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AdvancedMetalsandAlloysAdvancedMagneticCoolingHigh-PressureIntermetallicHydridesLightweightMetalMatrixNanocompositesSelf-PropagatingReactionsByMechanicalAlloyingTMVol.
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2007Sigma-AldrichCo.
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4IntroductionAboutOurCoverMetalsandalloyscouldbeconsideredthebackboneofhumancivilization.
Thecastingofsuchmetalsascopperandtintomakebronze,thefirstfunctionalmetalalloy,pavedourwaytothemoderntechnologicalsociety.
Mostofthemetalscrystallizeintocloselypackedcubic(forexample,Al,Cu,Fe)orhexagonalcrystallattices(shownonthecover,forexample,Gd,Ti,Zr,rareearthmetals),whicharelargelyresponsiblefortheirremarkableproperties.
Thecovershowsmetalcasting,thebeginningofalongtechnologicalprocessthatconcludesinsuchmarvelsasairplanes.
IntroductionNoothermaterialshavecontributedmoretothedevelopmentofmankindoverthemillenniathanmetalsandalloys.
Throughoutcenturies,studiesofmetalsbelongedtooneoftheoldestbranchesofAppliedMaterialsScience–Metallurgy.
Thischangedinthelate19thandearly20thcenturies,whenapplicationsofmetallicmaterialsspreadintootherareasofscienceandtechnologyincludingelectronics,energy,aeronauticsandspacetravel,tonameafew.
Currently,it'simpossibletoimagineaworldinwhichwecouldsuccessfullyfunctionwithoutmetalsandalloys.
Traditionally,metalsareportrayedasshinysolids,mostofwhicharegoodconductorsofheatandelectricity.
Theyareductileandmostwillmeltathightemperatures.
Metalandalloyshapescaneasilybechangedbymechanicalprocessing,atechniquethatcanbeusedforthepreparation,modificationandchemicalconversionofmetalalloysandcomposites.
Presently,thereare87knownmetals,61ofwhichareavailablethroughSigma-Aldrichinvariousformsandmodifications;thesearehighlightedinredintheperiodictablechartbelow.
Seepages14–15foranexpandedchart.
HHeLiBeBCNOFNeNaMgAlSiPSClArKCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKrRbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXeCsBaLaHfTaWReOsIrPtAuHgTlPbBiPoAtRnFrRaAc104105106CePrNdPmSmEuGdTbDyHoErTmYbLuThPaUNpPuAmCmBkCfEsFmMdNoLrPuremetalsatSigma-Aldrichvisitsigma-aldrich.
com/metalsfordetailsThisissueofMaterialMattersfocusesonmetalsandalloysforadvancedapplicationsincludingmagneticrefrigeration;high-pressure,high-capacity,hydrogenabsorbingsystems;nanocomposites;andmechanicallyinducedconversionofmetallicsolids.
LeadingexpertsfromtheAmesLaboratoryoftheU.
S.
DepartmentofEnergy,MoscowStateUniversity,UniversityofWisconsin–Milwaukee,andUniversityofMarylanddiscussrecentexperimentalresultsandshareideasandtechniquesassociatedwithmetals,alloys,andtheirapplications.
Inside,you'llalsofindnewlyintroducedproducts,whichincludebutarenotlimitedtomagneticrefrigerationalloys,hydrideformingintermetallics,magneticmaterialsandhigh-purityrareearthmetalsandfoils.
Inthe"YourMaterialsMatter"feature,wearepleasedtointroduceAlignedMulti-WalledCarbonNanotubes(MWCNTs)—anewSigma-AldrichproductsuggestedbyDr.
KarlGross,CEOofHy-EnergyLLC.
OurgoalatSigma-AldrichMaterialsScienceistoprovideinnovativematerialsthataccelerateyourresearch.
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"YourMaterialsMatter.
"AlignedMulti-WalledCarbonNanotubes(MWCNTs)JoePorwoll,PresidentAldrichChemicalCo.
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Dr.
KarlGross,ofHy-EnergyLLC,kindlysuggestedthathigh-qualitycarbonnanotubearraysareneededforresearchanddevelopmentofhigh-sensitivitygassensors.
Wearepleasedtoofferhighlyalignedarraysofmulti-wallcarbonnanotubes(MWCNTs)asnewproductsinourcatalog.
Thesearrays,availableonsilicone(AldrichProductNo.
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687812)substrates,canprovideauniqueplatformforawiderangeofmaterialsresearchanddevelopment,includinggasadsorptionsensorandsensorsubstrates,1catalysts,electronemissionsources,2andbatteryandcapacitordevelopment.
3Carbonnanotubearray,multi-walled,verticallyaligned,onsiliconwafersubstrate687804-1EACarbonnanotubearray,multi-walled,verticallyaligned,oncoppersubstrate687812-1EAReferences:(1)Collins,P.
G.
,Bradley,K.
Ishigami,M.
Zettl,A.
,Science,2000,287,1801.
(2)Bonard,J.
M.
,Stockli,T.
,Maier,F.
,DeHerr,W.
A.
,Chatelain,A.
,Ugarte,D.
,Salvetat,J.
