Synthesis of Bismuth Silicate Powders by Molten Salt Method

Abstract

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°C for 1 h, 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 2.82 eV.

Keywords:

• Bi₁₂SiO₂₀
• Bismuth silicate
• Low-temperature
• Molten salt method
• X-ray