ASTM D7527-10(2018)
(Test Method)Standard Test Method for Measurement of Antioxidant Content in Lubricating Greases by Linear Sweep Voltammetry
Standard Test Method for Measurement of Antioxidant Content in Lubricating Greases by Linear Sweep Voltammetry
SIGNIFICANCE AND USE
4.1 The quantitative determination of antioxidants in new greases measures the amount of the chemical compounds that were added to the base oil as protection against grease oxidation. For in-service oil greases, the voltammetric test method measures the amount of original (individual) antioxidants remaining after grease oxidation have reduced its concentration. Before making final judgment on the remaining useful life of the in-service grease, which might result in the replacement of the grease reservoir, it is advised to perform additional analytical techniques, such as Test Method D942 and D5483, which may be used to measure the remaining oxidative life of the used grease.
4.1.1 This test method is applicable to mineral oil-based and synthetic oil-based greases, based on all type of applied thickeners. This test method is applicable to greases containing at least one type of antioxidant. The presence of other types of additives like corrosion inhibitors or metal deactivators will not interfere with this test method.
4.2 When a voltammetric analysis is obtained using a neutral acetone test solution for a grease inhibited with a typical synergistic mixture of hindered phenol and aromatic amine antioxidants, there is an increase in the voltammogram current between 8 s to 12 s (or 0.8 V to 1.2 V applied voltage), see Note 1, for the aromatic amines, and an increase in the voltammogram current of the produced voltammogram between 13 s to 16 s (or 1.3 V to 1.6 V applied voltage), see Note 1, for the hindered phenols. In Fig. 1, x-axis = 1 s = 0.1 V. Hindered phenol antioxidants detected by voltammetric analysis include, but are not limited to, 2,6-di-tert-butyl-4- methylphenol; 2,6-di-tert-butylphenol and 4,4’-Methylenebis(2,6-di-tertbutylphenol). Aromatic amine antioxidants detected by voltammetric analysis include, but are not limited to, phenyl alpha naphthylamines, and alkylated diphenylamines.
4.3 For greases containing only aromatic amines as antioxidants...
SCOPE
1.1 This test method covers the voltammetric determination of antioxidants in new or in-service lubricating greases in concentrations from 0.0075 weight percent up to concentrations found in new greases by measuring the amount of current flow at a specified voltage in the produced voltammogram.
1.2 This test method is intended to monitor the antioxidant content in lubricating greases; it cannot be applied for lubricating greases that do not contain antioxidants.
1.3 This test method is designed to allow the user to monitor the antioxidant depletion rate of in-service greases through its life cycle as part of condition monitoring programs. This test method is performed in order to collect and trend early signs of deteriorating lubricant grease, and it may be used as a guide for the direction of any required maintenance activities. This will ensure a safe, reliable, and cost-effective operation of the monitored plant equipment.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7527 − 10 (Reapproved 2018)
Standard Test Method for
Measurement of Antioxidant Content in Lubricating Greases
by Linear Sweep Voltammetry
This standard is issued under the fixed designation D7527; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the voltammetric determination 2.1 ASTM Standards:
of antioxidants in new or in-service lubricating greases in D942 Test Method for Oxidation Stability of Lubricating
concentrations from 0.0075 weight percent up to concentra- Greases by the Oxygen Pressure Vessel Method
tions found in new greases by measuring the amount of current D1193 Specification for Reagent Water
flow at a specified voltage in the produced voltammogram. D5483 Test Method for Oxidation Induction Time of Lubri-
catingGreasesbyPressureDifferentialScanningCalorim-
1.2 This test method is intended to monitor the antioxidant
etry
content in lubricating greases; it cannot be applied for lubri-
D6810 Test Method for Measurement of Hindered Phenolic
cating greases that do not contain antioxidants.