P.
,Forro,L.
,PhysicalReviewLetters,1998,81,1441.
(3)Frackowiak,E.
,Gautier,S.
,Gaucher,H.
,Bonnamy,S.
,Beguin,F.
,Carbon,1999,37,61IntroductionFeatures:99.
9%asMWCNTCNTdiametersare100nm±10nmCNTlengthsare30m±3mArraydensity~2x109MWCNT/cm2Arraydimensions1sq.
cmGrownbyplasma-enhancedCVD(PECVD)GrownwiththenickelcatalysttipintactPackagedinacleanroom;stored,andshippedinsemiconductorgradepackaging.
DoyouhaveacompoundthatyouwishSigma-AldrichcouldlisttohelpmaterialsresearchIfitisneededtoaccelerateyourresearch,itmatters—pleasesendyoursuggestiontomatsci@sial.
comandwewillbehappytogiveitcarefulconsideration.
CNTarray(blacksquare)inthesemiconductorgradepackage.
InsetshowsSEMimageoftheverticallyalignedMWCNTs.
AdvancedMetalsandAlloysFeaturedinThisIssueMaterialsCategoryContentPageMaterialsforMagneticCoolingMaterialsexhibitinggiantmagnetocaloriceffect7UltraHigh-PurityMetalsforPreparationofMagneticRefrigerationMaterialsSigma-Aldrichproductssuitableforthepreparationofnovelsystemswithgiantmagnetocaloriceffect7MagneticAlloysandIntermetallicsMetalalloysusedaspermanentmagnets8HydrogenAbsorbingAlloysMetallicmaterialscapableofabsorbinglargequantitiesofhydrogenatvarioustemperaturesandpressures13High-PurityIron,Nickel,andZirconiumMaterialsusedforthepreparationofintermetallichydrogenabsorbingsystems13PureMetalsfromSigma-AldrichPeriodicTablechartdisplayingmetalproductoffering14–15CarbonNanotubesSingle-andMulti-walledcarbonnanotubes19High-PurityAluminumVariousformsofaluminummetalavailableinhighpurity20BinaryMetalAlloysMetalalloysconsistingoftwodifferentmetals24BinaryMetalCompoundsMetalcarbides,silicides,andphosphides25High-PurityMetalsManufacturedbyAAPLHighpuritymagnesium,calcium,strontium,andbariummanufacturedatAAPL—aSigma-AldrichMaterialsChemistryCenterofExcellence26High-PurityRareEarthMetalFoilsMetalfoilsforcoatingsandPVDprocesses27TOORDER:ContactyourlocalSigma-Aldrichoffice(seebackcover),orvisitsigma-aldrich.
com/matsci.
AdvancedMaterialsforMagneticCoolingProf.
V.
K.
PecharskyandProf.
K.
A.
Gschneidner,Jr.
AmesLaboratory,IowaStateUniversityIntroductionToday,near-room-temperaturerefrigerationisalmostentirelybasedonavapor-compressionrefrigerationcycle.
Overtheyears,allpartsofacommercialrefrigerator,suchasthecompressor,heatexchangers,refrigerant,andpackaging,havebeenimprovedconsiderablyduetotheextensiveresearchanddevelopmenteffortscarriedoutbyacademiaandindustry.
However,theachievedandanticipatedimprovementsinconventionalrefrigerationtechnologyareincrementalsincethistechnologyisalreadynearitsfundamentallimitofenergyefficiency.
Furthermore,chlorofluorocarbons,hydrofluorocarbons,andotherchemicalsusedasrefrigerantseventuallyescapeintotheenvironmentpromotingozonelayerdepletionandglobalwarming.
Ingeneral,liquidchemical-basedrefrigerationisamajorfactorcontributingtodeleterious,cumulativechangesintheglobalclimate.
Refrigerationisbasedontheuseofaworkingbodythatchangesitstemperatureinresponsetocertainthermodynamictriggerstocoolanobject.
Thesevariationsmustbeachievedquickly,repeatedly,reversibly,andwithminimumenergylosses.
Sinceamagneticfieldeffectivelycouplestomagneticmomentsofindividualatomsinasolid,magneticfieldisoneofthecommonthermodynamicvariablesthatcanalterthetemperatureofamagneticsolid.
Heatingandcoolingofsoftferromagneticmaterialsinresponsetoincreasinganddecreasingmagneticfields,respectively,hasbeenknownsincethelatterpartofthe19thcenturywhenWarburgreportedsmallbutmeasurablereversibletemperaturechangesinpureironinresponsetomagneticfieldchanges.
1Today,thisphenomenonisrecognizedastheMagnetocaloricEffect(MCE)andmaterialsexhibitinglarge,reversibletemperaturechangesinresponsetochangingmagneticfieldsareusuallyreferredtoasmagnetocaloricmaterials.
Theefficiencygainwhenreplacingamechanicalprocess(compressionandexpansionofavapor)withanelectronicprocess(magnetizationanddemagnetizationofasolid)toobtainareversiblechangeoftemperatureissubstantial,thusmakingmagneticrefrigerationoneofthefewviable,energy-efficientsolid-statecoolingtechnologies.
