ASTM E1782-2003 Standard Test Method for Determining Vapor Pressure by Thermal Analysis《用热分析法测定蒸气压力的标准试验方法》.pdf

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1、Designation: E 1782 03Standard Test Method forDetermining Vapor Pressure by Thermal Analysis1This standard is issued under the fixed designation E 1782; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n

2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes a procedure for the determi-nation of the vapor pressure of pure liquids or melts fromboiling point measurem

3、ents made using differential thermalanalysis (DTA) or differential scanning calorimetry (DSC)instrumentation operated at different applied pressures.1.2 This test method may be used for the temperature range273 to 773 K (0 to 500 C) and for pressures between 5 kPa to2 MPa. These ranges may differ de

4、pending upon the instru-mentation used and the thermal stability of materials tested.Because a range of applied pressures is required by this testmethod, the analyst is best served by use of instrumentationreferred to as high pressure differential thermal instrumentation(HPDSC or HPDTA).1.3 Computer

5、 or electronic-based instruments, techniques,or data treatment equivalent to this test method may also beused.NOTE 1Users of this test method are expressly advised that all suchinstruments or techniques may not be equivalent. It is the responsibility ofthe user of this test method to determine the n

6、ecessary equivalency priorto use. Only the manual procedures are to be considered valid.1.4 SI value units are the standard. The customary unitsgiven in parentheses are for information only.1.5 There is no ISO standard equivalent to this test method.1.6 This standard does not purport to address all

7、of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 177 Practice for Use

8、of the Terms Precision and Bias inASTM Test Methods2E 473 Terminology Relating to Thermal Analysis2E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2E 967 Practice for Temperature Calibration of DifferentialScanning Calorimeters/Differential Thermal An

9、alyzers2E 1142 Terminology Relating to Thermophysical Proper-ties2E 2071 Practice for Calculating Heat of Vaporization orSublimation from Vapor Pressure Data2SI 10 Standard for Use of the International System of Units(SI) The Modern Metric System33. Terminology3.1 Definitions:3.1.1 The following ter

10、ms are applicable to this test methodand can be found in either Terminology E 473 or TerminologyE 1142: boiling pressure, boiling temperature, differentialscanning calorimetry (DSC), differential thermal analysis(DTA), vapor pressure, vaporization point, vaporization tem-perature.3.2 Symbols:3.2.1 A

11、, B, CAntoine vapor pressure equation (1)4con-stants (log10, kPa, K):Antoine vapor pressure equation: Log10P 5 A 2B/T 1 C!where:P = vapor pressure, kPa, andT = temperature, K.4. Summary of Test Method4.1 A specimen in an appropriate container is heated at aconstant rate within a DTA or DSC instrumen

12、t operated underan applied constant vacuum/pressure between 5 kPa and 2 MPauntil a boiling endotherm is recorded. Boiling is observed atthe temperature where the specimen partial pressure equals thepressure applied to the test chamber. The pressure is recordedduring observance of the boiling endothe

13、rm and the boilingtemperature is recorded as the extrapolated onset temperature.This measurement is repeated using new specimens for each offive or more different pressures covering the pressure range ofinterest. The pressure-temperature data are fitted as Log10Pand 1/T (K1) to the Antoine vapor pre

14、ssure equation (see Fig.1). Vapor pressure values required for specific reports are thencomputed from the derived equation.1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.01 on TestMethods and Recommended Pr

15、actices.Current edition approved March 10, 2003. Published April 2003. Originallyapproved in 1996. Last previous edition approved in 1998 as E 1782 98.2Annual Book of ASTM Standards, Vol 14.02.3Annual Book of ASTM Standards, Vol 14.04.4The boldface numbers given in parentheses refer to a list of ref

16、erences at theend of the text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 The capability of the assembled system after calibrationshould be periodically checked by using this method on purewater as a reference substance and c

17、omparing the derivedvapor pressure data with the NBS/NRC steam tables attachedas Appendix X1.5. Significance and Use5.1 Vapor pressure is a fundamental thermophysical prop-erty of a liquid. Vapor pressure data are useful in processdesign and control, in establishing environmental regulationsfor safe

18、 handling and transport, for estimation of volatileorganic content (VOC), and in deriving hazard assessments.Vapor pressure and boiling temperature data are required forMaterial Safety Data Sheets (MSDS). The enthalpy of vapor-ization may also be estimated from the slope of the vaporpressure curve (

