Substitutional Solution Research Articles

Efficient catalysts based on substitutional solid solutions and intermetallic compounds of palladium for acetylene selective hydrogenation to ethylene

Efficient catalysts based on substitutional solid solutions and intermetallic compounds of palladium for acetylene selective hydrogenation to ethylene

Calphad-Type Description of Sugar alcohols potential candidate as phase change material

In this paper, the Sorbitol-Xylitol and Sorbitol-Erythritol two binary systems were computationally investigated. Experimental data including both phase diagrams and thermodynamic information are used as data supports in CALPHAD approach. Four binary phases that in the studied systems: (Erythritol), (Xylitol), (Sorbitol) and liquid are treated as substitution solution. The standard thermodynamic functions of Sorbitol were calculated from the available heat capacity data. Our calculations are in good agreement with the phase diagram data and experimental thermodynamic data available in the literature.

Thermodynamic assessment of the Cr–Mo–Si ternary system

Based on the experimental isothermal sections at 1000 and 1200 °C and the liquidus projection from the measurements by the present authors, the Cr–Mo–Si ternary system is thermodynamically assessed using the CALculation of PHAse Diagram method (CALPHAD). The parameters of the thermodynamic descriptions of all the phases in the Cr–Mo–Si ternary system are optimized on the basis of the reported thermodynamic data and the constitution models of the Cr–Mo, the Cr–Si and the Mo–Si terminal binary systems. Two solution phases, liquid and bcc_A2, were described as substitutional solutions. The intermetallic phases, CrSi, CrSi2 and MoSi2, were modeled by two sublattices, (Cr,Mo):Si, (Cr,Mo):Si2 and (Mo,Cr):Si2, respectively, while βCr5Si3 was modeled by three sublattices (Cr,Mo,Si)2:(Cr,Si)3:Cr3. Cr3Si and Mo3Si have the same crystal structure (cP8, Pm-3n) and present a continuous intermetallic phase M3Si with the two sublattice model (Cr,Mo,Si)3:(Cr,Si)1. Similarly, αCr5Si3 and Mo5Si3 with the same crystal structure (tI32, I4/mcm) form a continuous intermetallic phase M5Si3 with the three sublattice model (Cr,Mo)4:(Cr,Mo,Si)1:(Mo,Si)3. Since the very small solubilities of Cr and Mo, the Diamond-Si phase was treated as a pure element phase. Using the current optimized parameters, the isothermal sections, the liquidus projection and the reaction sequence chart are calculated. The comparison between the calculated results and the experimental investigations, including the isothermal sections, the liquidus projection, and the solidification processes of the as cast alloys, shows that the present calculation can well reproduce the experimental equilibria. The present modeling can finely describe the experimental information of the Cr–Mo–Si ternary system.

First-principles study and its experimental verification on the strength and ductility of O/Si solid solution strengthened Ti alloys

The lattice square degree, denoted by the c/a value, is a crucial factor that influences the slip mode of α-Ti alloys and thereby affects their plasticity. However, the relationship between the c/a value and the plasticity of α-Ti alloys has not been fully clarified. In this study, the powder metallurgy method (PM) was used to prepare Ti alloys with different square degrees by introducing interstitial O and substitutional Si solutes into α-Ti crystal. Then the mechanical properties, particularly plasticity, and lattice parameters of the resulted alloys were measured. By combining first-principles calculation with experimental studying, a plastic criterion based on the square degree was established. Subsequently, the mechanism of strength and plasticity was investigated by means of the density of states and charge density difference. Finally, the composition of α-Ti alloys with both O and Si solution atoms was designed, whose c/a values were calculated by the first-principles calculation and accorded with the proposed square degree criterion, and then the reliability of this criterion was verified by the experimental results. As a result, a high strength and plasticity α-Ti alloy with tensile strength 1106 MPa and elongation 23.2 % was successfully prepared. The findings of this research offer new insights into the alloying design of α-Ti alloys with high strength and moderate plasticity.