MagnetocaloricEffectThemagnetocaloriceffectoccurswhenamagneticsublatticeiscoupledwithanexternalmagneticfield,affectingthemagneticpartofthetotalentropyofasolid.
Similartotheisothermalcompressionofagas,duringwhichthepositionaldisorderandthecorrespondingcomponentofthetotalentropyofthegaseoussystemaresuppressed,exposingaparamagnetnearabsolutezerotemperatureoraferromagnetnearitsCurietemperature,TC,toachangeinmagneticfield(B)fromzerotoanynon-zerovalue,oringeneral,fromanyinitialvalueBitoafinalhighervalueBf(DB=Bf–Bi>0)greatlyreducesdisorderofaspinsystem.
Thus,themagneticpart(SM)ofthetotalentropy(S)issubstantiallylowered.
Inareversibleprocess,whichresemblestheexpansionofthegasatconstanttemperature,isothermaldemagnetization(DB1atm);p=pressure(atm);T=temperature(K);V=systemvolume(cm3);R=universalgasconstant(82.
06cm3atm/moleK).
ThermodynamicparametersofthedesorptionreactionweredeterminedusingtheVan'tHoffequationandfugacityvalues,correspondingtoexperimentalpressurevalues:RTln(fp)=DH–TDS(2)where,fp=fugacity;H=enthalpychange;S=entropychange.
Finally,thefugacityvalueswerecalculatedusingEquation3andrealmolarvolumesobtainedfromEquation1:RTln(fp)=RTlnp–*(Vid–Vreal)dpp0(3),where,Vreal=realabsorbed/desorbedhydrogenmolarvolumeVid=idealabsorbed/desorbedhydrogenmolarvolumeItisalsoworthnotingthatoursystemallowsforconductingexperimentalstudiesofhydrogenabsorptionbyintermetallicsaswellasinvestigatingthebehaviorofvariousmaterialsathighhydrogenpressures.
YNi5–H2SystemInteractionofhydrogenwithAB5-typeintermetallicsathighpressureshasbeenreported.
6ForLaCo5,La0.
5Ce0.
5Co5,andLaNi5itwasshownthatathighhydrogenpressurestheyformintermetallichydridesoftheapproximatecompositionRT5H9(R=rareearthmetal;T=transitionmetal),whichagreeswiththeoreticalpredictions.
6Forourstudies,wechoseaYNi5alloybecauseofitsuniqueproperties.
YNi5doesnoteasilyabsorbhydrogen7–9atlowpressures.
However,asshownbyTakeshita10,applying1550atmtothematerialsallowsthesynthesisofYNi5H3.
5hydride.
Pressure-composition-temperature(PCT)isothermsobtainedledtoaconclusionthatthepressureappliedwasnotsufficienttoobtainafullyhydrogenatedsample.
Theresultsofotherauthors11differedconsiderablyfromthatofTakeshita.
OurstudiesshowedthatanactiveinteractionofYNi5andhydrogenstartsatpressuresover500atmandtheequilibriumhydrogenabsorptionpressureat293Kis674atmwhilecorrespondingequilibriumdesorptionpressureis170atm.
Hydridecompositionat1887atmcorrespondstoYNi5H5(1.
3mass.
%H2).
Absorption-desorptionPCT-isothermsatthetemperaturesrangingfrom–20to80°CareshowninFigure2.
Ourdatadiffersfromthosereportedinreference10,wheretherearetwodesorptionplateausat300and1000atm(293K)andthehydridecompositioncorrespondstoYNi5H3.
5.
Ourdataalsodiffersfromtheresultsreportedinreference11,wherethedissociationpressureisonly12atmandthehydridecompositionisYNi5H4.
4.
101001000100000123456H/YNi5353Kdes313Kdes293Kdes273Kdes253KdesP(H2)(atm)353Kabs293KabsFigure2.
Absorption-desorptionisothermsforYNi5–H2system.
Theinconsistencyinthenumbersreportedbydifferentgroupsmaybeexplainedbyverylowhydrogenabsorptionanddesorptionratesobserved.
Inourcase,thetimetoreachequilibriumintheplateauregionwasbetween2and4hours;seeFigure3whichshowsthereadingsofthepressuretransducerinseveralconsecutivehydrogendesorptionsteps.
YNi5-H2020406080100120t,h22Cdes15129630PH2,atm18Figure3.
Dependenceofpressurechange(P)ontime(t)toequilibrium.
Anumberofauthors7–9comparedhydrogenabsorptionpropertiesofYNi5tootherAB5alloysandconcludedthatpeculiaritiesinitsinteractionwithhydrogencanbeexplainedneitherbythelow-temperatureheatcapacitynortheelectronicstructure,norbythesurfaceoxidationofYNi5.
Inouropinion,themostpossibleexplanationwasgiveninreference8,whereitwasshownthatamongallbinaryAB5-typeintermetalliccompoundsYNi5hasthelowestcompressibility.
Thus,thelowvolumeoftheYNi5unitcellcouldinfluencehydrogenabsorptionproperties.
UsingalnP(H2)vs.
