Hydration Heat Evolution and Kinetics of Blended Cement Containing
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Hydration heat evolution and kinetics of blended cement containing steel slag at different temperatures Fanghui Han a, b , Zengqi Zhang a , Dongmin Wang b , Peiyu Yan a, * a Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Department of Civil Engineering, Tsinghua University, Beijing, China b China University of Mining and Technology (Beijing), Beijing, China A R T I C L E I N F O Article history: Received 12 November 2014 Received in revised form 19 February 2015 Accepted 21 February 2015 Available online 23 February 2015 Keywords: Steel slag Blended cement Hydration heat Kinetics A B S T R A C T Hydration heat characteristics of blended cement containing up to 50% steel slag were studied at 25 C, 45 C and 60 C by isothermal calorimeter. Kinetics equations were used to explore kinetics of blended cement. Kinetics parameters, n,K, and E a , were calculated and analyzed. Results indicated that the activity of steel slag was very low. Steel slag accelerated the hydration of aluminates but decelerated the hydration of silicates in cement clinker. Small amount of steel slag affected little the hydration process of cement. Elevated temperature obviously promoted the hydration of blended cement. The hydration of blended cement containing no more than 35% steel slag was controlled by nucleation of hydrates in acceleration period and by diffusion of ions in decay period. The hydration of blended cement containing 50% steel slag was mostly dominated by phase boundary reaction, then directly by diffusion. E a increased with increasing steel slag content. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Mineral admixtures are widely used in modern concrete either in blended cements or added separately in the concrete mixer [1]. The use of mineral admixtures such as ground granulated blast furnace slag, fly ash and silica fume which have both pozzolanic and latent hydraulic properties can improve the properties of concrete and limit environmental impact as well as bring economic benefits. With the resource shortage and rising price of slag, fly ash and other quality mineral admixtures, developing more kinds of mineral admixtures that leads to sustainable concrete design and greener environment is a valuable work. Currently, steel slag shows a good potential as mineral admixture in concrete. Steel slag is the industrial waste discharged from the steel-refining process in a conversion furnace. It accounts for approximately 15–20% by mass of the steel output [2,3]. More than 80 million tons of steel slag is discharged in China every year [4]. However, the current utilization rate of steel slag in China is only 22%, far behind the developed countries [5]. Thus, intensive research work is needed for high utilization rate of steel slag. A more attractive approach is the replacement of cement by steel slag. The chemical compositions of steel slag consist of CaO 45–60%, SiO 2 10–15%, Al 2 O 3 1–5%, Fe 2 O 3 3–9%, FeO 7–20%, MgO 3–13%, and P 2 O 5 1–4% [6]. And its main minerals consist of C 3 S, C 2 S, C 4 AF, C 2 F, C 12 A 7 , RO phase (CaO-FeO-MnO-MgO solid solution) and free-CaO [6–8]. Due to the minerals of C 3 S, C 2 S, C 4 AF, C 2 F, and C 12 A 7 , steel slag has hydraulic properties. But the activity of the cementitious minerals in steel slag is much lower than that in Portland cement [9]. It is related to the crystalline state, the cementitious phases of steel slag crystallize much better than that of Portland cement clinker owe to the low cooling rate of steel slag. Meanwhile, steel slag has large amount of non-active components, such as RO phase and Fe 3 O 4 . The effect of steel slag on the early hydration of Portland cement has been studied by several researchers. Kourounis et al. [6] investigated the properties and hydration of blended cements with steel slag and found that blended cement developed lower early-age strength compared to Portland cement and its strength decrease was high when the content of steel slag was high. The addition of steel slag slowed down the hydration of blended cements, and the blended cements showed longer setting time than Portland cement. Tsakiridis et al. [8] studied the utilization of steel slag for Portland cement clinker production and pointed out that the addition of steel slag by 10.5% in the raw meal did not affect the hydration process during Portland cement production. Wang et al. [10] found that the dormant period of blended cement containing steel slag is longer than that of Portland cement. Monshi and Asgarani [11] found that blending 10% extra iron slag to a cement composed of 49% iron slag, 43% calcined lime and 8% steel slag kept the compressive strength of concrete for type I * Corresponding author. Tel.: +86 13501215836; fax: +86 01062785836. E-mail address: [email protected] (P. Yan). http://dx.doi.org/10.1016/j.tca.2015.02.018 0040-6031/ ã 2015 Elsevier B.V. All rights reserved. Thermochimica Acta 605 (2015) 43–51 Contents lists available at ScienceDirect Thermochimica Acta journa l home page : www.e lsevier.com/loca te/tca
