Polythermal Sections Research Articles

Experimental investigation of the 3Tl2Se + Sb2Te3 ↔ 3Tl2Te + Sb2Se3 phase diagram

Phase equilibriums were established in the 3Tl2Se+Sb2Te3↔3Tl2Te+Sb2Se3 mutual system mainly by the X-ray powder diffraction and differential thermal analyses, with the aid of microhardness and EMF measurements applied to equilibrated alloys. According to the obtained experimental results the phase diagrams in form of the polythermal section and isothermal section at 300K as well as the projection of the liquids surface have been constructed. It was found experimentally that the system is mutually reversible and is characterized by a wide solid solubility fields along the TlSbSe2–TlSbTe2 subsystem and within the Tl2Se–Tl9SbSe6–Tl9SbTe6–Tl2Te subsystem. The homogeneity and primary crystallization fields as well as the types and coordinates of non- and monovariant equilibriums were determined. The dependencies of crystallographic parameters, microhardness and EMF values upon the composition are discussed. From the EMF measurements, the partial molar functions of thallium (ΔG¯,ΔH¯,ΔS¯) were calculated for the revealed nonstoichiometric quaternary phases.

Experimental investigation of the Ag–Bi–I ternary system and thermodynamic properties of the ternary phases

The phase equilibriums in the Ag–Bi–I ternary system and thermodynamic properties of the ternary phases were experimentally determined by using DTA and XRD techniques and EMF measurements with the Ag4RbI5 solid electrolyte. According to the obtained experimental results, the polythermal sections of the ternary phase diagram, its isothermal section at 300K as well as the projection of the liquids surface have been revised. The fields of the primary crystallization and types and coordinates of nonvariant and monovariant equilibriums were determined. The partial molar functions of silver iodide and silver in the alloys as well as the standard thermodynamic functions of formation and the standard entropies of Ag2BiI5 and AgBi2I7 were calculated based on EMF measurements.

Phase equilibria in Mg-Y-Gd-Sm alloys

Differential thermal, metallographic, and electron microprobe analyses are used to study the effect of samarium on the temperatures and character of the phase equilibria in Mg-rich Mg-Y-Gd alloys containing up to 5 wt % yttrium or gadolinium and up to 8 wt % samarium. The magnesium solid solution is found to be in equilibrium only with the Mg41Sm5 and Mg24(Y,Gd)5 phases, which belong to the binary Mg-Sm and ternary Mg-Y-Gd systems, respectively. Partial polythermal sections of the Mg-Y-Gd-Sm phase diagram are constructed for the Mg-rich region.

Phase equilibria in the Cu-Cu2S-As system

Phase equilibria in the Cu-Cu2S-Assystem have been studied by DTA and X-ray powder diffraction. Cu0.667S0.333-As, Cu0.667S0.333-Cu0.735As0.265, and Cu0.8S0.2-As polythermal sections, an isothermal section at 300 K, and the liquidus projection have been constructed. Our data differ from reported data in the extents of primary crystallization phase fields and the coordinates of some invariant equilibrium points.

Contribution to the Ti-V-Sn System

Phase equilibria in Ti-V-Sn system were reevaluated. This analysis has shown essential disagreements with the recent boundary binary systems, and contradictions between the data, even between the data of the same authors. The structure and properties of Ti-V-Sn alloys along the section Ti3Sn-V were studied in the temperature interval from crystallization down to 1450 °C by differential thermal analysis, x-ray diffraction and metallography. The obtained results allowed the construction of partial solidus and liquidus projections, and polythermal section Ti3Sn-V. The latter was plotted for the first time. Mechanical properties of as-cast samples were measured at room temperature in compression tests. Maximum ultimate strength and yield strength (up to 3800 and 1300 MPa, respectively) were observed in samples with compositions corresponding to the phase boundary (V,βTi)/(V,βTi) + (Ti1−x V x )3Sn. Maximum plasticity (more than 70%) was observed for (Ti1−x V x )3Sn intermetallic solution and its vicinity.

