research article electrochemical synthesis of magnesium...

Research ArticleElectrochemical Synthesis of MagnesiumHexaboride by Molten Salt Technique

S Angappan1 N Kalaiselvi2 R Sudha1 and A Visuvasam1

1 CSIR-Central Electrochemical Research Institute Karaikudi 630006 India2Department of Physics Selvam Arts and Science College Namakkal 637003 India

Correspondence should be addressed to S Angappan angs67gmailcom

Received 24 March 2014 Revised 23 May 2014 Accepted 26 May 2014 Published 31 August 2014

Academic Editor Sarkarainadar Balamurugan

Copyright copy 2014 S Angappan et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The present work reports electrochemical synthesis of MgB6from molten salts using the precursor consists of LiFndashB

2O3ndashMgCl

2

An attempt has been made to synthesize metastable phase MgB6crystal by electrolysis method DTATGA studies were made to

determine the eutectic point of the melt and it was found to be around 900∘C The electrolysis was performed at 900∘C underargon atmosphere at current density of 15 Acm2 The electrodeposited crystals were examined using XRD SEM and XPS Fromthe above studies the electrochemical synthesis method for hypothetical MgB

6from chloro-oxy-fluoride molten salt system is

provided Mechanism for the formation of magnesium hexaboride is discussed

1 Introduction

Rare earth and alkaline earth metal borides belong to thegroup of nonoxide type metal-like compounds and havehigh melting point high chemical stability stable specificresistance low expansion coefficient at certain temperatureranges diverse magnetic orders and high neutron absorba-bility [1 2]They have possessed excellent corrosion and wearresistance chemical inertness and thermal shock resistancemore than that of oxide ceramics [3 4] The alkaline earthhexaborides were long thought to be simple polar semicon-ductors with single particle gap energy of several tenths of aneV and the energy gap is narrow as well as indirect band gap(Δ119864119892= 00150Ry)

Electrochemical synthesis of MgndashB system from moltensalts is an economic feasible and environmental friendly wayfor the preparation of different binary phases [5] Particularlythe MgndashB system was reported early [6 7] to contain fivephases whereas Serebryakova [8] reported only four phasesBorides can exist as a wide range of compositions and displaystructural features which depends strongly on the metal andboron ratio Markowsky et al proposed formation of threephases with higher B content as the result of thermal decom-position of MgB

2 (1) MgB

6 (2) unknown and (3) MgB

12

[9] However Duhart reexamined these data and claimed that

phase 1 corresponds to MgB4and phase 2 to MgB

6and the

formation of MgB12(phase 3) was not confirmed [10] MgB

6

andMgB4do not exist as individual phases and obviously are

metastable with rather long equilibration times According toSomsonov et al [11] MgndashB system has four stable boridesMgB2 MgB

4 MgB

6 and MgB

12 MgndashB system contains the

phases of MgB2 MgB

4 MgB

6 MgB

12 and Mg

2B14 So the

MgndashB system is known as multiphase system The aim ofthe present work is to study whether the thermodynamicallyunstable MgB

6[12 13] could be prepared as thermally stable

compound by electrochemical synthesis method

2 Experimental Procedure

Themixture of the salts LiF (1295mol) B2O3(2227mol)

andMgCl2(1714mol) (analytical grade fromMerck India)

was taken as an electrolyte in high-density graphite crucibleand acts as an electrolyte cell as well as anode for theelectrolytic process The Molybdenum rod of 1 cm diameterfitted to a stainless steel rod is used as cathode The cruciblewas filled with the stoichiometric quantities of electrolytesalts whichwere dried at 500∘Cunder argon atmosphereThewhole assembly was placed in an inconel reactor which waskept in an electrical heating furnace with thermocouple The

Hindawi Publishing CorporationInternational Scholarly Research NoticesVolume 2014 Article ID 123194 6 pageshttpdxdoiorg1011552014123194

2 International Scholarly Research Notices

10 20 30 40 50 60 70 80 90 100

0200400600800

100012001400

Inte

nsity

(au

)

2120579 (deg)

MgOMgB6

Figure 1 XRD pattern for MgB6

experimental setup for the electrosynthesis of magnesiumhexaboride is described elsewhere [14ndash17] Then the saltswere melted slowly under a continuous flow of argon gasThe melt was equilibrated at 900∘C for one hour beforeproceeding electrolysis [15ndash17] The bath was preelectrolyzedat 20 V for one hour to remove the impurities and moistureprior to electrolysis The cathode was centrally positioned atthe electrolytic cell Experiment was carried out at currentdensity of 15 Acm2 with the molar ratio of Mg B as 1 6After 5 hours of electrolysis the cathode was removed andthe deposit was cooled in atmosphere The deposit was thenscraped off and the electrolyte adhering to it was leachedwith warm 5 HCl solution Finally washing was done withdistilled water for several times the weight of the deposit wasdetermined and the nature of the powder was analyzed

