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<p>Glow discharge optical emission spectroscopy (GD-OES) was investigated as a rapid characterization method for End-of-Life (EoL) neodymium-iron-boron (NdFeB) permanent magnets to support recycling-oriented sorting and process selection. The method was applied to analyze the coating systems, near-surface contamination, and bulk material composition of EoL magnets originating from different application fields. Close attention was placed on the use of radio-frequency GD-OES (RF-GD-OES), a variant of GD-OES that enables the investigation of electrically non-conductive materials and coatings, making it suitable for the analysis of epoxy-coated EoL magnets. Various coating systems commonly found on EoL magnets, including epoxy coatings, zinc (Zn) coatings, multilayer system of nickel, copper and nickel (Ni/Cu/Ni), were successfully identified by RF-GD-OES. In addition to determining the elemental composition of the coating layers, the method enabled the determination of coating thicknesses through depth profiling. The obtained layer structures and coating thicknesses were compared with cross-sectional SEM investigations. An overlay of GD-OES depth profiles with SEM cross-sectional images demonstrated good agreement, indicating that GD-OES provides consistent information on coating architecture and layer thicknesses. Furthermore, the technique proved suitable for detecting oxygen- and carbon-rich surface regions associated with corrosion and contamination, as well as for identifying magnets treated by grain boundary diffusion (GBD) processes. To enable the assessment of rare earth element contents, an internal semi-quantitative calibration approach was developed for neodymium (Nd), dysprosium (Dy), and praseodymium (Pr). Compared with conventional characterization methods such as SEM/EDXS cross-sectional analysis, GD-OES requires significantly less sample preparation and provides rapid access to both elemental depth distributions and light-element information, including carbon, oxygen, and boron. The results demonstrate the potential of RF-GD-OES as an efficient characterization tool for the assessment and recycling-oriented sorting of EoL NdFeB magnets.</p>

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Surface induced investigation of the chemical composition of end-of-life magnets with GD-OES for the development of efficient recycling strategies

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  • 发表日期：

    2026年7月11日

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  • Frank Lindenmann,
  • Peter Fleissner,
  • Laura Grau,
  • Stefan Böhm,
  • Carlo Burkhardt

摘要

Glow discharge optical emission spectroscopy (GD-OES) was investigated as a rapid characterization method for End-of-Life (EoL) neodymium-iron-boron (NdFeB) permanent magnets to support recycling-oriented sorting and process selection. The method was applied to analyze the coating systems, near-surface contamination, and bulk material composition of EoL magnets originating from different application fields. Close attention was placed on the use of radio-frequency GD-OES (RF-GD-OES), a variant of GD-OES that enables the investigation of electrically non-conductive materials and coatings, making it suitable for the analysis of epoxy-coated EoL magnets. Various coating systems commonly found on EoL magnets, including epoxy coatings, zinc (Zn) coatings, multilayer system of nickel, copper and nickel (Ni/Cu/Ni), were successfully identified by RF-GD-OES. In addition to determining the elemental composition of the coating layers, the method enabled the determination of coating thicknesses through depth profiling. The obtained layer structures and coating thicknesses were compared with cross-sectional SEM investigations. An overlay of GD-OES depth profiles with SEM cross-sectional images demonstrated good agreement, indicating that GD-OES provides consistent information on coating architecture and layer thicknesses. Furthermore, the technique proved suitable for detecting oxygen- and carbon-rich surface regions associated with corrosion and contamination, as well as for identifying magnets treated by grain boundary diffusion (GBD) processes. To enable the assessment of rare earth element contents, an internal semi-quantitative calibration approach was developed for neodymium (Nd), dysprosium (Dy), and praseodymium (Pr). Compared with conventional characterization methods such as SEM/EDXS cross-sectional analysis, GD-OES requires significantly less sample preparation and provides rapid access to both elemental depth distributions and light-element information, including carbon, oxygen, and boron. The results demonstrate the potential of RF-GD-OES as an efficient characterization tool for the assessment and recycling-oriented sorting of EoL NdFeB magnets.