Structures, formation mechanisms, and ion-exchange properties of α-, β-, and γ-Na2TiO3

Abstract

α-, β-, and γ-Na₂TiO₃ were prepared from rutile TiO₂ and molten NaOH. Three models of β-Na₂TiO₃ with space groups of R, P, and P were proposed, and the R model was refined from the experimental data by using the Rietveld method. The structure of β-Na₂TiO₃ is a superstructure of α-Na₂TiO₃ and supposedly contains Ti₆O₁₉ clusters. The structures of Na₂TiO₃ were mainly determined by the particle sizes of rutile and the reaction temperatures. α-Na₂TiO₃ could be prepared from fine rutile particles (D(50) < 25.8 μm) and molten NaOH at 500 °C or quenching the melt of Na₂TiO₃ at 1000 °C quickly. γ- and β-Na₂TiO₃ were the thermodynamically stable phases of Na₂TiO₃ at around 500 °C and above 800 °C, respectively. α-Na₂TiO₃ was formed far beyond the thermodynamically stable state. The Na⁺ in α-Na₂TiO₃ was easier to exchange with H⁺ in water than that in β or γ phases. They all converted to amorphous phases after the 2nd, 6th, and 4th water washings at 25 °C, respectively. β-Na₂TiO₃ followed similar paths of ion-exchange as α-Na₂TiO₃, which was different from that of γ-Na₂TiO₃.