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Hydration Heat Evolution and Kinetics of Blended Cement Containing
Transcript of Hydration Heat Evolution and Kinetics of Blended Cement Containing
HydrationheatevolutionandkineticsofblendedcementcontainingsteelslagatdifferenttemperaturesFanghui Hana,b, Zengqi Zhanga, Dongmin Wangb, Peiyu Yana,*aKey Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Department of Civil Engineering, Tsinghua University, Beijing, ChinabChina University of Mining and Technology (Beijing), Beijing, ChinaARTICLEINFOArticlehistory:Received12November2014Receivedinrevisedform19February2015Accepted21February2015Availableonline23February2015Keywords:SteelslagBlendedcementHydrationheatKineticsABSTRACTHydration heat characteristics of blended cement containing up to 50% steel slag were studied at 25
C,45
C and 60
C by isothermal calorimeter. Kinetics equations were used to explore kinetics of blendedcement. Kinetics parameters, n,K, and Ea,were calculated and analyzed. Results indicated that the activityof steel slag was very low.Steel slag accelerated the hydration of aluminates but decelerated thehydration of silicates in cement clinker. Small amount of steel slag affected little the hydration process ofcement. Elevated temperature obviously promoted the hydration of blended cement. The hydration ofblended cement containing no more than 35% steel slag was controlled by nucleation of hydrates inacceleration period and by diffusion of ions in decay period. The hydration of blended cement containing50% steel slag was mostly dominated by phase boundary reaction, then directly by diffusion. Eaincreasedwith increasing steel slag content.2015 Elsevier B.V. All rights reserved.1. IntroductionMineraladmixturesarewidelyusedinmodernconcreteeitherinblendedcementsoraddedseparatelyintheconcretemixer[1].Theuseofmineraladmixturessuchasgroundgranulatedblastfurnaceslag,yashandsilicafumewhichhavebothpozzolanicandlatenthydraulicpropertiescanimprovethepropertiesofconcreteandlimitenvironmentalimpactaswellasbringeconomicbenets.Withtheresourceshortageandrisingpriceofslag,yashandotherqualitymineraladmixtures,developingmorekindsofmineraladmixturesthatleadstosustainableconcretedesignandgreenerenvironmentisavaluablework.Currently,steelslagshowsagoodpotentialasmineraladmixtureinconcrete.Steelslagistheindustrialwastedischargedfromthesteel-reningprocessinaconversionfurnace.Itaccountsforapproximately1520%bymassofthesteeloutput[2,3].Morethan80milliontonsofsteelslagisdischargedinChinaeveryyear[4].However,thecurrentutilizationrateofsteelslaginChinaisonly22%,farbehindthedevelopedcountries[5].Thus,intensiveresearchworkisneededforhighutilizationrateofsteelslag.Amoreattractiveapproachisthereplacementofcementbysteelslag.ThechemicalcompositionsofsteelslagconsistofCaO4560%,SiO2 1015%,Al2O3 15%,Fe2O339%,FeO720%,MgO313%,andP2O514%[6].AnditsmainmineralsconsistofC3S,C2S,C4AF,C2F, C12A7,ROphase(CaO-FeO-MnO-MgOsolidsolution)andfree-CaO[68].DuetothemineralsofC3S,C2S,C4AF,C2F, andC12A7,steelslaghashydraulicproperties.ButtheactivityofthecementitiousmineralsinsteelslagismuchlowerthanthatinPortlandcement[9].Itisrelatedtothecrystallinestate,thecementitiousphasesofsteelslagcrystallizemuchbetterthanthatofPortlandcementclinkerowetothelowcoolingrateofsteelslag.Meanwhile,steelslaghaslargeamountofnon-activecomponents,suchasRO phaseandFe3O4.Theeffectofsteelslag ontheearlyhydrationofPortlandcementhas beenstudied byseveralresearchers.Kourounisetal.[6]investigatedthepropertiesandhydrationofblendedcementswithsteelslag andfoundthatblendedcementdevelopedlowerearly-agestrengthcomparedtoPortlandcementandits strengthdecreasewashighwhenthecontentofsteelslag washigh.Theaddition ofsteelslag sloweddownthehydration ofblendedcements,andtheblended cementsshowedlongersettingtimethanPortlandcement. Tsakiridis etal. [8]studied theutilizationofsteelslag for Portlandcement clinkerproductionandpointedoutthattheaddition ofsteelslag by10.5%intherawmealdidnotaffectthehydrationprocessduring Portlandcement production.Wangetal.[10]foundthatthedormantperiodofblendedcementcontainingsteelslagislongerthanthatofPortlandcement.Monshiand Asgarani[11]found thatblending10%extraironslagtoacementcomposedof49%ironslag,43%calcinedlimeand 8%steelslag keptthecompressivestrengthofconcretefortype I*Correspondingauthor.Tel.:+8613501215836;fax:+8601062785836.E-mailaddress:[email protected](P.Yan).http://dx.doi.org/10.1016/j.tca.2015.02.0180040-6031/ 2015ElsevierB.V.Allrightsreserved.ThermochimicaActa605(2015)4351ContentslistsavailableatScienceDirectThermochimicaActaj our nal homepage: www. el sevi er . com/ l ocat e/ t caPortland cement.Kriskova etal. [12] foundthatmechanicalactivationsignicantly increasedthereactivity ofsteelslag duetotheincrease insurfaceareaandamorphousphase,and theamountofheat releasedpersurfaceareaincreasedwithmillingtime.Wangetal. [13]also foundthatsuper-ne steelslagexhibitedamuchhigheractivityatearlyages,butits activitywasstill obviouslylowerthanthatofPortlandcement.Liu and Li[14]pointedthattheearlyhydrationsofcement andsteelslag tendedtohinder eachother,especiallyinthecase oflargereplacementratioofsteelslag andhighneness ofsteelslag.Lietal. [15]proposedanewmethodfor modifying thechemicalandmineralogicalcompositionsofsteelslag