Enthalpies of formation of liquid and solid binary alloys based on 3d metals

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Extension of Solid Solubility and Structural Evolution in Nano-Structured Cu-Cr Solid Solution Induced by High-Energy Milling

In Cu-Cr alloys, the strengthening effects of Cr are severely limited due to the relatively low Cr solid solubility in Cu matrix. In addition, apart from the dissolved Cr, it should be noted that high proportion of Cr in Cu matrix work as the second phase dispersion strengthening. Therefore, it is of great significance to extend the Cr solid solubility and decrease the size of the undissolved Cr phase to nano-structure. In this work, the nano-sized Cu-5 wt.% Cr solid solution was achieved through high energy ball milling (HEBM) only for 12 h. The Cr solubility of ~1.15 at.% was quantitatively calculated based on XRD patterns, which means supersaturated solid solution was realized. Except for the dissolved Cr, the undissolved Cr phase was with nano-sized work as the second phase. Upon milling of the Cu-Cr powders with coarse grains, the crystallite sizes and grain sizes are found to decrease with the milling time, and remain almost unchanged at a steady-state with continued milling. In addition, it was found that the stored energy induced by dislocation density increment and grain size refinement would be high enough to overcome the thermodynamic barrier for the formation of solid solution.

Adsorbate-Induced Segregation of Cobalt from PtCo Nanoparticles: Modeling Au Doping and Core AuCo Alloying for the Improvement of Fuel Cell Cathode Catalysts

Platinum, when used as a cathode material for the oxygen reduction reaction, suffers from high overpotential and possible dissolution, in addition to the scarcity of the metal and resulting cost. Although the introduction of cobalt has been reported to improve reaction kinetics and decrease the precious metal loading, surface segregation or complete leakage of Co atoms causes degradation of the membrane electrode assembly, and either of these scenarios of structural rearrangement eventually decreases catalytic power. Ternary PtCo alloys with noble metals could possibly maintain activity with a higher dissolution potential. First-principles-based theoretical methods are utilized to identify the critical factors affecting segregation in Pt-Co binary and Pt-Co-Au ternary nanoparticles in the presence of oxidizing species. With a decreasing share of Pt, surface segregation of Co atoms was already found to become thermodynamically viable in the PtCo systems at low oxygen concentrations, which is assigned to high charge transfer between species. While the introduction of gold as a dopant caused structural changes that favor segregation of Co, creation of CoAu alloy core is calculated to significantly suppress Co leakage through modification of the electronic properties. The theoretical framework of geometrically different ternary systems provides a new route for the rational design of oxygen reduction catalysts.

Investigation of compound formation sequence in Al/Ni/…/Al/Ni multilayer system under conditions of an excessive amount of one component and its prediction using the analogy with gas system behavior

Interaction processes in Al/Ni/.../Al/Ni multilayer systems with an excess of one of the components are studied by of DSC, XRD and TEM methods. It is shown that the compounds formation sequence differs depending on which component is excessive. There is proposed a rule for compounds formation sequence in systems with an excess of one of the initial phases. It is based on the assumption that behaviour of two contacting solid phases system is analogical to that of a gas system: energy density change in a solid-state system is analogical to pressure change in gas system. The prediction is built on the calculation of parameter ΔH⁰/νV, where ΔH⁰ and νV are enthalpy change and volume of new phase forming as a result of the reaction.

Microstructural Evolution, Thermodynamics, and Kinetics of Mo-Tm₂O₃ Powder Mixtures during Ball Milling

The microstructural evolution, thermodynamics, and kinetics of Mo (21 wt %) Tm₂O₃ powder mixtures during ball milling were investigated using X-ray diffraction and transmission electron microscopy. Ball milling induced Tm₂O₃ to be decomposed and then dissolved into Mo crystal. After 96 h of ball milling, Tm₂O₃ was dissolved completely and the supersaturated nanocrystalline solid solution of Mo (Tm, O) was obtained. The Mo lattice parameter increased with increasing ball-milling time, opposite for the Mo grain size. The size and lattice parameter of Mo grains was about 8 nm and 0.31564 nm after 96 h of ball milling, respectively. Ball milling induced the elements of Mo, Tm, and O to be distributed uniformly in the ball-milled particles. Based on the semi-experimental theory of Miedema, a thermodynamic model was developed to calculate the driving force of phase evolution. There was no chemical driving force to form a crystal solid solution of Tm atoms in Mo crystal or an amorphous phase because the Gibbs free energy for both processes was higher than zero. For Mo (21 wt %) Tm₂O₃, it was mechanical work, not the negative heat of mixing, which provided the driving force to form a supersaturated nanocrystalline Mo (Tm, O) solid solution.

