the university of queensland bachelor of engineering thesis414932/mcelligott_jayd… · student...

UQ Engineering

Faculty of Engineering, Architecture and Information Technology

THE UNIVERSITY OF QUEENSLAND

Bachelor of Engineering Thesis

Corrosion of Ti biomaterials Student Name: Jayde MCELLIGOTT Course Code: MECH4500 Supervisor: Professor Andrej Atrens Submission date: 28 October 2016

A thesis submitted in partial fulfilment of the requirements of the Bachelor of Engineering degree in Mechanical Engineering

ii

AbstractThe experimental investigation of corrosion stability of Ti-35.4Zr-28Nb in synthetic

bodyfluidwasconductedtoaidinthedevelopmentofaporousTialloyforuseasabone

replacementmaterial. The corrosion analysiswas conducted using immersion testing

for 28 days, Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy

(EIS) and potentiodynamic polarisation curves. The corrosion performance of the Ti

alloywascomparedtothatofcommercialpurity(CPTi)Grade2underin-vitrotesting

conditionsin:

1. Hanks’solutionat37°C

2. 3.5%NaClsolutionat95°C

Immersiontestingresultsofboththematerialsshowednegligibleweight lossandlow

concentration of Ti, Zr and Nb,which indicates a low corrosion rate. In addition, the

electrochemicaltestingindicatedpassivationbehaviourwhichwasfurthersupportedby

thepartialstabilisationofcurrentdensityandoveralllowcurrentdensities(intheorder

of10-6A/cm2).TheOCPmeasurementalsodescribedapassivationbehaviourwithan

increaseinthecorrosionpotentialandastabilisedcurveovertime.

Overall,fromtheexperimentalresults,nosignificantevidenceofcrevicecorrosionwas

observedunderthetestingconditionsindicatingthatbothCPTiandtheTialloyarenot

sensitivetocrevicecorrosion.

iii

Acknowledgements

ItakethisopportunitytoexpressgratitudetoProfessorAndrejAtrensforhisadviceand

supportthroughoutthisyear.

IalsothankDrZhimingShiandMrAkifSoltanforsharingtheirwealthofknowledge

withme.Thankyouforspendingthetimetoexplainconceptsandmethods,andhelping

conducttheexperiments.

Finally,Ithankmyfamilyandfriendsfortheirlove,encouragementandsupport

throughoutthisjourney.

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TableofContents

Abstract...............................................................................................................................................ii

Acknowledgements.......................................................................................................................iii

ListofTables....................................................................................................................................vi

ListofFigures.................................................................................................................................vii

CorrosionofTibiomaterials........................................................................................................1

1. Introduction..............................................................................................................................1

1.1. ProjectAims.....................................................................................................................................21.2. ProjectScope...................................................................................................................................2

2. LiteratureReview....................................................................................................................3

2.1. Titanium...........................................................................................................................................32.2. OverviewofTitaniumCorrosion..............................................................................................32.3. CreviceCorrosionTesting...........................................................................................................42.4. PreviousWork................................................................................................................................52.5. ElectrochemicalTesting..............................................................................................................6

3. Methodology..............................................................................................................................7

3.1. ImmersionTesting........................................................................................................................73.1.1. SamplePreparation................................................................................................................................73.1.2. WeightLossMeasurements................................................................................................................73.1.3. CouponAssembly.....................................................................................................................................83.1.4. Hanks’solution.........................................................................................................................................93.1.5. NaClsolution............................................................................................................................................103.1.6. ScanningElectronMicroscopy(SEM)...........................................................................................11

3.2. ElectrochemicalTesting...........................................................................................................113.2.1. Samplepreparation..............................................................................................................................123.2.2. Hanks’solution.......................................................................................................................................123.2.3. NaClsolution............................................................................................................................................13

4. ExperimentalResults..........................................................................................................14

4.1. ImmersionTesting.....................................................................................................................144.1.1. SurfaceMorphology..............................................................................................................................144.1.1.1. Hanks’Solution...................................................................................................................................144.1.1.2. NaClSolution........................................................................................................................................154.1.2. WeightLossMeasurements..............................................................................................................17

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4.1.2.1. Hanks’Solution...................................................................................................................................174.1.2.2. NaClsolution........................................................................................................................................184.2. Surfacecomposition.................................................................................................................................184.2.1.1. Hanks’solution....................................................................................................................................184.2.1.2. NaClsolution........................................................................................................................................194.2.2. SolutionAnalysis....................................................................................................................................20

4.3. ElectrochemicalTesting...........................................................................................................204.3.1. SurfaceArea.............................................................................................................................................204.3.2. OpenCircuitPotential..........................................................................................................................204.3.2.1. Hanks’solution....................................................................................................................................204.3.2.2. NaClsolution........................................................................................................................................214.3.3. ElectrochemicalImpedanceSpectroscopy.................................................................................224.3.3.1. Hanks’solution....................................................................................................................................224.3.3.2. NaClsolution........................................................................................................................................254.3.4. PotentiodynamicPolarisationCurve.............................................................................................284.3.4.1. Hanks’solution....................................................................................................................................284.3.4.2. NaClsolution........................................................................................................................................29

5. Discussion...............................................................................................................................31

5.1. ImmersionTesting.....................................................................................................................315.1.1. SurfaceMorphology..............................................................................................................................315.1.2. WeightLossMeasurements..............................................................................................................315.1.3. SurfaceComposition.............................................................................................................................315.1.4. SolutionAnalysis....................................................................................................................................31

5.2. ElectrochemicalTesting...........................................................................................................325.2.1. OCP...............................................................................................................................................................325.2.2. EIS.................................................................................................................................................................325.2.3. PotentiodynamicPolarisationCurve.............................................................................................32

5.3. ExperimentalDifficulties.........................................................................................................33

6. Conclusion...............................................................................................................................35

7. References...............................................................................................................................36

8. Appendices..............................................................................................................................39

8.1. AppendixA....................................................................................................................................39

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ListofTablesTable1:Samplesusedineachcoupon...................................................................................................14

Table2:WeightlossmeasurementsforCPTiinHanks’solutionat37°Cafter28days 17

Table3:WeightlossmeasurementsforTialloyinHanks’solutionat37°Cafter28days

........................................................................................................................................................................17

Table4:WeightlossmeasurementsforCPTiinNaClsolutionat95°Cafter28days.....18

Table5:WeightlossmeasurementsforTialloyinNaClsolutionat95°Cafter28days18

Table6:Solutionanalysisafterimmersiontesting..........................................................................20

Table7:Surfaceareaofsamplesusedintheelectrochemicaltests..........................................20

Table8:CharacteristicsoftheBodeplotinHanks’solutionat37°C.......................................24

Table9:CharacteristicsoftheNyquistplotinHanks’solutionat37°C.................................25

Table10:CharacteristicsoftheBodeplotin3.5%NaClsolutionat23°C.............................26

Table11:CharacteristicsoftheNyquistplotin3.5%NaClsolutionat23°C.......................28

Table12:CharacteristicsofthepolarisationcurvesinHanks’solutionat37°C................29