byadding industrialwastestomoltenbasicoxygenfurnace steelslag, themodicationreducedthefree-CaOcontentandremarkablyimprovedthecementitious propertyofsteelslag.Wang etal. [16] foundthattheinitialalkalinity ofhydrationconditioncouldpromotetheearlyhydrationofactivecomponentsinsteelslag, but thehydrationdegreeofnon-activecomponentsisverylowevenunderstrongalkaline conditionwithpHvalue of13.8.Basedonareviewofcurrentliteratures,itisobviousthatblendedcementhasalowearly-agestrengthandlonginitialsettingtimebyreplacingpartofcementwithsteelslag.Inordertoimprovetheactivityofsteelslag,methodsofmechanicalactivation,mineralmodicationandalkalinityactivationareused.However,thehydrationheatevolutionofblendedcementcontainingsteelslagwhichbelongstothemaincharacteristicsoftheearly-stagehydrationprocesswasinvestigatedveryrarelyinthepast.Meanwhile,thereislittleinformationregardingthehydrationkineticsofblendedcementcontainingsteelslag,whichisimportanttounderstandthehydrationprocessandmechanismofblendedcement.Moreover,mostinvestigationsarecarriedoutwithsmallamountorsinglecontentofsteelslagoratroomtemperature.Therefore,studyofdetailedheatevolutionbehaviorandkineticsofblendedcementcontainingsteelslagareneeded.Inthispaper,thehydrationheatevolutionrateandcumulativehydrationheatofblendedcementcontaining0,10%,20%,35%and50%steelslagweremeasuredwithin168hat25
C,45
Cand60
Cbyanisothermalcalorimeter.Byapplyingthekineticsequations[1719],thereactionofblendedcementwasevaluatedasafunctionofhydrationtime,takingintoaccountthesteelslagcontentandcuringtemperature.Thenthehydrationreactionmechanismofblendedcementcontainingsteelslagwasdetermined.2.Experimental2.1.MaterialsP.I42.5PortlandcementconformingtoChineseNationalStandardGB175-2007andbasicoxygenfurnacesteelslagwereused.ThechemicalcompositionsofcementandsteelslagareshowninTable1. Themineralogicalphasesofsteelslag,whichweredeterminedbyXRDanalysis,usingaTTRIIIX-raydiffractom-eter(CuKa,45kV,200mA),aregiveninFig.1. AccordingtothecalculationmethodofalkalinityproposedbyMason[20],thealkalinityofsteelslagis3.59,whichisindicatedthatsteelslagusedinthispaperhashighalkalinity.AsshowninTable1, CaO,SiO2,Fe2O3,MgO,Al2O3 arethemainoxidesofsteelslag,itschemicalcompositionsaresimilartothatofPortlandcement.ButtherearesignicantdifferencesinmineralogicalphasesbetweenPortlandcementandsteelslag.ThemaindifferenceinsteelslagisthehighcontentsofironoxideandRO phase,whichhavenocementitiouspropertiesanddonotcombinetoformhydraulicphases.ThespecicsurfaceareasofPortlandcementandsteelslagare350m2/Kgand458m2/Kg,respectively.Theparticlesizedistributionwhichwasmeasuredbyalaserparticlesizeanalyzer(MASTERSIZER2000)ispresentedinFig.2.Itisevidentthatsteelslagwasnerthancementintherangeofneparticles,upto6mm,andsteelslagwascoarserthancementwhentheparticlesizewasgreaterthan60mm,whiletheparticlesizeofsteelslagbetween660mmaremuchlessthancement.2.2.TestmethodThehydrationheatevolutionrateandcumulativehydrationheatofblendedcementcontainingsteelslagweremeasuredwithanisothermalcalorimeter(TAMAirfromTA instruments).Thetestswereperformedatthreeconstanttemperatures(25
C,45
Cand60
C)within168h.TAMAirhaseightparalleltwin-chambermeasuringchannels:onechambercontainingthesample,anothercontainingthereference.Inordertoavoidconsiderabletempera-turedifferencesbetweenthepasteandtheisothermalenvironment,thebinderandwaterwerekeptatatemperatureclosetothemeasurementtemperaturebeforemixing.Aftermanuallymixinghomogeneously,thepasteswereimmediatelyplacedintothechambermaintainedataconstanttemperature.ThehydrationheatevolutionrateandcumulativehydrationheatofFig.1.XRDpatternofsteelslag.Fig.2.Particlesizedistributionofcementandsteelslag.Table1Chemicalcompositionsofcementandsteelslag(w/%).CompositionSiO2Al2O3Fe2O3CaOMgOSO3TiO2P2O5Na2Oeqf-CaOLOICement20.554.593.2762.502.612.930.530.832.08Steelslag12.772.1223.4949.173.540.231.020.910.451.86Na2Oeq=Na2O+0.658K2O;w:massfraction.44F.Hanetal./ThermochimicaActa605(2015)4351blendedcementcontainingsteelslagcanbecontinuouslymonitoredasafunctionoftime.Inordertoinvestigatethehydrationpropertiesofsteelslag,thesteelslagpasteswerepreparedbymixingsteelslagwithwaterorsodiumhydroxidesolutionswithpHvalueof13.0and13.6.Thewatertobinderratioandsodiumhydroxidesolutiontosteelslagratio(W/B)were0.4forallsamples.ThemixproportionsofpastesareshowninTable2.3.Resultsanddiscussion3.1.HydrationheatevolutionofsteelslagThehydrationheatevolutionrateandcumulativehydrationheatofsteelslagwithwaterorNaOHsolutiontosteelslagratioof0.4at25
