Carbide Surface Research Articles

Adsorption behaviour of metronidazole drug molecule on the surface of hydrogenated graphene, boron nitride and boron carbide nanosheets in gaseous and aqueous medium: A comparative DFT and QTAIM insight

In this present study, we have theoretically scrutinized the interaction mechanism of Metronidazole drug on the surface of graphene, boron carbide and boron nitride nanosheets in gas and aqueous phase applying density functional theory with B3LYP/6-31G method to sort a path for minimizing the adverse effects of this drug on the human and animal body. The maximum adsorption energy (A.E) value is −44.50 kj/mol which indicates the adsorption of all complexes is physisorption type and our complexes benefit from the short recovery time. Weak electrostatic nature of the interaction is also revealed by the QTAIM study. The reduction of E g for the adsorption of ML on BN sheet is the highest (up to 55%) indicating the highest sensitivity while the sensitivity trend is σ (BN) > σ (GNS) > σ (BC3). The UV–Vis spectra investigation also validates this sensitivity trend. The dipole moment and A.E data in case of the solvent effect upon the complexes claim the favourable adsorption process in aqueous medium. Consequently, this comparative study reveals the ability of BN nanosheet to sense ML drug is higher than that of GNS and BC3, which will help to protect human and wildlife from the side effect of this drug. Adsorption and desorption process of metronidazole drug with nanosheets. • The sensitivity of BN nanosheet towards metronidazole (ML) drug is highest due to the reduction of HOMO-LUMO gap up to 55%. • The energetic parameters show the spontaneous, exothermic physisorption of ML on the surface of GNS, BC3 and BN nanosheets. • The changes of adsorption energy and dipole moment in water media specify the good adsorption of ML in the human body. • The adsorbent (nanosheets) and adsorbate (ML) acts as donor and acceptor respectively. • The reactivity of the nanosheets increases due to the adsorption of ML drug molecule.

Formation of Iron Silicides Under Graphene Grown on the Silicon Carbide Surface

The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive intercalation of iron and silicon atoms into the graphene. Experiments are carried out in situ in ultrahigh vacuum. The elemental composition and chemical state of the surface of prepared samples and their atomic structure are determined by low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy using synchrotron radiation. The thickness of deposited iron and silicon layers varies in the range of 0.1–2 nm, and the sample annealing temperature is varied from room temperature to 600°C. We show that intercalation of silicon into the graphene/Fe/SiC system leads to the formation of a layer of Fe–Si solid solution coated with the surface silicide Fe3Si. The films are effectively protected by graphene from exposure to ambient environment, which opens possibilities for their practical application.

One step co-sintering of silicon carbide ceramic membrane with the aid of boron carbide

To reduce the sintering cycles and shorten the preparation periods of silicon carbide membrane, we report a fabrication route for silicon carbide membrane by co-sintering process with the aid of boron carbide. In this process, the SiC selective layer was coated on the SiC- B4C green substrate with spray method followed by sintering at 1900 ℃. With the increase of B4C content from 7 to 13 wt.%, the grain size and pore size of the substrate decreased, ascribing to the interface reaction between boron carbide and silica film on the silicon carbide surface. A straight and homogeneous selective layer formed on the substrate, presenting average thickness of 30 μm and average pore size of 0.28 μm. Thus, this technique is considered as a cost-effective and short-period method for the preparation of silicon carbide membrane.

Stress, strain and strain-rate cemented carbide properties determined with a fem-supported evaluation of impact test imprints

Cemented carbide materials are key in tool manufacturing, nowadays widely used in cutting, forming and other manufacturing processes. Commonly applied methods for obtaining their strain-rate dependent material properties are insufficient due to the high hardness, mechanical strength and low deformability. In this paper, we produce relevant data for stress-strain and strain-rate curves up to strain rates of approximately 200 s−1 with the aid of a developed FEM-supported evaluation method for remaining imprints on cemented carbide surfaces after applying impact loads at various durations and magnitudes. Regarding the impact duration, the impact loads were dynamically generated via electromagnetic or piezoelectric devices. The attained data are relevant to several applications including calculations to determine the stress and strain fields developed in cemented carbide tools imposed by impact loads at various conditions.

Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.

Thermal Effect of Surface Catalysis in Subsonic Dissociated-Air Jets. Experiment on a High-Frequency Plasmatron and Numerical Modeling

Experiments on heat transfer in subsonic dissociated-air jets are performed on 100 kW VGU-4 induction plasmatron. The heat fluxes to the water-cooled surfaces of copper, silver, tantalum, beryllium, niobium, gold, molybdenum, and quartz are measured at the stagnation point on a cylindrical flat-nosed model, 50 mm in diameter, having rounded edges at 50 and 100 hPa pressures in the low-pressure chamber and the high-frequency (HF) generator power of 30 to 70 kW. At the same pressures and the HF generator powers of 45 and 64 kW the convective heating of a specimen of sintered silicon carbide is studied in the surface temperature range from 1720 to 1910 K. The predominance of the surface catalyticity effect on the heat flux with respect to nitrogen and oxygen atom recombination is demonstrated. Under the experimental conditions the air plasma flow in the discharge channel of the plasmatron, the subsonic jet flow past the cylindrical model, and the heat transfer to the stagnation point on the model are numerically simulated. Basing on the comparison of the experimental and calculated data on the heat fluxes to the surfaces of metals (Tw = 300 K), quartz (Tw = 572–722 K), and silicon carbide (Tw = 1720–1910 K) the quantitative catalyticity gradation of the materials considered with respect to heterogeneous recombination of nitrogen and oxygen atoms is established.

Performance Characteristics of Carbide Coatings Obtained by High-Speed Gas-Flame Spraying

In this paper, we study the properties of carbide coatings based on the WC–Co–Cr system which determine their operational reliability. The relationship of the porosity, hardness, and wear resistance indicators is analyzed, and their effect on the corrosion resistance and adhesion of the coating to the steel base is evaluated. The effect of coating porosity on wear resistance under conditions of friction on a loose abrasive is considered. On the basis of the results, additions to the list of controlled coating parameters, which can be used in regulatory documents establishing the order and frequency of quality control of products with a carbide surface layer deposited by high-speed gas-flame spraying, are proposed.

Production and characterization of Al6061/zirconium carbide surface composites

Abstract In the present study, Al6061/zirconium carbide surface composites have been developed using the friction stir processing method. The volume fraction of the zirconium carbide particles was varied as 3%, 6% and 9%. The developed composites were characterized using optical microscopy, X-ray diffraction and scanning electron microscopy. Micrographs revealed uniform distribution of zirconium carbide particles, and addition of zirconium carbide particles was found to improve hardness and tensile properties of Al6061 alloy. Corresponding strengthening mechanisms have been discussed and associated with the microstructural studies. Fractographic analysis was found to show a reduction in ductility with increase in addition of zirconium carbide particles.

CO2 methanation over alumina-supported cobalt oxide and carbide synthesized by reverse microemulsion method

High surface area alumina-supported cobalt oxides and carbides were synthesized using a one-pot reverse microemulsion method (followed by carburization for carbides). Two reverse microemulsion synthesis variations gave fine powders having specific surface areas ranging from 178−272 m2/g, consisting of cobalt oxide or cobalt carbide nanoparticles (5−10 nm) dispersed on γ-alumina (10−13 wt% cobalt loadings). The resulted materials were tested for CO2 hydrogenation. Although all materials (two oxides and two carbides) were catalytically active, only cobalt carbides showed high selectivity to CH4 formation (up to 99 %), while also being significantly more active and stable than corresponding cobalt oxides (up to 89 % CO2 conversion for carbides). Investigation by in situ FTIR has shown significant differences in the reaction intermediates indicating different reaction mechanisms of CO2 hydrogenation on cobalt oxide and cobalt carbide surfaces.