Table13:Characteristicsofthepolarisationcurvesin3.5%NaClsolutionat37°C.........30

vii

ListofFiguresFigure1:Crevicecorrosionmechanism(TemenoffandMikos,2008)................................4

Figure2:(a)Schematicofcouponassembly,(b)SchematicofTiplate..............................8

Figure3:(a)CPTicouponassembly,(b)Ti35Zr28Nballoycouponassembly..................9

Figure4:Waterbathsetupshowingonecouponassembly..............................................10

Figure5:NaClsolutionimmersiontestingsetupshowingonecouponassembly...........11

Figure6:Electrochemicaltestingsetup..............................................................................12

Figure7:CPTisample4after28daysinHanks’solutionat37°C...................................14

Figure8:TiZrNbsample4after28daysinHanks’solutionat37°C................................15

Figure9:CPTisample2after28daysin3.5%NaClsolutionat95°C.............................16

Figure10:TiZrNbsample2after28daysin3.5%NaClsolutionat95°C........................16

Figure11:EDXspectraofTiZrNbsample4after28daysinHanks’solutionat37°C....19

Figure12:EDXspectraofTiZrNbsample1after28daysin3.5%NaClsolutionat95°C

........................................................................................................................................19

Figure13:OCPcomparisonofallsamplesinHanks’solutionat37°C.............................21

Figure14:OCPcomparisonofallsamplesin3.5%NaClsolutionat23°C.......................22

Figure15:BodeplotcomparisonofallsamplesinHanks’solutionat37°C....................23

Figure16:PhaseplotcomparisonofallsamplesinHanks’solutionat37°C...................24

Figure17:NyquistplotcomparisonofallsamplesinHanks’solutionat37°C................25

Figure18:Bodeplotcomparisonofallsamplesin3.5%NaClsolutionat23°C..............26

Figure19:Phaseplotcomparisonofallsamplesin3.5%NaClsolutionat23°C.............27

Figure20:Nyquistplotcomparisonofallsamplesin3.5%NaClsolutionat23°C.........27

Figure21:PolarisationcurvecomparisonofallsamplesinHanks’solutionat37°C.....28

Figure22:Polarisationcurvecomparisonofallsamplesin3.5%NaClsolutionat23°C30

1

CorrosionofTibiomaterials

1. IntroductionAbiomaterial, asdefinedby theNational InstitutesofHealth (NIH), is “any substance

(otherthanadrug)orcombinationofsubstances,syntheticornatural inorigin,which

can be used for any period of time, as awhole or as a part of a systemwhich treats,

augments, or replaces any tissue, organ, or function of the body” (Birla, 2014).

Biomaterials are used for orthopedic implants required for congenital defects, traffic

accidents,orsportsinjuries,aswellasbonetissuediseasesassociatedwithaging(Ozan

et al., 2015). According to the World Health Organization, in 2030 there will be 1.4

billionpeopleaged60yearsandolder,whichequatestoa56%increasefrom2015.This

increases the need for further research into materials suitable for biomedical

applications.

Materials suitable for theseapplicationsmustpossessproperties suchasnon-toxicity,

corrosion resistance, fatigue resistance, and biocompatibility (Watanabe et al., 2015).

There are four general categories for biomaterials: metals, polymers, ceramics and

composites(Binyaminetal.,2006).Ofthesematerials,metalsaremostcommonlyused,

inparticular titaniumand itsalloys.This isdue to itsbiocompatibility,highcorrosion

resistance,highstrength-to-weightratio,andreasonableformability(Assisetal.,2006,

Martins et al., 2008). Furthermore, titanium promotes osseointegration,which allows

forboneingrowthorthefixingofanimplanttoapatient’sbonestructure(Cremascoet

al.,2008).Currentapplicationsfortitaniumandtitaniumalloys includeboneandjoint

replacement,dentalimplants,fracturefixationandstents(Davis,2003).

However, titaniumhasahigherelasticmodulus thanbone.This isundesirableas this

mayresult instressshieldingand implant loosening(Fojtetal.,2013).Thishighlights

theneedforalloysandporousmaterials.

ElementssuchasNb,Ta,Zr,MoandSnareconsideredtobesafeTialloyingelements.

Theyarenon-toxicandnon-allergic,andareexcellentbetaphasestabilisers(Cremasco

2

etal.,2008).However,theuseofMoisstillconsideredtobecontroversial(Nnamchiet

al.,2016).

1.1. ProjectAimsTheaimofthisresearchprojectistoassessthecorrosionstabilityofTi-35.4Zr-28Nbin

asyntheticbodyfluid.ThisresearchwillaidinthedevelopmentofaporousTialloyfor

useasabonereplacementmaterial.

1.2. ProjectScopeThecorrosionperformanceoftheTialloywillbecomparedtothatofcommercialpurity

(CPTi)Grade2underin-vitrotestingconditionsinthefollowingsolutions:

1. Hanks’solutionat37°C

2. 3.5%NaClsolutionat95°C

The experimental investigation study corrosion of the Ti alloy using the following

methods:

1. Investigationofcrevicecorrosionduringimmersiontestingfor28days.

2. InvestigationofthecorrosionelectrochemistryusingmeasurementsoftheOpen

Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS) and

potentiodynamicpolarisationcurves.

3

2. LiteratureReview

2.1. TitaniumTitaniumalloys,particularlythosethatarefreeofvanadium(V)andaluminum(Al)as

opposedtothecommonaerospacegradeTi-6Al-4Valloy,havereceivedhighinterestas

titaniumisconsideredoneofthemostimportantbiocompatiblemetals(Bansiddhiand

Dunand,2014).Biocompatibilityisimportantasitisthebiologicalacceptanceofthe

implantbythebody.TheabsenceofVandAlfromtheTialloyiscriticalastheyare

elementsthatexhibithighcytotoxicityandnegativetissueresponseinvivoconditions.

Possibleimpactsincludeinducedseniledementia,neurologicaldisordersandallergic

reactions(Martinsetal.,2008).

Consequently,recentresearchhasfocusedonβ-titaniumalloysduetoincreased

biocompatibilityanddecreasedelasticmoduluscomparedtoα-phase.Similarelastic

modulusoftheboneandtheimplantpromotesaloadsharingbetweentheimplantand

naturalboneandminimisesstressshielding(Martinsetal.,2008).Thebetaphaseis

presentathightemperatures,soinordertostabiliseitatlowertemperaturesandobtain

anelasticmodulusclosertothatofthenaturalbone,theaforementionedbetaphase

stabilisersarerequired(Nnamchietal.,2016).

2.2. OverviewofTitaniumCorrosionJones(1996)describescorrosionasthe“destructiveresultofchemicalinteractions

betweenamaterialanditsenvironment”.Corrosioncanhavedetrimentaleffects

includingthelossofproduct,productefficiency,andcontamination,ormore

significantly,thelossofhumanlife(Jones,1996).

TheexcellentcorrosionpropertiesofTiareduetotheformationofoxidefilmonthe

surfaceoftitanium(Jones,1996).IfpassivitybreakdownofTidoesoccur,asismost

likelyinbio-applications,themostlikelysituationisintheformofcrevicecorrosion

(Crameretal.,2003).