1/Tplot,wefoundthevaluesofhydrogendesorptionenthalpyandentropyofaYNi5hydridetobe21.
86kJ/molH2and115.
8J/K·molH2respectively.
IntermetallicHydridesForquestions,productdata,ornewproductsuggestions,pleasecontacttheMaterialsScienceteamatmatsci@sial.
com.
11AB2–H2SystemsAsbasismaterialsforthesestudies,weselectedLavesphasesZrFe2andTiFe2withhighhydrogendesorptionpressures,whichdonotabsorbhydrogenatrelativelylowpressures.
Ithasbeenreportedthatusingtheultra-highpressureof10,000atm,itispossibletosynthesiseaZrFe2hydride.
12–14Ourstudiesshowedthatnoticeablehydrogenabsorptioninthefirstabsorption-desorptioncyclestartsatapproximately800atmwithoutanypreliminaryactivation.
Duringsubsequentcycling,absorptionstartsatlowerpressures.
Absorptionequilibriumpressureinthefirstrunhasbeenfoundtobe1120atmwhileinsecondandfurthercyclesitdecreasedto690atm(Figure4).
Thehydrogencontentinthehydrogenatedmaterialatroomtemperatureand1800atmis3.
5H/formulaunit.
Atthelowtemperatureof218Kandhydrogenpressureof1900atm,thematerial'scompositionisZrFe2H3.
7.
TheisothermsshowninFigure4revealanobvioushysteresis—atroomtemperaturetheabsorptionequilibriumpressureisabout690atm,whilethedesorptiononeisonly325atm.
1010010001000000.
511.
522.
533.
54H/ZrFe2PH2(atm)313Kdes293K1abs293K1des293K2abs293K2des273Kdes253KdesFigure4.
Absorption-desorptionisothermsforZrFe2–H2system.
Partialsubstitutionofzirconiumforscandiumreducesthehydrogendesorptionpressureofthehydride.
SimilartoZrFe2,Zr0.
5Sc0.
5Fe2andZr0.
8Sc0.
2Fe2crystallizeasC15Lavesphases.
HydrogenabsorptioninZr0.
5Sc0.
5Fe2startsat~100atmwithoutanypreliminaryactivation.
Thereisnosignificanthysteresisinthissystem,i.
e.
theabsorptionanddesorptionpressuresareveryclose.
Hydrogencontentinthematerialat295Kand1560atmreaches3.
6H/formulaunit(Figure5).
11010010001000000.
511.
522.
533.
54313Kdes293Kdes273Kdes253KdesH/Zr0.
5Sc0.
5Fe2PH2(atm)Figure5.
Absorption-desorptionisothermsforZr0.
8Sc0.
2Fe2–H2system.
Theshapeofthehydrogenabsorption-desorptionisothermssuggeststheformationoftwohydridephasesintheZr0.
5Sc0.
5Fe2–H2system.
Atroomtemperature,thecompositionofthefirstphase(β1)isclosetoadihydrideandthatofthesecondone(β2)correspondstoatrihydride(Table1).
Hydrogendesorptionenthalpiesandentropieshavebeencalculatedforbothphases.
Remarkably,thebehaviorofZr0.
5Sc0.
5Fe2resemblesthatoftheScFe1.
8–H2system,wherethestablemonohydrideandthemuchlessstableScFe1.
8H2.
4arealsoformed.
15,16Inourcase,however,substitutionofhalfofthescandiumforzirconiumleadstoasignificantincreaseofstabilityofthelowerhydridewithanenthalpyofformationlowerthanthatofthetrihydride(Table1).
Table1.
ThermodynamicparametersforZr1–xScxFe2–H2systems.
IMC*H/IMCPdes,atmT,Kfdes**,atmH,kJ/moleH2/S,J/K·moleH2ZrFe22.
086170325.
1468.
8253.
1273295.
731390.
5188396.
761921.
3(3)/121(1)Zr0.
5Sc0.
5Fe21.
32.
512.
518.
738.
860.
52246.
4105177254.
1272.
6295.
1310.
9254.
1272.
6295.
1310.
912.
518.
739.
762.
52247.
4111.
5195.
519(2)/95(6)25.
4(4)/125(1)Zr0.
8Sc0.
2Fe21.
849190290253.
4292.
1313.
15021234321(1)/117(5)*Intermetalliccompound**FugacityIntermetallicHydridesTOORDER:ContactyourlocalSigma-Aldrichoffice(seebackcover),orvisitsigma-aldrich.
com/matsci.
12ComparinghydridesScFe1.
8H1.
8,Zr0.
5Sc0.
5Fe2H2.
5(secondplateau)andZr0.
8Sc0.
2Fe2H1.
8showsthattheincreaseinzirconiumcontentinthealloysleadstothedecreaseinitshydrogendesorptionenthalpy.
However,entropychangegoesthroughamaximumatZr0.
5Sc0.
5Fe2H2.
5(Table1).
ForZr0.
8Sc0.
2Fe2–H2,hydrogenabsorptionalsostartsat100atmwithoutactivation.
Hydrogencompositionatroomtemperature(293K)and1650atmisZr0.
8Sc0.
2Fe2H3.
