Breakthroughinmaterialsscience:Kielresearchteamcanbondmetalswithnearlyallsurfaces

NormallyAluminiumcannotbejoinedwithplastic.BecauseofthenewmethodfromKielitisnowpossible,evenpermanently.
Foto/Copyright:JuliaSiekmann/CAU

Howmetalscanbeuseddependsparticularlyonthecharacteristicsoftheirsurfaces.AresearchteamatKielUniversityhasdiscoveredhowtheycanchangethesurfacepropertieswithoutaffectingthemechanicalstabilityofthemetalsorchangingthemetalcharacteristicsthemselves.Thisfundamentallynewmethodisbasedonusinganelectro-chemicaletchingprocess,inwhichtheuppermostlayerofametalisroughenedonamicrometerscaleinatightly-controlledmanner.Throughthisnanoscale-sculpturingprocess,metalssuchasaluminium,titanium,orzinccanpermanentlybejoinedwithnearlyallothermaterials,becomewater-repellent,orimprovetheirbiocompatibility.Thepotentialspectrumofapplicationsofthesesuperconnectionsisextremelybroad,rangingfrommetalworkinindustryrightthroughtosaferimplantsinmedicaltechnology.TheirresultshavenowbeenpublishedintheprestigiousjournalNanoscaleHorizonsoftheRoyalSocietyofChemistry.

Wehavenowappliedatechnologytometalsthatwaspreviouslyonlyknownfromsemiconductors.Tousethisprocessinsuchawayiscompletelynew,saidDr.JrgenCarstensen,co-authorofthepublication.Intheprocess,thesurfaceofametalisconvertedintoasemiconductor,whichcanbechemicallyetchedandtherebyspecificallymodifiedasdesired.Assuch,wehavedevelopedaprocesswhichunlikeotheretchingprocessesdoesnotdamagethemetals,anddoesnotaffecttheirstability,emphasisedProfessorRainerAdelung,headoftheFunctionalNanomaterialsteamattheInstituteforMaterialsScience.Adelungstressedtheimportanceofthediscovery:Inthisway,wecanpermanentlyconnectmetalswhichcouldpreviouslynotbedirectlyjoined,suchascopperandaluminium.

Howdoesthenanoscale-sculpturingprocessworkexactly?

Thesurfacesofmetalsconsistofmanydifferentcrystalsandgrains,someofwhicharelesschemicallystablethanothers.Theseunstableparticlescanbespecificallyremovedfromthesurfaceofametalbyatargetedetching.Thetopsurfacelayerisroughenedbytheetchingprocess,creatingathree-dimensionalsurfacestructure.Thischangesthepropertiesofthesurface,butnotofthemetalasawhole.Thisisbecausetheetchingisonly10to20micrometersdeepalayerasthinasaquarterofthediameterofhumanhair.Theresearchteamhasthereforenamedtheprocessnanoscale-sculpturing.

Thechangeduetoetchingisvisibletothenakedeye:thetreatedsurfacebecomesmatt.If,forexample,wetreatametalwithsandpaper,wealsoachieveanoticeablechangeinappearance,butthisisonlytwo-dimensional,anddoesnotchangethecharacteristicsofthesurface,explainedDr.Mark-DanielGerngrooftheresearchteamonmaterialssciencesfromKiel.

Throughtheetchingprocess,a3D-structurewithtinyhooksiscreated.Ifabondingpolymeristhenappliedbetweentwotreatedmetals,thesurfacesinter-lockwitheachotherinalldirectionslikeathree-dimensionalpuzzle.These3-Dpuzzleconnectionsarepracticallyunbreakable.Inourexperiments,itwasusuallythemetalorpolymerthatbroke,butnottheconnectionitself,saidMelikeBaytekin-Gerngro,leadauthorofthepublication.

Surfaceswithmultifunctionalproperties

Evenathinlayeroffatsuchasthatleftbyafingerprintonasurfacedoesnotaffecttheconnection.Inourtests,weevensmearedgearboxoilonmetalsurfaces.Theconnectionstillheld,explainedBaytekin-Gerngro.Laboriouscleaningofsurfaces,suchasthepre-treatmentofships'hullsbeforetheycanbepainted,couldthusberenderedunnecessary.