Passivemetalsareparticularlysusceptibletocrevicecorrosioninenvironments

containingchloride(Chengetal.,2007).

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2.3. CreviceCorrosionTestingOfparticularimportancetobiomaterialsiscrevicecorrosion.Crevicecorrosionoccurs

inareaswherenarrow,deepcracksarepresent.Anexampleisthepointofcontact

betweenascrewandplateofabonefixationdevice(TemenoffandMikos,2008).

AsdiscussedbyTemenoffandMikos(2008),crevicecorrosionisinitiatedwhenoxygen

isdepletedinacrevice;thecreviceactsastheanodewhilsttheremainingmetalisthe

cathode.Thislimitsthesupplyofoxygenfromoutsidethecreviceviadiffusiononly

(Chengetal.,2007).

Figure1showsthetheoreticalmechanismofcrevicecorrosion.Theconcentrationof

metalions(Mn+)inthecrevicesolutionincreasesduetoanodicdissolution.Theseions

thenattractchlorideions(Cl-)fromthebulkofthesolutioninordertomaintain

electricalneutrality.Unstablemetallicchloridesarethenformed,whichthenhydrolyse

toproduceH+ions.ThisresultsinalowerpHofthecrevicesolution.Thereductionin

pHfurtherdissolutionofthemetal,thusattractingmorechlorideions,andfurther

loweringthepH.Thisprocessisconsideredtobeautocatalytic.Thecrevicesolution

becomesincreasinglyaggressiveduetotheincreasedconcentrationofCl-andH+(Cheng

etal.,2007).Theoverallreactioncanbewrittenas:

𝑀𝐶𝑙! + 𝑛𝐻!𝑂 → 𝑀 𝑂𝐻 ! + 𝑛𝐻!𝐶𝑙!

Figure1:Crevicecorrosionmechanism(TemenoffandMikos,2008)

ThepHofnormalhumanbloodis7.4±0.05;valuesoutsideoftherange7-7.7are

deemedterminal(ZainalAbidinetal.,2011).Hence,itisimportanttolimitanypotential

corrosionfrombiomaterialswhichfluctuatesthepHoftheblood.

5

2.4. PreviousWorkPreviousresearchonbiocompatibleTialloyshasfocusedonavarietyoffactors.Intheir

research,Nnamchietal.(2016)performedpotentiodynamicpolarisationtestsonTi-Mo-

Nb-Zralloy.Similarly,Lopesetal.(2016)usedOCPandpotentiodynamicpolarisation

curvestotestTi-Nb-Fe.

Otherresearchhaveusedsimilaralloysbutdifferenttestingconditionsthatdidnot

simulatethebodyconditions.Forexample,Martinsetal.(2008)andCremascoetal.

(2008)testedTi-30Nb-ZrandTi-35Nbrespectivelyusingelectrochemicaltestingin

0.9%NaClsolutionat25°C.

Therehavealsobeenotherresearchthatusedsimilaralloysbutwithdifferenttesting

methods.Fojtetal.(2013)testedTi39Nbforcrevicecorrosionbuttheyconcludedthat

“giventheassumptionthatthecorrosionprocesswaslocalisedinthepores,noartificial

crevicewasformedonthespecimens,incontrasttothestandardizedprocedure.”Cheng

etal.(2007)alsotestedcrevicecorrosionofNiTiusingcompartmentalisedcell.

Niemeyeretal.(2009)andAssisetal.(2006)bothtestedTi-13Nb-13Zrbutdidn’ttest

specificallyforcrevicecorrosionbehaviour.Niemeyeretal.(2009)testsforcorrosion

behaviourofsample“withoxygenloadsbydopingthesampleswithtwoquantitiesof

interstitialoxygeninaPBSsolution”.SimilarlyXuetal.(2015)usedpotentiodynamic

polarisationcurvestoexaminethecorrosionofTi-Nb-Ta-Zr-Fe,howevercrevice

corrosionwasnotthemainfocus.

Pastworksalsoincludedstudiesofcrevicecorrosion,butwithdifferentmaterial.For

example,Chenghaoetal.(2015)testedCPTi,Ti-6Al-4VandTi-NiShapeMemoryAlloy

forcrevicecorrosion.

Therewasalsoonestudythatusedtheexactalloybuttheinvestigationfocusedon

mechanicalpropertiesratherthancorrosion.Ozanetal.(2015)testedTi-34Nb-25Zr,Ti-

30Nb-32Zr,Ti-28Nb-35.4ZrandTi-24.8Nb-40.72Zrfor“effectsofalloyingelementon

theirmicrostructures,mechanicalpropertiesandcytocompatibilities.”

6

2.5. ElectrochemicalTestingPolarisationcurvesareplotsofcurrentversuselectrodepotential.Thecorrosionrate,

icorr,canbefoundatEcorrviaextrapolationoftheTafelregion(Jones,1996).

7

3. MethodologyTwo different testingmethods were used to study the corrosion of Ti-35.4Zr-28Nb -

immersiontestingandelectrochemicaltesting.CPTiwastestedasacontrolmaterial.

3.1. ImmersionTesting

Immersion testingwas conducted using Hanks’ solution and 3.5%NaCl solution. The

sample preparation in both cases was the same. Weight loss measurements of the

samplesweretakenbeforeimmersiontestsandthecouponswereassembledfollowing

this. Another set of weight loss measurements were conducted after the immersion

tests.

3.1.1. SamplePreparation

1. CP Ti sampleswere cut to size (10mm x 10mm) using a Struers Discotom-6

cuttingmachine.TheTialloysampleswerealreadyavailableaspertherequired

size(10mmx10mm).

2. AllsamplesweregroundsequentiallyusingStruersTegraforce-5orbitalmachine

with a 320-grit followed by 600-, 1200- and 4000-grit silicon carbide abrasive

paper. The samples were rinsed with ethanol and dried with compressed air

betweeneachgrindingstep.

3. ThesampleswerethenpolishedusingStruersOxidePolishingSuspensionwith

hydrogenperoxide(OP-S+20%H2O2)to0.5micron.

4. After the polishing, the samples were placed in a beaker of ethanol and

ultrasonicallycleanedfor3–4minutes,anddriedwithcompressedair.

5. After the cleaning, all samples were placed in a zip lock bags and kept in a

desiccator.

3.1.2. WeightLossMeasurements

Priortotheweightlossmeasurements,allsampleswerephotographedusinganoptical

microscope.Thesampleswerethenweighedusingananalyticalbalanceandthesample

coupons assembled. After immersion testing had concluded, each sample was re-

photographedandre-weighed.Thereductioninweightwasthencalculated.

8

3.1.3. CouponAssemblyOnce all samples had been prepared, photographed and weighed, the coupons were

assembled.Eachcouponcontained3Tisamplesand4polytetrafluoroethylene(PTFE)

washerstosimulateacrevice(seeFigure2).Thefollowingstepswereusedtoassemble

eachcoupon:

1. Astackofalternatingwashersandsampleswasconstructed.

2. ATiplatewasplacedateachendofthestack.

3. FourTiboltsweretheninsertedthrougheachholeontheplate(seeFigure2).

4. Anutwasthreadedontotheendofeachboltandtightenedwithaspanneruntil

evenlytight.

