Home>ASTM Standards>ASTM B568-98(R2021) pdf free download

ASTM B568-98(R2021) pdf free download

ASTM B568-98(R2021) pdf free download.Standard Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
1. Scope
1.1 This test method covers the use ofX-ray spectrometry to determine thickness ofmetallic and some nonmetallic coatings. 1.2 The maximum measurable thickness for a given coating is that thickness beyond which the intensity of the character- istic secondary X radiation from the coating or the substrate is no longer sensitive to small changes in thickness. 1.3 This test method measures the mass of coating per unit area, which can also be expressed in units of linear thickness provided 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 radioisotope source are not covered by this test method. For information on this important aspect, reference should be made to current documents of the National Committee on Radiation Protection and Measurement, Federal Register, Nuclear Regulatory Commission, National Institute of Standards and Technology (formerly the National Bureau of Standards), and to state and local codes if such exist. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.6 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Summary of Test Method
4.1 Excitation—The measurement of the thickness of coat- ings by X-ray spectrometric methods is based on the combined interaction of the coating and substrate with incident radiation of sufficient energy to cause the emission of secondary radia- tions characteristic of the elements composing the coating and substrate. The exciting radiation may be generated by an X-ray tube or by certain radioisotopes. 4.1.1 Excitation by an X-Ray Tube—Suitable exciting radia- tion will be produced by an X-ray tube if sufficient potential is applied to the tube. This is on the order of35 to 50 kV for most thickness-measurement applications. The chief advantage of X-ray tube excitation is the high intensity provided. 4.1.2 Excitation by a Radioisotope —Of the many available radioisotopes, only a few emit gamma radiations in the energy range suitable for coating-thickness measurement. Ideally, the exciting radiation is slightly more energetic (shorter in wave- length) than the desired characteristic X rays. The advantages of radioisotope excitation include more compact instrumenta- tion essentially monochromatic radiation, and very low back- ground intensity. The major disadvantage of radioisotope excitation is the much lower intensities available as compared with X-ray tube sources. X-ray tubes typically have intensities that are several orders of magnitude greater than radioisotope sources. Due to the low intensity of radioisotopes, they are unsuitable for measurements on small areas (less than 0.3 mm in diameter). Other disadvantages include the limited number ofsuitable radioisotopes, their rather short useful lifetimes, and the personnel protection problems associated with high- intensity radioactive sources. 4.2 Dispersion—The secondary radiation resulting from the exposure of an electroplated surface to X radiation usually contains many components in addition to those characteristic of 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 be done either by diffraction (wavelength dispersion) or by electronic discrimination (energy dispersion). 4.2.1 Wavelength Dispersion—By means of a single-crystal spectrogoniometer, wavelengths characteristic of either the coating or the substrate may be selected for measurement. Published data in tabular form are available that relate spec- trogoniometer settings to the characteristic emissions of ele- ments for each of the commonly used analyzing crystals.

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