The phase formation and the structural details of thesynthesized compound were characterized by X-ray powderdiffraction (XRD) using CuK120572 (120582 = 1541 A) radiation with2120579 value range of 20 to 90 using PAnalytical Xrsquopert powderdiffractometer Differential thermal analysis and thermo-gravimetric analysis (TGADTA) of the reactionmixture wasdone using Rigaku ThermalmdashPlus TG 8120 with heatingspeed 20∘Cmin in a flow of air The Fourier transforminfrared (FTIR) spectra were recorded in the range of 400 to4000 cmminus1 using Perkin Elmer UK Paragonmdash500 spectrom-eter Scanning electron microscopy (SEM) was employed forthe morphological studies using JEOL JSM 35 CF Japanmake model UV Visible Spectrophotometer was employedfor the absorbance study using JASCO Model 7800 UVVisible Spectrophotometer Studying the binding energy ofboron and magnesium was done using X-ray photoelectronspectroscopyThermo Scientific UKMultilab 2000

3 Results and Discussion

Figure 1 presents the powder XRD pattern of the MgB6

synthesized by molten salt technique The lattice constantvalue 119886 = 4114 A is determined from the XRD data and iswell matched with the reported value (119886 = 4115 A) [18ndash20]forMgB

6(JCPDSdata card number 08-0421) existing in body

centered cubic crystal structure (the space group Pm3m)

9403

9072

8718

8588

1004

Residue8106

TGA

DTA00

05

10

15

20

0 100 200 300 400 500 600 700 800 900 1000 1100Exothermic is upward Universal V43A TA Instruments

11625∘C10687∘C

23621∘C

37005∘C

49714∘C

28857∘C34868∘C

55574∘C

59909∘C66756∘C

76144∘C

74232∘C

72323∘C

82000∘C

Tem

pera

ture

diffe

renc

e(∘

C)

Temperature (∘C)

80

90

100

85

95

Wei

ght (

)

minus05

minus10

(2159mg)

Figure 2 TGDTA curve for MgB6

[20] But indexing the plans for MgB6is difficult because

the information on its lattice parameters and structure systemis not available in 08-0421 The main building blocks of theMgB6structure are B

6octahedra Other than MgB

6some

additional traces of MgO are also present at 2120579 = 43 and625∘ due to the partial oxidation of Mg [21] The crystallinesize is found to be 42 nm calculated by using Debye-Scherrerequation as follows

119863 =119896120582

120573 cos 120579 (1)

where 119896 is the Scherrer constant usually taken as 09 120582 isthe wavelength characteristics of the Cu-K120572 radiation (120582 =15406 A) 120573 is the full width at half-maximum (FWHM) inradiations 120579 is the reflecting angle and119863 is the crystal size

The TGADTA curve for the reaction mixture is shownin Figure 2 The figure showed that the eutectic point of themelt is found to be 820∘C The melt temperature is keptapproximately 80∘C higher than the eutectic point to reducethe melt viscosity The LiF is used to increase the fluidityand electrical conductivity of the melt Its decompositionpotential is more cathodic than any other salts chosen Agradual weight loss observed up to 497∘C may be due to theremoval of moisture and inbound water associated with thesalts The weight gain which is observed up to 761∘C from497∘C due to B

2O3 begins to turn into liquid (melting point

450∘C) in the heating process These reactants whether inthe liquid or gaseous state play a crucial role in determiningthe shape of the final product Further this weight gain ismainly due to the oxidation of the reactants (2) [22 23]MgCl

2stretches excess Mg and also increases the electrical

conductivity of the melt This excess Mg combines withO forming MgO (from residual B

2O3) The formation of

2MgCl2sdot3B2O3is due to the solid-state reaction between

residual B2O3and MgCl

2turn into molten state (melting

point of MgCl2 708∘C) is confirmed by an exothermic peak

at 761∘C Finally the reactants can be oxidized thoroughlyat 761∘C [24] Further weight loss observed up to 1000∘Cis responsible for the transformation of the reactants intodesired product In the DTA curve a sharp exothermic spike

International Scholarly Research Notices 3

29058 ∘C

82099 ∘C

8040 Jg

3828 Jg

3211 Jgminus20

20

0

0 100 200 300 400 500 600 700 800 900 1000 1100minus40

40

Exo down

66922∘C

74483∘C

60158∘C

5153 Jg1471 Jg

Temperature (∘C) Universal V43A TA Instrument

Hea

rt fl

ow (m

W)

