1、Designation: D7590 091Standard Guide forMeasurement of Remaining Primary Antioxidant Content InIn-Service Industrial Lubricating Oils by Linear SweepVoltammetry1This standard is issued under the fixed designation D7590; the number immediately following the designation indicates the year oforiginal a
2、doption 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.1NOTECorrected figure placement and numbering editorially in March 2011.INTRODUCT
3、IONUnder normal thermal and oxidative working conditions, which degrade the chemical compositionof the oils basestock and gradually deplete the oils additive package, good oil condition monitoringprocedures are necessary to determine and planning corrective actions before the oil propertieschanges h
4、ave passed their warning limits. Antioxidant monitoring practices are a vital part of modernoil condition monitoring practices to achieve lubrication excellence. This guide addresses the correctguidelines for voltammetric data interpretation.1. Scope1.1 This guide covers the voltammetric analysis fo
5、r quali-tative measurements of primary antioxidants in new or in-service type industrial lubricants detectable in concentrationsas low as 0.0075 mass percent up to concentrations found innew oils by measuring the amount of current flow at a specifiedvoltage in the produced voltammogram.1.2 This guid
6、e can be used as a resource for a conditionmonitoring program to track the oxidative health of a range ofindustrial lubricants which contain primary antioxidants. Inorder to avoid excessive degradation of the base-oil, theseprimary antioxidants play a major role to protect the lubricantsagainst ther
7、mal-oxidative degradation. This guide can helpusers with interpretation and troubleshooting results obtainedusing linear sweep voltammetry (LSV).1.3 When used as part of oil condition monitoring practices,it is important to apply trend analysis to monitor the antioxi-dant depletion rate relative to
8、a baseline sample rather than usevoltammetry for an absolute measurement of the antioxidantconcentration. The trending pattern provides a proactive meansto identify the level of oil degradation or abnormal changes inthe condition of the in-service lubricant.1.4 The values stated in SI units are to b
9、e regarded asstandard. No other units of measurement are included in thisstandard.1.5 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 d
10、etermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4378 Practice for In-Service Monitoring of Mineral Tur-bine Oils for Steam and Gas
11、TurbinesD6224 Practice for In-Service Monitoring of LubricatingOil for Auxiliary Power Plant EquipmentD6304 Test Method for Determination of Water in Petro-leum Products, Lubricating Oils, and Additives by Coulo-metric Karl Fischer TitrationD6810 Test Method for Measurement of Hindered PhenolicAntio
12、xidant Content in Non-Zinc Turbine Oils by LinearSweep VoltammetryD6971 Test Method for Measurement of Hindered Phenolicand Aromatic Amine Antioxidant Content in Non-zincTurbine Oils by Linear Sweep VoltammetryD7214 Test Method for Determination of the Oxidation ofUsed Lubricants by FT-IR Using Peak
13、 Area IncreaseCalculation1This guide is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.09.0Con Oxidation of Turbine Oils.Current edition approved Dec. 1, 2009. Published February 2010.2For referenced ASTM standard
14、s, 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
15、9428-2959, United States.2.2 ISO Standards:3ISO 4406.2 Hydraulic fluid power - Fluids - Method forcoding the level of contamination by solid particles2.3 Other Standards:4VGB Guideline VGB-M 416 M In-Service Monitoring ofTurbine Oils3. Oil Condition Monitoring Programs3.1 Most industrial lubricants
16、consist of mineral or syntheticoils compounded with oxidation and rust inhibitors. Dependingupon their application and the performance level desired,specific required amounts of other additives such as metaldeactivators, pour depressants, extreme pressure additives, andfoam suppressants can also be
17、present.3.2 With modern formulations of industrial lubricants, theantioxidants play a major role in protecting the base-oil againstexcessive degradation. To prevent this base-oil degradation,resulting in the eventual build-up of deposits, varnish andsludge, the monitoring of the antioxidants represe
18、nts a proac-tive information on the remaining oxidative health of thein-service lubricant. Oxidation is a chemical reaction betweenoxygen atoms with the base oil hydrocarbon molecules, whichare converting the hydrocarbon molecules into oxidation prod-ucts and subsequently weak organic acids. The rat
