Graphite Substrate Research Articles

A study for hydrogen evolution on Pt–MnCu electrocatalyst

Electrocatalysts to be used in electrolysis, which is one of the hydrogen production methods, are very important. The development of electrocatalysts is related to the internal structure of combinated more than one metal. In the present work, the graphite substrate is coated with manganez (C/Mn), manganez-copper (C/MnCu) and this surface is modified with platinum nanoparticles (C/MnCu–Pt) using the electrodeposition method. Prepared electrocatalysts are used for characterization, hydrogen evolution reaction (HER) and stability using cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), cathodic current-potential curves, electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). Hydrogen gas is measured in a basic environment by establishing an experimental electrolysis setup on these electrocatalysts. Results showed that binary MnCu enhances the characteristic current density of Tafel curves, reduces the polarization resistance and enhances the hydrogen gas volume compared to graphite substrate and single Mn coating. Apart from that, much more effective results are obtained on the C/MnCu–Pt electrocatalyst. Namely, a very high exchange current density (io = 5.50 mA cm−2), a very low polarization resistance (3.2 Ω cm2) and a very low overpotential (50 mV) at 10 mA cm−2 are obtained on the C/MnCu–Pt electrocatalyst. In addition to high performance, C/MnCu–Pt electrocatalyst exhibits good stability in alkaline medium.

Sensitive determination of rare earth elements in liquid samples by spatial confinement assisted surface enhanced laser-induced breakdown spectroscopy

The rapid determination of rare earth elements (REEs) in liquid samples holds significant importance for various applications such as the exploration and development of REEs resources, quality control of the extraction process, regeneration and recycling of REEs, and monitoring of nuclear industry wastewater. This study employed spatial confinement assisted surface-enhanced laser-induced breakdown spectroscopy (SC-SE-LIBS) for REEs determination in liquid samples. Investigations were conducted into the impact of different material substrates, sample pretreatment methods, and spatial confinement cavity diameters on detection performance. The results reveal that the graphite substrate yields superior spectral signal intensity compared to other materials (Zn, Al, and Ni). The groove-constrained liquid–solid conversion (GCLSC) pretreatment method significantly enhances spectral stability and detection accuracy. The most favorable signal enhancement is achieved using a cylindrical spatial confinement cavity (CSCC) with an 8 mm diameter. Employing the optimized experimental conditions, quantitative analysis of six REEs (La, Ce, Pr, Nd, Gd, Y) in liquid samples was performed using analytical lines at wavelengths of La Ⅱ 394.91 nm, Ce Ⅱ 401.24 nm, Gd Ⅱ 404.99 nm, Nd Ⅱ 406.11 nm, Pr Ⅱ 417.94 nm, and Y Ⅱ 488.37 nm. The obtained calibration curves exhibited R2 fit coefficients above 0.99, with corresponding limits of detection (LoDs) of 0.021 μg/mL, 0.104 μg/mL, 0.312 μg/mL, 0.241 μg/mL, 0.036 μg/mL, and 0.045 μg/mL, respectively.

Polynomial-chaos-based conditional statistics for probabilistic learning with heterogeneous data applied to atomic collisions of Helium on graphite substrate

A formulation and an algorithm are presented to construct a truncated polynomial chaos representation of a vector-valued random output. This representation depends on a vector-valued random input with a known probability measure and a vector-valued random latent variable with an unknown probability measure. The construction of this PCE representation relies solely on a training set comprising a small number of independent realizations of the non-Gaussian dependent random output and input vectors. The training set consists of heterogeneous data, which poses challenges in accurately estimating the chaos coefficients. Despite the heterogeneity of the data, the proposed formulation and algorithm allow for the construction of a highly accurate global surrogate model. Additionally, we propose an alternative approach by constructing a surrogate model based on prior separation of the heterogeneous dataset into subsets, each containing “quasi-homogeneous” data. The separation method is designed to account for a partial overlap of the probability measure supports associated with the subsets. The identification of the PCE is performed offline. By utilizing the PCE, a fast online surrogate model is obtained, enabling analysis of large dynamical systems beyond the computational capabilities currently available. An application to atomic collisions of Helium on a graphite substrate is presented, where the training set was generated by Molecular Dynamics simulations done in a previous paper. The obtained results demonstrate accuracy of the proposed approach.

