翻译1环境化学实验教学的案例研究.docx

翻译1环境化学实验教学的案例研究.docx

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翻译1环境化学实验教学的案例研究

CreativeEducation

2012.Vol.3,No.4,600-602

PublishedOnlineAugust2012inSciRes（http:

//www.SciRP.org/journal/ce）DOI:

10.4236/ce.2012.34088

TeachinganEnvironmentalChemistryExperiment—A

CaseStudy

——SimpleTestforMeasuringtheEmissionSpectraofLamps

LinZhang,LongChen,MeiXiao,FengWu*,NanshengDeng

DepartmentofEnvironmentalScience,SchoolofResourcesandEnvironmentalScience,

WuhanUniversity,Wuhan,China

Email:

*fengwu@

ReceivedMay24th2012;revisedJune30th,2012;acceptedJuly10th,2012

Herewepresentthesignificance,content,results,andteachingeffectofaselectiveself-designexperi-ment—asimpletestformeasuringtheemissionspectraofartificiallightsources,anddiscussitsfunctionandpotentialproblemsinanenvironmentalchemistryclassforundergraduatestudents.Also,weproposeseveralwaystoreformexperimentalteaching,andprovidereferencestootherexperimentalcourses.

Keywords:

Self-DesignExperiment;Spectrophotometer;Spectrum;HighPressureMercuryLamp;

DeuteriumLamp

Introduction

LaboratorycoursesareacrucialcomponentofaNationalQualityCourse（NQC）—EnvironmentalChemistry.Inthisre-searchgroup,webelievethattheconstructionandreformofthissubjectisimportant,andourcoretaskistodevelopteach-ingquality,improvestudents’experimentalabilities,promotemotivationandenthusiasm,inspireaspiritofscientificexplora-tionandcreativity,thusenablingstudentstoconductscientificresearchandsolvepracticalproblems.

TheaimoftheNQCistosettlevariousproblemsregardingtheconstructionofcoursecontent,andweasNQCinstructorsmanageanddesignthelaboratoryteachingourselves,andin-creasinglyself-designcomprehensiveexperiments.Weofferopportunitiesforstudentstogainknowledge,developtheirre-searchabilities,andenhancetheirindependence.Meanwhile,wereformthelaboratoryteachingmethods,andencouragedis-cussionandanactiveclassatmosphere,toinspirestudents’brainstormingabilities,andtoenhancetheteachingeffect.

Inthefollowingcase—asimpletestforalampemissionspectrum,webrieflyillustratehowstudents’researchabilitiesareclearlyimprovedthroughdesigninganexperiment.

ObjectiveofThisStudy

Ultravioletandvisible（UV-Vis）spectrophotometryisoneofthemostpracticalandfunctionaltoolsinquantitativeanalysis,andaUV-Visspectrophotometer（UVVS）isoneofthemostcommonlyusedinstrumentsinlaboratoryteachingforenvi-ronmentalmajorundergraduates.Therefore,mostinstructorswillregardthisascritical.Whileinlaboratoryclass,thepur-poseofsettingupthisexperimentisto:

makestudentslearnabouttheinnerstructureandworkingprincipleofaUVVSthroughdisassemblingit,e.g.thecharacteristicsofemissionspectraofahighpressuremercurylamp（HPML）anddeute-

*Correspondingauthor.

riumlamp（DL）usingremoldedUVVS;increasetheirtheoreti-calknowledgeaboutopticsviadeterminingemissionspectraofseveralartificiallightsources;promotetheircomprehensivescientificresearchabilityandtheabilitytodesignexperimentsbycomposinganexperimentalplan,accomplishingitandsub-mittingthefinalresultintheformofanessay.

ExperimentalPrinciple

TheUVVSconsistsoffourmajorparts:

alightsource,abeamsplittingsystem,anabsorptioncell,andadetectionsys-tem（Figure1）.Inordertodeterminetheilluminationintensityofourtargetlamps（HPMLandDL）,indifferentwavelengths,weneedtoutilizethebeamsplittingsystemtosplitthecon-tinuousspectra,thusfullytakingadvantageofregularUVVS.Therefore,weonlyhavetoalterthelightsourceforothersourcestobeexamined,andafteradjustingthewavelengthwecanobtainthetransmissivity（T）fordifferentwavelengths.

Inthisexperiment,weneedabaselinetoquantifytherelativeemissionintensity.Therefore,thevalueofTforaspecificwavelengthhastobefixedto0%,inwhichtheremightbelu-minance.Therelativeintensityinotherwavelengthscanbequantifiedbysubsequentcomparison.Similarly,wecanalsofixthevalueofTofaspecificwavelengthto100%,andthenperformthesameprocessdescribedabove.Giventhefactthatthereisaglasscoveronthemercurylampandthereisnotransmissioninwavelengthslessthan280nm,280nmwaschosenasthebaselineandfixedto0%,andwedeterminedthespectraupto800nm.However,fortheDL,thecoverismadeofquartz,thushavinglowerabsorptionlimit（160nm）.There-foreweshouldset160nmasthebaseline,butbecausetheshortestwavelengthwecanuseintheUVVSis180nm,weset180nmasthebaseline,andalsocontinuedupto800nm.

Owingtothelimitsofthelaboratory,wecouldnotevacuatetheabsorptioncell.However,infact,theimpactofairisnegli-gible.

600Copyright©2012SciRes.

L.ZHANGETAL.

