Abstract
This work reports on the effect of the increment of Fe2O3 in a network of phosphate glasses involving Al2O3, Na2O and PbO by DTA and Mossbauer techniques. The analysis of Mossbauer suggests oxidation of Fe2+ ions in the distorted bipyramidal to Fe3+ in the same site. This procedure creates non-bridging oxygens joined with Fe-octa(2+) that weakens the phosphate network whenever the Fe2O3 content increases. The thermal parameters of the phosphate network will be affected by this weakness. Thus, both the glass transition temperature (T-gl) and the crystallization peak temperature (T-cp) on the one hand and the activation energies for glass transition E-gl and for crystallization (E-gl and E-cp) on the other hand will decrease as a function of Fe2O3. This decrease will be discussed following Lasocka's relationships that present a good correlation between T-gl and T-cp. Furthermore, the glass transition temperature (T-gl) was correlated with the glass fragility (m) and with the elastic parameters of the phosphate network such as the bulk (K) and shearing (G) moduli.