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外文翻译--使用NiSO46H2O过氧化氢为主要盐对镁合金进行化学镀镍 英文版.pdf

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外文翻译--使用NiSO46H2O过氧化氢为主要盐对镁合金进行化学镀镍 英文版.pdf

mainbinrevised261–3.electrolessplatingsolutionsandlittleapplications.Inaddition,thebasicnickelcarbonateornickelacetateofareharmfultotheSurfaceCoatingsTechnology2001.IntroductionTheuseofmagnesiumalloysinavarietyofapplications,particularlyinaerospace,automobiles,andmechanicalandelectroniccomponents,hasincreasedsteadilyinrecentyearsasmagnesiumalloysexhibitanattractivecombinationoflowdensity,highstrengthtoweightratio,excellentcastability,andgoodmechanicalanddampingcharacteristics.However,magnesiumisintrinsicallyhighlyreactiveanditsalloysusuallyhaverelativelypoorcorrosionresistance,whichisactuallyoneofthemainobstaclestotheapplicationofmagnesiumalloysinpracticalenvironmentsHence,theapplicationofasurfaceengineeringtechniqueisthemostappropriatemethodtofurtherenhancethecorrosionresistance.Amongthevarioussurfaceengineeringtechniquesthatareavailableforthispurpose,coatingbyelectrolessnickelisofspecialinterestespeciallyintheelectronicindustry,duetothepossessionofacombinationofproperties,suchasgoodcorrosionandwearresistance,deposituniformity,electricalandthermalconductivity,andsolderabilityetc.Asfarasmagnesiumalloysareconcerned,themainsaltsofelectrolessplatingsolutionsmostlyfocusattentionsonbasicnickelcarbonateornickelacetate4–9,whichresultinhighcost,lowefficiency,instabilityofAbstractInthispaper,theelectrolessnickelplatingonmagnesiumalloywasstudied,usingNiSO4d6H2Oasthemainsaltintheelectrolessplatingalkalinesolutions.TheeffectsofthebufferagentandplatingparametersonthepropertiesandstructuresoftheplatingcoatingsonmagnesiumalloywereinvestigatedbymeansofscanningelectronmicroscopySEM,energydispersiveXrayspectroscopyEDSandXraydiffractionXRD.Inaddition,theweightloss/gainofthespecimensimmersedinthetestsolutionandplatingbathwasmeasuredbyusingtheelectrobalance,toevaluatetheerosionofthealloyintheplatingsolutions.Theadhesionbetweentheelectrolessplatingcoatingsandthesubstrateswasalsoevaluated.ThecompositionsofthenonfluorideandenvironmentallyfriendlyplatingbathwereoptimizedthroughLatinorthogonalexperiment.ThebufferagentNa2CO3addedtotheplatingbathwasfoundtobeusefulinincreasingthegrowthrateoftheplatingcoating,adjustingtheadhesionbetweentheelectrolessplatingcoatingsandthesubstrates,andmaintainingthepHvaluewithintherangeof8.5–11.5,whichisrequiredforthesuccessfulelectrolessnickelplatingonmagnesiumalloywithNiSO4d6H2Oasthemainsalt.Trisodiumcitratedihydratewasfoundtobeanessentialcomponentoftheplatingbathtoplatemagnesiumalloy,withanoptimumconcentrationof30gLC01.Theobtainedplatingcoatingsarecrystallinewithpreferentialorientationof111,havingadvantagessuchaslowphosphoruscontent,highdensity,lowporosity,goodcorrosionresistanceandstrengthenedadhesion.D2004ElsevierB.V.Allrightsreserved.KeywordsMagnesiumalloyElectrolessplatingBufferCorrosionresistanceAdhesionTheelectrolessnickelplatingonmagnesiumastheJianzhongLia,,ZhongcaiShaoaSchoolofmaterialsandmetallurgy,NortheastebFacultyofEnvironmentandChemicalEngineering,ShenyangReceived23July2004acceptedAvailableonline02578972/seefrontmatterD2004ElsevierB.V.Allrightsreserved.doi10.1016/j.surfcoat.2004.12.009Correspondingauthor.Tel.862483687731fax862423981731.Emailaddressmengsuo66163.comJ.Li.alloyusingNiSO4d6H2Osalt,XinZhanga,YanwenTianarnUniversity,Shenyang110004,ChinaInstituteofTechnology,Shenyang110168,Chinaform19December2004January200520063010–3015www.elsevier.com/locate/surfcoattodevelopnewplatingsolutionsyetincludingfluoride,environment,therefore,itisurgentlyneededenvironmentallyfriendlyplatingbath.ItisdifficulttocarryoutelectrolessplatingonmagnesiumalloysduetothehighcorrosionrateofmagnesiumalloysintheplatingbathwithNiSO4d6H2OorNiCl2d6H2Oasthemainsalt.Itisreported10thatthecorrosionrateofmagnesiumanditsalloysinNaClsolutionssolelydependsonthepHofthebufferedchloridesolutions.TheobjectiveofthisstudywastofindabufferagentanddeterminehowthebufferagentaffectsthedissolutionofmagnesiumalloyinNiSO4d6H2Oalkalinesolutions,andthenonfluorideplatingsolutionsformagnesiumalloywithNiSO4d6H2Oasthemainsalt.Themicrostructure,compositionsandcorrosionbehaviorofthecoatingswereinvestigatedindetail.constanttemperatureof808C.Afreshbathwasusedforeachexperimenttoavoidanychangeinconcentrationofbathspecies.ThebathcompositionsandotherparametersusedintheseexperimentsaregiventhroughLatinorthogonalexperimentinTable3.Table1ChemicalcompositionoftheAZ91Dalloyinwt.AlMnNiCuZnCaSiKFeMg9.10.170.0010.0010.64b0.01b0.01b0.01b0.001BalJ.Lietal./SurfaceCoatingsTechnology20020063010–30153011Table2Optimizedprecleaningprocedure2.ExperimentalThesubstratematerialusedintheresearchwasAZ91Dingotcastalloy.ThechemicalcompositionofthealloyisgiveninTable1.Substrateswithasizeof50mmC240mmC220mmwereusedintheresearch.Thesubstratesweremechanicallypolishedwithemerypapersupto1000grittoensuresimilarsurfaceroughness.ThepolishedsubstrateswerethoroughlywashedwithdistilledwaterbeforepassingthroughtheprecleaningprocedureasshowninTable2.Thesubstrateswereairdriedafterthefluorideactivationthelaststepintheprecleaningprocedure.Inatypicalexperiment,theinitialweightofaairdriedsubstratewasmeasuredandthenquicklytransferredtotheplatingbath1000mLinaglasscontainerplacedinawaterbathwithaFinalweightsofthespecimensweredeterminedandthecoatingratesinmicrometerperhourwerecalculatedfromtheweightgain.Atthesametime,inordertostudytheeachbuffersinfluenceonthesubstratesandfindabufferappropriatefortheelectrolessplatingonmagnesiumalloy,testsolutionswithcompositionssimilartothoseoftheplatingbathexceptthatsodiumhypophosphitewasnotadded,werepreparedtosimulatethecorrosionratesofmagnesiumalloyinplatingbathandthebehaviorsofthebuffers.Duplicateexperimentswereconductedineachcase,andthecoatingratereportedistheaverageoftwoexperiments.ThegrowthratesoftheplatingcoatingweremeasuredusingtheelectrobalancemadeinAmerica,whichisthe0.1mgprecision.Intheresearch,thepHvalueofplatingbathwasmonitoredbyapHS25CmodelofprecisionpH/mVmeter.Morphologyofthecoatingswasanalyzedusingascanningelectronmicroscope.TheenergydispersiveXrayspectroscopyanalysiswasusedfordeterminingthecontentofphosphorusinthecoatings.CrystallinityofthecoatingswasinvestigatedbyRigakuD/maxrAXraydiffractometerwithCuKalpharadiation.Theadhesionstrengthoftheelectrolesslydepositednickelcoatingstothemagnesiumalloysubstrateswasdeterminedbyscratchtest.Duringthescratchtest,thespecimenwasmovedataconstantspeedofapproximately11.4mm/min.Scratchesweregeneratedonthespecimenusingadiamondindenterwithasphericaltipof300Amindiameter.Corrosionpotentialmeasurementin3.5wt.NaClsolutionwascarriedouttocomparativelyinvestigatethecorrosionbehaviorsofthebaresubstrateandthenickelplatedsubstrates.Theelectrochemicalcellusedforcorrosionpotentialmeasurementconsistedofabaresubstrateoranickelplatedsubstrateastheworkingelectrodeexposedarea1cm2,asaturatedcalomelelectrodeSCE,andaplatinumfoilcounterelectrode.Table3OptimizedbathcompositionandparametersBathspeciesandparametersQuantityNiSO4d6H2O25g/LNaH2PO2dH2O30g/LC6H5Na3O7d2H2O30g/LNa2CO330g/LNH3dH2OAdjustingpHpHvalue11Temperature80F28C3.Resultsanddiscussion3.1.ThebuffersbehaviorsinthetestNiSO4solutionsandthechoiceofanappropriatebufferFig.1showsthevariationofweightlossofmagnesiumalloyasafunctionoftheimmersiontimewithdifferentbuffersinthetestsolutions.Thecompositionsandthecontrolledtemperatureofthetestsolutionsweresimilartothoseoftheplatingbathexceptthatsodiumhypophosphitewasnotincluded.ThepHvaluesofthetestsolutionswereadjustedbyNH3dH2Otofixat11.TheweightlossincreaseslinearlywiththeimmersiontimeincreasingofmagnesiumalloysintheNa2CO3,Na2B4O7,andCH3COONatestsolutions.ItisrevealedinFig.1thatthecorrosionrateswereconstantthroughouttheexaminedimmersiontime.AsrecognizedfromtheslopeofeachsolidlineinFig.1,corrosionrateinthetestsolutioncontainingNa2CO3bufferisthelowestamongthethreetestedbuffers.Theindicatestheweightlossofthesubstratesisrelatedtothereactionbetweenthesubstratemetalandthehydrogenions.Butthecorrosionreactionbetweenthesubstratemetalandthehydrogenionsgoesgraduallyon,becausethelowconcentrationofhydrogenionsispresentedintheplatingalkalinesolutions.Andthen,theconcentrationofhydrogenionsisweaklydecreasedduringthetestprogress.Thisleadstotheconstantcorrosionratesintheshorttesttime,whichisshowninFigs.1and2.Atthesametime,knowingthatforMgOH2Kspat258C8.9C210C012atpH9,OHC010C05M,mostMg2diffusedintoplatingsolutiontoformupto10C02M.AtpH11,OHC010C03M,theMg2couldntexceed10C06M,thusmostMg2formedMgOH2andstayednearthesubstrate.MgOH2couldincreasetheadsorptionenergybarrierandreducethecorrosionrate.Therefore,higherpHresultedinlowercorrosionrate.AstotheNa2CO3bufferedsolutions,forMgCO3Kspat258C10C015,intestsolutions,Na2CO3N0.1M,thusthepossibleMg2b10C014M.ThismeansthatthedrivingforceforMgtoformMg2wasverylow.InsteadofdissolvingMg,theCO32C0ionwouldbondorbeadsorbedtothesubstrate2C0J.Lietal./SurfaceCoatingsTechnology3012obtainedslopesare0.015,0.022and0.056mgcmC02minC01forNa2CO3,Na2B4O7andCH3COONabuffers,respectively.Theseresultscanbeexplainedintermsofdissociationconstantsofthecorrespondingacids,whicharek24.7C210C011k14.4C210C07,k21C210C09k11C210C04,andk1.75C210C05forH2CO3,H2B4O7andCH3COOH,respectively.Theseconddissociationconstantofabinaryaciddecidesthebuffercapabilityofthebuffer.Obviously,theNa2CO3bufferhasthelowestcostandbestbuffercapabilityamongthetestedbuffers.Fig.2showstheweightlossofthesubstratesversusimmersiontimeinthetestsolutionswithpHvaluesat9,10and11,usingNa2CO3asthebuffer.CorrosionofthespecimensinnonbufferedtestsolutionswithpHvaluesat9,10and11wasalsoinvestigated.ThecorrespondingweightlosscurvesareshowninFig.2.Alltestsolutions051015202530350.20.00.20.40.60.81.01.21.41.61.8NaCH3COONa2B4O7Na2CO3Weightloss/mg.cm2Time/minFig.1.Thevariationofweightlossofmagnesiumalloyintestsolutionswithdifferentbuffers.usedfortheseexperimentshadcompositionssimilartothoseintheplatingbathexceptthatsodiumhypophosphitewasnotincluded.TheweightlosslinearlychangeswiththeincreaseoftheimmersiontimeinallcasesshowninFig.2.UnderthesamepHvalue,thecorrosionrateofthesubstratesinthebuffersolutionisobviouslylowerthanthatofthesubstratesinthenonbufferedsolution,asshownbytheslopesofthecurvesinFig.2.Thissuggeststhatthebuffersolutionhasaconsiderableeffectonthecorrosionrateofmagnesiumalloy.InboththeNa2CO3bufferedandnonbufferedtestsolutions,thecorrosionratesofmagnesiumalloydecreasewiththeincreaseofthepHvalue.This05101520253035012345solutionpH9pH10pH11pH9pH10pH11Weightloss/mg.cm2Time/mininnonbufferedsolutioninNa2CO3bufferedFig.2.ThevariationofweightlossofmagnesiumalloyintestsolutionswithdifferentpHvalues.20020063010–3015surfacetoformlocalMgCO3.Inthiscase,thesubstratesurfaceareaexposedtoH2OorHwasreducedalot,leadingtolowercorrosionrates.ThepKa2forNa2CO3is10.33,atpHlowerthan10.33someCO32C0ionsformedHCO3C0.ReactionMg2HCO3C0MgCO3H2potentiallyexisted.AtpHhigherthan10.33,HCO3C0isnegligible.ThereforeinFig.2,wecanseethatthecorrosionrateatpH11wasnotreducedasmuch,comparedtherateat10.H2B4O7andCH3COOHdonthavesuchadvantages.wasmonitoredwithapHS25CmodelofprecisionpH/mVmeter.Inthisresearch,thepreferredpHrangeoftheplatingbathforelectrolessplatingonmagnesiumalloyis8.5–11.5.Table4Coatingrate,surfaceappearanceandadhesionofthecoatingsobtainedfromtheplatingbathwithdifferentamountsofNa2CO3ConcentrationofNa2CO3gLC01CoatingrateAm/hSurfaceappearanceLCN0–Gravecorrosion–1012.32Pointcorrosion812016.41Darkgray763018.32Shining734018.91Shining615019.26Shining513040506010002000300040005000600070008000IntensityJ.Lietal./SurfaceCoatingsTechnology20020063010–301530133.2.TheeffectsofplatingparametersoncoatingsThecoatingrate,surfaceappearance,andadhesionofthecoatingsatdifferentconcentrationsofNa2CO3bufferarelistedinTable4.ThecriticalloadLCwasmeasuredunderprogressiveloadingconditions,whichcanbeusedtoaccuratelycharacterizetheadhesionstrengthofthedeposit/substratesystem13.TheadhesionbetweenthecoatingsandsubstratesdecreasesobviouslywiththeincreaseoftheconcentrationofNa2CO3.SurfaceappearanceoftheplatingcoatingsbecomesgraduallyshiningwiththeincreaseoftheNa2CO3concentration.Gravecorrosionofthesubstrateswasfoundinthenonbufferedplatingbath.ThegrowthrateofthecoatingsnoticeablyincreaseswiththeincreaseoftheNa2CO3concentration.Consideringthecombinationofgrowthrate,surfaceappearance,andadhesionofthecoatings,the17181920µm20304050607013141516Thecoatingthickness/Thetrisodiumcitratedihydratecontent/g.L1Fig.3.Relationshipbetweenthecoatingthicknessandthetrisodiumcitratedihydrateconcentration.optimumconcentrationoftheNa2CO3bufferwasdeterminedtobe30gLC01.Withthisconcentration,thepurposeofaddingNa2CO3inplatingbathiscommendablyachieved.Intheresearch,itwasfoundthatthepHvalueofplatingbathhadaconsiderableeffectonthegrowthrateandthesurfaceappearanceofthecoatings.ThehydrogenionsinplatingbathwerenotonlyastrictedbytheCO32C0ionsdissociatedfromthebufferNa2CO3,butlinkedwiththeOHC0ions.WhenthepHvalueoftheplatingbathwasbelow8.5,pointcorrosionordarkgraycoatingswereobtainedandthecoatinggrowthratewaslow.WhenthepHvalueoftheplatingbathwasabove11.5,theadhesionbetweencoatingsandsubstratesweredeteriorated,althoughthegrowthrateandthesurfaceappearanceofthecoatingsweresatisfying.Duringtheelectrolessplating,thepHvalueoftheplatingbath2θ/ºFig.4.XRDpatternsoftheelectrolessplatingcoating.Fig.5.Surfacemorphologyofaplatingcoating.

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