19、e of oxida-tion depends on the presence of antioxidant additives, whichcontrols the speed of oxidation, but eventually the antioxidantsare consumed. Consequently as part of modern proactivemaintenance strategies, it is vital to know at any time duringthe operating cycle of the lubricants, its condit
20、ion by assessingthe remaining activity of antioxidants, to prevent the oxidativedegradation of the base oil.3.3 Antioxidant monitoring guidelines have been part ofInternational Standards such as Practice D4378, PracticeD6224, and VGB Guideline VGB-M 416 M, as well Interna-tional OEM Maintenance Spec
21、ifications. This guide presentsguidelines for the lubricant professionals using voltammetrictechniques as part of their regular maintenance strategies, suchas data interpretation, oil analysis frequency, combination withother condition monitoring tests, etc.4. Summary of Linear Sweep Voltammetric (L
22、SV) TestMethod4.1 Linear Sweep Voltammetric (LSV) test can be per-formed on any type of industrial lubricant containing at leastone type of antioxidant. The voltammetric test is a comparativetest method. By establishing a comparison between its refer-ence oil (fresh oil or standard) and its used oil
23、, this guide canbe used without the specific knowledge on the category towhich the antioxidants belong.4.2 ASTM International has two standards, Test MethodD6810 and D6971, that shall enable the measurement of theremaining phenolic and aminic type of antioxidants. Nostandard test method has been dev
24、eloped for the detection ofother type of antioxidants by linear voltammetry, althoughLSV also has detection capabilities for these types of second-ary antioxidants (such as zinc dialkyl dithiophosphates).54.3 A measured quantity of sample is dispensed into a vialcontaining a measured quantity of a s
25、elected test solution andcontaining a layer of sand. When the vial is shaken, theantioxidants and other solution soluble oil components presentin the sample are extracted into the electrolytic test solutionand the remaining droplets suspended in the test solution areagglomerated by the sand. The san
26、d/droplet suspension isallowed to settle out and the antioxidants dissolved in the testsolution are quantified by voltammetric analysis. The resultsare calculated and reported as mass percent of antioxidant or asmillimoles (mmol) of antioxidant per litre of sample forprepared and fresh oils and as a
27、 percent remaining antioxidantfor in-service oils.4.4 Voltammetric analysis is a technique that applies elec-troanalytic methods wherein a sample to be analyzed is mixedwith an electrolyte and a solvent (acetone or ethanol based),and placed within an electrolytic cell. Data is obtained bymeasuring t
28、he current passing through the cell as a function ofthe potential applied, and test results are based upon current,voltage and time relationships at the cell electrodes. The cellconsists of a fluid container into which is mounted a small,easily polarized working electrode, and a large non-polarizabl
29、ereference electrode. The reference electrode should be massiverelative to the working electrode so that its behavior remainsessentially constant with the passage of small current; that is, itremains unpolarized during the analysis period. Additionalelectrodes, auxiliary electrodes, can be added to
30、the electrodesystem to eliminate the effects of resistive drop for highresistance solutions. In performing a voltammetric analysis, thepotential across the electrodes is varied linearly with time, andthe resulting current is recorded as a function of the potential.As the increasing voltage is applie
31、d to the prepared samplewithin the cell, the various additive species under investigationwithin the 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-potential curve pr
32、oduced during the practice of thevoltammetric test can be seen by reference to Fig. 1. Initiallythe 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, theelectroactive species (
33、for example, substituted phenols) beginto oxidize at the working electrode surface, producing ananodic rise in the current. As the potential is further increased,the decrease in the electroactive species concentration at theelectrode surface and the exponential increase of the oxidationrate lead to
34、a maximum in the current-potential curve shown inFig. 1.5. Significance and Use5.1 The quantitative determination of remaining antioxi-dants for in-service industrial oils by measuring the amount of3Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, Case po
