W.M. Pontuschka

Properties and structural features of iron doped BABAL glasses

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.

EPR measurements on single crystals of -NiSO4 · 6H2O

Abstract EPR measurements on single crystals of α - NiSO 4 · 6H 2 O were carried out at room temperature. From the results were deduced the spin Hamiltonian parameters D = 4.85 ± 0.09 cm −1 and E = 0.06 ± 0.01 cm −1 . From the results cosines of the crystalline field.

Approximate solution for kinetic differential equations

SummaryIn the present work we show the analysis of an approximate solution for the coupled kinetic differential equations of a defect involving processes of untrapping, retrapping and recombination annihilation, using the Poincaré-Dulac theorem.

Radiation-Induced Defects in Calcium Aluminate Glasses

In this work, MgF2 and CaF2 doped calcium aluminate glass samples have been investigated in order to describe the intrinsic defects that are formed in UV irradiated glasses. It is well known that calcium aluminate, when UV-illuminated, changes colour from blue to green. Thermoluminescence (TL), Optical Absorption (OA) and Electron Paramagnetic Resonance (EPR) measurements have been carried out and the results obtained were associated with the structural properties of the CaO—Al2O2—SiO2 system, in order to provide a defect model. Thermal treatments up to 150°C were performed for OA and TL measurements but the thermal decay curves could not be adjusted by an exponential function. The TL experimental results were fitted, according to a continuous model, with a Gaussian distribution function centred at 0.6eV and a frequency factor of 109s−1.