1、Designation: D 6810 07An American National StandardStandard Test Method forMeasurement of Hindered Phenolic Antioxidant Content inNon-Zinc Turbine Oils by Linear Sweep Voltammetry1This standard is issued under the fixed designation D 6810; the number immediately following the designation indicates t
2、he 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the voltammetric determi
3、nationof hindered phenol antioxidants in new or in-service non-zincturbine oils in concentrations from 0.0075 weight % up toconcentrations found in new oils by measuring the amount ofcurrent flow at a specified voltage in the produced voltammo-gram.1.2 This standard does not purport to address all o
4、f 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:2D 1193 Specification fo
5、r Reagent WaterD 4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD 4378 Practice for In-Service Monitoring of Mineral Tur-bine Oils for Steam and Gas TurbinesD 6224 Practice for In-Service Monitoring of LubricatingOil for Auxiliary Power Plant EquipmentD 6447 Test Method for Hydr
6、operoxide Number of Avia-tion Turbine Fuels by Voltammetric AnalysisD 6971 Test Method for Measurement of Hindered Phe-nolic and Aromatic Amine Antioxidant Content in Non-zinc Turbine Oils by Linear Sweep Voltammetry3. Summary of Test Method3.1 A measured quantity of sample is dispensed into a vialc
7、ontaining a measured quantity of alcohol-based electrolytesolution and containing a layer of sand. When the vial isshaken, the hindered phenol antioxidants and other solutionsoluble oil components present in the sample are extracted intothe solution and the remaining droplets suspended in thesolutio
8、n are agglomerated by the sand. The sand/dropletsuspension is allowed to settle out and the hindered phenolantioxidants dissolved in the solution are quantified by volta-mmetric analysis. The results are calculated and reported asweight percent of antioxidant or as millimoles (mmol) ofantioxidant pe
9、r litre of sample for prepared and fresh oils andas a percent remaining antioxidant for used oils.3.2 Voltammetric analysis is a technique that applieselectro-analytic methods when a sample to be analyzed ismixed with an electrolyte and a solvent and placed within anelectrolytic cell. Data is obtain
10、ed 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 polarizedworking electrode, and a larg
11、e nonpolarizable reference elec-trode. The reference electrode should be massive relative to theworking electrode so that its behavior remains essentiallyconstant with the passage of small current; that is, it remainsunpolarized during the analysis period. Additional electrodes,auxiliary electrodes,
12、 can be added to the electrode system toeliminate the effects of resistive drop for high resistancesolutions. In performing a voltammetric analysis, the potentialacross the electrodes is varied linearly with time, and theresulting current is recorded as a function of the potential. Asthe increasing
13、voltage is applied to the prepared sample withinthe cell, the various additive species under investigation withinthe oil are caused to electrochemically oxidize. The datarecorded during this oxidation reaction can then be used todetermine the remaining useful life of the oil type. A typicalcurrent-p
14、otential curve produced during the practice of thevoltammetric test can be seen by reference to Fig. 1. Initially,the applied potential produces an electrochemical reactionhaving a rate so slow that virtually no current flows through thecell. As the voltage is increased, as shown in Fig. 1, theelect
15、ro-active species (for example, substituted phenols) beginto oxidize at the working electrode surface, producing ananodic rise in the current. As the potential is further increased,1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct
16、 responsibility of SubcommitteeD02.09.0C on Oxidation of Turbine Oils.Current edition approved July 1, 2007. Published August 2007. Originallyapproved in 2002. Last previous edition approved in 2002 as D 6810-02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
17、tomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the decrease in the electro-active
18、 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 anti-oxidants in a new turbine oil measures the amount of this
