1、Designation: D7751 11Standard Test Method forDetermination of Additive Elements in Lubricating Oils byEDXRF Analysis1This standard is issued under the fixed designation D7751; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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 quantitative determinationof additive elements in unused lubricating oils and additiv
3、epackages, as shown in Table 1. The pooled limit of quantitationof this test method as obtained by statistical analysis ofinterlaboratory test results is 0.02% for magnesium, 0.003 %for phosphorus, 0.002 % for sulfur, 0.001 % for chlorine, 0.003% for calcium, 0.001 % for zinc, and 0.002 % for molybd
4、e-num.1.2 Additive packages require dilution with a contaminationfree diluent (base oil) prior to analysis. The dilution factor hasto be calculated from the expected concentrations to bring theconcentrations for all elements into the ranges listed in Table 1.1.3 Some lubrication oils will contain hi
5、gher concentrationsthan the maximum concentrations listed in Table 1. Thesesamples require dilution with a contamination free diluent(base oil) prior to analysis. The dilution factor has to becalculated from the expected concentrations to bring theconcentrations for all elements into the ranges list
6、ed in Table 1.1.4 This test method is limited to the use of energydispersive X-ray fluorescence (EDXRF) spectrometers em-ploying an X-ray tube for excitation in conjunction with theability to separate the signals of adjacent elements by using ahigh resolution semiconductor detector.1.5 This test met
7、hod uses inter-element correction factorscalculated from a fundamental parameters (FP) approach orfrom another matrix correction method.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6.1 The preferred concentration units
8、are mg/kg or mass%.1.7 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 regulatory limitations prior to
9、use.2. Referenced Documents2.1 ASTM Standards:2D4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalM
10、easurement System PerformanceD6300 Practice for Determination of Precision and BiasData for Use in Test Methods for Petroleum Products andLubricantsD6792 Practice for Quality System in Petroleum Productsand Lubricants Testing LaboratoriesD7343 Practice for Optimization, Sample Handling, Cali-bration
11、, and Validation of X-ray Fluorescence Spectrom-etry Methods for Elemental Analysis of Petroleum Prod-ucts and LubricantsE1621 Guide for X-Ray Emission Spectrometric Analysis2.2 ISO Standards:3ISO 4259 Determination and application of precision datain relation to methods of test3. Terminology3.1 Def
12、initions:3.1.1 energy dispersive X-ray spectrometry, nXRF spec-trometry applying energy dispersive selection of radiation.3.2 Abbreviations:3.2.1 EDXRFEnergy Dispersive X-ray FluorescenceSpectrometry.3.2.2 FPFundamental Parameters.4. Summary of Test Method4.1 A specimen is placed in the X-ray beam,
13、and theappropriate regions of its spectrum are measured to give thefluorescent intensities of magnesium, phosphorus, sulfur, chlo-rine, calcium, zinc, and molybdenum. Other regions of the1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the
14、direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Oct. 1, 2011. Published November 2011. DOI:10.1520/D7751-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStan
15、dards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959, United States.spectrum are measured to compensate for matrix variation. Tooptimize the sensitivity for each element or group of elements,a combination of optimized excitation and detection conditionsmay be used (no more than two conditions should be used in
17、order to keep the analysis time as short as possible, typicallyunder ten minutes). There may be a correction of measuredintensities for spectral overlap.4.1.1 Concentrations of the elements of interest are deter-mined by comparison of these intensities against a calibrationcurve using a fundamental
18、parameters (FP) approach, possiblycombined with corrections from backscatter. The FP approachuses the physical processes forming the basis of X-ray fluo-rescence emission in order to provide a theoretical model forthe correction of matrix effects. The correction term is calcu-lated from first princi
