Editorial Feature

The Role of XRF in Ensuring Compliance with Metal Safety Standards

In many industries, the quality and safety of the metals used in manufacturing, construction, and consumer goods are of utmost importance. To ensure that these materials fulfill strict safety standards, it is essential to conduct a thorough analysis of their elemental makeup. Among the numerous available analytical methods, X-ray fluorescence (XRF) is a vital approach for metal safety assessment. This article provides an overview of XRF and its application for metal analysis.

The Role of XRF in Ensuring Compliance with Metal Safety Standards

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What is XRF?

XRF spectrometer is an analytical instrument that helps analyze various metal-based materials by directing X-ray beams at them. This non-destructive method provides qualitative and quantitative elemental information regarding the material of interest. XRF analyzers measure the fluorescence emitted by a sample when excited by the primary X-ray source.

The fluorescence emitted by each component in the sample is specific to the element representing it. Thus, XRF is a promising method for elemental determination in industrial, research, and development laboratories.

Although XRF spectrometers belong to the family of atomic spectrometry techniques, their ability to determine almost all the elements in the periodic table to detection limits is often in the 1–10 mg kg−l range position XRF spectrometry at the forefront.

How does an XRF Spectrometer work?

An XRF spectrometer consists of an X-ray source and detector. The primary X-rays generated by the X-ray source are incident on the sample and may pass through filters to modify the X-ray beam. When the incident X-rays hit the atoms in the sample, they react to produce secondary X-rays that are collectively processed by the detector to produce an X-ray spectrum consisting of intensity peaks plotted against their energy. The peak energy in the spectrum indicates the elements present in the sample, and the peak intensity represents the number of elements present in the sample.

The electrons in a stable atom occupy different energy levels. Each energy level is filled with a certain number of electrons. When a high-energy primary X-ray beam collides with an atom, its equilibrium is affected, causing the ejection of an electron from the low-energy level to the high-energy level, creating a vacancy. Consequently, these atoms become unstable. The stability is reinstated by the de-excitation of the electron from a higher energy level to the vacancy. Here, de-excitation energy is emitted in the form of secondary X-rays.

The Role of XRF in Museum Metal Artifacts

Museum artifacts are primarily composed of gold and silver alloys. Determining the chemical composition of these alloys is crucial for the initial grouping or classification of the analyzed objects, in addition to their archaeological characteristics. These different groups may indicate distinct manufacturing techniques and can aid in addressing the questions of authenticity.

XRF analysis offers extensive possibilities for understanding ancient metallurgy, particularly in terms of corrosion and its effects on the materials. Corrosion can alter the composition of an alloy and create unevenness on its surface or within the material.

The structure of the corroded layer depends on various factors, including alloy composition, storage conditions, and previous treatments. This layer can vary in thickness and consists of different compounds, primarily oxides and carbonates.

Although XRF analysis has limitations in terms of depth resolution, it can still qualitatively identify the surface elemental changes caused by enrichment or depletion. When used with proper assessment and reference data, portable XRF devices can detect these changes. However, to study the distribution of corrosion products on a surface, micro-XRF analysis with a smaller beam spot size of approximately 80 µm is necessary. This technique helps identify the major and minor components of corrosion by detecting their specific elements.

To perform micro-XRF analysis, specific requirements must be met, including the ability to detect low-atomic-number elements, such as phosphorus (P), sulfur (S), and chlorine (Cl), and medium-Z elements, such as silver (Ag), tin (Sn), and antimony (Sb). Small beam spot sizes, precise scans, and high-performance optical and detection systems are also essential.

XRF Analysis of Irregularly Shaped Metal Alloys

When using XRF to analyze metal alloys, the X-ray signals of the samples are typically compared with those of standard references to obtain accurate measurements. To account for any errors caused by the irregular shape or position of the object during analysis, additional correction factors should be applied to the X-ray signals.

These correction factors help correct for any discrepancies in measurement caused by the object's shape or position, particularly when the angles of the X-rays are inconsistent. Using these factors ensures precise measurements of the metal content.

