Electrochemical studies of Na2CrO4-Na2So4 melts at 1200 K

The electrochemical response of Na₂SO₄-Na₂CrO₄ solutions at a Pt working electrode was established by cyclic voltammetry and chrono-potentiometry measurements at 1200 K. Experiments were made under conditions of controlled and electrochemically measured values of melt basicity for basic, neutral, and acidic melts. Despite the thermodynamic stability of chromite ions under reducing conditions, a direct conversion of chromate to chromite upon cathodic polarization was not observed. Rather, the cathodic reduction of chromate ions proceeds by a reversible one-electron charge transfer to an electroactive intermediate species formed through an equilibrium between CrO and oxide ions in the solution. An irreversible chemical reaction reduces the chromium solute species further to precipitate a solid. As a solute in a corrosive fused salt film, a chromate to chromite transition would not be expected to stabilize the oxidation state and basicity. However, chromate ions to provide a reduction reaction more favorable than sulfate reduction to sulfide; chromate reduction leads to the precipitation of solid NaCrO₂ or Cr₂O₃ in basic or neutral solutions, respectively. A large shift in melt basicity can only occur for mildly acidic solutions with high chromate solute.     

聚丙烯材料在硫酸钾装置中的应用

本文介绍了聚丙烯材料的性能、特点,利用其特点将聚丙烯材料用于管道或衬里管道,以输送腐蚀和磨蚀介质,结合使用条件分析了在使用温度下的腐蚀、磨蚀、强度使用寿命等问题。     

Thermodynamic assessment of the Li-Si system

The Li-Si binary system was thermodynamically assessed using experimental phase diagram and thermodynamic data. Due to inconsistencies in the experimental data, two optimizations were performed. In both cases, the obtained sets of parameters are different and are discussed. Supported by Portuguese JNICT-PRAXIS XXI program.     

Thermodynamic assessment of the copper-oxygen system

The Cu-O system shows complete miscibility between the metallic liquid and the oxide liquid above ∼1623 K and a miscibility gap below that temperature. Because of the practical importance of the system, a wealth of experimental data exists, both on the phase diagram and on the thermodynamic properties. These data have been reviewed, and a consistent set of thermodynamic model parameters has been optimized. An ionic two-sublattice model was used to describe the liquid phase and was found to represent accurately the experimental data.     

Thermodynamic assessment of the Fe-Zn system

The Fe-Zn binary system is assessed thermodynamically. A two-sublattice model is adopted to describe the intermetallic compounds, which are treated as nonstoichiometric. A set of parameters consistent with most of the available experimental data on both phase diagram and activities measurements is obtained through optimization. A comparison with previous work is also presented.     

Thermodynamic assessment of the Mo-Zr system

The Mo-Zr system was critically assessed using the calculation of phase diagrams (CALPHAD) technique. The solution phases (liquid, bcc, and cph) were modeled with the Redlich-Kister expression for the excess Gibbs energy. The intermetallic Mo₂Zr Laves phase, which has a measurable homogeneity range, was treated by a two-sublattice model with Mo and Zr on both sublattices. A set of self-consistent thermodynamic parameters for the Mo-Zr system was obtained. With the optimized functions for the Gibbs energy of the individual phases, most of the experimental information can be well reproduced.     

Thermodynamic assessment of the Ni-Ga system

Phase diagram and thermodynamic properties of the Ni-Ga system are assessed based on the CALPHAD approach, using all available experimental data and applying appropriate thermodynamic models. The liquid phase and the Ni-based solid solution (Ni) are treated as disordered solutions. The thermodynamic behavior of the ordered intermetallic compounds with appreciable ranges of homogeneity, Ni₃Ga and NiGa, are described by a two-sublattice model, and the order-disorder transformation between Ni₃Ga and fcc-(Ni) is also explicitly considered in this work. The other five intermetallic compounds are treated as stoichiometric line compounds. The phase diagram and the thermodynamic properties calculated from the optimized model parameters are in good agreement with most of the experimental data.     

