ASTM D2879-97(2002)e1

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An American National Standard
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Designation:D2879 –97 (Reapproved 2002)
Standard Test Method for
Vapor Pressure-Temperature Relationship and Initial
Decomposition Temperature of Liquids by Isoteniscope
This standard is issued under the fixed designation D2879; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Warnings were moved from notes to section text editorially December 2002.
1. Scope 2. Referenced Documents
1.1 This test method covers the determination of the vapor 2.1 ASTM Standards:
pressureofpureliquids,thevaporpressureexertedbymixtures D2878 Test Method for Estimating Apparent Vapor Pres-
in a closed vessel at 406 5% ullage, and the initial thermal sures and Molecular Weights of Lubricating Oils
decomposition temperature of pure and mixed liquids. It is E230 Specification and Temperature Electromotive Force
applicabletoliquidsthatarecompatiblewithborosilicateglass (EMF) Tables for Standardized Thermocouples
and that have a vapor pressure between 133 Pa (1.0 torr) and
3. Terminology
101.3 kPa (760 torr) at the selected test temperatures. The test
method is suitable for use over the range from ambient to 748 3.1 Definition of Term Specific to This Standard
3.2 ullage—that percentage of a closed system which is
K. The temperature range may be extended to include tem-
peratures below ambient provided a suitable constant- filled with vapor.
3.2.1 Discussion—Specifically,onFig.1,thatportionofthe
temperature bath for such temperatures is used.
volumeoftheisoteniscopetotherightofpointAwhichisfilled
NOTE 1—The isoteniscope is a constant-volume apparatus and results
with vapor.
obtained with it on other than pure liquids differ from those obtained in a
3.3 Symbols:
constant-pressure distillation.
1.2 Most petroleum products boil over a fairly wide tem-
perature range, and this fact shall be recognized in discussion
C = temperature, °C,
of their vapor pressures. Even an ideal mixture following
K = temperature, K,
p = pressure, Pa or torr,
Raoult’s law will show a progressive decrease in vapor
t = time, s,
pressureasthelightercomponentisremoved,andthisisvastly
P = experimentally measured total system pressure,
accentuated in complex mixtures such as lubricating oils e
P = partialpressureduetofixedgasesdissolvedinsample,
containing traces of dewaxing solvents, etc. Such a mixture a
P = corrected vapor pressure, Pa or torr.
c
may well exert a pressure in a closed vessel of as much as 100
timesthatcalculatedfromitsaveragecomposition,anditisthe K5C1273.15 (1)
closed vessel which is simulated by the isoteniscope. For
4. Summary of Test Method
measurement of the apparent vapor pressure in open systems,
Test Method D2878, is recommended. 4.1 Dissolved and entrained fixed gases are removed from
1.3 The values stated in SI units are to be regarded as the the sample in the isoteniscope by heating a thin layer of a
standard. The values in parentheses are for information only. sample at reduced pressure, removing in this process the
1.4 This standard does not purport to address all of the minimum amount of volatile constituents from the sample.
safety concerns, if any, associated with its use. It is the 4.2 The vapor pressure of the sample at selected tempera-
responsibility of the user of this standard to establish appro- tures is determined by balancing the pressure due to the vapor
priate safety and health practices and determine the applica- of the sample against a known pressure of an inert gas. The
bility of regulatory limitations prior to use. For specific hazard manometer section of the isoteniscope is used to determine
statements, see 6.5, 6.10, and 6.12. pressure equality.
4.3 The initial decomposition temperature is determined
from a plot of the logarithm of the vapor pressure versus the
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.11 on Engineering Sciences of High Performance Fluids and Solids.
Current edition approved April 10, 1997. Published October 1997. Originally Annual Book of ASTM Standards, Vol 05.01.
published as D2879–70. Last previous edition D2879–96. Annual Book of ASTM Standards, Vol 14.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D2879 –97 (2002)
FIG. 1 Isoteniscope
reciprocal of absolute temperature. The initial decomposition
temperature is taken as that temperature at which the plot first
departs from linearity as a result of the decomposition of the
sample.An optional method provides for the use of isothermal
rates of pressure rise for this purpose (see Annex A1). These
A Dewar, strip silvered, 110 mm ID by 400 mm deep.
are measured at several temperatures and the logarithm of the
B Borosilicate glass tube, 90 mm OD by 320 mm long.
C Glass rod, ⁄8-in. in diameter by 310 mm long. Three of these heater ele-
rate of pressure rise is plotted versus the reciprocal of absolute
ment holders are fused along their entire length to the outer surface of Tube
temperature. The decomposition temperature of the sample is
B at 120-deg intervals. Slots cut into the fused glass rods on ⁄8-in. centers
taken to be that temperature at which the rate of increase of serve as guides for the heating wire D.
