USP34-NF29-911-粘度-中文翻译

USP34-NF29621粘度Page1of3911VISCOSITYViscosityisapropertyofliquidsthatiscloselyrelatedtotheresistancetoflow.Itisdefinedintermsoftheforcerequiredtomoveoneplanesurfacecontinuouslypastanotherunderspecifiedsteady-stateconditionswhenthespacebetweenisfilledbytheliquidinquestion.Itisdefinedastheshearstressdividedbytherateofshearstrain.Thebasicunitisthepoise;however,viscositiescommonlyencounteredrepresentfractionsofthepoise,sothatthecentipoise(1poise=100centipoises)provestobethemoreconvenientunit.Thespecifyingoftemperatureisimportantbecauseviscositychangeswithtemperature;ingeneral,viscositydecreasesastemperatureisraised.Whileontheabsolutescaleviscosityismeasuredinpoisesorcentipoises,forconveniencethekinematicscale,inwhichtheunitsarestokesandcentistokes(1stoke=100centistokes)commonlyisused.Toobtainthekinematicviscosityfromtheabsoluteviscosity,thelatterisdividedbythedensityoftheliquidatthesametemperature,i.e.,kinematicviscosity=(absoluteviscosity)/(density).Thesizesoftheunitsaresuchthatviscositiesintheordinaryrangesareconvenientlyexpressedincentistokes.Theapproximateviscosityincentistokesatroomtemperatureofetheris0.2;ofwater,1;ofkerosene,2.5;ofmineraloil,20to70;andofhoney,10,000.粘度是液体的属性之一，它与流动阻力紧密相关。在规定的条件下，待测液体充满平面间的空隙，在不断转动过程中，所产生的力定义为粘度。该粘度等于剪切应力除以剪切应变率。基本单位是泊；但是经常遇到泊的分数表示的粘度，因此厘泊（1泊=100厘泊）是更常用的单位。由于粘度随温度变化明显，需指明温度。通常情况下，粘度随温度的升高而减小。尽管粘度的测量是以绝对粘度形式表示，其常用单位是泊或厘泊，但为方便期间常常得到的是运动粘度，常用单位是司和厘司（1司=100厘司）。为了从绝对粘度得到运动粘度，绝对粘度需要除以同温度下的液体密度。如，运动粘度=绝对粘度/密度。单位的大小便于表示常规范围内的粘度为厘司。在室温情况下，以厘司估计的粘度，醚为0.2；水为1；煤油为2.5；矿物油为20～70；蜂蜜为10,000。Absoluteviscositycanbemeasureddirectlyifaccuratedimensionsofthemeasuringinstrumentsareknown,butitismorecommonpracticetocalibratetheinstrumentwithaliquidofknownviscosityandtodeterminetheviscosityoftheunknownfluidbycomparisonwiththatoftheknown.如果已知测量仪器的准确尺寸，可以直接测得绝对粘度。但是更常用的做法是使用已知粘度的液体校准仪器，通过与已知粘度的液体相对比，测定未知粘度的液体。Manysubstances,suchasthegumsemployedinpharmacy,havevariableviscosity,andmostofthemarelessresistanttoflowathigherflowrates.Insuchcases,agivensetofconditionsisselectedformeasurement,andthemeasurementobtainedisconsideredtobeanapparentviscosity.Sinceachangeintheconditionsofmeasurementwouldyieldadifferentvaluefortheapparentviscosityofsuchsubstances,theinstrumentdimensionsandconditionsformeasurementmustbecloselyadheredtobytheoperator.许多物质，如制药中用到的胶，具有可变粘度。它们中的大多数在高流速的情况下，流动阻力较低。在这种情况下，为了测量粘度选定一个特定条件，得到的测量值被认为是表观粘度。因此测量条件的改变会造成这类物质的表观粘度值的不同。操作者必须严格遵守测量时的仪器尺寸和条件。