Figure1.

InnerstructureofaUVVS.

Instruments

InstrumentsincludedtheUV-9100UVVS,anHPML,anironsupport,ascrewdriver,nipperpliersandawrench.TheDLusedwasintheUVVSitself.

ExperimentalMethod

StudyoftheDLEmissionSpectrum

Beforedetermination,theUVVSwasswitchedonandtheDLwaspreheatedfor15min.Thenweputthelidon,adjustedthewavelengthto180nm,andmadeT=0%.Thewavelengthintervalwaspreliminarilysetat10nm,butwhenitapproachedthepeak,2nmwasmoreappropriate.BecausetheUV-9100UVVScannotachievemoreaccurateperformance,andlargerintervalscannotpreciselyportraythespectrum.ThewavelengthwasalteredandTwasrecordeduntil800nmwasreached.Af-tertheexperimentwascompleted,boththeDLandUVVSwereswitchedoff,andthepowercablewasunplugged.

StudyoftheHPMLEmissionSpectrum

Forthesakeofsafety,thepowercablewasunplugged.ToeliminatetheeffectofDLandthetungstenlamp,theyhadtoberemovedbeforetheexperiment.Theoutercoverwaslifted,andthetoplidonthelamphousewasremoved.ThenthethreewiresconnectedtotheDLwerescrewedoff,clampedbythenipperpliers,thenthetightenedscrewswereunscrewedusingascrewdriver.ThentheDLcouldbeextractedfromUVVS.Thetungstenlampwasremovedusingthesamemethod.Thentheoutercoverwasreplaced,andthedam-boardinfrontofthelightsourceswasremoved.Withtheironsupport,theHPMLwasfixedoppositetheopticalchannel.ThenthepositionofHPMLwasadjustedtofocusitsradiationontheopticalcol-lector.After15minpreheatingtheHPML,theUVVSwasswitchedon.Forthisexperiment,250nmwasselectedasthebaseline,and2nmwaschosenasthewavelengthintervaluntil800nmwasreached.AftertheexperimenttheUVVSwasre-stored,andtheHPMLwasremoved.

Results

ThedataarepresentedrespectivelyfortheemissionspectraoftheHPMLandDL.Toanalyzetheiraccuracy,theywerecomparedwithstandardemissionspectra（EmissionSpectraof

Copyright©2012SciRes.

mercurylight,deuteriumlightandtungstenlamp.Availableonline）indetail.AllthespectraarepresentedinFigures2and3.

Discussion

CoincidenceAnalysisbetweenStandardandExperimentalSpectra

Bycomparisonwithstandardspectra,wefoundtheexperi-mentalspectraofbothHPMLandDLcoincidedwiththemsignificantly.Inparticular,theemissionpeaksofHPMLat404nm,436nm,546nmand577-579nmwerealldelineated.Moreover,themainpeakat365nmwasaccuratelydepicted.However,thestandardspectrumoftheDLisfarmorecomplexthanthatoftheHPML,sincethespectralbandwidthofitsslitiscomparativelytiny,andcanscanadjacentwavelengths.There-fore,toclearlydemonstratethedistinction,thisstandardspec-trumwasfittedtoamodifiedandsmoothcurve,inwhichthepeakswereingoodagreementwiththeexperimentalspectrum,asshown.

DifferenceAnalysisbetweenHPMLandDLEmissionSpectra

Obviousdifferencesinemissionspectracanbeobserved

ExperimentalSpectrum

16

StandardSpectrum

14

12

10

8

T

6

4

2

0

200300400500600700800wavelengthλ（nm）

Figure2.

EmissionspectraofDL.

ExperimentalSpectrum

StandardSpectrum

15

10

T

5

0

300400500600700800wavelengthλ（nm）

Figure3.

EmissionspectraofHPML.

601

L.ZHANGETAL.

betweentheHPMLandDL—thespectrumoftheformerisscattered,whilethespectrumofthelatterismorecontinuous.Thisisbecausetheirradiationofthemercurylampdependsonatoms.Aftertheyabsorbenergyfromthehighvoltage,theelectronscanmovetohigherenergylevels,andthisprocessiscalledtransition.Becausehigherenergylevelsresultinunsta-blestates,someelectronswillreturntolowerenergylevels,releasingelectromagneticradiation.Moreover,withincreasingmercuryvaporpressure,theatomiccollisionbecomesmorefrequentandintense,sotheemissionspectrawillbemoreandmorecontinuous.Infact,theemissionspectrumofanultrahighpressuremercurylampisalmostbandspectrum.However,aDLcanradiateacontinuousspectrumintheultravioletband.ThatiswhytheDLcanbetheultravioletlightsourceforaUVVS.

EffectAnalysisofThisExperimentalMethod

Withthewidespreaduseofvariouslampsanddevelopmentsinlamptechnology,nowadaysthelifespan,energysavingperformance,lightcoloretc.aregreatlyimproved.Sometimes,theabsolutecalibrationofthespectralirradiance,especiallyinmodernresearch,isnecessary.Tangetal.（Tang&Li,1996）hasstudiedtheabsolutecalibrationinshortwaveareasoftheDL.Huangetal.（Huang,Wang,Zhang,Lin,&Li,2007）onceusedaDLtostandardizetheirradianceinwavelengthsbetween200and300nm,whileWangetal.（Wang&Zhu,1992）dis-cussedmethodstoautomaticallycollectmercurylampspectra.