19、ple expressions derived from basicphysical principles and contain physical constants and param-eters that include absorption coefficients, fluorescence yield,primary spectral distribution and spectrometry geometry. Thecalculation of concentrations in samples is based on makingsuccessively better est
20、imates of composition by an iterationprocedure.NOTE 1The algorithm used for the procedure is usually implementedin the instrument manufacturers software.4.2 The EDXRF spectrometer is initially calibrated using aset of standards to collect the necessary intensity data. Eachcalibration line and any co
21、rrection coefficient are obtained by aregression of this data, using the program supplied with thespectrometer. (WarningExposure to excessive quantities ofX-radiation is injurious to health. The operator needs to takeappropriate actions to avoid exposing any part of their body,not only to primary X-
22、rays, but also to secondary or scatteredradiation that might be present. The X-ray spectrometer shouldbe operated in accordance with the regulations governing theuse of ionizing radiation.)5. Significance and Use5.1 Lubricating oils are formulated with organo-metallicadditives, which act, for exampl
23、e, as detergents, antioxidants,antifoaming, or antiwear agents, or a combination thereof.Some of these additives contain one or more of the followingelements: magnesium, phosphorus, sulfur, chlorine, calcium,zinc, and molybdenum. This test method provides a means ofdetermining the concentrations of
24、these elements, which in turnprovides an indication of the additive content of these oils.5.2 Additive packages are the concentrates that are used toblend lubricating oils.5.3 This test method is primarily intended to be used for themonitoring of additive elements in lubricating oils.5.4 If this tes
25、t method is applied to lubricating oils withmatrices significantly different from the calibration materialsspecified in this test method, the cautions and recommenda-tions in Section 6 should be observed when interpreting theresults.6. Interferences6.1 The additive elements found in lubricating oils
26、 willaffect the measured intensities from the elements of interest toa varying degree. In general the X-radiation emitted by theelement of interest can be absorbed by itself (self-absorption)or by the other elements present in the sample matrix. Also theX-radiation emitted from one element can furth
27、er excite(enhance) another element. These inter-element effects aresignificant at concentrations varying from 0.03 mass %, due tothe higher atomic number elements (for example, molybde-num), to 1 mass %, for the lower atomic number elements (forexample, sulfur). If an element is present at significa
28、nt con-centrations and an inter-element correction for that element isnot employed, the results can be low due to absorption or highdue to enhancement.6.2 Absorption and enhancements effects will be correctedby corrections from the FP approach or by other matrixcorrection models.6.3 There can be spe
29、ctral overlap of one element ontoanother, and the instrument must include correction proceduresfor any such overlaps.7. Apparatus7.1 Energy Dispersive X-ray Fluorescent SpectrometerAny energy dispersive X-ray fluorescence spectrometer can beused if its design incorporates at least the following feat
30、ures:7.1.1 Source of X-ray ExcitationX-ray tube with palla-dium, silver, rhodium, or tungsten target. Other targets may besuitable as well. The voltage of the X-ray tube shall beprogrammable between 4 and at least 30 kV for preferentialexcitation of elements or groups of elements.7.1.2 X-ray Detecto
31、rSemiconductor detector with highsensitivity and a spectral resolution value not to exceed 175 eVat 5.9 keV.7.1.3 Primary Beam Filters (Optional)To make the exci-tation more selective and to reduce the intensity of backgroundradiation.7.1.4 Secondary or Polarization Targets, or Both(Optional)To make
32、 the excitation more selective and toimprove peak-to-background ratio.7.1.5 Signal Conditioning and Data Handling ElectronicsThat include the functions of X-ray intensity counting, spectrahandling by background variation correction, overlap correc-tions, inter-elements effects corrections, and conve
33、rsion ofX-ray intensity into concentration.7.1.6 Helium Purgeable Optical Path (Optional)Heliumpurge improves the sensitivity of low energy X-rays emittedfrom low atomic number elements (Z 22).7.1.7 Sample CellsProviding a depth of at least 6 mm andequipped with replaceable X-ray transparent film.7.
