1、Designation: D7527 10Standard 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, in the case of revi
2、sion, 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-service lubricati
3、ng 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 cannot be applied
4、 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 collect and trend earl
5、y 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 asstandard. No other un
6、its 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 determine the applica-bility of reg
7、ulatory limitations prior to use.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 Induction Time of Lu-bricating Greases by Pressure Diffe
8、rential Scanning Calo-rimetryD6810 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 Content in Non-zincTurbine Oils by Linear Sweep Voltammetry3.
9、 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 solution solubleoil components present in the sample are ext
10、racted 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 analysis.NOTE 1Voltages are listed with respect to reference el
11、ectrode. 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 the chemical compounds thatwere added to the base oil as
12、 protection against greaseoxidation. For in-service oil greases, the voltammetric testmethod measures the amount 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,
13、 which might result in thereplacement of the grease reservoir, it is advised to performadditional analytical techniques, 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 andsynthet
14、ic oil-based greases, based on all type of appliedthickeners. This test method is applicable to greases containing1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.G0.07 on Research Techniques.Cur
15、rent edition approved May 1, 2010. Published June 2010. DOI: 10.1520/D7527-10.2For 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 on
16、the ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.at least one type of antioxidant. The presence of other types ofadditives like corrosion inhibitors or metal deactivators will notinterfere with this test method.4.2 Wh
17、en 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 to 12 s (or 0.8 to 1.2 V applied voltage), seeNote 1, for
18、the aromatic amines, and an increase in thevoltammogram current of the produced voltammogram be-tween 13 to 16 s (or 1.3 to 1.6 V applied voltage), see Note 1,for the hindered phenols. In Fig. 1, x-axis=1s=0.1V.Hindered phenol antioxidants detected by voltammetric analy-sis include, but are not limi
19、ted to, 2,6-di-tert-butyl-4- meth-ylphenol; 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 alkylated diphenylamines.4.3 For greases containing only aro
20、matic amines as antioxi-dants, there will only be an increase in the current of theNOTEX-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
21、 a antioxidant 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 102produced voltammogram between 8 to 12 s (or 0.8 t
22、o 1.2 Vapplied voltage) for the aromatic amines, by using the neutralacetone test solution (first peak in Fig. 1).4.4 For greases containing ZDDP as antioxidants, thereshall be an increase in the voltammogram current between 6 to10 s (or 0.6 to 1.0 V applied voltage), see Note 1, for the ZDDP,when e
23、valuated in the neutral acetone test solution.4.5 For greases containing only hindered phenolic antioxi-dants, basic alcohol test solutions are recommended for use asdescribed in Test Method D6810. In basic alcohol test solu-tions, the voltammogram current for phenols increases between3 to 6 s (or 0
24、.3 to 0.6 V applied voltage), see Note 1.InFig. 2,x-axis=1s=0.1Vareasdescribed in Test Method D6810,where x-axis = time (seconds) and y-axis is current (arbitraryunits). Top line in Fig. 2 is fresh grease.5. Apparatus5.1 VoltammographThe instrument used to quantify theantioxidants is a voltammograph
25、 equipped with a three-electrode system and a digital or analog output. The three-electrode system consists 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 Meth
26、od D6810 andD6971). During operation, the voltammograph applies a linearvoltage ramp (0 to -1.8 V range with respect to the referenceelectrode) at a rate of 0.01 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 voltammetr
27、ic analyzer,using the gain ratio of 1V/20 A, and is outputted to an analogor digital recording device (0 to 1 V full scale) as shown inFigs. 1 and 2.5.2 Vortex MixerWith a 2800 to 3000 r/min motor and apad suitable for mixing test tubes and vials.5.3 SpatulaOr equivalent laboratory tool, capable of
28、de-livering samples from 50 to 300 mg.5.4 MicrobalanceCapable of weighing 50 to 300 6 1mgsamples.5.5 Solvent DispenserOr equivalent, capable of deliver-ing volumes of analysis solution (see 6.3) required in the testmethod, such as 5.0 6 0.1 mL.5.6 Glass Vials with Caps4 or 7 mL capacity, andcontaini