DSC

Figure 3 DSC curve for MgB6

is observed at 742∘Cwhichmay also be verified by confirmingthis process This is gratuitous to the DSC curve (Figure 3) at745∘C a sharp exothermic spine is observed that the heat ofdecomposition of salts is about 5133 Jg

The reaction was carried out for MgB6in MgCl

2ndashB2O3ndash

LiF system the main chemical reactions are

2MgCl2+ 3B2O3997888rarr 2MgCl

2sdot 3B2O3 (2)

2MgCl2sdot 3B2O3997888rarr MgB

6+MgO + 4O

2(g) + 2Cl

2(g) uarr

(3)

The overall reaction is

2MgCl2+ 3B2O3997888rarr MgB

6+MgO + 4O

2+ 2Cl2(g) uarr

(4)

Trace amount of the unreacted intermediate MgO waspresent in the synthesized compound as 06 and theremaining 994 was MgB

6as depicted from XRD pattern

The XPS spectrum for B 1s is shown in Figure 4(a) Thehigher binding energy value for B 1s exists at 1986 eV Thisreflects contributions from both trigonal BO

3and tetrahedral

BO4groups The electron transfer would come from trigonal

B 1s to BndashO 120590lowast orbital and from the unfilled tetrahedral B2p orbital to BndashO 120590lowast [25 26] This B 1s rarr 120590lowast resonance asexpected for sp2-bonded boron incorporated in the crystal[27] Figure 4(b) shows the Mg 1s spectra for MgB

6at 1314 eV

revealed that the auger spectral distribution over an extrudedenergy range far from the threshold there is an extra energyfor Mg rich compound [28] Figure 4(c) shows the O 1sspectrum for MgB

6existing at 544 eVThis may be due to the

core-hole Rydberg states containing O 1s rarr 120590lowast resonance[29 30] Figure 4(d) shows C 1s spectrum at 296 eV andreveals energy transitions between a carbon core level andan antibonding 120587lowast molecular orbital [31] The surface iscontaminated due to exposure to air during the processingof the sample

The Mg2+ cations in MgB6complex species have C

6vpyramidal structures interacting with a planar hexagonalB6

2minus dianionThe bonding between these twomay be due theelectrostatic attraction [12]

The FTIR spectrum of MgB6is shown in Figure 5

The OndashH stretching vibrations of water crystallization arerepresent at 3743 and 3413 cmminus1 respectively The absorptionat 2225 cmminus1 is assigned to OndashH stretching vibration ofcluster of water molecules of crystallization respectivelyThecharacteristic peak of MgndashB is observed at 1642 cmminus1 [32]Longitudinal optic mode frequency of MgndashO is observedat 705 cmminus1 this MgO as impurity phases is also observedin the XRD pattern The bending vibration for MgB

6is

observed at 437 cmminus1 The bending mode of MgndashB of BO4

anion is assigned to 499 cmminus1 The asymmetric stretchingvibration ofMgndashB of BO

4anion is observed at 1021 cmminus1The

asymmetric stretching vibration of BndashObond of trigonal BO3

units is observed at 1367 cmminus1 The frequencies observed inthe spectrum are in good agreement with the reported values[33 34]

The SEM image of the sample is shown in Figure 6The microstructure indicates that the particle diameters arein the range 4ndash8 120583m From the microstructure the moltenregions are clearly visible which give the clear indication ofMgB6formation The white regions in SEM represent the

impurity phase MgO present in the sample [35 36] Thepresent study reveals the formation of MgB

6phase as cubic

crystal structureThe mechanism of hexaboride formation was proposed

by many authors [12 14ndash17 37ndash47] According to Li and Jinthe negative charged boron atoms and the positive chargedalkaline earth metal atoms form complexes of M2+ metalcation and B

6

2minus dianion due to electrostatic attraction Theyalso suggested that the metal cations M2+ have definite roleon stabilizing the B

6

2minus dianion [12] Kaptay and Kuznetsovreported that the boron components are dissolved in ionicform in the melt to form boride phase on the cathode jointwith metal cations [37] Jose et al reported the ldquounstablestoichiometric wayrdquo for the deposition of Barium hexaboride[14] We reported earlier that the electrolytically dissociatedmetal and B ions deposit on the cathode as CeB

6and SmB

6

respectively [15 16] We also reported in our earlier studyon CaB

6that the calcium and boron are reduced at the

cathode to form submicron sized crystals [17] As reportedby Chen et al [38] the formation of MgB

6at 900∘C as one

of the secondary phases along with MgB4due the volatile

nature of Mg at this temperature resulted in Mg deficiencyon in situ Cu doping of MgB

2 The commonly accepted

mechanism of boron deposition in molten salts is a single-step three-electron electrochemical reaction [39ndash43] Glooret al investigated the multiexciton bound state of moleculesin divalent hexaboridesThey proposed that the larger energygain per one electron-hole pair decreases the semiconductinggap and produced intermediate phaseThismay be the reasonfor the formation of intermediate phase MgB

