ASTM B568-98 pdf free.Standard Test Method for Measurement of Coating Thickness by X-Ray Spectrometry.
If a referee test is required in order to resolve adisagreement, it shall be performed by using suitable StandardReference Material (SRM)* thickness standards from theNational Institute of Standards and Technology (NIST), if suchstandards are available. A suitable SRM standard is an SRMstandard of the same substratel/coating combination for whichthe XRF gage was calibrated, the thickness of which is withinthe range of the calibration， preferably close to that of the testspecimens being measured. The SRM shall be measured 5times，each measurement being made under the same condi-tions as used for the measurement of the test piece. If theaverage of the 5 measurements of the SRM differs from thecertified mass per unit area of equivalent thickness by morethan 10 %, the calibration is not valid.SRMs are issued by NIST and include coating thicknessSRMs for some coating systems. The stated mass per unit area of eachcoating thickness SRM is certified to be within 5 % of the true mass perunit area.
Operate each instrument in accordance with the manu-facturer’s instructions, paying attention to the factors listed inSection 6.Calibrate it in accordance with Section 7.The instrument calibration shallbe checked periodically or before a test series, by remeasuringone of the calibration standards or a reference specimen withknown mass per area or thickness. If there is a change of themeasured thickness that is large enough to preclude meetingthe requirements of section 11, recalibrate the instrument.If the X-ray absorption tech-nique is used, verify that the substrate thickness of the testspecimens exceeds the critical thickness.If not, make sure thatthe calibration has been made with a substrate having the samethickness and emission properties as the test specimens.
Measurement Area-The size of the measurementarea will depend on the size of the collimator used to restrictand control the size of the excitation beam. In no case shall themeasurement area be larger than the coated area available onthe test specimen. Suitable means must be provided to per-fectly align the test specimen relative to the excitation beam.Remove all foreign materials,such as dirt, grease,lacquer，oxides， and conversion coatingsfrom the surface before the measurement by cleaning withoutremoving any of the coating material. Avoid specimen areashaving visible defects such as flux，acid spots,and dross inmaking measurements.Use a sufficient measuring time toobtain a repeatability that will yield the desired accuracy (see6.1).Convert the intensity read-ings to thickness units.The conversion is made automaticallyby most commercial coating thickness instruments.
The equipment,its calibration,and its operation shallbe such that the coating thickness can be determined with anuncertainty of less than 10 % at 95 % confidence level. Although an uncertainty of less than 10 %may beachieved consistently for a great number of applications,theuncertainty may be greater when the coating thickness is lessthan 1 um.ASTM B568 pdf download.