Raman spectroscopy of the structures of Li2O-SiO2 and Li2O-GeO2 melts

An analysis of the Li₂O-SiO₂ and Li₂O-GeO₂ systems in the temperature range from 298 to 1373 K has been performed by Raman spectroscopy. A comparison of the spectroscopic data for the crystalline phases, glasses, and melts allowed us to determine the main anion groups existing in these systems and to establish the structural changes induced by changes in the temperature and composition.     

Some properties of the GeO<Subscript>2</Subscript>-PbO system in the solid and liquid states

The temperature dependence of the heat capacity of GeO₂-PbO oxides containing 60, 50, and 25 mol % GeO₂ is studied. The Raman spectra of GeO₂-PbO glasses and crystals are measured to refine their structures. The electrical conductivities of GeO₂-PbO melts are measured over wide composition and temperature ranges.     

Effect of chromium on the hydrogen solubility in liquid ternary iron-cobalt-chromium alloys

The experimentally determined hydrogen solubilities (Sieverts’ method) in liquid iron–cobalt–chromium melts were described based on own already published empirical equations and applying the regression analysis (Gauß-Jordan). The experimental results are represented as perspective isothermal planes. Addition of chromium increases the hydrogen solubilities. The hydrogen solubility increases with increasing temperature. The concentration dependencies of the interaction coefficients, enthalpies and entropies of hydrogen solution were calculated from the experimentally determined hydrogen solubility. Assuming a concentration dependence of the model parameter “λ” of the “Central Atoms” model the hydrogen solubilities in ternary iron-cobalt-chromium (x_cr ≤ 20%) melts were predicted. These predictions were made using the own experimentally determined hydrogen solubilities of the binary system iron-cobalt (x_Co ≤ 100%) and iron–chromium (x_Cr ≤ 25%) with iron, and referred to the other two binary systems cobalt–iron (x_Fθ ≤ 100%) and cobalt–chromium (x_cr ≤ 20%) with cobalt as “reference element”. The predicted hydrogen solubilities were compared with the own experimentally determined hydrogen solubilities. The deviations between these two results are less than 2%.     

The dependence of the oxidation state of vanadium on the oxygen pressure in melts of VOx,Na2O-VOx,and CaO-SiO2-VOx

The oxidation state of vanadium has been determined as a function of oxygen pressure in pure VO_x melts at 808 °C to 1000 °C, in Na₂O-VO_x melts with the initial molar ratios Na₂O/V₂O₅ = 0.2, 0.5, and 1.0 at 1000 °C, and in CaO-SiO₂-VO_x melts with the molar ratios CaO/SiO₂ = 0.71, 1.00, and 1.36 at 1600 °C. In the VO_x melts,x is close to 2.5 in the range of oxygen pressure fromP _{O 2} to 0.94 atm. The deviation, δ, from stoichiometric V₂O₅ (δ = 2.5-x) varies approximately proportionally toP _{O 2} ^-1/4, indicating an equilibrium between V⁴⁺ and V⁵⁺ ions. In the Na₂O-VO_x melts, and in the CaO-SiO₂-VO_x melts,x varies with logP _{O 2} according to an S-shaped function, withx approaching 1.5 at low and 2.5 at high oxygen pressures. At given oxygen pressures,x increases with Na₂O or CaO content, respectively. Hence, these oxides stabilize the higher valent vanadium ions. For the CaO-SiO₂-VO_x system, the determinedx-P _{O 2} dependence can be interpreted quantitatively in terms of V⁴⁺/V⁵⁺ and V³⁺/V⁴⁺ equilibria.     

Thermal stability and optical properties of a novel Tm~(3+) doped fluorotellurite glass

A series of fluorotellurite glasses based on（81–x）Te O2-（10＋x）KF-9La2O3（TKL）, where x=0 mol.%, 5 mol.%, 10 mol.%, 15 mol.%, doped with 2000 ppm Tm2O3, were prepared by the conventional melt quenching method.The influence of KF content on the thermal stability and optical spectroscopic properties of the Tm3＋ doped fluorotellurite glasses were investigated by differential scanning calorimetry（DSC）, X-ray diffraction（XRD）, density measurement, Fourier transform infrared spectroscopy（FTIR）, UV-VIS-NIR optical spectroscopy and fluorescence spectroscopy.Judd-Ofelt intensity parameters of Tm3＋ in as-prepared glasses were determined and used to calculate the spontaneous emission probabilities and the radiative lifetime for the 4f-4f transitions of the Tm3＋ ions.Stimulated emission cross sections in the 1470 nm region（σse） were evaluated by Füchtbauer-Ladenburg formula.The results showed that KF substitution of Te O2 was beneficial to improving the thermal stability, decreasing glass density and reducing the content of OH related groups for the investigated fluorotellurite glasses.The glass with composition of 66 Te O2-25KF-9La2O3（named TKL25） had the longest radiative lifetime of the 3H4（361 μs） and the largest FWHM×σse value（420.07×10–28 cm3）, which made it a promising material for S-band fiber amplifiers.     