6[44] Li et al

described the diffusion of Mg vapour into boron creatinga complex of MgndashB supersaturated solution encompassingthe formation of nonequilibrium MgB

6[45] Lee et al and

JQ Li also authenticated with S Li [45] and postulatedthat the path of the reaction of supersaturated MgndashB clustercomplex via spinodal decomposition leads to the formationof hypothetical phase MgB

6[46 47]


4500

5000

5500

6500

6000

200200 198198 196196 194194 192192 190190 188188 186186

Cou

nts

s

Binding energy (eV)

3 scans 4m 162 s 0 120583m CAE 100 002 eVB 1s scan

(a)

1308131013121314131613181320

Cou

nts

s

Binding energy (eV)

Mg 1s scan3 scans 3m 441 s 0 120583m CAE 100 002 eV

700E + 04

600E + 04

500E + 04

650E + 04

550E + 04

(b)

532534536538540542544546548550Binding energy (eV)

O 1s scan2 scans 3m 334 s 0 120583m CAE 100 002 eV

500E + 04

400E + 04

300E + 04

200E + 04

Cou

nts

s

(c)

285290295300305

Cou

nts

s

Binding energy (eV)

C 1s scan

600E + 03

800E + 03

100E + 04

120E + 04

140E + 04

160E + 04

180E + 043 scans 6m 402 s 0 120583m CAE 100 002 eV

(d)

Figure 4 XPS spectra for (a) B 1s (b) Mg 1s (c) O 1s and (d) C 1s

3743

62

3693

58

3413

20

2925

29 22

255

0

1642

64

1367

71

1021

81

705

6053

688

499

26 437

71

500100015002000250030003500

500100015002000250030003500

2030405060708090100

2030405060708090

100

Tran

smitt

ance

()

Wavenumber ( cmminus1)Sample name MS B6-NK2

Figure 5 FTIR spectrum of MgB6

4 Conclusion

In summary the electrochemical synthesis of hypotheticalmagnesium hexaboride by molten salt technology is pre-sented Various mechanisms for the formation of magnesium

Figure 6 SEM image of MgB6

hexaboride are discussed It is believed that the supersatu-rated MgB

6cluster complex is postulated for the metastable

magnesium hexaboride compound Further experimentalevidence is more needed to explore the thermodynamicallyunstable magnesium hexaboride


Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Director of CSIR-CECRI for his keen interest and encouragement and staff ofEMP Division for their support S Angappan acknowledgesthe Council of Scientific and Industrial Research (CSIR)India for providing the financial assistant to the projectEMPOWER (OLP 0060)

References

[1] K Segawa A Tomita K Iwashita M Kasaya T Suzuki and SKunii ldquoElectronic and magnetic properties of heavy rare-earthhexaboride single crystalsrdquo Journal of Magnetism and MagneticMaterials vol 104ndash107 no 2 pp 1233ndash1234 1992

[2] C L Perkins M Trenary T Tanaka and S Otani ldquoX-rayphotoelectron spectroscopy investigation of the initial oxygenadsorption sites on the LaB6(100) surfacerdquo Surface Science vol423 no 1 pp L222ndashL228 1999

[3] C Chen W Zhou and L Zhang ldquoOriented structure andcrystallography of directionally solidified LaB6-ZrB2 eutecticrdquoJournal of the American Ceramic Society vol 81 no 1 pp 237ndash240 1998

[4] S-Q Zheng Z-D Zou GH Min H Yu J Han andWWangldquoSynthesis of strontium hexaboride powder by the reaction ofstrontium carbonate with boron carbide and carbonrdquo Journal ofMaterials Science Letters vol 21 no 4 pp 313ndash315 2002

[5] G Kaptay I Sytchev M S Yaghmaee A Kovacs E Cserta andM Ark in Proceedings of the 6th International Symposium onMolten Salt Chemistry and Technology p 168 Shanghai China2001

[6] T Y Kosolapova Ed Preparation and Application of RefractoryCompounds Metallurgiya Moscow Russia 1986

[7] T I Serebryakova V A Neronov and P D Peshev HighTemperature Borides Metallurgiya Chelyabinsk Russia 1991

[8] T A Serebryakova ldquoClassification of boridesrdquo Journal of theLess-Common Metals vol 67 no 2 pp 499ndash503 1979

[9] L Markowsky Y Kondrashevsky and G Kaputovskaya ldquoThecomposition and the chemical properties of magnesiumboridesrdquo Zhurnal Organicheskoi Khimii vol 25 p 433 1955

[10] P Duhart ldquoThe borides of magnesium and aluminiumrdquo Annalidi Chimica vol 7 pp 339ndash365 1962

