Oxygen-ion activity and its influence on redox equilibria in a ternary soda-lime-silica glass system

The influence of oxygen-ion activity on redox equilibria in a ternary soda-lime-silica glass containing (in mol%) 20 Na2O , 10 CaO, 70 SiO2 was studied at 1400 °C in air atmosphere. On plotting lg K' (Κ' = [M^(x+n)+] / ([M^x+] [pO2]^n/4)) against the experimentally determined relative logarithm of oxygen-ion activity (Δlg O^2-) based on water-vapour solubility data in lithium and sodium silicate glasses at 1400 °C, linear relationships were found for Cu+ - Cu2+, Fe2+ - Fe3+, Ce3+ - Ce4+, Sn2+ - Sn4+, As3+ - As5+ and Cr3+ - Cr6+ redox reactions. The experimentally observed values of lg K' for Cu+ - Cu2+ and Cr3+ - Cr6+ redox pairs in ternary soda-lime-silica glass at 1400 °C in air were found to he on a vertical line corresponding to a particular value of Δlg O^2- for the glass. This value of Δlg O^2- for 20 Na2O · 10 CaO · 70 SiO2 glass indicates that under identical conditions the values of lg K' in this base glass should be around 1.80, 0.85, 0.50 and - 0.40 for Sn2+ - Sn4+, Fe2+ - Fe3+, As3+ - As5+ and Ce3+ - Ce4+ redox pairs, respectively. The predicted results of lg K' agree well with the results obtained by earlier workers. The observations open up a new possibility for predicting the values of lg K' for these redox pairs in ternary systems. The changes in coordinations and symmetries of the redox species during these redox reactions in silicate glasses greatly influence the slopes of the straight lines obtained for Ig K' versus Δlg O^2-

Optical absorption and fluorescent behaviour of selenium in ternary silicate glasses

Optical absorption and fluorescent behaviour of selenium in the ternary soda-lime-silica, soda-strontia-silica and soda-baria-silica glasses having molar composition 20Na2O-10RO-70SiO2 (where R = Ca, Sr and Ba) were studied systematically. Selenium in its elemental form was found to produce a variety of pink colour shades in soda-lime-siliea and soda-strontia-silica glasses by optical absorption measurements whereas the infrared transmission studies detected the presence of selenium as selenite (SeO3 2-) and selenate (SeO4 2-) ions which did not produce any color in glass. The results of optical measurements in the glass containing Se ⇌ SeO3 2- ⇌ SeO4 2- species were discussed in the light of the general principles of spectroscopy. The molar extinetion coefficient of selenium was calculated and found to be around 20 and 80 1 ∙ mol-1 ∙ cm-1 respectively, in soda-lime-siliea and soda-strontia-silica glasses at their wavelength maxima at around 485 and 500 nm, whieh dictated the intensity of the broad absorption bands marked due to selenium in the glass. However, the selenium was found to produce a golden yellow color in soda-baria-silica glass. This is due to the shift of the valence state of selenium towards the selenite (SeO3 2-) and selenate (SeO4 2-) state with increasing basicity of the glass. The values of the emission cross-section obtained for selenium based on the fluorescence spectral studies showed that the soda-lime-siliea glass emitted more intense fluorescence than the rest of the silicate glasses

Sn2+ - Sn4+ and Fe2+ - Fe3+ redox interaction in 30 Na2O—70 SiO2 glass

The role of stannous tin as a temperature-dependent reducing agent in a 30 Na2O—70 SiO2 glass containing Fe2+ and Fe3+ ions was investigated at 550 and 650 °C and different treatment times. The proportions of Fe2+ and Sn4+ ions were found to increase following a decrease in Sn2+ and Fe3+ contents during Sn2+ - Sn4+ and Fe2+ - Fe3+ mutual redox interaction on thermal treatments. These quantitative results obtained for the first time in a silicate glass were discussed for the redox pairs Sn2+ - Sn4+ and Fe2+ - Fe3+ in the light of standard reduction potentials of 0.15 and 0.77 eV, respectively, in aqueous solutions

Assessment of nickel oxide substituted bioactive glass-ceramic on in vitro bioactivity and mechanical properties

Many type of oxide substituted glass-ceramics like strontium, cobalt, barium and titanium have shown bioactivity with improved mechanical properties. The present work reports the in vitro bioactivity and mechanical properties of nickel oxide substituted in bioactive glass-ceramic and results were compared with 45S5 bioactive glass-ceramic. Bioactive glass ceramics were processed through controlled crystallization of their respective bioactive glasses. The formed crystalline phases in bioactive glass-ceramics were identified using X-ray diffraction (XRD) analysis. The formation of HA layer was assessed by immersing them in the simulated body fluid (SBF) for different soaking periods. The formation of hydroxyapatite was confirmed by FTIR spectrometry, SEM and pH measurement. Densities and mechanical properties of the samples were found to increase considerably with an increasing the concentration of nickel oxide. A decrease in glass transition temperature (Tg) with NiO addition showed that the nickel oxide had acted as an intermediate in smaller quantities in the bioactive glass. The cell culture studies demonstrated that the samples containing low concentration of NiO from 0 to 1.65 mol% were non-cytotoxic against osteoblast cells. Finally, this investigation clearly concluded that NiO doped bioactive glass would be potential biomaterials for biomedical applications