MeasurementofViscosity—Theusualmethodformeasurementofviscosityinvolvesthedeterminationofthetimerequiredforagivenvolumeofliquidtoflowthroughacapillary.Manycapillary-tubeviscosimetershavebeendevised,butOstwaldandUbbelohdeviscosimetersareamongthemostfrequentlyused.Severaltypesaredescribed,withdirectionsfortheiruse,bytheAmericanSocietyforTestingandMaterials(ASTM,D-445).Theviscosityofoilsisexpressedonarbitraryscalesthatvaryfromonecountrytoanother,therebeingseveralUSP34-NF29621粘度Page2of3correspondinginstruments.ThemostwidelyusedaretheRedwoodNo.IandNo.II,theEngler,theSayboltUniversal,andtheSayboltFurol.Eachoftheseinstrumentsusesarbitraryunitsthatbearthenameoftheinstrument.Standardtemperaturesareadoptedasamatterofconveniencewiththeseinstruments.FortheSayboltinstruments,measurementsusuallyaremadeat100°Fand210F;Redwoodinstrumentsmaybeusedatseveraltemperaturesupto250°F;andvaluesobtainedontheEnglerinstrumentusuallyarereportedat20°Cand50°C.Aparticularlyconvenientandrapidtypeofinstrumentisarotationalviscosimeter,whichutilizesaboborspindleimmersedinthetestspecimenandmeasurestheresistancetomovementoftherotatingpart.Differentspindlesareavailableforgivenviscosityranges,andseveralrotationalspeedsgenerallyareavailable.Otherrotationalinstrumentsmayhaveastationarybobandarotatingcup.TheBrookfield,Rotouisco,andStormerviscosimetersareexamplesofrotating-bobinstruments,andtheMacMichaelisanexampleoftherotating-cupinstrument.Numerousotherrotationalinstrumentsofadvanceddesignwithspecialdevicesforreadingorrecording,andwithwiderangesofrotationalspeed,havebeendevised.粘度的测量方法-测量粘度的常用方法涉及测定指定体积的液体流经毛细管所需的时间。已经定制了许多毛细管粘度计，但是奥斯特瓦尔德和乌氏粘度计是最常用的。美国测试与材料协会(ASTM,D-445)描述了几种类型的粘度计及其应用方向。针对油粘度的表述比较是随意，不同的国家之间因使用的仪器不同而有所差异。其中，广为使用的是红木1号和2号、恩格勒、赛波特通用和赛波特重油仪。每种仪器使用代表仪器名称的单位。为方便起见，这些仪器采用标准的温度。对赛波特仪，测量时的温度通常是100°F和210°F；红木仪有几个温度可用，最高250°F。恩格勒仪测得的事值通常报告温度为20°C和50°C。一种极其方便快捷的仪器是旋转粘度计，它利用浸没在待测物中的浮子和转子，测量旋转运动的阻力。不同的转子对应不同的粘度范围，有几个不同的转速可选择。其它的旋转装置有一个固定的浮子和旋转杯。Brookfield粘度计，Rotouisco，斯托默粘度计是浮子旋转仪器的例子。MacMichael是旋转杯仪器的例子。许多配有特殊的阅读或记录装置，和宽的转速范围的先进旋转仪已定制。Whereonlyaparticulartypeofinstrumentissuitable,theindividualmonographsoindicates.然而只有一种特定类型的仪器是合适的，在各个专论中有指示。Formeasurementofviscosityorapparentviscosity,thetemperatureofthesubstancebeingmeasuredmustbeaccuratelycontrolled,sincesmalltemperaturechangesmayleadtomarkedchangesinviscosity.Forusualpharmaceuticalpurposes,thetemperatureshouldbeheldtowithin±0.1°.粘度或表观粘度的测量，必须准确控制被测物质的温度，由于小的温度变化可能导致粘度的显著变化。通常制药用途，温度应当控制在±0.1°。ProcedureforCelluloseDerivatives—Measurementoftheviscosityofsolutionsofthehigh-viscositytypesofmethylcelluloseisaspecialcase,sincethe