EMU granted in process 2014/50887-4: ICP-MS

• Grant number: 17/20752-8
• Support type: Multi-user Equipment Program
• Duration: February 01, 2018 - January 31, 2025
• Field of knowledge: Engineering - Materials and Metallurgical Engineering
• Cooperation agreement: CNPq - INCTs
• Principal Investigator: Fernando Jose Gomes Landgraf
• Grantee: Fernando Jose Gomes Landgraf
• Home Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 14/50887-4 - INCT 2014: Rare-Earth Magnets Processing and Application for High-tech Industry, AP.TEM
• EMU web page: Página do Equipamento Multiusuário não informada
• Use scheduling: E-mail de agendamento não informado

Abstract

The development and optimization of fabrication processes for (Nd, Pr)-Fe-B alloys with restricted levels of impurities within the INCT PATRIA project is supported by the Chemical Laboratory of the Center for Metallurgical and Materials Technologies (CTMM) of the Sao Paulo Institute of Technological Research (IPT), through the chemical analysis of specimens produced, as well as the raw materials utilized. For these analyses, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has proven itself to be the most powerful technique for quantification of contaminants in high purity rare earth (RE) materials. It is important to note that this technique is not free from interference effects, which poses a great challenge to analysts. The detection process in the ICP-MS technique is based around the ionization of the sample´s elements and the separation of the analytes according to their mass to charge ratio (m/Z), which confers specificity to the technique. However, the physicochemical conditions inside the plasma are favorable for the generation of polyatomic ions that may have the same m/Z ratio as an analyte of interest, resulting in what is called spectral interference. As an example of a known issue in the analysis of neodymium oxide (Nd2O3), we may take the case of Gadolinium, whose 158Gd isotope has the same mass to charge ratio as the 142Nd16O species, which is commonly formed during the analyses. As such, the amount of moles detected for this mass to charge ratio (of 158/1) may be due to the presence of Gadolinium as well as that of Neodimium. There is no way to determine, a priori, which of the two generated the signal read by the equipment. There are ways to work around these difficulties, such as the analysis of alternative isotopes for the same elements or of polyatomic ions formed when these elements react with certain chemical species like oxygen or argon. Should there be no alternative to counter this spectral interference, it will be as good as impossible to determine trace amounts of Gd in a Nd oxide specimen. The same is true for terbium (159Tb) when the 142Nd16O1H species is present. Similar spectral interference processes take place for many other elements. Non-spectral or matrix interference effects can also accrue the challenge faced. More so due to the fact that, unlike its counterpart, matrix interference can be positive, or negative as well. Carrying on with example of Nd2O3 analysis, there are two possible sources of negative matrix interferences: i) space charge effect - in which the elements with masses lower than the Nd isotopes are repelled from the ion beam and have their signals suppressed; ii) ionization suppression effect - elements with ionization potential higher than that of Nd will ionize at a lower rates if they are part of Nd-rich solutions. On the other hand, positive interferences are not to be ruled out, since high concentration of Nd disrupts plasma equilibrium and may favor the ionization of some elements. A few different strategies can be applied in order to overcome these difficulties, such as: i) sample preparation that can separate a couple of the main elements contained in the matrix; ii) use of separation systems like High Performance Liquid Chromatography (HPLC) before the ICP-MS equipment; iii) optimization of ICP conditions in order to minimize the formation of polyatomic species; iv) use of collision/reaction cells as a means to remove interfering elements. Each strategy has its own limitations and possibilities. The extent of their application depends on the available resources, time and team. In the current project, strategies concerning the preparation of samples, optimization of the ICP conditions and use of the collision/reaction cells will be investigated with the intention of proving the CTMM/IPT with a reliable methodology for the analysis of samples from production process of rare earth magnets. (AU)