Thermal Conductivity of the Molten CaO-SiO2-FeO x System

Thermal conductivity measurements were carried out on synthetic steelmaking slag using the hot-wire method. Furthermore, local structure analysis in the melts was carried out in order to investigate the relationship with the composition dependence. The thermal conductivity of the CaO-SiO₂-FeO _x melts significantly decreased as the content of FeO _x increases, particularly at lower basicity. Both chemical analysis and the observation show that the amount of Fe²⁺ increases when CaO/SiO₂ is smaller, implying more basic behavior of FeO than FeO_1.5. According to further analyses by M?ssbauer spectroscopy, the degree of basicity of FeO_1.5 remains virtually unchanged in the composition range of interest. From the experimental results, it could be concluded that the thermal conductivity of the silicate melt containing iron oxide is highly dependent on the valence of the Fe ion and comparatively independent of the amphoteric behavior of FeO_1.5.     

Mechanical and Thermal Properties of Hot-Pressed ZrB2-SiC Composites

ZrB₂-SiC composites were hot pressed at 2473 K (2200 °C) with graded amounts (5 to 20 wt pct) of SiC and the effect of the SiC addition on mechanical properties like hardness, fracture toughness, scratch and wear resistances, and thermal conductivity were studied. Addition of submicron-sized SiC particles in ZrB₂ matrices enhanced mechanical properties like hardness (15.6 to 19.1 GPa at 1 kgf), fracture toughness (2 to 3.6 MPa(m)^1/2) by second phase dispersion toughening mechanism, and also improved scratch and wear resistances. Thermal conductivity of ZrB₂-SiC (5 wt pct) composite was higher [121 to 93 W/m K from 373 K to 1273 K (100 °C to 1000 °C)] and decreased slowly upto 1273 K (1000 °C) in comparison to monolithic ZrB₂ providing better resistance to thermal fluctuation of the composite and improved service life in UHTC applications. At higher loading of SiC (15 wt pct and above), increased thermal barrier at the grain boundaries probably reduced the thermal conductivity of the composite.     

A Pseudo-Multicomponent Approach to Important Ternary Silicate Melts

For the CaO-Al₂O₃-SiO₂, CaO-FeO-SiO₂, and MnO-FeO-SiO₂ ternary silicate melts, there are few models that can accurately predict their component activities. One model that can make a good correlation between the ternary activities and their sub-binary ones is a pseudo-multicomponent approach based on the molecular interaction volume model (MIVM). It does not need any linear or power series composition functions of binary parameters and also does not require any ternary adjustable parameters in addition to its composition equation. The results show that in the CaO-Al₂O₃-SiO₂ system, the predicted values of SiO₂ activity are in good agreement with the experimental data at 1873?K (1600?°C), and those of CaO and Al₂O₃ are in reasonable agreement with the graphical integration of data using the Gibbs?CDuhem equation at 1873?K (1600?°C) and experimental data at 1823?K (1550?°C). In the CaO-FeO-SiO₂ and MnO-FeO-SiO₂ systems, the predicted values of FeO and MnO activity are in good agreement with the experimental data, and those of CaO and SiO₂ are in reasonable agreement with the experimental data at 1823?K, 1873?K, and 1803?K (1550?°C, 1600?°C, and 1533?°C).     

Thermal Conductivity of Copper-Graphene Composite Films Synthesized by Electrochemical Deposition with Exfoliated Graphene Platelets

Samples of graphene composites with matrix of copper were prepared by electrochemical codeposition from CuSO₄ solution with graphene oxide suspension. The thermal conductivity of the composite samples with different thickness and that of electrodeposited copper was determined by the three-omega method. Copper-graphene composite films with thickness greater than 200 μm showed an improvement in thermal conductivity over that of electrolytic copper from 380 W/m.K to 460 W/m.K at 300 K (27 °C). The thermal conductivity of copper-graphene films decreased from 510 W/m.K at 250 K (–23 °C) to 440 W/m.K at 350 K (77 °C). Effective medium approximation (EMA) was used to model the thermal conductivity of the composite samples and determine the interfacial thermal conductance between copper and graphene. The values of interface thermal conductance greater than 1.2 GW/m².K obtained from the acoustic and the diffuse mismatch models and from the EMA modeling of the experimental results indicate that the interface thermal resistance is not a limiting factor to improve the thermal conductivity of the copper-graphene composites.     

