ASTM D971-99a(2004)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D971 − 99a(Reapproved 2004)
Standard Test Method for
Interfacial Tension of Oil Against Water by the Ring Method
This standard is issued under the fixed designation D971; 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 (´) 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. Scope 4. Significance and Use
1.1 This test method covers the measurement of the inter-
4.1 Interfacialtensionmeasurementsonelectricalinsulating
facial tension between mineral oil and water, under non-
oils provide a sensitive means of detecting small amounts of
equilibrium conditions.
soluble polar contaminants and products of oxidation. A high
value for new mineral insulating oil indicates the absence of
1.2 This standard does not purport to address all of the
most undesirable polar contaminants. The test is frequently
safety concerns, if any, associated with its use. It is the
applied to service-aged oils as an indication of the degree of
responsibility of the user of this standard to establish appro-
deterioration.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
5. Apparatus (Figs. 1 and 2)
2. Referenced Documents 4
5.1 Tensiometer —Force measurement on the tensiometer
2.1 ASTM Standards: maybemadeusingatorsionwire,loadcell,oranyothermeans
D117Guide for Sampling, Test Methods, and Specifications of linearly determining tension in the range of 0 to 100 mN/m.
for Electrical Insulating Oils of Petroleum Origin
5.1.1 Horizontal platform to hold the sample container
D923Practices for Sampling Electrical Insulating Liquids
should be capable of movement upward or downward using a
D2285Test Method for Interfacial Tension of Electrical mechanical screw, lever mechanism, electronic drive, or any
Insulating Oils of Petroleum OriginAgainst Water by the
other means of precisely changing vertical position of the
Drop-Weight Method (Withdrawn 2008) sample.
5.2 Rings made of platinum or platinum-iridium alloy may
3. Summary of Test Method
beused.Theringshouldbeweldedintoacontinuouscircleand
3.1 InterfacialTensionisdeterminedbymeasuringtheforce
attached to at least two parallel stirrups. Circumference of the
necessary to detach a planar ring of platinum wire from the
ring should be minimum 40 mm and diameter of the ring wire
surface of the liquid of higher surface tension, that is, upward
shouldbeabout0.3mm.Ratiooftheringmajorradius(R)and
from the water-oil interface. To calculate the interfacial
the wire radius (r) should be known (R/r) to at least three
tension, the force so measured is corrected by an empirically
significant figures. Stirrups should be at least 25 mm long.
determined factor which depends upon the force applied, the
5.2.1 The ring may be suspended from or rigidly fixed into
densities of both oil and water, and the dimensions of the ring.
the tensiometer force measuring system.
Measurements are made under rigidly standardized nonequi-
5.3 Sample Container—Glass beaker or clear cylindrical
librium conditions in which the measurement is completed
container having a minimum diameter of 45 mm.
within 60 s after formation of the interface.
6. Reagents
This test method is under the jurisdiction of ASTM Committee D27 on 6.1 Purity of Reagents—Reagent grade chemicals shall be
Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-
used in the test.
mittee D27.07 on Physical Test.
Current edition approved Oct. 1, 2004. Published November 2004. Originally
6.2 Purity of Water—Unless otherwise indicated, references
approved in 1948 as D971–48 T. Last previous edition approved in 1999 as
towatershallbeunderstoodtomeandistilledwaterorwaterof
D971–99a. DOI: 10.1520/D0971-99AR04.
equal purity.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
The last approved version of this historical standard is referenced on Tensiometers that use the Du Nouy principle for measuring interfacial and
www.astm.org. surface tension should be used.
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D971 − 99a (Reapproved 2004)
thoroughly with tap and then distilled water. Dry the glass
vessel if not for immediate use.
7.2 The ring should be cleaned by immersing it in a small
container of xylene, hexane or another suitable hydrocarbon
solvent for at least 5 s while spinning the ring back and forth.
Next, repeat this rinse using a container filled with acetone or
methyl ethyl ketone. Flame the ring in a gas flame, again
spinning it to obtain rapid, uniform heating. The ring should
barely glow orange and should be heated for no more than 5 s.
Clean the ring immediately before each measurement.
7.3 The tensiometer should be leveled by placing a bubble
level device on the sample platform, if not equipped with one,
and adjusting the tensiometer base until the platform is level.
8. Calibration of Apparatus
8.1 Calibrate the tensiometer against known weights and
adjust its zero point according to the procedure of its manu-
facturer. Make certain that all portions of the ring are in the
same horizontal plane.
FIG. 1 Interfacial Tensiometer
9. Procedure
9.1 Preparation of Test Specimens:
9.1.1 Obtainarepresentativetestspecimenofliquid,atleast
25 mL, to be studied in accordance with Test Method D923.
9.1.2 Obtain a fresh aliquot of distilled water (50 to 75 mL)
for interfacial tension measurements.
9.1.3 Test specimens should be covered, capped, or sealed
immediately after they are obtained. Atmospheric dust and
vapor can easily contaminate water, as can the growth of
bacteria. Store test specimen in the dark at ambient tempera-
ture.
9.2 Determination of Test Specimen Density:
9.2.1 Determine test specimen density at 25 6 1°C using a
liquid pycnometer or other density measuring device to
60.001 g/cm .
9.3 Interfacial Tension Measurement:
9.3.1 Introduce distilled water at a temperature of 256 1°C
into a clean sample container to a depth of 10 to 15 mm. Place
it on the tensiometer platform so that the r
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