Evgueni Jak

Experimental study and thermodynamic modeling of the phase equilibria in the FeO–FeO _1.5 –SbO _1.5 –SbO _2.5 –SiO ₂ system in air and 1 atm oxygen, and in equilibrium with Sb/Sb–Ag metal has been undertaken. Experimental data at 575°C–1600°C were obtained using high‐temperature equilibration of mixtures in sealed silica ampoules, Fe ₃ O ₄ basket/MgO crucible in sealed silica ampoule, or Re/Pt–Ir foils, followed by quenching, and electron probe X‐ray microanalysis of the phases. The primary phase fields of quartz/tridymite/cristobalite (SiO ₂ ), two high‐SiO ₂ immiscible liquids, olivine (Fe ₂ SiO ₄ ), wustite (FeO _{1+ x} ), spinel (Fe ₃ O ₄ ), schafarzikite (FeSb ₂ O ₄ ) and valentinite/senarmontite (Sb ₂ O ₃ ) were identified in the binary “FeO”–“Sb ₂ O ₃ ”, “Sb ₂ O ₃ ”–SiO ₂ and ternary “FeO”–“Sb ₂ O ₃ ”–SiO ₂ systems in equilibrium with Sb metal, as well as in more oxidizing conditions in equilibrium with Sb–Ag metal. The primary phase fields of tridymite/cristobalite (SiO ₂ ), two high‐SiO ₂ immiscible liquids, hematite (Fe ₂ O ₃ –Sb ₂ O ₅ ), spinel (Fe ₃ O ₄ ), tripuhyite (FeSbO ₄ ) and cervantite (SbO ₂ = Sb ₂ O ₄ ) were studied in air and at 1 atm O ₂ . All data were described with a thermodynamic model in attempt to incorporate minor Sb ₂ O ₅ contributions to liquid slag. According to present evaluation, Sb ₂ O ₅ concentrations in liquid slag are lower than those of Sb ₂ O ₃ even in the most oxidizing conditions studied (at 1 atm O ₂ ), although pentavalent antimony dominates in many stable solid oxide compounds (such as FeSbO ₄ ). These findings are essential to understand for evaluating the behavior of antimony impurities in fast‐quenched or slowly cooled fayalite slags in copper, lead smelting, or mixed recycling streams.

Integrated experimental and thermodynamic modeling study of the phase equilibria in the Na ₂ O–SnO–SnO ₂ –SiO ₂ system in air and in equilibrium with liquid metal has been undertaken for characterizing the thermochemistry of slag in smelting side streams enriched in Sn and optimizing the fuming process. New experimental phase equilibria data at 800°C–1635°C in air, and 610°C–1300°C in equilibrium with liquid metal were obtained using high‐temperature equilibration of synthetic mixtures with predetermined compositions in sealed silica ampoules or Re / Pt‐Ir foils, rapid quenching, and electron probe X‐ray microanalysis of the equilibrated phase compositions. Phase equilibria and liquidus isotherms in the quartz/tridymite (SiO ₂ ), cassiterite (SnO ₂ ), sodium silicates (Na ₂ Si ₂ O ₅ , Na ₂ SiO ₃ ), sodium stannates (Na ₂ SnO _3, Na ₄ Sn ₃ O ₈ ) and sodium tin silicates (Na ₈ SnSi ₆ O ₁₈ , and three new phases Na ₄ SnSi ₂ O ₈ , Na ₄ Sn ₂ Si ₃ O ₁₂ , Na ₂ Sn ₂ Si ₂ O ₇ ) primary phase fields in the NaO _0.5 –“SnO ₂ ”–SiO ₂ and NaO _0.5 –“SnO”–SiO ₂ systems were revealed. New experimental data were used to develop a thermodynamic database describing the Na ₂ O–SnO–SnO ₂ –SiO ₂ system.

Iron‐bearing silicate systems are fundamental components of oxide melts, glasses, and ceramic materials, where multivalent iron strongly influences structure, thermodynamic properties, and redox behavior. Accurate determination of iron oxidation state remains a central challenge in studies of high‐temperature silicate systems because ferric to ferrous ratio control oxygen activity, defect chemistry, and phase equilibria. In this study, a quantitative approach for estimating the Fe ³⁺ /(Fe ³⁺ + Fe ²⁺ ) ratio is presented based on direct measurement of oxygen concentration in oxide system by electron probe microanalysis (EPMA). Two sets of samples in the Cu─Si─Fe─O system were synthesized using equilibration and quenching techniques, producing phase assemblages involving slag/copper/tridymite or slag/copper/magnetite (or wüstite) phases. Equilibration experiments were conducted at 1250°C and 1300°C, over oxygen partial pressures ranging from 10 ⁻⁹ to 10 ^−6.5 atm, followed by rapid quenching of the samples to preserve high‐temperature equilibrium states. Elemental phase compositions, including metal cations and oxygen, were analyzed by EPMA. The measured oxygen concentrations were used to calculate valence states of metal cations (Cu ⁺ , Si ⁴⁺ , Fe ²⁺ , and Fe ³⁺ , respectively), enabling direct determination of the ferric to ferrous ratio in the samples. The experimental results have been compared with calculated and literature data, demonstrating that accurate oxygen quantification by EPMA provides a reliable approach for oxidation state determination in complex oxide systems. Beyond metallurgical slags, the proposed methodology is applicable to silicate melts, glasses, and ceramic materials, where multivalent cations control structure, defect chemistry, and thermodynamic behavior, offering a robust experimental tool for studies redox‐dependent properties in high‐temperature oxide materials.

Experimental study and thermodynamic modelling of the phase equilibria in the FeO-FeO1.5-SbO1.5-SbO2.5-SiO2 system in air and 1 atm oxygen, and in equilibrium with liquid Sb or Sb-Ag metal has been undertaken. New experimental phase equilibria data at 575-1600°C were obtained for this system using high-temperature equilibration of synthetic mixtures with predetermined compositions in sealed silica ampoules, Fe3O4 basket/MgO crucible in sealed silica ampoule, Re or Pt-Ir foils, followed by a rapid quenching technique, and electron probe X-ray microanalysis of the equilibrated phase compositions. The primary phase fields of quartz/tridymite/cristobalite (SiO2), two high-SiO2 immiscible liquids, olivine (Fe2SiO4), wustite (FeO1+x), spinel (Fe3O4), schafarzikite (FeSb2O4) and valentinite/senarmontite (Sb2O3) were identified in the binary “FeO”-Sb2O3, Sb2O3-SiO2 and ternary “FeO”-Sb2O3-SiO2 systems in equilibrium with Sb metal, as well as in more oxidizing conditions in equilibrium with Sb-Ag metal. The primary phase fields of quartz/tridymite/cristobalite (SiO2), two high-SiO2 immiscible liquids, hematite (Fe2O3-Sb2O5), spinel (Fe3O4), tripuhyite (FeSbO4) and cervantite (SbO2 = Sb2O4) were studied in air and at 1 atm O2. All data were described with a thermodynamic model in attempt to incorporate minor Sb2O5 contributions to liquid slag.