Nuclear Magnetic Resonance and FTIR Structural Studies on Borosilicate Glasses Containing Iron Oxide

Abstract

The structure of borosilicate glasses of composition 30Na2O-2Al2O3-25SiO2-xFe2O3 (43-x) B2O3 has been investigated in the composition range of 0.5 - 20 mol% Fe2O3. 27Al, 11B, 29 Si MAS NMR and FTIR spectroscopies have been used to measure the fraction of different structural species in the glasses. It is evidenced from NMR data that both sodium and Fe2O3 (in low region up to 7 mol%) are the main glass modifier. Structural determination for borosilicate glasses with a high content of (Fe2O3) was carried out by FTIR spectroscopy, where both 11B and 29Si MAS NMR are impossible because of the high quantities of paramagnetic iron (III) species present. NMR analysis was performed on borosilicate glasses containing up to 7 mol% Fe2O3 and the N4 values obtained by FTIR spectroscopy agree within error with the 11B NMR results of the same glass samples. Fe2O3 is a main glass modifier in the low-Fe2O3-content region (≤6 mol%). On other hand, it plays the role of glass former at higher content of Fe2O3. Increasing both N4 of boron tetrahedral units and chemical shift of silicon nuclei to reach maxima at 5 mol% Fe2O3 confirms the role of Fe2O3 as a glass modifier in the low composition region. On the other hand, fast decrease in N4 with further increasing Fe2O3 contents (≥6 mol%) is an evidence for iron oxide to inter the glass network as a network former.