ASTM_D_971_-_12.pdf

Designation:D97112Standard 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 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 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 and 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Method for Interfacial Tension of ElectricalInsulating Oils of Petroleum Origin Against Water by theDrop-Weight Method(Withdrawn 2008)33.Summary of Test Method3.1 Interfacial Tension is determined by measuring the forcenecessary to detach a planar ring of platinum wire from thesurface of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 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 under 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 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 oils as an indication of the degree ofdeterioration.5.Apparatus(Figs.1 and 2)5.1 Tensiometer4Force 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.6.2 Purity of WaterUnless otherwise indicated,referencesto water shall be understood to mean distilled water or water ofequal purity.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 edition 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 website.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 States1 7.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 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 rin