Application of the Hydrostatic Weighing Method for Research and Development of Reference Materials for Thickness and Surface Density of Metallic Single-layer Single-component Coatings

Verification, calibration and graduation of measuring instruments based on non-destructive methods for coating parameter inspection (in particular, X-ray fluorescence) require reference materials for coating thickness. These reference materials are specimens in the form of discs or rectangular parallelepipeds with metallic coatings deposited on them. The certified values of coating thickness for reference materials developed using X-ray fluorescence analysis are established indirectly – using the measured value of surface density and the density of the coating material, which until now in the Russian Federation and other countries has been a reference value. In practice, the density of the deposited coating material differs from the reference value, which leads to incorrect determination of coating thickness.

The aim of the study is to develop reference materials whose certified coating thickness characteristic will be established using the measured value of the coating material density. For this purpose – to determine the coating density – a physical and mathematical model was developed that implements the hydrostatic weighing method, based on the difference in volume between a sample with a coating and without a coating, and taking into account corrections for the density of the ambient air and the density of the working liquid. The experimental part was carried out on equipment from the State Primary Standard of the units of surface density and mass fraction of elements in coatings GET 168–2015.

As a result of the study, a measurement procedure for the density of coating materials was developed, tested and certified in the density range of coating materials (6–10) g/cm³ with an expanded uncertainty of measurements of the density of coating materials from 0.80% to 2.6%. Six types of reference materials of surface density and thickness of single-layer single-component coatings were developed and tested for approval in the coating thickness range (8–33) µm with an expanded uncertainty of coating thickness measurements from 1.5% to 2.9%

Using the developed and certified measurement method for the density of coating materials, metrological assurance of measurements of the thickness of single-layer coatings using the X-ray fluorescence method has been implemented. The field of application of reference materials of thickness and surface density of metallic single-layer single-component coatings is scientific research, mechanical engineering and instrument engineering.

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