[11] G V Samsonov T I Serebriakova and V A Neronov BoridesAtomizdat Moscow Russia 1975 (Russian)

[12] Q S Li and Q Jin ldquoTheoretical study on the aromaticity of thepyramidal MB

6(M = Be Mg Ca and Sr) clustersrdquoThe Journal

of Physical Chemistry A vol 107 no 39 pp 7869ndash7873 2003[13] G K Moiseev and A L Ivanovskii ldquoThermodynamic prop-

erties and thermal stability of magnesium boridesrdquo InorganicMaterials vol 41 no 10 pp 1061ndash1066 2005

[14] T P Jose L Sundar L J Berchmans A Visuvasam and SAngappan ldquoElectrochemical synthesis and characterization ofBaB6 from molten meltrdquo Journal of Mining and Metallurgy BMetallurgy vol 45 no 1 pp 101ndash109 2009

[15] K Amalajyothi L J Berchmans S Angappan and A Visu-vasam ldquoElectrosynthesis of cerium hexaboride by the moltensalt techniquerdquo Journal of Crystal Growth vol 310 no 14 pp3376ndash3379 2008

[16] L J Berchmans A Visuvasam S Angappan C Subramanianand A K Suri ldquoElectrosynthesis of samarium hexaboride usingtetra borate meltrdquo Ionics vol 16 no 9 pp 833ndash838 2010

[17] S Angappan M Helan A Visuvasam L J Berchmans andV Ananth ldquoElectrolytic preparation of CaB

6by molten salt

techniquerdquo Ionics vol 17 no 6 pp 527ndash533 2011[18] I Popov N Baadji and S Sanvito ldquoMagnetism and antiferro-

electricity in MgB6rdquo Physical Review Letters vol 108 no 10

Article ID 107205 2012[19] S V Okatov A L Ivanovskii Yu E Medvedeva and N I

Medvedeva ldquoThe electronic band structures of superconduct-ing MgB

2and related borides CaB

2 MgB

6and CaB

6rdquo Physica

Status Solidi B vol 225 pp R3ndashR5 2001[20] A L Ivanovskii ldquoSuperconducting MgB2 and related com-

pounds synthesis properties and electronic structurerdquo RussianChemical Reviews vol 70 pp 717ndash734 2001

[21] V G Pol S V Pol I Felner and A Gedanken ldquoCritical currentdensity in the MgB

2nanoparticles prepared under autogenic

pressure at elevated temperaturerdquo Chemical Physics Letters vol433 no 1ndash3 pp 115ndash119 2006

[22] M Zhang X Wang X Zhang et al ldquoDirect low-temperaturesynthesis of RB6 (R=Ce Pr Nd) nanocubes and nanoparticlesrdquoJournal of Solid State Chemistry vol 182 no 11 pp 3098ndash31042009

[23] P Peshev ldquoA thermodynamic analysis of lanthanum hexaboridecrystal preparation from aluminum flux with the use of com-pound precursorsrdquo Journal of Solid State Chemistry vol 133 no1 pp 237ndash242 1997

[24] J Ma Y Du M Wu et al ldquoA simple inorganic-solvent-thermalroute to nanocrystalline niobium diboriderdquo Journal of Alloysand Compounds vol 468 no 1-2 pp 473ndash476 2009

[25] A M Duffin C P Schwartz A H England J S Uejio D Pren-dergast and R J Saykally ldquopH-dependent x-ray absorptionspectra of aqueous boron oxidesrdquo Journal of Chemical Physicsvol 134 no 15 Article ID 154503 2011

[26] M E Fleet and S Muthupari ldquoBoron K-edge XANES of borateand borosilicate mineralsrdquo American Mineralogist vol 85 no7-8 pp 1009ndash1021 2000

[27] J L Blackburn Y Yan C Engtrakul et al ldquoSynthesis andcharacterization of boron-doped single-wall carbon nanotubesproduced by the laser vaporization techniquerdquo Chemistry ofMaterials vol 18 no 10 pp 2558ndash2566 2006

[28] S Altieri L H Tjeng F C Voogt T Hibma O Rogojanuand G A Sawatzky ldquoCharge fluctuations and image potential atoxide-metal interfacesrdquoPhysical ReviewB vol 66 no 15 ArticleID 155432 pp 1554321ndash1554326 2002

[29] S Sorensen T Tanaka R Feifel et al ldquoApplication of anatomic relaxationmodel for the interpretation ofO1s toRydbergexcited Auger electron spectra of molecular oxygenrdquo ChemicalPhysics Letters vol 398 no 1ndash3 pp 168ndash174 2004

