Mechanical activation for soft synthesis of bismuth silicates

Bismuth silicates are intensively investigated for their applications as condensers, sensors, data storage and optical devices, and photocatalysts. An increased interest in bismuth silicates stimulates developing new methods of their preparation. Synthesis of complex compounds in dry solid powder mixtures in the course of mechanical activation with the absence of any solvent and long-time high-temperature treatment is an attractive method in terms of "green" chemistry and time-effective one-stage approaches. In the present study, mechanical treatment of the mixtures of bismuth(III) compounds and silica with different Bi/Si atomic ratio is applied to prepare the Bi2SiO5, Bi4Si3O12, and Bi12SiO20 bismuth silicates. The effect of Bi precursor and milling time on the bismuth silicate formation in the course of mechanical treatment is investigated. The effect of subsequent thermal treatment of the activated mixture on the phase composition of the samples is also considered. The results obtained show the opportunity for the mechanochemical synthesis of gamma-Bi12SiO20 and metastable Bi2SiO5 directly in the course of milling of alpha-Bi2O3 and SiO2 center dot nF(12)O mixtures at room temperatures. The formation of target Bi4Si3O12 is shown to occur via the solid-phase reactions between Bi2SiO5 formed during the milling and silica unreacted in the course of subsequent thermal treatment at moderate temperature (< 600 degrees C). Based on the results obtained, the possible pathways of phase evolution during the mechanical activation and subsequent thermal treatment are proposed.