Fine-tuning of ceramic-based chemical sensors via novel microstructural modification

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1、SensorsandActuatorsB120(2006)2534Fine-tuningofceramic-basedchemicalsensorsvianovelmicrostructuralmodificationPartII:LowlevelCOsensingbymolybdenumoxide,MoO3Abdul-MajeedAzad∗DepartmentofChemicalandEnvironmentalEngineering,TheUniversityofToledo,3052NitschkeHall,Toledo,OH43606-3390,USAReceiv

2、ed2November2005;receivedinrevisedform27December2005;accepted23January2006Availableonline28February2006AbstractEmployingabuffergasmixtureofCOandCO2,theequilibriumoxygenpartialpressurewasvariedacrosstheMo/MoO3proximitylinebyvaryingtheratioofconcentrationofthetwogases,asdescribedinanearlie

3、rcommunication.ThisledtothereductionofMoO3inonecaseandoxidationofthereducedphase(MoorMoO2)intheotherwithaconcomitantvariationinthemicrostructuralfeaturesoftheresultingspecies.Theformationandgrowthofthenewoxidesurfaceunderconditionsofoxygenpotentialmodulationhasbeenfoundtoimpartenhanceds

4、ensingcharacteristicstotheMoO3-basedchemicalsensorsforlowlevelsofcarbonmonoxide(14100ppmCO)intheambient.©2006ElsevierB.V.Allrightsreserved.Keywords:Semiconductingoxides;MoO3;Chemicalsensors;Microstructure;Carbonmonoxide1.Introductionasfollows.Atagiventemperatureandstandardpressure(ambi-

5、ent;1atm),theoxidationofametaltoitsoxideorreductionofMaterialswithnanofeaturesareofimmenserelevanceisanoxidetometaloritssuboxideoccursatawell-definedfinitethefieldofsolid-stateceramic-basedchemicalsensors.Highpartialpressureofoxygen.Ifthetwophases(metal/metaloxideselectivity,enhancedsensit

6、ivityandshortresponsetimeareormetalsuboxide/metaloxide)areinequilibrium,theincum-someofthekeyfeaturessoughtinthesedevices.Sincethebentoxygenpartialpressureisrecognizedastheequilibriumsensingmechanismandcatalyticactivityofceramicsarepartialpressure.AccordingtotheGibbsphaserule,oneitherla

7、rgelymicrostructure-dominated,benignsurfacefeaturessuchsideofthisuniqueoxygenpressure,atagiventemperature,oneassmallgrainsize,largesurfacearea,highaspectratioand,ofthetwocoexistingphasesmustdisappear.FortheMo/MoO3open/connectedporosityarerequiredtorealizeasuccessfulsen-coexiste