CareshowninFig.3.ItcanbeseenfromFig.3(a)thatthehydrationprocessofsteelslagcanbedividedintove stages,whichissimilartothatofcement.Therststagewasassociatedtotherstpeakofthecurve,itcorrespondedtotherstminutesofreactionanditwasrelatedtothepartialdissolutionofsteelslag.Forpastesmixingsteelslagwithwater,NaOHsolutionsofpH13.0andpH13.6,thevaluesoftherstpeakwere56.2J/gh,66.5J/ghand89.5J/gh,respectively.Thenthehydrationheatevolutionratedecreasedrapidly,andreactionenteredthesecondstagecalleddormantperiodinwhichtheconcentrationofCa2+neededtoreachsaturationstatebeforefurtherhydrationofsteelslag[21].Thethirdandfourthstagesareassociatedtothesecondpeak.ThehydrationofactivecomponentsinsteelslagsuchasC2S,C3Smadereactionproductsprecipitate,andthenwiththereductionofactivephases,thehydrationheatevolutionratedecreased.Finally,thehydrationprocessenteredalowreactivityperiodandtheexothermicratedecreasedtoaverylowlevel.AsshowninFig.3(a),thedormantperiodsofpastesmixingsteelslagwithwaterandNaOHsolutionofpH13.0were43.3hand36.4h,respectively.ForpastemixingsteelslagwithNaOHsolutionofpH13.6,thehydrationprocessalmostdidnotexperiencedormantperiod.Theoccurringtimeofthesecondexothermicpeakwasabout80h,40hand20hforabovementionedthreepastes,respectively.ThepeakvalueofpastemixingsteelslagwithNaOHsolutionofpH13.0isalittlelargerthanthatofpastemixingsteelslagwithwater.ButincreasingalkalinityofsolutiontopH13.6increasedthevalueofsecondexothermicpeaknearlybythreetimes.ItisindicatedthatsteelslagwasstimulatedbyNaOHsolution.ItisduetothefactthatOHishelpfultodisintegratevitreousandthusacceleratethehydrationofC2SandC3S[22]. ThepromotingeffectwasnotobviouswhenpH13.0(Fig.3(a)and(b)),butthecumulativehydrationheatstillincreasedafter168hbyincreasingthealkalinityofsolutiontopH13.6.ThehydrationofcementcouldmakethepHvaluealittlehigherthan13.0inashorttime[23], evenforconcretewithlargeamountofmineraladmixture,thepHvalueofitsporesolutionwashigherthan12.0[24].AsshowninFig.3,theactivityofsteelslagwasstilllowwhenpH13.0.Therefore,thehydrationheatevolutionrateandcumulativehydrationheatweremuchlowerthanthatofcement.3.2.HydrationheatevolutionofblendedcementcontainingsteelslagThehydrationheatevolutionrateandcumulativehydrationheatofblendedcementcontainingsteelslagat25
CareshowninFigs.4and5, respectively.AsshowninFig.4(a),intheinitialhydrationtimeupto1h,thehydrationheatevolutionrateincreasedwithanincreaseinsteelslagcontentinblendedcement.Forblendedcement,steelslagalmostactedasinertmaterialintheinitialperiodduetoitslowactivity(Fig.3),anincreaseinthereplacementratioofsteelslagincreasedtheeffectivewatertocementratio,andtherewasmorespaceforthehydrationproductsofcement.Therstmaximumpeakwasformedinashorttimeduetothereleaseofsurfaceenergyandthefastreactionofaluminateswhenblendedcementcontactedwithwater[25]. Atthesametime,thecumulativehydrationheatincreasedwiththeincreasingamountofsteelslag(Fig.5(a)).ItcanbeseenfromFig.4(b)thattheendingtimeofdormantperiodincreasedwithincreasingdosageofsteelslag.Thiswasinagoodagreementwiththeinvestigationsthatthesettingtimeofcementandconcretebecamelongerbyreplacingpartofcementwithsteelslag,andanincreaseinsteelslagcontentincreasedthesettingtime[6,10,26,27]. ThereplacementofPortlandcementbysteelslagresultedinadecreasedhydrationheatevolutionrateandadecreasedpeakvalueofthesecondmaximumaswellasincreasedoccurringtimeofthesecondexothermicpeakcomparedtoPortlandcement(Fig.4(b)).Moreover,areductioninthetotalreleasedheatwiththeincreasingdosageofsteelslagwasobserved(Fig.5(b)).Thepromotingeffectofsteelslagonthehydrationofblendedcementisshownonlyintheinitialhydrationtime,thecumulativehydrationheatofPortlandcementexceedthatofblendedcementafterabout5.5h(Fig.5(a)).Thereactionofsteelslagwasmuchslowerthanthatofclinkerphases,andtheamountofcementdecreasedwithincreasingdosageofsteelslag,meanwhile,thespecicsurfaceareaofsteelslagwasonlyalittleTable2Mixproportionsofpastes.SampleW/B Massfraction(%)CementSteelslagCem0.41000SS109010SS208020SS356535SS505050Fig.3.Hydrationheatevolutionofsteelslagat25
C(a)hydrationheatevolutionrateand(b)cumulativehydrationheat.F. Hanetal./ThermochimicaActa605(2015)435145largerthanthatofPortlandcementandlargeparticlesexistedinsteelslag(Fig.2),sotheparticlesofsteelslagcannotactasnucleationsiteforthehydrationproductstodepositandgrowthduringtheprocessofnucleationandcrystalgrowth.Therefore,thehydrationheatevolutionrateandcumulativehydrationheatdecreasedwithanincreaseinsteelslagcontent.Itisnotedthatthecumulativehydrationheatofblendedcementcontaining10%steelslagwasalmostasmuchasthatofPortlandcementwithin168h.ItwasconsistentwiththeTsakiridissresultthatadditionof10.5%steelslaghadnoinuenceonthehydrationprocessofPortlandcement[8].Figs.6and7presentthehydrationheatevolutionandcumulativehydrationheatofblendedcementcontainingsteelslagat45
C,respectively.AsshowninFig.6(a),atthetemperatureof45
C,thepeakvalueoftherstheatevolutionwaslowerthanat25
Cexceptblendedcementcontaining35%steelslag.ThisphenomenonwasrelatedtotheincreasingrateoftheC3Ahydrationinthepresenceofgypsumwithincreasingtemperature.Thisreactionleadedtotheformationofprimaryettringiteonthesurfaceofthegrains,whichpreventedthefurtherhydrationforacertainperiodoftime[25]. Forblendedcementcontaining35%steelslag,thehydrationheatevolutionrateandcumulativehydrationheatwerehigherthanothersamplesintheinitialhydrationtimewithincreasingtemperaturefrom25
Cto45
C(Fig.6(a)andFig.7(a)).Itmightbeduetothecombinedeffectofelevatedtemperature,increasedwatertocementratioandsufcientquantityofcement,whichpromotedsignicantlytheinitialhydrationofsampleSS35.ItisapparentthatthecumulativehydrationheatofPortlandcementwasmorethanthatofblendedcementatabout4.0h,whichwasobviouslyshortened(Fig.6(a)andFig.7(a)).ItcanbeseenfromFig.6(b)thatthereactiontemperatureaffectedthehydrationprocessofblendedcementcontainingsteelslag.Anincreaseintemperaturefrom25
Cto45
Creducedtheendingtimeofdormantperiod,shortenedtheoccurringtimeofthesecondhydrationheatevolutionpeakbyabouttwotimesandincreasedthevalueofthesecondexothermicpeakbyaboutthreetimes.Theintensereactioncontinuedformorethan40hat25
