1、Designation: D2879 10Standard Test Method forVapor Pressure-Temperature Relationship and InitialDecomposition Temperature of Liquids by Isoteniscope1This standard is issued under the fixed designation D2879; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1
3、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 to liquids that are compatible with borosilicate gl
4、assand 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-peratures below ambient provided a suitable constant-tem
5、perature 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 over a fairly wide tem-perature range, and this fact
6、 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 lubricating oilscontaining traces of dewaxing solven
7、ts, 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 in open systems,Test Method D2878, is recommended.
8、1.3 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.1.4 WARNINGMercury has been designated by manyregulatory agencies as a hazardous material that can causecentral nervous system, kidney and liver damage. Mercury, orits vapor, may b
9、e hazardous to health and corrosive tomaterials. Caution should be taken when handling mercury andmercury containing products. See the applicable product Ma-terial Safety Data Sheet (MSDS) for details and EPAswebsitehttp:/www.epa.gov/mercury/faq.htmfor addi-tional information. Users should be aware
10、that selling mercuryor mercury containing products into your state or country maybe prohibited by law.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 he
11、alth practices and determine the applica-bility of regulatory limitations prior to use. For specificwarning statements, see 6.10, 6.12, and Annex A2.2. Referenced Documents2.1 ASTM Standards:2D2878 Test Method for Estimating Apparent Vapor Pres-sures and Molecular Weights of Lubricating OilsE230 Spe
12、cification and Temperature-Electromotive Force(EMF) Tables for Standardized Thermocouples3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 ullagethat percentage of a closed system which isfilled with vapor.3.1.1.1 DiscussionSpecifically, on Fig. 1, that portion ofthe volume of t
13、he isoteniscope to the right of point A which isfilled with vapor.3.2 Symbols:C = temperature, C,K = temperature, K,p = pressure, Pa or torr,Pe= experimentally measured total system pressure,Pa= partial pressure due to fixed gases dissolved in sample,Pc= corrected vapor pressure, Pa or torr.t = time
14、, s,K 5 C 1 273.15 (1)1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.11 on Engineering Sciences of High Performance Fluids and Solids.Current edition approved Oct. 1, 2010. Published October 20
15、10. Originallyapproved in 1970. Last previous edition approved in 2007 as D2879 97 (2007).DOI: 10.1520/D2879-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the
16、standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Test Method4.1 Dissolved and entrained fixed gases are removed fromthe sample in the isoteniscope by heating a thin laye
17、r of asample at reduced pressure, removing in this process theminimum amount of volatile 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 vaporof the sample against a known pressure of an inert gas. Themano
18、meter 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 taken as that temperature at which t
19、he 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 pressure rise is plotted versus th
20、e 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 greater than13.3 Pa (0.1 torr) at
21、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 higherpressures can be extrapolated to yie
22、ld 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. Vapor pressure, per se, is a thermody
23、-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-Temperature Air Bath(Fig. 2) for use overt
24、he temperature range from ambient to 748 K, controlled to 62K in 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 Pressure Measurement InstrumentationPressuretransducers of suitable ranges are the preferred mean
25、s for themeasurement of pressure in the gas handling system. Alterna-tively bourdon-type vacuum gauges or liquid manometers maybe used. Note that more than one gauge or transducer may berequired for use over the range of 2.00 kPa (15 torr) to 101 kPa(760 torr) for pressures.FIG. 1 IsoteniscopeA Dewa
26、r, 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. Slots cut into the fused glass
27、rods on38-in. centersserve as guides for the heating wire D.D Resistance wire, B. and S. No. 21 gauge, 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 isoteniscope holder.Transite disk
28、18 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 connected to power output of tempera
29、ture controller.T1Temperature-control thermocouple affixed to inside wall of Tube B.T2Temperature-indicating thermocouple affixed to isoteniscope.FIG. 2 Constant-Temperature Air BathD2879 1026.6 McLeod Vacuum Gauge0 to 2.00 kPa (0 to 15 torr),vertical primary standard type.6.7 Mechanical Two-Stage V
30、acuum Pump.6.8 Direct Temperature Readout, either potentiometric orelectronic.6.9 Thermocouplein accordance with American NationalStandard for Temperature Measurement Thermocouples (ANSIC96.1) from Specification and Temperature ElectromotiveForce Tables E230.6.10 Nitrogenpre-purified grade. (Warning
31、Compressed gas under high pressure. Gas reduces oxygenavailable for breathing. See A2.1.)6.11 Nitrogen Pressure Regulatorsingle-stage, 0 to 345kPa gauge (0 to 50 psig).6.12 Alcohol Lamp(WarningFlammable. Denaturedalcohol cannot be made nontoxic. See A2.2.)7. Hazards7.1 The apparatus includes a vacuu
32、m system and a Dewarflask (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
33、 glasses by theoperator.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
34、temperature exceeds thresholdlimit 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 gauge. Break the va
35、cuum with nitrogen(WarningCompressed 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 lay
36、er in the sample bulband manometer section. Reduce the system pressure to 133 Pa(1 torr). Remove dissolved fixed gases by gently warming thesample with an alcohol lamp until it just boils (WarningFlammable. Denatured alcohol cannot be made nontoxic. SeeA2.2.). Continue for 1 min.NOTE 3During the ini
37、tial evacuation of the system, 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 subs
38、tances differing in vaporpressure, 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 amou
39、nt of heating.In most cases, 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 thedegas
40、sing procedure has not completely 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 mi
41、nimizes such losses, so 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
42、short leg of the manometer 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 bulb
43、with a small flame until 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
44、 position in theconstant-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. Wh
45、en theisoteniscope reaches temperature equilibrium, make a finaladjustment 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 arms are equal in height, bala
46、nce isindicated. Read and record the nitrogen pressure in the systemat the balance point. Use a transducer, gauge, or liquidmanometer of appropriate range to measure the pressure in thegas handling system. Use the McLeod gauge to measurepressures below 2.00 kPa (15 torr) and the mercury manometerfor
47、 pressures from 2.00 kPa (15 torr) to 101 kPa (760 torr).8.4.1 It is extremely important 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 th
48、e nitrogen pressure is momentarily too low,FIG. 3 Vacuum and Gas Handling SystemD2879 103a bubble of sample vapor may escape. If either action occurs,the test is terminated immediately and restarted from 8.3.NOTE 5Because the densities of samples to be tested by this proce-dure are usually of the or
49、der of or less than 1 g/mL, small errors in the finaladjustment of the liquid level in the manometer have a negligible effect onthe measured values of vapor pressures above 133 Pa (1 torr = 1mmHg).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 8.4. When tempera-ture equilibrium is reached, make a final adjustment of pressureto establish balance. Read and record the system pressure.Repeat at intervals of 25 K until the system pressure exceeds
