Preparation of Submicron Metastable Spherical β-Bi₂O₃ Particles by Self-Propagating High-Temperature Synthesis Method

Sub-micrometer particles of β-Bi₂O₃ were successfully synthesized via a one-step self-propagating high-temperature synthesis (SHS) method for the first time. The experiments were carried out in the air at room temperature. The products were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). In this study, three experiments were designed to optimize the heat source, Bi source and additive for the reaction system. Results showed that the system composed of Al, Bi₂O₃ and Al₂O₃ powders could synthesize monodisperse high-purity β-Bi₂O₃ spherical particles with the average diameter of 369 nm and the as-prepared products kept stable after being exposed in air for one month. Then, the influences of the ratio of the three components on system were investigated. Interestingly, it was found that a slight adjustment on the ratio of Al:Bi₂O₃:Al₂O₃ had significant effects on the reactions happening in a system. Specifically, when the amount of Al₂O₃ exceeds the molar ratio of 2:1:1 (Al:Bi₂O₃:Al₂O₃), it is difficult to ignite the reaction system; when the amount is less than 2:1:0.5, the reaction system becomes too violent to obtain pure products. However, there are no obvious differences on the morphology and structure of final products with the two ratios because of few changes in adiabatic temperature. Preparation of β-Bi₂O₃ by SHS technique enjoying many advantages, such as high efficiency, inexpensive experimental equipment and simple processes, would has a promising prospect for industrial application.