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

Abstract

The structure of borosilicate glasses of composition 30Na 2 O-2Al 2 O 3 -25SiO 2 -xFe 2 O 3 (43-x) B 2 O 3 has been investigated in the composition range of 0.5 20 mol% Fe 2 O 3 . 27 Al, 11 B, 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 Fe 2 O 3 (in low region up to 7 mol%) are the main glass modifier. Structural determination for borosilicate glasses with a high content of (Fe 2 O 3 ) was carried out by FTIR spectroscopy, where both 11 B and 29 Si 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% Fe 2 O 3 and the N 4 values obtained by FTIR spectroscopy agree within error with the 11 B NMR results of the same glass samples. Fe 2 O 3 is a main glass modifier in the low-Fe 2 O 3 -content region (≤6 mol%). On other hand, it plays the role of glass former at higher content of Fe 2 O 3 . Increasing both N 4 of boron tetrahedral units and chemical shift of silicon nuclei to reach maxima at 5 mol% Fe 2 O 3 confirms the role of Fe 2 O 3 as a glass modifier in the low composition region. On the other hand, fast decrease in N 4 with further increasing Fe 2 O 3 contents ≥6 mol%) is an evidence for iron oxide to inter the glass network as a network former.