7(Figure6).
Furthercoolingto219Kwithsimultaneousincreaseinhydrogenpressureto1730atmresultsinmaximumhydridecompositioncorrespondingtoZr0.
8Sc0.
2Fe2H3.
8.
1010010001000000.
511.
522.
533.
54313Kdes293Kabs293Kdes253KdesH/Zr0.
8Sc0.
2Fe2P(H2)(atm)Figure6.
DesorptionisothermsforZr0.
5Sc0.
5Fe2–H2system.
PartialsubstitutionoftitaniumforscandiumallowedustosynthesizethefirstpseudobinaryintermetallichydrideinTi0.
5Sc0.
5Fe2–H2system.
Remarkably,whileTi0.
8Sc0.
2Fe2doesnotabsorbhydrogenevenatpressuresupto2500atm,at223K,thereactionbetweenTi0.
5Sc0.
5Fe2andhydrogenstartsatroomtemperaturealreadyat100atmwithoutanypreliminaryactivation(Figure7).
ThehydrogencontentofthehydridecorrespondstoTi0.
5Sc0.
5Fe2H3.
1(2.
0mass%).
1010010001000000.
511.
522.
533.
54333Kdes295Kdes273KdesP(H2)(atm)H/Ti0.
5Sc0.
5Fe2Figure7.
DesorptionisothermsforTi0.
5Sc0.
5Fe2–H2systemTheroomtemperatureequilibriumabsorptionanddesorptionpressuresforthismaterialare195and175atmaccordingly.
Coolingthehydrogenatedmaterialtobelow223Kshowedthatnonewhydridephasetransitionoccurs.
Hydrogencontentat217Kat2700atmis3.
4H/f.
u.
(2.
16mass.
%)andcalculatedthermodynamicparameterswereareΔH(kJ/moleH2)=17.
7(2)andΔS(J/K·moleH2)=103.
8(7)ConclusionsInteractionofhydrogenwithmulti-componentintermetalliccompoundsofAB5-andAB2-typewerestudiedinthecurrentwork.
Severalnewintermetallichydrideswithpotentialapplicationsinhigh-capacityhydrogenstoragehavebeenidentifiedandfullycharacterizedusingagas-volumetricanalyticaltechnique.
AcknowledgementsThisworkwassupportedinpartbyGeneralMotorsCorp.
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IntermetallicHydridesForquestions,productdata,ornewproductsuggestions,pleasecontacttheMaterialsScienceteamatmatsci@sial.
com.
13HydrogenAbsorbingAlloysNameChem.
CompositionHydrogenStorageCapacitywt.
%EquilibriumPressurePlateauProd.
No.
Zirconium-IronAlloyZeFe21.
65–1.
75(25°C,1800bar)~690bar(23°C)absorption~325bar(23°C)desorption693812-1GZirconium-IronAlloyZr0.
8Sc0.
2Fe21.
65–1.
75(22°C,1560bar)~190bar(20°C)693804-1GYttriumNickelAlloyYNi51.
25–1.
3(25°C,1890bar)~674bar(20°C)693928-5GLanthanumNickelAlloyLaNi51.
5–1.
6(25°C)~2bar(25°C)685933-10GLanthanumNickelAlloyLaNi4.
5Co0.
51.
4–1.
5(25°C)50636797-250MG636797-1GSingle-wall,short1–2NA.
5–2>90652512-250MGDouble-wall51.
3–2.
00.
550–80637351-250MG637351-1GMulti-wall,ArkemaCVD10–152–6.
1–10>90677248-5GMulti-wall110–170–5–9>90659258-2G659258-10GMulti-wall,powderedcylindercores–2–151–1010–40406074-100MG406074-500MG406074-1G406074-5GMulti-wall,asproduced6–20–1–5>7.
5412988-100MG412988-500MG412988-2G412988-10GGraphite,nanofibers80–2000.
5–10.
5–20>95636398-2G636398-10G636398-50GFormoreinformationabouttheseandotherrelatedmaterials,pleasevisitsigma-aldrich.
com/nano.
LightweightMetalMatrixNanocompositesForquestions,productdata,ornewproductsuggestions,pleasecontacttheMaterialsScienceteamatmatsci@sial.
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21Self-PropagatingReactionsInducedbyMechanicalAlloyingProf.
LaszloTakacsUniversityofMaryland,BaltimoreCountyIntroductionMechanicalalloyingisa"bruteforce"methodofaffectingalloyingandchemicalreactions.
Themixtureofreactantpowdersandseveralballsareplacedinthemillingjarofahigh-energyballmill,forexample,ashakermilloraplanetarymill(Figure1).
Thecollisionsandfrictionbetweentheballs,andbetweentheballsandthewallofthecontainer,resultindeformation,fragmentation,mixing,andcold-welding.
Thereactivityincreasesduetodefectformationandincreasedinterfacearea,andeventuallyalloyingand/orchemicalreactionstakeplace.
Neitheradditionalheatnorsolventareneeded.
Theproductisapowderthatcanbeconsolidatedusingtheusualmethodsofpowdermetallurgy.