C,butitshortenedforabout20hat45
C.Thus,thesecondexothermicpeakwithahighbutnarrowshapewasformed.AsshowninFig.7(b),theearly-stagecumulativehydrationheatofblendedcementhadaconsiderableincreasecomparedtosampleshydratingat25
C.Itwasfoundthatthe12haccumulativehydrationheatincreasedby118.14%forPortlandcementwithincreasingtemperaturefrom25
Cto45
C,while124.01%, 156.12%,155.92%and119.60%forsamplesSS10,SS20,SS35andSS50,respectively.Itiselucidatedthatelevatedtemperaturepromotedtheearly-agehydrationofblendedcementmoreobviouslythanthatofPortlandcementandthepromotingeffectbecamegreatwithanincreaseinsteelslagcontentinblendedcement.Comparedtohydratingat25
C,after168hofhydration,thecumulativehydrationheatincreasedby2.22%,0.68%,18.14%,35.36%and27.99%forsamplesCemSS10,SS20,SS35andSS50,respectively.Itisindicatedthatthehydrationofblendedcementcontaininglargeamountofsteelslagdevelopedsignicantlyatlaterstageofhydration.ItalsocanbeseenfromFig.7(b)thattheFig.4.Hydrationheatevolutionrateofblendedcementcontainingsteelslagat25
C(a)therstpeakand(b)hydrationwithin168h.Fig.5.Cumulativehydrationheatofblendedcementcontainingsteelslagat25
C(a)theinitialhydrationtimeand(b)hydrationwithin168h.46F.Hanetal./ThermochimicaActa605(2015)4351cumulativehydrationheatofPortlandcementandblendedcementcontainingnomorethan35%steelslaghadlittledifferenceinthelaterperiod.ButtherewasstillcertaingapbetweenPortlandcementandblendedcementcontaining50%steelslagduetosmallmassfractionofcementandlowactivityofsteelslag.Figs.8and9showthehydrationheatevolutionrateandcumulativehydrationheatofblendedcementat60
C,respective-ly.ItcanbeseenfromFig.8(a)thatthevalueoftherstexothermicpeakwaslowerat60
Ccomparedtohydratingat25
C.Thiswasaconsequenceoftheacceleratedformationofprimaryettringiteonthesurfaceofcementgrainsat60
Casitwasexplainedbefore.Itshouldbenotedthatincreasingtemperatureto60
CpromotedobviouslytheinitialhydrationofsamplesSS20andSS35(Fig.8(a)andFig.9(a)).AsshowninFig.8(b),asexpected,anincreaseintemperaturefrom45
Cto60
Creducedtheendingtimeofdormantperiodandincreasedthevalueofthesecondexothermicpeakfurther,meanwhile,itshiftedthepeaktoearliertime.Afterabout10hofhydration,thehydrationofblendedcementcontainingsteelslagenteredadiffusioncontrollingprocess.Thecumulativehydrationheatalsoincreasedsignicantlyasincreasingtemperature(Fig.9(b)).Whentemperatureraisedfrom25
Cto60
C,the12haccumulativehydrationheatincreasedby179.10%,194.98%,251.32%,268.77%and233.43%forsamplesCemSS10,SS20,SS35andSS50,respectively.Theactivitiesofcementandsteelslagweregreatlystimulatedatthetemperatureof60
C.ElevatedtemperaturecouldobviouslypromotetheearlyhydrationofactivecomponentsinsteelslagsuchasC2SandC3S.Moreover,fastreactionofcementinashorttimeresultedinahydrationenvironmentwithhighalkalinity,whichwasbenecialtothehydrationofsteelslag(Fig.3).Thus,forblendedcementcontainingsteelslag,muchmorehydrationheatgeneratedattheearlystageofhydrationat60
C.Comparedtohydratingat25
C,thecumulativehydrationheatwithin168hincreasedby15.49%,7.47%,26.47%,22.97%and32.26%forsamplesCemSS10,SS20,SS35andSS50,respectively.ItcanbefoundthattheamplitudeofincreaseofhydrationheatofblendedcementinthelaterperiodwasrelativelysmallcomparedtoPortlandcementat60
C.Itisduetothefactthatmostactivephasesofsteelslaghadhydratedintheearlyperiodandtheinertcomponents(ROphase,Fe2O3)cannotreactevenintheconditionofstrongalkalinityandelevatedtemperature[21].Thehydrationofsteelslagwasdifferentfromthatofpozzolanicmineraladmixture,suchasgranulatedblastfurnaceslagoryash,whichwillreactwithCa(OH)2 producedbycementatthelaterstageofhydration,moreover,elevatedtemperatureprovidedenergytoactivatealkali-hydroxideattackontheslagory ashparticles[28]. Forblendedcementcontainingsmallamountofgranulatedblastfurnaceslag,thecumulativehydrationheatwasmorethanPortlandcementat60
Cduetothereleasedlatentheatofcrystallizationofamorphousphaseinslag[29].However,steelslagdidnotreactwiththehydrationproductsofcement.Steelslagandcementaffectedeachothers hydrationbychangingthehydrationenvironment[10].Thus,forsteelslaginblendedcement,increasingtemperaturejustpromotedtheFig.6.Hydrationheatevolutionrateofblendedcementcontainingsteelslagat45
C(a)therstpeakand(b)hydrationwithin168h.Fig.7.Cumulativehydrationheatofblendedcementcontainingsteelslagat45
C(a)theinitialhydrationtimeand(b)hydrationwithin168h.F. Hanetal./ThermochimicaActa605(2015)435147hydrationofactivecomponentsandmadethesepartsofheatemitaheadoftime.Therefore,forblendedcementcontaining10%steelslag,thecumulativehydrationheatwasclosetoPortlandcementat25
Cand45
Cinthelaterperiod(Fig.5(b)andFig.7(b)),andithadacertaingapwithPortlandcementat60
