Coating Measurement Using Handheld X-Ray Fluorescence Abstract Handheld X-ray fluorescence (HHXRF) can be used to measure coating thicknesses with advantages in precision and portability compared to other technologies. For benchtop analysis, analyzing coatings applied over large surface areas often requires destructive procedures. HHXRF overcomes this limitation and provides a nondestructive coating thickness testing capability. A simple, user-friendly calibration built into the instrument interface enables the use of a certified standard to determine up to three layers of accurate and precise coating thicknesses. HHXRF coating measurements, which are independent of the substrate material, provide a user the freedom to analyze any deposited coating comprised of elements Ti through Pu. Because of the large elemental range of analysis, many corrosion-, wear-, and adhesion-resistant coatings measured in labs near the site of action can benefit from the precise results returned by HHXRF.

1. Coating Measurement Using Handheld X-Ray Fluorescence
Karen Paklin, Peter Faulkner, Dillon McDowell
Presented by Dillon McDowell – ECNDT 2018

2. Overview
¡ Basics of handheld X-ray fluorescence (HHXRF)
¡ Physics of coatings in XRF
– Beer-Lambert law of absorption
¡ Application of theory — experimental analysis
– Vanta™ instrumentation
– Results of lab testing
– Use of single-point calibration
¡ Overview of capabilities
– Key factors affecting thickness measurement
¡ Conclusion
– Strengths and limitations

3. X-ray Fluorescence Spectroscopy
¡ First demonstrated in 1912
¡ First handheld systems appeared in the late
1990s
¡ Exciting a sample with X-rays generates a
fluorescence response unique to the elements in
the sample
¡ Measuring that response provides compositional
information
¡ Used for various commercial applications
– Metals/alloys
– Soil/geologic samples
– Consumer products

4. XRF Theory — Beer-Lambert Law of Absorption
¡ Beer-Lambert law of absorption
I" = I$ exp( )*+, ∗.∗")
¡ I" = intensity of the X − ray exiting the sample
¡ I$ = intensity of the X − ray entering the sample
¡ MAC = mass attenuation coefDicient of the sample
¡ ρ = density ofthe sample
¡ t = thickness of the sample

5. Beer-Lambert in Action — Zinc (Zn) on Iron (Fe) (Galvanized Steel)

6. Experiment Overview
¡ Instrumentation: Olympus Vanta™ handheld XRF analyzer
– Model: VCR & VMR (rhodium (Rh) anode, silicon drift detector
(SDD ) system)
– Vanta analyzer used in the Work Station for sample
presentation consistency
¡ Used “Coating” method developed based on Beer-Lambert
– Uses 40 keV excitation conditions
¡ Tested multiple lab-assayed nickel (Ni) coatings on various
substrates (copper (Cu), iron (Fe)) as well as Cu coatings on
various other substrates (Ni, wood, polyethelyne)
¡ Single-point calibration feature used to inform algorithm of
testing regime
– Not required, but helps correct for common nonlinear effects

7. Results — Ni on Cu Substrate

8. Results – Cu on Various Substrates

9. Results — Ni on Fe Substrate (Comparison on VCR)

10. Key Factors Affect Coatings Measurement
¡ Substrate composition
– Nonmetallic substrates have more scattering effects,
which may impact predicted intensity
¡ Coating concentration
– Technique effective for “Pure” coatings (i.e. >85% of a
certain element)
– Multielement and/or oxide coatings have different (and
more complex) intensity responses
¡ Energy overlap potential of coating and substrate
– Neighboring elements have stronger interactions if
characteristic intensity is near absorption edge

11. Conclusion
¡ Strengths
– Very fast and effective on thin metallic coatings
– Performs better on thinner rather than thicker coatings (precision as low as 20 nm)
– Can measure multiple layers
– While out-of-box calibration is effective, single-point calibration provides the best accuracy
¡ Limitations
– Requires knowing sample configuration and composition in advance
– Currently only supports single-element coatings
– Substrate and interelement effects may impact performance, particularly on thicker coatings
– Maximum possible thickness varies from element to element

12. Olympus is a registered trademark, and Vanta is a trademark of Olympus Corporation.