Solubility in the Ternary Water–Salt System GdCl3–TbCl3–H2O at 25°С

Chapter 3 - Structure and Stability of Alloys

The work is the first attempt to employ the bond valence model (BVM) in the explanation and interpretation of the phase diagrams observed for the quasibinary systems based on the ternary halides Rb3(Cs3)Sb2(Bi2)Br9(I9) (A3B2X9) and K2(Rb2,Cs2,Tl2)TeBr6(I6) (A2BX6) belonging to the structural family of perovskite. The most characteristic features of the phase diagrams of such systems are (a) a monotonic increase in the melting and crystallization temperatures when the smaller A atom is replaced by a larger chemical analogue; (b) a gradual decrease in the melting and crystallization temperatures when the bromine atoms are replaced by iodine atoms, reaching the temperature minimum at a molar ratio of ~1 : 1, and then an increase of the temperatures to the pure iodine component of the system. With the isostructurality of the starting components, in case (a) a continuous series of solid solutions (CSSS) of substitution is formed, without a temperature minimum; if the starting components belong to different structural types, then a peritectic interaction with the wide concentration limits of solid solutions is observed. Under the same conditions concerning the isostructurality/non-isostructurality of starting components, in case (b), correspondingly, either a CSSS of substitution with a temperature minimum is formed or eutectic interaction with the wide concentration limits of solid solutions is observed. Within the framework of the BVM, in case (a) a monotonic increase of the melting and crystallization temperatures when replacing a smaller atom A with a larger analogue can be interpreted as a consequence of reducing the deficit of the bond valence sum (BVS) for cations A, resulting in the stabilization of the structure as a whole. In case (b), partial replacement of one halogen ion by a halogen ions of another sort leads either to a deficit (if a larger anion is replaced by a smaller one) or to an excess (if a smaller anion is replaced by a larger one) of the BVS values for the cations A and for the anion that replaced the main halogen sort. An increase in the excess or deficit of the BVS values destabilizes the structure of ternary halides, reducing the melting and crystallization temperatures; the maximum destabilization is achieved at a ~1 : 1 molar ratio of the components, which is expressed in reaching the characteristic temperature minimum of the respective systems. The approach described in the work can expectedly be employed in explanation and interpretation of another phase diagrams based on the structures featuring the closest packing formed by alkaline metals and halogens. Keywords: ternary halides; crystal structures; phase diagrams; bond valence model.

The diffusion of Aluminium is one of the most promising methods to build superficial coatings for stainless steel protection. Heat treatments at 800 o C performed on rods of AISI 304 steel, Aluminium coated by means of electrodeposition, displayed the possibility of forming intermetallic compounds. Depending on the duration of the heat treatment and on the cooling kinetics, these compounds can be continuous. At high cooling kinetics (water cooling) a two-phase structure composed of γ' (Ni 3 Al() and γ (substitutional solid solution) is obtained. At slow cooling rates (in furnace), a substitutional solid solution and some precipitates of γ'(Ni 3 Al) and β (NiAl) can be observed. At intermediate cooling rates (oil cooling and air cooling), only the substitutional solution and the γ' phase are present. Using furnace cooling from 800 o C until 500 o C, permanence at this temperature for 192 h and cobling furnace, the two-phase structure obtained is composed of the substitutional solid solution and the β(NiAl) phase. The existence of these phases and their composition have been reported by X-ray diffraction patterns and microanalysis. The possibility of forming a natural composite, constituted by a hard phase of aluminides diffused in a substitutional solid solution, has an important consequence on the mechanical and protection properties of these coatings. Moreover, the diffusion of Al improves the adhesion of coatings

This paper presents a theoretical and experimental study of the four-component Na+||F–,Cl–,MoO42–,WO42– system. A stable triangle and a square divide systems into stable tetrahedron, five-vertex and six-vertex. The prediction of the number and composition of crystallizing phases carried out for stable elements of the phase tree. Faceting elements contain sodium molybdates and tungstates and compounds Na3ClMoO4, Na3ClWO4, Na3FWO4, Na3FMoO4, which form a continuous series of solid solutions – Na2MoxW1–xO4, Na3ClMoxW1–xO4 and Na4F2MoxW1–xO4. A phase equilibria in the stable tetrahedron NaF–NaCl–D3–D4 experimentally studied by the method of differential thermal analysis. The absence of nonvariant equilibrium points in the tetrahedron and the stability of the continuous series of solid solutions established. The melting point and composition of the alloy maching to the point lying on the monovariant curve, connecting ternary eutectics E2 and E4 revealed. Phase reactions for various elements of the composition tetrahedron described.

