Influence of fluoride ions on the passive dissolution of titanium

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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