A new approach to determine and quantify structural units in silicate glasses using micro-reflectance Fourier-Transform infrared spectroscopy

Eight silicate unit vibrational modes were identified in a suite of PbO-SiO2 glasses using microreflectance Fourier Transform infrared (mu R-FTIR) spectra that were transformed using the Kramers-Kronig relation. The transformed FTIR spectra, in the 800-1200 cm(-1) range, were deconvolved systematically into eight Voigt-shaped bands at centers that were predicted from the second derivative of the spectra. The area of the eight bands varied as a function of SiO2 content, and these trends were combined with theoretical constraints to identify and assign the bands to seven provisional silicate units: SiO44- (830 and 860 cm(-1)), Si2O76- (900cm(-1)), Si6O1812-(950 cm(-1)), Si2O64- (980 cm(-1)), Si4O116- (1010 cm(-1)), Si2O52- (1050 cm(-1)), and SiO2 (1100 cm(-1)). The provisional units were then grouped according to their NBO/T values: NBO/T = 4 (SiO44), NBO/T = 3(Si2O76-), NBO/T = 2(Si2O1812- and Si2O64- NBO/T = 1 (Si4O116- T and Si2O52-) and NBO/T = 0 (SiO2). The derived quantities of each NBO/T unit compare favorably with nuclear magnetic resonance data for PbO-SiO2 glasses reported in the literature. This new approach for determining glass structure is advantageous because it may be performed on small Fe-bearing samples with minimal preparation, and analyses are rapid and relatively inexpensive.