1、Designation: D7527 10 (Reapproved 2018)Standard Test Method forMeasurement of Antioxidant Content in Lubricating Greasesby Linear Sweep Voltammetry1This standard is issued under the fixed designation D7527; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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 antioxidants in new or in
3、-service lubricating greases inconcentrations from 0.0075 weight percent up to concentra-tions found in new greases by measuring the amount of currentflow at a specified voltage in the produced voltammogram.1.2 This test method is intended to monitor the antioxidantcontent in lubricating greases; it
4、 cannot be applied for lubri-cating greases that do not contain antioxidants.1.3 This test method is designed to allow the user to monitorthe antioxidant depletion rate of in-service greases through itslife cycle as part of condition monitoring programs. This testmethod is performed in order to coll
5、ect and trend early signs ofdeteriorating lubricant grease, and it may be used as a guide forthe direction of any required maintenance activities. This willensure a safe, reliable, and cost-effective operation of themonitored plant equipment.1.4 The values stated in SI units are to be regarded assta
6、ndard. 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, health, and environmental practices and d
7、eter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-men
8、dations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D942 Test Method for Oxidation Stability of LubricatingGreases by the Oxygen Pressure Vessel MethodD1193 Specification for Reagent WaterD5483 Test Method for Oxidation
9、 Induction Time of Lubri-cating Greases by Pressure Differential Scanning Calorim-etryD6810 Test Method for Measurement of Hindered PhenolicAntioxidant Content in Non-Zinc Turbine Oils by LinearSweep VoltammetryD6971 Test Method for Measurement of Hindered Phenolicand Aromatic Amine Antioxidant Cont
10、ent in Non-zincTurbine Oils by Linear Sweep Voltammetry3. Summary of Test Method3.1 A measured quantity of sample is weighed into a vialcontaining a measured quantity of acetone based electrolytesolution and containing a layer of sand. When the vial isshaken, the dissolved antioxidants and other sol
11、ution solubleoil components present in the sample are extracted into thesolution, and the remaining droplets suspended in the solutionare agglomerated by the sand. The sand/droplet suspension isallowed to settle out, and the antioxidants dissolved in thesolution are quantified by voltammetric analys
12、is.NOTE 1Voltages are 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. Significance and Use4.1 The quantitative determination of antioxidants in newgreases measures the amount of
13、 the chemical compounds thatwere added to the base oil as protection against greaseoxidation. For in-service oil greases, the voltammetric test1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubco
14、mmittee D02.G0.07 on Research Techniques.Current edition approved April 1, 2018. Published June 2018. Originallyapproved in 2010. Last previous edition approved in 2010 as D7527 10. DOI:10.1520/D7527-10R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed
16、in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1method measures the amou
17、nt of original (individual) antioxi-dants remaining after grease oxidation have reduced its con-centration. Before making final judgment on the remaininguseful life of the in-service grease, which might result in thereplacement of the grease reservoir, it is advised to performadditional analytical t
18、echniques, such as Test Method D942and D5483, which may be used to measure the remainingoxidative life of the used grease.4.1.1 This test method is applicable to mineral oil-based andsynthetic oil-based greases, based on all type of appliedthickeners. This test method is applicable to greases contai
19、ningat least one type of antioxidant. The presence of other types ofNOTE 1X-axis represents time (seconds) and Y-axis represents current (arbitrary units). Upper line curve in Fig. 1 is voltammogram of a fresh Li-OHmineral grease showing valley indicators (dotted lines) before and after a antioxidan
20、t additives.FIG. 1 Aromatic Amine and Hindered Phenol Voltammetric Response in Neutral Test Solution with Blank Response ZeroedFIG. 2 Hindered Phenol Voltammetric Response in Basic Alcohol Test Solution with Blank Response ZeroedD7527 10 (2018)2additives like corrosion inhibitors or metal deactivato
