Experimental investigation and thermochemical assessment on the SnO2-CuO system

Differential thermal analysis/theromgravimetry (DTA/TG) measurements performed in air have established that above 1273 K the SnO₂-CuO initially stochiometric system transforms into a system of the SnO₂-CuO_x type, with the value of x depending on temperature T and p _{O 2} oxygen partial pressure values. The dissociation process of CuO to Cu₂O, as well as the formation of a liquid phase with an uptake of oxygen, has been experimentally verified. Above the minimum value of the oxygen partial pressure for which the only components of the system are SnO₂ and CuO (i. e., over p_{O 2} = 24 atm), the phase diagram was calculated by modeling the behavior of the liquid phase with a sub-regular approximation. A homogeneous liquid phase with no tendency toward immiscibility was found to be energetically favorable over the entire compositional range of the SnO₂-CuO system for T ≥ 1470 K. As a result of the calculations, the phase diagram is given for p_{O 2} = 24 atm; the diagram is a simple eutectic type with the eutectic composition placed in the CuO-rich domain (i.e., copper oxide molar fraction x = 0.873 and melting at 1470 K). The phase diagram calculated for the SnO₂-CuO system is compared with the data reported for other CuO-based systems.     

Equilibrium phase relationships in the system Cu-O under high oxygen pressure

The equilibrium phase relationships near the liquidus line of the system Cu₂O-CuO-O₂ (a part of wider system Cu-O) were determined under pure oxygen pressure from 0.001 to 11 MPa by three experimental methods: differential thermal analysis (DTA), thermogravimetry (TG), and thermobarometry (TB). The coordinates of the eutectic point between solid Cu₂O and CuO were found to be P _{O 2}=0.069±0.001 MPa and T=1364±1 K. It was proved experimentally that, at least at temperatures up to 1526 K and oxygen pressures up to 11 MPa, CuO melts incongruently with liberation of gaseous oxygen and with the temperature dependence of P _{O 2} obeying an Arrheniustype equation. The conditions for congruent melting of CuO were analyzed using the model, and it was found that congruent melting of CuO should occur at ≈ 1620 K under oxygen pressure ∼1000 MPa.     

Equilibrium phase relationships in the system Cu-O under high oxygen pressure

The equilibrium phase relationships near the liquidus line of the system Cu₂O-CuO-O₂ (a part of wider system Cu-O) were determined under pure oxygen pressure from 0.001 to 11 MPa by three experimental methods: differential thermal analysis (DTA), thermogravimetry (TG), and thermobarometry (TB). The coordinates of the eutectic point between solid Cu₂O and CuO were found to be P _{O 2}=0.069±0.001 MPa and T=1364±1 K. It was proved experimentally that, at least at temperatures up to 1526 K and oxygen pressures up to 11 MPa, CuO melts incongruently with liberation of gaseous oxygen and with the temperature dependence of P _{O 2} obeying an Arrheniustype equation. The conditions for congruent melting of CuO were analyzed using the model, and it was found that congruent melting of CuO should occur at ≈ 1620 K under oxygen pressure ∼1000 MPa.     

Thermodynamic analysis of aluminate stability in the eutectic bonding of copper with alumina

The interfacial reactions between Cu and Al₂O₃ which occur during the eutectic bonding process have been examined. A thermodynamic analysis of phase equilibria in the Cu–Al–O system shows that a five-phase equilibrium exists among solid copper with oxygen in solution, liquid copper with oxygen in solution, solid CaAlO₂, Al₂O₃ and oxygen gas at the invariant state T=1348 K, p_O2=5.6×10⁻⁷ atm (0.055 Pa). The existence of this invariant state has been confirmed experimentally by heating slightly oxidized copper disks placed in contact with alumina disks. The experimentally determined invariant state was found to be in good agreement with that calculated. During eutectic bonding the compound CuAlO₂ forms at the interface between copper and the alumina in specimens containing solid copper only at temperatures lower than 1348±3 K.     

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> System

Phase equilibria and thermodynamic data in the FeO-Fe₂O₃-SiO₂ system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O₂. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.     