Thermal Conductivity Measurements of Some Synthetic Al2O3-CaO-SiO2 Slags by Means of a Front-Heating and Front-Detection Laser-Flash Method

The thermal conductivities of some synthetic slags containing Al₂O₃, CaO, and SiO₂ have been determined in the temperature range between 1623?K (1350?°C) and 1823?K (1550?°C) by applying a front-heating front-detection laser-flash method. In this method, the temperature response curve is measured in the short initial time period immediately after irradiating a laser pulse. The resultant values obtained by this method are unaffected by the radiative heat transfer. The temperature dependence of the thermal conductivity values were found not to be significant for all slag samples currently investigated. The thermal conductivity (??) of samples is represented with standard deviation less than 2?pct of its value as a function of compositions as follows: $$ \lambda = - 0.48\left[ {{\text{Al}}_{ 2} {\text{O}}_{ 3} } \right] - 0.57\left[ {\text{CaO}} \right] - 0.55\left[ {{\text{SiO}}_{2} } \right] + 57.1{\text{ W m}}^{ - 1} {\text{ K}}^{ - 1} $$ where [Al₂O₃], [CaO], and [SiO₂] are molar percent of Al₂O₃, CaO and SiO₂, respectively. The equation is suggested to cover the region of the following compositions: 8.0?mol pct < Al₂O₃ <21.0?mol pct, 31.5?mol pct < CaO <41.5?mol pct and 43.0?mol pct < SiO₂ <58.1?mol pct. The addition of Al₂O₃ to slags with a constant CaO/SiO₂ molar ratio resulted in an increase in thermal conductivity. In contrast, the effects of addition of SiO₂ and CaO are found to be insignificant.     

Review and modeling of viscosity of silicate melts: Part I. Viscosity of binary and ternary silicates containing CaO, MgO, and MnO

A structurally related model for the calculation of the viscosity of silicate melts is proposed based on the general behavior of the viscosity of binary silicate melts. It relates viscosity to the degree of polymerization, as represented by the three types of oxygen in the melts. The model parameters for binary systems were optimized to give best fit to the experimental values. For ternary systems, it was assumed as a first approximation that the model parameters were linear functions of the parameters of the two binary silicate systems. The model has been applied to the CaO-SiO₂, MgO-SiO₂, and MnO-SiO₂ binary systems and the CaO-MgO-SiO₂ and CaO-MnO-SiO₂ ternary systems. Good agreement was obtained between calculated values and experimental data over the composition and temperature ranges in which experimental data exist. Comparison was made between the present model and the Urbain model. The present model has the capability of representing changes in viscosity due to substitution of cation species in silicate melts.     

Cryoscopic studies in fluoride-Oxide-Silica systems: Part II. systems containing Mg2+, Ca2+, Ba2+ and Pb2+

The depressions of the freezing temperatures of MgF₂, CaF₂, and BaF₂ by adding 2MO · SiO₂, 3MO · 2SiO₂, MO · SiO₂, 2MO · 3SiO₂, and MO · 2SiO₂ where M = Mg, Ca and Ba, have been measured, as have the depressions of the freezing temperature of PbF₂ resulting from additions of 2Pb · SiO₂, 3PbO · 2SiO₂ and PbO · SiO₂. The variations of the activities of the fluorides with liquidus composition have been calculated. These are shown to be in good agreement with a proposed theoretical model of the constitutions of these melts. In the alkaline earth systems with MO/SiO₂ > 1.5 linear chain silicate ions and free F⁻ ions are postulated and in melts of MO/SiO₂ < 1.5 reaction between F⁻ and silicate ions to form polyfluorosilicate anions is postulated. These conclusions are in agreement with those drawn from infrared absorption studies of CaF₂-CaO-SiO₂ glasses. The activity behavior in the reciprocal systems MF₂-M′O · SiO₂ and M′F₂-MO · SiO₂ is explained in terms of polymerization and preferred ionic association effects within the melts. In the lead fluoride-silicate systems fluorination of the silicate ions occurs at PbO/SiO₂ = 2 and, in contrast with the alkali and alkaline earth systems, it appears that polyfluorosilicate anions and free O²⁻ anions can coexist in lead fluorosilicate melts.     