D Resistance wire, B. and S. No. 21 gage, spirally wrapped around Tube B
pressureissufficienttoproduceariseof185Pa(0.0139torr/s).
and its attached guides.
E Glass wool pad.
NOTE 2—Vapor pressures less than 133 Pa (1.0 torr), but greater than
F Glass wool pad for centering Tube B and sealing annular opening.
13.3Pa(0.1torr)ataselectedtesttemperaturecanbedetermineddirectly
G Lower plate of insulated isoteniscope holder.
with reduced accuracy. In some cases the tendency of the sample to retain
Transite disk ⁄8 in. thick, loose fit in Tube B.
dissolved or occluded air may prevent direct determinations of vapor
With hole for isoteniscope.
pressure in this range. In such cases, data points obtained at higher
H Upper plate of insulated isoteniscope holder.
pressures can be extrapolated to yield approximate vapor pressures in this Transite disk ⁄8 in. thick, loose fit in Dewar A.
With hole for isoteniscope.
range.
J Glass wool insulation between plates G and H.
K Plate spacer rods.
5. Significance and Use
Heater leads connected to power output of temperature controller.
L
5.1 The vapor pressure of a substance as determined by
T Temperature-control thermocouple affixed to inside wall of Tube B.
isoteniscope reflects a property of the sample as received
T Temperature-indicating thermocouple affixed to isoteniscope.
including most volatile components, but excluding dissolved
FIG. 2 Constant-Temperature Air Bath
fixed gases such as air. Vapor pressure, per se, is a thermody-
namicpropertywhichisdependentonlyuponcompositionand
temperature for stable systems. The isoteniscope method is
heated. Vapor pressure at normal room temperature exceeds
designed to minimize composition changes which may occur
threshold limit value for occupational exposure. See A2.1.)
during the course of measurement.
6.6 McLeod Vacuum Gage, 0 to 2.00 kPa (0 to 15 torr),
6. Apparatus vertical primary standard type.
6.7 Mechanical Two-Stage Vacuum Pump.
6.1 Isoteniscope (Fig. 1).
6.8 Direct Temperature Readout, either potentiometric or
6.2 Constant-TemperatureAirBath (Fig.2)foruseoverthe
electronic.
temperature range from ambient to 748 K, controlled to62K
6.9 Thermocouple, in accordance with American National
in the zone occupied by the isoteniscope beyond point “A”
(Fig. 1). StandardforTemperatureMeasurementThermocouples(ANSI
C96.1) from Specification and Temperature Electromotive
6.3 Temperature Controller.
6.4 Vacuum and Gas Handling System (Fig. 3). Force Tables E230.
6.5 Mercury Manometer, closed end, 0 to 101.3 kPa (0 to 6.10 Nitrogen, pre-purified grade. (Warning—Compressed
760torr)range.(Warning—Poison.Maybeharmfulorfatalif gas under high pressure. Gas reduces oxygen available for
inhaled or swallowed. Vapor harmful; emits toxic fumes when breathing. See A2.2.)
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D2879 –97 (2002)
the McLeod gage. Break the vacuum with nitrogen
(Warning—Compressed gas under high pressure. Gas reduces
oxygen available for breathing. See A1.2.). Repeat the evacu-
ationandpurgeofthesystemtwicetoremoveresidualoxygen.
8.2 Place the filled isoteniscope in a horizontal position so
that the sample spreads out into a thin layer in the sample bulb
and manometer section. Reduce the system pressure to 133 Pa
(1 torr). Remove dissolved fixed gases by gently warming the
sample with an alcohol (Warning—Flammable. Denatured
alcohol cannot be made nontoxic. SeeA2.3.) lamp until it just
boils. Continue for 1 min.
NOTE 3—During the initial evacuation of the system, it may be
necessary to cool volatile samples to prevent boiling or loss of volatiles.
NOTE 4—If the sample is a pure compound, complete removal of fixed
gases may readily be accomplished by vigorous boiling at 13.3 Pa (0.1
FIG. 3 Vacuum and Gas Handling System
torr).Forsamplesthatconsistofmixturesofsubstancesdifferinginvapor
pressure, this procedure is likely to produce an error due to the loss of
volatile components. Gentle boiling is to be preferred in such cases. The
6.11 Nitrogen Pressure Regulator, single-stage, 0 to 345
rate of boiling during degassing may be controlled by varying both the
kPa gage (0 to 50 psig).
pressure at which the procedure is carried out and the amount of heating.
