1、Designation: D971 12Standard Test Method forInterfacial Tension of Oil Against Water by the Ring Method1This standard is issued under the fixed designation D971; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. 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 This test method covers the measurement of the
3、 inter-facial tension between mineral oil and water, under non-equilibrium conditions.1.2 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 a
4、nd determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D117 Guide for Sampling, Test Methods, and Specificationsfor Electrical Insulating Oils of Petroleum OriginD923 Practices for Sampling Electrical Insulating LiquidsD2285 Test Method for
5、Interfacial Tension of ElectricalInsulating Oils of Petroleum Origin Against Water by theDrop-Weight Method (Withdrawn 2008)33. Summary of Test Method3.1 Interfacial Tension is determined by measuring the forcenecessary to detach a planar ring of platinum wire from thesurface of the liquid of higher
6、 surface tension, that is, upwardfrom the water-oil interface. To calculate the interfacialtension, the force so measured is corrected by an empiricallydetermined factor which depends upon the force applied, thedensities of both oil and water, and the dimensions of the ring.Measurements are made und
7、er rigidly standardized nonequi-librium conditions in which the measurement is completedwithin 60 s after formation of the interface.4. Significance and Use4.1 Interfacial tension measurements on electrical insulatingoils provide a sensitive means of detecting small amounts ofsoluble polar contamina
8、nts and products of oxidation. A highvalue for new mineral insulating oil indicates the absence ofmost undesirable polar contaminants. The test is frequentlyapplied to service-aged oils as an indication of the degree ofdeterioration.5. Apparatus (Figs. 1 and 2)5.1 Tensiometer4Force measurement on th
9、e tensiometermay be made using a torsion wire, load cell, or any other meansof linearly determining tension in the range of 0 to 100 mN/m.5.1.1 Horizontal platform to hold the sample containershould be capable of movement upward or downward using amechanical screw, lever mechanism, electronic drive,
10、 or anyother means of precisely changing vertical position of thesample.5.2 Rings made of platinum or platinum-iridium alloy maybe used.The ring should be welded into a continuous circle andattached to at least two parallel stirrups. Circumference of thering should be minimum 40 mm and diameter of t
11、he ring wireshould be about 0.3 mm. Ratio of the ring major radius (R) andthe wire radius (r) should be known (R/r) to at least threesignificant figures. Stirrups should be at least 25 mm long.5.2.1 The ring may be suspended from or rigidly fixed intothe tensiometer force measuring system.5.3 Sample
12、 ContainerGlass beaker or clear cylindricalcontainer having a minimum diameter of 45 mm.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in the test.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or water ofequal pur
13、ity.1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-mittee D27.07 on Physical Test.Current edition approved May 1, 2012. Published May 2012. Originallyapproved in 1948 as D971 48 T. Last previous ed
14、ition approved in 2004 asD971 99a(2004). DOI: 10.1520/D0971-12.2For 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 standards Document Summary page onthe ASTM websit
15、e.3The last approved version of this historical standard is referenced onwww.astm.org.4Tensiometers that use the Du Nouy principle for measuring interfacial andsurface tension should be used.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United St
16、ates17. Preparation of Apparatus7.1 Glass containers can be cleaned by rinsing in xylene,hexane or another suitable hydrocarbon solvent, followed by arinse in acetone or methyl ethyl ketone. Following these rinsesthey can be cleaned using detergent in hot water and rinsedthoroughly with tap and then
17、 distilled water. Dry the glassvessel if not for immediate use.7.2 The ring should be cleaned by immersing it in a smallcontainer of xylene, hexane or another suitable hydrocarbonsolvent for at least 5 s while spinning the ring back and forth.Next, repeat this rinse using a container filled with ace
18、tone ormethyl ethyl ketone. Flame the ring in a gas flame, againspinning it to obtain rapid, uniform heating. The ring shouldbarely 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 bubblelevel
19、device on the sample platform, if not equipped with one,and adjusting the tensiometer base until the platform is level.8. Calibration of Apparatus8.1 Calibrate the tensiometer against known weights andadjust its zero point according to the procedure of its manu-facturer. Make certain that all portio
20、ns of the ring are in thesame horizontal plane.9. Procedure9.1 Preparation of Test Specimens:9.1.1 Obtain a representative test specimen of liquid, at least25 mL, to be studied in accordance with Test Method D923.9.1.2 Obtain a fresh aliquot of distilled water (50 to 75 mL)at room temperature for in
21、terfacial tension measurements.9.1.3 Test specimens should be covered, capped, or sealedimmediately after they are obtained. Atmospheric dust andvapor can easily contaminate water, as can the growth ofbacteria. Store test specimen in the dark at room temperature.9.1.4 Temperature of test specimen an
22、d temperature ofdistilled water should agree within 61C.9.2 Determination of Test Specimen Density:9.2.1 Determine test specimen density at room temperatureusing a liquid pycnometer or other density measuring device to60.001 g/cm3.9.3 Interfacial Tension Measurement:9.3.1 Introduce distilled water a
