Tellurite And Fluorotellurite Glasses For Active And Passive

2. Literature review; MDO 49
From fig. (2.9), all major peaks were identified as TeO2, Na6ZnO4 or Zn2Te3O8. The
viscosity-temperature study concluded that the tellurite melts are Newtonian fluids (i.e.
viscosity depends only on temperature and during fibre-drawing, draw speed should not
affect viscosity) and that the glass forming liquids can be drawn into fibres at
temperatures around 370 to 400°C, which corresponds to a viscosity of around 10 4 Pa.s.
It can be seen from table (2.3) that this is 50 to 100°C below the crystallisation exotherm
of these glasses, so devitrification should not be a problem during fibre-drawing.
Yoshida et al. [49] investigated the crack growth behaviour of zinc tellurite glasses
with and without sodium oxide (compositions (mol. %): 70TeO2-30ZnO and 70TeO2-
20ZnO-10Na2O). Fig. (2.10) shows the stress intensity factor-crack velocity (KI-v) curves
for the two tellurite compositions:
Fig. (2.10): KI-v curves for zinc tellurite glasses with and without Na2O [49].