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.