Development of AA 5083 based hybrid surface composites via friction stir processing

The demand for advanced materials with low density and high strength is always present in areas like aerospace, automotive, and military applications. Aluminum based hybrid composites are the new generation group of materials that have the prospective to satisfy the above need. In the present work, an attempt was made to develop AA 5083 reinforced with silicon carbide and titanium oxide surface composites. Number of passes, revolving speed, and welding speed were the process parameters considered and varied in three levels. Ultimate tensile strength was measured and modeling equation was developed by response surface methodology and suitability of the equation was checked by ANOVA. The model was best to predict the ultimate tensile strength of the processed workpiece and it was observed that number of passes was the dominating parameter followed by revolving speed. The ultimate tensile strength of the processed workpiece was 237Mpa with an increase of nearly 50%.

Near Fermi level electronic structure of Ti3SiC2 revealed by angle-resolved photoemission spectroscopy

An in-depth study of the Fermi surface and electronic structure of the ternary nanolamellar carbide ${\mathrm{Ti}}_{3}\mathrm{Si}{\mathrm{C}}_{2}$ is reported. The outputs of angle-resolved photoemission spectroscopy (ARPES) measured on single crystals and density functional theory calculations are systematically compared. The band structure is found to be dominated by Ti $d$ orbitals near the Fermi level. Band inversions near K points are responsible for the intricate shape of the ${\mathrm{Ti}}_{3}\mathrm{Si}{\mathrm{C}}_{2}$ pockets. Previous theory found that those pockets were giving opposite contributions leading to zero thermoelectric power in polycrystalline samples. Here we directly visualize them by ARPES, describe their precise shape, and examine the way they should behave regarding thermoelectric power. The presence of linear band crossings and the effect of spin-orbit coupling on the near Fermi level electronic structure are discussed, as well as potential consequences for magnetotransport and spin Hall effect.

Effect of Two Dental Restorative Materials on Adhesion and Molecular Structure of Oral Bacteria

Dental restorative materials are widely used to repair teeth and dentition defects. However, the dental restorative materials tend to react with oral bacteria when they are exposed to oral conditions, which leads to a change in the oral microecology. Herein, we have employed molecular dynamics simulations to investigate the interaction between different dental restorative materials and oral bacteria. It was found that the staphylococcal protein A (SPA) is more likely to attach on the surface of silicon carbide (SiC) substrate than hematite (Fe₂O₃) substrate surface. Furthermore, the tightly adhesion and accumulation of SPA on SiC surface changes the molecular structure of SPA, which will induce a change in the oral microecology. This study has demonstrated that the adhesion and molecular structure of oral bacteria is strongly dependent on dental restorative materials by molecular dynamics simulations, and Fe₂O₃ is more suitable to be a dental restorative material. It is therefore believed that molecular dynamics simulations can be used to further screen suitable materials for oral rehabilitation.

Recognition of dislocation structure of silicon carbide epitaxial layers by а neural network

Technological features of the growth of single crystal silicon carbide inevitably create condi-tions for the formation of crystal structure defects in them. A method is proposed for recognizing and analyzing a dislocation structure of single crystal silicon carbide based on the use of optical microscopy and a direct distribution neural network. The method was tested on homoepitaxial lay-ers of 4H-polytype silicon carbide. Software has been developed that allows building maps of the dislocation structure distribution over the surface of single crystal silicon carbide. The software was tested on digital images of the surface of silicon carbide epitaxial layers. The accuracy of recognition of dislocation structure was 95%. The dislocation mapping is used in the development of process technologies for reducing their density during the growth of single crystals.

Production and characterization of Al6061/zirconium carbide surface composites

Abstract In the present study, Al6061/zirconium carbide surface composites have been developed using the friction stir processing method. The volume fraction of the zirconium carbide particles was varied as 3%, 6% and 9%. The developed composites were characterized using optical microscopy, X-ray diffraction and scanning electron microscopy. Micrographs revealed uniform distribution of zirconium carbide particles, and addition of zirconium carbide particles was found to improve hardness and tensile properties of Al6061 alloy. Corresponding strengthening mechanisms have been discussed and associated with the microstructural studies. Fractographic analysis was found to show a reduction in ductility with increase in addition of zirconium carbide particles.

