Structural and physico-chemical characterization of some soda lime zinc alumino-silicate glasses

The physico-chemical characterization of the 15Na2O-20CaO-5Al2O3-(60-x)SiO2-xZnO glasses (where x stands for 0, 4, 7 and 10 wt.%), designed as Z(0/ 4 / 7/ 10) and obtained by quenching method, has been carried out by DSC measurements, leaching tests and electrical conductivity measurements in the corresponding melts. Fitted multi-component DSC exotherms of crystallization are discussed in terms of the structural modifications derived from the X-ray measurements and room temperature Raman spectra. Combeite, Na2Ca2Si3O9, was identified as the low-temperature phase crystallized in all glasses under discussion while wollastonite (CaSiO3) was separated as main crystalline phase from the Z4, Z7 and Z10 glasses treated at 800 °C for 20 h. Zn-containing compounds, gahnite (ZnAl2O4) and Ca1.94Zn0.43Al1.25Si1.38O7, were crystallized at 924 °C for a 20 h span in the Z10 glass. The lowest Q3 population, 44.18%, responsible for network connectivity is derived by fitting the Raman spectrum of the Z10 glass. According to the unequal behavior of the Z10 glass as regarding leaching data as well as electrical conductivity measurements of the corresponding melts, the 7% ZnO represents the threshold from where higher degree of network depolymerization and presence of both four- and six-folded zinc atoms are met in these glasses.