A molecular dynamics investigation on CO2–H2O–CH4 surface tension and CO2–CH4–H2O–graphite sheet contact angles

Introduction: We perform molecular dynamics (MD) simulations of nanoscopic liquid water drops on a graphite substrate mimicking the carbon-rich pore surface in the presence of CH4/CO2 mixtures at temperatures in the range 300 K–473 K.Methods: The surface tension in MD simulation is calculated via virial expression, and the water droplet contact angle is obtained through a cylindric binning procedure.Results: Our results for the interfacial tension between water and methane as a function of pressure and for the interfacial tension between water and CH4/CO2 mixtures as a function of their composition agree well with the experimental and computational literature.Discussion: The modified Young’s equation has been proven to bridge the macroscopic contact angle and microscopic contact with the experimental literature. The water droplet on both the artificially textured surface and randomly generated surface exhibits a transition between the Wenzel and Cassie–Baxter states with increased roughness height, indicating that surface roughness enhances the hydrophobicity of the solid surface.

Oxidation protection performance of ZrB2-LaB6 modified SiC coating at 1700 ℃

In response to the problem of high-temperature oxidation and volatilization of SiC coatings on carbon materials at 1700 ℃, this paper proposes to prepare ZrB2-LaB6 modified SiC coatings on graphite substrate surface by spark plasma sintering. The oxidation protection performance of five different ZrB2-LaB6-SiC coatings with different ratios of ZrB2 and LaB6 was tested at 1700 ℃ isothermal environment and thermal shock environment. The results showed that the oxidation protection efficiency of the coated samples with LaB6 content of 0, 3, 5, 8 and 10 wt% after oxidation for 100 min at 1700 ℃ was 96.6%, 98.0%, 96.9%, 96.4% and 95.5%, respectively. The coating with 3 wt% LaB6 had the best oxidation protection effect with the coating still maintaining its integrity and high oxidation protection efficiency after 20 thermal shock cycles with an overall oxidation protection efficiency after thermal cycling of 97.7%.

Synthesis and application of dual‐layer metal‐organic framework as a fiber coating based on copper‐based metal‐organic framework @ zeolitic imidazolate framework‐8 for solid‐phase microextraction of some selected parabens and their quantification using high performance liquid chromatography

AbstractHerein, the zeolitic imidazolate framework‐8 template was accommodated onto the surface of a pencil graphite substrate through the electrodeposition system. Then, Zn in the zeolitic imidazolate framework‐8 was replaced with Cu atoms via the galvanic replacement procedure. The modified template was used for the synthesis of another metal‐organic framework (copper‐benzene di carboxylic acid) by a solvothermal method. The prepared fiber was characterized by field emission‐scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction technique. Then, it was employed for direct immersion solid‐phase microextraction of methyl, ethyl, and butyl parabens. Various factors, such as the pH of the sample solution, stirring rate, desorption volume, the concentration of salt, extraction time, and desorption time, were selected and optimized. Under the optimized condition (extraction time = 30 min, desorption time = 2 min, desorption volume = 200 μL, salt concentration = 0% w/v, sample solution pH = 3.0, and stirring rate = 700 rpm), the linearity of the method was in the range of 1–200 μg/L (r2 > 0.9926). The limits of detection and quantification fall between 0.28–0.65 μg/L and 0.91–1.98 μg/L, respectively. The analysis of selected parabens in toothpaste and hand and face lotion, were also done using the suggested methodology.

The electrochemical kinetics of chloride oxidation over multi-metallic Pt-Ni-Co electrodes affected by metal deposition method and electrode support

Platinum, nickel, and cobalt oxides were coated on different electrode supports (graphite, stainless steel mesh, Ti foil and Ni form) by multistep electrode deposition method. Scanning electron microscopy, X-Ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry and linear sweep voltammetry were used to characterize electrodes. Results showed that the deposition process, such as applied current and deposition time, and the substrates influenced electrode morphology and electrochemical chlorine generation capability. Porous structure and Co3O4 crystalline could promote chloride oxidation on electrode surface. Graphite substrate exhibited the benefit of chloride oxidation and 0.6A × 20 s× 30 is the optimal deposition condition for electrode fabrication. The 0.6A × 20 s× 30-G electrode has the lowest chlorine evolution potential, largest difference in water oxidation and chloride oxidation potential, and the smallest transfer coefficient (α), meaning that this electrode is more favorable to chloride oxidation than other electrodes. Moreover, a mechanism of chlorine generation has been proposed in this study, indicating that chlorine radicals were formed on electrode surface. The high chlorine generation capability and good durability of Pt-Ni-Co-G electrode has the potential for application in water treatment process, such as disinfection and inorganic or organic pollutants decontamination.