Effects of High Hydrostatic Pressure on the Structural, Electronic, and Elastic Properties, and Li-Ion Diffusion Barrier of Lithium Lanthanum Titanate Electrolytes: A DFT Study

Lithium lanthanum titanate perovskites (LLTO) are excellent solid electrolytes because of their good ionic conductivity and elasticity. In this work, the effects of high hydrostatic pressure and the impact of the position of Li impurities on the structural, electronic, elastic, and Li-ion diffusion properties of LaTiO3 perovskite (LTO) and its LLTO substitutional solid solutions, were studied. Density-Functional Theory (DFT) and Hubbard-corrected Local Density Approximation (LDA+U) were used. Due to hydrostatic pressure, the octahedral distortion of LTO, LLTO-layered (L), and -rock-salt (RS) electrolytes decreases, while it increases for the LLTO-columnar (C). On the other hand, the energy band gap () of LTO and LLTO-C decrease as hydrostatic pressure increases. For the LLTO-L, increases with pressure. For the LLTO-RS, decreases from zero to 20 GPa and increases from 20 to 30 GPa. Pugh’s criterion indicates that all systems are ductile regardless of applied pressure. Poisson’s ratio shows that bonds in the LTO are metallic, and LLTO-C is ionic-covalent. Likewise, LLTO-L and -RS electrolytes have a transition from ionic-covalent to metallic behavior, as pressure increases. Li-ion diffusion barriers of LLTO electrolytes increase with increasing hydrostatic pressure, indicating a decrease in Li ionic conductivity.

Stabilities of substitutional solutes in α-iron under uniaxial strain

Nonuniform strain fields in ferritic/martensitic steels working in extreme conditions might induce segregation of alloying solutes. We optimized the structures of iron alloy systems under uniaxial tensile strains along [001] direction within density-functional theory. The calculated segregation energies of solutes Ni, Cu, Al, and Si decrease drastically in a linear fashion as the tensile strain increases up to 17.5%, while those of Co and Ti only change slightly. The segregation energies of solutes V, Nb, Ta, Cr, Mo, and W first decrease and then increase. These results might indicate that, for all solutes studied except Co and Ti, segregation behaviors happen in ferritic/martensitic steels under tensile strains. The shape deformation effect plays a major role in the segregation energies of solutes Cu, Al, Si, Ni, Nb, Ta, Cr, and Mo, while the volumetric effect is dominant for solutes V and W. The segregation energy changes owing to the tensile strain increase from 8% to 14% exhibit a linear relation with the Young modulus changes of the alloys relative to α-iron, which indicates a correlation between the stabilities of solutes and their bonding strength with iron neighbors. The linearly decreasing mixing energies of solutes Mg, Zn and Ga in α-iron with increasing uniaxial strain might suggest a new possible way of fabricating supersaturated iron solid solutions.

Synthesis and Basic Properties of Y1−xYbxVO4 Obtained by High-Energy Ball Milling and High-Temperature Treatment

The main objective of this work was to experimentally confirm that a continuous, substitutional solid solution of a general formula Y1−xYbxVO4 is formed in the pseudo-binary system YVO4–YbVO4, and to investigate its basic unknown properties as a function of composition for 0.00 < x < 1.00. To date, such a solid solution has been obtained and characterized to a limited extent, but only for a few selected compositions. This solution was obtained by a high temperature and, for the first time, using mechanochemical methods. For the solution obtained by the high-energy ball-milling method, unknown physicochemical properties were established over its entire range of homogeneity. The solution was synthesized from mixtures of yttrium orthovanadate (V) with ytterbium (III) orthovanadate (V) of different compositions and investigated by XRD, IR, SEM, and UV-Vis(DRS) methods. It was found that Y1−xYbxVO4 crystallizes in a tetragonal system. The results confirmed that the solid solution Y1−xYbxVO4 has a structure of YVO4 and YbVO4, and its structure is composed of YbO6 and YO6 octahedrons and VO4 tetrahedrons. Moreover, if the parameter (x) in the solid solution Y1−xYbxVO4 increases, its crystalline lattice contracts and the value of the energy gap decreases. This solid solution is stable in the air atmosphere at least up to ~1500 °C. The estimated band gap for this solid solution indicates that it belongs to the semiconductors.

