Effects of Calcium Oxide Addition on the Structure and Thermal Properties of Iron Phosphate Glasses

The calcium iron phosphate glasses were prepared and measured by X-ray diffraction, Fourier transform infrared spectra, Raman spectra, and differential scanning calorimetry. X-ray diffraction analysis has confirmed that all compositions are amorphous. Infrared and Raman spectra indicated that the glass formed the P-O-Fe and P-O-Ca bonds in Q(1) units and (P-O- Ca2+-O-P) ionic cross-links in Q(2) units. Increasing calcium oxide content in glass compositions was brought about by the Q(1) to Q(2) conversion, which resulted in the more formation of the non-bridging oxygen (P-O- Ca2+-O-P) ionic cross-links. The change of glass transition temperature and thermal stability is consistent with structural modification of the glasses. The analyses of the spectra revealed that calcium oxide played the dual role as a network former and modifier. Oxygen to phosphorus molar ratio about 3.0 would contain the relatively higher concentration of Q(1) and Q(2) units.