Effect of TiO <sub>2</sub> on microphase development during phase separation and crystallization in Na <sub>2</sub> O–B <sub>2</sub> O <sub>3</sub> –SiO <sub>2</sub> glass system
Tovhowani Innocent Kwinda, Dirk Enke, Sharon Koppka
Abstract
Abstract This study examines the incorporation of TiO 2 into sodium borosilicate glasses and its effect on the formation of glassy and crystalline microphases. Glasses in the composition range: 7Na 2 O–23B 2 O 3 –(70 ‐ X )SiO 2 – X TiO 2 (where X = 0–14.6 mol.% TiO 2 ) which exhibit phase separation were investigated. Raman studies confirm the formation of two different TiO 2 coordinations depending on the molar content of TiO 2 . Thermal properties of glasses are unaffected by TiO 2 addition. The domain size of microphase development in TiO 2 ‐containing glass indicates competition between phase separation and crystallization. Enrichment of titanium on the interphase between glassy microphases reduces the mass transfer and consequently limits the growth rate of glassy phases. This competes with the formation of anatase for which a nucleation‐controlled mechanism is proposed.