[30] R Feifel T Tanaka M Kitajima et al ldquoProbing the valencecharacter of O 1srarr Rydberg excited O2 by participator Augerdecay measurements and partial ion yield spectroscopy follow-ing x-ray absorptionrdquoThe Journal of Chemical Physics vol 126Article ID 174304 2007

[31] A Talapatra S K Bandyopadhyay P Sen P Barat S Mukher-jee and M Mukherjee ldquoX-ray photoelectron spectroscopy


studies of MgB2for valence state of Mgrdquo Physica C Supercon-

ductivity vol 419 no 3-4 pp 141ndash147 2005[32] S N Kumar S Das C Bernhard and G D Varma ldquoEffect of

graphene oxide doping on superconducting properties of bulkMgB2rdquo Superconductor Science and Technology vol 26 no 9

Article ID 095008 2013[33] K Nakamato Infrared and Raman Spectra of Inorganic and

Coordination Compounds JohnWiley New York NY USA 5thedition 1977

[34] S D Ross Inorganic Infrared and Raman Spectra McGrawHillLondon UK 1972

[35] X Chen T XiaMWangW Zhao andT Liu ldquoMicrostructuraltransformation during combustion synthesis of MgB2 super-conductorrdquo Physica C Superconductivity and its Applicationsvol 454 no 1-2 pp 38ndash42 2007

[36] R G Abhilash Kumar K Vinod R P Aloysius and USyamaprasad ldquoA simple and inexpensive method for rapidsynthesis of MgB

2superconductorrdquo Materials Letters vol 60

no 28 pp 3328ndash3331 2006[37] G Kaptay and S A Kuznetsov ldquoElectrochemical synthesis of

refractory borides from molten saltsmdashreview paperrdquo Plasmasamp Ions vol 2 pp 45ndash56 1999

[38] S K Chen M Majoros J L MacManus-Driscoll and B AGlowacki ldquoIn situ and ex situ Cu doping of MgB

2rdquo Physica C

Superconductivity and its Applications vol 418 no 3-4 pp 99ndash106 2005

[39] R Thompson ldquoThe chemistry of metal borides amp relatedcompoundsrdquo in Progress in Boron Chemistry R J Brothertonand H Steinberg Eds vol 2 pp 178ndash230 Pergamon PressOxford UK 1970

[40] P R Davis M A Gesley G A Schwind L W Swanson andJ J Hutta ldquoComparison of thermionic cathode parameters oflow index single crystal faces of LaB6 CeB6 and PrB6rdquo AppliedSurface Science vol 37 no 4 pp 381ndash394 1989

[41] S V Meschel and O J Kleppa ldquoStandard enthalpies of forma-tion of some borides of Ce Pr Nd and Gd by high-temperaturereaction calorimetryrdquo Journal of Alloys and Compounds vol226 no 1-2 pp 243ndash247 1995

[42] G Balakrishnan M R Lees and D M K Paul ldquoGrowth oflarge single crystals of rare earth hexaboridesrdquo Journal of CrystalGrowth vol 256 no 1-2 pp 206ndash209 2003

[43] C Y Zou Y M Zhao and J Q Xu ldquoSynthesis of single-crystalline CeB6 nanowiresrdquo Journal of Crystal Growth vol 291no 1 pp 112ndash116 2006

[44] T A Gloor M E Zhitomirsky and T M Rice ldquoMultiexcitonmolecules in the hexaboridesrdquo European Physical Journal B vol21 no 4 pp 491ndash497 2001

[45] S Li O Prabhakar T T Tan et al ldquoIntrinsic nanostructuraldomains possible origin of weaklinkless superconductivity inthe quenched reaction product of Mg and amorphous BrdquoApplied Physics Letters vol 81 no 5 pp 874ndash876 2002

[46] S Lee HMori TMasui Y Eltsev A Yamamoto and S TajimaldquoGrowth structure analysis and anisotropic superconductingproperties of MgB2 single crystalsrdquo Journal of the PhysicalSociety of Japan vol 70 no 8 pp 2255ndash2258 2001

[47] J Q Li L Li Y Q Zhou Z A Ren G C Che and Z X ZhaoldquoStructural features stacking faults and grain boundaries inMgB2 superconducting materialsrdquo httparxivorgabscond-mat0104350

Submit your manuscripts athttpwwwhindawicom

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materials


Journal ofNanomaterials


10 20 30 40 50 60 70 80 90 100

0200400600800

100012001400

Inte

nsity

(au

)

2120579 (deg)

