1、Designation: D6481 99 (Reapproved 2010)Standard Test Method forDetermination of Phosphorus, Sulfur, Calcium, and Zinc inLubrication Oils by Energy Dispersive X-ray FluorescenceSpectroscopy1This standard is issued under the fixed designation D6481; the number immediately following the designation ind
2、icates the year oforiginal adoption or, in 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 quantitative
3、determinationof additive elements in unused lubricating oils, as shown inTable 1.1.2 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
4、.1.3 This test method uses interelement correction factorscalculated from empirical calibration data.1.4 This test method is not suitable for the determination ofmagnesium and copper at the concentrations present in lubri-cating oils.1.5 This test method excludes lubricating oils that containchlorin
5、e or barium as an additive element.1.6 This test method can be used by persons who are notskilled in X-ray spectrometry. It is intended to be used as aroutine test method for production control analysis.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with
6、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 to use.2. Summary of Test Method2.1 A specimen is placed in the X-ray beam, and theappropriate regions of its spectrum are me
7、asured to give thefluorescent intensities of phosphorus, sulfur, calcium, and zinc.Other regions of the spectrum are measured to compensate forvarying background. If the detector does not completelyresolve all the elements in a single measurement, then toimprove selectivity, there is a combination o
8、f sequential andsimultaneous measurements employing primary and secondarybeam filters. There can be correction of measured intensitiesfor spectral overlap. Concentrations of the elements of interestare determined by comparison of these intensities against acalibration curve using empirical interelem
9、ent correction fac-tors and ratio to backscatter.2.2 The EDXRF spectrometer is initially calibrated using aset of prepared standards to collect the necessary intensity data.Each calibration line and any correction coefficient are ob-tained by a regression of this data, using the program suppliedwith
10、 the spectrometer.3. Significance and Use3.1 Some oils are formulated with organo-metallic addi-tives, which act, for example, as detergents, antioxidants, andantiwear agents. Some of these additives contain one or moreof these elements: calcium, phosphorus, sulfur, and zinc. Thistest method provide
11、s a means of determining the concentra-tions of these elements, which in turn provides an indication ofthe additive content of these oils.3.2 This test method is primarily intended to be used at amanufacturing location for monitoring of additive elements inlubricating oils. It can also be used in ce
12、ntral and researchlaboratories.4. Interferences4.1 The additive elements found in lubricating oils willaffect the measured intensities from the elements of interest toa varying degree. In general, for lubricating oils, theX-radiation emitted by the element of interest can be absorbedby itself (self-
13、absorption) or by the other elements present inthe sample matrix. Also the X-radiation emitted from oneelement can further excite (enhance) another element. Theseinterelement effects are significant at concentrations varyingfrom 0.03 mass %, due to the heavier elements, to 1 mass %,for the lighter e
14、lements. Enhancement effects can be minimisedby selective excitation. The measured concentration for a givenelement can be mathematically corrected for self-absorption1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibilit
15、y of SubcommitteeD02.03 on Elemental Analysis.Current edition approved May 1, 2010. Published May 2010. Originallyapproved in 1999. Last previous edition approved in 2004 as D6481 - 99 (2004).DOI: 10.1520/D6481-99R10.TABLE 1 Elements and Range of Concentrations DeterminedElement Concentration RangeP
16、hosphorus 0.02 to 0.3 mass %Sulfur 0.05 to 1.0 mass %Calcium 0.02 to 1.0 mass %Zinc 0.01 to 0.3 mass %1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.and for interelement effects by other elements present in thesample matrix. If an e
17、lement is present at significant concen-trations and an inter-element correction for that element is notemployed, the results can be low due to absorption or high dueto enhancement.4.2 If a sample containing barium as an additive above 0.03mass % is measured against a calibration derived from stan-d
18、ards without barium, then results will be low.4.3 If a sample containing chlorine as an impurity above0.03 mass % is measured against a calibration derived fromstandards without chlorine, then the results can be affected.4.4 There can be spectral overlap of one element ontoanother, especially for ph