Mechanicalalloyingisaveryflexibletechniqueandhasbeenusedtoprepareabroadvarietyofmaterials,includingdispersion-strengthenedalloys,amorphousalloys,andnanocomposites.
1High-energyballmillingisalsocalledmechanochemicalprocessingwhenused,ofteninconjunctionwithothersteps,forinorganicsynthesis,theprocessingofminerals,andtheactivationofbuildingmaterials.
2(a)(b)Figure1.
Crosssectionviewsofthemillingvialofashakermill(a)andaplanetarymill(b).
Mechanically-inducedSelf-propagatingReactions(MSR)arepossibleinhighlyexothermicpowdermixtures.
3Initially,millingresultsinactivation,similartoanyothermechanicalalloyingprocess.
Butatacriticaltime,calledtheignitiontime,thereactionratebeginstoincrease.
Asaresult,thetemperaturerises,furtherincreasingthereactionrateandeventuallyleadingtoaself-sustainingprocess.
Mostofthereactantsareconsumedwithinseconds.
Atthisstage,thereactionissimilartothermallyignitedself-propagatinghigh-temperaturesynthesis(SHS).
4Theabrupttemperatureincreaseisdetectableontheoutersurfaceofthemillingcontaineranditspresencedistinguishessuchmechanicallyinducedself-propagatingreactions(MSR)fromgradualprocesses(Figure2).
MSRcanhappeninabroadvarietyofsystems,suchasinFe2O3–Al,Ni–Al,Ti–C,Zn–S,andMo–Simixtures.
3Theignitiontimeisanimportantattributeoftheprocess;itcanvaryfromafewsecondstoseveralhoursdependingonthereactionandthemillingconditions.
3230282624220500100015002000250030003500Time(s)Temperature(°C)Figure2.
Temperatureoftheoutsidesurfaceofthevialduringballmillingofa5Ni+2PmixtureinaSPEX8000MixerMill.
Ignitionisindicatedbytherapidtemperatureriseat1220sec.
Thegradualtemperatureincreasebeforeignitioniscausedbydissipatedmechanicalenergy.
TheinvestigationofMSRcontributedconsiderablytoourunderstandingofmechanochemicalprocessesingeneral.
Thevariationoftheignitiontimewithprocessconditionsandmaterialpropertiestellsusaboutthemechanismoftheactivationprocess,whiledetailedstudiesofpartiallyactivatedpowdersprovidesinformationaboutthenatureofthecriticalstate.
MSRhasalsobeenconsideredasapracticalmeansfortheproductionofusefulmaterials,particularlyrefractorycompounds.
3RequirementsForSelf-SustainingReactionsMSR(aswellasSHS)requiresufficientself-heatingtopropagatethereaction.
Ameasureofself-heatingistheadiabatictemperature,definedasthefinaltemperature,ifallthereactionheatisusedtoheattheproducts.
Aruleofthumbisthatself-sustainingreactionsarepossible,iftheadiabatictemperatureisatleast1800K.
Sincethemainissueisself-heatingatthebeginningofthereaction,thequantity–ΔH298/C298(whereH298andC298arereactionenthalpyandspecificheatat298K),writtensimplyasΔH/C,isoftenusedasasimplersubstituteforadiabatictemperature;ΔH/C>2000KistheconditionforMSR.
Thissimpleconditionappliessurprisinglywelltothemostfrequentlystudiedclassesofreactions,namelycombinationreactionsbetweenatransitionmetalandametalloidelement(e.
g.
Ti-B,Nb-C,Mo-Si,Ni-P)andthermite-typereactionsbetweenanoxideandamorereactivemetal(e.
g.
Fe3O4-Al,CuO-Fe,ZnO-Ti).
MuchlowervaluesofΔH/CaresufficientforMSRwithchalcogenidesandchlorides.
Table1containsdataforafewtypicalreactions.
MechanicalAlloyingTOORDER:ContactyourlocalSigma-Aldrichoffice(seebackcover),orvisitsigma-aldrich.
com/matsci.
22Table1.
Typicalreactionsshowingmechanicallyinducedself-propagationandthecorrespondingreactionheats(ΔH)andratioofΔHintheheatcapacityoftheproducts(C).
Reaction–ΔH/formula(kJ/mol)ΔH/C(K)3CuO+2Al3Cu+Al2O3119078104CuO+3Fe4Cu+Fe3O446118503Fe3O4+4Al9Fe+4Al2O3337662225Ni+2PNi5P24362867Sn+2SSnS21542189Ti+2BTiB23167111Hf+CHfC2266011Mo+2SiMoSi21322055Asmoreexothermicreactionsbecomeincreasinglyeasytoself-sustain,reactionswithhigheradiabatictemperaturesareexpectedtorequireshorteractivationtimesbeforeignition.
Sucharelationshipindeedexists,butonlyiftheothermaterialparametersandthemillingconditionsareverysimilar.
Sofar,thebestcorrelationwasobservedforthereductionofCuO(AldrichProd.
No.
203130,450804,450812),NiO(AldrichProd.
No.
203882,637130,481793),Fe3O4(AldrichProd.
No.
310069,518158,637106),Cu2O(AldrichProd.
