Mössbauer and differential thermal analysis studies of iron alkali lead-phosphate glasses

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 Mössbauer techniques. The analysis of Mössbauer suggests oxidation of Fe2+ ions in the distorted bipyramidal to Fe3+ in the same site. This procedure creates non-bridging oxygens joined with Fe2+ octa 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.