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1、Efecrmchim~caAcruVol.24.pp.1273-1282.PerganwnPressLtd.1979PrintedinGreatBritain.THEINFLUENCEOFFLUORIDEIONSONTHEPASSIVEDISSOLUTIONOFTITANIUMJ.J.KELLYPhilipsResearchLaboratories,Eindhoven,TheNetherlands(Received25July1978;inreuisedjbrm3June1979)Abstract-Steadystate,potentials
2、tepandimpedancemeasurementswereusedtoinvestigatetheinfluenceoffluorideionsonthepassivedissolutionofTiin4.5MH,SO,solution.Theresultsindicatedthatmetaldissolutionoccursuioasurfacefilm,thepresenceofwhichwasconfirmedbyaSEMstudy.ElectrondiffractionandSIMSmeasurementshaveshownthi
3、sfilmtobepolycrystallineTiO,.Amechanisminvolvingsimultaneousformationanddissolutionofsurfaceoxideissuggestedtoexplaintheresults.Theioniccurrentthroughthefilmisfield-dependent.Thedissolutionrateoftheoxideisdeterminedmainlybythefluorideconcentrationofthesolution.INTRODUCTIONs
4、tepandimpedancemeasurements.SincetheresultsindicatedtheimportanceofthepassivatinglayerTitaniumshowstypicalpassivatingbehaviourinpresentonthemetal,thenatureofthislayerwasH,SOIsolution[11.Anactive/passivepeakisfoundininvestigatedwithvarioustechniques.Thethicknessoftheanodicpo
5、larizationcurve.Atsomewhathigherthestrippedfilmwasmeasuredusingscanningeleopotentialsthecurrentdropstoverylowvaluesandtronmicroscopy(SEM).Itsstructurewasstudiedbypassivecurrentdensitiesoflessthan1+4cm-’areelectrondiffractionandtransmissionelectronmicro-observed.Polarization
6、ofthemetaltohighervoltagesscopy(TEM).Theoxygen/titaniumratioofthinfilms,inH,S04solutiongivesrisetocompactTiOLwhichcouldnotbestrippedfromthesupportingfihns[2]:pseudo-amorphousoxideisformedatvol-metal,wasdeterminedbysecondaryionmassspec-tageslowerthanapprox50Vwhilepolycrystal
7、linetrometry(SIMS).Theseresultswereused,togetheranataseisobtainedathighervoltages.TheoxidefilmwiththeeIectrochemica1results,togaininsightintothicknessisdirectlyproportionaltotheformationthemechanismofpassivedissolution.voltage[2].WhenfluorideionsareaddedtotheH2S04elec-EXPER
8、IMENTALtrolyte,thegeneralformofthepolarizationcurveremainsunchangedbutthecurrentsb
