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In order to study the segregation of arsenic impurities at the metal/oxide interface during high temperature exposure, isothermal oxidation behavior of arsenic bearing steels with various Ce content was systematically investigated. The result showed that oxidation mass gain of arsenic bearing steel in the temperature range of 950–1150 °C was decreased as a whole with increasing Ce content from 0 to 0.035 wt.%. At 1100 and 1150 °C, the best results are obtained for 0.027 and 0.035 wt.% Ce. Moreover, Ce addition could prevent grain boundaries oxidation, which reduced or even eliminated the formation of visible oxide particles along grain boundaries at 1000 and 1050 °C. In case of oxidation at 1050 and 1100 °C, the arsenic enrichment amount at the scale/metal interface was firstly decreased with increasing Ce content from 0 to 0.027 wt.% and then slightly increased as Ce content increased from 0.027 to 0.035 wt.%. This variation was attributed to the separation behavior of oxide scale, the formation of a continuous solid Fe2SiO4 layer and the arsenious rare earth particles promoted by Ce addition.

Many developed techniques for rare-earths’ (REs) recovery from magnet scraps are highly sensitive to the oxidative roasting process of scraps under high temperature. This study focused on phase evolution, microstructural changes and element distribution during the roasting of the widely used Nd–Fe–B and high-potential Ce–Fe–B scrap powders at 800°C. The sustained oxidation of Fe to Fe2O3 and the constant formation of composite RE oxides were the main reaction processes with increasing roasting cycles for the two scrap powders. The complete oxidation phases consisted of NdBO3, NdFeO3 and Fe2O3 for the Nd–Fe–B scrap powder, while the final products were NdBO3, GdFeO3 and Fe2O3 as well as individual CeO2 for the Ce–Fe–B scrap powder. An oxygen diffusion front was observed, forming a dark gray oxidized layer with almost the same thickness on the large particle surface. Additionally, a Fe2O3 layer covered the particle surface when the oxidation of the two scrap powders was complete. In oxidized Nd–Fe–B particles, the observed white regions corresponded to the oxidized intergranular Nd-rich phase as indicated by the almost same size and position before and after roasting. In Ce–Fe–B particles, the oxidized intergranular phase appeared to gather and grow, and a RE-rich layer appeared between the oxide/unoxidized layer. Conclusively, the iron-outward diffusion and the oxygen-inward diffusion were dominated by the oxidation of both Nd–Fe–B and Ce–Fe–B particles.

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