Up-Date of a Thermodynamic Database of the ZrO<Subscript>2</Subscript>-Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System for TBC Applications

The thermodynamic database of the ZrO₂-Gd₂O₃-Y₂O₃-Al₂O₃ system is up-dated taking into account new data on lattice stabilities of ZrO₂, Gd₂O₃ and Y₂O₃ and heat capacity measurements for the monoclinic phase Gd₄Al₂O₉ and phase with garnet structure Gd₃Al₅O₁₂. New data for the heat capacities of Gd₂Zr₂O₇ (pyrochlore) and GdAlO₃ (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr_1−x Gd _x )O_2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd₄Al₂O₉ phase from a peritectic one to a congruent one in the Gd₂O₃-Al₂O₃ system. Correspondently, in the ternary system ZrO₂-Gd₂O₃-Al₂O₃, the melting character of the three-phase assemblage Gd₂O₃ (B), Gd₄Al₂O₉ and GdAlO₃ changed from eutectic to transition type U. The T ₀-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO₂-Gd₂O₃-Y₂O₃ system.     

Phase Diagram and Thermodynamic and Transport Properties of the DyBr<Subscript>3</Subscript>-LiBr Binary System

The phase diagram of the DyBr₃-LiBr binary system was derived from DSC measurements. It exhibits two eutectics and has two stoichiometric compounds. The first compound, Li₃DyBr₆, melts congruently at 803 K. The second one, Li₆DyBr₉ decomposes in the solid state at 656 K. The composition of the two eutectic mixtures, x(DyBr₃) = 0.156 and 0.321, respectively, was determined by the Tamman method. The respective eutectic temperatures are 787 and 791 K. The electrical conductivity of Li₃DyBr₆ compound was measured in the liquid and solid phase. It was found to be a solid electrolyte with a high electrical conductivity at around room temperature. Some additional electrical conductivity measurements performed on solid samples confirmed the existence of Li₆DyBr₉.     

Subsolidus Phase Relations of the CaO-REO<Subscript>x</Subscript><Emphasis Type="Bold">-</Emphasis>CuO Systems (RE = Eu,Tb, Dy,Ho, Er,Lu and Sc) at 900 °C in Air

The subsolidus phase relations of the CaO-REO_x-CuO systems (RE = Eu, Tb, Dy, Ho, Er, Lu and Sc) were investigated in air at 900 °C. The pseudo-ternary sections with RE = Tb, Dy, Ho, Er and Lu have a similar structure. They have in common with the RE = Eu system a solid solution of Ca_0.833?xRE_xCuO_2+y composition but the system with RE = Eu differs by the presence of an Eu₂CuO₄ phase instead of RE₂Cu₂O₅ for RE = Tb, Dy, Ho, Er and Lu. In contrast, the CaO-ScO_1.5-CuO section does not contain a Ca_0.833?xSc_xCuO_2+y solid solution and is dominated by the CaSc₂O₄ phase, which has no equivalent in the other systems at 900 °C in air.     

Synthesis and electrochemical properties of SnO2-CuO nanocomposite powders

1 Introduction Since YOSHIO et al[1] announced the commercia- lization of tin oxide as negative electrodes of 1ithium-ion batteries, the tin oxide anode has attracted much attention due to its high specific capacity, which is about twice that of graphite…     

The effect of boron oxide on the crystallization behavior of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel phase during the cooling of the CaO-SiO<Subscript>2</Subscript>-10 mass.% MgO-30 mass.%Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

The microstructural characteristics of the CaO-SiO₂-B₂O₃-10 mass.% MgO-30 mass.% Al₂O₃ systems solidified during slow cooling from 1600 °C were investigated using SEM-EDS and a thermochemical computation package. The effect of boron oxide on the crystallization behavior of the spinel in the aluminosilicate system was observed because boron oxide is believed to become a potential flux to reduce the melting point of the liquid oxides. The primary crystalline phase was spinel, mainly MgAl₂O₄, irrespective of the boron content. The liquidus temperature T _L continuously decreased as the boron oxide content increased, indicating that the boron oxide decreased the activity of the MgAl₂O₄ spinel phase in liquid melts at high temperatures. The size of the spinel crystals increased as the temperature range for the solid + liquid coexisting region, viz. the mushy zone, increased. In the present systems, because the T _L continuously decreased with the increase in the boron oxide content, the viscosity of the liquid oxide may have affected the crystallization behavior of the spinel during cooling. Based on these results, an injection of a small amount of B₂O₃ flux into molten steel containing liquid aluminosilicate inclusions is not recommended because large spinel crystals can originate from the changes in the thermophysical properties of the liquid inclusions due to the incorporation of boron oxide into the aluminosilicate networks.     

