Bo Wang

This paper investigates the effects of different iron powders on powder-in-tube (Ba, K)Fe _₂ As _₂ (Ba-122) superconducting tapes. The correlations between the particle size of iron powders and the microstructure, compositional homogeneity, and superconducting properties of the synthesized Ba-122 precursor and final tapes were systematically studied. The results show that the precursor prepared with μ m iron powder possesses fine grains and excellent chemical uniformity, which result in high phase purity and lower ferromagnetism that facilitating a high transport critical current density ( J _c ) in tapes. In comparison, the tapes prepared with ∼30 μ m iron powder exhibits local compositional segregation and residual iron particles due to incomplete reactions. However, they contain larger Ba-122 grains which align more easily along the rolling direction, resulting in a significantly higher degree of c -axis texture. This enhanced texture effectively compensates for the adverse effects of reduced uniformity, enabling the 30 μ m sample to achieve a transport J _c for tapes comparable to that of the μ m sample. In contrast, when iron powder with a particle size of ∼70 μ m is used, severe incomplete reactions lead to excessively large iron particles, which drastically lower material uniformity and density, thus significantly reducing the J _c . These findings indicate that controlling the iron powder particle size within an appropriate range are crucial for achieving high J _c in Ba-122 superconducting tapes.

The influence of electrolytic temperature on the purity grade of electrolytic pure iron, variations in elemental content, macroscopic morphology, and microstructural characteristics was studied using electrodeposition experiments alongside glow discharge mass spectrometry and scanning electron microscopy. As electrolyte temperature increased, the total impurity content in electrolytic pure iron decreased; the iron reached a purity level of 4N1 (99.991%) when electrolyzed at 75 °C. The content of gaseous elements also decreased with increasing temperature, with a total content of only 46.07 ppm during electrolysis at 75 °C. Among the major metallic elements, the Ni content was minimally affected by temperature, while the concentrations of other metallic elements were at their lowest during electrolysis at 75 °C, remaining below 0.5 ppm, except for elements such as Co, Cu, Ni, and Zn. With an increase in the electrolyte temperature, the macroscopic morphology evolved into a smooth, silver-white surface. The microstructure on the surface evolved into an irregular polygonal nucleus structure, and the microstructure on the cross-section exhibited a striped characteristic. Therefore, electrolytic pure iron with a purity exceeding 4N, exhibiting both excellent macroscopic and compact structures, can be prepared at an electrolytic temperature of 75 °C.