Insights into the regulation of FeNa catalysts modified by Mn promoter and their tuning effect on the hydrogenation of CO2 to light olefins

This study unravels the effect of Mn promoter on the surface enrichment and competition of promoters and the evolutions of the chemical and structural of Fe species during the reaction, and illustrates the regulation of FeMn and FexCy for CO2 conversion and hydrogenation of intermediates. With the contents of Mn promoter increasing from 0.5% to 10.0%, the selectivity of light olefins decreasing from 38.73% to 30.58% and the ratio of olefin to paraffin decreases from 4.97 to 3.56. The surface ratio of Mn/Fe and Na/Fe is much higher than the impregnation ratio, which confirms the surface enrichment of Mn and Na promoters. It turns out that the iron oxides are transformed into iron carbides in the bulks and oligomeric FexOy on the surface after reaction. The enrichment of Mn promoters leads to more surface Fe species near the Mn promoters for the strong adsorption of CO2 and decreases the surface actual density of FexCy sites for the hydrogenation of CO to hydrocarbons, which consequently decreases the conversion of CO2 and the FTY value. The increasing content of Mn promoters from 0.5% to 3.0% also increases the adsorption ability of H2 on the surface of iron carbides, which is possibly associated with the hydrogenation of intermediates and leading to decreasing of the ratio of olefins to paraffins ranging from C2-C4.

Mechanism of the scratching of monocrystalline silicon carbide with a diamond grit at different wear stages

An investigation was conducted to explore the mechanisms of the scratching of monocrystalline silicon carbide with a single diamond grit. The scratching was repeated on a silicon carbide workpiece to generate different wear shapes of the diamond grit. The forces were recorded during each scratching and the wear of the diamond grit together with the silicon carbide morphologies was monitored at a fixed interval. Based on the different diamond wear shapes determined through scratching experiments, a smoothed particle hydrodynamics method was used to simulate the scratching process. In addition to the items monitored in the experiments, the simulation was also used to analyze the change of subsurface damages on silicon carbide and to predict the mechanisms of diamond damage. It is shown that double-edged abrasive grits might lead to a better silicon carbide surface quality in scratching. The simulation results indicate that the maximum equivalent stress distribution might be used to predict the damage of the diamond grits during scratching. The findings of this article will be of benefit to the optimal selection of machining parameters and the optimal design of diamond tools for abrasive machining of monocrystalline silicon carbide.

Low Temperature Activation of Methane on Metal-Oxides and Complex Interfaces: Insights from Surface Science.

ConspectusThe abundance of cheap, natural gas has transformed the energy landscape, whereby revealing new possibilities for sustainable chemical technologies or impacting those that have relied on traditional fossil fuels. The primary component, methane, is underutilized and wastefully exhausted, leading to anthropogenic global warming. Historically, the manipulation of methane remained "clavis aurea," an insurmountable yet rewarding challenge and thus the focus of intense research. This is primarily due to an inability to dissociate C-H bonds in methane selectively, which requires a high energy penalty and is an essential prerequisite for the direct conversion of methane into a large set of value-added products. The discovery of such processes would promise an energy gainful use of natural gas benefiting several essential chemical processes associated with C1 chemistry. This first C-H bond dissociation step of the methane molecule appears in numerous catalytic mechanisms as the rate-determining step or most essential barrier sequence for all subsequent steps that follow in the production of C-C, C-O, or Cx-Hy-Oz bonds found in value added products. A main goal is to catalytically reduce the energy barrier for the first C-H bond dissociation to be able to achieve the activation of methane at low or moderate temperatures. As such there is great value in understanding the fundamental nature of the active sites responsible for bond breaking or formation and thus be able to facilitate better control of this chemistry, leading to the development of new technologies for fuel production and chemical conversion. Surface science studies offer enhanced perspectives for a careful manipulation of bonds over the last layer atoms of catalyst surfaces, an essential factor for the design of atomically precise catalysts and unravelling of the reaction mechanism. With the advent of new surface imaging, spectroscopy, and in situ tools, it has been possible to decipher the surface chemistry of complex materials systems and further our understanding of atomic active sites on the surfaces of metals, oxides, and carbides or metal-oxide and metal-carbide interfaces. The once considered near impossible step of C-H bond activation is now observed at low temperatures with high propensity over a collection of oxide, metal-oxide, and metal-carbide systems in a conventional or inverse configuration (oxide or carbide on metal). The enabling of C-H activation at low temperature has opened interesting possibilities for the specific production of chemicals such as methanol directly from methane, a step toward facile synthesis of liquid fuels. We highlight the most recent of these results and present the key aspects of active site configurations engineered from surface science studies which enable such a simple reactive event through careful manipulation of the last surface layer of atoms found in the catalyst structure. New concepts which help in the activation and conversion of methane are discussed.

