ASTM_E_1508_-_12a.pdf

Designation:E150812aStandard Guide forQuantitative Analysis by Energy-Dispersive Spectroscopy1This standard is issued under the fixed designation E1508;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.Scope1.1 This guide is intended to assist those using energy-dispersive spectroscopy(EDS)for quantitative analysis ofmaterials with a scanning electron microscope(SEM)orelectron probe microanalyzer(EPMA).It is not intended tosubstitute for a formal course of instruction,but rather toprovide a guide to the capabilities and limitations of thetechnique and to its use.For a more detailed treatment of thesubject,see Goldstein,et al.(1)This guide does not cover EDSwith a transmission electron microscope(TEM).1.2 UnitsThe values stated in SI units are to be regardedas standard.No other units of measurement are included in thisstandard.1.3 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 use.2.Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to MetallographyE673 Terminology Relating to Surface Analysis(Withdrawn2012)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsFor definitions of terms used in this guide,see Terminologies E7 and E673.3.2 Definitions of Terms Specific to This Standard:3.2.1 accelerating voltagethe high voltage between thecathode and the anode in the electron gun of an electron beaminstrument,such as an SEM or EPMA.3.2.2 beam currentthe current of the electron beam mea-sured with a Faraday cup positioned near the specimen.3.2.3 Bremsstrahlungbackground X rays produced by in-elastic scattering(loss of energy)of the primary electron beamin the specimen.It covers a range of energies up to the energyof the electron beam.3.2.4 critical excitation voltagethe minimum voltage re-quired to ionize an atom by ejecting an electron from a specificelectron shell.3.2.5 dead timethe time during which the system will notprocess incoming X rays(real time less live time).3.2.6 k-ratiothe ratio of background-subtracted X-ray in-tensity in the unknown specimen to that of the standard.3.2.7 live timethe time that the system is available todetect incoming X rays.3.2.8 overvoltagethe ratio of accelerating voltage to thecritical excitation voltage for a particular X-ray line.3.2.9 SDD(silicon drift detector)An x-ray detector char-acterized by a pattern in the biasing electrodes which inducesgenerated electrons to move laterally(drift)to a small-areaanode for collection,resulting in greatly reduced capacitancewhich to a first approximation does not depend on the activearea,in contrast to conventional detectors using flat-plateelectrodes.(2)3.2.10 shaping timea measure of the time it takes theamplifier to integrate the incoming charge;it depends on thetime constant of the circuitry.3.2.11 spectrumthe energy range of electromagnetic ra-diation produced by the method and,when graphicallydisplayed,is the relationship of X-ray counts detected to X-rayenergy.4.Summary of Practice4.1 As high-energy electrons produced with an SEM orEPMA interact with the atoms within the top few micrometresof a specimen surface,X rays are generated with an energycharacteristic of the atom that produced them.The intensity of1This guide is under the jurisdiction ofASTM Committee E04 on Metallographyand is the direct responsibility of Subcommittee E04.11 on X-Ray and ElectronMetallography.Current edition approved Dec.1,2012.Published February 2013.Originallyapproved in 1993.Last previous edition approved in 2012 as E1508 12.DOI:10.1520/E1508-12A.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 such X rays is proportional to the mass fraction of that elementin the specimen.In energy-dispersive spectroscopy,X raysfrom the specimen are detected by a solid-state spectrometerthat converts them to electrical pulses proportional to thecharacteristic X-ray energies.If the X-ray intensity of eachelement is compared to that of a standard of known orcalculated composition and suitably corrected for the effects ofother elements present,then the mass fraction of each elementcan be calculated.