Temperature dependence of the refractive index of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> melts: Role of electronic polarizability of oxygon controlled by network structure

Refractive indexes for the Al₂O₃-Na₂O-SiO₂ system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800 K). Two kinds of sample were used: xAl₂O₃-(40-x)Na₂O-60SiO₂ and yAl₂O₃-yNa₂O-(100-2y)SiO₂, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative to positive on increasing the concentration of Al₂O₃. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO₂, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases. The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration of Al₂O₃ has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Raman spectra and conductivity of PbO–PbCl<Subscript>2</Subscript>–CsCl melts

The structure and the conductivity of homogeneous CsCl–PbCl₂–PbO melts with different compositions are studied. The Raman spectra (RS) of the chloride and oxide–chloride melts containing lead oxide have been measured. It is found that the CsCl (71.3 mol %)–PbCl₂ (28.7 mol %) system with the addition of 12 mol % PbO and the CsCl (18.3 mol %)–PbCl₂ (81.7 mol %) system with the addition of 18 mol % PbO contain Pb₃O₂Cl⁺ oxide–chloride groups. The temperature dependences of the electrical conductivity are measured in the PbCl₂–CsCl chloride melts containing 28.7 and 81.7 mol % lead chloride and in homogeneous molten mixtures CsCl (71.3 mol %)–PbCl₂ (28.7 mol %) with the addition of 12 mol % PbO and the CsCl (18.3 mol %)–PbCl₂ (81.7 mol %) with the addition of 18 mol % PbO. Significant degradation of the ion conductive properties of the PbO–PbCl₂–CsCl oxide–chloride melts as compared to those of the PbCl₂–CsCl chloride electrolytes has been revealed. It is shown that the decrease in the electrical conductivity of the PbCl₂–CsCl oxide–chloride melts as lead oxide is added is due to the presence of Pb₃O₂Cl⁺ oxide–chloride groups.     

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.     

Partial and integral enthalpies of mixing of Cu-Fe-Ti melts at 1873 K

The partial enthalpy of mixing of titanium in Cu-Fe-Ti melts are studied by high-temperature isoperibolic calorimetry at 1873 K in the composition range x _Ti = 0–0.6 along three sections with a ratio x _Fe / x _Cu = 1/3, 1, and 3. The integral enthalpy of mixing of the ternary melts is calculated by integrating the Gibbs-Duhem equation and is described in terms of the Redlich-Kister-Muggianu model. Function ΔH demonstrates negative values over a wide concentration range. The contribution of a ternary interaction to the enthalpy of mixing of Cu-Fe-Ti melts is mainly positive. The first partial enthalpies of mixing of Al, Sn, Si, Y, Zr, Hf, and Ni with Cu-Fe-Ti melts are negative and indicate an increase of the thermodynamic stability of the liquid phase upon the dissolution of these additions.     

Critical assessment of activity coefficients of oxides in molten binary and ternary silicates,aluminates and aluminosilicates

Critical assessment is made of the activity coefficients of CaO, MgO, MnO, FeO, Al₂O₃ and SiO₂ in molten silicates, aluminates and aluminosilicates. In this assessment due consideration is given to the consistency of the free energies of formation of the interoxide compounds derived from the oxide activity data, compared with those derived from the compiled thermochemical data. For most oxides, it is found that by using an empirical formulation of the melt composition in ternary systems, the composition dependence of the oxide activity coefficient, γOX, can be represented by a single curve. For example, over a wide composition range in the FeO‐CaO‐SiO₂ system, the log(γCaO) is a single function of the melt composition in mol fraction as (?SiO₂ + 0.3xFeO); this relation being similar to that in the binary CaO‐SiO₂ melts. Therefore, with respect to γCaO, this ternary system is reduced to a pseudo binary system as xCaO ‐ (?SiO₂ + 0.3xFeO). With respect to γCaO, the ternary system CaO‐Al₂O₃‐SiO₂ is reduced to a pseudo binary system as xCaO ‐ (?SiO₂ + 0.4 xAl₂O₃). With γSiO₂, this ternary system is reduced to a pseudo binary system as (?CaO + xAl₂O₃) ‐ xSiO₂.     

