Raman spectroscopy of borosilicate and germanate-silicate glasses and melts

33 mol % Na₂O · 67 mol % SiO₂ + xB₂O₃ (GeO₂) glasses and melts with x = 0 and 20 mol % are studied by high-temperature Raman spectroscopy. The laws of formation of the anion structure of glasses and melts of borosilicate and germanate-silicate systems are shown to be different. The dominant anion groups in the systems are identified, and the structural changes occurring with increasing temperature and during a glass-melt transition are detected.     

Thermodynamic study of Na2O-SiO2 melts at 1300° and 1400 °C

The vapor pressures of Na above stirred Na₂O-SiO₂ melts in equilibrium with graphite and CO were determined at 1300° and 1400 °C using the transpiration technique. Compositions studied ranged from about 60 mole pct SiO₂ to close to SiO₂ saturation. Activities of components Na₂O and SiO₂ were calculated from the data. Log a_Na2_O (pure liquid as standard state) varies from about −8.7 and −8.5 at silica saturation to −6.3 and −6.1 at 40 mole pct Na₂O at 1300° and 1400 °C, and the molar Gibbs energy of mixing, ΔG _m, at the disilicate composition (X_Na2_O = 0.33) at each of these temperatures is −83.0 and −85.4 kJ, respectively. The Toop and Samis, Yokokawa and Niwa, and Lin and Pelton solution models for binary silicates were applied to the ΔG _m data at 1350 °C and parameters for the models were estimated to give best fits. All three models show good correspondence with the measured ΔG _m curve. The capabilities of the models in predicting activity data in this system have been compared. D. N. Rego, Formerly Graduate Student at Carnegie-Mellon University, G.K. Sigworth, Formerly with Carnegie-Mellon University,     

Solubility and thermodynamic properties of Li2O in LiF-CaF2 melts

Solubility of Li₂O in LiF-CaF₂ melts was studied as a function of temperature, and it was found to increase from 10.6 wt pct at 1058 K to 14.8 wt pct at 1133 K. The liquidus temperature of 4LiF • CaF₂ + Li₂O (saturated) melt was determined to be 1004.5 ± 2.5 K. Activity of Li₂O in the melt was determined as a function of temperature using conventional and Temkin ap-proaches. The partial molar Gibbs energy, enthalpy, and entropy of formation were deduced at the given temperature and composition range studied. The results showed that the system ex-hibits a negative deviation from Temkin's ideality.     

Raman spectra of hydroxide-halide melts

The Raman spectra of molten binary mixtures based on sodium hydroxide and containing (mol %) 35 NaCl, 30 NaBr, and 30 NaI have been recorded at various temperatures. An increase in the vibrational frequency and the force constant of the O-H bond is detected under isothermal conditions upon a variation of the anionic composition of a melt in the series I ?? Br ?? Cl. Based on the experimental data, the viscosity of the hydroxide-halide melts is estimated.     

Raman spectroscopy of glasses and melts of the Na<Subscript>2</Subscript>O-GeO<Subscript>2</Subscript> system

Glasses and melts of the system X mol % Na₂O · GeO₂ (X = 0, 10, 20, 30) are investigated using high-temperature Raman spectroscopy. Addition of an oxide modifier is shown to bring about an increase in the coordination number of central germanium atoms along with the depolarization of the three-dimensional GeO₂ network. The glass-melt transition in germanate systems with a low oxide-modifier content is accompanied by the transition of six-coordinated germanium atoms into four-coordinated (with oxygen) ones and a simultaneous formation of nonbridge oxygen atoms.     

The kinetics of the exchange of cobalt(II) ions between NaCl and Na2O-SiO2-Fe2O3 melts in the temperature range 1200 to 1400 K

Studies of the equilibria and kinetics of the Co²⁺ ion exchange in the Na₂O-SiO₂-Fe₂O₃/NaCl system were performed over the 1200 to 1400 K temperature range by measuring the emf of galvanic cells of the following composition: $$( - )Co\left| {\frac{{NaCl - CoCl_2 }}{{Na_2 O - SiO_2 - Fe_2 O3}}} \right.\left| {NaCl - CoCl_2 } \right.\left| {Co( + )} \right.$$ Distribution coefficients α of the Co²⁺ ions between the salt phase and silicate melt are of the l0^?2 order. Differential equations describing the transfer process of the Co²⁺ ions from the salt phase to the silicate phase were solved. The diffusion coefficients D_Co ²⁺ in the Na₂O-SiO₂-Fe₂O₃ melt were determined by substituting the Co²⁺ ion concentration change in fused NaCI into the differential equations. The values of D_Co ²⁺ are about 10^?5 cm²S^?1 and they decrease with decreasing temperature and increasing Fe_?2O_?3 content in slags. The diffusion coefficient of the cobalt (II) ions in slags determined in this way is consistent with that determined by the otating disk method.     

An interacting pair model for alkaline binary and ternary liquid silicates: Application to the systems Na2O-K2O-SiO2 and Na2O-Cs2O-SiO2

Among all the available models describing the structure of molten silicates, that of Pelton et al. allows accurate fitting of the experimental data of the free energies in the binary systems MO-SiO₂ with M=Fe, Mn, Pb, and Ca. An extension to the ternary systems MO-M′O-SiO₂, where M and M′ are alkaline metals, is proposed. A statistical treatment of the configurations of the solution gives a meaning to the new parameters. The mixed alkaline effect is quite well shown by the application of the model to the ternary systems K₂O-Na₂O-SiO₂ and Cs₂O-Na₂O-SiO₂, in particular, in the calculation of the configurational entropy.     

