A novel technique for determining magnet cleanliness - NMR spectroscopy

Current state-of-the-art techniques for determining HDA magnet cleanliness require the use of a Scanning Electron Microscope fitted with an EDX analyzer. A faster and more convenient approach for this determination utilizes the resonance characteristics of certain nuclei in a highly homogeneous magnetic field. This is called Nuclear Magnetic Resonance Spectroscopy (NMR). One of these nuclei is hydrogen, thus easily obtainable proton spectra can be used to determine tbe presence or absence of magnetic or magnetizable particles in the magnetic field. Particles removed from samarium/cobalt and neodymium/ iron/boron magnets were used in this work. Three different NMR phenomena were observed. The particles dramatically altered the homogeneity of the magnetic field. It was also noted that the shape and the resolution of the residual protons in the deuterated solvent was affected. A third and less expected effect was that the line shape of the proton spectra was significantly broadened. It is proposed that this technique be employed to determine magnet cleanliness. It can also be used to determine contamination by any other magnet or magnetizable particulates. Although tbe NMR system is no less esoteric than the SEM/EDX combination, the possible savings are dramatic. The use of NMR would cut the analysis time to approximately two minutes per sample.