Theoretical Insights into Effect of Surface Composition of Pt-Ru Bimetallic Catalysts on CH3OH Oxidation: Mechanistic Considerations

A deeper mechanistic understanding on CH3OH oxidation on Pt-Ru alloys with different Ru surface compositions is provided by DFT-based theoretical studies in this paper. The present results show that alloying and surface compositions of Ru can change CH3OH oxidation pathway and activity. The optimal surface composition of Ru is speculated to be ca. 50% since the higher Ru surface composition can lead to formation of carbonaceous species that can poison surface. Our present calculated Ru surface composition of ca. 50% exhibits excellent consistency with experimental studies. The origin of enhanced catalytic activity of Pt-Ru alloys is determined. The significantly decreased surface work functions after alloying suggest more electrons are transferred into adsorbates. The calculated lower electrode potentials after alloying imply that lower overpotentials are required for CH3OH oxidation. The excellent inconsistency with experimental study on decreased onset potentials after alloying further confirms accuracy of our present calculated results.

A First-Principles Study of Gas Molecule Adsorption on Carbon-, Nitrogen-, and Oxygen-Doped Two-Dimensional Borophene

A first-principles study was performed to investigate the adsorption properties of gas molecules (CO, CO2, NO, and NO2) on carbon- (C-), nitrogen- (N-), and oxygen-doped (O) borophene. The adsorption energies, adsorption configurations, Mulliken charge population, surface work functions, and density of states (DOS) of the most stable doped borophene/gas-molecule configurations were calculated, and the interaction mechanisms between the gas molecules and the doped borophene were further analyzed. The results indicated that most of the gas molecules exhibited strong chemisorption at the VB site (the center of valley bottom B–B bond) of the doped borophene (compared to pristine borophene). Electronic property analysis of the C-doped borophene/CO2 and the NO2 adsorption system revealed that there were numerous charge transfers from the C-doped borophene to the CO2 and NO2 molecules. This indicated that C-doped borophene was an electron donor, and the CO2 and NO2 molecules served as electron acceptors. In contrast to variations in the adsorption energies, electronic properties, and surface work functions of the different gas, C-, N-, and O-doped borophene adsorption systems, we concluded that the C-, N-, and O-doped borophene materials will improve the sensitivity of CO, CO2, and NO2 molecule; this improvement of adsorption properties indicated that C-, N-, and O-doped borophene materials are excellent candidates for surface work functions transistor to detect gas molecules.

INVESTIGATION OF THE PROCESS OF RESTORATION OF DAMAGED PIPELINE SURFACES BY THE METHOD OF SURFACE RIVETING

Представлены результаты экспериментальных исследований процесса восстановления поврежденных поверхностей трубопроводов различных диаметров методом поверхностного наклепа, реализующего явление поверхностного пластического деформирования, приводящее к изменению распределения напряжений по толщине, выполнено обоснование оптимальных режимов его проведения . При этом было осуществлено численное моделирование процесса накатки, определены оптимальные значения следующих параметров: глубины и силы ППД, скорости ППД, подачи ролика, формы рабочей поверхности используемого ролика. При анализе были учтены следующие физико-механические характеристики: глубина наклепа, величина остаточных напряжений, глубина распределения остаточных напряжений, время обкатки, нагрузка на ролик. Доказано очевидное преимущество роликов большего радиуса профиля - они позволяют обеспечить необходимое изменение шероховатости обрабатываемой поверхности при обкатке с большей подачей, что приводит к снижению времени технологического процесса. При этом в принятом диапазоне параметров режимов обкатки (нагрузка 2500÷3000Н, глубина вдавливания 0.04÷0.06мм) величины компонентов остаточных напряжений оказались практически идентичными для исследованных режимов всех рассмотренных роликов. Полученные результаты были положены в основу технологии восстановительного ремонта трубопроводов различного диаметра без остановки производственного процесса на Нововоронежской АЭС и создана промышленная установка с числовым программным управлением для реализации данной технологии Here we present the results of experimental studies of the process of restoration of damaged surfaces of pipelines of various diameters by the method of surface work hardening, which implements the phenomenon of surface plastic deformation, leading to a change in the distribution of stresses along the thickness. At the same time, we carried out a numerical simulation of the knurling process, we determined the optimal values of the following parameters: the depth and strength of the SPD, the speed of the SPD, the feed of the roller, the shape of the working surface of the roller used. The analysis took into account the following physical and mechanical characteristics: work hardening depth, residual stress value, residual stress distribution depth, running time, roller load. We proved the obvious advantage of rollers with a larger profile radius - they allow one to provide the necessary change in the roughness of the machined surface during rolling with a higher feed, which leads to a decrease in the time of the technological process. In this case, in the accepted range of parameters of the running modes (load 2500-3000N, indentation depth 0.04-0.06 mm), the values of the residual stress components turned out to be almost identical for the considered modes for all the considered rollers. We used the results as the basis for the technology of restorative repair of pipelines of various diameters without stopping the production process at the Novovoronezh NPP and an industrial unit with numerical control was created to implement this technology