Thermoelectric properties of quaternary chalcogenide Cu2ZnSnS4 synthesised by mechanical alloying

ABSTRACT

The quaternary chalcogenide Cu₂ZnSnS₄ has emerged as a potential thermoelectric (TE) material due to its low thermal conductivity (κ), high Seebeck coefficient (S) and composition including earth-abundant, low-cost and non-toxic elements. In this work, Cu₂ZnSnS₄ was synthesised from a mixture of Cu, Zn, Sn and S powders using a mechanical alloying method. As a result, Cu₂ZnSnS₄ powders were formed after 16?h of milling, without additional heat treatment. After milling, the powders were heat-treated at 723?K for 24?h and then sintered by spark plasma sintering under an applied pressure of 60?MPa at 873?K for 10?min. The heat-treated Cu₂ZnSnS₄ sample showed a wide-band-gap of 1.49?eV. The sintered Cu₂ZnSnS₄ sample exhibited S and κ values of 170 μV K^?1 and 1.06 W m^?1 K^?1, respectively with an electrical conductivity σ of 1240 S m^?1 and a dimensionless figure of merit (ZT) of 0.022 at 663?K.     

Cryoscopic studies in fluoride-oxide-silica systems: Part I. systems containing Li+, Na+ and K+

The depressions of the freezing temperatures of NaF and KF by additions of 3M₂O · 2SiO₂, M₂O -SiO₂, M₂O · 2SiO₂ and SiO₂ (where M = Li, Na and K) have been measured and the variations of the activities of NaF and KF with liquidus composition have been calculated. These activities are shown to be in good agreement with a proposed theoretical model of the anionic constitutions of these melts. In melts of M₂O/SiO₂ > 1 linear chain silicate ions and free F⁻ ions are postulated and in melts of M₂O/SiO₂ < 1 reaction between F⁻ and silicate ions to produce polyfluorosilicate anions is postulated. The effect of alkali cation type on the deviation of the liquidus activities from the proposed ideal behavior in melts of M₂O/SiO₂ > 1 and the degrees of polymerization of the fluorosilicate ions in melts of M₂O/SiO₂ < 1 are explained in terms of coulombic interactions and the effects of cation size on the polarization behavior. In the reciprocal systems MF-M₂ ^′O · SiO₂ and MF-M₂ ^′O · 2SiO₂ deviations from proposed ideality are correlated with the signs and magnitudes of the standard free energy changes for the exchange reactions. The conclusions as to the dependency of solution mechanism of fluorides in their alkali silicates on M₂O/ SiO₂ ratio are in agreement with conclusions drawn from studies of infrared absorption in these systems.     

Nitrogen solubility in CaO-CaF2-SiO2 melts

The preceding paper^[5] demonstrated that nitrogen dissolves in silicate melts either as a free ion or complex anion, being incorporated into silicate networks. In the present study, the influence of CaF₂ addition to CaO-SiO₂ melts on the nitrogen solubility was investigated along the liquidus at 1573 K and within the liquidus at 1723 K at constant CaF₂ levels. In the latter case, as the SiO₂ content increases from CaO saturation, the total nitrogen content decreases to reach the minimum and then starts to increase up to the SiO₂ saturation. This is in accord with the abovementioned mechanism of nitrogen dissolution, which is supported by the changing behavior of free and incorporated nitrogen contents with the slag composition. The role of CaF₂ is complicated through the formation of fluorosilicates. The CaF₂ seems not to function simply as a diluent but to enhance the dissolution of nitrogen by releasing oxygen from silicate networks, promoting the formation of free nitride ions. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

Effects of Transition Metal Oxides on Thermal Conductivity of Mould Fluxes

The thermal conductivity of the mould fluxes containing transition metal oxides was measured by hotline method at different temperatures. The relationship between the thermal conductivity of mold fluxes and the contents of transition metal oxides was discussed. The synthetic slags were composed of 30.0% — 35.4% CaO, 34.7% — 38.6% SiO₂, 6% Al₂O₃, 9% Na₂O, 14.4% CaF₂, 0–4% Cr₂O₃ and 0–8% MnO in mass percent. The results indicated that Cr₂O₃ and MnO had a negative effect on thermal conductivity of mold fluxes. The thermal conductivity of mold fluxes was about 0.25 — 0.55 W/(m K) when the temperature reached 1300 °C, and it increased sharply to about 1.32–1.99 W/(m K) when the temperature reduced from 1300 to 1000 °C. The thermal conductivity of mold fluxes containing Cr₂O₃ and MnO was 10%—25% lower than those of original fluxes. The decrease in thermal conductivity was attributed to the change of molecular structure of mold fluxes. In addition, the poor integrity and regulation of polycrystal structure, complexity of crystal structure, and effects of impurities in the boundary and lattice distortion leaded to the reduction in the thermal conductivity. Na₂CrO₄, Mn₂SiO₄ and other minor phases were also found in the samples containing Cr₂O₃ and MnO, respectively.     

