Shunpei Ozawa

The extraction of Nd from waste Nd–Fe–B alloys by the glass slag method

We report the use of molten slag materials to extract neodymium from waste Nd–Fe–B magnets. X-Ray diffraction and EPMA studies revealed that the Nd–Fe–B alloys produced by the glass slag method using boron trioxide consisted of α-Fe and Fe2B phases. No Nd-containing phase such as the Nd2Fe14B phase and the Nd oxide phase was found in the resultant alloys. The chemical analyses confirmed that the Nd content in the Nd–Fe–B alloys produced by the glass slag method was less than 0.01 wt.% Nd. On the other hand, the slag materials contained a large amount of neodymium. The Nd in the Nd–Fe–B alloys was successfully extracted by the glass slag method using boron trioxide.

Production of Nd-Fe-B alloys by the glass slag method

The microstructures of the Nd–Fe–B alloy with the stoichiometric composition of Nd2Fe14B produced by the glass slag method were investigated. The Nd–Fe–B melts in the molten slag materials such as lead silicate glass, soda-lime glass, and Pyrex glass experienced a large undercooling over 160 K below solidification. When the Nd–Fe–B melts were solidified either in the molten lead silicate glass or in the molten soda-lime glass, the resultant Nd–Fe–B alloys had coarse dendrites of α-Fe phase together with grains of Nd2F14B. On the other hand, the Nd–Fe–B alloys exhibited columnar dendrite grains of Nd2Fe14B phase when the Nd–Fe–B melts were solidified in the molten Pyrex glass.

Magnetic properties of Nd–Fe binary alloys produced by a metallic mold casting method

Nd–Fe binary alloys with the composition of Fe–23 at. % Nd (∼Nd5Fe17) and Fe–80 at. % Nd (the eutectic composition) were produced by the metallic mold casting method. The microstructures and magnetic properties of the resultant cylindrical specimens with 1–5 mm in diameter and 50 mm in length were investigated. The cylindrical specimens of Fe–23 at. % Nd alloy consisted of Nd and Nd2Fe17 phases together with a small amount of Nd5Fe17 phase. The coercivity of the cylindrical specimens was as low as the original alloy ingot. On the other hand, the cylindrical specimens of Fe–80 at. % Nd alloy consisted mainly of Nd and Nd5Fe17 phases and showed a high coercivity over 5 kOe. It was found that the coercivity was dependent on the grain size of the cylindrical specimens produced by the metallic mold casting method.

Effects of cooling rate on microstructures and magnetic properties of Nd–Fe–B alloys

Abstract The microstructures and magnetic properties of Nd–Fe–B alloys produced by rapid solidification processing techniques were examined by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and in a vibrating sample magnetometer. Two rapid solidification processing techniques, metallic mold casting and melt-spinning, were used to investigate the influences of cooling rates on the microstructure and magnetic properties of the Nd–Fe–B alloys. The Nd–Fe–B alloys had equiaxed Nd 2 Fe 14 B grains together with α-Fe dendrites when produced by the metallic mold casting technique with moderately high cooling rates (3.3×10 2 to 1.2×10 3 K s −1 ). The Nd–Fe–B alloys had fine equiaxed Nd 2 Fe 14 B grains with or without amorphous phase when produced by the melt-spinning technique with high cooling rates (4.3×10 5 K s −1 to 1.5×10 6 K s −1 ). The relationships among the cooling rate, microstructure, and coercivity of the Nd–Fe–B alloys were determined.

Solidification behavior in undercooled Nd–Fe–B alloys

The solidification behavior of Nd–Fe–B undercooled melts with the stoichiometric composition of Nd2Fe14B was studied. The melts experienced a large undercooling of 180 K during static furnace cooling. The resultant alloy ingots consisted of fragmented dendritic iron phase together with the Nd2Fe14B phase. However, quenching the undercooled melts at various undercooling levels significantly changed the resultant microstructures. Nd–Fe–B alloy ingots with columnar Nd2Fe14B phase were obtained by quenching the melts with an undercooling of 50 K.

Containerless Solidification of Undercooled Nd2Fe14B by Electrostatic Levitation Furnace

Containerless solidification of undercooled Nd2Fe14B was investigated using the electrostatic levitation furnace developed by the National Space Development Agency of Japan. Spherical samples with diameters close to 2 mm were laser melted and radiatively cooled in vacuum at rates between 100 K/s and 50 K/s. Two recalescence peaks were observed in the cooling curves. They were respectively attributed to phase segregation of primary Fe and solidification of the Nd2Fe14B () phase. The sample that solidified with the higher undercooling level showed a more refined microstructure and a higher saturation magnetization than that solidified with the lower undercooling level.