19、See Practice E 2071).6. Interferences6.1 This test method is limited to materials that exhibit asingular sharp boiling endotherm under the conditions outlinedin this test method.6.2 Oxidation, pyrolysis, or polymerization of condensedorganic materials retained at temperatures above their ambientboil

20、ing point may be encountered at the elevated pressures ofthis method. This will be observed as an exotherm or asignificantly broadened endotherm, or both, and shall not beconsidered a valid pressure-temperature datum point. Use of aninert gas for elevated pressures or for back-filling after evacu-at

21、ion of the sample chamber is recommended to minimize therisk of oxidation.6.3 Partial blockage of the pinhole in the DSC containerscould occasionally be encountered. This may be observed asnoise spikes on the boiling endotherm and shall not beconsidered a valid pressure-temperature datum point.7. Ap

22、paratus7.1 The essential equipment required to provide the mini-mum instrument capability of this test method includes (seeFig. 2):7.1.1 Differential Scanning Calorimeter (DSC) or Differen-tial Thermal Analyzer (DTA), consisting of:7.1.1.1 DSC/DTA Test Chamber, composed of a furnace(s)to provide uni

23、form controlled heating of a specimen andreference at a constant rate within the 273 to 773 K temperaturerange of this test method; a temperature sensor to provide anindication of the specimen/furnace temperature to 61K;adifferential sensor to detect a difference (temperature or heatflow) between th

24、e specimen and reference equivalent to 5 mW;and a means of sustaining an inert gas or vacuum test chamberenvironment at pressures above and below ambient.7.1.1.2 Temperature Controller, capable of executing aspecific temperature program by operating the furnace(s)FIG. 1 Vapor Pressure Curve with Exp

25、erimental Data andAntoine Equation FigNOTE“A”, DSC/DTA instrument; “B,” pressure transducer;“C,”pressure/vacuum source; “D,” pressure stabilizer; “E,” pressureregulator; and “F,” relief valve.FIG. 2 Schematic of ApparatusE 1782 032between selected temperature limits to 61 K at a rate oftemperature c

26、hange of 5 K/min constant within 61%.7.1.1.3 Recording Device, to record and display the DSC/DTA curve with a Y-sensitivity of 5 mW/cm or 0.5 K/cm andan X-sensitivity of 10 K/cm.7.1.2 Pressure/Vacuum System, consisting of:7.1.2.1 Means of Sealing The Test Chamber, at any appliedabsolute pressure wit

27、hin the 5 kPa to 2 MPa range of this testmethod.7.1.2.2 Source of Pressurized Gas, or vacuum capable ofsustaining a regulated inert gas pressure to the test chamber ofbetween 5 kPa and 2 MPa.7.1.2.3 Pressure Transducer(s), to measure the pressure inthe test chamber to within 1 % including any temper

28、aturedependence of the transducer(s) over the range of 5 kPa to 2MPa.NOTE 2Distance (or dead volume) between the pressure transducerand the specimen in the test chamber should be minimized to ensureaccurate recording of the pressure at the time of boiling.7.1.2.4 Pressure Regulator, or similar devic

29、e to adjust theapplied pressure in the test chamber to 62 % of the desiredvalue.7.1.2.5 Ballast, or similar means to maintain the appliedpressure in the test chamber constant to 61%.7.1.2.6 Valves, to control delivery of the inert gas/vacuum tothe test chamber or to isolate components of the pressur

30、e/vacuum system, or both. Valves shall be rated in excess of the2 MPa upper pressure limit of this test method.7.1.3 Containers, (pans, capillary tubes, etc.) that are inertto the specimen and reference materials and which are ofsuitable structural shape and integrity to contain the specimenand refe

31、rence in accordance with the following specific re-quirements:7.1.3.1 It is imperative that the containers used in this testmethod be capable of retaining the specimen in a mannerwhich minimizes sample loss through vaporization prior toboiling and which promotes the development of vapor-liquidequili

32、brium at boiling. When both conditions are met a sharpendotherm with little or no baseline curvature at the onset willbe observed.NOTE 3Studies byASTM task group E37.01.05 and others (2, 3) havedetermined glass cylindrical containers of 2 to 4 mm inside diameter by 25mm long are suitable for thermoc

33、ouple inserted style DTA instruments;and a hermetic sealable pan (approximately 40 L vol) with a singlepinhole in the center of the lid of #125 m diameter is suitable for DSCinstruments. For purposes of this test method, pinhole diameters of 50 to75 m are recommended. These pinhole dimensions for DS

34、C containerswere established specifically for use with heating rates of nominally 5K/min. Use of heating rates other than 5 K/min are not recommended forthis test method. Higher rates may result in some self-pressurization of thespecimen and lesser rates will extend measurement times and will tend t