23、t room temperature into aclean sample container to a depth of 10 to 15 mm. Place it onthe tensiometer platform so that the ring comes down in thecenter of the container and is not close to any wall. Make sureno foam is present at the water surface. If foam is visible,discard the water. Foam indicate
24、s that the water is contami-nated or that the vessel is not clean.9.3.2 Clean the ring and mount it in the tensiometer. Followthe manufacturers instructions on zeroing the ring in air.9.3.3 Raise the platform until the ring is immersed to adepth not to exceed 6 mm into the water.9.3.4 Slowly lower t
25、he platform and follow the manufactur-ers instructions on how to adjust the tensiometer reading.Increase torque on the reading dial while maintaining thetorsion arm in the zero position. As the film of liquid adheringto the ring approaches the breaking point, proceed slowly withadjustments. This wil
26、l ensure that the torsion beam will be inthe zero position when rupture occurs. Rupture the surface bycontinuing to increase the force and lowering the vessel.Record the reading when rupture occurs.FIG. 1 Interfacial TensiometerFIG. 2 Top View of Interfacial TensiometerD971 1229.3.5 Surface tension
27、is calculated as described in 10.2,using the value 0.997 g/cm3for (D-d), the difference in densitybetween water and air. A value of 7173 mN/m must beobtained. If low values are found, clean and rinse the samplecontainer thoroughly and obtain a fresh sample of water froma different source of supply.
28、If low surface tension values arestill obtained, check calibration of the tensiometer and examinethe ring to ensure the plane of the ring is parallel to the watersurface.9.3.6 Carefully layer the oil on the surface of the water (withthe ring submerged) until a depth of at least 10 mm is reached.One
29、such procedure is to pipette the oil onto the surface slowlyso that minimum mixing occurs and so that oil does not touchthe surface of the submerged ring. Make sure that the oil is notso deep as to cover the ring cross bar.9.3.7 Allow the oil-water interface to age for 30 6 1 s afterthe last of the
30、oil has been layered onto the water.9.3.8 Lower the platform as in 9.3.4 and record the value atrupture. Time this part of the measurement so that, as nearly aspossible, 30 s are required to draw the ring through theinterface. Proceed very slowly as the breaking point isapproached, since the break i
31、s usually sluggish (due to viscos-ity of the oil). Complete the entire operation, from the time ofpouring the oil onto the water until the interface ruptures, inabout 60 6 10 s.10. Calculation10.1 Calculate the interfacial tension of the sample bymeans of the following equation;Interfacial tension,
32、mN/m 5 P 3Fwhere:P = scale reading when film ruptures, mN/m (Note 1), andF = factor converting scale reading in mN/m to interfacialtension obtained as described in 10.2.NOTE 1If the scale is not graduated in millinewtons per metre, or ifeither the ring or the platinum wire are of different diameters
33、 than thosefor which the scale is graduated, correct the scale readings to millinewtonsper metre for the particular ring used.10.2 Using the value of diameter ratio, R/r, specified by themanufacturer for the rings used, determine the correction factorF to three digits by means of the following equat
34、ion.Alternatively, prepare a graph5of correction factors, F. Thegraph should cover even increments of P/(D d) from 0 to 800and should give correction factors to three digits:F 5 0.725011.452PC2D 2 d!10.04534 21.679R/rwhere:P = scale reading, mN/m,C = circumference of ring, mm,D = density of water at
35、 test temperature, g/mL,d = density of test specimen at test temperature, g/mL,R = radius of ring, mm, andr = radius of wire of ring, mm.11. Report11.1 Report the following information:11.1.1 Identification of test specimen,11.1.2 Density used for calculations (water and testspecimen), and11.1.3 Tes
36、t method used and interfacial tension in mN/m.12. Precision and Bias12.1 The following criteria should be used for judging theacceptability of results (95 % confidence).12.2 Repeatability The difference between successive testresults obtained by the same operator with the same apparatusunder constan
37、t operating conditions on identical test materialwould, in the long run, in the normal and correct operation ofthe test method, exceed the following values only in one casein twenty: 0.04 X, where X denotes mean value.12.2.1 Reproducibility The difference between two singleand independent results, o
38、btained by different operators work-ing identical test material would, in the long run, in the normaland correct operation of the test method, exceed the followingvalues only in one case in twenty: 0.10 X, where X denotesmean value.12.3 BiasThere being no criteria for measuring bias inthese test-pro
39、duct combinations, no statement of bias can bemade.13. Keywords13.1 interfacial tension; surface tension; tensiometer; trans-former oilASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this stand
40、ard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andi
41、f not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, wh
42、ich you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
43、United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).5For a description of procedure, see Zuidema and Waters, Industrial andEngineering Chemistry, Analytical Edition, IENAA, Vol 13, 1941, p. 312.D971 123
