Oxidation behavior of Nd-Fe-B magnets

Abstract

This corrosion study was performed to determine the reaction kinetics of Nd-Fe-B type magnets in oxidizing environments. Thus the oxidation model developed provides basic information for the development of oxidation-resistant magnets. The oxidation of Nd-Fe-B magnets was studied at temperatures between 20 and 150 °C. The oxidation rates of the magnets were measured as functions of humidity in air, temperature, and alloy composition. Aerated salt and distilled water, at room temperature, were used as accelerating environments. The morphology of the reaction products was analyzed with scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) and used to aid the interpretation of the reaction kinetics. The kinetics for the oxidation of magnets generally exhibit a parabolic weight increase in humid air at room temperature. Minor alloying additions affect the corrosion rate. In aerated distilled water, Nd-Fe-B magnets generally exhibit a linear weight loss. The magnets in aerated salt water show an inverse parabolic weight loss. Magnetization of the magnets substantially reduced the oxidation rate in the salt water test. The oxidation mechanism will be discussed.