Thermal and radiative characteristics of oxyfluoride glass singly doped with lanthanide ions

Rare earths-doped oxyfluoride glasses based on germanium oxide and lead fluoride were prepared from commercial raw materials. The glasses with general composition of 50GeO2-(50-x-y)PbO-yPbF2-xLnF3 (Ln=Pr3+-Yb3+), contained different concentrations of optically active dopants (x=0.2 mol.% and 2 mol.%) and PbF2 (y≤15 mol.%). The differential thermal analysis (DTA) was used to determine both thermal characteristic and thermal stability properties of the glasses in the function of the kind of dopant, its concentration, and a glass composition. Characteristic glass temperatures such as glass transition temperature (Tg), glass crystallization temperature (Tc) and temperature corresponding to the maximum of the crystallization rate (Tpc) were evaluated. On the basis of obtained results, the thermal stabilities of glasses under study were evaluated using various thermal stability criteria (Dietzel factor ?T, Saad-Poulain factors H' and S). It was found that the increase in rare earth fluoride contents influenced thermal characteristics when the characteristic temperatures of the individual glass was shifted towards higher values. The effect of the PbF2 content and the kind of rare earth impurity on the glass stability was observed. Absorption spectra of lanthanide-doped glasses were measured at room temperature and used to determine the phenomenological intensity parameters Ωt and next, to estimate radiative properties of lanthanide ions in this matrix. Radiative transition probabilities of luminescent states of Ln3+, branching ratios and radiative lifetimes were determined. The variation of the Ωt along the lanthanide series was presented and discussed.     

Kinetics studies on the dissolution of nitrogen in the CaO-Al2O3-SiO2 and CaO-Al2O3-TiO x melts

The rate of nitrogen dissolution in CaO-Al₂O₃-SiO₂ and CaO-Al₂O₃-TiO _x melts was measured by ¹⁴N–¹⁵N isotope exchange reaction. The rate constant for the CaO-Al₂O₃-SiO₂ melts at the ratio of mass pct CaO/mass pct Al₂O₃ = 1 increases as SiO₂ content increases, whereas the rate constant for the same melts at the ratio of mass pct CaO/mass pct SiO₂ = 1 increases as Al₂O₃ content increases. The rate constant for the CaO-Al₂O₃-TiO _x melts at the ratio of mass pct CaO/mass pct Al₂O₃ = 1 decreases as the TiO _x content increases. The activation energies of nitrogen dissolution in CaO-Al₂O₃-SiO₂ melts are about 1.5 to 3 times larger than that of molten pure iron. Moreover, the rate constant of nitrogen dissolution is independent of the ratio of Ti³⁺/Ti⁴⁺.     

Solubility of Li<Subscript>2</Subscript>O in an LiCl–KCl Melt

The phase diagrams of the binary LiCl–Li₂O system and the quasi-binary [LiCl–KCl]–Li₂O systems containing 10 and 20 mol % KCl have been built using thermal analysis of cooling curves and isothermal saturation curves. The solubility of Li₂O in LiCl–KCl melts is determined in the temperature range 500–800°C. The solubility of Li₂O in the melts LiCl, LiCl–KCl (10 mol %) and LiCl–KCl (20 mol %) decreases as the KCl content increases;at 650°C, it is 11.5, 7.7, and 3.9 mol %, respectively.     

Solubilities and raman spectra of NdOCl in some chloride melts of interest for the electrowinning of magnesium from its oxide

Some fundamental data related to the solvent proposed for a new technical electrolytic process for magnesium production based on MgO as the raw material are presented. Liquidus data are obtained for MgCl₂-rich melts in the MgCl₂-NdOCl system. The solubility of MgO and NdOCl in pure liquid NdCl₃, MgO in NdCl₃-MgCl₂ and in MgCl₂-NdCl₃-NaCl liquid mixtures, and NdOCl in CaCl₂ and Cs₂MgCl₄ have also been studied. The solubility of MgO decreases when MgCl₂ is added to the pure NdCl₃ and further by additions of NaCl as expected. A so far unidentified compound having the composition Mg _x Nd _y OCl_2x-3y-2 where x and y are larger than 1 seems to be formed in very small amounts in these melts. This compound seems to precipitate at temperatures higher than 910 °C in the NdCl₃-MgO quasi-binary system containing about 8 mol pct MgO and seems to remain suspended in the melt in small quantities. The first liquid-solid phase transition observed, however, was the NdCl₃ (1)=NdCl₃ (s) transition <758 °C. X-ray diffraction (XRD) data of filtered samples of this solid show new X-ray lines not detected in MgCl₂, NdCl₃, NaCl, MgO, and NdOCl. The published phase diagram of the quasi binary system MgCl₂-NdOCl is, according to the present work, not correct because the solubility of MgO seems to be much less than previously reported. Raman spectroscopic data of NdCl₃-MgCl₂-NdOCl melts show the known features of the NdCl₃-MgCl₂ and NdCl₃-NdOCl melts. Raman bands due to dissolved species of the unidentified compound were not detected. In view of the obvious small concentration of this species in the liquid phase, this was reasonable. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

