High-purity synthesis of La2SiO5 by solid-state reaction between La2O3 and different characteristics of SiO2. Issue 16 (November 2020) - Arbelaez, Lizeth
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 La2 SiO5 and to characterize the La2 O3 : 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 La2 O3 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 La2 SiO5 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 (La2 O3 /SiO2 : 1 μm/0.02 μm) to improve the reactivity and La2 SiO5 phase formation.