MgOMgB6

Figure 1 XRD pattern for MgB6

experimental setup for the electrosynthesis of magnesiumhexaboride is described elsewhere [14ndash17] Then the saltswere melted slowly under a continuous flow of argon gasThe melt was equilibrated at 900∘C for one hour beforeproceeding electrolysis [15ndash17] The bath was preelectrolyzedat 20 V for one hour to remove the impurities and moistureprior to electrolysis The cathode was centrally positioned atthe electrolytic cell Experiment was carried out at currentdensity of 15 Acm2 with the molar ratio of Mg B as 1 6After 5 hours of electrolysis the cathode was removed andthe deposit was cooled in atmosphere The deposit was thenscraped off and the electrolyte adhering to it was leachedwith warm 5 HCl solution Finally washing was done withdistilled water for several times the weight of the deposit wasdetermined and the nature of the powder was analyzed

The phase formation and the structural details of thesynthesized compound were characterized by X-ray powderdiffraction (XRD) using CuK120572 (120582 = 1541 A) radiation with2120579 value range of 20 to 90 using PAnalytical Xrsquopert powderdiffractometer Differential thermal analysis and thermo-gravimetric analysis (TGADTA) of the reactionmixture wasdone using Rigaku ThermalmdashPlus TG 8120 with heatingspeed 20∘Cmin in a flow of air The Fourier transforminfrared (FTIR) spectra were recorded in the range of 400 to4000 cmminus1 using Perkin Elmer UK Paragonmdash500 spectrom-eter Scanning electron microscopy (SEM) was employed forthe morphological studies using JEOL JSM 35 CF Japanmake model UV Visible Spectrophotometer was employedfor the absorbance study using JASCO Model 7800 UVVisible Spectrophotometer Studying the binding energy ofboron and magnesium was done using X-ray photoelectronspectroscopyThermo Scientific UKMultilab 2000

3 Results and Discussion

Figure 1 presents the powder XRD pattern of the MgB6

synthesized by molten salt technique The lattice constantvalue 119886 = 4114 A is determined from the XRD data and iswell matched with the reported value (119886 = 4115 A) [18ndash20]forMgB

6(JCPDSdata card number 08-0421) existing in body

centered cubic crystal structure (the space group Pm3m)

9403

9072

8718

8588

1004

Residue8106

TGA

DTA00

05

10

15

20

0 100 200 300 400 500 600 700 800 900 1000 1100Exothermic is upward Universal V43A TA Instruments

11625∘C10687∘C

23621∘C

37005∘C

49714∘C

28857∘C34868∘C

55574∘C

59909∘C66756∘C

76144∘C

74232∘C

72323∘C

82000∘C

Tem

pera

ture

diffe

renc

e(∘

C)

Temperature (∘C)

80

90

100

85

95

Wei

ght (

)

minus05

minus10

(2159mg)

Figure 2 TGDTA curve for MgB6

[20] But indexing the plans for MgB6is difficult because

the information on its lattice parameters and structure systemis not available in 08-0421 The main building blocks of theMgB6structure are B

6octahedra Other than MgB

6some

additional traces of MgO are also present at 2120579 = 43 and625∘ due to the partial oxidation of Mg [21] The crystallinesize is found to be 42 nm calculated by using Debye-Scherrerequation as follows

119863 =119896120582

120573 cos 120579 (1)

where 119896 is the Scherrer constant usually taken as 09 120582 isthe wavelength characteristics of the Cu-K120572 radiation (120582 =15406 A) 120573 is the full width at half-maximum (FWHM) inradiations 120579 is the reflecting angle and119863 is the crystal size

The TGADTA curve for the reaction mixture is shownin Figure 2 The figure showed that the eutectic point of themelt is found to be 820∘C The melt temperature is keptapproximately 80∘C higher than the eutectic point to reducethe melt viscosity The LiF is used to increase the fluidityand electrical conductivity of the melt Its decompositionpotential is more cathodic than any other salts chosen Agradual weight loss observed up to 497∘C may be due to theremoval of moisture and inbound water associated with thesalts The weight gain which is observed up to 761∘C from497∘C due to B

2O3 begins to turn into liquid (melting point

450∘C) in the heating process These reactants whether inthe liquid or gaseous state play a crucial role in determiningthe shape of the final product Further this weight gain ismainly due to the oxidation of the reactants (2) [22 23]MgCl

2stretches excess Mg and also increases the electrical

conductivity of the melt This excess Mg combines withO forming MgO (from residual B

2O3) The formation of

2MgCl2sdot3B2O3is due to the solid-state reaction between

residual B2O3and MgCl

2turn into molten state (melting

point of MgCl2 708∘C) is confirmed by an exothermic peak

at 761∘C Finally the reactants can be oxidized thoroughlyat 761∘C [24] Further weight loss observed up to 1000∘Cis responsible for the transformation of the reactants intodesired product In the DTA curve a sharp exothermic spike


29058 ∘C

82099 ∘C

8040 Jg

3828 Jg

3211 Jgminus20

20

0

0 100 200 300 400 500 600 700 800 900 1000 1100minus40

40

Exo down

66922∘C

74483∘C

60158∘C

5153 Jg1471 Jg


Hea

rt fl

ow (m

W)

