Phase Relations and Glass Formation in the System PbO-GeO,

Phase relations in the system PbO-GeO2 were determined using the quenching technique. The five compounds detected were: 4PbO-GeO2, 3PbO-2GeO2, PbO-GeO2, and PbO-4GeO2. The 3:2 and 1:1 compounds melt congruently at 744° and 799°, respectively. The 4:1 compound melts incongruently at 726°C to PbO plus liquid, whereas the 1:4 compound melts incongruently to GeO2 plus liquid at 790°C. The 1:2 compound has a temperature range of stability between 707° and 730°. The data indicate that no liquid immiscibility gap exists in the system. Indices of refraction for glasses in the system were compared with lead silicate glasses. An addition of ∼65%PbO to GeO2 is required to prepare a glass with an index near 2.0 whereas with SiO2, ∼85% PbO is required. It appears that the lead germanate glasses have higher indices than all other two-component oxide glasses. The addition of PbO to GeO2 decreases the rutile-to-quartz transformation temperature from 1000°C for pure GeO2 to 990°C. Infrared spectra of lead germanate glasses (∼60w% PbO) show that transmission is good up to 5.5μ but decreases drastically between 5.5 and 6.5μ.