High-temperature steam oxidation resistance of Cr[sbnd]Si substitutional solid solution coating on Zr-4

Zirconium alloy has been used as fuel cladding in LWR for a long time. However, during the loss-of-coolant accident, the zirconium alloy cladding will be exposed to steam environment at 1200 °C, and the damage to the cladding is inestimable. Therefore, in this study, Cr and CrSi coating were prepared on the surface of Zr-4 alloy by magnetron sputtering, and their steam oxidation behaviors at 1200 °C were investigated. The Cr-coated Zr-4 revealed an α-Zr(O) layer with ZrO2 particles at the interface after oxidation at 1200 °C. However, the CrSi coated Zr-4 exhibited excellent oxidation resistance due to the introduction of Si atoms. During oxidation, the diffusion barrier of Zr2Si layer with ZrSi ionic bonds was formed in situ because of the inward diffusion of Si atoms, which effectively inhibited the inter-diffusion of Zr and Cr. The aggregation of ZrO2 at the grain boundaries of the coating was prevented, which cut off the short-circuit path of oxygen diffusion inward. Moreover, the first principles calculation was employed to compare the adsorption energies of the external Zr atoms by Zr2Si and ZrCr2 diffusion layers. The adsorption energy of the in situ formed Zr2Si layer for Zr atoms is higher than that of the ZrCr2 layer, which is evidence of the barrier effect of the Zr2Si layer. Thus, the CrSi coated Zr-4 in this work showed a high prospective in the practical applications.

Evolution of the Structure and Phase Composition of a High-Entropic CoCrFeNiCu Alloy during Prolong Annealing

Abstract—The thermal stability of a high-entropy alloy (HEA) CoCrFeNiCu was studied during long-term annealing for 204 days in the temperature range 873–1273 K. The alloy obtained by mechanochemical alloying of metal powders in a planetary mill during 120 min in an Ar environment is a substitutional solid solution based on a high-entropy phase with a face-centered cubic structure (FCC). Upon annealing, the initial FCC phase decomposes within 1–3 days into a copper-enriched FCC1 phase and a copper-depleted FCC2 phase with similar crystal lattice parameters of 3.60 and 3.57 Å, respectively. During the entire annealing time, the intensities of the diffraction lines of theFCC1 and FCC2 phases are redistributed, the dynamics and nature of which depends on the temperature and duration of the process. After the first three days and until the end of the annealing, the HEA retains the FCC structure of the substitutional solid solution, and the unit cell parameters of the formed FCC phases remain constant with an error of 0.1% up to 204 days. The five-component matrix formed after annealing has the chemical composition Co0.23Cr0.23Fe0.23Ni0.23Cu0.08 and is stable. Also, during the entire period of annealing, an increase in the grain size is observed: at first, when an active rearrangement of the structure occurs, the size increases rapidly, then, in the period from 1 to 30 days, grain growth is limited by the diffusion of components, and at very long time intervals, grain growth is even more inhibited.

Synthesis and phase transformations of hexagonal, orthorhombic, and cubic ScxLu1-xFeO3 (0 ≤ x ≤ 1) nanocrystals

Hexagonal, orthorhombic, and cubic ScxLu1-xFeO3 (0 ≤ x ≤ 1) nanocrystals were obtained through solution combustion synthesis with subsequent heat treatment. The structure and phase transformations of the nanocrystals were comprehensively characterized using EDX, PXRD, and 57Fe MS methods. It was observed that an increase in the Sc content within the ScxLu1-xFeO3 structure led to a phase transition from the orthorhombic phase to the hexagonal phase, and further to the bixbyite-type cubic phase. It was determined that the hexagonal phase was present throughout the entire doping range. Hexagonal substitutional solid solutions were stabilized with the content of scandium cations in range of 50–80 mol.%. The substitution limits of scandium for lutetium were determined for each phase. Based on the obtained results, the possibility of controlled synthesis of ScxLu1-xFeO3 nanoparticles with desired composition and crystal structure was successfully demonstrated, that open up the way to the design of novel advanced functional materials.

