Designation:D7739−11StandardPracticeforThermalOxidativeStabilityMeasurementviaQuartzCrystalMicrobalance1ThisstandardisissuedunderthefixeddesignationD7739;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thislaboratorypracticecoversthequantitativedetermi-nationofsurfacedepositsproducedduringthethermaloxida-tionofgasturbinefuelsbymonitoringtheoscillationfre-quencyofaquartzcrystalduringthermalexposure.Inthispractice,“thermaloxidativestability”referstothetendencyofafueltoresistsurfacedepositformationduringheating.1.2ThevaluesstatedinSIunitsaretoberegardedasthestandard.Thevaluesgiveninparenthesesareforinformationonly.1.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.SummaryofPractice2.1Aquartzcrystal,fittedwithgoldelectrodes,isfullyimmersedintestfuelcontainedwithinareactor.Anoscillatorcircuit,connectedtothecrystal,suppliesenergytoexcitethequartzcrystalandmonitorsitsresonantfrequency(nominally5MHz)overtimeviaacomputerinterface.Thereactorisequippedwithamagneticstirbar,pressuregauge/transducer,oxygensensor(notrecommendedforcertaintestconditions,see4.11),andthermocoupletomonitorandcontroltestconditions.Priortotesting,thefuelisbubbledwiththetestgasfor30mintoequilibrate.Afterequilibration,thereactorvesselisisolatedandraisedtotesttemperatureandpressure.Asdepositsaccumulateonthecrystalsurfaceduringtherun,thecrystalfrequencydecreases.Theshiftinresonancefrequencycanbequantitativelyrelated,inrealtime,tosurfacedepositaccumulationviaavariationoftheSauerbreyequation.23.SignificanceandUse3.1Thetendencyofajetfueltoresisttheformationofdepositsatelevatedtemperatureisindicativeof...
