Effect of the Addition of Multivalent Ions and the Irradiation of U. V. Rays on Colour Development in Silver-containing Glasses

It is known that the addition of SnO, Sb2O3, Fe2O3 and CeO2 etc., the oxides of multivalent elements, promote the development, and stabilization of the colloidal colours obtained by reheating the glasses containing Au, Ag, and Cu. In order to know the mechanism of the function of so called thermoreducing agents, or sesitizers, in developing colours a series of experiments has been carried out taking Ag-glass as an example.The composition of base glass was Na2O 18.0, CaO 8.5, Al2O3 1.5, and SiO2 72.0% by weight, and to which 0.025 gram atom of Ag2O, and 1 or 4 gram atoms of 11 thermoreducing agents, i.e., TiO2, V2O5, Cr2O3, MnO2, FeC2O4⋅2H2O, CoO, NiO, SnO, Sb2O3, Ce2 (C2O4)3, UO2(NO3)2 were added.The 20 glass samples prepared from the different combinations of sensitizers given above were subjected to the combinations of following heat treatments:1) Holding for 10 minutes at 650°C followed, respectively, by cooling to 400°C in 2 hours at constant rate and then quenching to ordinary temperature.2) Irradiation by ultraviolet rays.3) Preheating at 800°C for 10 minutes.The spectral transmission between 250 and 750mμ of the specimens which have developed colours by applying the combined treatments of above three types were measured, and the results were compared with the transmission of those containing no sensitizer and have passed through the exactly the same pretreatments.Within the scope of the present experiments it has been shown that the ions of Cr, Co, Sn act effectively in the colour development by heat treatment, while those of Cr, Fe, Sn, Sb, Ce are effective in developing by ultraviolet irradiation.Considering that these effects may be ascribed to the increase of the concentration of atomic silver, Ag°, during the heat treament, where the constants of the equilibria, such asAg°→←Ag+M+→←M2+, in which M is a multivalent element, are highly temperature dependent, the author was able to explain satisfactory the function of the thermoreducing agents, or sensitizers, by the difference of the temperature dependency of the equilibria.