Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 296
It can be seen the 3M H2SO4 etch rates was approximately linear (correlation coefficient
≈ 0.96), however the correlation coefficients for the HCl and H2SO4 1M solutions were
low (≈ 0.53 and 0.63 for H2SO4 and HCl respectively), as a result of forcing the fits to
pass through zero. The linear fits which were not made to pass through zero showed
higher correlation coefficients (all > 0.87). The 3M H2SO4 solution showed the highest
etch rate (≈ 0.008 wt. % per second), followed by 1M HCl (≈ 0.0035 wt. % per second),
then lastly 1M H2SO4 (≈ 0.0015 wt. % per second).
7.2.2.2. Durability of fluorotellurite glasses
Fig. (7.29) shows the weight loss of glass MOF001 (65TeO2-10Na2O-25ZnF2 mol. %)
after immersion in distilled water at 21 and 60°C (see section 7.1.2.1 for further
experimental details). Both sets of data were best fitted with an exponential decay (fig.
(7.29a)). As expected, the overall weight loss of the 60°C sample was higher than the
21°C sample after 21 days (4.63 and 0.34 wt % respectively). The plot of wt. % loss vs.
(t) 1/2 (fig. (7.29b)) was linear, indicating the attack mechanism was diffusion controlled.
Glasses immersed in water at both temperatures (21 and 60°C) exhibited frosted surfaces,
and were opaque to the eye after 21 days treatment.