1、Designation: D 2879 97 (Reapproved 2007)An American National StandardStandard Test Method forVapor Pressure-Temperature Relationship and InitialDecomposition Temperature of Liquids by Isoteniscope1This standard is issued under the fixed designation D 2879; the number immediately following the design
2、ation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by
3、agencies of the Department of Defense.1. Scope1.1 This test method covers the determination of the vaporpressure of pure liquids, the vapor pressure exerted by mixturesin a closed vessel at 40 6 5 % ullage, and the initial thermaldecomposition temperature of pure and mixed liquids. It isapplicable t
4、o liquids that are compatible with borosilicate glassand that have a vapor pressure between 133 Pa (1.0 torr) and101.3 kPa (760 torr) at the selected test temperatures. The testmethod is suitable for use over the range from ambient to 748K. The temperature range may be extended to include tem-peratu
5、res below ambient provided a suitable constant-temperature bath for such temperatures is used.NOTE 1The isoteniscope is a constant-volume apparatus and resultsobtained with it on other than pure liquids differ from those obtained in aconstant-pressure distillation.1.2 Most petroleum products boil ov
6、er a fairly wide tem-perature range, and this fact shall be recognized in discussionof their vapor pressures. Even an ideal mixture followingRaoults law will show a progressive decrease in vaporpressure as the lighter component is removed, and this is vastlyaccentuated in complex mixtures such as lu
7、bricating oilscontaining traces of dewaxing solvents, etc. Such a mixturemay well exert a pressure in a closed vessel of as much as 100times that calculated from its average composition, and it is theclosed vessel which is simulated by the isoteniscope. Formeasurement of the apparent vapor pressure
8、in open systems,Test Method D 2878, is recommended.1.3 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
9、 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. For specific hazardstatements, see 6.5, 6.10, and 6.12.2. Referenced Documents2.1 ASTM Standards:2D 2878 Test Method for Estimating Apparent Va
10、por Pres-sures and Molecular Weights of Lubricating OilsE 230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized Thermocouples3. Terminology3.1 Definition of Term Specific to This Standard3.2 ullagethat percentage of a closed system which isfilled with vapor.3.2.1 Discuss
11、ionSpecifically, on Fig. 1, that portion of thevolume of the isoteniscope to the right of point A which is filledwith vapor.3.3 Symbols:C = temperature, C,K = temperature, K,p = pressure, Pa or torr,t = time, s,Pe= experimentally measured total system pressure,Pa= partial pressure due to fixed gases
12、 dissolved in sample,Pc= corrected vapor pressure, Pa or torr.K 5 C 1 273.15 (1)4. Summary of Test Method4.1 Dissolved and entrained fixed gases are removed fromthe sample in the isoteniscope by heating a thin layer of asample at reduced pressure, removing in this process theminimum amount of volati
13、le constituents from the sample.4.2 The vapor pressure of the sample at selected tempera-tures is determined by balancing the pressure due to the vapor1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of Subcommitte
14、eD02.11 on Engineering Sciences of High Performance Fluids and Solids.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1970. Last previous edition approved in 2002 as D 2879 97 (2002)e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AS
15、TM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of the sample against a know
16、n pressure of an inert gas. Themanometer section of the isoteniscope is used to determinepressure equality.4.3 The initial decomposition temperature is determinedfrom a plot of the logarithm of the vapor pressure versus thereciprocal of absolute temperature. The initial decompositiontemperature is t
17、aken as that temperature at which the plot firstdeparts from linearity as a result of the decomposition of thesample. An optional method provides for the use of isothermalrates of pressure rise for this purpose (see Annex A1). Theseare measured at several temperatures and the logarithm of therate of
