dsc测量比热容教学文案

dsc测量比热容abstract•Thisstudypresentsamethodologytodeterminethespecificheatcapacity(Cp)ofmaterialsforthermalenergystorage(TES)byDSC.ThreedifferentDSCmethodsareconsideredtobeappliedinthemethodology,andareexplainedandcomparedinthisstudyinordertoselectthemostproperoneforCpdetermination.•Toperformthisstudy,theCpofthreematerialscommonlyusedinsensibleTESsystems,slate,water,andpotassiumnitrate(KNO3),isdetermined.一、introductionlackoffossilenergeticresourcesitspriceneedtodecreaseCO2emissionsleadtodedevelopnewenergysystemsabletotakeprofitofrenewableenergyandbeenvironmentallyfriendlyandlessexpensiveTESsystemsareapossiblesolutionSolarenergyabundantcleanandeasyaccessible.problem:asthehoursofmaximumenergydemandmatchwiththehoursofnosolarirradiationwiththeaimtofillthisexistingenergysupplygap,TESsystemsarepresentedasthesolutiontostoretheenergyanduseitanytimeTEStechnologiessensibleheatstoragetheprocessbywhichtheheatisaccumulatedduetotheincreaseofthematerialtemperaturewithoutexperimentingstructuralchanges,nophasechangelatentheatstoragephasechange,thermochemicalenergymaterialselectionAhighstoragecapacityTherefore,needahighspecificheatcapacity.dTTfTiTmCPQ(1)•定义：在程序控制温度下，测量物质与参比物之间的能量差随温度变化关系的一种技术。•DSC曲线峰包围的面积正比于热焓的变化•可以测定多种热力学和动力学参数，例如比热容、反应热、转变热、相图、反应速率、结晶速率、高聚物结晶度、样品纯度等。该法使用温度范围宽（-175~725℃）、分辨率高、试样用量少。适用于无机物、有机化合物及药物分析。差示扫描量热法（DSC）（DifferentialScanningCalorimetry）采用试样和一标准物质在相同条件下进行扫描，然后量出二者的纵坐标进行计算。要求标准物质在所测温度范围内没有发生物理化学变化，且比热容已知。常用的标准物质是蓝宝石。具体作法是在DSC内先用两个空样品皿，以一定的升温速度作一条基线，然后放入蓝宝石样品在相同条件下作一条DSC曲线，最后在同样条件下作未知试样的DSC曲线，如图threeDSCmethodsforCpmeasurementThedynamicmethodhastraditionallybeenusedtomeasurePCMlatentheatbutalsoforCpmeasurementsapplyinghighheatingratesinthetemperaturerangeofstudyTheareasmethodisbasedontheCpvalue,thus,howmuchheatfluxisneededtoheatupamaterialfortemperatureincrease,andconsistsofconsecutiveisothermalstagesdiffering1℃withnoheatingsegmentsamidTheisostepmethodisanintermediatebetweenthesetwo,asitisasuccessionofdynamicmethodsappliedtoheatupthematerialjust1℃betweenisothermalsegments.Thismethodhasbeentestedinglasstransitionpharmaceuticalstudieswithgoodresultsobtained,butithasnotbeenusedforTESmaterialsCpdetermination,therebyitsselectionforthisstudy二、MaterialsToensuretheperformanceofthemethodologyinarepresentativevarietyofmaterialphaseformsandchemicalstructures,threedifferentmaterialswidelyusedinsensibleheatstoragesystemshavebeenchosentoperformthisstudy.Water.Itsthermalpropertiesarewellknown,andtherefore,thesevaluescanbeusedasareferencetoseetheapproachonthemeasurementseachmethodhas.CommercialBi-distillatedwaterfromPanreachasbeenusedtoperformtheexperimentsSlate.Itisawidelyusedconstructionmaterialanditsperformancedependsonitsspecificheatcapacity,thereforeauthorsfinditaninterestingmaterialtobetested.TheslatesamplesusedinthisstudyweretakenfromaquarryintheCatalanPyrenees.Potassiumnitrate.Itisaninorganicsaltmainlyusedasmoltensaltinconcentratedsolarpowerplants(CSPPlants).Ithashighmeltingpoint(320℃)and,asallinorganicsalts,acomplexchemicalstructure,andthatiswhyitisalsofoundtobeusefulforthispaper’spurpose.ItisimportanttoremarkthatthismaterialselectionrespondstotheneedtotestthemethodologyandnottotieittoaconcretematerialtypeoraspecificTESapplication.Therefore,materialsusedindifferentTESsystemsandwithwhichauthorscommonlyworkhavebeenselected.•determinedbydifferentialscanningcalorimetry(DSC)•Standard40uLaluminiumcrucibles•weighwithaanalyticalbalancewithaprecisionof0.01mg.Theproceduretodeterminethespecificheatcapacityofamaterialconsistsofthreedifferentmeasurements,alldoneunderthesameconditions,thus,usingthesameDSCmethod:Blankmeasurement.Itisnecessarytorunanexperimentwithanemptycrucibletomeasuretheheatfluxthatcorrespondstothecruciblematerialinordertosubtractthissignalandconsideronlythesapphireandmaterialsampleones.Sapphiremeasurement.Sapphireisthematerialusedasreferenceasitsspecificheatcapacityiswellknownateverytemperatureanditssignalishugelystableovertemperature,datanecessaryforthematerial’sCpcalculation.Materialmeasurement.NeededtodeterminetheCpvalueofthematerialunderstudy.三、MethodologyPCmQmWK/S(2)Thesensitivityoftheanalysisistiedtotheheatingrateandthesamplemass.•literaturestudiesfoundhighheatingratesofabout10–20K/minaredesired•Eq.(2)shows,minorsamplemassesareneeded.•TheCpwasmeasuredbetween15and16℃,25–26℃and35–36℃forallthematerialsunderstudy.Thesemeasurementrangeswereselectedinordertoensurethatwaterwasinliquidstateandtobeabletotakethecertainknownwater4.18J/g℃Cpvalueat25℃asareferencetoevaluateeachmethodperformance.3.1.DSCmeasurementmethods3.1.1.DynamicmethodItisatemperaturecontrolledmethodthatachievesthethermalequilibriumbeforeandafteracontrolledheatingsegment,itconsistsofthreesegments.•10–15mintohomogenizethematerialtemperature•highheatingrate•anotherisothermalstageagainfor10–15minthelowerandhighertemperaturesofthemethodcanbe150℃smspsmQmmCQCpm（3）Similartothepreviousexplaineddynamicmethod,theisostepmethodThismethodusesEq.(3)tocalculatetheCpofthematerialalongeachheatingsegment.3.1.2.isostepmethod3..1.3.Areasmetho