Phase equilibria in the Cu-Tl-Ge system

The Cu-Tl-Ge system has been studied by DTA and powder X-ray diffraction. Several polythermal sections, the isothermal section at 400 K, and the liquidus surface projection have been constructed for the phase diagram of this system. Primary phase fields and the types and coordinates of invariant and monovariant equilibria have been determined. An immiscibility region of the Cu-Tl binary subsystem considerably (up to 60 at % Ge) protrudes into the triangular diagram and crosses peritectic and eutectic curves that originate from the Cu-Ge subsystem. This gives rise to a number of four-phase monotectic equilibria in the ternary system. Crystallization ends with peritectic equilibrium and eutectic equilibria, which are all degenerate in the vicinity of thallium. Intermediate ternary phases are not formed in the system. Solubilities in the initial components and in binary phases of the Cu-Ge system do not exceed 0.5 at %.

Phase diagram of the Sb–Te–I system and thermodynamic properties of SbTeI

Abstract The Sb–Te–I system was investigated by using differential thermal analysis, X-ray diffraction analysis and electromotive force measurements with an antimony electrode. A number of polythermal sections and the projection of the liquidus surface were constructed. The fields of the primary crystallization, as well as the types and coordinates of nonand monovariant equilibriums were determined. It is shown that the quasi-binary sections SbI3–Sb2Te3, SbI3–Te, and SbI3–TeI4 triangulate the Sb–Te–I system, leading to four independent subsystems. From the electromotive force measurements, the partial molar functions of antimony as well as the standard integral thermodynamic functions of SbTeI were calculated. The latter were found to have the following values: ΔG0 f,298 = −55.77 ± 1.7 kJ · mol−1; ΔH0 f,298 = −55.72 ± 1.39 kJ · mol−1; S0 298 = 153.5 ± 2.8 J · K−1 · mol−1.

Phase diagram and thermodynamic properties of compounds of the AgI–TlI–I system

The AgI–TlI–I system was investigated by a combination of DTA and XRD methods and EMF measurements with the Ag4RbI5 solid electrolyte. A series of polythermal sections and the projection of the liquidus surface were constructed. The fields of the primary crystallization and the types and coordinates of non- and monovariant equilibriums were determined. As a result, the self-consistent phase diagram of the AgI–TlI–I was drawn. The partial molar functions (ΔG¯, ΔH¯, ΔS¯) of silver iodide and silver in the alloys as well as the standard thermodynamic functions of formation and the standard entropies of AgTl3I5, AgTl2I3, and AgTlI2 were calculated from the EMF measurements.

Phase diagram of the Tl-TlI-S system and thermodynamic properties of the compound Tl6SI4

Phase equilibria in the Tl-TlI-S composition region of the Tl-S-I system were studied by differential thermal analysis, x-ray powder diffraction, and measurements of the microhardness and the emf of concentration circuits relative to a thallium electrode. A series of polythermal sections, an isothermal section at 300 K, and a projection of the liquidus surface were constructed. Primary crystallization regions of six phases, including the ternary compounds Tl6SI4 and Tl3SI, were outlined, and the types and coordinates of non- and monovariant equilibria were determined. It was shown that the ternary compound Tl6SI4 forms tie lines with Tl, TlI, Tl2S, Tl4S3, and TlS in the subsolidus region and that the homogeneity region of Tl6SI4 below 400 K does not exceed 1 mol %. From the emf measurement data, the standard thermodynamic functions of formation and standard entropy of the compound Tl6SI4 were calculated: G ,298 0 = −601.7 ± 2.5 kJ/mol, ΔH ,298 0 = −595.1 ± 4.0 kJ/mol, and S 298 0 = 672 ± 10 J/(mol K).

Phase equilibria in the Tl2Te-SnTe-Bi2Te3 system

phase equilibria in the Tl2Te-SnTe-Bi2Te3 system were studied by differential thermal analysis (DTA), X-ray powder diffraction, and microhardness measurements. Some polythermal sections and isothermal (at 600 and 800 K) sections of the phase diagram and a projection of the liquidus surface were constructed. It was shown that the system is characterized by the formation of solid solutions with the Tl5Te3 structure (δ) and solid solutions based on SnTe (γ1), Tl2Te (α), Bi2Te3 (β), and two TlBiTe2 (γ2 and γ′2) phases. Their homogeneity regions were determined. The liquidus surface consists of the primary crystallization fields of the β-, γ1-, γ′2-, and δ phases and the compounds SnBi2Te4 and SnBi4Te7. The liquidus of the α phase is degenerate. The primary crystallization fields of phases were determined, and the types and coordinates of in- and monovariant equilibria were found.

