Ref [3435]

In the above calculation of diffusion coef 1047297cient from the results

of CV and CP the number of exchanged electrons was assumed to

be 3 Actually the number of exchanged electrons can be deduced

from combining the results of CV and CP as stated in Ref [3637]

By using Eqs (3) and (5) the following formula was obtained

n frac14

I p

V 1=2 1

ip1=2

05

061

2

D2C 2

D1C 21

p2RT

F (6)

where the concentration (C) and diffusion coef 1047297cients (D)

subscripted with 1 and 2 are related to CV and CP respectively

According to the results obtained from Fig 2b Ip=V1=2 frac14 eth0068

000082THORNAS1=2V1=2 and Fig 3b it 1=2 frac14 25 102 AS 1=2 the

number of exchanged electrons n301 was achieved almostentirely consistent with the theoretical expectation

313 Square wave voltammetry

SWV with a better accuracy to calculate the number of

electrons exchanged in an electrochemical process was then

employed to con1047297rm the number of exchanged electrons in this

experiment

For a single electrochemical reversible process the differential

intensity measured at each step between the successive pulses

exhibits a Gaussian relationship with the potential Mathematical

analysis of the Gaussian peak yields a simple equation associating

with the width of the half peak (W12) with temperature and the

number of electrons exchanged (n) [3839]

W 1=2 frac14 352RT

nF (7)

where R is the universal gas constant T denotes the absolute

temperature in K n represents the number of exchanged electrons

and F designates the Faradays constant

Fig 4 shows a typical SWV of DyCl3 (373 105mol cm3) in the

LiCl-KCl melts on a W electrode at the frequency of 20 Hz A sharp

peak (Ec) associated with the reduction of Dy(III) ion can be clearly

observed in the same potential range as CV and CPHowever peak Ecis not exactly symmetric as predicted by the theory of nucleation

effect Due to which the rise of the current is delayed by the

overpotential caused by the solid phase formation thus the

increasing part of the differential current is sharper than the

decreasing one The disturbance of the signal due to the nucleation

Fig 3 (a) CPs of LiCl-KCl-DyCl3 (346 105molcm3) melts at 773 K Working

electrode W (S068 cm2) Applied current -16 -18 -20 -22 and -24 mA (b)

Relationship

between

the

square

root

of

the

transition

time

and

the

applied

current

Table 1

Diffusion coef 1047297cients of Dy(III) in LiCl-KCl eutectic at 773 K

Reference 105 D cm2 s1 Dy(III) Concentration (104ppm) Technique

[17]

147

201

CP

[6] 046 20 CP

[6] 07 06 CP

this work 051 061 CV

this work 172 057 CP

90 L-L Su et al Electrochimica Acta 147 (2014) 87 ndash95

7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264


However large differences were observed between signals L aL cand AaAc in Fig 5a As for the red curve peak Ec at -204 V and Ea at

about -183 V can be ascribed tothe reduction of Dy(III) tometal and

its subsequent re-oxidation respectively according to the above

results of LiCl-KCl-DyCl3 system and Ref [617] Between peaks EaEcand AaAc two broad anodic peaks at about -130 and -165 V were

observed The CVs measured subsequently in the same system at

different terminal potentials display a broad anodic peak at

approximate -13 V which actually consist of two close peaks Ia and

IIa similar to their cathodic peaks Ic and IIc (Fig 5b) In addition the

SWV in Fig 6 (curve 2) also revealed the existence of the two close

peaks Ic and IIc at approximate -13 V According to the co-reduction

principle redox peaks IaIc IIaIIcand IIIaIIIc should be ascribed tothe

formation

and

dissolution

of

at

least

three

AlxDyy intermetalliccompounds Moreover the closer the deposition potential of the

intermetallic compound to that of Dy metal the higher Dy content

could be formed in the AlxDyy intermetallic compound [1215]