19、osphorus on sulfur, and the instru-ment must include correction procedures for any such overlaps.5. Apparatus5.1 Energy Dispersive X-ray Fluorescent AnalyzerAnyenergy dispersive X-ray fluorescent analyzer can be used if itsdesign incorporates at least the following features.5.1.1 Source of X-ray Exc
20、itation, X-ray tube with palla-dium, silver, or rhodium target programmable between 4 and atleast 25 keV for preferential excitation to simplify the samplespectra. (WarningOperation of an analyzer using an X-raytube source is to be conducted in accordance with the manu-facturers safety instructions
21、and federal, state, and localregulations)5.1.2 X-ray Detector, gas filled proportional counter withhigh sensitivity and a resolution value not to exceed 1300 eVat 5.9 keV.NOTE 1The limited data from instruments with solid state detectors inthe inter-laboratory precision study did not support their i
22、nclusion in themethod.5.1.3 Primary Beam Filters, to make the excitation moreselective.5.1.4 Secondary Beam FiltersWhen a proportionalcounter is used, these are necessary as a means of discriminat-ing between an analytes X rays and other analytes and thespectrum from the X-ray tube.5.1.5 Multi-Chann
23、el Analyzer, for discrimination betweenan analytes X rays and background X rays.5.1.6 Optional Helium Purgeable Optical Path.5.2 Sample Cells, providing a depth of at least 6 mm andequipped with replaceable X-ray transparent film. Suitablefilms include polypropylene and polycarbonate with thicknessf
24、rom 3.5 to 8 m.5.3 Instrument Setting-Up Samples (Elemental ReferenceSamples), to quantify spectral overlaps. These are requiredwhen the instruments software does not include referencespectra to deconvolute spectra.5.4 Drift Correction Monitors, to correct for instrumentaldrift. At least two samples
25、 are necessary to correct bothsensitivity and baseline drifts. For each element and scatterregion, there shall be one providing a count rate similar tosamples from the upper end of the calibration and anotherproviding a count rate as if from a blank. This last can be ablank oil. For the high concent
26、ration of each element, a glassdisk, XRF fusion bead, or pressed pellet have all been found tobe satisfactory. They can be the same samples as in 5.3.6. Reagents and Materials6.1 Reagent grade chemicals shall be used in all tests.Unless otherwise indicated, it is intended that all reagentsconform to
27、 the specifications of the Committee on AnalyticalReagents of the American Chemical Society where suchspecifications are available.2Other grades can be used, pro-vided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determ
28、ination.6.2 Helium, at least 99.5 % purity, for the optical path of thespectrometer.6.3 Diluent Solvent, a suitable solvent free of metals,phosphorus, and chlorine, and containing less than 10 ppm ofsulfur (for example, deodorized kerosene, white oil, or mineraloil).6.4 Calibration Standard Material
29、s:6.4.1 Certified concentration solutions,3of liquid organo-metallic salts, each containing calcium or zinc, or both. Thesolutions shall be sulfur free or the certificate shall state theconcentration of sulfur. Alternatively, the following standardmaterials can be used.6.4.1.1 Calcium 2-Ethylhexanoa
30、te, approximately 12.3mass % calcium, with a certified value.6.4.1.2 Zinc Cyclohexanebutyrate, approximately 16.2 mass% zinc, with a certified value.6.4.2 Bis(2-Ethylhexyl)Hydrogen Phosphate, 97 % purity(9.62 mass % phosphorus).6.4.3 Di-n-butyl Sulfide, 97 % purity, (21.9 mass % sulfur).6.4.4 Stabil
31、izers, 2-ethylhexanoic acid, 2-ethylamine. Also,proprietary stabilizer/chelating solutions are available commer-cially. Stabilizers shall be free of the additive element.NOTE 2In addition to the calibration standard materials identified in6.4.1-6.4.3, single or multielement calibration standards can
32、 also beprepared from materials similar to the samples being analyzed, providedthe calibration standards to be used have previously been characterized byindependent primary (for example, gravimetric or volumetric) analyticaltechniques to establish the elemental concentration mass % levels.7. Prepara
33、tion of Calibration Standards7.1 To ensure complete solution of all components, preparecalibration standards by precisely weighing the organo-metallic solutions and phosphorus and sulfur solutions with thediluent solvent along with the appropriate stabilizer. Table 2lists suggested concentrations wh
34、en determining empiricalinfluence coefficients. Complete sets of standards based onTable 2 are commercially available.8. Calibration8.1 Spectrometer SettingsFollow the manufacturers rec-ommendations, and set up a series of measurement conditions,(X-ray tube voltage, X-ray tube current, primary beam
