Preparation of parylene-coated bonded NdFeB magnets

The anisotropic parylene-coated bonded NdFeB magnets with parylene C coating on the surface of NdFeB powders are prepared by warm compaction process. The parylene C coating is characterized by focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray Spectroscopy (EDS), revealing a parylene C film of 300-500 nm thickness on the surface of NdFeB powders. The parylene-coated NdFeB magnets show excellent magnetic properties of maximum energy product ((BH)max, 104 kJ/m3), degree of alignment (DOA, 0.476) and density (6.17 g/cm3) than non-coated NdFeB magnets (60 kJ/m3, 0.337, 5.72 g/cm3). And with the increasing thickness of parylene C coating, (BH)max and density increase first, and then decrease while DOA keeps a growing trend all the time. The parylene-coated NdFeB magnets also exhibit better corrosion resistance according electrochemical test. The mechanisms for the improvement of magnetic properties and corrosion resistance are the good lubricating property and super chemical stability of parylene C coating on the surface of NdFeB powders.