Feasibility of laser-induced breakdown spectroscopy for determination of neodymium in magnet alloys

Abstract

The quantification of rare earth elements in (Nd–Pr)–FeB alloys used in the production of super magnets is required to ensure the quality of the raw material and a final product with suitable properties. Laser-induced breakdown spectroscopy is attractive to this aim by avoiding the need for decomposition of the refractory material, but quantitative analysis requires proper calibration approaches to overcome matrix effects. This work proposes a novel analytical method for Nd determination in (Nd,Pr)–Fe–B alloys after sample fusion pretreatment. The instrumental parameters were optimized aiming at higher sensitivity (delay time = 0.50 μs, pulse energy = 20 mJ, number of laser pulses = 401, and spot size = 65 μm) and the performance of three different calibration approaches, namely external standard calibration (EC), multi-energy calibration (MEC), and slope ratio calibration (SRC) was evaluated. EC based on standards spiked with increasing amounts of Nd₂O₃ on Al₂O₃ as diluent yielded accurate results (relative errors < 20%), whereas accuracy of MEC was impaired (relative errors > 57%), because of the lack of emission lines with suitable sensitivity. SRC stood out due to calibration with a single standard and accurate results, as demonstrated by agreement with reference values at 95% confidence level and relative errors <3%.