ISOTHERMAL SECTION OF THE ZrO2–HfO2–Eu2O3 SYSTEM PHASE DIAGRAM AT 1100 °C

Phase equilibria and structural transformations in the ternary ZrO2–HfO2–Eu2O3 system at 1100 °C were studied by X-ray diffraction over the entire composition range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100 °C. Fields of solid solutions based on the cubic (F) modification with fluorite-type structure and tetragonal (T) and monoclinic (M) modifications of ZrO2 (HfO2), cubic (C) modification of Eu2O3, and an ordered intermediate phase with pyrochlore-type structure, Ln2Zr2O7 (Ln2Hf2O7)(Py), were established to exist in the system. The solubility of Eu2O3 in M-HfO2(ZrO2) is pretty low and approximately less than 1 mol%, which is confirmed by XRD. The boundaries of phase fields and lattice parameters of the phases were determined. The lattice parameters for F phase vary from а = 0.5305 nm in two-phase sample (C+F) containing 6.75 mol% ZrO2–8.25 mol% HfO2–85 mol% Eu2O3 to а = 0.5283 nm for sample containing 27 mol% ZrO2–33 mol% HfO2–40 mol% Eu2O3 and to а = 0.5275 nm in two-phase sample (Py+F) containing 29.25 mol% ZrO2–35.75 mol% HfO2–35 mol% Eu2O3, and from а = 0.5232 nm in two-phase sample (Py+F), containing 32.625 mol% ZrO2–39.875 mol% HfO2–27.5 mol% Eu2O3 to а = 0.5218 nm sample containing 33.75 mol% ZrO2–41.25 mol% HfO2–25 mol% Eu2O3 and to а = 0.5176 nm in two-phase sample (F+M) containing 40.5 mol% ZrO2–49.5 mol% HfO2–10 mol% Eu2O3 along the section Eu2O3–(55 mol% HfO2–45 mol% ZrO2). The fluorite-type structure (F) is in equilibrium with all phases that exist in the ternary ZrO2–HfO3–Eu2O3 system at 1100 °C and forms substitutional solid solutions with phases of the binary systems. In the ZrO2–HfO2–Eu2O3 system, an infinite series of solid solutions form from the Ln2Zr2O7 (Ln2Hf2O7) (Py) phase. The isothermal section of the ZrO2–HfO2–Eu2O3 phase diagram at 1100 °C contains one three-phase regions (T + M + F) and six two-phase regions (F + C, two-F + Py, F + M, F + T, T + M). No new phases were found in the ZrO2–HfO2–Eu2O3 system at 1100 °C and the nature of phase equilibria was determined by the constitution of the boundary binary systems.

Nickel Based Ni–Ce<sub>1–<i>x</i></sub>Zr<sub><i>x</i></sub>O<sub>2</sub> Catalysts Prepared by Pechini Method for CO<sub>2</sub> Methanation

Nickel-based Ni–Ce1 – xZrxO2 catalysts were prepared by Pechini method and their catalytic performance towards CO2 methanation reaction was studied. It was shown that the catalysts exhibit high catalytic activity comparable to the activity of industrial methanation catalyst NIAP-07-05. The catalysts were characterized using a complex of X-ray diffraction methods with experiments on synchrotron radiation, high-resolution electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It is shown that the preparation method makes it possible to achieve a high dispersion of nickel-containing particles formed during the decomposition of the Ni–Ce–Zr–O substitutional solid solution obtained during the synthesis. However, due to the decorating effect, the surface of nickel-containing particles is poorly accessible to reagents. For this reason, the Ni–Ce1 – xZrxO2 catalysts obtained by the Pechini method are less active than the supported Ni/Ce1 – xZrxO2 catalysts.

SINGLE-ATOM ALLOY Pd<sub>1</sub>Ag<sub>6</sub>/Al<sub>2</sub>O<sub>3</sub> EGG-SHELL CATALYST FOR SELECTIVE ACETYLENE HYDROGENATION

In this work, a single-atom alloy Pd1Ag6/Al2O3 catalyst for the selective hydrogenation of acetylene was obtained with an egg-shell distribution of the active phase over the catalyst granules. The formation of an egg-shell structure was confirmed by electron probe microanalysis. It was found that metals are predominantly localized at a depth of 130–160 µm from the surface of the granules. Transmission electron microscopy and X-ray photoelectron spectroscopy have revealed the formation of a substitutional PdAg solid solution with electron density transfer from Ag to Pd. The formation of Pd1 single sites was confirmed by FTIR spectro-scopy of adsorbed CO. In the selective hydrogenation of acetylene the synthesized single-atom alloy Pd1Ag6/Al2O3 with egg-shell distribution showed high selectivity, which radically exceeds the selectivity of the palladium counterpart.