35、filter,2Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, D.C. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States P
36、harmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.3These certified concentrated solutions are commercially available.D6481 99 (2010)2secondary beam filter, measurement time, and multichannelanalyzer region of interest) to measure the K spectrum ofphosphorus,
37、 sulfur, calcium, and zinc. Include at least oneregion of backscatter.8.2 Fill respective sample cells nearly full with the calibra-tion standard solutions. Follow the manufacturers recommen-dation to ensure that the cell is full enough such that X-raycount rate does not depend on the amount of samp
38、le in the cell.Make sure that no wrinkles or bulges are present in the film.The film must be flat, and the cell shall be vented.8.3 Place the sample cell in the X-ray beam to measure andrecord the intensity for each element and scatter region in eachcalibration standard in accordance with the condit
39、ions set byfollowing 8.1. Measure each standard two times, using afreshly prepared cell for each measurement.8.4 Measure any instrument setting up samples necessary toquantify spectral overlaps. Use at least the measurement timeof the calibration standards8.5 Measure and record the intensity for eac
40、h element andscatter region of the drift correction monitors. Use at least themeasurement time of the calibration standards.NOTE 3An instrument setting up sample used in 8.4 can also be usedas a drift correction monitor in 8.5 if its elemental composition is suitable.8.6 Use the instruments regressi
41、on software to generate theoptimum calibration curve for each element by applying theappropriate corrections. Suggested corrections are given inTable 3. The variable sulfur content results in a change inbackground for phosphorus because of filter fluorescence. (If afilter is not used, there will be
42、a spectral overlap of sulfur onphosphorus and an overlap correction will be necessary).Sulfur also affects the sensitivity for calcium because of itshigh absorption for that element. Because phosphorus X rayshave an energy below the absorption edge of the sulfur filter, itoverlaps sulfur. (If a filt
43、er is not used, there will also be aspectral overlap of phosphorus on sulfur). Zinc is the heaviestelement in lubricating oil, and therefore, all matrix effects canin practice be corrected by taking a ratio to the high energybackscatter.NOTE 4No instruments in the interlaboratory precision study tha
44、testablished the precision statements used theoretical correction coeffi-cients for mass absorption effects.9. Procedure9.1 Fill a sample cell nearly full with a portion of the sampleto be analyzed. Follow the manufacturers recommendation toensure that the cell is full enough such that X-ray count r
45、atedoes not depend on the amount of sample in the cell. Make surethat no wrinkles or bulges are present in the film. The film mustbe flat. The cell shall be vented, by cutting a hole in the top, ifnecessary.9.2 Place the sample cell in the X-ray beam to measure andrecord the intensity for each eleme
46、nt and scatter region in eachcalibration standard in accordance with the conditions set byfollowing 8.1.10. Calculation10.1 Set the instruments software to calculate the results inmass % to three decimal places.11. Report11.1 Report the following information:11.1.1 Total content for each element, ph
47、osphorus, sulfur,calcium, and zinc in mass %.11.1.2 State that the results were obtained by Test MethodD6481.12. Quality Control (QC)12.1 Typically, one or more stable QC samples that aresimilar in composition to test samples are analyzed regularlyby the testing laboratory. Because data quality requ
48、irementscan vary among testing laboratories, individual laboratoriescan determine the frequency of QC sample analysis and theacceptable control limits.12.2 When QC results are not within control limits, carryout corrective action, such as drift correction or recalibration,or both.12.3 The QC sample
49、precision can be compared withprecision of this test method to determine data quality.TABLE 2 Recommended Concentrations for Standards(all values mass %)Standard Calcium Phosphorus Sulfur Zinc10 0 002 0.005 0.005 0.050 0.053 0.600 0 0 04 0 0.300 0 05 1.00 0 1.00 06 0 0 0 0.3007 0.005 0.250 0.800 0.3008 0.500 0.150 0.500 0.1509 0.010 0.200 0.100 0.25010 0.050 0.010 0.400 0.07511 0.100 0.150 0.200 0.20012 0.200 0.200 0.800 0.10013 0.400 0.005 0.800 0.30014 0.600 0.100 0.500 0.05015 0.800 0.010 0.050 0.10016 1.00 0.300 1.00 0.15017 0.400 0.050 0.600 0.250TABLE 3 Suggeste
