Effect of Cooling Rate on the Crystalline Morphology of Bi2O3‐Fe2O3 Pseudo‐Binary System

Abstract

Herein, the crystallographic morphology of the 80%Bi2O3‐20%Fe2O3 pseudo‐binary system under different cooling rates (100, 6.3, 0.12 K s−1) is investigated using an optical microscopy system. The interfacial morphology evolution and interfacial kinetics in two dimensions during crystal growth are systematically studied. At the low cooling rate (ΔT < 10 K), blade‐like crystals appear slowly in the melt. In turn, the emergence of numerous irregularly shaped grains in the melt at the high cooling rate (ΔT > 100 K) indicates a rapid solidification process. Tetragonal crystals appear typically during melt solidification accompanied with triangular crystals simultaneously (15 K < ΔT < 35 K). The X‐ray diffraction and EDS data reveal that both kinds of polygonal crystals are attributed to Bi25FeO40. In addition, the crystal growth kinetics are presented as the dependence of the growth rate on the subcooling, and thus the growth mechanism of crystals is discussed. According to the results, Bi25FeO40 crystals grow through a two‐dimensional nucleation mechanism.