No.
208825,566284),andZnO(AldrichProd.
No.
204951,255750,544906),withthesamemetal(Ti,ZrorHf).
3Theseareductile-brittlesystems5wheremillingresultsinafinedispersionoftheoxideparticlesinthemetalmatrix.
Thedevelopmentofthemicrostructuredependsprimarilyontheductilecomponentanditiskeptthesameforeachseries.
Thechangescausedbymechanicalmillingduringtheactivationperiod—decreaseofgrainsize,mixing,andformationoflatticedefects—dependmainlyonthemechanicalpropertiesofthereactants.
Althoughitisdifficulttoquantifythisrelationship,theincreasingwidthoftheX-raydiffractionlinesindicatesthatthecrystallitesizedecreasesandtheaccumulatedlatticestrainofthemetalcomponentincreasesasthepowderapproachesignition.
6,7Whilereducingthegrainsizeandtherebyincreasingtheinterfaceareaiscertainlyakeycomponentoftheactivationprocess,agglomerationisalsonecessarytoensureefficientmatterandheattransfer.
AninterestingcaseisthereductionofMoS2(AldrichProd.
No.
234842)withaluminumpowder(AldrichProd.
No.
202584,653608).
Thisreactionisgradual,althoughΔH/C=2093KiswellovertheacceptedthresholdforanMSRprocess.
However,MoS2preventsagglomeration,reducingtheareaoftheactiveinterface.
8Themechanicalintensityofthemillingactiondependsonthenumberandenergyofthecollisionsbetweenthemillingballsandbetweentheballsandthecontainerwall.
Thechargeischaracterizedbytheball-to-powdermassratio,aparameterapproximatelyproportionaltotherateofspecificenergyinput.
Fortypicalmillingconditions,ignitiontakesplacewhenthepowderhasreceivedacriticalamountofmechanicalenergyandtheignitiontimeisinverselyproportionaltotheball-to-powdermassratio.
Iftoomuchpowderisused,theenergyofeachindividualimpactisdistributedinaverylargevolumeandthestressesarenotlargeenoughtocauseactivation.
Iftheamountofpowderistoolittle,theheatlosstothemillingtoolsandtotheatmospherequenchesanyincipientself-sustainingreaction.
UnderstandingMechanicallyInducedSelf-PropagatingReactionsAmechanicalalloyingexperimentmaylookquitesimple,buttheunderlyingprocessisverycomplexconsistingofthecomponentsonverydifferentlengthandtimescales.
Thus,thecompletemodelingofamechanochemicaleventrequiresanadequatedescriptionofthemacroscopicprocesses,suchastheoperationofthemill,thecollisionsbetweenthemillingballs,andthetransportofthepowderwithinthemillingcontainer.
Onthemicroscopicscale,theeffectofanindividualcollisiononthepowdercaughtbetweentheimpactingsurfacesmustbeunderstoodandtheformationoflatticedefectsandtheelementaryinterfacereactionsmustbedescribed.
SignificantadvancesweremadetowardageneraltheoryofgradualmechanicalalloyingbyProf.
Courtneyandhisstudents.
9ThekeymomentofanMSRisignition.
Onceweunderstandwhatmakesthestateofthematerialcriticalatignition,weshouldbeabletousethisunderstandingofMSRforlearningabouttheinitialphaseofothermechanicalalloyingprocesses.
Unfortunately,manydetailsaresystemspecificandidentifyingthegeneralfeaturesisconsequentlydifficult.
Whetherignitiontakesplaceornotmaybeverysensitivetocompositionandmillingconditions.
Forexample,Figure3showstheX-raydiffractionpatternsoftwox(Zn+S)+(1–x)(Sn+2S)mixtures.
10ThisisanunusualsystemasthecombinationreactionsZn+S→ZnSSn+2S→SnS2arebothself-sustaining,buttheprocessisgradualinmixturesofthetwofor0.
1990%purity357391-250G357391-1KGPowder,<100nm,surfacearea70–90m2/g594911-100G594911-250GTantalum(Ta)TaCPowder,5μm280801-10GTitanium(Ti)TiCPowder,–325mesh307807-100G307807-500GPowder,<4μm594849-25G594849-100GPowder,130nmparticlesize(spherical)636967-25G636967-100G636967-250GTungsten(W)WCPowder,10μm241881-100GZirconium(Zr)ZrCPowder,5μm336351-50G336351-250GPhosphidesCalcium(Ca)Ca3P299%purity400971-100G400971-500GGallium(Ga)GaP99.
99%purity521574-2GNickel(Ni)Ni2PPowder,–100mesh,98%purity372641-10GIndium(In)InPPieces,3–20mesh,99.
998%purity366870-1GIron(P2Fe)P2FePowder,–40mesh,99.
5%purity691593-5GIron(P3Fe)P3FePowder,–40mesh,99.
