Chromium In Glasses Research Articles

Chromium enriched peraluminous glasses: Incorporation limit, crystalline phase equilibrium and impact of chromium on the rheological properties of the glass

Chromium is a multivalent element with very low solubility in silica-based glasses. It is incorporated into glass via the solubilisation of Cr2O3 as Cr3+ through an acido-basic reaction, and is in redox equilibrium with Cr6+ and Cr2+ oxidation states depending on the surrounding atmosphere. The least soluble form of chromium is Cr3+, which is also the most common form of chromium in glass elaborated in air. This study investigated the behavior of chromium in peraluminous glasses, which are potential matrices for nuclear waste containment. Chromium is often present in nuclear waste solutions as a corrosion product coming from the waste reprocessing steps. Consequently, it is important to understand the effect of chromium addition to peraluminous glasses, both in terms of the microstructure and the processing ability of the glass melt. The study investigated the effect of chromium added as a Cr2O3 chromium (+III) oxide on the homogeneity, the viscosity, and the glass transition temperature (Tg) of peraluminous glasses. The chromium redox state and its effect on the incorporation limit of chromium was determined. Peraluminous glasses have an incorporation limit of between 0.50 and 0.55 wt% Cr2O3 in air, and between 1.25 and 1.50 wt% Cr2O3 in a reducing environment. Chromium (+III) oxide was found to have a limited effect on the viscosity of peraluminous glasses up to 2 wt% of Cr2O3, despite the presence of crystals above 0.5 wt%. The addition of chromium oxide had no significant effect on the Tg of the glass, except after a slow cooling of the sample containing the highest content of 2.0 wt% Cr2O3. Two forms of chromium were identified under UV-visible spectroscopy for the glasses elaborated in air: Cr3+ (6-fold) and Cr6+ (4-fold).

XANES Determination of Chromium Oxidation States in Glasses: Comparison With Optical Absorption Spectroscopy

The oxidation state of chromium in glasses melted in an air atmosphere with and without refining agents was investigated by Cr K‐edge X‐ray absorption near‐edge structure (XANES) and optical absorption spectroscopy. A good agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between both methods. We show that the chemical dependence of the absorption coefficient of Cr(III) is less important in XANES than in optical absorption spectroscopy. The comparison of optical absorption and XANES spectra of glasses melted under different conditions provides an indirect assessment of the molar extinction coefficient of Cr(VI) in glasses.

EXAFS studies of the effect of glass composition on the coordination of trivalent chromium in glasses in the system Na 2OAl 2O 3SiO 2

A recent study of the epr and optical characteristics of Cr 3+ [Hollis et al., submitted to Phys. Chem. Glasses; Hollis and Harris, submitted to Phys. Chem. Glasses] has shown the importance of nearest neighbour and second nearest neighbour coordination of the Cr 3+ in determining optical absorption and fluorescence parameters. In this study, station 8.1 of the Daresbury S.R.S., UK was used to determine the near neighbour environment of these glasses. The results show clear evidence that the next nearest neighbours to the chromium are affected by the phasefield of the system Na 2OAl 2O 3SiO 2 to which any particular glass belongs. This systematic behaviour follows that of the optical and epr parameters observed in the previous study [Hollis et al., submitted to Phys. Chem. Glasses; Hollis and Harris, submitted to Phys. Chem. Glasses]. This result implies that a non-random structure of the glass exists in the nearest and next nearest neighbour coordination spheres of the chromium. A significant effect on the optical properties of trivalent chromium is produced by the site distortions at the chromium ion [Hollis et al., submitted to Phys. Chem. Glasses; Hollis and Harris, submitted to Phys. Chem. Glasses]. These distortions in turn result from the packing of the next nearest neighbours, which are studied here.

Nonradiative relaxation of trivalent chromium in glass

The properties of Cr 3+ in glass including the dependence of the luminescence spectrum on excitation wavelength, the nonexponentiality of the decay and its dependence on excitation and recording wavelength, and the temperature quenching of the luminescence are described on the basis of a simple model.

Determination of chromium in glasses by photometric titration

Determination of chromium in glasses by photometric titration