标准号:QJ 1345-1988

关于离子液体电镀的文献

ElectrodepositionofNiandCocoatingsfrom
ionicliquid
M.Srivastava*,G.YoganandanandV.K.WilliamGrips
Theaimofthepresentstudyistocomparethestructureandpropertiesofnickel,cobaltand
nickel–cobaltalloycoatingsobtainedfromionicliquid(IL)withthoseobtainedfromaqueous
electrolyte.Cholinechloride,acheapandnon-toxicIL,hasbeenchosenforelectrodeposition.
ThecoatingsobtainedfromILdisplayedhighermicrohardnesscomparedwiththoseobtained
fromaqueouselectrolyte.Adifferenceinthesurfacemorphologywasobserved.X-raydiffraction
studiesshowedthatthenickelrichcoatingsexhibitedfacecentredcubiccrystalstructure,
whereasthoserichincobaltdisplayedhexagonalclosepackedstructure.Comparisoninthe
corrosionbehaviourofthecoatingsshowedthattheNicoatingpossessedbettercorrosion
resistanceirrespectiveoftheelectrolyteadopted.
Keywords: Coatings,Electrodeposition,Choline,Structure,Corrosion,Ionicliquid
Introduction
Overthelastdecade,ionicliquids(ILs)havebeenwidely
employedinthemetalfinishingindustryforthe
electrodepositionofmetals,alloys,semiconductorsand
especiallyelementswithnegativereductionpotentials
becausehydrogenevolutioncanbesignificantlysup-
pressed,e.g.Al,Ta,Nb,Mo,WandCr.
1–6
Another
importantapplicationistheelectroplatingofmetalson
watersensitivesubstratessuchasAl,Mg,steel,etc.
7–10
TheadvantagesofILsincludewideelectrochemical
window,widetemperaturerangeforliquidstateand
highconductivity.Ionicliquidsusuallycontainlarge
non-symmetricionsthathavelowlatticeenergyand
hencelowmeltingpoints.
11
Themostcommonlyused
ionsareimidazolium,pyridiniumandcholinebased.
12
AmongthevariousILs,cholinebasedcholinechloride
ChCl,aquaternaryammoniumsalt,hasbeenadoptedin
thepresentstudybecauseofitslowtoxicity,anditis
comparativelycheaper.
Theelectrodepositionofavarietyofmetalsfrom
ChClhasbeenreported.
9,12–15
Inthepresentstudy,Ni,
CoandNi–Coalloyshavebeenchosen.Nicanbeused
inapplicationslikedecorative,wear/corrosionresistance
andelectrocatalysis,whereasCoandNi–Coalloysare
widelyadoptedinmagneticapplications.
16–20
Nickel
anditsalloysaregenerallydepositedfromaqueous
electrolytes;however,theaqueousdepositioninvolves
theevolutionofhydrogen,whichdeterioratesthequality
ofthecoatings.
21
ThemeritsofILsmakethema
favourableelectrolyteforelectrodeposition.Thedeposi-
tionofNianditsalloyshasbeenreportedfrom
chloroaluminateandotherILsandisrelativelyless
studiedinthecholinebasedIL.
22–24
Abbott etal. have
reportedthemechanismofdepositionofNifromChCl/
ethyleneglycolandChCl/ureausingcyclicvoltammetry
andchronocoulometrytogetherwithatomicforcemic-
roscopyandscanningelectronmicroscopy.
25
Theyhave
observedthattheprocessofdepositionisslowandthe
morphologycompositioncanbechangedbyjudiciously
choosingthecomplexingagentsandadditives.
25
Huang
etal. studiedthevoltammetricbehaviourofNi(II)and
Pd(II)ionsinN-butyl-N-methylpyrrolidiniumdicyana-
mideILtosubstitutePtinelectrocatalyticreactions.
1
Theyobservedthatthereductionpotentialsofthe
twoionsoverlapeachother,whiletheyarewidely
separatedinaqueousbaths,leadingtothedifficultyin
co-deposition.Gou etal. havereportedtheelectro-
depositionofNiandNi–Znalloysfrom1-ethyl-3-
methylimidazoliumchloride.
21
Theyobservedthatthe
compositionandmorphologyoftheelectrodeposits
dependontheappliedpotential.Zhu etal. observed
thattheadditionofacetonitriledoesnotaffectthe
nucleationandgrowthmechanismofNidepositedfrom
trifluoromethylsulphonylamidebasedIL.
23
Lahiriand
Tadisinahavereportedthatthestructureofhexagonal
closepacked(hcp)nickelsynthesisedfrom1-ethyl-3-
methylimidazoliumchlorideconsistedoflotsofpores.