Gas sensing properties of nano-crystalline SnO<Subscript>2</Subscript>-CuO compounds

We fabricated a micro gas sensor for hydrogen sulfide (H₂S) gas using MEMS technology and the sol-gel process, and synthesized SnO₂-CuO as a sensing material by the sol-gel method. Synthesized particles of SnO₂-CuO were characterized with an average particle size of about 40 nm as measured by FE-SEM imagery and XRD peaks. The sensing material was coated on the micro platform and annealed at 400 °C. The maximum gas sensitivity (R_s= R_g/R_a) was 0.005 at 300 °C for 1.0 ppm — H₂S. The gas sensitivity showed linear behavior with increasing H₂S concentration.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10⁻³ atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Subsolidus phase relations of the SrO–Ta2O5–CuO system at 900 °C in air

The subsolidus phase relations of the SrO–Ta₂O₅–CuO system were investigated in air. The samples were equilibrated at 900 °C. The ternary oxide Sr₃Ta₂CuO₉ compound is stable under these conditions. This phase presents a solid solution range, its actual composition being Sr₃Ta_2−xCu_1+xO_9+δ with 0.0 ≤ x ≤ 0.2. Up to about 5 at.% Cu can be incorporated in the Sr_3−xTa_1+xO_5.5+δ phase. Similarities with the SrO–Nb₂O₅–CuO system are discussed.     

Thermodynamic reassessment of the Cu-O phase diagram

Parts of the copper-oxygen equilibrium phase diagram were reassessed using the calculation of phase diagram technique (CALPHAD). The model parameters were optimized to yield the best fit between calculated and experimentally determined phase equilibria at elevated oxygen pressures up to 11 MPa. The Cu-O liquid phase is represented by the two-sublattice model for ionic liquids containing copper on the cation sublattice with formal valences of Cu⁺¹, Cu⁺², and Cu⁺³. The presence of Cu⁺³ ions in the liquid phase, corresponding to a formation of Cu₂O₃ species, was the key assumption of this model. Congruent melting of CuO at 1551 K under an oxygen pressure of ∼126.8 MPa is predicted, which is considerably below previous theoretical values.     

Thermodynamic optimization of the Na<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript> pseudo-binary system

The Na₂O-B₂O₃ system is thermodynamically optimized by means of the CALPHAD method. A two-sublattice ionic solution model, (Na⁺¹)_P(O⁻²,BO₃ ⁻³,B₄O₇ ⁻²,B₃O_4.5)_Q, has been used to describe the liquid phase. All the solid phases were treated as stoichiometric compounds. A set of thermodynamic parameters, which can reproduce most experimental data of both phase diagram and thermodynamic properties, was obtained. Comparisons between the calculated results and experimental data are presented.     

DSC Study of Solid-Liquid Equilibria for Energetic Binary Mixtures of Methylnitramine with 2,4-Dinitro-2,4-diazapentane and 2,4-Dinitro-2,4-diazahexane

Binary phase diagrams for two mixtures of methylnitramine (1) + 2,4-dinitro-2,4-diazapentane (2) (eutectic temperature T _E = 285.1 K, eutectic composition x ₁ = 0.565) and methylnitramine (1) + 2,4-dinitro-2,4-diazahexane (2) (eutectic temperature T _E = 280.3 K, eutectic composition x ₁ = 0.653) were studied using differential scanning calorimetries (DSC). For both systems simple eutectic behavior was observed. The eutectic compositions were also determined using Gray’s model and the fractional transformation method.     

Critical evaluation and optimization of the thermodynamic properties and phase diagrams of the CrO-Cr2O3, CrO-Cr2O3-Al2O3, and CrO-Cr2O3-CaO systems

Available thermodynamic and phase diagram data have been critically assessed for all phases in the CrO-Cr₂O₃, CrO-Cr₂O₂-Al₂O₃, and CrO-Cr₂O₂-CaO systems from 298 K to above the liquidus temperatures and for oxygen partial pressures ranging from equilibrium with metallic Cr to equilibrium with air in the case of the first two systems and toP _{O 2} = 10^?3 atm for the CrO-Cr₂O₃-CaO system. All reliable data have been simultaneously optimized to obtain one set of model equations for the Gibbs energy of the liquid slag and all solid phases as functions of composition and temperature. The modified quasichemical model was used for the slag. The models permit phase equilibria to be calculated for regions of composition, temperature, and oxygen potential where data are not available.     

Phase Equilibria in the System FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

Liquidus data are presented for mixtures in the ternary system FeO-Fe₂O₃-SiO₂ in equilibrium with a gas phase with O₂ pressures ranging from 10^?10.9 to 1 atm. Data obtained are combined with previously published data to construct lines of equal O₂ pressures and lines of equal CO₂/H₂ mixing ratios along the liquidus surface. Courses of crystallization of selected mixtures under conditions of constant total composition, constant O₂ pressures, and constant CO₂/H₂ mixing ratios are discussed.