Redox ratio and optical absorption of polyvalent ions in industrial glasses

Abstract

The changes in glass structure and redox ratio, R (reduced ion to oxidized ion) of Mn 2+ -Mn 3+ , Cu + -Cu 2+ , Cr 3+ -Cr 6+ , Ni 2+ -Ni 3+ and Co 2+ -Co 3+ couples and optical absorption due to Mn 3+ , Cu 2+ , Cr 3+ , Ni 2+ and Co 2+ ions in industrial soda-lime-silica glass were investigated as a function of Na 2 O concentration in the range 11-19 mol%. With increasing Na 2 O concentration in the experimental glasses, the basicity, expressed as calculated basicity, Λ cal , increased. 29 Si NMR and X-ray diffraction were used to investigate the structural change in glasses. The NMR spectra showed high non-bridging oxygens (NBOs) when the basicity of glass was increased. The results were interpreted to be due to the tetrahedral networks; Q 4 species were depolymerized by replacing the bridging oxygens (BOs) with NBOs to Q 3 species. These results confirmed the shift of broadening peaks of XRD patterns. The redox reactions of the Mn 2+ -Mn 3+ , Cu + -Cu 2+ and Cr 3+ -Cr 6+ couples shifted more toward their oxidized ions due to the oxygen partial pressure, p(O 2 ), during melting and the oxide ion activity, a O2-, increased with increasing glass basicity. These changes caused the redox ratio of these ion couples to decrease. The Ni 2+ -Ni 3+ and Co 2+ -Co 3+ couples were assumed to be present only in the Ni 2+ and Co 2+ ions in these glasses, respectively. The optical absorption bands due to Mn 3+ , Cu 2+ , Cr 3+ , Ni 2+ and Co 2+ ions were also investigated. Their spectra occurred at constant wavelengths with different optical densities or intensities as a function of glass basicity. The increase in the intensities of the absorption bands of these absorbing ions, except for Cr 3+ ion, at the maximum wavelength, depends not only on the ion concentration but also on the increase of polarizability of oxide (-II) species, α oxide(-II) , surrounding the ions. This value affected directly the extinction coefficients of the ions, ε ion . The increase of ε ion caused the colour of glasses appearing in high intensity. In the case of Cr 3+ ion, the results were reversed such that the lower the concentration, the higher the intensities of colour.

Structural and vibrational characterization of medieval like glass samples

“…The characteristic large band of the reproduced glasses are shifted at higher 2θ angles with respect to the value of 21.5°found for the pure amorphous silica, where all the SiO 4 tetrahedra are connected through bridging oxygens (BO) (presence of only Q 4 units) [44][45][46][47][48]. Even if the exact relationship between the peak position and MRO is still widely debated in literature [40][41][42][43], the 2θ increase with potassium content (Fig.…”

Solubility of chromium oxide in binary soda-silicate melts

“…Other studies report the dissolution of chromium oxides in glass melts [6][7][8][9][10][11]. The authors have demonstrated that the solubility of chromium oxide strongly depends on glass basicity (melt composition), temperature and oxygen fugacity [6][7][8]12]. This latter parameter influences the redox properties of the glass and yields to the stabilization of high or low oxidation states of the multivalent elements in the melt.…”

Vibrational spectral analysis of structural modifications of Cr2O3 containing oxyfluoroborate glasses

“…Extensive investigations on the infrared, Raman, optical absorption, luminescence and electron spin resonance spectroscopy of different transition metal ions in a variety of inorganic glasses have been made in the recent years in view of their technological applications [28][29][30][31][32]. Transition metal ions are known to influence the optical, electrical and magnetic properties of glasses due to their high sensitive response to the changes in the surrounding actions.…”