Tellurite And Fluorotellurite Glasses For Active And Passive

9. Conclusions; MDO 387
higher temperatures (≈ 60°C), and bridging bond severance (Te-O-Te + H2O
2[Te-OH]), and cationic leaching (Na + , Te +4 , and Zn +2 ) at higher temperatures (≈
60°C).
• HCl showed a different etched surface morphology after attack of the TeO2-
Na2O-ZnF2 glasses, possibly due to the preferential etching of the oxide
components of the glass by this halide containing acid.
• HF, acetic, and phosphoric acids produced good etched surfaces for the TeO2-
Na2O-ZnF2 glasses, and the later two should be investigated further.
• Infrared spectroscopy showed the 4% HF etch introduced significant OH content
Ion-exchange
into the 65TeO2-10Na2O-25ZnF2 mol. % glass. If this method was used to clean
preforms, it could introduce a high OH surface ‘skin’ to the preform, with
disparate viscosity behaviour to the ‘dry’ glass, unwanted stresses, and crystal
nucleation sites. Therefore, if a ‘wet’ method must be used to clean preform
surfaces, high concentration HF (e.g. 40 %) for short times should be used.
• Ag + /Na + ion-exchange of TeO2-Na2O-ZnO based glasses using molten salt, and
Ag-layer heat treatments routes resulted in measurable silver contents (by EDX)
in the glasses to around 1 to 2 µm depth.
• Around 2.5 at. % Ag + was incorporated into the glasses heat treated at the
surfaces, and around 10 at. % at 0.25 µm depth for the glass dipped in the molten
salt, which was quite heavily pitted (6.8 at. % batched sodium in both glasses).