A NEW APPROACH TO DETERMINE AND QUANTIFY STRUCTURAL UNITS IN SILICATE GLASSES USING MICRO-REFLECTANCE FOURIER-TRANSFORM INFRARED SPECTROSCOPY

Abstract

Eight silicate unit vibrational modes were identified in a suite of PbO-SiO2 glasses using microreflectance Fourier Transform infrared (μR-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- (900 cm-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 (Si6O1812- and Si2O64-), NBO/T = 1 (Si4O116- 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.