X-Ray Fluorescence (XRF): How It Works and Where It’s Used

What Is XRF Analysis?

X-ray fluorescence (XRF) is a non-destructive analytical technique that identifies elemental composition and measures coating thickness by irradiating a sample with X-rays and analysing the characteristic fluorescent X-rays emitted in response. Handheld XRF analysers have made the technique practical for field use on large or immovable parts that can’t be brought to a benchtop instrument.

X-Ray Fluorescence (XRF) Applications

• X-ray fluorescence can benefit soil surveys, investigations of igneous, sedimentary, and metamorphic petrology, and much more.
• Quality control is essential in many industries, including mining (for example, for determining ore grade), cement production, ceramic and glass manufacture, and metallurgy.
• Studies of the natural world (such as the composition of dust on air filters)
• Sulfur levels in crude oils and finished petroleum products are a major concern for the petroleum industry.
• Portable X-ray fluorescence spectrometers (for use in geological and environmental research) are also used in the field.
• Bulk chemical analyses of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) and trace elements (in abundances >1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) in rock and sediment are ideal applications for X-ray fluorescence. – The lowest detectable concentrations of trace elements are on the order of a few ppm.
• X-ray fluorescence analysis is restricted to large samples (typically > 1 gram) that can be prepared as a powder and homogenised effectively; materials for which compositionally similar, well-characterised standards are available; materials containing high abundances of elements for which absorption and fluorescence effects are reasonably well understood; and materials for which X-rays can be efficiently absorbed by the sample.
• When working with rocks, ores, sediments, and minerals, grinding the material to a powder is standard practice. This allows for direct analysis, which is useful for analyzing trace elements. The proportionality comparison to the standards is complicated by the vast variation in abundances of several elements, especially iron, and the diversity in particle sizes present in a powdered sample. This is why it is standard practice to combine the powdered sample with a chemical flux before melting it in a furnace or gas burner. The abundances of the (now somewhat diluted) elements can be estimated by melting the material into a homogeneous glass, which can then be examined.

Where Does X-Ray Fluorescence (XRF) Shine, and Where Does It Fall Short?

Strengths

Particular fields of study that benefit greatly from X-ray fluorescence analysis are:

• Analysis of rocks and sediments for their principal chemical components (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P)
• Rock and sediment samples were analysed chemically for the presence of trace elements (>1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zn).

Also Read – What Is a Heavy Metal Test? Methods, Detection Limits & Applications

X-Ray Fluorescence (XRF) Test Limitations

• Depending on the wavelength and intensity of the input X-rays, the XRF can theoretically detect X-ray emissions from nearly all elements.
• The capacity of commonly accessible commercial tools to precisely and correctly determine the abundance of elements with Z11 in most natural earth materials is severely lacking.
• Different isotopes of an element can be analysed with different equipment (see TIMS and SIMS), as XRF analyses cannot do so.
• Since wet chemical analysis and Mossbauer spectroscopy can distinguish between ions of the same element in different valence states, these methods are used instead of XRF examinations when analysing rocks and minerals.

Test Procedure (Coating Thickness)

• Develop a calibration curve using standard samples with known coating thicknesses on the same base material as the test sample
• Irradiate the sample surface with primary X-rays from the XRF analyser
• Measure the intensity of fluorescent X-rays emitted from both the substrate and coating layer(s)
• Calculate coating thickness from the absorption of the substrate signal or the emission intensity of the coating layer(s), referenced against the calibration curve
• For handheld analysers, a one-point calibration shot (roughly 30 seconds) can refine results, with full readings often available in as little as 10 seconds

Key Limitations

XRF’s information depth is limited — typically only a few tens of microns for the signal actually reaching the detector, even though X-rays can penetrate roughly 100 microns into the material. This makes XRF excellent for surface layers and moderate-thickness coatings, but less suited to characterising deep subsurface structure, where techniques like ultrasonic thickness gauging are more appropriate.

Industry Specifications Referencing XRF

• Common applications: metal finishing, electroplating QC, recycled metal sorting, archaeometry, semiconductor thin-film analysis

Conclusion

Handheld XRF’s biggest practical advantage is that it eliminates the need to cut samples from large or high-value parts just to verify coating thickness or alloy composition — a genuinely non-destructive answer in seconds, provided the calibration model matches the substrate and coating combination being measured.

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