34、1.8 Sample FilmSuitable films include polypropylene,polyester, and polycarbonate with thickness from 3.5 to 8 m.TABLE 1 Elements and Range of ApplicabilityElement Concentration Range in mass %Magnesium 0.02 to 0.4Phosphorous 0.003 to 0.25Sulfur 0.002 to 1.5Chlorine 0.001 to 0.4Calcium 0.003 to 1.0Zi
35、nc 0.001 to 0.25Molybdenum 0.002 to 0.05D7751 112Athick film may limit the performance for low atomic numbers(for example, Magnesium).7.2 Instrument Setting-Up Samples (Elemental ReferenceSamples) (Optional)To quantify spectral overlaps. These arenot required when the instruments software does inclu
36、desoftware to deconvolute spectra.7.3 Drift Correction Monitors (Optional)To correct forinstrumental drift.At least two samples are necessary to correctboth sensitivity and possible changes in the background. Foreach element and scatter region, there shall be one providing acount rate similar to sam
37、ples from the upper end of thecalibration and another providing a count rate as if from ablank. This last can be a blank oil. For the high concentrationof each element, a glass disk, XRF fusion bead, or pressedpellet have all been found to be satisfactory. Elementalreference samples (7.2) may also b
38、e used.7.3.1 Drift correction is usually implemented automaticallyin software, although the calculation can readily be donemanually. For X-ray instruments that are highly stable, themagnitude of the drift correction factor may not differ signifi-cantly from unity.7.4 Quality Control (QC) Samples (Op
39、tional)Samples foruse in establishing and monitoring the stability and precision ofan analytical measurement system. Use homogeneous materi-als, similar to samples of interest and available in sufficientquantity to be analyzed regularly for a long period of time.7.5 For additional information, also
40、refer to Practice D7343.NOTE 2Verification of system control through the use of QC samplesand control charting is highly recommended.8. Reagents and Materials8.1 Purity of Reagents4Reagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform
41、to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available. Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determ
42、ination.8.2 Diluent SolventAsuitable solvent containing less than10 mg/kg of sulfur and containing less than 1 mg/kg of metalsas well as of all other elements of interest (for example, baseoil).8.3 Helium GasMinimum purity 99.9 %.8.4 Calibration Standard Materials:8.4.1 Commercially available calibr
43、ation solutions.8.4.2 Certified concentration solutions, of liquid organome-tallic salts, the following standard materials can be used:8.4.2.1 Calcium 2-Ethylhexanoate, approximately 12.3mass % calcium.8.4.2.2 Zinc Cyclohexanebutyrate, approximately 16.2 mass% zinc.8.4.2.3 Bis(2-Ethylhexyl)Hydrogen
44、Phosphate, 97 % purity(approximately 9.62 mass % phosphorus).8.4.2.4 Di-n-butyl Sulfide, 97 % purity (approximately 21.9mass % sulfur).8.4.2.5 Magnesium-2-ethylhexoate, (2.99 % magnesium).8.4.2.6 1-Chlorooctane, 98 % purity, (23.9 mass % chlo-rine).8.4.2.7 Commercially available single element stand
45、ard formolybdenum based on molybdenumsulfonate.8.4.2.8 Stabilizers, 2-ethylhexanoic acid, 2-ethylamine, alsoproprietary stabilizer/chelating solutions are available commer-cially. Stabilizers shall be free of the additive element.NOTE 3In addition to the calibration standard materials identified in8
46、.4, single or multielement calibration standards can also be prepared frommaterials similar to the samples being analyzed, provided the calibrationstandards to be used have previously been characterized by independentprimary (for example, gravimetric or volumetric) analytical techniques toestablish
47、the elemental concentration mass % levels.9. Hazards9.1 Occupational health and safety standards for X-rays andionizing radiation shall be observed. It is also recommendedthat proper practices be followed as presented by most manu-factures documentation or described in Guide E1621.10. Sampling and T
48、est Specs and Units10.1 Samples shall be taken in accordance with the instruc-tions in Practices D4057 or D4177. For sample handling, alsorefer to Practice D7343.10.2 When reusable sample cells are used, clean and drycells before each use. Disposable sample cells shall not bereused. For each sample,
49、 an unused piece of X-ray film isrequired for the sample cell. Avoid touching the inside of thesample cell, the portion of the window film in the cell, or theinstrument window that is exposed to X-rays. Oil fromfingerprints can affect the reading when determining low levelsof analytes. Wrinkles in the film will affect the intensity of theX-rays transmitted, therefore, it is essential that the film be tautand clean to ensure reliable results. When handling the windowfilm, avoid touching the central part (the part that actuallyforms the optical window) as this
