Comparative Evaluation of Anti-Corrosion Coatings for NdFeB-Type Magnets with Respect to Performance and Recyclability via Hydrogen-Assisted Recycling (HPMS)

Carlo Burkhardt,Antje Lehmann,Maximilian Mungenast,Benjamin Podmiljšak,Laura Grau,Spomenka Kobe,Mirko Trautz,Peter Fleissner

doi:10.3390/materproc2021005087

Carlo Burkhardt, Antje Lehmann + Show 6 more

Open Access

https://doi.org/10.3390/materproc2021005087

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Abstract

Various anti-corrosion coatings used on commercially available NdFeB-type magnets were comparatively examined for their durability and suitability for magnet reprocessing by hydrogen-assisted recycling (HPMS). Layer thickness and structure were determined by systematic microstructural analysis, and a standardized corrosion test was used to assess the durability of each layer. Chemical composition of the coatings was analyzed using SEM/EDS and ICP-OES. HPMS behavior was investigated using in situ video monitoring. The results of the presented investigations are an important contribution for the implementation of a sorting and labeling system to support and facilitate a commercially viable recycling of permanent magnets on an industrial scale.

Highlights

It is impossible to imagine the future without permanent magnets based on rare earth elements (REEs)
In HPMS, the EOL magnet is exposed to hydrogen in a closed vessel at slightly elevated pressure for a short time, which hydrogenates and expands the Nd-rich grain boundary phase, causing the bulk material to disintegrate into friable, hydrogenated, and demagnetized NdFeB granules/powder that can be mechanically separated from the remaining impurities [4]
The findings of this study are an important input for a recycling, sorting, and labelling system for permanent magnets developed under the EU-funded MaXycle and SUSMAGPRO projects, which is planned to be introduced to facilitate commercially attractive EOL

Summary

Introduction

It is impossible to imagine the future without permanent magnets based on rare earth elements (REEs). They are essential for converting electricity into mechanical energy, especially for electric motors and electric generators. They are key materials for the fulfilment of the “European Green Deal” towards a carbon neutral society [1]. To enable a commercially viable circular economy for NdFeB magnets using HPMS for different scrap sources, it is vital to investigate the influence of different anti-corrosion coatings currently on the market, since (1) different penetration properties for hydrogen may have a significant influence on the kinetics of the hydration reaction and regarding (2). The findings of this study are an important input for a recycling, sorting, and labelling system for permanent magnets developed under the EU-funded MaXycle and SUSMAGPRO projects, which is planned to be introduced to facilitate commercially attractive EOL magnet recycling [6]

Materials and Methods

Microstructural Analysis

Specification

ICP-OES

Discussion

Conclusions

Geometry