Substitutional Solution Research Articles

Thermodynamic modeling of the Al–Co–W, Al–Ni–Ta and Co–Ni–W ternary systems

Thermodynamic descriptions of the Al–Co–W, Al–Ni–Ta and Co–Ni–W ternary systems are the foundation for developing thermodynamic database and material design for the Ni-based alloys. In the present work, the Al–Co–W, Al–Ni–Ta and Co–Ni–W systems were optimized based on the reliable experimental data by means of the CALPHAD method. The liquid, γ (Fcc_A1) and β (Bcc_A2) phases were described as substitutional solution model, and the γ’ (Fcc_L12), B2 (Bcc_B2), μ (Co7W6) and Ni3Ta phases were described with sublattice models. The Co3W phase was treated as a stoichiometric compound due to the limited homogeneity range in the Al–Co–W system and described as (Co, Ni)3W in the Co–Ni–W system. The self-consistent thermodynamic parameters for the Al–Co–W, Al–Ni–Ta and Co–Ni–W systems were obtained. Comprehensive comparisons between the calculated results and measured phase equilibrium data show that most experimental information is satisfactorily accounted for by the present thermodynamic description.

Solid State Reactions: Preparation of Solid Solutions and Pure Alkaline-Earth Titanates to Study their Dependence on Vegard’s Law

This laboratory experiment consists of the synthesis of two series of alkaline-earth titanates (calcium–strontium and strontium–barium) to corroborate Vegard′s law by obtaining their X-ray diffraction patterns and plotting the lattice parameter versus mole fraction of both cations. This experiment allows students to understand the key concepts in the solid state chemistry of a lattice parameter, a cubic Bravais network, a perovskite type structure, substitutional solid solutions, Vegard′s law and its deviations, Miller indices, and X-ray diffraction principles. In addition, it gives students the opportunity to acquire technical skills in ceramic synthesis and X-ray diffraction pattern interpretation.

Ag8GeS6(Se6)–Ag8GeTe6 SYSTEMS: PHASE RELATIONS, SYNTHESIS, AND CHARACTERIZATION OF SOLID SOLUTIONS

Phase equilibria in the Ag8GeS6-Ag8GeTe6 and Ag8GeSe6-Ag8GeTe6 systems were studied using differential thermal analysis and powder X-ray diffraction technique. The T-x phase diagrams were constructed. It has been found that both systems are partially quasi-binary and are characterized by the formation of continuous series of substitutional solid solutions between Ag8GeTe6 and high-temperature cubic modifications of Ag8GeS6 and Ag8GeSe6. When solid solutions are formed, the temperatures of polymorphic phase transitions of these compounds decrease. This leads to the stabilization of the ion-conducting cubic phase in the 40 mol% Ag8GeTe6 range of compositions at room temperature and below. The regions of homogeneity based on Ag8GeS6 and Ag8GeSe6 are 15 and 10 mol.%, respectively. The crystal lattice parameters of the identified solid solutions were calculated from the XRD data, and their linear dependence on the composition is shown

Characterization of CrAl coating on stainless steel bipolar plates for polymer electrolyte membrane fuel cells

CrAl alloy coating has advanced potential to improve corrosion inhibition, hydrophobicity, and electrical conductivity for metallic BPs. The feasibility of CrAl coating for surface modification of the BPs is thoroughly examined through comparative analysis with stainless steel 316L (SS316L). The coated specimen can reach high polarization resistance (Rp) and 93% inhibition efficiency (η) from Tafel plots. Based on the various surface properties of CrAl coating, corrosion resistance mechanisms for substitutional solid solution and nanograin structures containing hydrophobic and low surface free energy are proposed.

Thermodynamic assessment of the ternary Ni–Ti-Hf system

The Ni–Ti-Hf ternary system has been assessed by CALPHAD method combined with first-principles calculations. Based on experimental results in the literature, the whole system is evaluated completely. The liquid, γ-Ni, β-(Hf, Ti), α-(Hf, Ti) are modeled using the substitution solution model. Ordered and disordered bcc phases use single Gibbs energy description, while the other intermetallic compounds use corresponding sublattice model to describe. The formation enthalpies of the hypothetical end members of each phase in Ni–Ti-Hf ternary system have been calculated using first principles and incorporated into the modeling. According to the experimental results, the sublattice model of the newly discovered ternary phase τ is determined as (Ni)11(Hf, Ti)14 and the phase is added to the thermodynamic optimization. By comparing the experimental data with the calculated results, the thermodynamic description of this work is in good agreement with the reasonable experimental results. The calculated Ni–Ti-Hf ternary system is summarized by means of isothermal sections, vertical sections, liquidus projection and reaction scheme.

