Synthesis of Bismuth Silicate Powders by Molten Salt Method

The bismuth silicate powders were prepared by reaction of Bi2O3 and SiO2 as raw materials in KCl-K2CO3, NaCl-Na2CO3, K2CO3-Na2CO3, KCl-NaCl, NaCl-Na2SO4, and KCl-K2SO4 molten salts. Pure Bi12SiO20 powders were synthesized in KCl-K2CO3 flux at 635 degrees C for 1h, which was lower than that of conventional solid state reaction. X-ray diffraction reveals that the phases of the samples are different in various molten salts. Only Bi12SiO20 phase can be observed in the molten salts with ions. However, a mixture of Bi12SiO20, Bi2SiO5, and Bi4Si3O12 phase are observed in the molten salts without ions. Therefore, the carbonates are not only used as the flux and reaction medium, but also inhibit the formation of other bismuth silicates in the synthesis of Bi12SiO20 powders by molten salt synthesis. The scanning electronic microscopy image indicates that the mechanism of molten salt synthesis in the case of KCl-K2CO3 and NaCl-Na2CO3 are dissolution-precipitation mechanism. UV-Vis spectra reveals the absorption edge for the sample is shifted to longer wavelengths compared with Bi12SiO20 single crystal, and the band gap energy (Eg) is 2.82eV.