1、Designation: D6971 09 (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 indica
2、tes 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 det
3、erminationof 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
4、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:
5、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
6、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 Rela
7、tedProducts3. 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 c
8、omponents 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 quan
9、tified 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
10、-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 tim
11、erelationships 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 es
12、sentiallyconstant 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 voltam
13、metricanalysis, 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
14、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 juri
15、sdiction 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 D6
16、971 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 Nat
17、ional 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 States1Fig. 1. Initially the applied potential produces an electrochemi-cal reaction having a
18、rate so slow that virtually no current flowsthrough the cell. As the voltage is increased, as shown in Fig.1, the electro-active species (for example, substituted phenols)begin to oxidize at the working electrode surface, producing ananodic rise in the current. As the potential is further increased,
19、the decrease in the electro-active species concentration at theelectrode surface and the exponential increase of the oxidationrate lead to a maximum in the current-potential curve shown inFig. 1.4. Significance and Use4.1 The quantitative determination of hindered phenol andaromatic amine antioxidan
20、ts in a new turbine oil measures theamount of these compounds that has been added to the oil asprotection against oxidation. Beside phenols, turbine oils canbe formulated with other antioxidants such as amines whichcan extend the oil life. In in-service oil, the determinationmeasures the amount of o
21、riginal (hindered phenol and aromaticamine) antioxidants remaining after oxidation has reduced itsinitial concentration. This test method is not designed orintended to detect all of the antioxidant intermediates formedduring the thermal and oxidative stressing of the oils, which arerecognized as hav
22、ing some contribution to the remaining usefullife of the in-service oil. Nor does it measure the overallstability of an oil, which is determined by the total contributionof all species present. Before making final judgment on theremaining useful life of the in-service oil, which might result inthe r
23、eplacement of the oil reservoir, it is advised to performadditional analytical techniques (as in accordance with TestMethods D6224 and D4378; see also Test Method D2272),having the capability of measuring remaining oxidative life ofthe in-service oil.4.1.1 This test method is applicable to non-zinc
24、type ofturbine oils as defined by ISO 6743 Part 4, Table 1. These arerefined mineral oils containing rust and oxidation inhibitors,but not antiwear additives.4.2 The test is also suitable for manufacturing control andspecification acceptance.4.3 When a voltammetric analysis is obtained for a turbine
25、oil inhibited with a typical synergistic mixture of hinderedphenol and aromatic amine antioxidants, there is an increase inthe current of the produced voltammogram between 8 to 12 s(or 0.8 to 1.2 V applied voltage) (see Note 1) for the aromaticamines, and an increase in the current of the producedvo
26、ltammogram between 13 and 16 s (or 1.3 to 1.6 V appliedvoltage) (see Note 1) for the hindered phenols in the neutralacetone test solution (Fig. 1: x-axis1s=0.1V).Hinderedphenol antioxidants detected by voltammetric analysis include,but are not limited to, 2,6-di-tert-butyl-4-methylphenol; 2,6-di-ter
27、t-butylphenol; and 4,4-Methylenebis (2,6-di-tert-butylphenol). Aromatic amine antioxidants detected by volta-mmetric analysis include, but are not limited to, phenyl alphanaphthylamines, and alkylated diphenylamines.NOTE 1Voltages listed with respect to reference electrode. Thevoltammograms shown in
28、 Figs. 1 and 2 were obtained with a platinumreference electrode and a voltage scan rate of 0.1 V/s.4.4 For turbine oil containing only aromatic amines asantioxidants, there will only be an increase in the current of theproduced voltammogram between 8 to 12 seconds (or 0.8 to1.2 V applied voltage) (s
29、ee Note 1) for the aromatic amines, byusing the neutral acetone test solution (first peak in Fig. 1).4.5 For turbine oils containing only hindered phenolicantioxidants, it is preferable to use a basic alcohol test solutionNOTE 1x-axis = time (seconds) and y-axis is current (arbitrary units). Top lin
30、e in Fig. 1 is voltammogram of a fresh R 2,6-di-tert-butylphenol; alkylated diphenylamine; aromatic amine antioxi-dant; hindered phenol antioxidant; in-service oils; linear sweepvoltammetry; non-zinc turbine oils; phenyl alpha naphthylam-ine; turbine oilASTM International takes no position respectin
31、g the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard 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 standa
32、rd is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif 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 Internationa
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35、, 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 Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D02-1548.D6971 09 (2014)6
