On the structural units in titanium-containing glasses and their influence on the opacity of glass coatings

Abstract

A probable order of the formation of structural units in glasses of the Na systems as a function of the alkali oxide content is analyzed in terms of the strengths of the cation-oxygen bonds of the glass components. The principle of the structure formation in silicate glasses is proposed. It is demonstrated that the chemical composition of glasses can be used to predict the existence of structural groups favoring the crystallization of titanium-containing phases in the glass and, consequently, the influence of the composition on the opacity of enamel coatings.

Effect of TiO2 on microphase development during phase separation and crystallization in Na2O–B2O3–SiO2 glass system

“…The formation of new bands (<200 and 640 cm −1 ) at higher TiO 2 content results from higher amount of Ti-O-Ti structural units which promote formation of anatase nano-crystals composed of [TiO 6 ] units. 7 Since all samples were X-ray amorphous after synthesis, it should be noted that the formed nano-crystals are not detectable by XRD technique (cf. Figure S1).…”

“…In boron-containing glasses such as Na 2 O-B 2 O 3 -SiO 2 , crystallization occurs when Na 2 O < 1/3B 2 O 3 + TiO 2 . 7 Thermal treatment of Na 2 O-B 2 O 3 -SiO 2 glass compositions within the immiscibility dome with TiO 2 content of 6 mol.% lead to silicarich and Na 2 O-B 2 O 3 -TiO 2 -rich phases. Ti 4+ ions as well as anatase accumulates in the acid-soluble, sodium-rich borate phase.…”

“…3,4 Therefore, crystallization is induced when more Ti-O-Ti bonds are formed and occurs in boron-free titanium-containing alkali silicate glasses when Na 2 O/TiO 2 < 1. 7 Selfprecipitated TiO 2 can further form crystalline domains such as anatase, rutile, titanosilicates, and other various phases depending on the composition. [8][9][10][11] The knowledge of formation of TiO 2 structural units in the glass system X 2 O/YO 2 -B 2 O 3 -TiO 2 which is close to [6].…”

“…TiO 2 contents above 5.8 mol.% in binary TiO 2 –SiO 2 and 25 mol.% in 25X 2 O–25TiO 2 –50SiO 2 (X: Na, K, and Rb) promote the formation of Ti–O–Ti‐rich domains and prevent randomly distribution 3,4 . Therefore, crystallization is induced when more Ti–O–Ti bonds are formed and occurs in boron‐free titanium‐containing alkali silicate glasses when Na 2 O/TiO 2 < 1 7 . Self‐precipitated TiO 2 can further form crystalline domains such as anatase, rutile, titanosilicates, and other various phases depending on the composition 8–11 …”

“…However, the structural role of TiO 2 on the phase separation mechanism and the influence of crystal formation on microphase development (pore structure and porosity) in a simple ternary glass system, for example, Na 2 O–B 2 O 3 –SiO 2 has not yet been investigated. In boron‐containing glasses such as Na 2 O–B 2 O 3 –SiO 2 , crystallization occurs when Na 2 O < 1/3B 2 O 3 + TiO 2 7 . Thermal treatment of Na 2 O–B 2 O 3 –SiO 2 glass compositions within the immiscibility dome with TiO 2 content of 6 mol.% lead to silica‐rich and Na 2 O–B 2 O 3 –TiO 2 ‐rich phases.…”