Germanate Melts Research Articles

Melts and glasses of the K2O-GeO2 system: Physicochemical modelling with correction based on the results of Raman spectroscopy

A Gibbs free energy minimization approach realized in “Selector-C” software is used to study germanate melts and glasses of the K2O–GeO2 system. A database of the thermodynamic properties of structural units of germanate melts was compiled by according to the results of high-temperature Raman spectroscopy for the correction of physicochemical models. Three mechanisms for the introduction of potassium cations into the germanium-oxygen network are identified along with the effect of composition and temperature on these mechanisms. It is shown that the germanate anomaly maximum shifts with increasing temperature towards low-alkaline compositions due to the appearance of non-bridging oxygen atoms in the system.

In situ Raman spectroscopy of K2O-GeO2 melts

Raman spectra of potassium germanate melts K2O-GeO2, containing 10, 20, 30 and 40 mol.% K2O were measured. Based on a comparison of melts and glasses spectra we were able to determine the basic structural units formed in the system and to reveal the structural features of potassium-germanate melts during vitrification. It was shown that in melts, in contrast to glasses, an increase of the K2O content leads to a monotonic decrease of the fraction of germanium atoms in the octahedral coordination and the formation of [GeO4] tetrahedra with one and two non-bridging oxygen atoms. During cooling of germanate melts and their glass transition, an increase of the coordination number of germanium atoms and an increase of the degree of polymerisation of the network occur due to the formation of Ge–O–Ge bridging bonds.

A Limited Review of Water Diffusivity and Solubility in Glasses and Melts

A limited review of the literature dealing with water solubility and diffusion in oxide glasses and melts is presented, with an emphasis on simple and commercial compositions and on work during the past decade. Several methods for determination of water solubilities and diffusivities are discussed. Experimental results are presented for silicate, borate, and germanate glasses and melts. Water diffusivities always increase with increasing temperature and modifier oxide content in these melts. Variations in water solubility and diffusivity with alkali and alkaline earth identity for otherwise identical compositions are small, while variations with the identity of the glass‐forming oxide are large. Water solubility increases with increasing modifier oxide content in alkali silicate melts, but decreases with increasing modifier oxide content in alkali borate and germanate melts.

Surface Tension and Density of Bismuth Germanate Melts as a Function of Composition and Temperature

The surface tension and density of xBi(2)O(3)-(1-x)GeO2 (BGO) melts have been measured systematically from their respective melting points up to around 1480 K within 0.25 <= x <= 0.86. With the addition of Bi2O3, the density of this system increased smoothly with a positive curvature. Deviation of molar volume from ideality of this system melts decreased firstly, past a minimum at about x=0.4, and then increased. Partial molar volumes of Bi2O3 and GeO2 have also been calculated based on the measured density data and compared with those of a binary bismuth borate system. On increasing the content of Bi2O3, the surface tension of BGO melts increased slowly when x <similar to 0.40, past a maximum at about x=0.50, and then decreased rapidly. In addition, the temperature coefficient of surface tension remained positive within the lower content range of Bi2O3, changed sign from positive to negative at about x=0.38, and then was almost independent of the composition within the measured temperature range when the Bi2O3 content was increased further.

Solubilities of CO2 in Binary Alkali Germanate Melts

Solubilities of CO2 in Binary Alkali Germanate Melts

Molecular Dynamic Simulation on the Structure of Sodium Germanate Melts

Molecular Dynamic Simulation on the Structure of Sodium Germanate Melts

Growth of calcium aluminum germanate garnets in molten bismuth germanate glasses

Selected calcium (and calcium/lead) bismuth germanate melts can partially crystallize, even upon rapid cooling, to small (up to 0.35 mm, but longer in completely crystalline samples) hexagonal needles that appear to be CaBi 2Ge 2O 8. This tendency to crystallize upon cooling can be suppressed by adding small amounts of Al 2O 3. The addition of larger amounts of Al 2O 3 yields a considerable number of well formed garnets that range up to 0.15 mm in size. These crystals can be separated from the adhering glass by appropriate dissolution techniques. The density, refraction, and infrared spectrum of the garnets suggest the formula Ca 3Al 2Ge 3O 12. The amorphous garnet-like arrangement of the atoms in these melts appears to be an important factor in their formation.

A Calorimetric Study of the Liquid System Lead(II) Oxide‐Germanium Dioxide at 900°C

AbstractThe partial enthalpies of liquid lead(II) oxide and of tetragonal germanium dioxide in lead germanate melts were measured calorimetrically at 900°C in the range 0 to 65 mole‐% GeO2. The corresponding integral enthalpies of mixing were calculated. A relatively sharp dependence of the partial enthalpies on composition in the range from N = 0.3 to 0.45 probably is due to the formation of Ge2O.

Electrical Conductance of Alkali Germanate Melts at 1300°C

Electrical conductance data are presented for a series of binary alkali germanate melts containing from zero to (where ). The equivalent conductance at 1300°C and the activation energies for conductance change rather sharply (increase and decrease respectively) with the addition of less than 2 mole % of alkali oxide. Equivalent conductance is related to cation‐oxygen attraction forces while activation energy is related to cation volume. Some of the specific deviations can be explained in terms of the presence of octahedra. Results are compared with similar data for alkali silicate melts, molten salts, and alkali germanate glasses.

Structure of Molten Oxides. II. A Density Study of Binary Germanates Containing Li2O, Na2O, K2O, and Rb2O

An improved counterbalanced sphere viscometer—densitometer was used to obtain density information between 1050° to 1500°C for a series of binary germanate melts containing as much as 60 mole% Li2O, Na2O, K2O, and Rb2O. Densities and the expansion coefficient of molten GeO2 between 1100° to 1400°C were estimated from the binary data. The molar volume, expansion coefficient, partial molar volume and partial molar expansion deviations suggest a mode of network alteration that differs from that observed for silicate melts. This confirms the previously reported viscosity results for binary alkali germanate melts. It is suggested that a gradual change from tetrahedral to octahedral configuration occurs for GeO2 with the addition of alkali oxide. The maximum stability of octahedrally coordinated germanium at 1300°C appears to occur for melts containing from 15 to 30 mole% M2O. A rapid return to tetrahedral configuration appears to take place for most germanate melts as the alkali oxide content is increased above 30 mole%. These alkali-rich germanate melts possess properties that are similar to those found for their silicate analogs. It is suggested that discrete anions also exist in these alkali rich germanate melts.