ImagesoftheassembledcouponsareshowninFigure3.

Figure2:(a)Schematicofcouponassembly,(b)SchematicofTiplate

(a) (b)

9

Figure3:(a)CPTicouponassembly,(b)Ti35Zr28Nballoycouponassembly

3.1.4. Hanks’solutionAfterallthecouponswereassembled,immersiontestingcommencedinHanks’solution

usingthefollowingsteps:

1. 1 litre of Hanks’ Balanced Salts was prepared with the addition of 0.35 g/L

sodiumbicarbonate,asperinstructions(seeAppendixA).

2. TwoCPTi couponswere placed in one beaker and twoTi alloy couponswere

placedinanotherbeaker.

3. 500mlofHanks’solutionwasaddedtoeachbeaker.

4. Thebeakerswerecoveredingladwraptominimiseevaporationeffects.

5. Thebeakerswerethenplacedinawaterbathat37°C(seeFigure4).

6. After28daysthebeakerswereremoved.

7. ThecouponswereremovedfromtheHanks’solution,rinsedwithdistilledwater

and driedwith air. The couponswere placed in a zip lock bag and kept in the

desiccator.

8. After several days of drying, the coupons were disassembled and the samples

werere-weighedandphotographed.

(a)

(b)

10

Figure4:Waterbathsetupshowingonecouponassembly

3.1.5. NaClsolution

The immersions tests inNaCl solutionwereconductedsimilarly to the tests inHanks’

solution(seeFigure5).Thefollowingstepswerefollowed:

1. 1 litreof3.5%NaCl solutionwaspreparedusing35gofNaCland1Ldistilled

water.

2. Two CP Ti coupons were placed in one flask and two Ti alloy coupons were

placedinanotherflask.

3. 600mlofNaClsolutionwasaddedtoeachflask.

4. Eachflaskwasplacedonaseparatehotplate.

5. The condenser was then inserted into mouth of the flask using a B55 socket

adaptor.

6. Hosing was connected between the condensers and tap. The water was then

slowlyturnedonforthecoolingsystemtofunction.

7. A thermocouple sensor connected to the hot platewas inserted in the flask to

measureandcontrolthesolutiontemperatureto95°C.

8. After28daysthehotplatewasturnedoff.Whentheflaskhadcooledsufficiently

itwasremovedfromthehotplate.

9. Thecouponswereremovedfromtheflask,rinsedwithdistilledwateranddried

withair.Thecouponswereplacedinaziplockbagandkeptinthedesiccator.

10. After several days of drying, the coupons were disassembled and the samples

werere-weighedandphotographed.

11

Figure5:NaClsolutionimmersiontestingsetupshowingonecouponassembly

3.1.6. ScanningElectronMicroscopy(SEM)ThesurfacemorphologywasconductedusingaJEOLJSM-6460ScanningElectron

MicroscopewithEnergy-DispersiveX-raySpectroscopy(EDX)microanalysis

capabilities.

3.2. ElectrochemicalTestingElectrochemicaltestswereconductedinbothHanks’solutionandNaClsolutionusinga

PARSTAT 2263 Advanced Electrochemical System. The software used was Princeton

Applied Research Electrochemistry PowerSuite. A silver/silver chloride electrode

saturatedwithpotassiumchloride(Ag/AgClSat.KCl)wasusedasareferenceelectrode.

Beforetestingcouldcommence,thesampleswerepreparedasfollow.

12

3.2.1. SamplepreparationThesampleswerepreparedinthefollowingway:

1. Thesamplesweregroundsequentiallyusing320-,600-,1200-,4000-gritsilicon

carbideabrasivepaper, asper the immersion testing.Thesampleswere rinsed

withethanolanddriedwithcompressedairbetweeneachstep.

2. Acopperwirewaslaserweldedtoeachsample.

3. Thesampleswerethensetinanepoxyresin,withthecopperconnectioncovered

byepoxy,andexposingasurfaceareaofapproximately1cm2.

4. EachsamplewasnumberedusingaDremylforidentificationpurposes.

5. Allsampleswererepolishedusing4000-gritsiliconcarbidetoremoveanyepoxy

resinontheoutersurface.

6. Thesurfaceareaofeachsamplewasmeasuredandrecorded.

3.2.2. Hanks’solutionThetestingwassetupusingthefollowingsteps:

1. Abeakerwasfilledwith500mlofHanks’solution.

2. Thebeakerwasplacedinawaterbathat37°C.

3. The beaker was left for 30 minutes to ensure the solution in the beaker has

equilibrated to the temperatureof thebath.Thesamplewas thenclamped into

placeandloweredintothesolution.

4. The counter electrodewas placed on the side of beaker. The sample (working

electrode)andthereferenceelectrodewereplacedincloseproximity(seeFigure

6).

Figure6:Electrochemicaltestingsetup

13

OpenCircuitPotential(OCP)

Thecorrosionpotential(Ecorr)wasmonitoredoveraperiodof7200seconds,withdata

beingrecordedevery2seconds.

ElectrochemicalImpedanceSpectroscopy(EIS)

OncetheOCPhadfinished,theEISwasconducted.Theelectrochemical impedance(Z)

wasmeasuredoverafrequencyrangefrom100kHzto10mHz,usinganACamplitude

of10mV.Atotalof40datapointswerecollected.

Potentiodynamicpolarisationcurve

The final electrochemical testwas the polarisation curve. Scanswere carried out at a

scanrateof0.1660mV/sintherangefrom-0.2500to3.0000volts.

Atthecompletionofpolarisationcurve,thesamplewasremovedfromthesolutionand

rinsedwithdistilledwater,driedwithcompressedairandplacedinziplockedbag.

3.2.3. NaClsolution

Before thesamplescouldbe tested inNaClsolutiontheyweregroundusing4000-grit

siliconcarbidetoremoveanypassivefilmthatcouldhaveformedonthesamplesurface.

Thesamplewasthenrinsedwithethanolanddriedwithcompressedair.Thetestwas

then set up as per themethodology in section 3.2.2, however, substituting 500ml of

3.5%NaClsolutionatroomtemperature(23°C)fortheHanks’solution.

14

4. ExperimentalResultsTheexperimentalresultsfortheimmersionandelectrochemicaltestingcanbefoundin

sections4.1and4.3respectively.

4.1. ImmersionTestingTable1showsthesampledesignationforimmersiontestinginboththeHanks’andNaCl

solutions.Table1:Samplesusedineachcoupon

Coupon Material Samples

1 Tialloy 1,2,3

2 Tialloy 4,5,6

3 CPTi 1,2,3

4 CPTi 4,5,6

4.1.1. SurfaceMorphology

4.1.1.1. Hanks’Solution

Figure7showsthesurfacemorphologyasobservedbySEMofaCPTisampleimmersed

in Hanks’ solution for 28 days. The image shows no evidence of pitting or crevice

corrosion.However,potentialfiliformcorrosioncanbeseen.

