ASTM_D_971_-_20.pdf

Designation:D97120Standard Test Method forInterfacial Tension of Insulating Liquids Against Water bythe 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 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 U.S.Department of Defense.1.Scope1.1 This test method covers the measurement of the inter-facial tension between insulating liquid that has a relativedensity(specific gravity)less than water and water,undernon-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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.See 7.2 for a specific warning statement.1.3 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D923 Practices for Sampling Electrical Insulating Liquids3.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 surface tension,that is,upwardfrom the water insulating liquid interface.To calculate theinterfacial tension,the force so measured is corrected by anempirically determined factor which depends upon the forceapplied,the densities of both the insulating liquid and water,and the dimensions of the ring.Measurements are made underrigidly standardized nonequilibrium conditions in which themeasurement is completed within 60 s after formation of theinterface.4.Significance and Use4.1 Interfacial tension measurements on electrical insulatingliquids provide a sensitive means of detecting small amounts ofsoluble polar contaminants 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 mineral oils as an indication of thedegree of deterioration.NOTE1Different liquid matrixes are reviewed in Appendix X1.5.Apparatus(Figs.1 and 2)5.1 Tensiometer3Force measurement on the 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,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 the 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 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.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 April 1,2020.Published May 2020.Originallyapproved in 1948 as D971 48 T.Last previous edition approved in 2012 asD971 12.DOI:10.1520/D0971-20.2For 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 website.3Tensiometers 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 StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.6.2 Purity of WaterUnless otherwise indicated,referencesto water shall be understood to mean distilled water or water ofequal purity.7.Preparation of Apparatus7.