C(Fig.9(b).Meanwhile,thecumulativehydrationheatofblendedcementcontainingsteelslagcannotexceedthatofPortlandcementwithin168hatelevatedtemperatures(Fig.7(b)andFig.9(b)).3.3.HydrationkineticsofblendedcementcontainingsteelslagSeveralstudieshavedescribedthehydrationkineticsofPortlandcementandmanykineticsmodelshavebeenbuilttomimicthehydrationprocessofPortlandcement[30]. Inordertoinvestigatethehydrationkineticsofblendedcementcontainingsteelslag,ahydrationkineticsequationwasusedinthispaper.Thisequation,thegeneralformofwhichispresentedinEq.(1),hasalsobeenusedtostudythehydrationreactionofPortlandcementandblendedcementcontaininggranulatedblastfurnaceslag[31],thealkali-activatedreactionofslag[17,32]andthepozzolanicreactionofmetakaolin[33]orricehuskash[34].11a 1=3hinKt(1)wherea isthedegreeofhydration;Kistherateconstant;tisthehydrationtime;nisaconstantrelatedwiththehydrationmechanism.Thevalueofnissmallerthan1indicatesthatnucleationkineticscontrolsthereactionrate,whileitiscloserto1 indicatesthattheprocessisgovernedbyphaseboundarykinetics,andthevalueisequalorlargerthan2indicatesthatthekineticscorrespondstoadiffusionprocess.Thedegreeofreaction,a,whichcanberepresentedastheratioofthecumulativehydrationheatattime,t, totheultimatetotalhydrationheat,Qmax,anditisshowninEq.(2).a Qt Qmax(2)AformulaofhydrationkineticsproposedbyKnudson(Eq.(3))[19]isusedtodeterminetheultimatetotalhydrationheat,Qmax.1Qt 1Qmaxt50Qmaxtt0(3)wheret50isthehydrationreactiontimewhenthecumulativehydrationheatis50%ofthetotalhydrationheat(i.e.,half-lifeperiod);(tt0)isthehydrationtimestartingfromtheaccelerationperiod.Thecurvesofln[1-(1-a)1/3]vs. ln(tt0)relationshipforblendedcementcontainingsteelslagareshowninFig.10.ItcanbeseenfromFig.10thatEq.(1)hasbeensimulatedwellduringtheaccelerationperiod(Fig.10lineAB)anddecayperiod(Fig.10 lineCD),butEq.(1)wasnotapplicablefordecelerationperiodduetothefactthatthecorrespondinglineofdecelerationperiodwasacurve(Fig.10lineBC).Fordecelerationperiod,Equation[1-(1-a)1/3]=Kln(tt0)hasbeenttedontothe[1-(1-a)1/3]vs. ln(tt0)Fig.9.Cumulativehydrationheatofblendedcementcontainingsteelslagat60
C(a)theinitialhydrationtimeand(b)hydrationwithin168h.Fig.8.Hydrationheatevolutionrateofblendedcementcontainingsteelslagat60
C(a)therstpeakand(b)hydrationwithin168h.48F.Hanetal./ThermochimicaActa605(2015)4351relationshipforblendedcementcontainingsteelslag.Fig.11presentsanexampleofSS20toelucidatethisrelationship.ThekineticsparametersofblendedcementcontainingsteelslagatdifferenttemperaturesareshowninTable3.AsshowninFig.10,apparently,forallsamplesstudiedinthispaper,thereactionfastenteredtheaccelerationperiod,andaftertheintensereaction,thetimeofenteringthedecayperiodwasalsoshortenedwithincreasingtemperatures.Theseresultswereagreementwiththehydrationheatevolutionrateandcumulativehydrationheat(Figs.49).ItcanbeseenfromTable3thatthevaluesofnforblendedcementscontainingsteelslagweresmallerthan1inaccelerationperiod,whichisindicatedthatthehydrationreactionratewascontrolledbynucleationkinetics.Whilethevaluesofnbecamelargerthan2indecayperiod,elucidatingthatthehydrationprocessbecameadiffusioncontrollingprocessatlaterstageofhydration.Duetothedifferentcontrollingmechanism,thereactionrateinaccelerationperiodwasabout1020timesofthatindecayperiod.Thevalueofnwasalsorelatedtothereactionresistanceofblendedcement.AsshowninTable3,thevalueofnincreasedwithanincreaseinreplacementratioofsteelslagatthreeexaminedtemperatures.Itisindicatedthatincreasingsteelslagcontentincreasedthereactionresistanceofblendedcement.TheactivitiesofactivephasesinsteelslagsuchasC2SandC3Swerelowduetotheslowlycoolingresultinginaperfectcrystallization.C3Sisthemaincementitiousphaseofcement,butcluster-gatheredC2Swithlargesizeandngerstructureisthemaincementitiousphaseofsteelslag[6].Thus,thereactionresistanceofsteelslagFig.10.Curvesofln[1-(1-a)1/3]vs.ln(tt0)andsegmentallysimulatelinesfor:(a)Cem,(b)SS10,(c)SS20,(d)SS35and(e)SS50.Symbolsrepresenttheexperimentaldataandtheredsolidlinesshowthestimulatedlines.(Forinterpretationofthereferencestocolorinthisgurelegend,thereaderisreferredtothewebversionofthisarticle.)F. Hanetal./ThermochimicaActa605(2015)435149washigherthanthatofPortlandcement.Asexpected,thereactionrate,K, decreasedwithincreasingsteelslagcontentinthreehydrationperiods(Table3). Itwasfoundthatincreasingtemperaturereducedthevaluesofninaccelerationperiod.Thiswasrelatedtotheoverallaccelerationofhydrationkineticswithincreasingtemperature.ElevatedtemperaturepromotedthehydrationofPortlandcementandactivecomponentsofsteelslag(Figs.69) andincreasedthereactionrate,K, ofblendedcementaswell(Table3).However,increasingtemperatureincreasedthevaluesofninthedecayperiodbecausethatdiffusionofreactantsthroughthereactionproductlayertooccurreactionsonthesurfacesofunhydratedparticlewasthemaincontrollingfactor.Elevatedtemperatureleadedtoformadensemicrostructurewithplentyofhydrationproducts,soitresultedinahigherreactionresistancecomparedtohydratingat25
C.Itisnotedthatincreasingtemperatureincreasedthereactionrateinthedecayperiodalthoughhighertemperatureleadedtohigherreactionresistance.Itmightbebecausethatelevatedtemperatureprovidedsufcientenergytoovercomethereactionresistance.Equation[1-(1-a)1/3]=Kln(tt0)wasthederivationofempiricalformuladx/dt =K/tanditwasapplicableforthedualcontrollingreactionofchemicalreactionanddiffusion[31]. ItcanbeseenfromFig.10thatblendedcementcontainingnomorethan35%steelslagexperiencedtheprocessofdualcontrollingreaction.Butforblendedcementcontaining50%steelslag,thevalueofnwascloseto1inaccelerationperiodanditbecamelargerthan2indecayperiod.Moreover,asshowninFig.10(e),curvesBCwerealmoststraightlinesatthreeexaminedtemperatures.Itiselucidatedthattheearly-stagekineticsbehaviorofsampleSS50ismostlydominatedbyphaseboundaryreaction,afterwhichitdirectlyentereddiffusioncontrollingprocess.ForsampleSS50,thehydrationheatevolutionratewasrapidintheinitialhydrationtime(Figs.4,6,8(a)),thenlotsofhydratesdepositontheunhydratedparticles,thereactionsoccurredonthephaseboundarybetweencrystalandporesolution.Moreover,furtherimprovementofhydrationdegreewashinderedduetolowmassfractionofcementandlowactivityofsteelslag(Fig.3).Theapparentactivationenergy,Ea,ofblendedcementcontainingsteelslagwasdeterminedfromtheEq.(4):K01K02 t502t501expEaT1 T2RT1T2