Figure7:CPTisample4after28daysinHanks’solutionat37°C

15

Figure 8 shows similar morphology for the TiZrNb alloy after immersion in Hanks’

solutionfor28days.Theformationofasurfacelayercanbeseenontheouteredgeof

the sample. This is analysed further in section 4.2.1.1There is no evidence of crevice

corrosion.

Figure8:TiZrNbsample4after28daysinHanks’solutionat37°C

4.1.1.2. NaClSolution

Figure 9 show the corrosionmorphology of typical CP Ti samples immersed in 3.5%

NaClsolutionfor28days.AnimageofatypicalTiZrNbsampleisshowninFigure10.

CP Ti shows a predominantly uniform surface and there is no evidence of crevice

corrosionasillustratedinFigure9.

16

Figure9:CPTisample2after28daysin3.5%NaClsolutionat95°C

The TiZrNb sample shows two distinct sections. The outer area of the samplewas in

contactwithboththewasherandNaClsolution.Theinnersectionwasincontactwith

thewasheronly.Anumberofscratchescanbeseenalongtheouteredgeofthesample

fromthepolishingstep.Thereisnoevidenceofcrevicecorrosion.

Figure10:TiZrNbsample2after28daysin3.5%NaClsolutionat95°C

17

4.1.2. WeightLossMeasurementsEachsamplewasweighedbeforeandaftertheimmersiontesting.Thechangeinweight

hasbeencalculatedinmass(g).Thechangeinweightwascalculatedusingthefollowing

equation:

∆𝑚 𝑔 = 𝑤𝑒𝑖𝑔ℎ𝑡!"#$%" − 𝑤𝑒𝑖𝑔ℎ𝑡!"#$%

4.1.2.1. Hanks’Solution

Table2andTable3 show theweight lossmeasurements forCPTiand theTialloy in

Hanks’solutionat37°Cafter28days.

Table2:WeightlossmeasurementsforCPTiinHanks’solutionat37°Cafter28days

SampleWeight(g)

Δm(g)Before After

1 0.2973 0.2970 0.0003

2 0.3027 0.3027 0.0000

3 0.3068 0.3068 0.0000

4 0.2977 0.2976 0.0001

5 0.3165 0.3163 0.0002

6 0.2983 0.2982 0.0001

Table3:WeightlossmeasurementsforTialloyinHanks’solutionat37°Cafter28days

SampleWeight(g)

Δm(g)Before After

1 0.8013 0.8011 0.0002

2 0.8116 0.8113 0.0003

3 0.8053 0.8050 0.0003

4 0.7903 0.7903 0.0000

5 0.8013 0.8012 0.0001

6 0.7308 0.7308 0.0000

18

4.1.2.2. NaClsolution

Table5showtheweightlossmeasurementsforCPTiandtheTialloyinNaClsolutionat

95°Cafter28days.

Table4:WeightlossmeasurementsforCPTiinNaClsolutionat95°Cafter28days

SampleWeight(g)

Δm(g)Before After

1 0.1415 0.1414 0.0001

2 0.1348 0.1346 0.0002

3 0.2351 0.2350 0.0001

4 0.1250 0.1245 0.0005

5 0.0719 0.0719 0.0000

6 0.1209 0.1209 0.0000

Table5:WeightlossmeasurementsforTialloyinNaClsolutionat95°Cafter28days

SampleWeight(g)

Δm(g)Before After

1 0.7878 0.7877 0.0001

2 0.6664 0.6661 0.0003

3 0.7724 0.7724 0.0000

4 0.8077 0.8077 0.0000

5 0.8109 0.8108 0.0001

6 0.7184 0.7182 0.0002

4.2. Surfacecomposition

4.2.1.1. Hanks’solution

Figure11showsthesurfacecompositionofatypicalTiZrNbsampleimmersedinHanks’

solutionfor28days.Tracesofcalcium(Ca),phosphorus(P)andoxygen(O)arepresent.

19

Figure11:EDXspectraofTiZrNbsample4after28daysinHanks’solutionat37°C


Figure12showsthesurfacecompositionofatypicalTiZrNbsampleimmersedin3.5%

NaCl solution for28days.Thepresenceof oxygen suggests the formationof anoxide

layer.AslightdecreaseinbothZrandNbcontentsisalsoobserved,whencomparedto

theoriginalcomposition.

Figure12:EDXspectraofTiZrNbsample1after28daysin3.5%NaClsolutionat95°C

Element (keV) Mass% Error% Atom% C K 0.277 19.03 0.11 39.84 O K* 0.525 7.76 0.57 12.20 Na K* 1.041 0.58 0.10 0.63 Mg K* 1.253 1.60 0.08 1.66 Si K 1.739 0.27 0.06 0.24 P K 2.013 19.83 0.07 16.10 Ca K 3.690 35.82 0.10 22.48 Ti K 4.508 10.79 0.14 5.66 Zr L 2.042 4.32 0.19 1.19 Total 100.00 100.00

011011

200 µm200 µm200 µm200 µm200 µm

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00keV

TiZrNb-C2S1-011

0

400

800

1200

1600

2000

2400

2800

3200

3600

4000

Counts

CO

NaMg

Si

P

P

CaKesc

Ca

CaTiTi

Zr

Element (keV) Mass% Error% Atom% C K 0.277 2.09 0.09 10.51 O K 0.525 0.86 0.34 3.25 Ti K 4.508 37.29 0.09 47.00 Zr L 2.042 33.79 0.14 22.37 Nb L 2.166 25.96 0.13 16.87 Total 100.00 100.00

015015

100 µm100 µm100 µm100 µm100 µm

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00keV

TiZrNb-C1S1-015

040080012001600200024002800320036004000440048005200

Counts

CO

TiZr

Zr Zr

NbNb

Nb

Nb

20

4.2.2. SolutionAnalysisAftereachimmersiontestthesolutionwasanalysedfortheconcentrationofTi,Zrand

Nb.TheresultsareshowninTable6.

Table6:Solutionanalysisafterimmersiontesting

Solution MaterialSolutionconcentration(mg/L)

Ti Zr Nb

Hanks’solutionCPTi 0.001 - -

TiZrNb 0.002 0.001 0.016

3.5%NaClsolutionCPTi 0.002 - -

TiZrNb 0.003 0.006 0.016

4.3. ElectrochemicalTesting

4.3.1. SurfaceArea

Table7presentsthesurfaceareaofeachsample.

Table7:Surfaceareaofsamplesusedintheelectrochemicaltests

Material Sample Dimensions(mm) Surfacearea(cm2)

Tialloy1 Diam=8mm 0.50

2 Diam=8mm 0.50

CPTi

1 10.3x11.3 1.16

2 10.5x13.3 1.40

3 11.4x10.7 1.21

4.3.2. OpenCircuitPotential


Figure13showsacomparisonofOCPresultsforallCPTiandTialloysamplesinHanks’

solution at 37 °C. The corrosion potential is seen to increase quickly towards more

positive potentials during the first hour (3600s). After that, the corrosion potential

changesmore slowly until it reaches a relatively stable level. This is observed for all

samples.

