High-purity synthesis of La2SiO5 by solid-state reaction between La2O3 and different characteristics of SiO2

Abstract

The solid-state reaction between lanthanum oxide and different characteristics of silica has been investigated to define new process conditions that favor the formation of La2SiO5 and to characterize the La2O3: SiO2 reaction mechanisms. Silica with different crystalline structures (amorphous or quartz-type silica) and various average particle sizes of ~36, 12, 1, and 0.02 μm were used. The 1:1 M ratio mixtures between La2O3 and different types of SiO2 were ground and subsequently heated at 1200 and 1500 °C for 10 h. The morphology of the ground mixtures, their thermal properties, and the phases obtained after heating were determined in this study. The phases identified after each solid-state synthesis were quantified using Rietveld refinements. The results obtained indicate that an amorphous silica with a small particle size (<1 μm) is more advantageous in the La2SiO5 powder synthesis. An alternative synthesis method of using an amorphous colloidal silica with a particle size of 0.02 μm is proposed, and the purity level achieved at 1500 °C after 10 h is higher than 90 vol%. A reaction mechanism was suggested that highlights the strong effect of the size ratio (La2O3/SiO2: 1 μm/0.02 μm) to improve the reactivity and La2SiO5 phase formation.