Mixed alkali effect on calcium aluminogermanate glasses

Abstract

Germanate glasses containing 0–6.44 wt% Li 2O were prepared by progressive weight percent substitution of Na 2O for Li 2O, at a constant ratio of concentration of CaO, Al 2O 3 and GeO 2. The mixed alkali effect on the optical properties, chemical resistance and electrical resistivity of calcium aluminogermanate glasses have been studied. The results of FT-IR spectra show that absorption band in 800–900 cm −1 region corresponds to GeO 4 groups and the Ge remains in 4-coordination state for these germanate glasses. As 0 ≤ Na 2 O ( Li 2 O + Na 2 O) ≤ 0.5 , the refraction index of and reflectance decrease with increasing Na 2O content, during 1 ≥ Na 2 O ( Li 2 O + Na 2 O) ≥ 0.5 , then its values are increasing with increasing Na 2O content. The leaching results indicate that Haze uv values for these germanate glasses with different content of Li 2O and Na 2O are greater than those of glasses containing only Li 2O or Na 2O, but the variations of pH value when the glasses are immersed in acidic solutions are greater in single alkali germanate glasses than in mixed alkali glasses. For the electrical resistivity measured, a maximum value occurs at Na 2 O ( Li 2 O + Na 2 O) = 0.5 .