21

Figure13:OCPcomparisonofallsamplesinHanks’solutionat37°C


Figure14showsacomparisonofOCPresultsforallCPTiandtheTialloyin3.5%NaCl

solutionatroomtemperature(23°C).ThecorrosionpotentialofTi35Zr28NbandCPTi-

01 samples remain relatively stable for the duration of immersion. The corrosion

potentialofCPTi-02increasesquicklytowardsamorepositivepotentialbeforeitbegins

tostabilise,asillustratedinFigure13.

22

Figure14:OCPcomparisonofallsamplesin3.5%NaClsolutionat23°C

4.3.3. ElectrochemicalImpedanceSpectroscopyEISresultsincludethebode,thephaseandNyquistplots.Abodeplotgraphsimpedance

(Z) versus frequency, while the phase plot shows the phase of impedance versus

frequency.TheNyquistplotistherealversusimaginarypartoftheimpedance.


Thebode,phaseandNyquistplotscomparingallsamplesinHanks’solutionat37°Care

presentedinFigure14,Figure16andFigure17respectively.

23

Figure15 showshighmodulusof impedance (Z) at low frequencies for all samples in

Hanks’solutionat37°C.ThisisalsoshowninTable8.

Figure15:BodeplotcomparisonofallsamplesinHanks’solutionat37°C

24

Table8:CharacteristicsoftheBodeplotinHanks’solutionat37°C

Material Sample |Z|(kΩ)

CPTi

1 264

2 334

3 280

Tialloy1 714

2 452

Figure16showsthephaseangleapproaching90°formediumtolowfrequencies.Thisis

seenforallsamplesinHanks’solutionat37°C.

Figure16:PhaseplotcomparisonofallsamplesinHanks’solutionat37°C

Figure 17 shows the capacitance arcs of all samples in Hanks’ solution at 37 °C. The

estimatedarcdiametersareshowninTable9.

25

Figure17:NyquistplotcomparisonofallsamplesinHanks’solutionat37°C

Table9:CharacteristicsoftheNyquistplotinHanks’solutionat37°C

Material Sample Diameter(kΩ)

CPTi

1 507

2 753

3 538

Tialloy1 2350

2 630


Thebode,phaseandNyquistplotscomparingallsamplesin3.5%NaClsolutionatroom

temperature(23°C)arepresentedinFigure18,Figure19andFigure20respectively.

Figure18 showshighmodulusof impedance (Z) at low frequencies for all samples in

NaClsolutionat23°C.ThisisalsoshowninTable10.

26

Figure18:Bodeplotcomparisonofallsamplesin3.5%NaClsolutionat23°C

Table10:CharacteristicsoftheBodeplotin3.5%NaClsolutionat23°C

Material Sample |Z|(kΩ)

CPTi1 390

2 177

Tialloy1 651

2 619

Figure19showsthephaseangleapproaching90°formediumtolowfrequencies.Thisis

seenforallsamplesinNaClsolutionat23°C.

27

Figure19:Phaseplotcomparisonofallsamplesin3.5%NaClsolutionat23°C

Figure 20 shows the capacitance arcs of all samples in NaCl solution at 23 °C. The

estimatedarcdiametersareshownTable11.

Figure20:Nyquistplotcomparisonofallsamplesin3.5%NaClsolutionat23°C

28

Table11:CharacteristicsoftheNyquistplotin3.5%NaClsolutionat23°C

Material Sample Diameter(kΩ)

CPTi1 3126

2 366

Tialloy1 5956

2 1554

4.3.4. PotentiodynamicPolarisationCurvePotentiodynamic polarisation curves show corrosion potential versus current density

(A/cm2). The corrosion potential, passivation current density and film breakdown

potentialcanbefoundfromthepolarisationcurves.


Figure21comparesthepolarisationcurvesforallCPTiandTialloysamplesinHanks’

solution at 37 °C. The open circuit potential (OCP), film breakdown potential (Eb),

passivecurrentdensity(ipass)andpassiverange(Eb–OCP)isshowninTable12.

Figure21:PolarisationcurvecomparisonofallsamplesinHanks’solutionat37°C

29

It can be observed from the polarisation curve that the corrosion potential increased

positivelywiththeimmersiontime.Theregionofconstantanodiccurrentdensitywith

increasingcorrosionpotentialrepresentsthepassivationprocess.

There is evidence of passive film breakdownwhen the anodic anodic current density

increasessuddenlyafter theEb.There isalsoevidenceofa re-passivestatewhere the

currentdensitystabilisesagain.

Overall, the polarisation curves showvery low ipass values, in the order of 10-6A/cm2

(refertoTable12).

Table12:CharacteristicsofthepolarisationcurvesinHanks’solutionat37°C

Material SampleOCP

(mV)

Eb

(mV)

ipass

(μA/cm2)

PassiveRange

(mV)

CPTi

1 -70 1020 1.02 1090

2 -165 820 0.43 985

3 -191 940 0.82 1131

Tialloy1 -327 480 0.77 807

2 -141 860 1.30 1001


Figure22compares thepolarisationcurves forallCPTiandTialloysamples in3.5%

NaCl solution at room temperature (23 °C). The open circuit potential (OCP), film

breakdownpotential(Eb),passivecurrentdensity(ipass)andpassiverange(Eb–OCP)is

showninTable13.

30

Figure22:Polarisationcurvecomparisonofallsamplesin3.5%NaClsolutionat23°C

Figure22shows thecorrosionpotential increasedpositivelywith the immersion time

andthespontaneousformationofaprotectivefilm(asshowninFigure21).Thereisalso

evidence of passive film breakdown and a re-passive state. It is noted that the film

breakdownpotentialishigherinNaClsolutionthanHanks’solution.

Thepolarisationcurvesshowverylowipassvalues,intheorderof10-6A/cm2(seeTable

13).

Table13:Characteristicsofthepolarisationcurvesin3.5%NaClsolutionat37°C

Material SampleOCP

(mV)

Eb

(mV)

ipass

(μA/cm2)

PassiveRange

(mV)

CPTi1 -201.2 1068 0.57 1269

2 -488.7 1196 1.04 1685

Tialloy1 -334.8 1136 1.13 1471

2 -157.6 1180 0.57 1338

31

5. Discussion

5.1. ImmersionTesting

5.1.1. SurfaceMorphology

SurfacemorphologyofCPTiandTi-35Zr-28Nbshowslittlechangestothesurface.No

evidenceofpittingorcrevicecorrosion.Filiformcorrosionwasfoundonthesurfaceof

theCPTi,howeverthisisindicativeofpassivematerials.

5.1.2. WeightLossMeasurementsThechange inweightof thesamples inbothHanks’solutionandNaClsolutionwas in

the order on 0.0001g. Therefore, the weight loss is considered negligible. This also

indicatesalowcorrosionrate.