DSC




2ndashB2O3ndash



2sdot 3B2O3 (2)


6+MgO + 4O

2(g) + 2Cl

2(g) uarr

(3)



6+MgO + 4O

2+ 2Cl2(g) uarr

(4)




3and tetrahedral



6at 1314 eV









6is








6phase as cubic



6


6


6and SmB

6




6at 900∘C as one





6[44] Li et al


6[45] Lee et al and


6[46 47]


4500

5000

5500

6500

6000

200200 198198 196196 194194 192192 190190 188188 186186

Cou

nts

s

Binding energy (eV)


(a)

1308131013121314131613181320

Cou

nts

s

Binding energy (eV)


700E + 04

600E + 04

500E + 04

650E + 04

550E + 04

(b)



500E + 04

400E + 04

300E + 04

200E + 04

Cou

nts

s

(c)

285290295300305

Cou

nts

s

Binding energy (eV)

C 1s scan

600E + 03

800E + 03

100E + 04

120E + 04

140E + 04

160E + 04

180E + 043 scans 6m 402 s 0 120583m CAE 100 002 eV

(d)


3743

62

3693

58

3413

20

2925

29 22

255

0

1642

64

1367

71

1021

81

705

6053

688

499

26 437

71

500100015002000250030003500

500100015002000250030003500

2030405060708090100

2030405060708090

100

Tran

smitt

ance

()



4 Conclusion









Acknowledgments


References




















6by molten salt






2 MgB

6and CaB

6rdquo Physica





























2rdquo Physica C


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




29058 ∘C

82099 ∘C

8040 Jg

3828 Jg

3211 Jgminus20

20

0

0 100 200 300 400 500 600 700 800 900 1000 1100minus40

40

Exo down

66922∘C

74483∘C

60158∘C

5153 Jg1471 Jg


Hea

rt fl

ow (m

W)

DSC




2ndashB2O3ndash



2sdot 3B2O3 (2)


6+MgO + 4O

2(g) + 2Cl

2(g) uarr

(3)



6+MgO + 4O

2+ 2Cl2(g) uarr

(4)




3and tetrahedral



6at 1314 eV









6is








6phase as cubic



6


6


6and SmB

6




6at 900∘C as one





6[44] Li et al


6[45] Lee et al and


6[46 47]


4500

5000

5500

6500

6000

200200 198198 196196 194194 192192 190190 188188 186186

Cou

nts

s

Binding energy (eV)


(a)

1308131013121314131613181320

Cou

nts

s

Binding energy (eV)


700E + 04

600E + 04

500E + 04

650E + 04

550E + 04

(b)



500E + 04

400E + 04

300E + 04

200E + 04

Cou

nts

s

(c)

285290295300305

Cou

nts

s

Binding energy (eV)

C 1s scan

600E + 03

800E + 03

100E + 04

120E + 04

140E + 04

160E + 04

180E + 043 scans 6m 402 s 0 120583m CAE 100 002 eV

(d)


3743

62

3693

58

3413

20

2925

29 22

255

0

1642

64

1367

71

1021

81

705

6053

688

499

26 437

71

500100015002000250030003500

500100015002000250030003500

2030405060708090100

2030405060708090

100

Tran

smitt

ance

()



4 Conclusion









Acknowledgments


References




















6by molten salt






2 MgB

6and CaB

6rdquo Physica





























2rdquo Physica C


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




4500

5000

5500

6500

6000

200200 198198 196196 194194 192192 190190 188188 186186

Cou

nts

s

Binding energy (eV)


(a)

1308131013121314131613181320

Cou

nts

s

Binding energy (eV)


700E + 04

600E + 04

500E + 04

650E + 04

550E + 04

(b)



500E + 04

400E + 04

300E + 04

200E + 04

Cou

nts

s

(c)

285290295300305

Cou

nts

s

Binding energy (eV)

C 1s scan

600E + 03

800E + 03

100E + 04

120E + 04

140E + 04

160E + 04

180E + 043 scans 6m 402 s 0 120583m CAE 100 002 eV

(d)


3743

62

3693

58

3413

20

2925

29 22

255

0

1642

64

1367

71

1021

81

705

6053

688

499

26 437

71

500100015002000250030003500

500100015002000250030003500

2030405060708090100

2030405060708090

100

Tran

smitt

ance

()



4 Conclusion









Acknowledgments


References




















6by molten salt






2 MgB

6and CaB

6rdquo Physica





























2rdquo Physica C


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Acknowledgments


References




















6by molten salt






2 MgB

6and CaB

6rdquo Physica





























2rdquo Physica C


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















2rdquo Physica C


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article electrochemical synthesis of magnesium...

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