Measuring Metal Coating Thickness at Line

Significance of Metal Coating Thickness Measurement

Metal coatings are essential for improving surface characteristics such as corrosion resistance, wear protection, electrical conductivity and adhesion. Precise control of coating thickness is vital to minimize material costs and avoid functional failures. Industries ranging from automotive and aerospace to metal fabrication rely on fast, non-destructive techniques at-line or on-site to ensure product quality and compliance.

Study Objectives and Overview

This application note presents the capabilities of the Thermo Scientific Niton XL5 Plus handheld XRF analyzer for measuring coating thickness and coat weight directly on large or fixed parts. It outlines the analytical method setup, instrument configuration and validation through practical examples involving mono- and multi-layer metal coatings.

Methodology and Fundamental Parameter Approach

The Niton XL5 Plus employs a proprietary fundamental parameter (FP) algorithm to quantify up to four coating layers on various substrates (metals, alloys, plastics or wood) without requiring empirical calibration standards. Users define the number of layers and their compositions—elemental, alloy or pseudo-element—via intuitive on-screen profiles. Measurement results are obtained in seconds, with no sample preparation needed.

Used Instrumentation

The key features of the handheld XRF analyzer include:

• Miniaturized 5 W Ag-anode X-ray tube with 5–50 kV and 5–500 μA operating range
• Large silicon drift detector with graphene window for enhanced light element sensitivity
• ProGuard window protection against damage
• Macro and micro cameras for sample documentation
• Standard 8 mm spot and optional 3 mm collimator for fine or broad area analysis
• FP-based software capable of measuring coat weight or thickness up to four layers

Main Results and Discussion

Three real-world examples demonstrate “out-of-the-box” accuracy:

• Silver plated on copper: Measured thickness 12.88 μm vs. laboratory value 13 μm.
• Zirconium conversion coating over hot-dip galvanized steel: Measured Zr coat weight 40.24 mg/m2 vs. lab value 38 mg/m2; Zn layer near expected 80 g/m2.
• Electroless NiP on Kovar alloy: Measured NiP thickness 18.58 μm vs. certified 20 μm.

These cases cover simple mono-layer and complex multi-element alloy coatings, confirming high accuracy without empirical adjustment.

Benefits and Practical Applications

• Quality control at incoming inspection and final product stages by verifying alloy grade and coating specs
• Cost reduction through minimization of coating overuse or underuse
• Non-destructive testing eliminating the need for sample cutting
• Rapid, on-site results facilitate immediate process adjustments
• Automated averaging, report generation and audit-trail capabilities support compliance with ISO 3497 and ASTM B568

Future Trends and Potential Uses

Handheld XRF is poised for integration into automated production lines and connected quality systems. Advances in detector technology and machine-learning algorithms may expand detection limits to thicker or more complex organic and inorganic coatings. Remote operation and cloud-based analytics will further enhance process control and traceability.

Conclusion

The Thermo Scientific Niton XL5 Plus handheld XRF analyzer offers a versatile, non-destructive solution for accurate metal coating thickness and coat weight measurement directly at-line. Its rapid fundamental parameter approach, combined with user-friendly software and robust hardware, streamlines quality assurance across multiple industries.

References

1. S. Piorek, Coatings, Paint and Thin Film Deposits, Chapter 4 in Portable X-ray Fluorescence Spectrometry Capabilities for In Situ Analysis, Potts & West, RSC Publishing 2008
2. ASTM B568-98 (2009) Standard Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
3. ISO 3497-2000 Measurements of Coating Thickness – X-ray Spectrometric Methods