The isothermal section of the Gd–Dy–Co ternary system at 800 K

Mg0.5Zr2(AsO4)x(PO4)3 − x arsenate phosphates have been prepared by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and impedance spectroscopy. The results indicate the formation of a continuous series of solid solutions with the Sc2(WO4)3 structure (sp. gr. P21/n) in the composition range 0 < x < 3. The unit-cell parameters of the solid solutions increase linearly with composition, as a consequence of arsenic substitution for phosphorus, which has a smaller ionic radius. The number of observed stretching and bending bands of the AsO 4 3- and PO 4 3- ions in the IR spectra of the solid solutions agrees with that predicted by factor group analysis for space group P21/n. The observed gradual shift of the absorption bands of the AsO4 tetrahedra to lower frequencies with increasing arsenic content on the tetrahedral site supports the X-ray diffraction evidence of the formation of substitutional solid solutions. The cation conductivity of Mg0.5Zr2(AsO4)x(PO4)3 − x with 0 ≤ х ≤ 1 has been shown to exceed the conductivity of the parent magnesium zirconium arsenate.

The thermopower composition dependences at 293 K are measured for 10 series of continuous solid solutions (CSS): Cr-V, Mo-Nb Mo-V, Nb-V, Cr-Mo, Ti-Zr, Ti-Hf, Hf-Zr, Sc-Zr, Sc-Hf. The data for 15 series of CSS are analysed tagether for the first time. It is found that thermopower-composition dependences are different when CSS are formed by two isoelectronic or two nonisoelectronic metals. In the latter case there is a singularity on the thermopower­ composition isotherm. The investigation of temperature dependence of thermopower is carried out for two series of CSS. The properties of disordered systems are of great interest now. It is natural to try to understand the properties of the simplest disordered systems at first. The Substitution binary solid solu­ tions, whose structures are closest to the elementary metals are the simplest systems among the metallic alloys. The series of continuous solid solutions (CSS) are of particular interest because in their analysis we can use our knowledge of electronic structure of both metals. However, the thermoelectric properties of CSS are studied poorly. Indeed, only few series of CSS were studied experimentally. The attempts of the theoretical interpretation were made for alloys Ag-Au and Pd-Ag. The behaviour of these alloys is substantially different (Fig. 1). The thermopower of Ag-Au alloys changes mark­ edly only at the ends of the diagram, while in the middle part it changes weakly. The thermopower of Pd-Ag alloys changes consider­ ably within the whole composition range 0-100%. The behaviour of alloys Cr-V looks much more complicated (Fig. 4). The presence of

Phase equilibria in the ZrO2–HfO2–Nd2O3 system at 1500 °C and 1700 °C

The uranium--niobium binary system exhibits a continuous series of solid solutions above 850 deg C. At lower temperatures a miscibility gap exists, containing a niobium-rich and a uranium-rich body-centered cubic phase. A monotectoid transformation occurs at 634 deg C. The beta-uranium phase is restricted by niobium and disappears at 4 wt.% Nb. Below 634 deg C alpha uranium and the niobium-rich gamma co-exist. The uranium--niobium--zirconium ternary system exhibits a continuous series of solid solutions at high temperatures. Miscibility gaps in the uranium-niobium and uranium--zirconium binary systems close with addition of the third element. Addition of both zirconium and niobium stabilizes the body-centered cubic gamma phase to lower temperatures. The beta-uranium phase is eliminated in ternary alloys of 4 wt.% Nb or more. The delta phase of the uranium-zirconium binary system extends into the ternary system to no more than 10 wt.% Nb. Over the major portion of the uranium-rich corner of the ternary system the equilibrium phases are alpha-U and gamma solid solution. The uranium-niobium binary system is the more dominant of the limiting systems. No new ternary phases were found. The relation of microstructures to irradiation stability is discussed. The relation of lattice strain to limits of solid solubility is also discussed. (auth)

This paper provides a consistent thermodynamic data set for the Cr‐Si‐Ti system and its whole reaction scheme via experimental investigation and thermodynamic modeling. Alloys were prepared by arc melting of cold‐pressed pellets and annealing at 800 °C for 44 days and at 1000 °C for 21 day. Water‐quenched samples were analyzed by using X‐ray diffraction (XRD) and differential thermal analysis (DTA) techniques. The incipient melting points along the isopleth Cr5Si3– Ti5Si3 were measured by using the Pirani technique. The temperatures for 9 invariant reactions involving liquid phase below 1500 °C were accurately measured. The isothermal sections at 800 and 1000 °C and the isopleth Cr5Si3– Ti5Si3 were determined. The optimal thermodynamic data set for the Cr‐Si‐Ti system obtained by considering the present experimental results and reliable literature data describes these experimental data very well. This description predicts, for temperatures above 1500 °C, the existence of a continuous series of solid solutions between βCr5Si3 and Ti5Si3, having a melting point maximum substantially above the melting point of binary Ti5Si3. More work is needed for experimental confirmation of these predictions.

