ASTM_D_5723_-_95_2019.pdf

Designation:D572395(Reapproved 2019)Standard Practice forDetermination of Chromium Treatment Weight on MetalSubstrates by X-Ray Fluorescence1This standard is issued under the fixed designation D5723;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 practice covers the use of X-ray fluorescence(XRF)techniques for determination of the coating weight ofchromium treatments on metal substrates.These techniques areapplicable for determination of the coating weight as chro-mium or total coating weight of a chromium-containingtreatment,or both,on a variety of metal substrates.1.2 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.3 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Summary of Practice2.1 ExcitationThe measurement of chromium treatmentcoating weights by XRF methods is based on the combinedinteraction of the chromium coating and substrate with anintense beam of primary radiation.Since each element fluo-resces at an energy characteristic of the particular element,thisinteraction results in the generation of X rays of defined energy.The primary radiation may be generated by an X-ray tube orderive from a radioisotope.2.2 DetectionThe secondary beam(fluorescent X rays ofthe elements and scattered radiation)is read by a detector thatcan discriminate between the energy levels of fluorescingradiations in the secondary beam.The detection system in-cludes the radiation detector with electronics for pulse ampli-fication and pulse counting.2.3 Basic Principle:2.3.1 A relationship exists between the treatment coatingweight and secondary radiation intensity.This relationship isusually linear within the desired coating weights of thechromium treatments on metal substrates.The measurementsare based on primary standards of known coating weights andinstrument calibration that correlates the secondary radiationintensity with the coating weight quantitatively.2.3.2 The coating weight is determined by measurement ofthe fluorescent X rays of the coating.The detection system isset to count the number of X rays in an energy region that ischaracteristic of X rays from the element of interest.Theelement of interest in this practice is chromium.2.3.3 If a linear relationship exists,the coating weight andnumber of counts of X rays of a chromium treatment on aparticular substrate can be expressed by a conversion factorthat represents the number of counts for a particular coatingweight unit/unit area.This is usually expressed in mg/ft2ormg/m2of chromium or total coating weight.2.3.4 The exact relationship between the measured numberof counts and corresponding coating weight must be estab-lished for each individual combination of substrate andchromium-containing treatment.Usually determined by thetreatment supplier,this relationship is established by usingprimary standards having known amounts of the same treat-ment applied to the same substrate composition as the speci-mens to be measured.2.3.5 Some X-ray apparatus have a data handling systemwhereby a coating weight versus X-ray counts curve may beestablished within the system for the direct readout of coatingweight.If such apparatus does not permit the entry of aconversion factor as described in 2.3.3,it is calibrated using abare,untreated specimen and a minimum of three specimenswith known coating weights of the treatment and substratecombination of interest.The coating weight to be measuredmust be within the range of these known coating weights.Morethan three known specimens must be used if the relationship ofX-ray counts to coating weight is not linear over the range tobe measured.The treatment supplier should be consulted forrecommendations for establishing the curve in the instrumentfor the particular treatment and substrate combination ofinterest.1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.53 on Coil Coated Metal.Current edition approved Dec.1,2019.Published December 2019.Originallyapproved in 1995.Last previous edition approved in 2015 as D5723 95(2015).DOI:10.1520/D5723-95R19.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis inte