Influence of pulse-plasma modification of VK10KS solid alloy surface by titanium and boron on its structure and properties

Modification of the surface of VK10KS solid alloy with titanium alongside with boron by the method of pulse-plasma exposure (electro-explosive alloying) is considered. In this case, a superhard (27,500 MPa nanohardness) layer is formed with a thickness of 2.0 – 2.5 μm and a low (μ = 0.10) friction coefficient compared to the friction coefficient of a hard alloy in the sintered state (μ = 0.41). This layer consists of finely dispersed high-hard phases TiB2, (Ti, W)C, W2C (according to scanning, transmission electron microscopy and X-ray phase analysis). Below is a hardened (with a nanohardness of 17,000 MPa) surface layer (heat affected zone) 10 – 15 μm thick, identified by W2C and WC carbides and alloyed with a cobalt binder. This layer smoothly passes into the base. By profilometric studies it was established that after electroexplosive alloying with titanium and boron, the roughness increases (Ra = 2.00 μm) compared to the initial one (Ra = 1.32 μm), but remains within the specifications (Ra = 2.50 μm). The authors have revealed changes that occur in the surface carbide and near-surface cobalt phases during electroexplosive alloying. In the carbide phase, accumulations of dislocations were indicated. In the cobalt binder, deformation bands (slip bands), single dislocations, and also finely dispersed tungsten carbide precipitates were found. This change can be explained by stabilization of the cubic modification of cobalt, the crystal lattice of which has a large number of slip planes during deformation and a greater ability to harden compared to the hexagonal modification of cobalt. Additional alloying with a cobalt binder will positively affect the operational stability of tungsten carbide alloys as a whole due to their stabilization.

Modification of the WC-Co carbide surface with high-intensity pulsed ion beam

The paper presents the results of WC-Co surface modification with high-intensity pulsed ion beams at high energy density 7-8 J/cm2 per one pulse. One, five and ten pulses regimes of irradiation have been studied using scanning electron microscopy of both the surface morphology and cross-section, X-ray diffraction analysis and a nano-hardness tester. Beam irradiation with high energy density resulted in phase transformation from hexagonal α-WC to cubic ß-WC1-x. XRD analysis shows that the volume content of new formed cubic phase in the modified layer is ~ 97%.

Predicting the Effect of Dopants on CO2 Adsorption in Transition Metal Carbides: Case Study on TiC (001)

A previous work has shown that doping the TiC (001) surface with early transition metals significantly affects CO2 adsorption and activation, which opens up a possible way to control this interesting chemistry. In this work, we explore other possibilities, which include nontransition metal elements (Mg, Ca, Sr., Al, Ga, In, Si, and Sn) as well as late transition metals (Pd, Pt, Rh, and Ir) and lanthanides (La and Ce), often used in catalysis. Using periodic slab models with large supercells and state-of-the-art density functional theory (DFT) based calculations, we show that, in all the studied cases, CO2 appears as bent and, hence, activated. However, the effect is especially pronounced for dopants with large ionic crystal radii. This can increase desorption temperature by up to 230 K, almost twice the value predicted when early transition metals are used as dopants. However, a detailed analysis of the results shows that the main effect does not come from the electronic structure perturbations but from the distortion that the dopant generates into the surface atomic structure. A simple descriptor is proposed that would allow predicting the effect of the dopant on CO2 adsorption energy in transition metal carbide surfaces without the need for DFT calculations.