In most cases, satisfactory degassing can be obtained at 133 Pa (1 torr).
6.12 Alcohol Lamp.(Warning—Flammable. Denatured al-
However, extremely viscous materials may require degassing at lower
cohol cannot be made nontoxic. See A2.3.)
pressures. Samples of high volatility may have to be degassed at higher
pressures. In the event that the vapor pressure data indicate that the
7. Hazards
degassing procedure has not completely removed all dissolved gases, it
7.1 The procedure requires measuring pressures with de-
may be necessary to apply a correction to the data or to disregard data
vicescontainingmercury(Warning—See6.5).Spillageofthis
points that are so affected (see 8.7). The degassing procedure does not
prevent the loss of volatile sample components completely. However, the
material creates a safety hazard in the form of toxic vapor in
described procedure minimizes such losses, so that for most purposes the
the room. This can be prevented by use of catchment vessels
degassed sample can be considered to be representative of the original
under the devices. If these fail, and the ventilation of the room
sample less the fixed gases that have been removed.
3 2 3 2
during occupancy is below 0.01 m (s·m ), 2 ft /min·ft ),
thorough cleaning of the floor followed by inspection with a 8.3 After the sample has been degassed, close the vacuum
mercury vapor-detecting device is recommended. The follow- line valve and turn the isoteniscope to return the sample to the
ing procedures for floor cleaning have been found effective: bulb and short leg of the manometer so that both are entirely
7.1.1 A 5% aqueous solution of sodium polysulfide pen- filled with the liquid. Create a vapor-filled, nitrogen-free space
etrates well into porous surfaces, but should not be used on between the bulb and the manometer in the following manner:
polished metal objects. maintain the pressure in the isoteniscope at the same pressure
7.1.2 Sweeping with flowers of sulfur, or agricultural col- used for degassing; heat the drawn-out tip of the sample bulb
loidal sulfur, is effective on nonporous floors. with a small flame until sample vapor is released from the
7.1.3 Sweepingwithgranularzinc,about20mesh(840µm) sample; continue to heat the tip until the vapor expands
that has been rinsed in 3% hydrochloric acid, is effective in sufficiently to displace part of the sample from the upper part
catching macro-drops. of the bulb and manometer arm into the manometer section of
7.2 The apparatus includes a vacuum system and a Dewar the isoteniscope.
flask (constant temperature air bath) that is subjected to 8.4 Place the filled isoteniscope in a vertical position in the
elevated temperatures. Suitable means should be employed to
constant-temperature bath. As the isoteniscope approaches
protect the operator from implosion of these systems. These temperature equilibrium in the bath, add nitrogen to the
means include wrapping of vacuum vessels, use of safety
gas-sampling system until its pressure equals that of the
shield in front of Dewar flask, and use of safety glasses by the
sample. Periodically adjust the pressure of the nitrogen in the
operator.
gas-handling system to equal that of the sample. When the
isoteniscope reaches temperature equilibrium, make a final
8. Procedure
adjustmentofthenitrogenpressuretoequalthevaporpressure
of the sample. Pressure balance in the system is indicated by
8.1 Addtotheisoteniscopeaquantityofsamplesufficientto
fill the sample bulb and the short leg of the manometer section the manometer section of the isoteniscope. When the liquid
levels in the manometer arms are equal in height, balance is
(Warning—Poison. Can be harmful or fatal if inhaled or
swallowed. Vapor harmful; emits toxic fumes when heated. indicated. Read and record the nitrogen pressure in the system
at the balance point. Use the McLeod gage to measure
Vapor pressure at normal room temperature exceeds threshold
limit value for occupational exposure. SeeA1.1.) to point A of pressuresbelow2.00kPa(15torr)andthemercurymanometer
for pressures from 2.00 kPa (15 torr) to 101 kPa (760 torr).
Fig. 1.Attach the isoteniscope to the vacuum system as shown
in Fig. 3, and evacuate both the system and the filled 8.4.1 It is extremely important that adjustments of the
isoteniscope to a pressure of 13.3 Pa (0.1 torr) as measured on nitrogen pressure be made frequently and carefully. If the
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D2879 –97 (2002)
nitrogen pressure is momentarily too great, a bubble of
nitrogen may pass through the manometer and mix with the
sample vapor. If the nitrogen pressure is momentarily too low,
a bubble of sample vapor may escape. If either action occurs,
the test is terminated immediately and restarted from 8.3.
NOTE 5—Because the densities of most samples are very much less
than that of mercury, small errors in the final adjustment of the levels of
theliquidlevelinthemanometerhaveanegligibleeffectonthemeasured
values of vapor pressure above 133 P
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