Inaddition,theresearchteamexposedthepuzzleconnectionstoextremeheatandmoisture,tosimulateweatherconditions.Thisalsodidnotaffecttheirstability.Carstensenemphasised:Ourconnectionsareextremelyrobustandweather-resistant.Abeneficialside-effectoftheprocessisthattheetchingmakesthesurfacesofmetalwater-repellent.Theresultinghookstructurefunctionslikeaclosely-interlocked3Dlabyrinth,withoutholeswhichcanbepenetratedbywater.Themetalsthereforepossessakindofbuilt-incorrosionprotection.Weactuallydon'tknowthiskindofbehaviourfrommetalslikealuminium.Alotuseffectwithpuremetalsi.e.withoutapplyingawater-repellentcoatingthatisnew,saidAdelung.

Potentiallylimitlessapplications

Therangeofpotentialapplicationsisextremelybroad,frommetalworkingindustriessuchasship-buildingoraviation,toprintingtechnologyandfireprotection,rightthroughtomedicalapplications,saidGerngro.Becausethenanoscale-sculpturingprocessnotonlycreatesa3Dsurfacestructure,whichcanbepurelyphysicallybondedwithoutchemicalsthetargetedetchingcanalsoremoveharmfulparticlesfromthesurface,whichisofparticularlygreatinterestinmedicaltechnology.

Titaniumisoftenusedformedicalimplants.Tomechanicallyfixthetitaniuminplace,smallquantitiesofaluminiumareadded.However,thealuminiumcantriggerundesirableside-effectsinthebody.Withourprocess,wecanremovealuminiumparticlesfromthesurfacelayer,andtherebyobtainasignificantlypurersurface,whichismuchmoretolerableforthehumanbody.Becauseweonlyetchtheuppermostlayeronamicrometerscale,thestabilityofthewholeimplantremainsunaffected,explainedCarstensen.

Theresearchershavesofarappliedforfourpatentsfortheprocess.Businesseshavealreadyshownsubstantialinterestinthepotentialapplications.Andourspecialistcolleaguesinmaterialsscienceshavealsoreactedenthusiasticallytoourdiscoveries,saidadelightedAdelung.

Originalpublication:

M.Baytekin-Gerngross,M.D.Gerngross,J.CarstensenandR.Adelung:Makingmetalsurfacesstrong,resistant,andmultifunctionalbynanoscale-sculpturing.NanoscaleHorizon.DOI:10.1039/C6NH00140H

http://pubs.rsc.org/en/content/articlelanding/2016/nh/c6nh00140h#!divAbstract

Contact:

Prof.Dr.RainerAdelung

FunctionalNanomaterials

InstituteforMaterialsScience

KielUniversity

Tel.:+49(0)431/8806116

E-mail:ra@tf.uni-kiel.de

Dr.JrgenCarstensen

FunctionalNanomaterials

InstituteforMaterialsScience

KielUniversity

Tel.+49(0)431/880-6181

E-mail:jc@tf.uni-kiel.de

Details,whichareonlyamillionthofamillimetreinsize:Thisiswhattheresearchfocus"KielNano,SurfaceandInterfaceScienceKiNSIS"atKielUniversityhasbeenworkingon.Inthenano-cosmos,differentlawsprevailthaninthemacroscopicworld-thoseofquantumphysics.Throughintensive,interdisciplinarycooperationbetweenmaterialsscience,chemistry,physics,biology,electricalengineering,computerscience,foodtechnologyandvariousbranchesofmedicine,theresearchfocusaimstounderstandthesystemsinthisdimensionandtoimplementthefindingsinanapplication-orientedmanner.Molecularmachines,innovativesensors,bionicmaterials,quantumcomputers,advancedtherapiesandmuchmorecouldbetheresult.Moreinformationatwww.kinsis.uni-kiel.de