Models of p-T-x 1-x 2 diagrams for ternary systems with vapor-liquid equilibria and continuous solutions in subcritical and supercritical regions

We consider model p-T-x1-x2 diagrams for ternary systems with continuous solutions in subcritical and supercritical vapor-liquid regions. Phase equilibria are analyzed with the parameters of state of the system varying as dependent on components’ volatilities. The methodology is described, and sample constructions of isobaric-isothermal diagrams and polythermal sections are made proceeding from p-T and T-x1-x2 projections of the four-dimensional diagram.

Tree of phases of the Li,Na,Ba‖F,Br quaternary reciprocal system and study of the LiF-NaBr-BaFBr stable triangle

The Li,Ba‖F,Br ternary reciprocal system was investigated by differential thermal analysis. The T-x diagrams of the polythermal sections studied and the liquidus of the system were constructed. It was deter-mined that the system is of the adiagonal section type with a subordinate diagonal (according to Bergman’s classification). The characteristics and enthalpies of melting of the alloys corresponding to invariant equilibrium points were found. The Li,Na,Ba‖F,Br quaternary reciprocal system was partitioned, and the tree of phases was constructed. The LiF-NaBr-D1(BaFBr) stable triangle was experimentally studied, the liquidus was constructed, and the characteristics of the alloy corresponding to a ternary eutectic were determined.

Phase equilibria in the Ag2Te-PbTe-Bi2Te3 system

Phase equilibria in the Ag2Te-PbTe-Bi2Te3 quasi-ternary system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and emf of concentration circuits with an Ag4RbI5 solid electrolyte. Some polythermal sections and isothermal (600 and 800 K) sections of the phase diagram, and also a projection of the liquidus surface were constructed. The primary crystallization fields of phases were determined, and the types and coordinates of invariant and monovariant equilibria were found. The system is characterized by the formation of a wide continuous band of high-temperature solid solutions (γ phase) with a cubic structure along the PbTe-AgBiTe2 section. With decreasing temperature (T ≤ 715 K), AgBiTe2 and γ solid solutions, close in composition to this compound, experience solid-phase decomposition to form Bi2Te3, ternary tetradymite-like phases of the PbTe-Bi2Te3 boundary system, and the low-temperature phase of Ag2Te.

Phase equilibria and some properties of solid solutions in the Tl5Te3-Tl9BiTe6-Tl5Te2Br system

Phase equilibria in the Tl5Te3-Tl9BiTe6-Tl5Te2Br system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and also emf relative to a thallium electrode. Polythermal and isothermal sections of the phase diagram at 760 and 800 K, and projections of the liquidus and solidus surfaces were constructed. The unit cell parameters, microhardness, and emf in the alloys were described as functions of concentration. The system is characterized by the formation of complete solid solutions with the Tl5Te3 structure.

Liquidus surface of the Mg-Sm-Tb phase diagram

Differential thermal, electron microprobe, and X-ray diffraction analyses and metallography are used to study Mg-Sm-Tb alloys containing up to 30% Sm or Tb. Polythermal sections and the solidification surface of the Mg-Sm-Tb phase diagram are constructed for the Mg-rich region. In the composition range under study, nonvariant transition-type equilibrium L + Mg24Tb5 = (Mg) + Mg41Sm5 is found to exist at a temperature of 539°C.

Phase diagrams of sections in the EuS-Cu2S-Nd2S3 system

Phase equilibria in the EuS-Cu2S-Nd2S3 system were studied in an isothermal (970 K) section and NdCuS2-EuS and Cu2S-EuNdCuS3 polythermal sections. The complex sulfide EuNdCuS3 has an orthorhombic crystal lattice (space group Pnma; a = 1.10438(2) nm, b = 0.40660(1) nm, c = 1.14149(4) nm), is isostructural to BaLaCuS3, and melts incongruently at 1470 K: EuNdCuS3 (0.50 EuS; 0.50 NdCuS2) ai 0.18 EuS ss (0.88 EuS; 0.12 NdCuS2) + 0.82 L (0.415 EuS; 0.585 NdCuS2); ΔH = 17.8 kJ/mol. Within the range 0.5 mol % EuS, EuNdCuS3-based solid solutions were not found. At 970 K, the tie lines pass from the compound EuNdCuS3 to Cu2S, EuS, NdCuS2, and EuNd2S4 phases and lie between the NdCuS2 phase and solid solutions (ss) of γ-Nd2S3 with EuNd2S4. Eutectics are formed between the compounds NdCuS2 and EuNdCuS3 at 32.0 mol % EuS T = 1318 K and between the compounds Cu2S and EuNdCuS3 at 20.5 mol % EuNdCuS3 and T = 1142 K. Five main subordinate triangles were identified in the system.

