Structural features of lead iron phosphate glasses

Lead iron-phosphate glasses were investigated for use as wasteform because of their improved chemical durability. There is a controversy if lead should or should not be used in iron phosphate glasses, and on the role of Fe in the inhibition of corrosion. The structure of the 43.3PbO.13.7Fe(2)O(3).43P(2)O(5) (mol%) glass, which has a dissolution rate in aqueous solution at 90 degreesC of 1.26 x 10(-9) g/cm(2) min(-1), and the same O/P ratio, 3.5, as the lead-free 40Fe(2)O(3).60P(2)O(5) glass, was investigated. Glass samples were produced by melting batches of Fe2O3, PbO, and NH4H2PO4 at 1100 degreesC for 1 h, and pouring the liquid into steel mold. Samples were annealed at 450 degreesC for 3 h. Some samples were crystallized by heating at 700 degreesC for 24 h. X-ray diffraction, Mossbauer, EPR, infrared, and Raman scattering spectroscopy were performed and compared to spectra obtained after crystallization. The crystalline phase Fe2Pb(P2O7)(2) was identified after crystallization. The hyperfine parameters from the Mossbauer spectrum indicates that Fe2+ and Fe3+ ions are in octahedral coordination, and some of the Fe3+ ions in the starting batch are reduced to Fe2+ ions after melting. The infrared and Raman scattering spectra are representative of a mixture of chain-terminating Q(1) species and chain-forming Q(2) species. No Raman bands related to P=O vibrations and Q(0) species were observed. From the EPR measurements it is concluded that all Fe3+ ions are not constrained to central positions of tetrahedral and octahedral sites of the glass formers. (C) 2002 Elsevier Science B.V. All rights reserved.