A Study of the Coloration of Titanium-containing Glasses

Abstract

Using 9 base glasses given in Table 1 in the text a series of experiments was made to know the influences of the composition of base glass, melting atmosphere, heat treatment as well as the temperature at the observation.
It was confirmed that the titanium containing glasses may be colorless, blue and yellow to brown; they often become turbid or deep color during the heat treament; some of them change the color reversibly at the temperatures 300°-500°C.
From the observation of the spectral transmission curves the following conclusions were obtained:
(1) In glass coexist both Ti³⁺ and Ti⁴⁺.
(2) Melting in reducing atmosphere raised the concentration of Ti³⁺ giving blue color to glass. In this case the co-ordination number of oxygen is 6.
(3) There are two formes of Ti⁴⁺, one the network modifier in the form (TiO₆), and the other network former in the form (TiO₄) or (TiO₄)_n, the former gives colorless glass, while the latter the glass of the color changing from yellow to brown according to the increase of n.
The equilibrium such as
(TiO₆)→←(TiO₄)→←(TiO₄)_n
may be considered.
(4) It may be considered that the equilibrium (TiO₆)→←(TiO₄) goes towared (TiO₄) with the increase of the basicity of glass, and also with the elevation of temperature; and that (TiO₄)→←(TiO₄)_n goes toward (TiO₄)_n with decreasing temperature.
Based on these relations the change of color and turbidty of the glass may be explained.