ASTM_D_6481_-_14.pdf

Designation:D648114Standard 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 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.Scope*1.1 This test method covers the quantitative 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.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 containchlorine 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 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 measured 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 of 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 interelement 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 the spectrometer.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 determining 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 amanufacturing 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,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 significant 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,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 section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 element can be mathematically corrected for self-absorptionand for interelement effects by other elements present in thesample matrix.If an element 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 calibratio