Distribution and Coordination State of Titanium Oxides in Microstructures Formed by Spinodal Decomposition in Multicomponent Borosilicate Glass

Abstract

Tetrahedrally coordinated titanium oxides implanted into inorganic materials aid in the removal of air-based pollutants by photocatalytic reactions. We investigated the distribution and the coordination state of titanium oxides in a phase-separated glass formed by the spinodal decomposition to obtain porous glass containing tetrahedrally coordinated titanium oxides. Various glass compositions containing titanium oxides were prepared by partially replacing SiO2 with B2O3 and small amounts of TiO2 in multicomponent silicate glass compositions where a spinodal decomposition had been confirmed. Interconnected microstructures that consist of two different phases were observed in heat-treated glass samples using transmission electron microscopy and these microstructures underwent spinodal decomposition. Compositional analyses of these microstructures using energy dispersion spectroscopy revealed that the decomposed phase with higher concentration of SiO2 contains smaller amount of titanium oxides than the other phase. Thermodynamic analysis was conducted to evaluate the distribution of titanium oxides in the glass phases, formed by a phase separation in the multicomponent borosilicate glass, where glass was regarded as a super-cooled liquid phase. In the thermodynamic analysis, the calculated activity of TiO2 in the two decomposed glass phases indicated that the glass phase with higher concentration of SiO2 contains lower concentration of titanium oxides. Porous glasses containing titanium oxide were fabricated from the spinodal-decomposed borosilicate glass by leaching one of the separated phases with an acid solution. Ti K-edge X-ray absorption near edge structure spectra indicated that the porous glass contains tetrahedrally coordinated titanium oxides.