Abstract
The chemical durability, density and structure of the BABAL glasses with batch compositions (100-x)(0.30BaO·0.50B2O3·0.20Al2O3)·xFe 2O3 (1 < x < 10 mol%), were investigated using Mossbauer spectroscopy, electron paramagnetic resonance (EPR), X-ray diffraction, Raman and differential thermal analysis (DTA). The chemical durability for the glass of composition 27BaO·45B2O3·18Al 2O3·10Fe2O3 (mol%) at 90 °C in distilled water was 700 times lower than that of iron phosphate glass 40Fe2O3·60P2O 5 (mol%). The Mossbauer spectra indicate the presence of iron (II) and iron (III) in tetrahedral or octahedral coordination. The results obtained from the gef = 4.3 EPR line are typical of the occurrence of iron (III) occupying substitutional sites and the line gef = 2.0 is related to the association of two or more Fe ions found in the interstices (or holes occupied by the glass modifier cations) of the glass network. The paths of X-ray diffraction are typical for glasses based in borate glasses. The Raman spectra showed that the boroxol ring disappears with the increase of iron content, concomitant with the appearance of BO4 and tetraborate structural units. At these conditions, an increase of dissolution rate and clustering of iron ions is observed.
Highlights
As long been known[1], the considerable practical interest of borate glasses stems mainly from the complex influence of boron oxide on the physical properties[2]
Duplicated measurements were conducted for each glass and the average dissolution rate (DR), normalized to the glass surface area, and the corrosion time was calculated from the weight loss
The dissolution rates (DRs) of the BABAL glasses measured from the weight loss experiments conducted in distilled water at 90 °C are given in Table 1 and Fig. 1
Summary
As long been known[1], the considerable practical interest of borate glasses stems mainly from the complex influence of boron oxide on the physical properties[2]. The local structure of iron doped aluminoborate glasses has been studied using 57Fe Mössbauer, Raman spectroscopy and electron paramagnetic resonance (EPR)[6,7]. The boroxol ring is the main structural group present in borate glasses and the addition of modifier oxide like CaO gradually converts three-coordinated boron into four-coordinated boron units, resulting in the formation of diborate, tetraborate and pentaborate glass network superstructural units[7]. The EPR spectra of most glasses containing iron exhibit the two well known resonances at the effective g values gef ≈ 2 and gef ≈ 4.3 that have been considered as a signature of the presence of Fe3+ ions in a glassy host[9].
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