19、material that has been added to the oil as protection againstoxidation. Beside phenols, turbine oils can be formulated withother antioxidants such as amines which can extend the oil life.In used oil, the determination measures the amount of original(phenolic) antioxidant remaining after oxidation ha
20、ve reducedits initial 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 having some contribution to the remaining usefullife of the used or in-service oil. Nor
21、 does it measure theoverall stability of an oil, which is determined by the totalcontribution of all species present. Before making final judg-ment on the remaining useful life of the used oil, which mightresult in the replacement of the oil reservoir, it is advised toperform additional analytical t
22、echniques (in accordance withPractices D 6224 and D 4378), having the capability of mea-suring remaining oxidative life of the used oil.4.1.1 This test method is applicable to non-zinc turbine oils.These are refined mineral oils containing rust and oxidationinhibitors, but not antiwear additives. Th
23、is test method has notyet been established with sufficient precision for antiwear oils.4.2 This test method is also suitable for manufacturingcontrol and specification acceptance.4.3 When a voltammetric analysis is obtained for a turbineoil inhibited with a typical hindered phenol antioxidant, there
24、 isan increase in the current of the produced voltammogrambetween 3-5 s (or 0.3 to 0.6 V applied voltage) (see Note 1)inthe basic test solution (Fig. 1x-axis 1 second = 0.1 V).Hindered phenol antioxidants detected by voltammetric analy-sis include, but are not limited to, 2,6-di-tert-butyl-4-methylp
25、henol; 2,6-di-tert-butylphenol and 4,4-methylenebis(2,6-di-tert-butylphenol).NOTE 1Voltages listed with respect to reference electrode. Thevoltammograms shown in Figs. 1 and 2 were obtained with a platinumreference electrode and a voltage scan rate of 0.1 V/s.4.4 For non-zinc turbine oils containing
26、 aromatic (aryl)amine compounds (antioxidants and corrosion inhibitors),there is an increase in the current of the produced voltammo-gram between 7-11 s (0.7 to 1.1 V applied voltage in Fig. 2)(see Note 1) which does not interfere with the hindered phenolmeasurement in the basic test solution. For t
27、he measurement ofthese aromatic amine antioxidants, refer to Test MethodD 6971, where the neutral test solution shall be used.5. Apparatus5.1 Voltammetric AnalyzerThe instrument used to quan-tify the hindered phenol antioxidants is a voltammographequipped with a three-electrode system and a digital
28、or analogoutput. The combination electrode system consists of a glassyNOTEx-axis = time (seconds) and y-axis is current (arbitrary units). Top line in Fig. 1 is voltammogram of a fresh R and contain-ing1gofsand white quartz suitable for chromatography,within the size range of 200 to 300 6 100 m.6. S
29、ampling6.1 Obtain the sample in accordance with Practice D 4057.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American
30、 Chemical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent issufficiently pure to permit its use without lessening the accu-racy of the determination.7.2 Purity of WaterUnless otherwise specified, referencesto water that conf
31、orms to Specification D 1193, Type II.7.3 Analysis Materials:7.3.1 Alcohol Test Solution (Basic Test Solution)Proprietary yellow solution, ethanol solvent (1:10 distilledwater/ethanol solution) containing a dissolved base electrolyte.(WarningCorrosive, poison, flammable, skin irritant; harm-ful if i
32、nhaled.)7.3.2 Alcohol Cleansing Pads70 % isopropyl alcoholsaturated cleansing pads.8. Procedure8.1 The voltammetric analyzer used in this test methodgives linear results between 2 to 50 mmol for hindered phenolsusing an oil sample size of 0.40 and 5.0 mL of the analysissolvent. The corresponding ran
33、ge of weight percents dependson the molecular weight of the hindered phenol and the densityof the base oil. For instance, the weight % range of 0.044 to 1.1is equal to 2 to 50 mmol/L for a hindered phenol containing3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Societ
34、y, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.NO
35、TEx-axis = time (seconds) and y-axis is current (arbitrary units). Top line in Fig. 2 is fresh oil, and lower line is used oil.FIG. 2 Amine and Hindered Phenols Peaks in the Basic Test Solution with Blank Response ZeroedD6810073one hydroxyl group and with a molecular weight of 220 g/mol(2,6-di-tert-
