ASTM E1782-2008 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 08Standard 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 () 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 measureme

3、nts 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 dep

4、ending 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).1.31.4 There

5、is no ISO standard equivalent to this test method.1.5 This standard does not purport to address all 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 r

6、egulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Te

7、st MethodE 967 Test Method for Temperature Calibration of Differ-ential Scanning Calorimeters and Differential ThermalAnalyzersE 1142 Terminology Relating to Thermophysical PropertiesE 2071 Practice for Calculating Heat of Vaporization orSublimation from Vapor Pressure DataSI 10 Standard for Use of

8、the International System of Units(SI) The Modern Metric System3. Terminology3.1 Definitions:3.1.1 The following terms are applicable to this test methodand can be found in either Terminology E 473 or TerminologyE 1142: boiling pressure, boiling temperature, differentialscanning calorimetry (DSC), di

9、fferential thermal analysis(DTA), vapor pressure, vaporization point, vaporization tem-perature.3.2 Symbols:3.2.1 A, B, CAntoine vapor pressure equation (1)3con-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

10、 of Test Method4.1 A specimen in an appropriate container is heated at aconstant rate within a DTA or DSC instrument 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 pressu

11、re equals thepressure applied to the test chamber. The pressure is recordedduring observance of the boiling endotherm 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

12、 pressure range ofinterest. The pressure-temperature data are fitted as Log10Pand 1/T (K1) to the Antoine vapor pressure equation (see Fig.1). Vapor pressure values required for specific reports are thencomputed from the derived equation.4.2 The capability of the assembled system after calibrationsh

13、ould be periodically checked by using this method on purewater as a reference substance and comparing the derivedvapor pressure data with the NBS/NRC steam tables attachedas Appendix X1.1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsi

14、bility of Subcommittee E37.01 on ThermalTest Methods and Practices.Current edition approved March 1, 2008. Published June 2008. Originallyapproved in 1996. Last previous edition approved in 2003 as E 1782 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custome

15、r Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers given in parentheses refer to a list of references at theend of the text.1Copyright ASTM International, 100 Barr Harbor Drive, PO B

16、ox C700, West Conshohocken, PA 19428-2959, United States.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 handling and transport, for estimat

17、ion 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 (See Practice E 2071).6. Interference

18、s6.1 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 ambientboiling point may be encountered at the

19、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-ation of the sample chamber is recomme

20、nded 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. Apparatus7.1 The essential equipment r

21、equired 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 uniform controlled heating of a specime

22、n 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 the specimen and reference equivalent

23、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 Experimental Data andAntoine Equation F

24、itNOTE“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 082between selected temperature limits to 61 K at a rate oftemperature change of 5 K/min constant within 61%

25、.7.1.1.3 Recording Device, to provide a means of acquiring,storing and displaying measured or calculated signals or both.The minimum output signals are heat flow, temperature andtime.7.1.2 Pressure/Vacuum System, consisting of:7.1.2.1 A pressure vessel, or similar means of sealing thetest chamber at

26、 any applied absolute pressure within the 5 kPato 2 MPa range of this test method.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

27、to within 1 % including any temperaturedependence of the transducer(s) over the range of 5 kPa to 2MPa.NOTE 1Distance (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 Pr

28、essure Regulator, or similar device 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

29、 isolate components of the pressure/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 integri

30、ty to contain the specimenand reference 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 manner thatminimizes sample loss through vaporization prior to boilingand that promotes the d

31、evelopment of vapor-liquid equilibriumat boiling. When both conditions are met a sharp endothermwith little or no baseline curvature at the onset will beobserved.NOTE 2Studies byASTM task group E37.01.05 and others (2, 3) havedetermined glass cylindrical containers of 2 to 4 mm inside diameter by 25

32、mm long are suitable for thermocouple 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.

33、 These pinhole dimensions for DSC 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 m

34、easurement times and will tend topromote 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 subam

35、bient temperature to within61 K 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

36、.Arating of 10 % in excess ofthe 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 pressu

37、re/vacuum system is certi-fied for 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 e

38、mployed.9. Sampling9.1 Typical specimen 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 p

39、retreatment used with this testmethod.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 3The effect of pressure on the melting temperature of pu

40、rematerials used to calibrate the 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 gener

41、al experiences these effects should 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 ine

42、rt reference in suitablecontainers (see 7.1.3) into the test chamber.NOTE 4If 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

43、 that at least partially negates 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 5It is recommended to flush residual oxygen from the testchamber by either purging for several minutes with inert g

44、as or byE 1782 083evacuation and 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 refe

45、rence at a constant rate of 5K/min, 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 6Most pressure gauges report pressure relative to ambientpressure. In such cases, the measured pre

46、ssure shall be added to orsubtracted 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 t

47、he pressure rangecapability of the equipment.NOTE 7A 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 vap

48、or pressure curve.12. Calculation12.1 Determine and tabulate each boiling temperature (as Toor Tein Fig. 3) along with its corresponding observed pressure,P.NOTE 8Traditionally, the extrapolated onset temperature (To) of anendotherm recorded by DSC is used as the transition temperature; the peakmaxi

49、mum 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 pressure (log10P) versus the reciprocal of theabsolute temperature (1/T, K1). Examine this plot for anyabrupt deviation from linearity as evidence of instability.NOTE 9Deviations from linearity (curvature) due to expected de-creases in enthalpy of vaporization wit