Synthesis and photoluminescence properties of garnet red emitting CaY2Al4SiO12:Eu3+ phosphors

Eu3+ doped CaY2Al4SiO12 garnet phosphors were synthesized by using the sol-gel method. The crystal structure of the synthesized phosphors was characterized by X-ray diffraction and Rietveld refinements. The results of X-ray diffraction and Rietveld refinements of the powders sintered at 1400 °C showed the formation of a single phase and the effective concentration of Eu3+ ions in this garnet host lattice.The composition of the substitutional solid solutions of CaY2-xEuxAl4SiO12 (x = 0.01, 0.03, 0.06, 0.09, 0.12, and 0.15) exhibit efficient red photoluminescence peaking at 596 nm, which can be assigned to the 5D0 → 7F1 intra-configurational transition of Eu3+ located at the dodecahedral site in the garnet structure. The photoluminescence properties, such as excitation and emission spectra, decay curves, and quantum yield, are presented. The thermal stability of the as-prepared phosphors was determined. Additionally, the optical bandgap for the samples was estimated with UV–visible diffuse reflectance spectra using the Tauc relation. The correlation between the structural features and luminescence properties was determined. These phosphors with high thermal stability and high color purity can be potentially used in white-light-emitting diodes.

Ceria–Zirconia-Supported Ruthenium Catalysts for Hydrogen Production by Ammonia Decomposition

Commercial cerium–zirconium oxide supports (Ce0.5Zr0.5O2, Ce0.75Zr0.25O2, and Ce0.4Zr0.5Y0.05La0.05O2) were used to prepare Ru/CeZrOx catalysts. According to the XRD and IR spectroscopy data, the supports consist of ceria-based substitutional solid solutions. The specific surface areas of supports and catalysts are similar and range from 71–89 m2/g. As shown by TEM and XRD methods, the size of support particles equals 6–11 nm. According to the TEM data, the size of ruthenium particles does not exceed 1.3 nm. The catalyst activity in the ammonia decomposition process was studied. The Ru/Ce0.75Zr0.25O2 catalyst at temperature 500 °C and GHSV 120,000 h−1 demonstrated the highest hydrogen productivity of 53.3 mmol H2/(gcat·min) and compares well with the best results reported in the literature. The kinetics of ammonia decomposition reaction were calculated using the Temkin–Pyzhov exponential expression. The developed mathematical model well described the experimental data. The studied catalysts demonstrated high activity for the ammonia decomposition reaction.

Experimental investigation and thermodynamic description of the Fe–Hf–Nb system

According to solidification microstructure of as-cast alloys and phase constituents of annealed samples, the liquidus surface projection and phase relationships at 1373 and 1273 K in the Fe–Hf–Nb system were constructed. A ternary phase τ with AlCuHf-structure was found, and the composition ranges of Nb in τ at 1373 and 1273 K were ∼ 20.5–30.8 at.% and ∼ 20.8–30.2 at.%, respectively. Moreover, the maximum solubilities of Nb in FeHf2 was determined to be ∼ 16.9 at.% and ∼ 16.0 at.% at 1373 and 1273 K, and the maximum solubilities of Hf in μ was measured to be ∼ 4.6 at% and ∼ 3.3 at.% at 1373 and 1273 K. Fe2Hf and Fe2Nb with the same C14 structure formed a homogeneous solid solution from Fe2Hf to Fe2Nb at 1373 and 1273 K. Seven primary solidification regions in the liquidus surface projection and two three-phase regions and seven two-phase regions in the isothermal sections at 1373 and 1273 K were experimentally determined. On the basis of experimental data, the thermodynamic parameters of individual phases in the Fe–Hf–Nb system were optimized by CALculation of PHAse Diagram (CALPHAD) method. Four solution phases (liquid, bcc, fcc, and hcp) were described as the substitutional solution. The intermetallic phases FeHf2, λ1, λ2, λ3 and τ were modeled as (Fe)1(Hf,Nb)2, (Fe,Hf,Nb)2(Fe,Hf,Nb)1, (Fe)2(Hf)1, (Fe)2(Hf,Nb)1, and (Fe,Hf,Nb)1(Fe,Hf,Nb)1 by a two-sublattice model, respectively. μ was described as (Fe,Hf,Nb)1(Hf,Nb)4(Fe,Hf,Nb)2(Fe,Hf,Nb)6 by a four-sublattice model. A set of self-consistent thermodynamic parameters of the Fe–Hf–Nb system was obtained.

