Chapter 10: Germanate Glasses Containing a Modifier Oxide and Either SiO₂ or B₂O₃ Check Access

Since there are no anomalies in the properties of alkali silicate glasses, all the germanate anomalies gradually shift in position and decrease in magnitude as GeO₂ is replaced by SiO₂ until they disappear at high SiO₂ concentrations. In contrast, the germanate anomalies in the thermal expansion coefficient and glass transformation temperature do not disappear as GeO₂ is replaced by B₂O₃. In this case, the positions of the germanate anomalies gradually shift from those found for alkali germanate glasses to those found for alkali borate glasses. Since the other properties of alkali borate glasses do not exhibit anomalies, the behavior of those properties resembles those of the alkali silicogermanate glasses as GeO₂ is replaced by B₂O₃, although the behavior of the density and refractive index of the potassium borogermanate glasses are complicated by the unusual behavior of the potassium borate glasses. The density, refractive index, and thermal expansion coefficient of lead silicogermanate glasses do not exhibit any anomalies. The thermal expansion curves of these glasses indicate that most of these glasses are phase separated. The properties of alkaline earth borogermanate glasses have only been measured at high alkaline earth oxide concentrations, so no information is available regarding the behavior of the anomalies in these glasses.