5%purity691658-5GSilicidesCalcium(Ca)CaSi2Technicalgrade21240-250G-F21240-1KG-FChromium(Cr)CrSi2Powder,–230mesh,99%purity372692-25GMagnesium(Mg)Mg2SiPowder,–20mesh,99%purity343196-25GNiobium(Nb)NbSi2Powder,–325mesh399493-10GTungsten(W)WSi2Powder,–325mesh99%purity399442-10GVanadium(V)VSi2Powder,–325mesh399450-10GZirconium(Zr)ZrSi2Powder,325mesh99%purity399426-50GFormoreinformationabouttheseandotherrelatedmaterials,pleasevisitsigma-aldrich.
com/matsci.
MechanicalAlloyingTheprimaryfocusofourmanufacturingfacilityinUrbana,Illinois,USAisonthepurificationofinorganicsandmetalsforavarietyofhightechnologyapplications.
Ourcapabilitiesintheareaofmetalspurificationutilizeseveralroutestoproducesomeofthepurestalkaliearthandrareearthmetalsintheworld.
Thesetechniquescanalsobeusedinthemanufactureofalloysandothermaterialsforyourresearchorcommercialrequirements.
Ourproprietarytechniquesallowustomanufacturebarium,calcium,strontium,andmagnesiumwithtracemetalpuritiesupto4N(99.
99%).
Wealsomanufacturerareearthmetalsinpuritiesexceeding4Nthroughanumberofdifferenthightemperatureroutes.
OneareaofcustomizationhasfocusedonthemanufactureofprepackagedMolecularBeamEpitaxy(MBE)cruciblesforuseinthinfilmmanufacturingofadvancedmaterials.
Wehavesuccessfullymanufacturedhighpuritybarium,calcium,andstrontium(aswellasotherhighpuritymetals)andmeltedthematerialintoanMBEcrucible.
ThisallowsforincreasedloadinginthecrucibleaswellassignificantlyreducedoutgassingofthematerialsintheMBEvacuumchamber.
Pleasecontactustodayforyourspecificrequirements:matsci@sial.
com.
High-PurityMetalsManufacturedbyAAPL—ASigma-AldrichMaterialsChemistryCenterofExcellenceMetalCommentsPurity,%Prod.
NoMagnesium(Mg)dendriticpieces,purifiedbydistillation99.
998(metals)474754-5G474754-25G99.
99(metals)465992-5G465992-25GCalcium(Ca)dendriticpieces,purifiedbydistillation99.
99(metals)441872-5G441872-25G99.
9(metals)596566-5G596566-25GStrontium(Sr)dendriticpieces,purifiedbydistillation99.
99(metals)441899-5G441899-25G99.
9(metals)460346-5G460346-25GBarium(Ba)dendriticpieces,purifiedbydistillation99.
99(metals)474711-5G474711-25G99.
9(metals)441880-5G441880-25GUltraPureMetalsforHighTechnologyApplicationssigma-aldrich.
comHigh-PurityRareEarthMetalFoilsMetalDimensionsPurity*Prod.
No.
Lanthanum(La)25mmX25mmX1mm,~3.
9gTotalREM:99.
5%La/TotalREM:99.
9%694908Cerium(Ce)25mmX25mmX1mm,~4.
2gTotalREM:99.
5%Ce/TotalREM:99.
9%693766Neodymium(Nd)25mmX25mmX1mm,~4.
4TotalREM:99.
5%Nd/TotalREM:99.
9%693758Samarium(Sm)25mmX25mmX1mm,~4.
9gTotalREM:99.
9%Sm/TotalREM:99.
95%693731GadoliniumGd)25mmX25mmX1mm,~4.
8gTotalREM:99.
5%Gd/TotalREM:99.
95%693723Terbium(Tb)25mmX25mmX1mm,~4.
9gTotalREM:99.
5%Tb/TotalREM:99.
9%693715Dysprosium(Dy)25mmX25mmX1mm,~5.
6gTotalREM:99.
5%Dy/TotalREM:99.
9%693707HolmiumFoil(Ho)25mmX25mmX1mm,~5.
5gTotalREM:99.
5%Dy/TotalREM:99.
9%693693Erbium(Er)25mmX25mmX1mm,~5.
6gTotalREM:99.
5%Dy/TotalREM:99.
9%693685Thulium(Tm)25mmX25mmX1mm,~5.
8gTotalREM:99.
5%Dy/TotalREM:99.
95%693677Ytterbium(Yb)25mmX25mmX1mm,~4.
4gTotalREM:99.
5%Dy/TotalREM:99.
95%693669Lutetium(Lu)25mmX25mmX1mm,~6.
2gTotalREM:99.
5%Dy/TotalREM:99.
9%693650Yttrium(Y)25mmX25mmX1mm,~2.
8gTotalREM:99.
5%Dy/TotalREM:99.
9%693642*REM:RareearthmetalsRareearthmetalfoilsareusedinthermalandelectronbeam(e-beam)evaporationprocessesforcoatingsandthinfilmsviaphysicalvapordeposition(PVD).
Thelow-temperaturee-beamtechniqueisparticularlysuitedforapplicationssuchasfuelcellsandsolarpanels.
Therareearthmetalfoilscanalsobeusedinthepreparationofalloysandcompositesthatcontainhighlyvolatilecomponents(Ca,Mg,etc.
).
Formoreinformation,pleasevisitsigma-aldrich.
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