ASTM_B_568_-_98_2014.pdf

Designation:B56898(Reapproved 2014)Standard Test Method forMeasurement of Coating Thickness by X-Ray Spectrometry1This standard is issued under the fixed designation B568;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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the use of X-ray spectrometry todetermine thickness of metallic and some nonmetallic coatings.1.2 The maximum measurable thickness for a given coatingis that thickness beyond which the intensity of the character-istic secondary X radiation from the coating or the substrate isno longer sensitive to small changes in thickness.1.3 This test method measures the mass of coating per unitarea,which can also be expressed in units of linear thicknessprovided that the density of the coating is known.1.4 Problems of personnel protection against radiation gen-erated in an X-ray tube or emanating from a radioisotopesource are not covered by this test method.For information onthis important aspect,reference should be made to currentdocuments of the National Committee on Radiation Protectionand Measurement,Federal Register,Nuclear RegulatoryCommission,National Institute of Standards and Technology(formerly the National Bureau of Standards),and to state andlocal codes if such exist.1.5 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:2E135 Terminology Relating to Analytical Chemistry forMetals,Ores,and Related Materials2.2 International Standard:ISO 3497 Metallic CoatingsMeasurement of CoatingThicknessX-ray Spectrometric Methods3.Terminology3.1 Definitions of technical terms used in this test methodmay be found in Terminology E135.4.Summary of Test Method4.1 ExcitationThe measurement of the thickness of coat-ings by X-ray spectrometric methods is based on the combinedinteraction of the coating and substrate with incident radiationof sufficient energy to cause the emission of secondary radia-tions characteristic of the elements composing the coating andsubstrate.The exciting radiation may be generated by an X-raytube or by certain radioisotopes.4.1.1 Excitation by an X-Ray TubeSuitable exciting radia-tion will be produced by an X-ray tube if sufficient potential isapplied to the tube.This is on the order of 35 to 50 kV for mostthickness-measurement applications.The chief advantage ofX-ray tube excitation is the high intensity provided.4.1.2 Excitation by a Radioisotope Of the many availableradioisotopes,only a few emit gamma radiations in the energyrange suitable for coating-thickness measurement.Ideally,theexciting radiation is slightly more energetic(shorter in wave-length)than the desired characteristic X rays.The advantagesof radioisotope excitation include more compact instrumenta-tion essentially monochromatic radiation,and very low back-ground intensity.The major disadvantage of radioisotopeexcitation is the much lower intensities available as comparedwith X-ray tube sources.X-ray tubes typically have intensitiesthat are several orders of magnitude greater than radioisotopesources.Due to the low intensity of radioisotopes,they areunsuitable for measurements on small areas(less than 0.3 mmin diameter).Other disadvantages include the limited numberof suitable radioisotopes,their rather short useful lifetimes,andthe personnel protection problems associated with high-intensity radioactive sources.4.2 DispersionThe secondary radiation resulting from theexposure of an electroplated surface to X radiation usuallycontains many components in addition to those characteristicof the coating metal(s)and the substrate.It is necessary,therefore,to have a means of separating the desired compo-nents so that their intensities can be measured.This can bedone either by diffraction(wavelength dispersion)or byelectronic discrimination(energy dispersion).1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1972.Last previous edition approved in 2009 as B568 98(2009).DOI:10.1520/B0568-98R14.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959