Thermodynamic assessment of the Hg-Sn system

A thermodynamic assessment of the Hg-Sn system has been carried out using the CALPHAD method. The comprehensive assessment covers the extensive phase diagram data as well as the enthalpy, activity, and vapor pressure data. Two cases of intermetallic compounds in the Hg-Sn system are considered. Case 1 considers the intermetallic compounds β, γ, and HgSn₄ as having no solubility and can thus be treated as the stoichiometric phases β-HgSn₃₈, γ-HgSn₁₂, and HgSn₄. Case 2 uses a sublattice model to more accurately describe a solubility of the γ phase; it also considers the stoichiometric δ-HgSn₇ phase. The ε phase was considered to be metastable and neglected in the thermodynamic assessment. Thermodynamic parameters have been optimized using all the assessed experimental thermodynamic and phase equilibrium data. Both calculated phase diagrams of the Hg-Sn system (Cases 1 and 2) and the thermodynamic data are reasonable and satisfactory when compared with literature data. Future crucial experiments are suggested.     

Thermodynamic assessment of the Co-O system

The thermodynamic properties of CoO, Co₃O₄, and the liquid phase were assessed, and an optimized set of parameters of Gibbs energy functions is proposed. The two stable solid oxides, CoO and Co₃O₄, were both treated as stoichimetric compounds. The paramagneticantiferromagnetic transition of CoO is well represented by a magnetic ordering model. The Co₃O₄ spinel phase was described as a normal spinel at room temperature and with cation redistribution at high temperatures. A high-temperature anomaly of Co₃O₄ was interpreted as a normal-inverse spinel transition. An ionic two-sublattice model was used to model the liquid phase. A calculated phase diagram is presented, and values for the thermodynamic properties are compared with experimental data.     

Thermodynamic assessment of the Ni-Zn system

The Ni-Zn binary phase diagram has been evaluated using the CALPHAD method. In this analysis, the intermetallic β, β₁, and γ phases are described using the sublattice model. The δ (Ni₂Zn₁₅) phase is treated as a stoichiometric compound because of its narrow solution range. The parameters used for the model were derived from an optimization procedure using the available experimental data in the literature.     

Thermodynamic assessment of the Ni-Zn system

The Ni-Zn binary phase diagram has been evaluated using the CALPHAD method. In this analysis, the intermetallic β, β₁, and γ phases are described using the sublattice model. The δ (Ni₂Zn₁₅) phase is treated as a stoichiometric compound because of its narrow solution range. The parameters used for the model were derived from an optimization procedure using the available experimental data in the literature.     

Thermodynamic assessment of the Co-O system

The thermodynamic properties of CoO, Co₃O₄, and the liquid phase were assessed, and an optimized set of parameters of Gibbs energy functions is proposed. The two stable solid oxides, CoO and Co₃O₄, were both treated as stoichimetric compounds. The paramagneticantiferromagnetic transition of CoO is well represented by a magnetic ordering model. The Co₃O₄ spinel phase was described as a normal spinel at room temperature and with cation redistribution at high temperatures. A high-temperature anomaly of Co₃O₄ was interpreted as a normal-inverse spinel transition. An ionic two-sublattice model was used to model the liquid phase. A calculated phase diagram is presented, and values for the thermodynamic properties are compared with experimental data.     

Thermodynamic assessment of the Hg-Sn system

A thermodynamic assessment of the Hg-Sn system has been carried out using the CALPHAD method. The comprehensive assessment covers the extensive phase diagram data as well as the enthalpy, activity, and vapor pressure data. Two cases of intermetallic compounds in the Hg-Sn system are considered. Case 1 considers the intermetallic compounds β, γ, and HgSn₄ as having no solubility and can thus be treated as the stoichiometric phases β-HgSn₃₈, γ-HgSn₁₂, and HgSn₄. Case 2 uses a sublattice model to more accurately describe a solubility of the γ phase; it also considers the stoichiometric δ-HgSn₇ phase. The ε phase was considered to be metastable and neglected in the thermodynamic assessment. Thermodynamic parameters have been optimized using all the assessed experimental thermodynamic and phase equilibrium data. Both calculated phase diagrams of the Hg-Sn system (Cases 1 and 2) and the thermodynamic data are reasonable and satisfactory when compared with literature data. Future crucial experiments are suggested.