Nitrogen solubility in CaO-SiO2, CaO-MgO-SiO2, and BaO-MgO-SiO2 melts

Nitrogen solubility in molten CaO-SiO₂, CaO-MgO-SiO₂, and BaO-MgO-SiO₂ silicate systems was measured as functions of nitrogen and oxygen partial pressures and composition at 1823 K. Experimental findings indicate that nitrogen exists as a free nitride ion or is associated with silicate networks, depending principally on the slag composition. A special analytical technique was developed to separately determine the two species. Its dissolution mechanism, which is similar to that for hydrogen, was proposed, being supported by the detection of a Si-N bond by infrared spectroscopy. Neither the content of free nor incorporated nitrogen was demonstrated to have a very good correlation with the CaO or SiO₂ activity in the melts, probably because the activity coefficient of nitrogen is affected by the slag composition. Formerly Graduate Student, Department of Metallurgy, The University of Tokyo.     

A Chemical Approach of the Molecular Entity Vacancy Model to the CaO‐Al2O3‐SiO2 Ternary Silicate Melt

A chemical approach of the molecular entity vacancy model (MEVM) to the CaO‐Al₂O₃‐SiO₂ ternary silicate melts has been suggested. The activities of all components in the melts were simultaneously predicted by using only the binary parameters of its sub‐binary melts which were determined by fitting the activities of their two components. The results indicated that the predicted values of activity of SiO₂ were in good agreement with the experimental data at both temperatures 1823 K and 1873 K, and those of CaO and Al₂O₃ were in reasonable agreement with the experimental data at 1823 K and were smaller than the graphical integration data of the Gibbs‐Duhem equation at 1873 K. The approach may be extended to some solution systems with the chemical interaction.     

Stability of complex molybdenum(III) ions in molten alkali metal chlorides

High-temperature absorption spectroscopy is used to study the effect of temperature in the range 550?C750°C and the cation composition of a solvent salt on the spectroscopic characteristics and stability of MoCl ₆ ^3? complex ions in melts based on alkali metal chlorides (LiCl; CsCl; LiCl-KCl, NaCl-CsCl, KCl-CsCl, and NaCl-KCl-CsCl eutectic mixtures; and equimolar NaCl-KCl mixture).     

Measurement and Analysis of Thermal Conductivity of Rocks in the Tarim Basin,Northwest China

As a parameter that describes heat transmission properties of rocks, thermal conductivity is indispensable for studying the thermal regime of sedimentary basins, and retrieving high-quality data of thermal conductivity is the basis for geothermal related studies. The optical scanning method is used here to measure the thermal conductivity of 745 drill-core samples from the Tarim basin, the largest intermontane basin with abundant hydrocarbon potential in China, and water saturation correction is made for clastic rock samples that are of variable porosity. All the measured values, combined with previously published data in this area, are integrated to discuss the distribution characteristics and major controlling factors that affect the thermal conductivity of rocks in the basin. Our results show that the values of thermal conductivity of rocks generally range from 1.500 to 3.000 W/m·K with a mean of 2.304 W/m·K. Thermal conductivity differs considerably between lithological types: the value of a coal sample is found to be the lowest as being only 0.249 W/m·K, while the values for salt rock samples are the highest with a mean of 4.620 W/m·K. Additionally, it is also found that the thermal conductivity of the same or similar lithologic types shows considerable differences, suggesting that thermal conductivity cannot be used for distinguishing the rock types. The thermal conductivity values of mudstone and sandstone generally increase with increasing burial depth and geological age of the formation, reflecting the effect of porosity of rocks on thermal conductivity. In general, the mineral composition, fabric and porosity of rocks are the main factors that affect the thermal conductivity. The research also reveals that the obvious contrast in thermal conductivity of coal and salt rock with ther common sedimentary rocks can induce subsurface temperature anomalies in the overlying and underlying formations, which can modify the thermal evolution and maturity of the source rocks concerned. This rinding is very important for oil and gas resources assessment and exploration and needs further study in detail. The results reported here are representative of the latest and most complete dataset of thermal conductivity of rocks in the Tarim basin, and will provide a solid foundation for geothermal studies in future.     

