A robust and cost-effective protocol to fabricate calibration standards for the thickness determination of metal coatings by XRF

The XRF analysis is the most widespread in the industry setting to determine the thickness of metallic coatings, thanks to its ease of use, robustness, and non-destructive nature. However, accurate measurement requires primary standards that are expensive, not always available, and must be periodically replaced due to a limited shelf-life. In this context, we propose a versatile and cost-effective way for measuring the thickness of metallic coatings. Our method relies on a calibration curve based upon self-produced standards made through electroplating process and measured by a cross-sectional microscopy observation, either by SEM or light microscope. Thickness distribution was sufficiently homogeneous to be consistent with certified standard specifications: 5% of thickness variation in the central portion of the coatings (1 cm2) could be achieved for cathode length starting from 5 cm. Moreover, thickness distribution can be quantitatively predicted, relying only on primary current simulations, almost on simple shaped objects. The self-produced standard fit the calibration curve with a R2 > 0.999. Comparing different XRF quantitative methods with Student's t-test, we demonstrated that the proposed protocol is as effective as certified standards-based methods in terms of accuracy but at significantly lower costs.