Novel Ir1–xCoxO2 thin films: Growth and characterization

Ir1–xCoxO2 thin films have been prepared by reactive co–sputtering deposition at room temperature. Composition, structure, electronic properties and electric and magnetic behavior have been analyzed by different techniques including XRR, XRD, TEM microscopy, SQUID magnetometry, electrical resistivity and XAS spectroscopy. After annealing, an Ir1–xCoxO2 substitutional solid solution phase with rutile crystal structure was achieved for a wide Co-doping range 0 ≤ x ≤ 0.6. Starkly departing from the highly insulating behavior of CoO and Co3O4, the electrical resistivity at room temperature of our films is only slightly higher than that of IrO2. Likewise, our work shows that the magnetic response of the doped films is very similar to that of the paramagnetic parent IrO2. Neither ferromagnetism nor enhanced paramagnetism is observed. XAS spectra indicate a Co3+ oxidation state and, correspondingly, an oxidation state of ∼5+ for Ir ions in the polycrystalline Ir0.6Co0.4O2 film. By application of sum rules, a 13 % increase in the spin–orbit coupling is found despite the lattice shrinkage causes a detrimental bandwidth broadening.

Experimental determination and thermodynamic calculation of phase equilibria in Ag-Zr-Y system

The phase equilibria of the Ag-Zr-Y system at 800, 600 and 500 °C were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive X-ray spectrometry (EDS) techniques. The solubilities of Y in the Ag2Zr and AgZr phases and of Zr in the Ag51Y14, Ag2Y and AgY phases were measured, and no ternary compound was found in these isothermal sections. By means of the CALPHAD method, thermodynamic parameters of the Ag-Zr-Y system were assessed based on the experimental data from the present work and the literature. Substitutional solution model was used to describe the solution phases and sublattice models were used to describe binary compounds. A set of self-consistent and accurately described thermodynamic parameters of the Ag-Zr-Y system were obtained. The representative isothermal sections and liquidus projection were calculated, and the Hill reaction scheme of the Ag-Zr-Y system was constructed. The calculated results are in agreement with the experimental data.

First-principle exploration for RE solid-solution influence on Ni mechanical properties

Rare earth element (abbreviated as RE) doped nickel alloy is very attracted for the neutron shielding application for excellent neutron absorption and good mechanical behavior. RE solid-solution influence on Ni alloy mechanical properties has been comprehensively investigated by first-principles calculations in this work. The elastic constant and generalized stacking fault energy analysis indicate that RE substitutional solution would decrease the mechanical strength (For example, bulk modulus: BNi = 198.9 GPa, BNi31RE = 174.7 ∼ 189.8 GPa, Young's modulus: ENi = 242 GPa, ENi31RE = 183.1 ∼ 226.1 GPa and shear modulus: GNi = 93.25 GPa, GNi31RE = 69.05 ∼ 86.88 GPa) while increase the plastic deformation (intrinsic stacking fault energy: γis,Ni52 = 137.1 mJ/m2, γis,Ni51RE = 57.69 ∼ 94.17 mJ/m2 and critical intrinsic stress: τcrit,Ni52 = 31.08, τcrit,Ni51RE = 13.89 ∼ 20.00). Furthermore, the influence has a correlation with atomic radii difference Δr/rNi (the bigger difference is, the greater influence is), which is due to that hybridization strength and bonding strength decreases as Δr/rNi increases. The work provide a theoretical guidance for RE doped nickel alloys plastic deformation promotion.