Effects of niobium doping on perovskite La0.5Sr0.5Fe1−xNbxO3−δ structure

Solid-state electrochemical, X-ray and spectroscopic characterization of substitutional solid solutions of iron–copper hexacyanoferrates

1. The methods of x-ray diffraction and high-temperature thermal analyses were used to construct the constitution diagram of the system TiCr2-TaCr2, which constitutes a section of the ternary system Ti-Ta-Cr. 2. It was established that a continuous series of solid solutions forms both between the high- and low-temperature modifications of the compounds TiCr2 and TaCr2. 3. In the system NbCr2-TaCr2, in addition to a continuous series of solid solutions between the isomorphous compound modifications, the presence of a phase with an iron-tungsten carbide structure was discovered in the temperature range 1350–1400°C. 4. An equilibrium diagram of the ternary system TiCr2-TaCr2-NbCr2 was constructed with the aid of three sections.

Purpose. This work is aimed at synthesis and cgrowth, X-ray investigation, study of the phase diagram and concentration behavior of lattice parameter and density of (Cu 1-х Ag x ) 7 SiS 5 I solid solutions. Methods. Alloys of Cu 7 SiS 5 I – Ag 7 SiS 5 I system were synthesized by means of direct one-temperature method from pre-synthesized Cu 7 SiS 5 I and Ag 7 SiS 5 I compounds. Growth of single crystals of (Cu 1-х Ag x ) 7 SiS 5 I solid solutions was carried out by means of crystallization from a solution-melt. Interaction in Cu 7 SiS 5 I – Ag 7 SiS 5 I system was investigated by means of differential-thermal analysis (Pt/PtRh thermocouple, heating speed 700 K/h), X-ray phase analysis (DRON 4-07, emission CuKα, angle scan step 2Θ - 0.02 deg, exposition - 0.5 s) and densimetric methods. Results. According to the results of the X-ray phase analysis, calculations of the parameters of the elementary cell of Cu 7 SiS 5 I and Ag 7 SiS 5 I compounds and based on them alloys were carried out. The diffraction patterns of Cu 7 SiS 5 I and Ag 7 SiS 5 I compounds are indexed in face-centered cubic lattice . The number and nature of the reflexes on the diffractograms of alloys containing 10-90 mol.% of Cu 7 SiS 5 I indicate that a continuous series of solid solutions is formed in the system. According to the results of differential-thermal analysis and X-ray phase analysis, a phase diagram of Cu 7 SiS 5 I - Ag 7 SiS 5 I system was constructed. It is characterized by the formation of unbounded a-solid solutions based on both compounds with a minimum on the liquidus curve (2nd type by Rozebom). The coordinates of the minimum point are 16 mol.% Cu 7 SiS 5 I, 1165 K. It is established that the compositional depenedences of the lattice parameter and density occur with a slight deviation upward from the from linear dependence. Conclusions. The synthesis and growth of single crystals of (Cu 1-х Ag x ) 7 SiS 5 I solid solutions were carried out. Alloys of Cu 7 SiS 5 I – Ag 7 SiS 5 I system were synthesized by means of direct one-temperature method from pre-synthesized Cu 7 SiS 5 I and Ag 7 SiS 5 I compounds. Growth of single crystals of (Cu 1-х Ag x ) 7 SiS 5 I solid solutions was performed by means of crystallization from a solution-melt. Interaction in Cu 7 SiS 5 I – Ag 7 SiS 5 I system was investigated by means of differential-thermal analysis, X-ray phase analysis and densimetric methods. The diffraction patterns of Cu 7 SiS 5 I and Ag 7 SiS 5 I compounds were indexed in face-centered cubic lattice . According to the results of X-ray diffraction studies, it was found that a continuous series of solid solutions is formed in Cu 7 SiS 5 I – Ag 7 SiS 5 I system. The phase diagram of Cu 7 SiS 5 I - Ag 7 SiS 5 I system is characterized by the formation of unbounded a-solid solutions based on both compounds with a minimum on the liquidus curve (2nd type by Rozebom) with the coordinates of the minimum point constituting 16 mol.% Cu 7 SiS 5 I, 1165 K. It is shown that the concentration changes of the lattice parameter and density observed with a slight deviation upward from the linear dependence.

Over the entire range of compositions in the system TiTe3O8ZrTe3O8, solid solutions are formed at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of titanium isopropoxide, zirconium n‐butoxide, and tellurium tetrachloride. A continuous series of solid solutions is indexed in a cubic with a increasing linearly from 1.096 to 1.131 nm as Ti is substituted by Zr. At all Ti:Zr ratios the structures contain TeO4 groups.