Enthalpies of mixing of liquid ternary Co-Li-Sn alloys

ABSTRACT

The partial and integral molar enthalpies of mixing of liquid Co-Li-Sn alloys were determined using drop calorimetry. The investigations were performed along six sections by the addition of lithium to mixtures with the compositions [Formula: see text]/[Formula: see text] ≈ 2:98, [Formula: see text]/[Formula: see text] ≈ 1:9, and [Formula: see text]/[Formula: see text] ≈ 3:17 as well as by the addition of cobalt to mixtures with the compositions [Formula: see text]/[Formula: see text] ≈ 3:17, [Formula: see text]/[Formula: see text] ≈ 1:2, and [Formula: see text]/[Formula: see text] ≈ 1:1 at a temperature of 1,173 K. The Co-Li-Sn system shows exothermic behavior of the integral molar enthalpy of mixing in the investigated concentration range. The integral molar enthalpy of mixing of liquid Co-Li system was calculated by Miedema's model to fit our measured ternary data using an extended Redlich-Kister-Muggianu model for substitutional solutions.

GRAPHICAL ABSTRACT

Enthalpy of mixing of liquid Co-Sn alloys

A literature overview of enthalpy of mixing data for liquid Co-Sn alloys shows large scattering but no clear temperature dependence. Therefore drop calorimetry was performed in the Co-Sn system at twelve different temperatures in 100 K steps in the temperature range (673 to 1773) K. The integral enthalpy of mixing was determined starting from 1173 K and fitted to a standard Redlich-Kister polynomial. In addition, the limiting partial molar enthalpy of Co in Sn was investigated by small additions of Co to liquid Sn at temperatures (673 to 1773) K. The integral and partial molar enthalpies of the Co-Sn system generally show an exothermic mixing behavior. Significant temperature dependence was detected for the enthalpies of mixing. The minimum integral enthalpy values vary with rising temperature from approx. -7820 J/mol at T = 1173 K to -1350 J/mol at T = 1773 K; the position of the minimum is between (59 and 61) at.% Co. The results are discussed and compared with literature data available for this system. X-ray studies and scanning electron microscopy of selected alloys obtained from the calorimetric measurements were carried out in order to check the completeness of the solution process.

Morphology of epitaxial magnetic alloy nanostructures grown on WSe2(0001) studied by grazing-incidence small-angle X-ray scattering

The morphology of epitaxial alloy nanostructures grown on a van der Waals-type WSe2(0001) surface was studied using grazing-incidence small-angle X-ray scattering (GISAXS). Assemblies of 111-oriented islands of (Co,Cr)Pt3and (Co,Fe)Pt alloys were grown at different deposition temperatures, with nominal thicknesses from 0.1 to 3 nm, resulting in various island densities. Evaluation of the GISAXS patterns indicates that for similar growth conditions CrPt3islands are flatter than CoPt or FePt islands and exhibit larger island volumes. These features are correlated with the better wetting behaviour and more negative formation enthalpy of the CrPt3alloy. For dense arrays of self-assembled CoPt islands, much smaller island volumes are extracted from GISAXS experiments than are observed by scanning tunnelling microscope imaging, which indicates that only the upper parts of the islands contribute to the GISAXS signal. Another aspect that needs to be taken into account for interpreting GISAXS patterns is the sensitivity of GISAXS to facetting and thus its capacity to extract the island shape. The latter is strongly dependent on the island size. For islands with an average volume smaller than ∼20 nm3, the shape cannot be determined unequivocally. Furthermore, for dense island assemblies with some size dispersity, the identification of steep side-wall facets from the GISAXS patterns is not straightforward as observed for truncated tetrahedron-shaped CoPt3islands.