Effects of partial replacement of nitrite with different fruit and vegetable powder on physicochemical and sensory aspects of fried beef meatballs

Fruit and vegetable powders can replace sodium nitrite in the meat-processing industry. However, basic information on the physicochemical and sensory aspects of fried beef meatballs is limited. In the present work, Chinese cabbage, celery, and cranberry powders were used to assess the effects of different addition levels and marinating times on the characteristics of fried beef meatballs. By combining 10 g/kg cranberry powder with 60 mg/kg NaNO2, the highest a* value (13.34) and the lowest cooking loss (28.05%) were obtained. Results from low-field NMR indicated that the relaxation time T2b in three fruit and vegetable powder-added groups was significantly lower than that of the control. T2b values and the pH both exhibited a decreasing trend as the amount of fruit and vegetable powder additions increased. Concerning different marinating times by using cranberry powder on the properties of fried beef meatballs, marinating for 12 h displayed the best effect. The present work provided a potential solution for nitrite substitution in fried beef meatballs.

Observation of hybrid solid solution and superior energy storage in 0.8Ba(Zr0.35Ti0.65)O3-0.2ZnO films

Unusual substitutional and interstitial solid solutions were observed in (1−x)Ba(Zr0.35Ti0.65)O3-xZnO thin films, where one Zn2+ cation substituted one B-site Zr4+/Ti4+ site and two Zn2+ cations substituted one A-site Ba2+ site simultaneously. Such a hybrid solid solution with an appropriate ZnO content remarkably increases both the electric breakdown strength (Eb) by widening the bandgap and the energy storage efficiency (η) by suppressing the hysteresis of the ferroelectric loop. As a result, the films with x = 0.2 show superior energy storage performance with a recoverable energy storage density (Wrec) of 130.3 J/cm3 and η of 89.1%. This work confirms the feasibility of forming an unconventional hybrid solid solution, which may shed light on further work on perovskite oxides with improved ferroic functionalities.

Thermodynamic modeling of B–Mo–Nb ternary system with modified B–Nb description

Based on a critical evaluation of the literature data, the B–Mo–Nb ternary system has been assessed by means of the CALPHAD (CALculation of PHAse Diagrams) technique. There is no ternary compound reported in this system. According to their crystal structures, the substitutional solution is adopted to model the ternary liquid, and the sublattice models are used to describe the Mo2B, αMoB, (Mo,Nb)B, (Mo,Nb)B2, Mo2B5, MoB4, Nb3B2, Nb5B6, Nb3B4, Nb2B3, (Mo,Nb) and (B) phases. The modeling covers the whole composition and temperature ranges. Due to the same crystal structure, the sublattice model of the NbB phase in the B–Nb binary system is adjusted as (Me,Va)0.5(B,Va)0.5, in order to be consistent with the βMoB phase in the B–Mo binary system. The obtained thermodynamic parameters of the B–Mo–Nb system are demonstrated to be self-consistent and reasonable by adequately comparing the calculated and reported thermodynamic information and phase diagram. Based on the present thermodynamic parameters, the liquidus projection and reaction scheme of B–Mo–Nb system are presented.

Phase equilibria in the Ag8SiSe6-Ag8SiTe6 system and characterization of the solid solutions Ag8SiSe6-xTex

Due to polymorphism and complex crystal structure, compounds of the argyrodite family and phases based on them exhibit several interesting functional properties, such as thermoelectric, photoelectric, optical, as well as ionic conductivity for Cu+ and Ag+ cations. The paper presents the results of the study of phase equilibria in the Ag8SiSe6-Ag8SiTe6 system by DTA, XRD, and SEM methods. Refined data on the melting temperature (1278 K) and polymorphic transitions (315 K and 354 K) of the Ag8SiSe6 compound are presented. The crystallographic parameters of LT-Ag8SiSe6 (Cubic, F-43m, a = 1.0965 nm) and IT-Ag8SiSe6 (Cubic, P4232, a = 1.0891 nm) are also determined. It has been established that the investigated system is quasi-binary and its phase diagram is characterized by the formation of a continuous series of substitutional solid solutions between HT-Ag8SiSe6 and Ag8SiTe6. This process is accompanied by a strong decrease in the temperatures of polymorphic transformations of Ag8SiSe6, which leads to the stabilization of the ion-conducting cubic phase at room temperature in the >10 mol% Ag8SiTe6 compositions area. The crystal lattice parameters of the synthesized solid solutions are calculated by indexing the powder diffraction patterns. The stabilization of the high-temperature cubic phase at room temperature achieved by us presents new opportunities for the development of environmentally friendly thermoelectrics and ion-electronic conductors based on silicon argyrodites with desired composition and properties.