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1、时光荏苒,岁月如白驹过隙,不经意间,我们即将从多彩的大学毕业,完成一个从大学生到社会人的转变。四年的大学生涯,让我明白了许许多多的科学知识和人生哲理,以及数不尽的感悟和成长。然只有将所学的理论知识付诸于社会的实践,才能检验和实现理论自身的价值,也只有将理论付诸于实践才能使理论得以检验。同样,一个人的价值也是通过实践活动来实现的,也只有通过实践才能锻炼人的品质,彰显人的时代风貌。而毕业实习作为大学的最后一课,也是最后一刻,我倍加珍惜,从而可以较深层次的理解社会,以便为将来能更好的胜任工作打下坚实的基础。外文文献:RefrigerantHistoryThefir
2、stpracticalrefrigeratingmachinewasbuiltbyJacobPerkinsin1834;itusedetherinavapor-compressioncycle.ThefirstabsorptionmachinewasdevelopedbyEdmondCarr‚in1850,usingwaterandsulfuricacid.Hisbrother,FerdinandCarr‚demonstratedanammonia/waterrefrigerationmachinein1859.Amixturecalledchemogene
3、,consistingofpetroletherandnaphtha,waspatentedasarefrigerantforvapor-compressionsystemsin1866.Carbondioxidewasintroducedasarefrigerantinthesameyear.Ammoniawasfirstusedinvapor-compressionsystemsin1873,sulfurdioxideandmethyletherin1875,andmethylchloridein1878.Dichloroethene(dilene)wa
4、susedinWillisCarrier'sfirstcentrifugalcompressors,andwasreplacedwithmethylenechloridein1926.Nearlyalloftheearlyrefrigerantswereflammable,toxic,orboth,andsomealsowerehighlyreactive.Accidentswerecommon.ThetaskoffindinganonflammablerefrigerantwithgoodstabilitywasgiventoThomasMidgleyin
5、1926.Healreadyhadestablishedhimselfbyfindingtetraethyllead,toimprovetheoctaneratingofgasoline.WithhisassociatesHenneandMcNary,Midgleyobservedthattherefrigerantstheninusecomprisedrelativelyfewchemicalelements,clusteredinanintersectingrowandcolumnoftheperiodictableofelements.Theeleme
6、ntattheintersectionwasfluorine,knowntobetoxicbyitself.Midgleyandhiscollaboratorsfelt,however,thatcompoundscontainingitshouldbebothnontoxicandnonflammable.Theirattentionwasdrawntoorganicfluoridesbyanerrorintheliterature.Itshowedtheboilingpointfortetrafluoromethane(carbontetrafluorid
7、e)tobehighcomparedtothoseforotherfluorinatedcompounds.Thecorrectboilingtemperaturelaterwasfoundtobemuchlower.Nevertheless,theincorrectvaluewasintherangesoughtandledtoevaluationoforganicfluoridesascandidates.Theshorthandconvention,laterintroducedtosimplifyidentificationoftheorganicf
8、luoridesfora时光荏苒,岁月如白驹过隙,不