Antioxidant Content in Non-Zinc Turbine Oils by Linear
1.3 Thistestmethodisdesignedtoallowtheusertomonitor
Sweep Voltammetry
the antioxidant depletion rate of in-service greases through its
D6971 Test Method for Measurement of Hindered Phenolic
life cycle as part of condition monitoring programs. This test
and Aromatic Amine Antioxidant Content in Non-zinc
method is performed in order to collect and trend early signs of
Turbine Oils by Linear Sweep Voltammetry
deterioratinglubricantgrease,anditmaybeusedasaguidefor
the direction of any required maintenance activities. This will 3. Summary of Test Method
ensure a safe, reliable, and cost-effective operation of the
3.1 A measured quantity of sample is weighed into a vial
monitored plant equipment.
containing a measured quantity of acetone based electrolyte
1.4 The values stated in SI units are to be regarded as solution and containing a layer of sand. When the vial is
standard. No other units of measurement are included in this shaken, the dissolved antioxidants and other solution soluble
standard. oil components present in the sample are extracted into the
solution, and the remaining droplets suspended in the solution
1.5 This standard does not purport to address all of the
are agglomerated by the sand. The sand/droplet suspension is
safety concerns, if any, associated with its use. It is the
allowed to settle out, and the antioxidants dissolved in the
responsibility of the user of this standard to establish appro-
solution are quantified by voltammetric analysis.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
NOTE 1—Voltages are listed with respect to reference electrode. The
1.6 This international standard was developed in accor- voltammograms shown in Figs. 1 and 2 were obtained with a platinum
reference electrode and a voltage scan rate of 0.1 V⁄s.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4. Significance and Use
Development of International Standards, Guides and Recom-
4.1 The quantitative determination of antioxidants in new
mendations issued by the World Trade Organization Technical
greases measures the amount of the chemical compounds that
Barriers to Trade (TBT) Committee.
were added to the base oil as protection against grease
oxidation. For in-service oil greases, the voltammetric test
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.09.0E on Oxidation of Greases. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2018. Published June 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2010. Last previous edition approved in 2010 as D7527 – 10. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7527-10R18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7527 − 10 (2018)
NOTE 1—X-axis represents time (seconds) andY-axis represents current (arbitrary units). Upper line curve in Fig. 1 is voltammogram of a fresh Li-OH
mineral grease showing valley indicators (dotted lines) before and after a antioxidant additives.
FIG. 1 Aromatic Amine and Hindered Phenol Voltammetric Response in Neutral Test Solution with Blank Response Zeroed
FIG. 2 Hindered Phenol Voltammetric Response in Basic Alcohol Test Solution with Blank Response Zeroed
method measures the amount of original (individual) antioxi- and D5483, which may be used to measure the remaining
dants remaining after grease oxidation have reduced its con- oxidative life of the used grease.
centration. Before making final judgment on the remaining 4.1.1 Thistestmethodisapplicabletomineraloil-basedand
useful life of the in-service grease, which might result in the synthetic oil-based greases, based on all type of applied
replacement of the grease reservoir, it is advised to perform thickeners.This test method is applicable to greases containing
additional analytical techniques, such as Test Method D942 at least one type of antioxidant. The presence of other types of
D7527 − 10 (2018)
additiveslikecorrosioninhibitorsormetaldeactivatorswillnot 5.5 Solvent Dispenser—Or equivalent, capable of delivering
interfere with this test method. volumes of analysis solution (see 6.3) required in the test
method, such as 5.0 mL 6 0.1 mL.
4.2 When a voltammetric analysis is obtained using a
neutral acetone test solution for a grease inhibited with a
5.6 Glass Vials with Caps—4 mL or 7 mL capacity, and
typical synergistic mixture of hindered phenol and aromatic containing 1 g of sand white quartz suitable for
amine antioxidants, there is an increase in the voltammogram
chromatography, within the particle size range of 200 µm to
current between 8 s to 12 s (or 0.8 V to 1.2 V applied voltage), 300 µm 6 100 µm.