As for the black curve in Fig 5a CV of AlCl3-rich system much

higher current intensities of peaks Aa and Ac were obviously

observed compared to that of AlCl3-poor system Besides other

differences could also be observed in the two curves of Fig 5a For

example the broad anodic peak at -13 V in the red curve separated

into two redox peaks IaIc and IIaIIc in the black curve The CVs

measured at various cathodic terminal potentials in AlCl3-rich

system (Fig 5c) and the SWV (curve 3 in Fig 6) also present two

clearly separated redox peaks IaIc and IIaIIc However the redox

signals IIIaIIIc and EaEc corresponding to the formation and

dissolution of an intermetallic compound with higher Dy content

Fig 5 (a) CVs of LiCl-KCl-AlCl3-Dy2O3 (09 wt) melts with different AlCl3concentrations 08 wt (red curve) and 12 wt (black curve) (b) CVs of the LiCl-

KCl-AlCl3 (08 wt)-Dy2O3 (09 wt) melts (c) CVs of the LiCl-KCl-AlCl3 (12 wt

)-Dy2O3 (09 wt) melts at different inversion potentials Working electrode

W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1

Fig 7 CVs of LiCl-KCl-DyCl3 melts (black dotted curve) and LiCl-KCl-AlCl3-DyCl3melts (red solid curve) on an Al electrode Temperature 773 K Scan rate 01

Fig 6 SWVs of LiCl-KCl-DyCl3 (373 105molcm3) melts (curve 1) and LiCl-KCl-

AlCl3-Dy2O3 (09 wt) melts with different AlCl3 concentrations 08 wt (curve 2)

and 12 wt (curve 3) Working electrode W (S068 cm2) Temperature 773 K

Pulse height 10 mV potential step 5 mV frequency 20 Hz Vs1


7252019 1-s20-S0013468614019264


and the redox couple of Dy(III)Dy(0) vanished from both the CV

(Fig 5c) and SWV (curve 3 in Fig 6) curves In the meanwhile a

new

couple

of

peaks

marked

as

IVaIVc emerged

with

its

cathodicand anodic potential at approximate -216 and -205 V respectively

which should be ascribed to be the reduction and oxidation of Al-Li

alloy [1217] The reason of the difference between the two curves

in Fig 5 could be as follows With the increase of AlCl3concentration a much thicker layer of Al was deposited on the

W electrode which would facilitate the diffusion of Dy metal

Subsequently the initially generated intermetallic compound

AlxDyy tends to be transformed into another intermetallic

compounds AlxDyy with high Al content Therefore peaks IIIa

IIIc and EaEc which correspond to the formationdissolution of an

intermetallic compound with high Dy content and the redox

couple Dy(III)Dy(0) respectively could not be observed In

addition when the deposited AlxDyy intermetallic compounds

were not fully mantle the Al-covered electrode Al-Li alloys would

have the chance to be formed [15]

Electrochemical behaviors of LiCl-KCl melts containing both

Al(III) and Dy(III) cations were also investigated on an Al electrode

Fig 7 provides a comparison about the CVs of LiCl-KCl-DyCl3 and

LiCl-KCl-AlCl3-DyCl3 melts using Al as the working electrode The

CV of LiCl-KCl-DyCl3 melts without Al(III) cations (black dotted

curve) is consistent with Ref [17] Peaks IcIa are ascribed to the

formation and dissolution of Al-Dy alloys on the Al electrode The

red solid curve in Fig 7 shows a typical co-reduction behavior of

Al(III) and Dy(III) ions on the Al electrode which is very similar to

that obtained in LiCl-KCl-DyCl3 melts although the peaks become

more bulky This could be caused by the formation of different Al-

Dy alloys through the co-reduction of Al(III) and Dy(III) cations at

more cathodic potential [50]

33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)

and Al(III) ions andexamine the formation of AlxDyy intermetallic compounds at

various concentration ratio of Al(III) and Dy(III) both potentio-

static and galvanostatic electrolyses were carried out on a

tungsten electrode However only a very small amount of Al-

Dy alloys that adhered to the W electrode could be obtained even

the experiment was repeated for several times This phenomenon

is probably caused by the small cathode current and the high melt

point of the Al-Dy alloys Therefore we further used an Al plate

electrodewith the size of 15 cm 15 cm 02 cm for electrolysis

To prepareAl-Dy alloys at more anodic potential potentiostatic

electrolysis at -14 V -15 V and -16 V each for 3 h respectively

was performed Fig 8 shows the XRD patterns and the cross-

section SEM images coupled with EDS analysis of the cathodic

deposits of potentiostatic electrolysis It turns out that the

electrolysis at -14 V achieved nothing but Al metal while

electrolysis at -15V and -16 V produced a uniform layer covering

on the Al plateelectrode (Fig 8a and c) ByXRD analyses (Fig 8b)

the composition of the deposition layer obtained at -15 V was

con1047297rmed to be Al metal and the intermetallic compound Al3Dy

with crystallographic structure of rhombohedral lattice (R-3 m)

