Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 316
have been leached from the glass, and the solution again probably donated a proton to the
oxygen ion.
H2O
≡Te-O - Na + + H + Cl - ≡Te-OH + Na + Cl - (7.11)
Hydrolysis of bridging oxygens, and attack of ZnO [22] are likely to also to have
occurred with HCl. Fig. (7.27) shows the etch rates of the glass from fig. (7.25) and
(7.26), which were best fitted by exponential curves. The solutions initially showed
similar etch rates, however the rate of the 3M H2SO4 solution was higher after 120 sec.
Fig. (7.28a) shows the etch rates of glass MOD012 (75TeO2-10ZnO-10Na2O-5GeO2
mol. %), immersed in 1M HCl, 1M H2SO4, and 3M H2SO4 at 21°C. All were best fitted
linearly, however the correlation between the data and fits for the 1M solutions were
lower than the 3M solution. This was partially due to forcing the fit to pass through zero.
Fig. (7.28b) shows better correlation when the linear fitting was not forced through zero.
It can be seen that the etch rates for this glass were of the order 3M H2SO4 > 1M HCl >
1M H2SO4. This is to be expected, the 3M H2SO4 will have more protons available to
attack the glass than the 1M HCl, however; HCl is a ‘stronger’ acid (or proton donor)
than H2SO4, therefore the 1M solution etches more rapidly than the 1M H2SO4.
7.3.2.2. Durability of fluorotellurite glasses
Fig. (7.29a) shows the degradation of glass MOF001 (65TeO2-10Na2O-25ZnF2 mol. %)
after immersion in distilled water at 21 and 60°C. The weight loss was best fitted