Effect of Ar pressure on the wettability of copper droplet on graphite substrate by molecular dynamics simulation

Effect of Ar pressure on the wettability of copper droplet on graphite substrate by molecular dynamics simulation

A Computational Study of Cluster Dynamics in Structural Lubricity: Role of Cluster Rotation

We present a computational study of sliding between gold clusters and a highly oriented pyrolytic graphite substrate, a material system that exhibits ultra-low friction due to structural lubricity. By means of molecular dynamics, it is found that clusters may undergo spontaneous rotations during manipulation as a result of elastic instability, leading to attenuated friction due to enhanced interfacial incommensurability. In the case of a free cluster, shear stresses exhibit a non-monotonic dependency on the strength of the tip-cluster interaction, whereby rigid clusters experience nearly constant shear stresses. Finally, it is shown that the suppression of the translational degrees of freedom of a cluster’s outermost-layer can partially annihilate out-of-plane phonon vibrations, which leads to a reduction of energy dissipation that is in compliance with Stokesian damping. It is projected that the physical insight attained by the study presented here will result in enhanced control and interpretation of manipulation experiments at structurally lubric contacts.

Evaluation of equi‐biaxial strength of thin sic coatings using ring‐on‐ring testing and digital image correlation

AbstractTo assess the strength of coatings under multi‐axial stress conditions, a method was developed to evaluate the biaxial strength of thin silicon carbide (SiC) coatings using a ring‐on‐ring test. A graphite substrate was used as an intermediary to transmit stress from the load ring to the coated specimen, and the thin coating was subjected to a uniform equi‐biaxial stress. The strain in the thin film was continuously monitored using digital image correlation, allowing the identification of the time at which and when the initial crack occurred; the stress applied to the loading area at time was determined to be the fracture strength of the thin SiC films. The obtained fracture strength ranged from 209 to 1014 MPa and was dependent on specimen volume. Notably, the thinnest specimen exhibited the highest strength, whereas the strengths of thicker specimens approached previously reported bulk strengths.

Affinity of Phospholipids Vesicles with Pyrolytic Carbon Shoulder Implant

Shoulder hemiarthroplasty is a minimally invasive procedure that requires less surgical time and better preserves healthy cartilage compared to total arthroplasties. However, patient outcomes are not always conclusive, and this is because metal humeral heads induce cartilage erosion and the release of local tissue metal toxicity. The recently developed InSpyre (Tornier-Wright) consists of a graphite substrate coated with pyrolytic carbon (PyC). Due to its specific surface characteristics and previous medical applications (heart valves and joint implants), PyC could suppress metal toxicity and limit tissue wear due to its Young's modulus close to that of bone (30 MPa vs. 50MPa respectively). In a previous study, we found that phospholipids adsorbed 3 times more onto PyC after friction against living cartilage compared to cobalt alloy. As PLs are known to be involved in lubrication, this suggests a reduction in friction against the tissue by the affinity of PyC to PLs. However, it is not known how PLs affect the electrochemical resistance of PyC and whether friction is necessary to promote PLs adsorption. This study aims to determine whether the physicochemical structure of PLs affects the reactivity of PyC by comparing its electrochemical properties in cell culture medium without, with PLs vesicles, and with disrupted PLs vesicles. A custom electrochemical setup based on a Petri dish with pyrolytic carbon disks was used. The electrolyte is a synthetic synovial fluid based on DMEM/F12 (cell culture medium, CCM) with or without hyaluronic acid (HA)-phospholipid vesicles (PLs). These vesicles represent synthetic surface-active phospholipids, conferring the lubricating capacity of synovial fluid. Characterization of the biomaterial/electrolyte interface and the adsorption process was performed by EIS measurements performed after 10 and 60min of exposure. Measurements were performed from 1mHz up to 105 Hz, at 9 cycles/dec with an ac amplitude of ± 10mV. Tests were performed in an incubator (95% humidity, 5% CO2, 37°C). Analogous electrochemical tests with a surfactant (Triton X-100) were performed to simulate disrupted phospholipid vesicles, to reproduce the physicochemical modification of synovial fluid of joint disease. Statistical differences between solutions were performed using a nonparametric Kruskal-Wallis test (SPSS Inc, Chicago, IL). The significance level was set at P<0.05. The OCP of PyC in DMEM with and without PLS is decreasing reaching an average potential of 51 and 83 mV/AgAgCl, respectively (Fig 1A, B). This negative evolution of the OCP of PyC indicates the formation of a non-protective layer on the biomaterial surface. The lower OCP in the presence of PLs vesicles suggests a surface modification due to PLs adsorption. By adding the surfactant to the solution, the OCP started at a lower potential value (14 mV/AgAgCl) and increased during a 1h exposure (Fig 1 C). The addition of PLs produced a change on the electrochemical reactions (taking place on the biomaterial/body fluid interface, cathodic and anodic reaction) at the OCP. The EIS plots show a typical passive state shape characterized by high impedance values with non-ideal capacitive behavior. The EIS results were fitted with a Randles circuit including a phase angle element (CPE) to replace the capacitor for the non-ideal behavior of the capacitive elements due to different physical phenomena. It was found that the addition of PLs strongly increases the resistance of PyC after a one-hour polarization (Fig 1D). The presence of PLs vesicles resulted in a greater increase in charge transfer resistance compared with DMEM under identical conditions. These changes in charge transfer resistance and capacity are attributed to the formation of a phospholipid layer on the PyC surface. Addition of surfactant (Triton X100) resulted in similar capacitance and charge transfer resistance to DMEM after 1 h of exposure, suggesting that the disrupted vesicles do not adsorb or protect PyC (Fig 1D,E). Surface analysis and observations are required to confirm these preliminary results. This study reveals that the physicochemical structure of synthetic synovial fluid impacts the chemical resistance of PyC, conferring better protection with the addition of PLs vesicles. Joint disease was simulated by disrupting PLs vesicles with the introduction of a surfactant. It reveals the loss of protective behavior, emphasizing that concentration is not the main factor in the chemical resistance of biomaterials. The affinity of PLs with the current main metallic orthopedic implants, Cobalt and Titanium alloys, is an ongoing project to define how phospholipid vesicles impact their corrosion resistance. Figure 1