(4)wheret501 andt502 arethehydrationtimewhenthecumulativeheatreleasedis50%ofthetotalhydrationheatatcuringtemperatureT1 andT2,respectively.Risgasconstant(8.314J/mol).Table4presentstheapparentactivationenergyoftheoverallreactionofblendedcementcontainingsteelslaginthetempera-turerangeof2560
C.Itisevidentthatanincreaseinreplacementratioofsteelslagincreasedtheapparentactivationenergy.Itwasrelatedtothelowactivityofsteelslagandlargeamountofinertphasesasitwasexplainedbefore.ItisnotedthatthedifferenceinapparentactivationenergybetweenPortlandcementandblendedcementcontaining10%steelslagwassmall.ItisindicatedthatsmallamountofsteelslagaffectedlittlethehydrationprocessorpropertiesofPortlandcement,whichwasconsistentwiththehydrationheatevolutionrateandcumulativehydrationheat(Figs.49) aswellaspreviousinvestigations[8,11].However,Wuetal.[35]determinedEa=49kJ/molforblendedcementcontaining50%granulatedblastfurnaceslag(GBFS),whichwashighercomparedtoEa=46.39kJ/molwithrespecttoblendedcementcontaining50%steelslag.Thehydrationpropertiesofsteelslagwerepoorwhenitwasmixedwithwater(Fig.3),butforGBFS,almostnoreactionsoccurredasitcontactedwithwater.TheglassphaseofGBFShadcertainactivityandthecrystallizationactivationenergyofvitreousbodywasabout421256kJ/mol[36], whichmeansthatmuchmoreenergyshouldbeprovidedforthehydrationofGBFS.However,elevatedtemperatureandalkalinityenvironmentcansignicantlyactivatethehydrationofGBFS,whichwillreactwithCa(OH)2 producedbycementhydrationinblendedcement[29]. ComparedtoGBFS,thehydrationmecha-nismofsteelslaginblendedcementwasdifferent,steelslagdidnotreactwithhydrationproductsofcement.IncorporationofsteelslaginPortlandcementcouldbeseenasincorporationofakindofmaterialwithlowhydrationactivity,inotherwords,blendedcementcontainingsteelslagcouldbeseenasalowqualityofcement.Therefore,theapparentactivationenergyofblendedcementcontainingsteelslagwaslowerthanthatofblendedcementcontainingGBFSatthesamelevelofreplacement.Fig.11.Curvesof[1-(1-a)1/3]vs.ln(tt0)andsimulatelinesindecelerationperiodforsampleSS20.Symbolsrepresenttheexperimentaldataandtheredsolidlinesshowthestimulatedlines.(Forinterpretationofthereferencestocolorinthisgurelegend,thereaderisreferredtothewebversionofthisarticle.)Table3Kineticsparametersofblendedcementcontainingsteelslagatdifferenttemperatures.SampleT(
C)AccelerationperiodDecelerationperiodDecayperiodnKKnKCem250.490.027430.199962.700.00147SS100.530.022490.209042.440.00134SS200.500.023580.192022.450.00142SS350.580.017500.147032.350.00104SS500.910.006590.106712.340.00068Cem450.350.074700.262053.850.00277SS100.370.064800.235403.890.00188SS200.420.055650.201523.940.00131SS350.540.035110.135773.030.00081SS500.770.018460.139144.210.00074Cem600.290.112750.296042.890.00433SS100.340.100810.282624.300.00280SS200.440.074190.248805.110.00154SS350.480.066400.246641.380.00170SS500.700.031130.237751.290.00146Table4Apparentactivationenergyoftheoverallreactionofblendedcementcontainingsteelslag.SampleW/B Temperaturerange(
C)Ea(kJ/mol)Cem0.4256040.01SS10256041.43SS20256042.14SS35256043.58SS50256046.3950F.Hanetal./ThermochimicaActa605(2015)43514.Conclusion(1)ThehydrationprocessofsteelslagcanbedividedintovestagesanditissimilartothatofPortlandcement.Butcomparedtocementhydration,theendingtimeofdormantperiodandtheoccurringtimeofsecondexothermicweremuchlonger,andthevalueofsecondexothermicpeakwasmuchsmaller.TheactivityofsteelslagwasstilllowwhenpHvalueofsolutionwas13.0,butincreasingalkalinityofsolutiontopH13.6stimulatedsignicantlytheactivityofsteelslag.(2)Thehydrationheatevolutionrateandcumulativehydrationheatincreasedwithincreasingsteelcontentinblendedcementintheinitialhydrationtime.Atthetemperatureof45
Cor60
C,thepeakvalueoftherstheatevolutionwaslowerthanthatat25
CduetothefastreactionofC3Aatelevatedtemperatures.(3)Increasingsteelslagcontentinblendedcementincreasedtheoccurringtimeofsecondexothermicanddecreasedthevalueofsecondexothermicpeakaswellasreducedthecumulativehydrationheat.Anincreaseintemperaturefrom25
Cto45
Cor60
Cincreasedthevalueofsecondexothermicpeak,shiftsthepeaktoearliertimeandobviouslyincreasedthecumulativehydrationheatofblendedcement.Thepromotingeffectofelevatedtemperaturewasobviousforblendedcementcontaininghighcontentofsteelslag.(4)SmallamountofsteelslagaffectedlittlethehydrationprocessofPortlandcement,buttheretardingeffectofsteelslagonthehydrationofPortlandcementbecameobviouswhenthereplacementratioofsteelslagwashigh.(5)Increasingtemperaturecouldpromotethehydrationofactivecomponentsinsteelslagandmadethesepartsofheatemitaheadoftime.ThecumulativehydrationheatofblendedcementcontainingsteelslagcannotexceedthatofPortlandcementwithin168hatelevatedtemperatures.