Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 300
The 3M HCl solution attack resulted in a weight loss versus time with an exponential
decay fit, and the 1M HCl solution gave a linear fit, with an etch rate of around 3.0 wt. %
per minute (fig (7.31a)). Linear fits also correlated highly (correlation coefficients > 0.97)
when wt. % loss was plotted against (t) 1/2 illustrated in fig. (7.31b), indicating attack was
diffusion controlled.
Fig. (7.32) shows optical micrographs of glass MOF001 (65TeO2-10Na2O-25ZnF2
mol. %) after etching in 40 % HF at 21°C (see section 7.1.2.1 for further experimental
details). HF was clearly a better etchant than NaOH, HCl and H2SO4. Although the etch
formed some ridges after long exposure times, there was no opaque layer formed at the
glass surface, as seen with all other etchants shown in fig. (7.23) to (7.31). Fig. (7.33)
shows the etch rate of 4 % HF at 21°C on this glass. This glass followed an
approximately linear etch rate of 0.92 wt. % per minute (correlation coefficient of around
0.91). Fig. (7.34) shows infrared spectra of the unetched glass (MOF001), and glass of
this composition immersed in 4% HF at 21°C for 2 and 10 min. It can be seen from fig.
(7.34) that the OH bands increased significantly with increasing etching time.