ASTM D7751-16(2021)
(Test Method)Standard Test Method for Determination of Additive Elements in Lubricating Oils by EDXRF Analysis
Standard Test Method for Determination of Additive Elements in Lubricating Oils by EDXRF Analysis
SIGNIFICANCE AND USE
5.1 Lubricating oils are formulated with organo-metallic additives, which act, for example, as detergents, antioxidants, antifoaming, or antiwear agents, or a combination thereof. Some of these additives contain one or more of the following elements: magnesium, phosphorus, sulfur, chlorine, calcium, zinc, and molybdenum. This test method provides a means of determining the concentrations of these elements, which in turn provides an indication of the additive content of these oils.
5.2 Several additive elements and their compounds are added to the lubricating oils to give beneficial performance (Table 2).
5.3 Additive packages are the concentrates that are used to blend lubricating oils.
5.4 This test method is primarily intended to be used for the monitoring of additive elements in lubricating oils.
5.5 If this test method is applied to lubricating oils with matrices significantly different from the calibration materials specified in this test method, the cautions and recommendations in Section 6 should be observed when interpreting the results.
SCOPE
1.1 This test method covers the quantitative determination of additive elements in unused lubricating oils and additive packages, as shown in Table 1.
1.2 Additive packages require dilution with a contamination free diluent (base oil) prior to analysis. The dilution factor has to be calculated from the expected concentrations to bring the concentrations for all elements into the ranges listed in Table 1.
1.3 Some lubrication oils will contain higher concentrations than the maximum concentrations listed in Table 1. These samples require dilution with a contamination free diluent (base oil) prior to analysis. The dilution factor has to be calculated from the expected concentrations to bring the concentrations for all elements into the ranges listed in Table 1.
1.4 This test method is limited to the use of energy dispersive X-ray fluorescence (EDXRF) spectrometers employing an X-ray tube for excitation in conjunction with the ability to separate the signals of adjacent elements by using a high resolution semiconductor detector.
1.5 This test method uses inter-element correction factors calculated from a fundamental parameters (FP) approach or from another matrix correction method.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6.1 The preferred concentration units are mg/kg or mass %.
1.7 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.
1.8 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: D7751 − 16 (Reapproved 2021)
Standard Test Method for
Determination of Additive Elements in Lubricating Oils by
EDXRF Analysis
This standard is issued under the fixed designation D7751; 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 ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method covers the quantitative determination
mendations issued by the World Trade Organization Technical
of additive elements in unused lubricating oils and additive
Barriers to Trade (TBT) Committee.
packages, as shown in Table 1.
1.2 Additivepackagesrequiredilutionwithacontamination
2. Referenced Documents
free diluent (base oil) prior to analysis. The dilution factor has
2.1 ASTM Standards:
to be calculated from the expected concentrations to bring the
D4057 Practice for Manual Sampling of Petroleum and
concentrationsforallelementsintotherangeslistedinTable1.
Petroleum Products
1.3 Some lubrication oils will contain higher concentrations
D4177 Practice for Automatic Sampling of Petroleum and
than the maximum concentrations listed in Table 1. These
Petroleum Products
samples require dilution with a contamination free diluent
D6299 Practice for Applying Statistical Quality Assurance
(base oil) prior to analysis. The dilution factor has to be
and Control Charting Techniques to Evaluate Analytical
calculated from the expected concentrations to bring the
Measurement System Performance
concentrationsforallelementsintotherangeslistedinTable1.
D6300 Practice for Determination of Precision and Bias
Data for Use in Test Methods for Petroleum Products,
1.4 This test method is limited to the use of energy
Liquid Fuels, and Lubricants
dispersive X-ray fluorescence (EDXRF) spectrometers em-
D6792 Practice for Quality Management Systems in Petro-
ploying an X-ray tube for excitation in conjunction with the
leum Products, Liquid Fuels, and Lubricants Testing
ability to separate the signals of adjacent elements by using a
Laboratories
high resolution semiconductor detector.
D7343 Practice for Optimization, Sample Handling,
1.5 This test method uses inter-element correction factors
Calibration, and Validation of X-ray Fluorescence Spec-
calculated from a fundamental parameters (FP) approach or
trometry Methods for Elemental Analysis of Petroleum
from another matrix correction method.
Products and Lubricants
1.6 The values stated in SI units are to be regarded as
E1621 Guide for ElementalAnalysis by Wavelength Disper-
standard. No other units of measurement are included in this
sive X-Ray Fluorescence Spectrometry
standard. 3
2.2 ISO Standards:
1.6.1 The preferred concentration units are mg/kg or mass
ISO 4259 Determination and application of precision data in
%.
relation to methods of test
1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety, health, and environmental practices and deter-
3.1.1 energy dispersive X-ray spectrometry, n—XRF spec-
mine the applicability of regulatory limitations prior to use.
trometry applying energy dispersive selection of radiation.