For example, when studying gold-based alloys, the precision of the measurement setup can significantly affect results. In some cases, highly accurate results can be achieved with appropriate equipment, with an error of less than 1% owing to the shape of the object. Improved detectors can further reduce errors, particularly when analyzing jewelry. However, to minimize errors in the X-ray machine, it is essential to have a stable and reliable system.

Recent Studies

A study published in the Journal of Hazardous Materials examined the environmental and health implications of low-cost jewelry for adults on Chinese e-commerce platforms. In this study, eight heavy metal impurities (lead (Pb), cadmium (Cd), and mercury (Hg)) were analyzed using portable XRF, and all 106 samples contained heavy metals, with mercury being the most common. 

The results showed that 71% of the samples exceeded the European Union (EU) limit for Pb, and 51% exceeded the EU limit for Cd. These findings suggest the need for stricter regulations and monitoring in the jewelry industry to protect the environment and human health. This study highlights the importance of using portable XRF for rapid, non-destructive, and in situ analysis of heavy metals in jewelry and addresses the lack of literature on environmental risk assessments of low-cost jewelry for adults from China.

Another study published in Manufacturing Letters proposed a novel XRF method for quality inspection of thin lithium (Li) metal anodes. This method was used to determine the Li coating thickness to calculate the Li mass absorption coefficient.

The high correlation between the calculated and previously reported coefficient values in the literature indicated that this method could be a promising tool for quality inspection. The suggested XRF method could also potentially be used to detect internal and surface defects in Li coatings, as well as to identify chemical impurities.

This study demonstrated the potential of incorporating the XRF analysis system as a quality inspection tool for the commercialization and large-scale manufacturing of Li metal anodes and next-generation electric vehicle (EV) batteries.

Conclusion

Overall, the use of XRF spectrometry is essential for evaluating the quality and safety of metals across various industries. By utilizing X-ray beams to analyze materials, XRF spectrometry provides both qualitative and quantitative elemental information without harming the sample. The technology is highly effective at identifying a broad range of elements with great precision.

More from AZoOptics: XRF For Authenticating Metallic Objects in the Art World

References and Further Reading 

Bonizzoni, L., Maloni, A.,  Milazzo, M. (2006). Evaluation of effects of irregular shape on quantitative XRF analysis of metal objects. X‐Ray Spectrometry, 35(6), 390-399.

https://doi.org/10.1002/xrs.926 

Karydas, A. G. (2007). Application of a portable XRF spectrometer for the non‐invasive analysis of museum metal artifacts. Annali di Chimica: Journal of Analytical, Environmental and Cultural Heritage Chemistry, 97(7), 419-432.  

https://doi.org/10.1002/adic.200790028

Jurowski, K. (2023). The toxicological assessment of hazardous elements (Pb, Cd and Hg) in low-cost jewelry for adults from Chinese E-commerce platforms: In situ analysis by portable X-ray fluorescence measurement. Journal of Hazardous Materials, 460, 132167. 

https://doi.org/10.1016/j.jhazmat.2023.132167

Xu, S., Haddad, D., Balogh, M. P. (2023). X-ray fluorescence for lithium metal anode quality inspection. Manufacturing Letters, 35, 1-5.  

https://doi.org/10.1016/j.mfglet.2022.10.00

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Bhavna Kaveti

Written by

Bhavna Kaveti

Bhavna Kaveti is a science writer based in Hyderabad, India. She has a Masters in Pharmaceutical Chemistry from Vellore Institute of Technology, India, and a Ph.D. in Organic and Medicinal Chemistry from Universidad de Guanajuato, Mexico. Her research work involved designing and synthesizing heterocycle-based bioactive molecules, where she had exposure to both multistep and multicomponent synthesis. During her doctoral studies, she worked on synthesizing various linked and fused heterocycle-based peptidomimetic molecules that are anticipated to have a bioactive potential for further functionalization. While working on her thesis and research papers, she explored her passion for scientific writing and communications.

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