see Note 1, for the aromatic amines, and an increase in the
6. Reagents and Materials
voltammogram current of the produced voltammogram be-
tween 13 s to 16 s (or 1.3 Vto 1.6 Vapplied voltage), see Note
6.1 Purity of Reagents—Reagent-grade chemicals shall be
1, for the hindered phenols. In Fig. 1, x-axis=1s=0.1V.
used in all tests. Unless otherwise indicated, where applicable
Hindered phenol antioxidants detected by voltammetric analy-
reagents shall conform to the specifications of the Committee
sis include, but are not limited to, 2,6-di-tert-butyl-4- methyl-
on Analytical Reagents of the American Chemical Society.
phenol; 2,6-di-tert-butylphenol and 4,4’-Methylenebis(2,6-di-
Other grades may be used, provided it is first ascertained that
tertbutylphenol). Aromatic amine antioxidants detected by
the reagent’s purity suffices to permit its use without lessening
voltammetric analysis include, but are not limited to, phenyl
the accuracy of the determination.
alpha naphthylamines, and alkylated diphenylamines.
6.2 Purity of Water—Unless otherwise specified, water that
4.3 For greases containing only aromatic amines as
shall conform to Specification D1193, Type II.
antioxidants, there will only be an increase in the current of the
6.3 Analysis Materials:
producedvoltammogrambetween8 sto12 s(or0.8 Vto1.2 V
6.3.1 Acetone Test Solution (Neutral)—Proprietary Green
applied voltage) for the aromatic amines, by using the neutral
test solution, acetone solvent (1:10 distilled water/acetone
acetone test solution (first peak in Fig. 1).
solution) containing a dissolved neutral electrolyte.
4.4 For greases containing ZDDP as antioxidants, there
(Warning—Corrosive, Poison, Flammable, and Skin Irritant.
shall be an increase in the voltammogram current between 6 s
Harmful if inhaled.)
to 10 s (or 0.6 V to 1.0 V applied voltage), see Note 1, for the
6.3.2 Alcohol Test Solution (Basic)—Proprietary Yellow
ZDDP, when evaluated in the neutral acetone test solution.
test solution, Ethanol solvent (1:10 distilled water/ethanol
4.5 For greases containing only hindered phenolic solution) containing a dissolved base electrolyte. (Warning—
Corrosive, Poison, Flammable, and Skin Irritant. Harmful if
antioxidants, basic alcohol test solutions are recommended for
use as described in Test Method D6810. In basic alcohol test inhaled.)
6.3.3 Alcohol Cleansing Pads—70 % isopropyl alcohol
solutions, the voltammogram current for phenols increases
between 3 s to 6 s (or 0.3 Vto 0.6 Vapplied voltage), see Note saturated cleansing pads (alcohol prepared skin cleansing pads,
for the preparation of the skin prior to injection (antiseptic)).
1.In Fig. 2, x-axis=1s=0.1Vareas described in Test
Method D6810, where x-axis = time (seconds) and y-axis is
7. Sampling
current (arbitrary units). Top line in Fig. 2 is fresh grease.
7.1 It is important to accurately sample the in-service
5. Apparatus
grease. Since sample composition may depend upon sampling
5.1 Voltammograph—The instrument used to quantify the
position, it is recommended that samples be collected from
antioxidants is a voltammograph equipped with a three-
more than one location.
electrode system and a digital or analog output. The three-
7.2 Samples of an in-service grease can be non-
electrode system consists of a glassy 3 mm diameter carbon
homogeneous. It should be agreed with the customer how to
disc working electrode, a platinum wire (0.5 mm diameter)
prepare the lubricating grease samples for analysis.