1.8 This international standard was developed in accor-
3.2 Abbreviations:
dance with internationally recognized principles on standard-
1 2
This test method is under the jurisdiction of ASTM Committee D02 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Subcommittee D02.03 on Elemental Analysis. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2021. Published August 2021. Originally the ASTM website.
approved in 2011. Last previous edition approved in 2016 as D7751 – 16. Available from International Organization for Standardization (ISO), 1, ch. de
DOI:10.1520/D7751-16R21. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7751 − 16 (2021)
TABLE 1 Elements and Range of Applicability
calculation of concentrations in samples is based on making
Element PLOQ in mass % Max Concentration in successively better estimates of composition by an iteration
mass %
procedure.
Magnesium 0.018 0.10
NOTE 1—The algorithm used for the procedure is usually implemented
Phosphorous 0.024 0.125
in the instrument manufacturer’s software.
Sulfur 0.008 1.94
Chlorine 0.0007 0.05
4.2 The EDXRF spectrometer is initially calibrated using a
Calcium 0.002 0.44
Zinc 0.040 0.143 set of standards to collect the necessary intensity data. Each
Molybdenum 0.004 0.047
calibration line and any correction coefficient are obtained by a
regression of this data, using the program supplied with the
spectrometer. (Warning—Exposure to excessive quantities of
X-radiation is injurious to health. The operator needs to take
3.2.1 EDXRF—Energy Dispersive X-ray Fluorescence
appropriate actions to avoid exposing any part of their body,
Spectrometry.
not only to primary X-rays, but also to secondary or scattered
3.2.2 FP—Fundamental Parameters.
radiation that might be present.The X-ray spectrometer should
be operated in accordance with the regulations governing the
4. Summary of Test Method
use of ionizing radiation.)
4.1 A specimen is placed in the X-ray beam, and the
appropriate regions of its spectrum are measured to give the 5. Significance and Use
fluorescent intensities of magnesium, phosphorus, sulfur,
5.1 Lubricating oils are formulated with organo-metallic
chlorine, calcium, zinc, and molybdenum. Other regions of the
additives, which act, for example, as detergents, antioxidants,
spectrum are measured to compensate for matrix variation. To
antifoaming, or antiwear agents, or a combination thereof.
optimize the sensitivity for each element or group of elements,
Some of these additives contain one or more of the following
a combination of optimized excitation and detection conditions
elements: magnesium, phosphorus, sulfur, chlorine, calcium,
(for example, different primary beam filters (7.1.3), secondary
zinc, and molybdenum. This test method provides a means of
or polarization targets (7.1.4), and so forth) may be used. The
determiningtheconcentrationsoftheseelements,whichinturn
measuring time should be kept as short as possible, typically
provides an indication of the additive content of these oils.
under10 minperspecimen.Avoidusingdifferentmeasurement
conditions that yield only marginally better results for a
5.2 Several additive elements and their compounds are
specific analyte. There may be a correction of measured
added to the lubricating oils to give beneficial performance
intensities for spectral overlap.
(Table 2).
4.1.1 Concentrations of the elements of interest are deter-
5.3 Additive packages are the concentrates that are used to
mined by comparison of these intensities against a calibration
blend lubricating oils.
curve using a fundamental parameters (FP) approach, possibly
combined with corrections from backscatter. The FP approach
5.4 This test method is primarily intended to be used for the
uses the physical processes forming the basis of X-ray fluo-
monitoring of additive elements in lubricating oils.
rescence emission in order to provide a theoretical model for
5.5 If this test method is applied to lubricating oils with
the correction of matrix effects. The correction term is calcu-
lated from first principle expressions derived from basic matrices significantly different from the calibration materials
specified in this test method, the cautions and recommenda-
physical principles and contain physical constants and param-
eters that include absorption coefficients, fluorescence yield, tions in Section 6 should be observed when interpreting the
primary spectral distribution and spectrometry geometry. The results.
TABLE 2 Lubricants and Additive Materials
Element Compounds Purpose/Application
Calcium Sulfonates, phenates Detergent inhibitors, dispersants
Chlorine Trace contaminants, cleaning agents
Magnesium Sulfonates, phenates Detergent inhibitors
Molybdenum Dialkylithiophosphate dialkyldithiocarbamate, other Friction modifier additives
molybdenum complexes
Phosphorus Dithiophosphates, phosphates phosphites Anti-rusting agents, extreme pressure additives, anti-wear
Sulfur Base oils, sulfonates, thiophosphates, polysulfides and Detergents, extreme pressure additives, anti-wear
other sulfurized components
Zinc Dialkyldithiophosphates, dithiocarbamates, phenolates Anti-oxidant, corrosion inhibitors, anti-wear additives, detergents, crankcase
carboxylates oils, hypoid gear lubricants, aircraft piston engine oils, turbine oils, automatic
transmission fluids, railroad diesel engine oils, brake lubricants
D7751 − 16 (2021)
6. Interferences not required when the instrument’s software does include
software to deconvolute spectra.