18、 pressure rise is plotted versus the reciprocal of absolutetemperature. The decomposition temperature of the sample istaken to be that temperature at which the rate of increase ofpressure is sufficient to produce a rise of 185 Pa (0.0139 torr/s).NOTE 2Vapor pressures less than 133 Pa (1.0 torr), but
19、 greater than13.3 Pa (0.1 torr) at a selected test temperature can be determined directlywith reduced accuracy. In some cases the tendency of the sample to retaindissolved or occluded air may prevent direct determinations of vaporpressure in this range. In such cases, data points obtained at higherp
20、ressures can be extrapolated to yield approximate vapor pressures in thisrange.5. Significance and Use5.1 The vapor pressure of a substance as determined byisoteniscope reflects a property of the sample as receivedincluding most volatile components, but excluding dissolvedfixed gases such as air. Va
21、por pressure, per se, is a thermody-namic property which is dependent only upon composition andtemperature for stable systems. The isoteniscope method isdesigned to minimize composition changes which may occurduring the course of measurement.6. Apparatus6.1 Isoteniscope (Fig. 1).6.2 Constant-Tempera
22、ture Air Bath (Fig. 2) for use over thetemperature range from ambient to 748 K, controlled to 62Kin the zone occupied by the isoteniscope beyond point “A”(Fig. 1).6.3 Temperature Controller.6.4 Vacuum and Gas Handling System (Fig. 3).6.5 Mercury Manometer, closed end, 0 to 101.3 kPa (0 to760 torr) r
23、ange. (WarningPoison. May be harmful or fatal ifinhaled or swallowed. Vapor harmful; emits toxic fumes whenheated. Vapor pressure at normal room temperature exceedsthreshold limit value for occupational exposure. See A2.1.)6.6 McLeod Vacuum Gage, 0 to 2.00 kPa (0 to 15 torr),vertical primary standar
24、d type.FIG. 1 IsoteniscopeA Dewar, strip silvered, 110 mm ID by 400 mm deep.B Borosilicate glass tube, 90 mm OD by 320 mm long.C Glass rod,18-in. in diameter by 310 mm long. Three of these heater ele-ment holders are fused along their entire length to the outer surface of TubeB at 120-deg intervals.
25、 Slots cut into the fused glass rods on38-in. centersserve as guides for the heating wire D.D Resistance wire, B. and S. No. 21 gage, spirally wrapped around Tube Band its attached guides.E Glass wool pad.F Glass wool pad for centering Tube B and sealing annular opening.G Lower plate of insulated is
26、oteniscope holder.Transite disk18 in. thick, loose fit in Tube B.With hole for isoteniscope.H Upper plate of insulated isoteniscope holder.Transite disk18 in. thick, loose fit in Dewar A.With hole for isoteniscope.J Glass wool insulation between plates G and H.K Plate spacer rods.LHeater leads conne
27、cted to power output of temperature controller.T1Temperature-control thermocouple affixed to inside wall of Tube B.T2Temperature-indicating thermocouple affixed to isoteniscope.FIG. 2 Constant-Temperature Air BathD 2879 97 (2007)26.7 Mechanical Two-Stage Vacuum Pump.6.8 Direct Temperature Readout, e
28、ither potentiometric orelectronic.6.9 Thermocouple, in accordance with American NationalStandard for Temperature Measurement Thermocouples (ANSIC96.1) from Specification and Temperature ElectromotiveForce Tables E 230.6.10 Nitrogen, pre-purified grade. (WarningCompressedgas under high pressure. Gas
29、reduces oxygen available forbreathing. See A2.2.)6.11 Nitrogen Pressure Regulator, single-stage, 0 to 345kPa gage (0 to 50 psig).6.12 Alcohol Lamp.(WarningFlammable. Denatured al-cohol cannot be made nontoxic. See A2.3.)7. Hazards7.1 The procedure requires measuring pressures with de-vices containin
30、g mercury (WarningSee 6.5). Spillage of thismaterial creates a safety hazard in the form of toxic vapor inthe room. This can be prevented by use of catchment vesselsunder the devices. If these fail, and the ventilation of the roomduring occupancy is below 0.01 m3(sm2),2ft3/minft2),thorough cleaning
31、of the floor followed by inspection with amercury vapor-detecting device is recommended. The follow-ing procedures for floor cleaning have been found effective:7.1.1 A 5 % aqueous solution of sodium polysulfide pen-etrates well into porous surfaces, but should not be used onpolished metal objects.7.
