ASTM_D_6971_-_09_2014.pdf

Designation:D697109(Reapproved 2014)Standard Test Method forMeasurement of Hindered Phenolic and Aromatic AmineAntioxidant Content in Non-zinc Turbine Oils by LinearSweep Voltammetry1This standard is issued under the fixed designation D6971;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.1.Scope1.1 This test method covers the voltammetric determinationof hindered phenol and aromatic amine antioxidants in new orin-service type non-zinc turbine oils in concentrations from0.0075 mass%up to concentrations found in new oils bymeasuring the amount of current flow at a specified voltage inthe produced voltammogram.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:2D1193 Specification for Reagent WaterD2272 Test Method for Oxidation Stability of Steam Tur-bine Oils by Rotating Pressure VesselD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4378 Practice for In-Service Monitoring of Mineral Tur-bine Oils for Steam,Gas,and Combined Cycle TurbinesD6224 Practice for In-Service Monitoring of Lubricating Oilfor Auxiliary Power Plant EquipmentD6810 Test Method for Measurement of Hindered PhenolicAntioxidant Content in Non-Zinc Turbine Oils by LinearSweep Voltammetry2.2 ISO Standards:3ISO 6743 Part 4,Lubricants,Industrial Oils,and RelatedProducts3.Summary of Test Method3.1 A measured quantity of sample is dispensed into a vialcontaining a measured quantity of acetone based electrolytetest solution and a layer of sand.When the vial is shaken,thehindered phenol and aromatic amine antioxidants and other testsolution soluble oil components present in the sample areextracted into the test solution and the remaining dropletssuspended in the test solution are agglomerated by the sand.The sand/droplet suspension is allowed to settle out and thehindered phenol and aromatic amine antioxidants dissolved inthe test solution are quantified by voltammetric analysis.Theresults are calculated and reported as mass%of antioxidant oras millimoles(mmol)of antioxidant per litre of sample forprepared and fresh oils and as a percent remaining antioxidantfor in-service oils.3.2 Voltammetric analysis is a technique that applieselectro-analytic methods wherein a sample to be analyzed ismixed with an electrolyte and a test solution,and placed withinan electrolytic cell.Data is obtained by measuring the currentpassing through the cell as a function of the potential applied,and test results are based upon current,voltage,and timerelationships at the cell electrodes.The cell consists of a fluidcontainer into which is mounted a small,easily polarized,working electrode,and a large,non-polarizable,referenceelectrode.The reference electrode should be massive relativeto the working electrode so that its behavior remains essentiallyconstant with the passage of small current;that is,it remainsunpolarized during the analysis period.Additional electrodes,such as auxiliary electrodes,can be added to the electrodesystem to eliminate the effects of resistive drop for highresistance test solutions.In performing a voltammetricanalysis,the potential across the electrodes is varied linearlywith time,and the resulting current is recorded as a function ofthe potential.As the increasing voltage is applied to theprepared sample within the cell,the various additive speciesunder investigation within the oil are caused to electrochemi-cally oxidize.The data recorded during this oxidation reactioncan then be used to determine the remaining useful life of theoil type.A typical current-potential curve produced during thepractice of the voltammetric test can be seen by reference to1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.09.0C on Oxidation of Turbine Oils.Current edition approved May 1,2014.Published July 2014.Originally approvedin 2004.Last previous edition approved in 2009 as D6971 09.DOI:10.1520/D6971-09R14.2For 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.3Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Fig.1.Initially the applied potential produces an electrochem