Magnetic characteristics of solid solutions Ni1–xMxMnSb (M = Ti, V, Cr)

The results of an experiment on the study of the crystal and magnetic structures of substitutional solid solutions of the Ni0.90M0.10MnSb (M = Ti, V, Cr) systems using thermal neutron diffraction in the temperature range ~ 3–300 K are presented. It is found that all the studied compositions have ferromagnetic ordering along the c axis. In the spectra of Ni0.90V0.10MnSb and Ni0.90Cr0.10MnSb solid solutions, a reflection appears in the region 2Θ = 28.6°, which indicates the formation of antiferromagnetic ordering. It has been found that this reflection disappears at a temperature T = 75 K in Ni0.90V0.10MnSb, while it is observed in the spectrum of Ni0.90Cr0.10MnSb over the entire temperature range under study. Within the framework of density functional theory (DFT), an ab initio calculation of the crystal structure and magnetic moments for Ni1–xMxMnSb (M = Ti, V, Cr; x = 0; 0.125; 0.250) was carried out. It has been established that titanium, vanadium, and chromium ions participate in electron transfer only with Mn and Sb ions. The DFT results predict the existence of magnetic moments for Ti, V, and Cr ions. It was found that the spins of Ti, V, and Cr ions are antiferromagnetically coupled with the spins of Mn and Ni ions. The results obtained are of interest for the development of new concepts and models of structural design, which makes it possible to synthesize fundamentally new functional materials with already specified physical properties.

Chemical Deposition of CdxPb1 – xS/CdyS Thin-Film Composite Structures

Thin films of CdxPb1 – xS (0 ≤ x ≤ 0.094) substitutional solid solutions of cubic structure B1 (space group Fm) were prepared by chemical deposition and characterized by X-ray diffraction, scanning electron microscopy, EDX elemental analysis, and Raman spectroscopy. Once the cadmium sulfate concentration in the batch reached some critical value (0.1 mol/L), the films formed involved two autonomous phases: CdxPb1 – xS substitutional solid solutions and hexagonal cadmium sulfide CdyS of structure В4 (space group P63mc). The method and its parameters as proposed are efficient for manufacturing heterostructures in the CdS–PbS system in one-pot deposition.

Magnetic Photocatalysts Based on Nanocrystalline Manganese-Doped Titanium Dioxide

Manganese-doped anatase with a nanosized morphology (as spherically shaped nanoparticles) has been synthesized under hydrothermal conditions. It has been shown that manganese is incorporated into the titanium dioxide structure to form substitutional solid solutions. At high dopant concentrations, part of the introduced manganese goes to the formation of α-MnO2. A significant increase in the optical activity in the visible range and a decrease in the bandgap width down to ~2.4 eV are observed for manganese-doped anatase because of the appearance of extrinsic (multivalent Mn ions) and intrinsic compensating (oxygen vacancies) defects. It has been found that manganese-doped samples are diluted magnetic semiconductors, and the magnetic characteristics increase with increasing manganese content. All manganese-containing samples demonstrate photocatalytic activity in the degradation reaction of indigo carmine when irradiated with visible light. The degree of dye degradation depends on the content of manganese in the samples and reaches 90%.