32、1.2 Sweeping with flowers of sulfur, or agricultural col-loidal sulfur, is effective on nonporous floors.7.1.3 Sweeping with granular zinc, about 20 mesh (840 m)that has been rinsed in 3 % hydrochloric acid, is effective incatching macro-drops.7.2 The apparatus includes a vacuum system and a Dewarfl
33、ask (constant temperature air bath) that is subjected toelevated temperatures. Suitable means should be employed toprotect the operator from implosion of these systems. Thesemeans include wrapping of vacuum vessels, use of safetyshield in front of Dewar flask, and use of safety glasses by theoperato
34、r.8. Procedure8.1 Add to the isoteniscope a quantity of sample sufficient tofill the sample bulb and the short leg of the manometer section(WarningPoison. Can be harmful or fatal if inhaled orswallowed. Vapor harmful; emits toxic fumes when heated.Vapor pressure at normal room temperature exceeds th
35、resholdlimit value for occupational exposure. See A1.1.) to point A ofFig. 1. Attach the isoteniscope to the vacuum system as shownin Fig. 3, and evacuate both the system and the filledisoteniscope to a pressure of 13.3 Pa (0.1 torr) as measured onthe McLeod gage. Break the vacuum with nitrogen(Warn
36、ingCompressed gas under high pressure. Gas reducesoxygen available for breathing. See A1.2.). Repeat the evacu-ation and purge of the system twice to remove residual oxygen.8.2 Place the filled isoteniscope in a horizontal position sothat the sample spreads out into a thin layer in the sample bulban
37、d manometer section. Reduce the system pressure to 133 Pa(1 torr). Remove dissolved fixed gases by gently warming thesample with an alcohol (WarningFlammable. Denaturedalcohol cannot be made nontoxic. See A2.3.) lamp until it justboils. Continue for 1 min.NOTE 3During the initial evacuation of the s
38、ystem, it may benecessary to cool volatile samples to prevent boiling or loss of volatiles.NOTE 4If the sample is a pure compound, complete removal of fixedgases may readily be accomplished by vigorous boiling at 13.3 Pa (0.1torr). For samples that consist of mixtures of substances differing in vapo
39、rpressure, this procedure is likely to produce an error due to the loss ofvolatile components. Gentle boiling is to be preferred in such cases. Therate of boiling during degassing may be controlled by varying both thepressure at which the procedure is carried out and the amount of heating.In most ca
40、ses, satisfactory degassing can be obtained at 133 Pa (1 torr).However, extremely viscous materials may require degassing at lowerpressures. Samples of high volatility may have to be degassed at higherpressures. In the event that the vapor pressure data indicate that thedegassing procedure has not c
41、ompletely removed all dissolved gases, itmay be necessary to apply a correction to the data or to disregard datapoints that are so affected (see 8.7). The degassing procedure does notprevent the loss of volatile sample components completely. However, thedescribed procedure minimizes such losses, so
42、that for most purposes thedegassed sample can be considered to be representative of the originalsample less the fixed gases that have been removed.8.3 After the sample has been degassed, close the vacuumline valve and turn the isoteniscope to return the sample to thebulb and short leg of the manomet
43、er so that both are entirelyfilled with the liquid. Create a vapor-filled, nitrogen-free spacebetween the bulb and the manometer in the following manner:maintain the pressure in the isoteniscope at the same pressureused for degassing; heat the drawn-out tip of the sample bulbwith a small flame until
44、 sample vapor is released from thesample; continue to heat the tip until the vapor expandssufficiently to displace part of the sample from the upper partof the bulb and manometer arm into the manometer section ofthe isoteniscope.8.4 Place the filled isoteniscope in a vertical position in theconstant
45、-temperature bath. As the isoteniscope approachestemperature equilibrium in the bath, add nitrogen to thegas-sampling system until its pressure equals that of thesample. Periodically adjust the pressure of the nitrogen in thegas-handling system to equal that of the sample. When theisoteniscope reach
46、es temperature equilibrium, make a finalFIG. 3 Vacuum and Gas Handling SystemD 2879 97 (2007)3adjustment of the nitrogen pressure to equal the vapor pressureof the sample. Pressure balance in the system is indicated bythe manometer section of the isoteniscope. When the liquidlevels in the manometer
47、arms are equal in height, balance isindicated. Read and record the nitrogen pressure in the systemat the balance point. Use the McLeod gage to measurepressures below 2.00 kPa (15 torr) and the mercury manometerfor pressures from 2.00 kPa (15 torr) to 101 kPa (760 torr).8.4.1 It is extremely importan
48、t that adjustments of thenitrogen pressure be made frequently and carefully. If thenitrogen pressure is momentarily too great, a bubble ofnitrogen may pass through the manometer and mix with thesample vapor. If the nitrogen pressure is momentarily too low,a bubble of sample vapor may escape. If eith
49、er action occurs,the test is terminated immediately and restarted from 8.3.NOTE 5Because the densities of most samples are very much lessthan that of mercury, small errors in the final adjustment of the levels ofthe liquid level in the manometer have a negligible effect on the measuredvalues of vapor pressure above 133 Pa (1 torr).8.5 Increase the temperature of the constant-temperaturebath 25 K. As the temperature rises, maintain pressure balancein the system in the manner described in 7.4 . When tempera-ture equilibrium is reached, make a final adjustment o