(PDF in XRD data base 18ndash0020) When electrolysis was

performed at more negative potential of -16 V the intermetallic

compound Al3Dy with crystallographic structures of R-3 m and

hexagonal lattice (P63mmc) (PDF in XRD data base 65ndash6363)

could be both obtained

It is well known that potentiostatic electrolysis has the

advantage of controlling the composition of the compound

produced by the cathodic reaction According to the co-reduction

Fig 8 SEM-EDS and XRD results of the potentiostatic electrolysis products of LiCl-KCl-AlCl3 (12 wt)-Dy2O3 (09 wt) melts on the Al electrodes (a) SEM image (deposited

at -16 V) (b) XRD pattern (deposited at -150 V and -160 V) (c) Enlarged SEM image (deposited at -16 V) (d) EDS result (deposited at -16 V)


7252019 1-s20-S0013468614019264


behaviors above at least two kinds of AlxDyy intermetallic

compounds

(DyAl3 and

DyAl2)

could

be

formed

by

potentiostaticelectrolysis at -15 and -16V since two very close pairs of

redox peaks were observed in CVs and SWV However only one

kind of intermetallic compound Al3Dy was acquired which was

against with our expectation The main reason might be the low

current density at our experimental concentration Under this

condition even though the intermetallic compound DyAl2 was

formed the formation rate was much slower than its diffusion

rate then the transformation of DyAl2 into the more stable Al-

rich phase (DyAl3) on the Al electrode would take palce Hence

ultimately only one kind of intermetallic compound DyAl3 was

observed in Fig 8 similar phenomena had been observed in the

potentiostatic electrolysis for the preparation of Al-Gd alloys

[15] The fact that intermetallic compound Al3Dy with more

crystallographic structures was obtained by electrolysis at more

negative potential to some extent shows the importance of

nucleation overpotential for the growth of Al-Dy alloys onto the

electrode

To provide a stable current to equably form more AlxDyyintermetallic compounds galvanostatic electrolysis with the

current intensity of -50 mA was also carried out for 25 h in our

experiment During the electrolysis the cathode potential was

controlled within the range of -13 V to -175 V to prevent the

deposition of pure Dy and in the meanwhile cover the two much

more anodic redox peaks (IaIc and IIaIIc) associated with the

formation of AlxDyy intermetallic compounds As shown in the

SEM image in Fig 9a a much thicker layer of approximate 40

mm of

the deposits was obtained than that gained by potentiostatic

electrolysis (Fig 8a) The XRD result in Fig 9b con1047297rms that the

deposits are composed of intermetallic compounds DyAl3 and

DyAl

although

DyAl2 was

still

not

observed

which

proves

onceagain that DyAl2 could not be stable at this temperature and easily

be transformed into DyAl3 The EDS analyses coupled with SEM in

Fig 8d and Fig 9d also con1047297rmed the co-existence of Dy and Al in

the deposits of electrolysis

4

Conclusions

Electrochemical behaviors of Dy(III) cations on an inert W

electrode were studied in molten LiCl-KCl-DyCl3 salts by

combining various electrochemical techniques (ie CV CP and

SWV) The electroreduction of Dy(III) ions on the tungsten

electrode is a single step process with transfer of three electrons

The reduction shows a reversible behavior for polarization rates

range of 50 V 300mV1 which is controlled by the diffusion of

Dy(III) cations in solution Accordingly the diffusion coef 1047297cient of

Dy(III) ion in the LiCl-KCl melts was measured by both CV and CP

techniques The adsorption effect which is surface based was

also observed prior to the reduction of Dy(III) to Dy(0)