29、ng1gofsand white quartz suitable for chromatogra-phy, within the particle size range of 200 to 300 6 100microns.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 o
30、f the Committeeon Analytical Reagents of the American Chemical Society.3Other 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 conf
31、orm to Specification D1193, Type II.6.3 Analysis Materials:6.3.1 Acetone Test 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 inhale
32、d.)6.3.2 Alcohol Test Solution (Basic)Proprietary Yellow4test solution, Ethanol 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 alcoholsaturat
33、ed cleansing pads (alcohol prepared skin cleansing pads,for the preparation 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 fro
34、mmore than one location.7.2 Samples of an in-service grease can be non-homogeneous. 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 to 50 mmol/kg for different typ
35、es ofantioxidants using a grease sample size of 250 mg and 5.0 mLof the test solution. The corresponding range of weightpercents depends on the molecular weight of the antioxidantslike hindered phenol and aromatic amine, and the density of thegrease. For instance, the weight percent range of 0.044 t
36、o 1.1is equal to 2 to 50 mmol/kg for a hindered phenol containingone hydroxyl group and with a molecular weight of 220 g/mole(2,6-di-tert-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-m
37、ents below 2 mmol or for fresh oils with high noise to signalratios, the sample size should be increased to 600 mg.8.2 General Voltammetric Test ProcedureThe test proce-dure for voltammetric analysis will consist of the blank reading(calibration), followed by a standard reading (fresh grease) andfin
38、ally the reading of the (in-service or oxidized grease)sample.8.2.1 Blank Reading(0 mmol/kg = 0 mass percent). Theblank reading (voltammetric number) is a measurement of thetest solution by itself. The blank measurement gives a referencenumber with no antioxidant present (the zero baseline).3Reagent
39、 Chemicals, 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 Na
40、tional 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 suppli
41、ers, please providethis information to ASTM International Headquarters. Your comments will receivecareful consideration at a meeting of the responsible technical committee,1whichyou may attend.D7527 1038.2.2 Standard Reading(30-150 mmol/kg). Concentrationdependent on density of fresh oil and molecul
42、ar weight ofantioxidant). The standard reading is a measurement of a fresh,unused grease (containing one or more different types ofantioxidants) mixed with an appropriate analysis solvent. Thismeasurement gives you the voltammetric reading that indicatesthe response for the concentration of antioxid
43、ants in the freshgrease being tested.8.2.3 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 a
44、nd Standard measure-ments, and reflects the concentration of one or more differenttypes of antioxidants present (fresh grease) or remaining(in-service or oxidized grease) in the grease sample. Voltam-metric readings for in-service or oxidized grease will decreaseas the concentration of the antioxida
45、nts namely, hinderedphenols, aromatic amines or ZDDP type of antioxidants aredepleted.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
46、 the area above thebaseline between the two 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 antiox
47、idant concentration (see Sec-tion 9).8.4 Calibration (Blank Reading):8.4.1 Pipette 5.0 mL of analysis solution intoa7mLvial orother suitable container containing1gofsand.8.4.2 Insert the electrode of the voltammetric analyzer intothe analysis solution to wet the bottom surface of the electrode,remov
48、e, and rub the bottom electrode surface dry with a lintfree paper towel. Insert the electrode into the vial so that thebottom of the electrode is submerged in the analysis solutionwithout resting on the sand layer on the bottom of the vial.Place the vial/probe upright into rack or foam block for tes
49、ting.8.4.3 Perform the voltammetric analysis (see 5.1). Recordthe voltammetric reading in the voltage range of aromaticamines, 0.8 to 1.2 V, see Note 1, and the phenols, 1.3 to 1.6 V,see Note 1, in neutral test solution (Fig. 1).8.4.4 Remove the combination electrode from the blanksolution, and rub the bottom surface dry of the electrode witha lint-free paper towel.8.4.5 Run at least two tests of the analysis solution to ensurethe electrode is clean and the correct minimum blank value hasbeen obtained.8.4.6 Calibration FrequencyRecalibration with freshlyprep
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