Determination of Trace Elements and Main Components in Permanent Magnet Alloys by HR-Array ICP-OES Application Note · PlasmaQuant 9100 Elite

Introduction

Permanent magnets are employed in a large variety of applications and devices in the fields of clean energy technologies and consumer products. Today, they are utilized as key components in electric generators as part of wind turbines, motors of electric vehicles as well as tools, energy saving lighting, cellphones, hard disk drives and flat panel television devices. Their applications stretch into the fields of medical instrumentation (MRI) and even magnetic toys.

Nowadays, neodymium magnets are the strongest type of commercially available magnets with superior performance compared to traditional magnetic compounds such as AlNiCo and ferrite magnets. Additionally, neodymium magnets are cheaper in comparison to other rare earth element (REE) based magnets like samarium-cobalt compounds.

Neodymium magnets are predominantly alloys of neodymium, iron and boron in the structure of Nd2Fe14B. Additives like dysprosium, terbium or other REEs are often used to increase the curie temperature, the temperature where a magnetic compound loses its ferromagnetic properties, in order to allow for high temperature applications of this magnet type. The resulting Curie temperature and hence, the magnetic properties at elevated temperatures, strongly depend on the contents and ratios of the REE additives. Neodymium magnets are highly susceptible to corrosion if they are employed in a humid, caustic or acidic environment. Therefore, protective coatings of metals such as Nickel orNickel-Copper layers need to be applied via an electroplating process, whereas the thickness of the applied layers are a direct measure for the corrosion resistance of the entire magnet assembly.

Since the contents of the main components (Neodymium, Iron and Boron), the additives (Dysprosium, Terbium, REEs) and the base metals of the protective coating define the magnetic properties and corrosion resistance, and hence the applicability of the magnets, a stringent quality control is required as part of the production process. In this regard, spectroscopic methods such as optical emission spectroscopy with inductively coupled plasma (ICP-OES) represent an ideal tool to analyze main elemental components in the percentage range alongside traces of additives and impurities in the sub mg/kg range. REEs and transition metals are infamous to produce extremely line-rich spectra with a high risk of spectral interferences on the most prominent analyte lines. High contents of iron, neodymium, dysprosium and terbium produce thousands of highly pronounced emission lines. This complicated spectral situation requires a high-resolution spectrometer in order to resolve severe interferences and allow for the use of sensitive emission lines for the analysis of trace concentrations. Additionally, a high robustness of the plasma system is required to allow for minimal dilution factors of the digested samples. In combination with a high base sensitivity, this allows for optimal analytical performance in the trace and major concentration ranges. In this regard, the high-resolution Array ICP-OES, the PlasmaQuant 9100 Elite offers an industry-leading spectral resolution of 2 pm @ 200nm to resolve even most severe spectral interferences, a highly robust plasma and torch system to run highly concentrated sample aliquots and a high sensitivity to achieve LODs in the sub mg/kg range in highly demanding sample types such as REE magnets.