The concentration ratio of Dy(III) ions to Al(III) ions has a great

in1047298uence on the co-reduction In a Dy-rich system three signals

corresponding to the formation of three AlxDyy were observed on

the tungsten electrode However when Al(III) cations were

suf 1047297cient only two of which with higher Al content were

observed SEM-EDS and XRD characterizations identi1047297ed inter-

metallic compound DyAl3 was produced by potentiostatic

electrolysis at -15 V and -16 V while two intermetallic com-

pounds DyAl3 and DyAl were obtained through galvanostatic

electrolysis at -50 mA

Fig 9 SEM (ac)-EDS (d) and XRD (b) results of the galvanostatic electrolysis products of LiCl-KCl-AlCl3 (12 wt)- Dy2O3 (09 wt) melts on the Al electrode Current -50 mA

Time 25 h Temperature 773 K


7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264
























deposits











by

measuring

the

immersion

depth

of

the

electrode

in

the







3

Results

and

discussion


Electrode


In

the

present

work

investigations

of

dysprosium

began









tigations





-204

V

and

the

corresponding

anodic

peak

(Ea)

at

-184

V

























Ip= 0061(nF)32C0D12V12(RT)12S (3)






(cm2)



I p









the

average

mid-peak

potential

(-196

V

vs

Ag

+

Ag)


7252019 1-s20-S0013468614019264



























proves

the


process

of

Dy(III)

to Dy(0)

and

















Similar

phenomena

were

observed

in

the

case

of

cerium







n frac14

I p

V 1=2 1

ip1=2

05

061

2

D2C 2

D1C 21

p2RT

F (6)










experiment







W 1=2 frac14 352RT

nF (7)














Relationship

between

the

square

root

of

the

transition

time

and

the

applied

current

Table 1



[17]

147

201

CP

[6] 046 20 CP

[6] 07 06 CP




7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264













formation

and

dissolution

of

at

least

three


















W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1







7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264
























deposits











by

measuring

the

immersion

depth

of

the

electrode

in

the







3

Results

and

discussion


Electrode


In

the

present

work

investigations

of

dysprosium

began









tigations





-204

V

and

the

corresponding

anodic

peak

(Ea)

at

-184

V

























Ip= 0061(nF)32C0D12V12(RT)12S (3)






(cm2)



I p









the

average

mid-peak

potential

(-196

V

vs

Ag

+

Ag)


7252019 1-s20-S0013468614019264



























proves

the


process

of

Dy(III)

to Dy(0)

and

















Similar

phenomena

were

observed

in

the

case

of

cerium







n frac14

I p

V 1=2 1

ip1=2

05

061

2

D2C 2

D1C 21

p2RT

F (6)










experiment







W 1=2 frac14 352RT

nF (7)














Relationship

between

the

square

root

of

the

transition

time

and

the

applied

current

Table 1



[17]

147

201

CP

[6] 046 20 CP

[6] 07 06 CP




7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264













formation

and

dissolution

of

at

least

three


















W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1







7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264



























proves

the


process

of

Dy(III)

to Dy(0)

and

















Similar

phenomena

were

observed

in

the

case

of

cerium







n frac14

I p

V 1=2 1

ip1=2

05

061

2

D2C 2

D1C 21

p2RT

F (6)










experiment







W 1=2 frac14 352RT

nF (7)














Relationship

between

the

square

root

of

the

transition

time

and

the

applied

current

Table 1



[17]

147

201

CP

[6] 046 20 CP

[6] 07 06 CP




7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264













formation

and

dissolution

of

at

least

three


















W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1







7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264













formation

and

dissolution

of

at

least

three


















W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1







7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264













formation

and

dissolution

of

at

least

three


















W (S068

cm2)

Temperature

773

K

Scan

rate

01

Vs1







7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264




new

couple

of

peaks

marked

as

IVaIVc emerged

with

its




























33

Preparation

and

characterization

of

the

Al-Dy

alloys

To

con1047297rm

the

co-reduction

of

Dy(III)
































7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264



compounds

(DyAl3 and

DyAl2)

could

be

formed

by

















electrode









mm of




DyAl

although

DyAl2 was

still

not

observed

which

proves





4

Conclusions

























7252019 1-s20-S0013468614019264


7252019 1-s20-S0013468614019264


1-s2.0-S0013468614019264

Documents

Transcript of 1-s2.0-S0013468614019264