auxiliary electrode, and a 0.5 mm diameter platinum wire
(reference electrode, as described in Test Method D6810 and
8. Procedure
D6971). During operation, the voltammograph applies a linear
8.1 Thevoltammographusedinthistestmethodgiveslinear
voltageramp(0 Vto–1.8 Vrangewithrespecttothereference
results between 2 mmol⁄kg to 50 mmol⁄kg for different types
electrode) at a rate of 0.01 V⁄s to 0.5 V⁄s (0.1 optimum) to the
of antioxidants using a grease sample size of 250 mg and
auxiliary electrode. The current output of the working elec-
trode is converted to voltage by the voltammetric analyzer,
usingthegainratioof1 V⁄20 µA,andisoutputtedtoananalog 3
Reagent Chemicals, American Chemical Society Specifications, American
or digital recording device (0 V to 1 V full scale) as shown in Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
listed by the American Chemical Society, see Annual Standards for Laboratory
Figs. 1 and 2.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
5.2 Vortex Mixer—With a 2800 r⁄min to 3000 r⁄min motor
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD.
and a pad suitable for mixing test tubes and vials.
The sole source of supply known to the committee at this time is Fluitec, 2850
5.3 Spatula—Or equivalent laboratory tool, capable of de-
Scherer Dr., Suite 500, St. Petersburg, FL 33716; Friendship Building, Rijnkaai 37,
B.2000Antwerp, Belgium. If you are aware of alternative suppliers, please provide
livering samples from 50 mg to 300 mg.
this information to ASTM International Headquarters. Your comments will receive
5.4 Microbalance—Capable of weighing 50 mg to 300 mg
careful consideration at a meeting of the responsible technical committee, which
6 1 mg samples. you may attend.
D7527 − 10 (2018)
5.0 mLof the test solution. The corresponding range of weight different types of antioxidants present (fresh grease) or remain-
percents depends on the molecular weight of the antioxidants ing (in-service or oxidized grease) in the grease sample.
likehinderedphenolandaromaticamine,andthedensityofthe Voltammetric readings for in-service or oxidized grease will
grease. For instance, the weight percent range of 0.044 to 1.1 decrease as the concentration of the antioxidants namely,
is equal to 2 mmol⁄kg to 50 mmol⁄kg for a hindered phenol hindered phenols, aromatic amines or ZDDP type of antioxi-
containing one hydroxyl group and with a molecular weight of dants are depleted.
220 g⁄mole (2,6-di-tert-butyl-4-methylphenol) and an oil den-
8.3 Voltammetric Reading—As part of the procedure, once
sityof1g/mL.Below2 mmol,thenoisetosignalratiobecomes
the operator has selected the valleys before and after the
large decreasing the accuracy of the measurements. For mea-
antioxidant peaks (as shown in Fig. 1), the software (R-DMS )
surements below 2 mmol or for fresh oils with high noise to
will automatically identify and calculate the area above the
signal ratios, the sample size should be increased to 600 mg.
baseline between the two valley indicators. This calculated
8.2 General Voltammetric Test Procedure—The test proce-
area is then used for the sample reading (in-service or oxidized
dureforvoltammetricanalysiswillconsistoftheblankreading
grease), which will be established by comparing the in-service
(calibration), followed by a standard reading (fresh grease) and
grease area to its standard (see Fig. 3) and makes the necessary
finally the reading of the (in-service or oxidized grease)
calculations of remaining antioxidant concentration (see Sec-
sample.
tion 9).
8.2.1 Blank Reading—(0 mmol⁄kg = 0 mass percent). The
8.4 Calibration (Blank Reading):
blank reading (voltammetric number) is a measurement of the
8.4.1 Pipette 5.0 mLof analysis solution into a 7 mLvial or
testsolutionbyitself.Theblankmeasurementgivesareference
other suitable container containing 1 g of sand.
number with no antioxidant present (the zero baseline).
8.4.2 Insert the electrode of the voltammetric analyzer into
8.2.2 Standard Reading—(30 mmol⁄kg to 150 mmol⁄kg).
the analysis solution to wet the bottom surface of the electrode,
Concentration dependent on density of fresh oil and molecular
remove, and rub the bottom electrode surface dry with a lint
weight of antioxidant). The standard reading is a measurement
free paper towel. Insert the electrode into the vial so that the
of a fresh, unused grease (containing one or more different
bottom of the electrode is submerged in the analysis solution
types of antioxidants) mixed wit
...
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