35、opromote preboiling vaporization.7.2 Auxiliary equipment considered useful in conductingthis test method include:7.2.1 Acoolant system that can be coupled directly with thecontroller to the furnace to hasten its recovery from elevatedtemperatures or to sustain a subambient temperature to within61 K

36、of a lower limit temperature.7.2.2 Abalance to weigh specimens or specimen containers,or both, to 60.1 mg.7.2.3 Asyringe or micropipet to deliver liquid specimens of1to5L610 %.7.2.4 Pressure relief valve to prevent accidental overpres-surization in the pressure system.Arating of 10 % in excess ofthe

37、 upper use pressure is suggested provided it does not exceedthe maximum working pressure rating of any individualcomponent in the system.8. Precautions8.1 Safety Precautions:8.1.1 Pressures in addition to ambient are employed in thistest method. Ensure that the pressure/vacuum system is certi-fied f

38、or operation at the extremes of pressure encountered withthis test method. Incorporation of a pressure relief device isrecommended.8.1.2 Adequate provisions shall be available for retentionand disposal of any spilled mercury if mercury-containingpressure devices are employed.9. Sampling9.1 Typical s

39、pecimen sizes used for individual pressuremeasurements are 1 to 5 mg of solid or 1 to 5 L of liquid.Similar size specimens should be used for each individualmeasurement of a given sample.9.2 Samples are assumed to be tested as received. Reportany special sampling or pretreatment used with this testm

40、ethod.10. Calibration10.1 Perform calibration according to Practice E 967, usingthe heating rate and specimen containers intended for this testmethod. Accomplish temperature calibration at ambient pres-sure.NOTE 4The effect of pressure on the melting temperature of purematerials used to calibrate th

41、e temperature axis has been shown to be0.01 K at the maximum pressure of this method (4). The effects ofvacuum on the heat transfer characteristics and subsequent thermal lag ofvarious differential thermal instruments (DSC and DTA) have not beenestablished. From general experiences these effects sho

42、uld not alter thetemperature axis calibration by more than1Kattheminimum pressure ofthis test method.10.2 Calibrate the pressure transducer according to therecommendations of the manufacturer or similar appropriateprocedure.11. Procedure11.1 Place the specimen and inert reference in suitablecontaine

43、rs (see 7.1.3) into the test chamber.NOTE 5If hermetic sealable DSC pans with pinholed lids are used,make sure there is no sample material on the outer surfaces of thecontainer and that a good hermetic seal is accomplished. Either will resultin preboiling vaporization that at least partially negates

44、 the function of thepinhole. Be certain, also, that the pinhole is free of dirt or debris.11.2 Seal the test chamber and apply the desired pressure.NOTE 6It is recommended to flush residual oxygen from the testchamber by either purging for several minutes with inert gas or byE 1782 033evacuation and

45、 back-filling with inert gas.11.3 Allow the pressure to stabilize and equilibrate the testchamber at a start temperature which shall be at least 30 Kbelow the expected boiling temperature to ensure stabletemperature control and baseline.11.4 Heat the specimen and reference at a constant rate of 5K/m

46、in, recording the DSC/DTA curve until the vaporization iscomplete.11.5 Record the absolute pressure in the test chamber at thetime the boiling endotherm is observed.NOTE 7Most pressure gauges report pressure relative to ambientpressure. In such cases, the measured pressure shall be added to orsubtra

47、cted from atmospheric pressure measured by a barometer to obtainabsolute pressure.11.6 Restore the test chamber to ambient conditions uponcompletion of the heating curve.11.7 Repeat 11.1-11.6 with a new specimen at each of fouror more additional pressures throughout the pressure rangecapability of t

48、he equipment.NOTE 8A minimum of five measurements at different pressures arerequired for this test method. Additional measurements should improvethe fit of the Antoine vapor pressure equation and reduce the uncertaintyof the Antoine constants used to calculate the vapor pressure curve.12. Calculatio

49、n12.1 Determine and tabulate each boiling temperature (as Toor Tein Fig. 3) along with its corresponding observed pressure,P.NOTE 9Traditionally, the extrapolated onset temperature (To) of anendotherm recorded by DSC is used as the transition temperature; the peakmaximum temperature (Te) is used for thermocouple inserted DTAconfigurations. The convention employed during temperature calibrationshall be used for these calculations.12.2 If necessary, correct the observed pressures and tem-peratures by the amount determined from the calibrations. Plotthe logarithms of