Geometrical Construction of Auxiliary Axes in an Ellingham Diagram

To facilitate the assessment of the oxide stability in H2-H2O or CO-CO2 atmospheres, auxiliary axes are constructed in the Ellingham diagram. Based on A. Ghosh’s approach, the geometrical interpretation of the diagram is proposed for the reaction 2X + O2 = 2Y, where X and Y could be originated from H2 and H2O or CO and CO2. Two cases are considered when oxygen partial pressures are lower and higher than one bar. By a geometrical method, it is proved that with an appropriate set-up of values relating to the auxiliary axes, the axes representing the ratio between the equilibrium partial pressure of hydrogen and that of water vapour, as well as the ratio between the equilibrium partial pressure of carbon monoxide and that of carbon dioxide, can be constructed. The geometrical method on the construction of axes using thermodynamic derivation is explained in the paper.

Nonisothermal desorption at nucleate boiling in a layer of aqueous salt solution

This paper presents the results of experimental studies of nonisothermal desorption at nucleate boiling of layers of aqueous salt solutions of LiBr and CaCl2. The height of the layers is 2.8 mm. The wall temperature is 120 °C. The drop in the temperature of the interfacial surface (Ts) for salt solutions and distillate is associated with low thermal conductivity of the metal wall (titanium) and intense heat flow at nucleate boiling. A heat balance for a free liquid interface has been worked out. In 75 seconds after the beginning of evaporation, the heat flux for aqueous becomes quasi-permanent, and for aqueous salt solutions of CaCl2 and LiBr, the heat flux continuously decreases with time. This is due to the increase in the salt concentration in the solution and the drop in the equilibrium partial pressure of the vapor.

Evaporation of layers of salt solutions

Nonisothermal evaporation of layers of water and aqueous salts solutions of H2O/LiBr, H2O/CaCl2 and H2O/LiCl was studied experimentally. The liquid layer was placed on a horizontal heated wall. The initial concentration of salt C0 was 10 %. The wall temperature Tw = 75 °C and ambient air pressure was 1 bar. It was shown that the heat flux q increases for water for the final evaporation stage and falls for salt solutions due to the increase in salt concentration C and due to a significant drop in the equilibrium partial pressure of water vapor.

Thermochemistry of MgCr2O4, MgAl2O4, MgFe2O4 spinels in SO2−O2−SO3 atmosphere

The present paper investigates high-temperature sulphate corrosion of basic refractory ceramics containing magnesium spinels (MgAl2O4, MgFe2O4, MgCr2O4 and their solid solutions) widely used in metallurgy, chemical, ceramic and glass industry. This group of refractories are exposed to a number of destructive factors during a working campaign. One of such factors is gas corrosion caused by sulphur oxides. However, gas sulphate corrosion of basic refractory materials containing magnesium spinels, which has a great practical meaning for the corrosion resistance of the material main components, is not sufficiently examined. This work presents a thermodynamic analysis of (MgCr2O4, MgAl2O4, MgFe2O4)?SO2?O2?SO3 system aimed to calculate: i) the standard free enthalpy of chemical reactions, ii) the equilibrium composition of the gas mixture initially containing SO2 and O2 and iii) sulphates equilibrium dissociation pressure and equilibrium partial pressure for the reaction of SO3 with the spinels to predict the temperature range of corrosion products? stability. A thermochemical calculation provides information about equilibrium state in the analysed system. In real conditions the state of equilibrium does not have to be achieved. For this reason, the results of calculations were compared with experimental data. The experiment results were consistent with the theoretical predictions.

Low-Temperature Synthesis and Thermodynamic and Electrical Properties of Barium Titanate Nanorods

Studies regarding the morphology dependence of the perovskite-type oxides functional materials properties are of recent interest. With this aim, nanorods (NRs) and nanocubes (NCs) of barium titanate (BaTiO3) have been successfully synthesized via a hydrothermal route at temperature as low as 408 K, employing barium acetate, titanium isopropoxide, and sodium hydroxide as reagents without any surfactant or template. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD), used for the morphology and structure analyses, showed that the NRs were formed by an oriented attachment of the NCs building-blocks with 20 nm average crystallites size. The thermodynamic properties represented by the relative partial molar free energies, enthalpies, and entropies of the oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressure of oxygen, indicated that NRs powders have lower oxygen vacancies concentration than the NCs. This NRs characteristic, together with higher tetragonallity of the structure, leads to the enhancement of the dielectric properties of BaTiO3ceramics. The results presented in this work show indubitably the importance of the nanopowders morphology on the material properties.

Solubility of Bismuth in Liquid Bi-S Based Free Cutting Steel

Solubility of bismuth in liquid Bi-S based free cutting steel was measured using a vapor-liquid equilibration method at 1540–1600 °C, and the recovery rate of bismuth in the steel with different temperatures under an atmospheric pressure was also measured. The results showed that the solubility of bismuth in liquid Bi-S based free cutting steel from experiment under a constant volume at 1540, 1560, 1580, and 1600 °C were 0.174, 0.181, 0.205, and 0.220 mass%, respectively, and the relationship of bismuth solubility vs. temperature could be expressed as lg[%Bi] = −6049/T + 2.572. Meanwhile, the solubility of bismuth increased with the increase of Mn content, but decreased with the increase of C content. The recovery of bismuth in this experiment reached a maximum when the temperature was at bismuth boiling point or so, and then it was decreased with the increase of temperature when the temperature was above 1560 °C, which might be attributed to the accelerating of bismuth evaporation that were caused by the increase of bismuth equilibrium partial pressure above the surface of the molten steel with increasing temperature.

Comparison of Thermodynamic Databases for the Modeling of SiC Growth by PVT

The numerical modeling of the SiC bulk growth process by physical vapor transport has been established as the essential tool for the process development, especially for understanding and predicting the favorable growth conditions. An accurate computation of mass transfers is strongly dependent on the equilibrium partial pressure calculations. In this paper, we compare the relative impact of the different thermodynamic databases available on the full PVT process modeling. We found that whatever the database used, the trends regarding growth rate calculation, crystal shape, Si/C ratio are correctly described and none of the database would bring about unacceptable errors from the process development point of view even if some discrepancies in the absolute values could be obtained.