Novel Permanent Magnetic Surface Work Hardening Process for 60/40 Brass

Surface work hardening is a process of deforming a material surface using a thin layer. It hardens and strengthens the surface while keeping the core relatively soft and ductile to absorb stresses. This study introduces a permanent magnate surface work hardening under two opposite permanent poles of a magnet to investigate its influence on a brass surface. The gap between the brass and the north magnet pole—fixed in the spindle of a vertical machine—was filled with martensitic stainless steel balls. The rotational speed and feed rates were 500–1250 rpm and 6–14 mm min−1, respectively. The novel method improved the surface hardness for all parameters by up to 112%, in favor of high speed, and also increased yield by approximately 10% compared to ground samples. Surface roughness showed higher values for all speed–feed rate combinations compared to the ground sample. Nevertheless, it showed better roughness than other treated conditions with high and low feed rates. The ultimate tensile strength and ductility remained unchanged for all conditions other than the untreated brass. A factorial design and nonlinear regression analysis were performed to predict the microhardness equation and effectiveness of the independent variable—speed and feed rate—for the proposed process.

Effects of Sequential Operation with Heat Treatment and Mechanical Milling on Work Hardening for Superalloy GH4169

Engineering components are usually manufactured with sequential production processes. Work hardening due to previous production processes affects the machinability of the workpiece in subsequent operations. In this research, the surface work hardening of a workpiece manufactured by two sequential processes with heat treatment/milling (HT + M) and milling/heat treatment (M + HT) of superalloy GH4169 was investigated. First, the surface microstructure characteristics, including plastic deformation and grain size of the machined workpiece surface processed by the two sequential processes, were quantitatively presented. Then, the microhardness on the machined workpiece surface and its cross-section was measured and analyzed. Finally, a surface microhardness calculation model considering twin boundary deformation was proposed. Here, we also present the microstructure evolution principle of the machined workpiece surface by the two sequential processes. It was found that the degree of work hardening of HT + M machining was 179%, whereas that of M + HT was only 101%. The research results can be applied to the optimized selection of process sequence for manufacturing superalloy GH4169.

First Principle Research on Ga Rich GaAs0.5P0.5(001) β2(4×2) and As(P) rich β2(2×4) Reconstruction Surfaces With and Without Cs Adsorption

Based on first principle calculations, Ga rich and As(P) rich clean GaAs0.5P0.5(001) reconstruction surfaces and adsorbed surfaces with 0.125ML coverage of Cs at different sites are researched. Formation energy of Ga rich GaAs0.5P0.5(001) β2(4×2) reconstruction surface is smaller than that of As(P) rich one, and the work functions of Ga rich β 2 (4×2) and As(P) rich β2(2×4) surfaces are 4.657 eV and 5.187 eV, respectively. The adsorption energies of Cs adatoms on both surfaces are negative, showing that Cs adsorption is a stable exothermic process. The work functions of two surfaces both decrease after Cs adsorption, and the average variation of As(P) rich β2(2×4) surface is larger. Mulliken charge analysis shows that Cs adatoms transfer electrons to GaAsP substrate, resulting in Cs-GaAsP dioples which lower the work functions. When Cs atoms are located at D 2 of Ga rich surface and D 2 ' of As(P) rich surface, work function values of the two reconstruction surfaces reach the minimums, which are 2.834eV and 2.859eV, respectively. By calculating dipole moments, it can be found that Cs adatoms on the topmost layer form larger effective dipole moments with GaAsP substrate than the Cs atoms located in the trench.