(6)Forblendedcementcontainingnomorethan35%steelslag,thehydrationreactionratewascontrolledbynucleationkineticsintheaccelerationperiodandthenbydiffusioninthedecayperiod,butinthedecelerationperiod,thehydrationexperienceddualcontrollingreactionofchemicalreactionanddiffusion.Theearly-stagekineticsbehaviorofblendedcementcontaining50%ofsteelslagwasmostlydominatedbyphaseboundaryreaction,afterwhichitdirectlyentereddiffusioncontrollingprocess.(7)Anincreaseinsteelslagcontentinblendedcementincreasedthevalueofnanddecreasedthereactionrate,K. Thevalueofnreducedandthereactionrate,K, increasedwithincreasingtemperatureinaccelerationperiod,whileindecayperiod,anincreaseintemperatureincreasedthevalueofn,althoughthereactionrate,K, increasedaswell.(8)Theapparentactivationenergyofblendedcementcontainingsteelslagincreasedwithanincreaseinsteelslagcontent.AcknowledgmentAuthorswouldliketoacknowledgetheNationalNaturalScienceFoundationofChina(grantNos.U1134008and51278277).References[1]B.Lothenbach,K.Scrivener,R.D.Hooton,Supplementarycementitiousmaterials,Cem.Concr.Res.41(2011)12441256.[2]B.Das,S.Prakash,V.N.Misra,Anoverviewofutilizationofslagandsludgefromsteelindustries,Resour.Conserv.Recycl.50(2007)4057.[3]E.Furlani,G.Tonello,S.Maschio,Recyclingofsteelslagandglassculletfromenergysavinglampsbyfastringproductionofceramics,WasteManage.30(2010)17141719.[4]J.Li,Q.Yu,J.Wei,T.Zhang,Structuralcharacteristicsandhydrationkineticsofmodiedsteelslag,Cem.Concr.Res.41(2011)324329.[5]H.Yi,G.Xu,H.Cheng,etal.,Anoverviewofutilizationofsteelslag,Proc.Environ.Sci.16 (2012)791801.[6]S.Kourounis,S.Tsivilis,P.E.Tsakiridis,etal.,Propertiesandhydrationofblendedcementswithsteelmakingslag,Cem.Concr.Res.37(2007)815822.[7]C.Shi,Characteristicsandcementitiouspropertiesofladleslagnesfromsteelproduction,Cem.Concr.Res.32(2002)459462.[8]P.E.Tsakiridis,G.D.Papadimitrious,S.Tsivilis,C.Koroneos,UtilizationofsteelslagforPortlandcementclinkerproduction,J.HazardMater.152(2008)805811.[9]Q.Wang,P.Yan,J.Yang,B.Zhang,Inuenceofsteelslagonmechanicalpropertiesanddurabilityofconcrete,Constr.Build.Mater.47(2013)14141420.[10]Q.Wang,P.Yan,S.Han,Theinuenceofsteelslagonthehydrationofcementduringthehydrationprocessofcomplexbinder,Sci.ChinaTechnol.Sci.54(2011)388394.[11]A.Monshi,M.K.Asgarani,ProducingPortlandcementfromironandsteelslagsandlimestone,Cem.Concr.Res.29(1999)13731377.[12]L.Kriskova,Y.Pontikes,.Cizer,etal.,Effectofmechanicalactivationonthehydraulicpropertiesofstainlesssteelslags,Cem.Concr.Res.42(2012)778788.[13]Q.Wang,J.Yang,P.Yan,Cementitiouspropertiesofsuper-nesteelslag,PowderTechnol.245(2013)3539.[14]S.Liu,L.Li,Inuenceofnenessonthecementitiouspropertiesofsteelslag,J.Therm.Anal.Calorim.117 (2014)629634.[15] Z.Li,S.Zhao,X.Zhao,T.He,Cementitiousproperttmodicationofbasicoxygenfurnacesteelslag,Constr.Build.Mater.48(2013)575579.[16]Q.Wang,J.Yang,P.Yan,Inuenceofinitialalkalinityonthehydrationofsteelslag,Sci.ChinaTechnol.Sci.55(2012)33783387.[17]A.Fernndez-Jimnez,F. Puertas,Alkali-activatedslagcements:kineticsstudies,Cem.Concr.Res.27(1997)359368.[18]C.Shi,P.V.Krivenko,D.Roy,Alkali-ActivatedCementsandConcretes,SponPress,2006.[19]T. Knudsen,Onparticlesizedistributionincementhydration,Paris,Proceedingof7thInternationalCongressontheChemistryofCement,volI1980,pp.170.[20]B.Mason,Theconstitutionofsomeopen-heartslag,J.IronSteelInst.11 (1994)6980.[21]Q.Wang,P.Yan,Hydrationpropertiesofbasicoxygenfurnacesteelslag,Constr.Build.Mater.24(2010)11341140.[22]N.Yang,Physicalandchemicalfoundationofalkalinecementitiousmaterial,J.Chin.Ceram.Soc.24(1996)209215(inChinese).[23]H.F.M.Taylor,CementChemistry,2nded.,ThomasTelford,London,1997.[24]Rasheeduzzafar,S.E.Hussain,Effectofmicrosilicaandblastfurnaceslagonporesolutioncompositionandalkali-silicareaction,Cem.Concr.Compos.13(1991)219225.[25]V.Tydlitt,T.Matas,R.Cern,Effectofw/candtemperatureontheearly-stagehydrationheatdevelopmentinPortland-limestonecement,Constr.Build.Mater.50(2014)140147.[26]I.A.Altun,I.Ylmaz,StudyonsteelfurnaceslagswithhighMgO asadditiveinPortlandcement,Cem.Concr.Res.32(2002)12471249.[27]A.Rai,J.Prabakar,C.B.Raju,R.K.Morchalle,Metallurgicalslagasacomponentinblendedcement,Constr.Build.Mater.16(2002)489494.[28]D.M.Roy,G.M.Idorn,Hydration,structure,andpropertiesofblastfurnaceslagcements,mortars,andconcrete,ACIJ.(1982)444457.[29]F.Han,R.Liu,D.Wang,P.Yan,Characteristicsofthehydrationheatevolutionofcompositebinderatdifferenthydratingtemperature,Thermochim.Acta586(2014)5257.[30]J.J.Thomas,J.J.Biernacki,J.W.Bullard,S.Bishnoi,etal.,Modelingandsimulationofcementhydrationkineticsandmicrostructuredevelopment,Cem.Concr.Res.41(2011)12571278.[31]X.Wu,Kineticstudyonhydrationofblastfurnaceslagcement,J.Chin.Ceram.Soc.16(1988)423428(inChinese).[32]D.Ravikumar,N.Neithalath,Reactionkineticsinsodiumsilicatepowderandliquidactivatedslagbindersevaluatedusingisothermalcalorimetry,Thermochim.Acta546(2012)3243.[33]J.Cabrera,M.F. Rojas,Mechanismofhydrationofthemetakaolinlimewatersystem,Cem.Concr.Res.31 (2001)177182.[34]Q.Feng,H.Yamamichi,M. Shoya,S.Sugita,Studyonthepozzolanicpropertiesofricehuskashbyhydrochloricacidpretreatment,Cem.Concr.Res.34(2004)521526.[35]X.Wu,D.M.Roy,C.A.Langton,Earlystagehydrationofslag-cement,Cem.Concr.Res.13(1983)277286.[36]R.Roy,Crystalchemistryofnon-metallicmaterials,LectureNotesforMaterialsScience,ThePennsylvaniaStateUnivarsity,1981,pp.249.F.Hanetal./ThermochimicaActa605(2015)435151