A numerical study on the effects of DP steel microstructure on the yield locus and the stress–strain response under strain path change

The mechanical response of dual phase (DP) steel exhibits a complex dependence on the microstructure. The chemical composition and microstructure characteristics of the phases have significant effects on the contrast between the response of the phases, which affects, not only the strength and ductility, but also the anisotropic response of DP steel under strain path changes. In this work, extended dislocation-based models of the ferrite and martensite phases of DP steel are proposed and used in a finite element based representative volume element approach to account for the contrast between the local response of the phases. The flow stress of each phase is computed as a function of the amount of substitutional and interstitial solute elements and the microstructural characteristics of the phase. Particular attention is paid to the phase model of the martensite phase. The model parameter controlling the storage of dislocations is related to the carbon content, which appears to be the most important parameter affecting the strength of martensite and its contrast with the local response of the ferrite phase. The model predicts a significant effect of the contrast between the local responses of the phases and the microstructure characteristics of each phase on the yield locus after prestraining and on the stress–strain behaviour after strain path change, i.e., forward-reverse shear loading and cyclic uniaxial tension–compression loading.

The thermodynamic and mechanical properties of Earth-abundant metal ternary boride Mo2(Fe,Mn)B2 solid solutions for impact- and wear-resistant alloys

Substitutional solid solutions of the Mo2FeB2–Mo2MnB2 system exhibit high stability and a sufficient level of mechanical properties to be used as a reinforcement phase in high-manganese alloys (steels), providing both impact- and wear-resistance.

Dynamics of cluster structure change in melts that forms a continuous series of solid solutions during equilibrium and nonequilibrium crystallization

The article describes the dynamics of changes in the melt structure during cooling of solid substitution solutions in the process of quasi-equilibrium (CRC) and non-equilibrium explosive crystallization (NRCC), taking into account clustering processes. The boundaries of the transition to the solid state are determined as the structure of clusters changes during crystallizations of the KRK and NRK types. The boundaries are determined taking into account the critical overheating and pre-crystallization supercooling relative to the liquidus line . It is determined that during quasi–equilibrium crystallization, the melt changes its structure in the following sequence , and during non-equilibrium explosive crystallization - in the sequence . The phase rule is used to calculate the first crystals that appeared during various types of crystallization. Alloy cooling curves describing various types of alloy crystallization.

New approach to the compound energy formalism (NACEF) Part II. Thermodynamic modelling of the Al–Nb system supported by first-principles calculations

In the present work, a new assessment of the Al–Nb system, using a combined first-principle and CALPHAD approach, is presented. Formation enthalpies of all ordered configurations of the intermetallic phases (σ, D022 and A15) were estimated from ab initio calculations. The liquid, fcc and bcc phases are described by a substitutional solution model. The intermetallic phases D022 and A15 are described with the New Approach to the Compound Energy Formalism (NACEF). To model the σ phase, four descriptions are applied. In first, σ phase is described with the five-sublattice (5SL) model using combined CEF model where a modification was applied which allows to respect the formation enthalpies of end-members obtained from ab initio calculations. Then, a comparison with the results obtained using the NACEF approach applied to the five-sublattice (5SL), three-sublattice (3SL) and two-sublattice (2SL) models is presented. In all cases, assessments derived from the different descriptions of σ phase show very good agreement with the available experimental and ab initio data with a limited number of used parameters. In this sense, self-consistent thermodynamic descriptions of the Al–Nb system is provided. Moreover, this work shows from the example of the σ phase that the NACEF approach, contrary to what is commonly considered, allows the compatibility between different descriptions using different numbers of sublattices. This is particularly interesting for the construction of multi-component databases.

Flüssigkeitsmanagement auf der Intensivstation

Volume management is an essential component of intensive care medicine. In addition to the estimation of the amount of fluid needed by a critically ill patient with the options of pharmaceutical and instrumental volume management, the question of the suitable substitution solution for volume treatment triggered a lively discussion in the last decade. For this purpose, crystalloid and colloidal substitution solutions are available. The use of colloidal solutions is associated with an elevated risk for acute kidney injury and with an increased mortality, so that substitution with crystalloid solutions has become established as the clinical standard. Various isotonic formulations are available for this purpose. In 2012 an Australian open-label study provided evidence that the substitution of a balanced chloride-reduced crystalloid solution in an intensive medical care situation was superior to a physiological saline solution with respect to the incidence of acute kidney injury. The potential reasons were presumed to be the formation of a hyperchloremic acidosis and vasoconstriction of the vas afferens by the supraphysiological chloride concentration in 0.9% saline. More recent high-ranking published data now question these findings and provide the opportunity to re-evaluate the currently available evidence.

