The Sintering Process and Reaction Kinetics of Fe-Se System after Ball Milling Treatment

The formation mechanism of superconducting phase beta-FeSe during sintering process plays a vital role in determining superconductive properties and understanding the mechanism of superconductivity in the iron-based superconductor. In the present work, the sintering process and reaction kinetics of Fe-Se system after ball milling were investigated. It was found that most of the crystalline Se would transform into the amorphous state after long-time ball milling. Some Se can also enter the Fe crystal lattice forming solid solution and lead to the lattice distortion of Fe. According to thermal analysis, the reaction between Fe and Se during the subsequent sintering process orderly underwent the formation of FeSe2, Fe7Se8, and alpha-FeSe. Finally, alpha-FeSe would transform into the superconducting phase beta-FeSe after sintering for a long time at elevated temperature. Additionally, the Flynn-Wall-Ozawa (FWO) multiple scanning method under non-isothermal conditions was employed to study the kinetic mechanism and it is found that random nucleation followed by a gradual growth of nuclei (Avrami-Erofeev equation, n=2) is the kinetics mechanism of solid-solid reaction between Fe and Se during sintering process. The value of the activation energy decreases from 70.19 kJ/mol to 63.16 kJ/mol as the reaction proceeds.