Investigation of SiC formation on the graphite surface by CO-H2-SiO gas

FINEX process, which utilizes hydrogen (H2) as a part of reductants, has emerged as an environmentally sustainable ironmaking process to meet the upcoming carbon-neutral era. In the H2-enriched atmosphere, local slag holdup in the carbonaceous particle bed may increase due to the increased melting temperature of slags by the rapid reduction of iron oxide and the resulting lower wettability of the carbonaceous materials by liquid slag. In-situ SiC formation on the carbon surface gains much attention as a method to reduce the slag holdup. In this study, as a fundamental study, we investigated the SiC formation on the surface of a graphite substrate under a CO-H2-SiO gas environment at 1873 K. It was found that as the partial pressure of H2 increased, the penetration depth of a SiC layer formed on the graphite surface increased, and the surface roughness became enhanced. A reaction rate analysis revealed that the H2-CO gas mixture accelerated the SiC formation on the graphite surface compared to the N2-CO gas mixture. This effect was attributed to the high bimolecular diffusivity of H2-CO. Our results demonstrate that under a CO-H2-SiO gas environment, the fast diffusion of H2 gas through micropores in the graphite significantly enhances the formation of SiC on the graphite surface. The results obtained in this study show that the acceleration of SiC formation under an H2-enriched atmosphere would improve the wettability of molten slag and reduce the slag holdup in the FINEX process.

A Simple Method to Measure the Contact Angle of Metal Droplets on Graphite

The determination of solid–liquid interfacial tension plays an important role in science and technology. Here, we propose a simple method to directly measure the contact angle between metal droplets and a graphite substrate for the determination of metal–graphite interfacial tension. The proposed method involves the synthesis of micro- and nanosized metal droplets on graphite by arc melting. Owing to its small volume, the rapid cooling of the prepared metal droplets on the graphite substrate leads to the freezing of equilibrium contact configuration after solidification. We observe that the measured contact angle between micro- and nanosized Au (or Ag) particles and the graphite substrate is almost size independent, even though the size of the particles synthesized herein is 1–3 orders of magnitude smaller than that studied in previous works. In addition, the interfacial tensions of Au and Ag on the step edges (edge plane) of graphite are found to be larger than that on the (0001) plane (basal plane). The proposed method provides a simple approach to determine the solid–liquid interfacial tension and may be effective in the study of interface related science and technology.

Wetting and interfacial reactivity of graphite by liquid TiCuNi

Understanding the wetting and interfacial reactivity of graphite in contact with molten alloys is important to optimize brazing or to prepare carbon-based composites and coatings.In this work, the isothermal wetting of graphite substrates by a molten Ti-based alloy, namely TiCuNi (Ti: 70 wt.%), was tested at 1000 °C at different holding times by the sessile drop method with the aim to understand the interfacial reactivity. A final contact angle of 15° was achieved after 60 min of liquid-solid contact as a result of spreading kinetics. A thorough microstructural characterization by SEM and TEM was performed and evaluated with the help of the relevant phase diagrams: a limited interfacial reactivity to form TiC particles at the metal/graphite interface occurred. The interfacial compounds grew with time and determined the spreading of the liquid on the graphite substrate which resulted to be reaction-limited.

