Chemical Characterization in the Production Chain of Permanent Magnets by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) – Precise Quantification of Nd, Pr, Fe and B in Super-Magnets Samples

Abstract

Super-magnets, materials whose strong magnetic activity is an attractive differential for the high-tech industry, may have their magnetic performance affected by small variations in their chemical composition. For example, the neodymium and praseodymium content can change the physicochemical properties of the permanent magnets. Aiming at a strict chemical quality control, this work developed an analytical method to quantify the major elements in the materials involved in the production process of didymium (the mixture of neodymium and praseodymium) super-magnets. The simultaneous determination of Nd (401.225 nm), Pr (414.311 nm), Fe (259.837 nm) and B (249.678 nm) in three different sample types (didymium oxide, metallic didymium and (Nd,Pr)-Fe-B alloy) was performed by sample dissolution in acidic media, followed by instrumental measurements using an Inductively Coupled Plasma Optical Emission Spectrometer. Linear calibration curves were obtained with high coefficient of determination (0.9983 ≤ R2 ≤ 0.9999) and with appropriate limits for determining these elements at the percentage level, reaching detection limits less than 0.07 cg g-1. The precision of the method was improved by weighing of the solutions during all the dilution steps and was evaluated by the coefficient of variation associated to instrumental precision (0.3 – 0.7%), method intermediate precision (1.9 – 3.1%) and also by the typical mass fraction provided as uncertainty (0.04 – 0.20 cg g-1), reaching the pressing need to distinguish the content of the rare earth elements in less than 1 cg g-1. The accuracy of the method was assessed by spiked and recovery test (96-104% for spikes equal to or greater than 0.50 cg g-1) and also by the use of different analytical methods, involving the participation of other laboratories, obtaining an acceptable degree of agreement (85 – 107%).

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

“…An iCAP 7400 Duo ICP optical emission spectrometer (ThermoFisher Scientic, Cambridge, England) equipped with dual view (axial and radial) plasma was used as a reference. 31 The spectrometer was equipped with a charge injection device (CID) detector array (166.25 to 847.00 nm detection range), and an argon-purged Echelle polychromator. The sample introduction system was a cyclonic spray chamber with a Meinhard nebulizer.…”

“…Reference values were established by ICP OES analysis aer sample dissolution. 31 About 0.5 g of each calcined sample were accurately weighed into a 50 mL conical polypropylene tube (Falcon, Corning™) and mixed with 15 mL of 25% w/v nitric acid and 5 mL of 27% w/v hydrochloric acid and le at room temperature until complete dissolution (ca. 4 h).…”

“…The limits of detection (LOD, 99.7% condence level) and quantication (LOQ) were calculated at 0.5% w/w and 1.5% w/w according to IUPAC recommendations. 31 For accuracy assessment, three (Nd,Pr)-Fe-B alloy samples were analyzed by EC-LIBS and ICP OES reference methods (Table 1). Although no signicant differences were found at the 95% condence level, as evaluated by a paired t-test, the relative errors from +12 to +20% indicate a moderate matrix effect 3.2.2.…”