21、rs will notinterfere with this test method.4.2 When a voltammetric analysis is obtained using aneutral acetone test solution for a grease inhibited with atypical synergistic mixture of hindered phenol and aromaticamine antioxidants, there is an increase in the voltammogramcurrent between 8 s to 12 s
22、 (or 0.8 V to 1.2 V applied voltage),see Note 1, for the aromatic amines, and an increase in thevoltammogram current of the produced voltammogram be-tween 13 s to 16 s (or 1.3 V to 1.6 V applied voltage), see Note1, for the hindered phenols. In Fig. 1, x-axis=1s=0.1V.Hindered phenol antioxidants det
23、ected by voltammetric analy-sis include, but are not limited to, 2,6-di-tert-butyl-4- methyl-phenol; 2,6-di-tert-butylphenol and 4,4-Methylenebis(2,6-di-tertbutylphenol). Aromatic amine antioxidants detected byvoltammetric analysis include, but are not limited to, phenylalpha naphthylamines, and alk
24、ylated diphenylamines.4.3 For greases containing only aromatic amines asantioxidants, there will only be an increase in the current of theproduced voltammogram between 8 s to 12 s (or 0.8 V to 1.2 Vapplied voltage) for the aromatic amines, by using the neutralacetone test solution (first peak in Fig
25、. 1).4.4 For greases containing ZDDP as antioxidants, thereshall be an increase in the voltammogram current between 6 sto 10 s (or 0.6 V to 1.0 V applied voltage), see Note 1, for theZDDP, when evaluated in the neutral acetone test solution.4.5 For greases containing only hindered phenolicantioxidan
26、ts, basic alcohol test solutions are recommended foruse as described in Test Method D6810. In basic alcohol testsolutions, the voltammogram current for phenols increasesbetween 3 s to 6 s (or 0.3 V to 0.6 V applied voltage), see Note1.InFig. 2, x-axis=1s=0.1Vareasdescribed in TestMethod D6810, where
27、 x-axis = time (seconds) and y-axis iscurrent (arbitrary units). Top line in Fig. 2 is fresh grease.5. Apparatus5.1 VoltammographThe instrument used to quantify theantioxidants is a voltammograph equipped with a three-electrode system and a digital or analog output. The three-electrode system consis
28、ts of a glassy 3 mm diameter carbondisc working electrode, a platinum wire (0.5 mm diameter)auxiliary electrode, and a 0.5 mm diameter platinum wire(reference electrode, as described in Test Method D6810 andD6971). During operation, the voltammograph applies a linearvoltage ramp (0 V to 1.8 V range
29、with respect to the referenceelectrode) at a rate of 0.01 V s to 0.5 V s (0.1 optimum) to theauxiliary electrode. The current output of the working elec-trode is converted to voltage by the voltammetric analyzer,using the gain ratio of 1 V 20 A, and is outputted to an analogor digital recording devi
30、ce (0 V to 1 V full scale) as shown inFigs. 1 and 2.5.2 Vortex MixerWith a 2800 r min to 3000 r min motorand a pad suitable for mixing test tubes and vials.5.3 SpatulaOr equivalent laboratory tool, capable of de-livering samples from 50 mg to 300 mg.5.4 MicrobalanceCapable of weighing 50 mg to 300 m
31、g6 1 mg samples.5.5 Solvent DispenserOr equivalent, capable of deliveringvolumes of analysis solution (see 6.3) required in the testmethod, such as 5.0 mL 6 0.1 mL.5.6 Glass Vials with Caps4 mL or 7 mL capacity, andcontaining 1 g of sand white quartz suitable forchromatography, within the particle s
32、ize range of 200 m to300 m 6 100 m.6. Reagents and Materials6.1 Purity of ReagentsReagent-grade chemicals shall beused in all tests. Unless otherwise indicated, where applicablereagents shall conform to the specifications of the Committeeon Analytical Reagents of the American Chemical Society.3Other
33、 grades may be used, provided it is first ascertained thatthe reagents purity suffices to permit its use without lesseningthe accuracy of the determination.6.2 Purity of WaterUnless otherwise specified, water thatshall conform to Specification D1193, Type II.6.3 Analysis Materials:6.3.1 Acetone Test
34、 Solution (Neutral)Proprietary Green4test solution, acetone solvent (1:10 distilled water/acetonesolution) containing a dissolved neutral electrolyte.(WarningCorrosive, Poison, Flammable, and Skin Irritant.Harmful if inhaled.)6.3.2 Alcohol Test Solution (Basic)Proprietary Yellow4test solution, Ethan