35、stale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.org.4Available from VGB PowerTech e.V., P. O. Box 10 39 32, D-45039 Essen,Klinkestrae 27 - 31, D-45136 Essen, http:/www.vgb.org.5“Remaining Useful Life Measurements of Diesel Engine Oils, AutomotiveEngine Oils, Hydraulic Fluids, and Greases Us
36、ing Cyclic Voltammetric Methods,”STLE, Lubrication Engineering, Vol 51, 3, pp. 223 229.D7590 0912these additives that have been added to the oil as protectionagainst oxidation. Industrial lubricants, such as turbine oils,compressor oils, gear oils, hydraulic oils, bearing lubricantsand greases can b
37、e formulated with a wide variety of antioxi-dants types such as phenols and amines (as primary antioxi-dants), which are working synergistically and therefore allimportant to be monitored individually. For in-service oils, theLSV determines and compares the amount of original primaryantioxidants rem
38、aining after oxidation have reduced its initialconcentration.5.2 This guide covers procedures for primary antioxidantssuch as amines and phenols, as described by Test MethodD6971 and D6810.5.3 LSV is not designed or intended to detect all of theantioxidant intermediates formed during the thermal and
39、 oxi-dative stressing of the oils, which are recognized as havingsome contribution to the remaining useful life of the used orin-service oil. In order to measure the overall stability of an oil(including contribution of intermediates present), and beforemaking final judgment on the remaining useful
40、life of the usedoil (which might result in the replacement of the oil reservoir),it is advised to perform additional analytical techniques (inaccordance with Practice D4378 and Practice D6224).5.4 This guide is applicable to a wide range of industrialoils, both mineral or synthetic based, which can
41、contain rustand oxidation inhibitors, antiwear additives such as zincdialkyl dithiophosphates on gear oils, circulating oils, trans-mission oils and other industrial lubricating oils.5.5 The test is also suitable for manufacturing control andspecification acceptance.5.6 When a voltammetric analysis
42、is obtained for a indus-trial lubricant inhibited with at least one type of antioxidant,there is an increase in the current of the produced voltammo-gram between 5 to 8 s (or 0.5 to 0.8 V applied voltage) (seeNote 1) for the zinc dialkyl dithiophosphate type of antioxidant(Fig. 1), an increase in th
43、e current of the produced voltammo-gram between 8 to 12 s (or 0.8 to 1.2 V applied voltage) (Fig.2) (see Note 1) for the aromatic amines, and increase in thecurrent of the produced voltammogram between 13 and 16 s(or 1.3 to 1.6 V applied voltage) (see Note 1) for the hinderedphenols or carbamates in
44、 the neutral acetone solution (Fig. 2 :x-axis1s=0.1V),orboth. Hindered phenol antioxidantsdetected by voltammetric analysis include, but are not limitedto, 2,6-di-tert-butyl-4-methylphenol; 2,6-di-tert-butylphenoland 4,4-Methylenebis(2,6-di-tert-butylphenol). Aromaticamine antioxidants detected by v
45、oltammetric analysis include,but are not limited to, phenyl alpha naphthylamines, andalkylated diphenylamines.NOTE 1Voltages listed with respect to reference electrode. Thevoltammograms shown in Figs. 1-6 were obtained with a platinumreference electrode and a voltage scan rate of 0.1 V/s.5.7 For ind
46、ustrial lubricants containing zinc dialkyl dithio-phosphate type of antioxidants, there is an increase in thecurrent of the produced voltammogram between 5 to 8 s (or 0.5to 0.8 V applied voltage) (see Note 1) by using the neutralacetone test solution ( see Fig. 1). There is no correspondingASTM Inte
47、rnational standard describing the test method pro-cedures for measuring zinc dialkyl dithiophosphates type ofantioxidants in industrial lubricants.5.8 For industrial lubricants containing only aromaticamines as antioxidants, there is an increase in the current of theproduced voltammogram between 8 t
48、o 12 s (or 0.8 to 1.2 Vapplied voltage) (see Note 1) for the aromatic amines, by usingthe neutral acetone test solution (first peak in Fig. 2)asdescribed in Test Method D6971.FIG. 1 Zinc Dialkyl Dithiophosphate (ZDDP) Voltammetric Response in the Neutral Test Solution with Blank Response ZeroedD7590
49、 09135.9 For industrial lubricants containing only hindered phe-nolic antioxidants, it is preferable to use a basic alcoholsolution rather than the neutral acetone solutions, to achieve anincrease in the current of the produced voltammogram between3 to 6 s (or 0.3 to 0.6 V applied voltage) (see Note 1) in basicalcohol solution (Fig. 3 : x-axis1s=0.1V)asdescribed in TestMethod D6810.FIG. 2 Aromatic Amine and Hindered Phenol Voltammetric Response in the Neutral Test Solution with Blank Response ZeroedFIG. 3 Hindered Phenol Voltammetric Response in Basic Test Solution wi
