Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 325
Fraction silver
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Depth / microns
Model
EDX
Fig. (7.41): Silver concentration profile (EDX data and model) modelling for glass ST08
(79TeO2-5ZnO-10Na2O-5PbO-1Yb2O3 mol. %), where one flat side was dipped into a
molten salt solution (2AgNO3-49NaNO3-49KNO3 mol. %) at 270°C for 5 hours (error
bars +1 at. %).
This provided a relatively good fit. It is interesting to note that by this method of ion-
exchange around three times the amount of silver was incorporated into the glass near the
surface, compared to the heat treated samples. However, at 1.5 µm depth, the level of
silver was approximately equal to the heat treated samples at 1 and 2 µm for the 100 and
300 µm layers respectively, i.e. this treatment produced a steeper silver concentration
profile. The heat treated samples would have reached thermal equilibrium across the
whole of the sample relatively quickly during treatment (i.e. no temperature gradient)
relative to the time scale of the experiment (12 hours). The surface of the sample treated
with molten salt was dipped into the melt, creating a sharper temperature gradient, as the
atmosphere around the bulk of the glass would have been at a lower temperature.