First-principles investigation of V-doping effects on Fe3Cr4C3 carbide in hypereutectic Fe–Cr–C hardfacing coating

The mechanical property improvement of M 7C3 carbides in hypereutectic Fe–Cr–C hardfacing coating is required for its widespread application and longer service life. Vanadium is a frequently used alloying element, while the effects of V doping on the stability and tensile properties of M 7C3 carbide have been rarely reported. In this article, the formation enthalpy, structural stability, anisotropic tensile properties and electronic structure of V-doped M 7C3 (Fe3Cr4C3) carbide were calculated by the first-principles method. The mechanism by which the tensile property of Fe3Cr4C3 carbide can be improved by V-atom doping is discussed. The results show that the formation enthalpy (−0.24 eV/atom) of Fe3Cr3VC3 carbide is lower than that (0.48 eV/atom) of Fe3Cr4C3 carbide, which indicates that the formation of Fe3Cr3VC3 carbide is more facile. The absence of an imaginary frequency in the phonon dispersion spectra reveals that the Fe3Cr3VC3 carbide model is stable. Compared with Fe3Cr4C3 carbide, the tensile strength of Fe3Cr3VC3 carbide in the (0001) crystal face is increased from 44.42 to 48.46 GPa and that in the (1111) crystal face is also increased, from 28.99 to 34.19 GPa. The reasons that the tensile property of Fe3Cr4C3 can be improved by V doping are the electron redistribution and the formation of stronger bonds in Fe3Cr3VC3 carbide.

Теория гетерогенного катализа. Теория хемосорбции

This monograph is a continuation of the monograph by V.V. Sadovnikov. Lateral interaction. Moscow 2006. Publishing house "Anta-Eco", 2006. ISBN 5-9730-0017-6. In this work, the foundations of the theory of heterogeneous catalysis and the theory of chemisorption are more easily formulated. The book consists of two parts, closely related to each other. These are the theoretical foundations of heterogeneous catalysis and chemisorption. In the theory of heterogeneous catalysis, an experiment is described in detail, which must be carried out in order to isolate the stages of a catalytic reaction, to find the stoichiometry of each of the stages. This experiment is based on the need to obtain the exact value of the specific surface area of the catalyst, the number of centers at which the reaction proceeds, and the output curves of each of the reaction products. The procedures for obtaining this data are described in detail. Equations are proposed and solved that allow calculating the kinetic parameters of the nonequilibrium stage and the thermodynamic parameters of the equilibrium stage. The description of the quantitative theory of chemisorption is based on the description of the motion of an atom along a crystal face. The axioms on which this mathematics should be based are formulated, the mathematical apparatus of the theory is written and the most detailed instructions on how to use it are presented. The first axiom: an atom, moving along the surface, is present only in places with minima of potential energy. The second axiom: the face of an atom is divided into cells, and the position of the atom on the surface of the face is set by one parameter: the cell number. The third axiom: the atom interacts with the surrounding material bodies only at the points of minimum potential energy. The fourth axiom: the solution of the equations is a map of the arrangement of atoms on the surface. The fifth axiom: quantitative equations are based on the concept of a statistically independent particle. The formation energies of these particles and their concentration are calculated by the developed program. The program based on these axioms allows you to simulate and calculate the interaction energies of atoms on any crystal face. The monograph is intended for students, post-graduate students and researchers studying work and working in petrochemistry and oil refining.

Photo-Irradiation Tunes Highly Active Sites over β-Ni(OH)2 Nanosheets for Electrocatalytic Oxygen Evolution Reaction

A facile photo-irradiation method is developed to tune active sites over β-Ni(OH)2 nanosheets. Photo-irradiated β-Ni(OH)2 nanosheets possess disordered surface atoms and preferred growth of highly active crystal face, which exhibits...

Crystal face dependent intrinsic wettability of metal oxide surfaces

Knowledge of intrinsic wettability at solid/liquid interfaces at the molecular level perspective is significant in understanding crucial progress in some fields, such as electrochemistry, molecular biology and earth science. It is generally believed that surface wettability is determined by the surface chemical component and surface topography. However, when taking molecular structures and interactions into consideration, many intriguing phenomena would enrich or even redress our understanding of surface wettability. From the perspective of interfacial water molecule structures, here, we discovered that the intrinsic wettability of crystal metal oxide is not only dependent on the chemical components but also critically dependent on the crystal faces. For example, the $( {1\bar{1}02} )$ crystal face of α-Al2O3 is intrinsically hydrophobic with a water contact angle near 90°, while another three crystal faces are intrinsically hydrophilic with water contact angles <65°. Based on surface energy analysis, it is found that the total surface energy, polar component and Lewis base portion of the hydrophobic crystal face are all smaller than the other three hydrophilic crystal faces indicating that they have different surface states. DFT simulation further revealed that the adsorbed interfacial water molecules on each crystal face hold various orientations. Herein, the third crucial factor for surface wettability from the perspective of the molecular level is presented, that is the orientations of adsorbed interfacial water molecules apart from the macro-level chemical component and surface topography. This study may serve as a source of inspiration for improving wetting theoretical models and designing controllable wettability at the molecular/atomic level.

First-principle study of electronic structure of montmorillonite at high pressure

The first-principle method was used to study the electronic structure of montmorillonite under high pressure. The calculated results show that the Si–O bond is more stable than the Al–O bond as the pressure was increased, while the H–O bond is almost independent of this variable. More importantly, band structure of montmorillonite changes from indirect bandgap to direct bandgap and vice-versa at 33.2 GPa and 39.2 GPa, respectively. Furthermore, density of state split phenomenon appeared in conduction band region. By calculating the montmorillonite elasticity constants under different levels of stress, the results show that C33 and C66 perpendicular to the crystal face are greatly affected by the stress. Moreover, C44 with the minimum changes during the entire stress process. The calculated results will not only help to understand the electronic structure of montmorillonite under pressure, but also provide theoretical guidance for deal with the safe problems of tunnel engineering.

Reconsidering XPS Quantification of Substitution Levels of Monolayers on Unoxidized Silicon Surfaces

In this preprint, we reevaluate the use of X-ray photoelectron spectroscopy (XPS) to determine substitution levels of reactions on non-oxidized silicon surfaces. XPS is the most commonly used method to determine the yields of reactions on surfaces. We go back to the most basic assumptions, and work through the calculations to provide a revised set of calculations that take into account (i) possible adventitious hydrocarbon contamination, (ii) the effect of choosing a different silicon crystal face [Si(100) versus Si(111)], and (iii) the utility of choosing a small heteroatom tag to enable a more accurate measure of substitution levels. We provide a simple algorithm and summary of the equations one can use to make it easy for the reader/researcher.

Reconsidering XPS Quantification of Substitution Levels of Monolayers on Unoxidized Silicon Surfaces

In this preprint, we reevaluate the use of X-ray photoelectron spectroscopy (XPS) to determine substitution levels of reactions on non-oxidized silicon surfaces. XPS is the most commonly used method to determine the yields of reactions on surfaces. We go back to the most basic assumptions, and work through the calculations to provide a revised set of calculations that take into account (i) possible adventitious hydrocarbon contamination, (ii) the effect of choosing a different silicon crystal face [Si(100) versus Si(111)], and (iii) the utility of choosing a small heteroatom tag to enable a more accurate measure of substitution levels. We provide a simple algorithm and summary of the equations one can use to make it easy for the reader/researcher.