5.1.3. SurfaceComposition

Presenceofcalcium(Ca),phosphorus(P)andoxygen(O)suggeststhatthesurfacelayer

may be calcium phosphate, Ca10(PO4)6(OH)2 (also called hydroxyapatite). Calcium

phosphateisacorrosioninhibitor,knowntoplayaprotectiveroleforTiandTialloys,

resultinginadecreaseincorrosionrate.TheslightdecreaseinbothZrandNbcontents

confirmsalowcorrosionrate.

5.1.4. SolutionAnalysis

LowconcentrationofTiwasdetectedinbothsolutionsforCPTi.Lowconcentrationof

Ti,ZrandNbwasdetectedinbothsolutionsfortheTialloy.Itwasnotedthatahigher

concentrationofNbwasfoundcomparedtoZr,despitehavingalowercontent.

The concentrationdetected in the solutionswas typicallyhigher for theNaCl solution

thanHanks’solution.ThiswasexpectedasNaClcontainshigherchloridecontent.Itwas

alsoatanelevatedtemperature,furtherincreasingcorrosionrates.

OverallthelowconcentrationofTi,Zr,Nbdetectedwasconsiderednegligibleindicating

alowcorrosionrate.

Fromtheabovediscussion,itcanbeobservedthatthecorrosionofCP

32

Ti and Ti alloy is a passivation process in both the Hanks’ solution and 3.5% NaCl

solution.

5.2. ElectrochemicalTesting

5.2.1. OCP

ThetrendsshowninFigure13andFigure14 indicate thespontaneous formationofa

protectivefilmonthesurfaceofallsamples.Anincreaseincorrosionpotentialindicates

thickeningoftheprotectivefilm.Overall,bothCPTiandTi35Zr28Nbexhibitpassivation

behaviour inHanks’ solution andNaCl solution. Passivation behaviour is indicative of

lowcorrosionrates.

5.2.2. EIS

Highmodulusofimpedance(Z)atlowfrequenciesisseenforallsamplesinbothHanks’

solutionandNaClsolution.Thisindicateshighpolarisationresistanceandconsequently

lowcorrosionrate.

Thephaseplotsshowthephaseangleapproach90°formediumtolowfrequencies.This

indicates a highly capacitive behaviour of all samples in Hanks’ solution and NaCl

solution. This is typical of passivematerials, suggesting that a highly stable filmwas

formedonalltestedsamples.

A wide capacitance arc indicates an increase in reaction resistance. This indicates a

densepassivefilmisformedonthesurface.ThisisseeninallsamplesinHanks’solution

andNaCl,indicatingalowcorrosionrate.

5.2.3. PotentiodynamicPolarisationCurveThenatureof thepolarisation curves indicate that all samples exhibit self-passivation

behaviour.Partialstabilisationofcurrentdensitysuggeststhataprotectivepassivefilm

isformedwithinthepotentialrange.

33

Atapproximately1Vthepassivefilmisseentobreakdowninallsamples.Thisiscaused

by the chloride ions from the solution. The restoration time for the passive film is

shorterforCPTi,suggestingithasamorestableandprotectivefilm.

Thepolarisationcurvesshowvery lowIcorrvalues(intheorderof10-6A/cm2).This is

typical of passive materials. Overall, the passivation behaviour of both the materials

indicatelowcorrosionrates.

5.3. ExperimentalDifficultiesThroughout the experimental procedure, there were several difficulties, which could

havepotentiallyaffectedtheresults,includingbutnotlimitedto:

• Potentialinconsistenciesinsamplepreparation:Thesampleswereunabletobe

automatically ground and polished using Struers Tegraforce-5 orbital machine

duetonatureofthecorrosiontesting.Thesampleswereunabletobemounted

duetothecouponassemblyconfiguration.Therefore,itwasrestrictedtomanual

surfacepreparationonly.Thismadeitdifficulttoensurethesurfacepreparation

wasconsistentforallsamples.

• Scratchesduringpolishing:Thereweresuspecteddiamondparticlesembedded

in the polishing cloth from previous usagewhere diamond pastewas used for

polishing.Thisresultedinfaintscratchesonthesamplesurfaceduringthefinal

polishingstep.

• Inconsistenciesincouponassembly:Duetothesmallandslightlyvariedsizesof

the samples it was difficult to perfectly align the stack of PTFE washers and

samples. Thismay have resulted in a difference in crevice simulation between

samples.

• Evaporation of the water bath: Over the 28 days of testing the water bath

experiencedsomewaterevaporation,requiringthewaterbathtobetoppedupto

therequiredwater level.Thisresulted inminordisturbances to thewaterbath

temperature.

• Evaporation during immersion testing: Over the duration of the immersion

testing the beaker/flask experienced evaporation. This may have affected the

concentration of the solution. Steps were taken to minimise these effects,

includingcoveringthebeakerandtheuseofacoolingsystem.

34

• Cleaningsamples:Beforethesampleswereweighed, theywerecleanedusinga

solution of nitric acid (HNO3) and hydrofluoric acid (HFl). This may have

influenced the corrosion. However, the overall weight loss was considered

negligible.

35

6. ConclusionThe experimental investigation of corrosion stability of Ti-35.4Zr-28Nb in synthetic

bodyfluidwasconductedtoaidinthedevelopmentofaporousTialloyforuseasabone

replacementmaterial. The corrosion analysiswas conductedusing immersion testing,

OCP,EISandpotentiodynamicpolarisationcurves

Based on the experimental results and corrosion analysis, no significant evidence of

crevicecorrosionwasobservedunderthetestingconditionsindicatingthatbothCPTi

andtheTialloyarenotsensitivetocrevicecorrosion.Thisconclusionoflowcorrosion

ratewasmadebasedonthefollowingobservations:

• Lowweight lossand lowconcentrationofTi,ZrandNb foundafter immersion

testing

• CorrosionpotentialincreasesandstabilisesduringOCPmeasurementindicating

atypicalpassivationbehaviour

• Highmodulusof impedance (Z)at low frequencies, indicatinghighpolarisation

resistance

• Phase angle close to 90° for medium to low frequencies, indicating a highly

capacitivebehaviour

• Awidecapacitancearc,indicatingpassivefilmformation

• Polarisationcurvesshowpartialstabilisationofcurrentdensityandoverall low

currentdensities(intheorderof10-6A/cm2),indicatingpassivationbehaviour.

Further tests could be conducted using an increased immersion time (>28 days) in

Hanks’solutionat37°Ctounderstandthelong-termeffects.Furtherresearchcouldalso

investigatetheeffectsofporosityonthecorrosionstabilityofTi-35.4Zr-28Nb.

36

7. References

ASSIS,S.L.D.,WOLYNEC,S.&COSTA,I.2006.Corrosioncharacterizationoftitanium

alloysbyelectrochemicaltechniques.ElectrochimicaActa,51,1815-1819.

BANSIDDHI,A.&DUNAND,D.C.2014.TitaniumandNiTifoamsforbonereplacement.

BINYAMIN,G.,SHAFI,B.M.&MERY,C.M.2006.Biomaterials:Aprimerforsurgeons.

SeminarsinPediatricSurgery,15,276-283.

BIRLA,R.2014.BiomaterialsforTissueEngineering.IntroductiontoTissueEngineering.

JohnWiley&Sons,Inc.