Development of a semi-empirical interatomic potential appropriate for the radiation defects in V-Ti-Ta-Nb high-entropy alloy

High-entropy alloys (HEAs) hold promise as candidate structural materials in future nuclear energy systems. Body-centred cubic V-Ti-Ta-Nb HEAs have received extensive attention due to their excellent mechanical properties. In this work, the Finnis-Sinclair interatomic potential for quaternary V-Ti-Ta-Nb HEAs has been fitted based on the defect properties obtained with the density functional theory (DFT) calculations. The new potential for Nb accurately reproduces the vacancy formation energy, vacancy migration energy and interstitial formation energy. The typical radiation defect properties predicted by the alloy potential were consistent with the DFT results, including the binding energies between substitutional solute atoms, the binding energy between substitutional atoms and vacancies, and the formation energy of interstitial solute atoms. In addition, the mixing enthalpies of the alloys were also consistent with the DFT results. The present potential can also describe reasonably the collision cascade process of quaternary V-Ti-Ta-Nb HEAs.

Synthesis of Co-Ni Alloy Particles with the Structure of a Solid Substitution Solution by Precipitation in a Supercritical Carbon Dioxide.

Mixed Co-Ni bimetallic systems with the structure of a solid substitution solution have been synthesized using the supercritical antisolvent precipitation (SAS) method, which uses supercritical CO2 as an antisolvent. The systems obtained have been characterized in detail using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, and magnetostatic measurements. It has been found that Co-enriched systems have a defective hexagonal close-packed (hcp) structure, which was described by a model which embedded cubic fragments of packaging into a hexagonal close-packed (hcp) structure. It has been shown that an increase in water content at the precipitation stage leads to a decrease in the size of cubic fragments and a more uniform distribution of them in Co-enriched systems. It has also been shown that mixed systems have the greatest coercivity in the line of samples. Ni-enriched bimetallic systems have a cubic close-packed (ccp) structure with modified crystal lattice parameters.

Processes of Current Transport in p-Si-n-(Si<sub>2</sub>)<sub>1−</sub><i><sub>y</sub></i><sub>−</sub><i><sub>z</sub></i>(GaP)<i><sub>y</sub></i>(ZnSe)<i><sub>z</sub></i> Heterostructure Produced by Liquid Phase Epitaxy

The possibility of growing multicomponent epitaxial films of a semiconductor solid solution of molecular substitution (Si2)1−y−z(GaP)y(ZnSe)z on Si and GaP substrates by liquid-phase epitaxy is shown. The distribution profiles of the atoms of the solid solution components Ga, P, Zn, Se, and Si over the thickness of the epitaxial film have been determined. The current-voltage (I−V) characteristics of p-Si-n-(Si2)1−y−z(GaP)y(ZnSe)z heterostructures have been studied. A temperature-independent I−V characteristic has been found, the existence of which is explained on the basis of a theory considering the possibility of "blurring" of the impurity level. By comparing the theoretical and experimental results, the half-width of the blurring band for the energy levels of atoms of Si2 and GaP molecules was determined, which had values equal to 0.146 and 0.34 eV, respectively.

Activity of Mono-, Bi-, and Trimetallic Catalysts Pt-Ni-Cr/C in the Bicyclohexyl Dehydrogenation Reaction.

The influence of metals with different redox properties and a carbon carrier on the activity of mono-, bi- and trimetallic Pt-Ni-Cr/C catalysts has been studied in the bicyclohexyl dehydrogenation reaction as the hydrogen release stage in hydrogen storage. An increase in the conversion (X > 62%) of bicyclohexyl and selectivity for biphenyl (S > 84%) was observed on trimetallic catalysts Pt-Ni-Cr/C compared with the monometallic catalyst Rt/C (X > 55%; S > 68%). It has been established that the increase in the conversion of bicyclohexyl and selectivity for biphenyl in the dehydrogenation reaction on trimetallic catalysts is due to an increase in the activity of Pt nanoparticles in the vicinity of local Cr-Ni clusters of solid substitution solutions.