35、ol solvent (1:10 distilled water/ethanolsolution) containing a dissolved base electrolyte. (WarningCorrosive, Poison, Flammable, and Skin Irritant. Harmful ifinhaled.)6.3.3 Alcohol Cleansing Pads70 % isopropyl alcoholsaturated cleansing pads (alcohol prepared skin cleansing pads,for the preparation
36、of the skin prior to injection (antiseptic).7. Sampling7.1 It is important to accurately sample the in-servicegrease. Since sample composition may depend upon samplingposition, it is recommended that samples be collected frommore than one location.7.2 Samples of an in-service grease can be non-homog
37、eneous. It should be agreed with the customer how toprepare the lubricating grease samples for analysis.8. Procedure8.1 The voltammograph used in this test method gives linearresults between 2 mmol kg to 50 mmol kg for different typesof antioxidants using a grease sample size of 250 mg and3Reagent C
38、hemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand Nati
39、onal Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.4The sole source of supply known to the committee at this time is Fluitec, 2850Scherer Dr., Suite 500, St. Petersburg, FL 33716; Friendship Building, Rijnkaai 37,B.2000 Antwerp, Belgium. If you are aware of alternative supplier
40、s, please providethis information to ASTM International Headquarters. Your comments will receivecareful consideration at a meeting of the responsible technical committee,1whichyou may attend.D7527 10 (2018)35.0 mL of the test solution. The corresponding range of weightpercents depends on the molecul
41、ar weight of the antioxidantslike hindered phenol and aromatic amine, and the density of thegrease. For instance, the weight percent range of 0.044 to 1.1is equal to 2 mmol kg to 50 mmol kg for a hindered phenolcontaining one hydroxyl group and with a molecular weight of220 g mole (2,6-di-tert-butyl
42、-4-methylphenol) and an oil den-sity of 1g/mL. Below 2 mmol, the noise to signal ratio becomeslarge decreasing the accuracy of the measurements. For mea-surements below 2 mmol or for fresh oils with high noise tosignal ratios, the sample size should be increased to 600 mg.8.2 General Voltammetric Te
43、st ProcedureThe test proce-dure for voltammetric analysis will consist of the blank reading(calibration), followed by a standard reading (fresh grease) andfinally the reading of the (in-service or oxidized grease)sample.8.2.1 Blank Reading(0 mmol kg = 0 mass percent). Theblank reading (voltammetric
44、number) is a measurement of thetest solution by itself. The blank measurement gives a referencenumber with no antioxidant present (the zero baseline).8.2.2 Standard Reading(30 mmol kg to 150 mmol kg).Concentration dependent on density of fresh oil and molecularweight of antioxidant). The standard re
45、ading is a measurementof a fresh, unused grease (containing one or more differenttypes of antioxidants) mixed with an appropriate analysissolvent. This measurement gives you the voltammetric readingthat indicates the response for the concentration of antioxidantsin the fresh grease being tested.8.2.
46、3 Sample Reading(Of in-service grease). The samplereading is a measurement of an in-service/ oxidized greasemixed with the same type of analysis solvent as the standard.This measurement will provide voltammetric readings thatnormally range between the Blank and Standardmeasurements, and reflects the
47、 concentration of one or moredifferent types of antioxidants present (fresh grease) or remain-ing (in-service or oxidized grease) in the grease sample.Voltammetric readings for in-service or oxidized grease willdecrease as the concentration of the antioxidants namely,hindered phenols, aromatic amine
48、s or ZDDP type of antioxi-dants are depleted.8.3 Voltammetric ReadingAs part of the procedure, oncethe operator has selected the valleys before and after theantioxidant peaks (as shown in Fig. 1), the software (R-DMS4)will automatically identify and calculate the area above thebaseline between the t
49、wo valley indicators. This calculatedarea is then used for the sample reading (in-service or oxidizedgrease), which will be established by comparing the in-servicegrease area to its standard (see Fig. 3) and makes the necessarycalculations of remaining antioxidant concentration (see Sec-tion 9).8.4 Calibration (Blank Reading):8.4.1 Pipette 5.0 mL of analysis solution into a 7 mL vial orother suitable container containing 1 g of sand.8.4.2 Insert the electrode of the voltammetric analyzer intothe analysis solution to wet the bottom surface
