1、Designation: D6481 14Standard 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 indicates the year of
2、original 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. Scope*1.1 This test method covers the quantitative determinationof a
3、dditive 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.1.3 This test me
4、thod 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 containchlorine or barium as an
5、 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 its use. It is th
6、eresponsibility 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 measured to give th
7、efluorescent 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 of sequential ands
8、imultaneous 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 interelement correction fa
9、c-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 the spectrometer
10、.3. Significance and Use3.1 Some oils are formulated with organo-metallicadditives, which act, for example, as detergents, antioxidants,and antiwear agents. Some of these additives contain one ormore of these elements: calcium, phosphorus, sulfur, and zinc.This test method provides a means of determ
11、ining the concen-trations of these elements, which in turn provides an indicationof the additive content of these oils.3.2 Several additive elements and their compounds areadded to the lubricating oils to give beneficial performance(Table 2).3.3 This test method is primarily intended to be used at a
12、manufacturing location for monitoring of additive elements inlubricating oils. It can also be used in central 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,
13、 for lubricating oils, theX-radiation emitted by the element of interest can be absorbedby itself (self-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 significa
14、nt at concentrations varyingfrom 0.03 mass %, due to the heavier elements, to 1 mass %,for the lighter elements. Enhancement effects can be minimisedby selective excitation. The measured concentration for a given1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,
15、Liquid Fuels, and Lubricantsand is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved Dec. 1, 2014. Published January 2015. Originallyapproved in 1999. Last previous edition approved in 2010 as D6481 99 (2010).DOI: 10.1520/D6481-14.*A Summary of Changes se
16、ction appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1element can be mathematically corrected for self-absorptionand for interelement effects by other elements present in thesample matrix. If an elem
17、ent 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-dard
18、s 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 phosp
19、horus 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 Excita
20、tion , X-ray tube withpalladium, silver, or rhodium target programmable between 4and at least 25 keV for preferential excitation to simplify thesample spectra. (WarningOperation of an analyzer using anX-ray tube source is to be conducted in accordance with themanufacturers safety instructions and fe
21、deral, 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 inclusi
22、on in themethod.5.1.3 Primary Beam Filters, to make the excitation moreselective.5.1.4 Secondary Beam FiltersWhen a proportional coun-ter is used, these are necessary as a means of discriminatingbetween an analytes X rays and other analytes and thespectrum from the X-ray tube.5.1.5 Multi-Channel Ana
23、lyzer, 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 thicknessfrom 3.
24、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 are n
25、ecessary 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 concentration
26、 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 the s
27、pecifications 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 determinatio
28、n.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 Materials:6.4.
29、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-Ethylhexanoate, ap
30、proximately 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 Stabilizers,
31、 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 also
32、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.2Reagent Chemica
33、ls, 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 Pharmacopeiaand National
34、 Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.3These certified concentrated solutions are commercially available.TABLE 1 Elements and Range of Concentrations DeterminedElement Concentration RangePhosphorus 0.02 to 0.3 mass %Sulfur 0.05 to 1.0 mass %Calcium 0.02 to 1.0 mass %Zi
35、nc 0.01 to 0.3 mass %D6481 1427. Preparation 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.
36、Table 3lists suggested concentrations when determining empiricalinfluence coefficients. Complete sets of standards based onTable 3 are commercially available.8. Calibration8.1 Spectrometer SettingsFollow the manufacturersrecommendations, and set up a series of measurementconditions, (X-ray tube volt
37、age, X-ray tube current, primarybeam filter, secondary beam filter, measurement time, andmultichannel analyzer region of interest) to measure the Kspectrum of phosphorus, sulfur, calcium, and zinc. Include atleast one region of backscatter.8.2 Fill respective sample cells nearly full with the calibr
38、a-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 sample 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.
39、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 conditions set byfollowing 8.1. Measure each standard two times, using afreshly prepared cell for each measurement.8.4 Measure any instr
40、ument setting up samples necessary toquantify spectral overlaps. Use at least the measurement timeof the calibration standards8.5 Measure and record the intensity for each element andscatter region of the drift correction monitors. Use at least themeasurement time of the calibration standards.NOTE 3
41、An 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 regression software to generate theoptimum calibration curve for each element by applying theappropriate corrections. Suggested correction
42、s are given inTable 4. The variable sulfur content results in a change inbackground for phosphorus because of filter fluorescence. (If afilter is not used, there will be a spectral overlap of sulfur onphosphorus and an overlap correction will be necessary).Sulfur also affects the sensitivity for cal
43、cium 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 filter is not used, there will also be aspectral overlap of phosphorus on sulfur). Zinc is the heaviestelement in lubricating oil, and
44、 therefore, all matrix effects canin practice be corrected by taking a ratio to the high energybackscatter.NOTE 4No instruments in the interlaboratory precision study thatestablished the precision statements used theoretical correction coeffi-cients for mass absorption effects.9. Procedure9.1 Fill a
45、 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 ratedoes not depend on the amount of sample in the cell. Make surethat no wrinkles or bulges are present in the film. The film must
46、be 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 element and scatter region in eachcalibration standard in accordance with the conditions set byfollowing 8.1.TABLE 2 Lubricants and Add
47、itive MaterialsElement Compounds Purpose/ApplicationCalcium Sulfonates, phenates Detergent inhibitors, dispersantsPhosphorus Dithiophosphates, phosphates phosphites Anti-rusting agents, extreme pressure additives, anti-wearSulfur Base oils, sulfonates, thiophosphates, polysulfides andother sulfurize
48、d componentsDetergents, extreme pressure additives, anti-wearZinc Dialkyldithiophosphates, dithiocarbamates, phenolatescarboxylatesAnti-oxidant, corrosion inhibitors, antiwear additives, detergents, crankcaseoils, hypoid gear lubricants, aircraft piston engine oils, turbine oils, automatictransmissi
49、on fluids, railroad diesel engine oils, brake lubricantsTABLE 3 Recommended Concentrations for Standards(all values mass %)Standard Calcium Phosphorus Sulfur Zinc100002 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 4 Suggested Corrections for Optimum Cal