6.1 The additive elements found in lubricating oils will
7.3 Drift Correction Monitors (Optional)—To correct for
affect the measured intensities from the elements of interest to
instrumentaldrift.Atleasttwosamplesarenecessarytocorrect
a varying degree. In general the X-radiation emitted by the
both sensitivity and possible changes in the background. For
element of interest can be absorbed by itself (self-absorption)
each element and scatter region, there shall be one providing a
or by the other elements present in the sample matrix.Also the
count rate similar to samples from the upper end of the
X-radiation emitted from one element can further excite
calibration and another providing a count rate as if from a
(enhance) another element. These inter-element effects are
blank. This last can be a blank oil. For the high concentration
significant at concentrations varying from 0.03 % by mass, due
to the higher atomic number elements (for example, of each element, a glass disk, XRF fusion bead, or pressed
pellet have all been found to be satisfactory. Elemental
molybdenum), to 1 % by mass, for the lower atomic number
elements (for example, sulfur). If an element is present at reference samples (7.2) may also be used.
7.3.1 Drift correction is usually implemented automatically
significant concentrations and an inter-element correction for
that element is not employed, the results can be low due to in software, although the calculation can readily be done
manually. For X-ray instruments that are highly stable, the
absorption or high due to enhancement.
magnitude of the drift correction factor may not differ signifi-
6.2 Absorption and enhancements effects will be corrected
cantly from unity.
by corrections from the FP approach or by other matrix
7.4 Quality Control (QC) Samples—Samples for use in
correction models.
establishing and monitoring the stability and precision of an
6.3 There can be spectral overlap of one element onto
analytical measurement system. Use homogeneous materials,
another, and the instrument must include correction procedures
similar to samples of interest and available in sufficient
for any such overlaps.
quantity to be analyzed regularly for a long period of time.
7.5 Foradditionalinformation,alsorefertoPracticeD7343.
7. Apparatus
7.1 Energy Dispersive X-ray Fluorescent Spectrometer—
8. Reagents and Materials
Any energy dispersive X-ray fluorescence spectrometer can be
8.1 Purity of Reagents —Reagent grade chemicals shall be
used if its design incorporates at least the following features:
used in all tests. Unless otherwise indicated, it is intended that
7.1.1 Source of X-ray Excitation—X-ray tube with
all reagents conform to the specifications of the Committee on
palladium, silver, rhodium, or tungsten target. Other targets
Analytical Reagents of the American Chemical Society where
may be suitable as well. The voltage of the X-ray tube shall be
such specifications are available. Other grades may be used,
programmablebetween4 kVandatleast30 kVforpreferential
provided it is first ascertained that the reagent is of sufficiently
excitation of elements or groups of elements.
high purity to permit its use without lessening the accuracy of
7.1.2 X-ray Detector—Semiconductor detector with high
the determination.
sensitivityandaspectralresolutionvaluenottoexceed175 eV
8.2 Diluent Solvent—Asuitable solvent containing less than
at 5.9 keV.
10 mg/kg of sulfur and containing less than 1 mg/kg of metals
7.1.3 Primary Beam Filters (Optional)—To make the exci-
as well as of all other elements of interest (for example, base
tation more selective and to reduce the intensity of background
oil). If diluted samples are analyzed at low levels of sulfur, a
radiation.
lower sulfur content of the diluent solvent should be used and
7.1.4 Secondary or Polarization Targets, or Both
mustbecorrectedforwhenrecalculatingtheconcentrationsfor
(Optional)—To make the excitation more selective and to
theoriginal,not-dilutedsample.Theprecisionstatedinthistest
improve peak-to-background ratio.
method does not apply to diluted samples.
7.1.5 Signal Conditioning and Data Handling Electronics—
8.3 Helium Gas—Minimum purity 99.9 %.
That include the functions of X-ray intensity counting, spectra
handling by background variation correction, overlap
8.4 Calibration Standard Materials:
corrections, inter-elements effects corrections, and conversion
8.4.1 Commercially available calibration solutions.
of X-ray intensity into concentration.
8.4.2 Certified concentration solutions, of liquid organome-
7.1.6 Helium Purgeable Optical Path (Optional)—Helium tallic salts, the following standard materials can be used:
purge improves the sensitivity of low energy X-rays emitted 8.4.2.1 Calcium 2-Ethylhexanoate, approximately 12.3 %
from low atomic number elements (Z< 22). by mass calcium.
8.4.2.2 Zinc Cyclohexanebutyrate, approximately 16.2 %
7.1.7 Sample Cells—Providing a depth of at least 6 mm and
by mass zinc.
equipped with replaceable X-ray transparent film.
7.1.8 Sample Film—Suitable films include polypropylene,
polyester, and polycarbonate with thickness from 3.5 µm to
ACS Reagent Chemicals, Specifications and Pro
...
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