36、butyl-4-methylphenol) and an oil density of 1g/mL. Below 2 mmol, the noise to signal ratio becomes largedecreasing the accuracy of the measurements. For measure-ments below 2 mmol or for fresh oils with high noise to signalratios, the sample size should be increased to 0.60 mL and thevolume of analy
37、sis solvent decreased to 3.0 mL.8.2 General Voltammetric Test ProcedureThe test proce-dure for voltammetric analysis will consist of the blank reading(calibration), followed by a standard reading and finally the testsample (in-service oil) reading.8.2.1 Blank Reading(0 mmol/L = 0 weight %).8.2.1.1 D
38、efinitionThe blank reading (voltammetric num-ber) is a measurement of the analysis solution by itself. Theblank measurement gives a reference number with no antioxi-dant present (the zero baseline).8.2.2 Standard Reading(30 to 150 mmol/Lweight %dependent on density of fresh oil and molecular weight
39、ofantioxidant).8.2.2.1 DefinitionThe standard reading is a measurementof a fresh, unused oil (containing phenolic antioxidant) mixedwith an appropriate analysis solvent. This measurement givesyou a voltammetric reading (standard reading) that indicatesthe voltammetric response for the concentration
40、hinderedphenol antioxidant being analyzed for the oil being tested.8.2.3 Test Sample (In-Service Oil) Reading:8.2.3.1 DefinitionThe sample reading is a measurement ofa fresh or in-service oil mixed with the same type of analysissolvent as the standard. This measurement will provide volta-mmetric rea
41、dings that normally range between the blank andstandard measurements, and reflect the concentration of hin-dered phenol antioxidant present (fresh oil) or remaining(in-service oil) in the oil sample. Voltammetric readings forin-service oil will decrease as hindered phenol antioxidants aredepleted.8.
42、3 Voltammetric ReadingAfter the operator has selectedthe valleys before and after the antioxidant peaks (as shown inFig. 1), the software (R-DMS) will automatically identify andcalculate the area above the baseline between the two valleyindicators. This calculated area is then used for the test samp
43、lereading (in-service oil), which will be established by compar-ing the in-service oil area to its standard (see Fig. 3) and makeremaining antioxidant calculations (see Section 9). If peakshifting is occurring, it is advised to repeat the voltammetrictest after performing the cleaning of the electro
44、de. If after thissecond test the peak shifting remains persistent, it is advised todrag the valley indicators manually to their shifted locations.8.4 Calibration (Blank Reading) ProcedurePipette 5.0mL of analysis solution into a 7mL vial or other suitablecontainer containing1gofsand. Insert the elec
45、trode of thevoltammetric analyzer into the analysis solution to wet thebottom surface of the electrode, remove, and rub dry thebottom electrode surface with a lintfree paper towel. Insert theelectrode into the vial so that the bottom of the electrode issubmerged in the analysis solution without rest
46、ing on the sandlayer on the bottom of the vial. Place the vial/probe upright intothe rack or foam block for testing. Perform the voltammetricanalysis (see 5.1). Record the voltammetric reading in thevoltage range of the phenols, 0.3 to 0.6 V (see Note 1) in basicsolution and Fig. 1. Remove the combi
47、nation electrode fromthe blank solution and rub dry the bottom surface of theelectrode with a lint free paper towel. Run at least two tests ofthe analysis solution to assure the electrode is clean and theminimal blank value has been obtained.NOTEStandard (top line) and sample used oil (lower line).F
48、IG. 3 Voltammetric Reading for a Used Oil Sample Comparing Hindered Phenols Peaks (in the Basic Test Solution)D68100748.4.1 Calibration FrequencyRecalibration with freshlyprepared blank solution can be performed before each testingsession, or with the use of a new batch of test solutions.8.5 Standar
49、d and In-Service Oil Sample Preparation Pro-cedures:8.5.1 Preparing Solution StepRemove the seal and cap ofthe test solution vial. Pipette 5.0 mL of analysis solution into a7mL vial or other suitable container containing1gofsand.Pipette 0.40 mL of the selected oil sample also into the 7mLvial.8.5.2 For measurements below 2 mmol or for fresh oils withhigh noise to signal ratios, the sample size should be increasedto 0.60 mL and the volume of analysis solvent decreased to 3.0mL.8.5.3 Shaking Solution StepCap the vial and shake vigor-ously using a vortex mixer