24
ThedepositionofCohasbeencarriedoutfromvarious
ILslikeimidazoliumbased26
andamidetype.
27
Schaltin
etal. havereportedthatCometalcannotbedeposited
fromimidazoliumchlorideatCoCl2 concentrationsof
,33mol.-%,whilethereisnothresholdconcentration
fordepositionfromimidazoliumtrifluoromethylsulpho-
nylimide.
26
Fukui etal. havestudiedtheinfluenceof
organicadditiveslikecoumarinandthioureainthe
electrodepositionofCofromamidetypeIL.
27
They
observedthattheadditionofasmallamountofthiourea
iseffectiveinreducingtheoverpotentialofco-deposition
andimprovingthesurfacemorphology.Yang etal.
fabricatedConanowiresfromimidazoliumchlorideand
SurfaceEngineeringDivision,CouncilofScientificandIndustrial
Research,NationalAerospaceLaboratories,PostBagNo.1779,
Bangalore560017,India
*Correspondingauthor,emailmeenu_srivas@yahoo.co.uk
 2012InstituteofMaterials,MineralsandMining
PublishedbyManeyonbehalfoftheInstitute
Received11November2011;accepted27February2012
424 SurfaceEngineering 2012 VOL 28 NO 6 DOI10.1179/1743294412Y.0000000008ethyleneglycolmixtureusingporousanodicalumina
template.
28
ThenanowiresobtainedfromILhada
smoothersurfaceandbettermagneticpropertiesthan
thoseobtainedfromaqueoussolution.Althoughthe
depositionofNiandCousingvariousILshadbeen
described,scarceinformationisavailableonthe
comparativebehaviourofILandaqueousdeposited
coatings.
28
Inthepresentinvestigation,Ni,CoandNi–Coalloys
havebeendepositedusingChClastheIL,andcom-
parisonhasbeenmadewiththesimilarcoatingsob-
tainedfromtheaqueoussulphamateelectrolyte.
Experimental
Thecoatingswereelectrodepositedusingamixture
comprisingcholinechlorideChClandmetalhalideMX
intheratioof1:2.TheMXadoptedwasnickelchloride
forNicoating,cobaltchlorideforCocoatingandnickel
andcobaltchlorideforNi–Coalloydeposition.TheNi–
CoalloysweredepositedwithvaryingCocontents
rangingfrom5to90wt-%.TheChClandMXwere
mixedandheatedto100uCfornearlyhalfanhourand
thencooledto70uC.Thecoatingsweredepositedona
2?562?5cmbrasssubstrateemployingacurrentdensity
of0?5Adm22
for8htoobtainadepositofthickness
35¡5 mm.TheanodesemployedwereNisheetforNi,
Ni–CoalloyplatingandCosheetforCoplating.The
coatingswerewashed,driedthoroughly,cut,mounted
suitablyandmetallographicallypolishedformicrohard-
nessstudies.Thedetailsonthedevelopmentofthe
coatingsfromtheaqueouselectrolytesaredescribed
elaboratelyelsewhere.
29
Thecoatingsweredeposited
fromconventionalsulphamateelectrolyteataconstant
currentdensityof0?5Adm22
for8hdurationto
obtainathicknessof40¡5 mm.Themicrohardnesswas
measuredacrossthecross-sectionofthecoatingsusing
Knoopsindenteremployingaloadof50gf,andthe
valuesreportedaretheaverageoffivemeasurements
performedatvariouslocations.Fieldemissionscanning
electronmicroscopyCarlZeissSupra40VPwasusedto
studythesurfacemorphology,andenergydispersivex-
rayanalysiswasusedtoidentifytheelementalcomposi-
tionofthecoatings.X-raydiffractionwasusedtoresolve
thestructureofthecoatings.Thecrystalorientationwas
determinedusingRigakuX-raydiffractometeremploying
Cu Ka radiationofwavelength0?154nm.Thecrystallite
sizewasdeterminedusingScherrerequation, D50?9l/
bcos h,
30
where D isthecrystallitesize, l istheincident
radiationwavelength, b isthecorrectedpeakwidthat
halfmaximumintensityand h istheangularposition.
Corrosionresistanceofthecoatingswasdeterminedin
3?5%NaClmediumusingpotentiodynamicpolarisation
andelectrochemicalimpedancestudies.
Resultsanddiscussion
Depositionofnickelandcobaltcoatings
ThesurfacemorphologyoftheNicoatingdepositedfrom
ILandaqueouselectrolyteisshowninFig.1.Itisseen
fromthefigurethatthesurfacemorphologyofthe
coatingobtainedfromILisdenseandnodularinnature.
Thedepositmorphologyissimilartothatobservedby
Abbott etal. fortheNidepositedfromChCl:2EGand
ChCl:2urea.