CHENG,F.T.,LO,K.H.&MAN,H.C.2007.Anelectrochemicalstudyofthecrevice

corrosionresistanceofNiTiinHanks’solution.JournalofAlloysandCompounds,

437,322-328.

CHENGHAO,L.,LI,AMP,APOS,NAN,J.,CHUANJUN,Y.&NAIBAO,H.2015.Crevice

CorrosionBehaviorofCPTi,Ti-6Al-4VAlloyandTi-NiShapeMemoryAlloyin

ArtificialBodyFluids.RareMetalMaterialsandEngineering,44,781-785.

CRAMER,S.D.,COVINO,B.S.&COMMITTEE,A.I.H.2003.Corrosion:Fundamentals,

TestingandProtection,ASMInternational.

CREMASCO,A.,OSÓRIO,W.R.,FREIRE,C.M.A.,GARCIA,A.&CARAM,R.2008.

ElectrochemicalcorrosionbehaviorofaTi–35Nballoyformedicalprostheses.

ElectrochimicaActa,53,4867-4874.

DAVIS,J.2003.Overviewofbiomaterialsandtheiruseinmedicaldevices.Handbookof

materialsformedicaldevices.Illustratededition,Ohio:ASMInternational,1-11.

FOJT,J.,JOSKA,L.&MÁLEK,J.2013.CorrosionbehaviourofporousTi–39Nballoyfor

biomedicalapplications.CorrosionScience,71,78-83.

37

JONES,D.A.1996.Principlesandpreventionofcorrosion/DennyA.Jones,UpperSaddle

River,NJ,UpperSaddleRiver,NJ:PrenticeHall.

LOPES,É.,SALVADOR,C.,ANDRADE,D.,CREMASCO,A.,CAMPO,K.&CARAM,R.2016.

Microstructure,MechanicalProperties,andElectrochemicalBehaviorofTi-Nb-Fe

AlloysAppliedasBiomaterials.MetallurgicalandMaterialsTransactionsA,47,

3213-3226.

MARTINS,D.Q.,OSÓRIO,W.R.,SOUZA,M.E.P.,CARAM,R.&GARCIA,A.2008.Effectsof

ZrcontentonmicrostructureandcorrosionresistanceofTi–30Nb–Zrcasting

alloysforbiomedicalapplications.ElectrochimicaActa,53,2809-2817.

NIEMEYER,T.C.,GRANDINI,C.R.,PINTO,L.M.C.,ANGELO,A.C.D.&SCHNEIDER,S.G.

2009.CorrosionbehaviorofTi–13Nb–13Zralloyusedasabiomaterial.Journalof

AlloysandCompounds,476,172-175.

NNAMCHI,P.S.,OBAYI,C.S.,TODD,I.&RAINFORTH,M.W.2016.Mechanicaland

electrochemicalcharacterisationofnewTi–Mo–Nb–Zralloysforbiomedical

applications.JournaloftheMechanicalBehaviorofBiomedicalMaterials,60,68-

77.

OZAN,S.,LIN,J.,LI,Y.,IPEK,R.&WEN,C.2015.DevelopmentofTi–Nb–Zralloyswith

highelasticadmissiblestrainfortemporaryorthopedicdevices.Acta

Biomaterialia,20,176-187.

TEMENOFF,J.S.&MIKOS,A.G.2008.Biomaterials:theintersectionofbiologyand

materialsscience/J.S.Temenoff,A.G.Mikos,UpperSaddleRiver,N.J.,Upper

SaddleRiver,N.J.:Pearson/PrenticeHall.

WATANABE,Y.,SATO,H.&MIURA-FUJIWARA,E.2015.FunctionallyGradedMetallic

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MetallicBiomaterials:ProcessingandApplications.Berlin,Heidelberg:Springer

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XU,Y.-F.,XIAO,Y.-F.,YI,D.-Q.,LIU,H.-Q.,WU,L.&WEN,J.2015.CorrosionbehaviorofTi–

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39

8. Appendices

8.1. AppendixA

HANKS' BALANCED SALTS [HBSS]Without Sodium Bicarbonate and Phenol RedProduct Number H1387

Product DescriptionAlthough there have been many modifications to the original formulas in efforts to produce fully defined media, salt solutions still play an important role in tissue culture. A salt solution's basic function, to maintain the pH and osmotic balance in the medium and to provide the cells with water and essential inorganic ions, is as valuable today as when it was first developed a century ago.

Components g/LCalcium Chloride (anhydrous) 0.1396Magnesium Sulfate(anhydrous) 0.09767Potassium Chloride 0.4Potassium Phosphate Monobasic 0.06(anhydrous)Sodium Chloride 8.0Sodium Phosphate Dibasic (anhydrous) 0.04788D-Glucose 1.0

Precautions and Disclaimer REAGENTFor R&D use only. Not for drug, household or other uses.

Preparation Instructions Powdered salts are hygroscopic and should be protected from moisture. The entire contents of each package should be used immediately after opening. Preparing a concentrated salt solution is not recommended as precipitates may form. Supplements can be added prior to filtration or introduced aseptically to sterile salt solution.1. Measure out 90% of final required volume of

water. Water temperature should be 15-20 °C.2. While gently stirring the water, add the powdered

medium. Stir until dissolved. Do NOT heat. 3. Rinse original package with a small amount of

water to remove all traces of powder. Add to solution in step 2.

4. To the solution in step 3, add 0.35 g sodium bicarbonate or 4.7 ml of sodium bicarbonate solution [7.5%w/v] for each liter of final volume of medium being prepared. Stir until dissolved.

5. While stirring, adjust the pH of the medium to 0.1-0.3 pH units below the desired pH since it may rise during filtration. The use of 1N HCl or 1N NaOH is recommended.

6. Add additional water to bring the solution to final volume.

7. Sterilize immediately by filtration using a membrane with a porosity of 0.22 microns.

8. Aseptically dispense medium into sterile container.

Storage and Stability Store the dry powdered salts at 2-8 °C under dry conditions and liquid medium at 2-8 °C in the dark. Deterioration of the powdered medium may be recognized by any or all of the following: [1] color change, [2] granulation/clumping, [3] insolubility. Deterioration of the liquid medium may be recognized by any or all of the following: [1] pH change, [2] precipitate or particulates, [3] cloudy appearance [4] color change. The nature of supplements added may affect storage conditions and shelf life of the medium. Product label bears expiration date.

ProcedureMaterials Required but Not ProvidedWater for tissue culture use [W3500]Sodium Bicarbonate [S5761] orSodium Bicarbonate Solution, 7.5% [S8761]1N Hydrochloric Acid [H9892]1N Sodium Hydroxide [S2770]Medium additives as required

References1. Hanks, J. (1976) Hanks' Balanced Salt Solution

and pH Control. Tissue Culture Association Manual. 3, 3.

Revised: April 2007

Sigma-Aldrich, Inc. warrants that its products conform to the information contained in this and other Sigma-Aldrich publications. Purchaser must determine the suitability of the product(s) for their particular use. Additional terms and conditions may apply. Please see reverse side of the invoice or packing slip.

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