Phase equilibria in the Tl-TlCl-Te system and thermodynamic properties of the compound Tl5Te2Cl

The Tl-Te-Cl system was studied in the Tl-TlCl-Te composition region by differential thermal analysis, X-ray powder diffraction, and emf and microhardness measurements. A series of polythermal sections, an isothermal section at 400 K, and a projection of the liquidus surface of the phase diagram were constructed. The ternary compound Tl5Te2Cl characterized by a wide homogeneity region and incongruent melting by a syntectic reaction at 708 K was shown to exist. This compound was found to crystallize in tetragonal lattice (space group I4/mcm) with the parameters a = 8.921 A, c = 12.692 A, Z = 4. Wide phase separation regions were also found in the system, including a three-phase separation region in the Tl-TlCl-Tl2Te subsystem. Regions of primary crystallization of phases, and the types and coordinates of in- and monovariant equilibria in the T-x-y diagram were determined. From emf measurement data, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl5Te2Cl, as follows: −ΔG2980 = 355.9 ± 1.1 kJ/mol, −ΔH2980 = 377.1 ± 5.0 kJ/mol, and S2980 = 474.1 ± 6.8 J/(mol K).

The CuGaSe2–CuInSe2–2CdS system and single crystal growth of the γ-phase

Phase equilibria in the CuInSe2–CuGaSe2–2CdS system are investigated using differential–thermal analysis and phase X-ray diffraction. Isothermal section of the system at 870K, polythermal section ‘CuIn0.75Ga0.25Se2’–2CdS, and the liquidus projection in the CuInSe2-rich part have been constructed. Single crystals of the intermediate γ-solid solutions with the sphalerite structure have been grown by Bridgman method. The crystals are of the p-type conductivity, and their band gap energy varies from 1.16 to 1.32eV.

Phase diagram and thermodynamic properties of the system As–Te–I

The As–Te–I system has been investigated primarily by means of DTA, XRD analyses and EMF measurements with an arsenic electrode. The T–x diagram of the binary As–I system was accurately redefined and its phase diagram was constructed. A projection of the liquidus surface, an isothermal section at 300 K, and a series of polythermal sections of the phase diagram were constructed. The previously reported ternary compounds As 5Te 7I, As 4Te 5I 2 and As 8Te 7I 5 were confirmed to be equilibrium phases; the positions of phase areas with their participation were established. Areas of primary crystallization of phases, types and coordinates of the invariant equilibria on the T–x–y diagram were determined. From the X-ray powder diffraction (XRD) analysis, the crystallographic parameters of As 4Te 5I 2 and As 8Te 7I 5 were determined. From the EMF measurements, the partial molar functions of arsenic ( Δ G ¯ , Δ H ¯ , Δ S ¯ ) as well as standard integral thermodynamic functions of ternary compounds were calculated.

Phase equilibria in the Cu-Bi-Se system and thermodynamic properties of copper selenobismuthates

The Cu-Bi-Se system was studied using DTA, X-ray powder diffraction, and electromotive force (e.m.f.) measurements in (−) Cu (solid)|Cu4RbCl3I2 (solid)|(Cu in alloy) (solid) (+) concentration cells in the range 300–430 K. Polythermal sections and a 300-K isothermal section of the phase diagram are constructed, as well as a liquidus surface projection. The existence of ternary compounds CuBi3Se5, CuBiSe2, and Cu3BiSe3 is verified, and phase fields involving them are established. Primary separation fields and the types and coordinates of invariant and monovariant equilibria are determined. E.m.f. data were used to calculate partial molar functions \( (\Delta \bar G,\Delta \bar H,\Delta \bar S) \) of copper in alloys and the standard thermodynamic functions of formation and entropies of the ternary compounds and the end-member (Cu9BiSe6) of solid solutions based on the low-temperature Cu2Se phase.