Dissolution Behavior of Rhodium in the Na2O-SiO2 and CaO-SiO2 Slags

To understand the behavior of rhodium during its recovery process, the dissolution behaviors of rhodium in Na₂O-SiO₂ and in CaO-SiO₂ slags at temperatures ranging from 1423 K to 1623 K (from 1150 °C to 1350 °C) and from 1773 K to 1873 K (from 1500 °C to 1600 °C), respectively, in an oxidizing atmosphere were investigated. The solubility of rhodium in the slags was found to increase with increasing oxygen partial pressure, temperature, and the basic oxide content. The correlation between the solubility of rhodium and the oxygen partial pressure suggested that rhodium dissolved into the slags as RhO_1.5. The dissolution of rhodium was slightly endothermic: the enthalpy change of the dissolution of solid rhodium was determined to be 50 ± 10 kJ/mol for the 50(mass pct)Na₂O-50SiO₂; and 188 ± 94 kJ/mol for the 56(mass pct)CaO-44SiO₂ slag systems. The increase in the solubility of rhodium with the basic oxide content indicated that rhodium exhibits acidic behavior in slags. The correlation between the solubility of rhodium and the sulfide capacity of the slags suggested that the ionic species of rhodium in slags is the rhodate ion, RhO ₂ ^? . The rhodate capacity of the slags was defined, and its application to estimate the possible rhodium content in various slag systems was proposed.     

The densities and structures of melts in the system CaO-“FeO”-SiO2

The densities of melts in the systems CaO-SiO₂, CaO-“FeO,” “FeO”-SiO₂ and in ternary melts containing 33 and 44 mole pct SiO₂ have been measured from the liquidus temperature to 1600°C. Structural interpretation of melt density and expansivity has provided information on the nature of the ions present in these systems, and, in conjunction with known thermodynamic behavior, has indicated the natures of the interactions occurring among these ions. The influence of temperature, silica content andCaO/FeO ratio on the structures of ternary iron-calcium silicates is discussed.     

Thermodynamic behavior of phosphorus in CaO-CaF2-SiO2 and CaO-Na2O-SiO2 systems

In order to understand the thermodynamic behavior of phosphorus, such as the polymerization of phosphate ions in slag melts, the influence of phosphorus content of slag melts on the partition of phosphorus between slags and carbon-saturated iron or silver was investigated for the CaO-CaF₂-SiO₂ and CaO-Na₂O-SiO₂ systems at 1573 and 1473 K, respectively. The predominant species changes from PO ₄ ³ to P₂O₇ ^4-approximately at 2 mass pct of phosphorus in slag melts, which is defined as the critical phosphorus content, for the CaO-CaF₂-SiO₂ system which is doubly saturated with CaO and 3CaO · SiO₂. The critical phosphorus content was found to be about 1 mass pct for the CaO-CaF₂-SiO₂ melts saturated with 2CaO · SiO₂. On the other hand, in the case of the 20CaO-35Na₂O-45SiO₂ system, PO₄/^3- is the predominant species until the slag becomes saturated with Ca₃(PO₄)₂. No effect of sulfur on the phosphorus partition ratio was observed for the CaO-CaF₂-SiO₂ system. Formerly Undergraduate Student, Department of Metallurgy, The University of Tokyo.     

Experimental studies of the viscosities in the CaO-Fe n O-SiO2 slags

In the present work, the viscosities in the CaO-Fe _n O-SiO₂ ternary system have been measured by the rotating cylinder method involving a spindle and crucible made of iron. Nine slag compositions in the ternary system have been chosen with CaO varying between 5.5 and 45.5 pct mass, FeO between 10.0 and 70.0 pct mass, and one measurement each in the binary Fe _n O-SiO₂ and CaO-SiO₂ melts. The measurements have been carried out in the temperature range of 1423 to 1753 K. The viscosity in this system is described as a function of temperature and composition using the model approach developed earlier at the present laboratory. The isoviscosity lines have been predicated at 1573, 1673, and 1723 K. Good agreement between the calculated results and the experimental data has been obtained.     

The sulfur partition ratio and the sulfide capacity of Na2O-SiO2 slags at 1200 °C

The sulfur partition ratio between carbon-saturated iron and Na₂O-SiO₂ slags and the sulfide capacity of these slags have been measured at 1200 °C. The two measurements are consistent with each other and the results are compared with other investigations. These slags have higher sulfide capacities and partition ratios than equivalent CaO-based slags and are thus attractive desulfurizers. Both the sulfide capacity and the partition ratio increase with increasing Na₂O. The activity coefficient of Na₂S has been calculated; it also increases with increasing Na₂O. The solubility of sulfur in a slag of 0.4 mole fraction Na₂O is estimated to be 5 pct.     

Potentiostatic polarization measurements on solid platinum-molten PbO-GeO2, PbO-SiO2, and Na2 O-SiO2 interfaces

Potentiostatic polarization measurements were carried out to investigate the mechanism of the charge transfer process on solid platinum-molten PbO-GeO₂, PbO-SiO₂, and Na₂O-SiO₂ interfaces over a temperature range of 900° to 1135°C in an atmosphere of air and argon-oxygen gas mixtures.