Thermodynamic properties of indium oxide

Abstract

Equilibrium decomposition pressures of oxygen were established at a variety of temperatures over small lumps of In₂O₃, by continuous analysis of a hydrogen carrier gas stream for water vapour. The analysis was done by utilizing the variation of thermal conductivity of gas with changes in composition. The steady-state partial pressures developed in the carrier gas were independent of flow rate from 20 to 160 cc/min, and they agree with the equilibrium values established in previous experimental work. The equation

?G_T^o = 219,000 ? 8.648T log T ? 51.065T (± 2kcal)

is suggested for calculating the free energy of the following reaction over the temperature range 430 to 850°K:

In₂O_3(s) ? 2In_(l) + 3/2 O_2(g)

Résumé

Les pressions d'oxygène, de décomposition à l'équilibre de petits morceaux de In₂O₃, ont été établies à diverses températures, en analysant en continue la vapeur d'eau d'un gaz éluant d'hydrogène. L'analyse a été faite en se basant sur la variation de la conductivité thermique du mélange gazeux en foncdon de sa composition. Les pressions partielles, développées dans le gaz entraineur, en régime permanent, étaient indépendantes du débit, dans la gamme de 20 à 160 cc/min; elles concordent avec les valeurs d' équilibre établies lors de travaux antérieurs. L'équation

?G_T^o = 219,000 ? 8.648T log T ? 51.065T (± 2kcal)

est proposée pour calculer l'enthalpie libre de la réaction suivante, sur l'intervalle de température de 430 à 850°K:

In₂O_3(s) ? 2In_(l) + 3/2 O_2(g) .     

Delamination of Sensitized Al-Mg Alloy During Fatigue Crack Growth in Room Temperature Air

Fatigue crack growth experiments in air at 295?K (22?°C) were conducted on 6.35?mm thick plate samples of a commercial Al-Mg alloy machined from the L-T orientation. Thermal exposures for times up to 2000?hours at 343?K, 353?K, 373?K, and 448?K (70?°C, 80?°C, 100?°C, and 175?°C) produced sensitization and delamination in the S-T plane during fatigue testing, dependent on the level of thermal exposure and K _max employed. Identical tests conducted in a ??dry?? environment produced no delamination, indicating that environment may enhance the phenomena.     

The free energies of mixing of melts in the systems 2FeO-SiO2-2MnO-SiO2 and 2.33FeO-TiO2-2.33MnOTiO2

The free energies of mixing in melts in the system 2FeO · SiO₂-2MnO · SiO₂ at 1450°C and the system 2.33FeO · TiO₂-2.33MnO · TiO₂ at 1475°C have been obtained from measurement of the equilibrium Mn + FeO = Fe + MnO established between the melts and ironmanganese foils. Both systems exhibit ideal silicate mixing. The phase diagram for the system 2FeO-SiO₂-2MnO ·SiO₂ is calculated.     

Measurement of the surface tensions of Fe-saturated iron silicate and Fe-saturated calcium ferrite melts by Padday’s cone technique

Padday’s cone technique allows determination of the surface tension of a liquid from measurement of the maximum excess force exerted on a cone during its immersion in, or withdrawal from, the liquid and knowledge of the density of the liquid. As the technique does not require rupture of the meniscus, an equilibrium measurement is obtained. The surface tensions of Fe-saturated iron silicate melts and Fe-saturated calcium ferrites, measured at 1410 °C using iron cones, are in good agreement with values in the literature obtained using the hollow cylinder technique. The maximum excess forces exerted on Pt-Rh cones immersed in liquid iron oxides at 1460 °C in the composition range from saturation with iron toX _Fe2_O3 = 0.205 have been measured. The surface tensions of these melts cannot be determined unambiguously from the experimental measurements because of an uncertainty in the densities of the melts. However, it is shown that the literature values for the surface tension of liquid iron oxide are incorrect because of an error in the experimental procedures used.     

Synthesis of Al-Zr Alloys <Emphasis Type="Italic">Via</Emphasis> ZrO<Subscript>2</Subscript> Aluminum-Thermal Reduction in KF-AlF<Subscript>3</Subscript>-Based Melts

Physical–chemical investigations of KF-AlF₃ melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF₃ and KF-NaF-AlF₃ melts with additions of Al₂O₃ and ZrO₂ were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO₂ in KF-AlF₃ and KF-NaF-AlF₃ melts on Al₂O₃ concentration was measured.