Redox equilibria and kinetics of gas-slag reactions

Measurements of redox equilibria involving a number of transition metals (Fe, Mn, Ti, and V) are summarized and discussed with respect to the effects of oxygen activity and chemistry of the melts on the oxidation state of the transition metal oxide. Recently measured data on kinetics of CO-CO₂ on surfaces of calcium silicate-based slags containing 1 to 68 wt pct FeO _x or 18 to 38 wt pct MnO _x are presented and discussed in terms of the limiting steps and the dependence of the limiting step on concentration of the transition metal oxides in the melts. Similar data on nonferrous-type slags containing PbO, ZnO, or TiO _x in the presence or absence of FeO _x are also reviewed. The review also includes recent investigations of the effects of iron oxide on the diffusivity of iron and oxygen in slags. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Experimental study of phase equilibria in the systems PbO x -CaO and PbO x -CaO-SiO2

The reported experimental work on the systems PbO _x -CaO and PbO _x -CaO-SiO₂ in air is part of a wider research program that combines experimental and thermodynamic computer modeling techniques to characterize zinc/lead industrial slags. Extensive experimental investigation by high-temperature equilibration and quenching techniques followed by electron probe microanalysis was carried out in the temperature range 640 °C to 1500 °C (913 to 1773 K) and in the composition ranges 0 to 65 mol pct SiO₂ and 0 to 42 mol pct CaO. Liquidus and solidus data were reported for most of the primary phase fields. Liquidus surfaces in the systems CaO-Pb-O and PbO _x -CaO-SiO₂ in air were completely reconstructed. Extensive solid solutions of PbO in α′ dicalcium silicate and Ca₂Pb₃Si₃O₁₁ were measured.     

Synthesis and Characterization of Lithium Borate Glasses Containing La<Subscript>2</Subscript>O<Subscript>3</Subscript>

The glass series with general formula 15 Li₂O–(85 − x) B₂O₃–x La₂O₃ was prepared. Electrical and optical properties of these glasses were studied. It is observed that the conductivity of these glasses decreases while density, glass transition temperature and refractive index increases with the addition of La₂O₃. Ion concentration of La³⁺ in glasses, polaron radius, field strength, molar refractivity and molar electronic polarizability were calculated. The absorption coefficient and direct optical band gaps are evaluated using the absorption edge calculations. The different factors that play a role for controlling the refractive indices such as electronic polarizability, field strength of cations and rigidity of glass structure are discussed in accordance with the obtained index data.     

Calorimetric study and description of the composition dependence of the mixing enthalpy of liquid Cu—Fe—Co aloys

The partial enthalpy of cobalt in ternary liquid Cu-Fe-Co alloys is studied at a temperature of 1873 K along sections characterized by ratios x _Cu/x _Fe = 3, 1, and 1/3 in the composition range x _Co = 0–0.55. The experiments have been carried out on a high-temperature isoperibolic calorimeter. The composition dependences of the partial mixing enthalpy of the cobalt and the integral mixing enthalpy of Cu-Fe-Co melts are described using the Muggianu-Redlich-Kister equation over the entire concentration triangle. The contributions of a ternary interaction to the partial mixing enthalpy of cobalt and the integral mixing enthalpy of Cu-Fe-Co melts are calculated.     

Activity coefficient of oxygen in copper-sulfur melts

Activity coefficients of oxygen in sulfide-rich and metal-rich melts in the copper-sulfur system were determined at 1423 and 1523 K by means of a modified coulometric titration technique using the following cell: O (in Cu-S melts) |ZrO₂(+CaO)| air, Pt. The activity coefficient values increase rapidly with sulfur composition in the vicinity ofx _s = 0.3333. The data obtained for the matte saturated with the metal-rich melts are in good agreement with those obtained by Kuxmann and Benecke and Schmiedl. Those obtained for the metal-rich melts are in good agreement with the results of Sano and Sakao. Formerly Research Associate at The University of Wisconsin     

Experimental study and modeling of the thermodynamic properties of Cu-Fe-Ni melts

The partial mixing enthalpy of nickel in ternary liquid Cu-Fe-Ni alloys is studied at 1873 K along sections characterized by ratios x _Cu: x _Fe = 3, 1, and 1/3 at x _Ni = 0–0.55. The investigations are undertaken using a high-temperature isoperibolic calorimeter. The temperature and composition dependence of the excess mixing Gibbs energy of liquid Cu-Fe-Ni alloys are described in terms of the Muggianu-Redlich-Kister model using the data obtained, the literature data on the activities of liquid alloy components, and the thermodynamic properties of melts of the boundary binary systems. This model is used to calculate isotherms of the thermodynamic properties of the liquid alloys over the entire composition range. The contribution of a ternary interaction to the integral mixing enthalpy of liquid Cu-Fe-Ni alloys is found to be mainly positive.