Antioxidant performance and oxidation mechanism of a liquid silicon infiltration (LSI) SiC–Si coating at an ultra-high temperature of 1873 K

A novel SiC–Si coating with a high amount of net-like distributed Si was fabricated on the graphite substrate by liquid silicon infiltration (LSI) method to improve the oxidation-resistant performance. The mass gain of this LSI coating after 300 h oxidation at 1873 K was only 3.018%, suggesting an excellent static antioxidant property at 1873 K. The detailed oxidation mechanism of this LSI coating was explored in this work. It was found that the high amount of Si with the net-like distribution in this LSI coating promoted the passivation growth of SiO2 glass layer and prevented the SiO2 glass from crystallizing into cristobalite. In addition, the Si in this coating retarded the active oxidation and enhanced the coating stability. In contrast, the infiltration (VSI) SiC–Si coating presented an apparent mass loss, and the pack cementation (PC) SiC coating showed the catastrophic failure. The oxidation mechanisms of these two coatings were also discussed against the backdrop of the LSI coating with high antioxidant performance.

Simulation of Hydrogen and Oxygen Adsorption on Palladium Nanoparticles Located on a Graphite Substrate with Various Defects

Simulation of Hydrogen and Oxygen Adsorption on Palladium Nanoparticles Located on a Graphite Substrate with Various Defects

Palladium Nanoparticles Grown by Using Successive Ionic Layer Adsorption and Reaction Method: Ethanol Electrooxidation and Electrochemical Quartz Crystal Microbalance Studies

A facile wet chemical method namely successive ionic layer adsorption and reaction (SILAR) is implemented to grow palladium nanoparticles on graphite substrate. The grown Pd nanoparticles are successfully applied for electrooxidation of ethanol in alkaline solution. The electrocatalytic activity of grown Pd nanoparticles is studied by performing cyclic voltammetry (CV) measurements. Electrooxidation of ethanol by Pd nanoparticles is shown to be affected by growth parameters such as precursor concentration and number of SILAR growth cycles. Excessive growth of Pd nanoparticles due to large number of SILAR growth cycles shifts the pattern of cyclic voltammograms from period-one cyclic voltammograms to high order periodic/aperiodic cyclic voltammograms. Pd nanoparticles are also grown on gold coated quartz crystal and implemented to track any mass changes that occur during electrochemical surface oxidation/reduction over Pd nanoparticles, with and without ethanol in alkaline solution. To measure the mass changes occurring during CV measurements electrochemical quartz crystal microbalance (EQCM) is implemented in situ along with potential scanning.

The Etching Mechanisms of Diamond, Graphite, and Amorphous Carbon by Hydrogen Plasma: A Reactive Molecular Dynamics Study

AbstractUnderstanding how hydrogen plasma etches various potential products during the diamond growth process can contribute to improving the knowledge of diamond growth. However, due to the absence of an in situ characterization technique during the etching process, the complex chemical reactions involved in the process obscure the atomic‐scale etching mechanisms. In this paper, the etching mechanisms of diamond (001), graphite (0001), and amorphous carbon substrates irradiated by hydrogen plasmas are investigated and compared using molecular dynamics simulations based on ReaxFF. When the incident energy of H atoms is 1 eV, the rate of carbon loss from graphite and amorphous carbon are far higher than that from diamond. As the incident energy of H atoms increases, the etching rate of diamond shows a slow increase, while the etching rates of amorphous carbon and graphite exhibit more significant increases. It can be concluded that the etching rate of diamond is significantly lower than that of graphite and amorphous carbon under H plasma. In the Chemical Vapor Deposition (CVD) process of diamond growth, the generated graphite and amorphous carbon are rapidly etched, leaving only diamond. This offers a plausible explanation for the growth mechanism of diamond through CVD.

High-Yield Synthesis of SiC@SiO2 Core–Shell Nanowires on Graphite Substrates for Energy Applications

High-Yield Synthesis of SiC@SiO₂ Core–Shell Nanowires on Graphite Substrates for Energy Applications

Falling Angle of Fe‐C‐Based Alloy Droplet on Coke and Graphite

The hold‐up of molten pig iron and slag melt in the coke packed bed of blast furnace (BF) causes a decrease of void between coke lumps and inhibits gas permeability. Smooth dripping of those liquids in the coke bed is desirable to keep the productivity of BF. Herein, the conditions for smooth flowing of molten iron on coke surface are calrified, and the falling angles of Fe‐C and actual pig iron droplets on coke and graphite are measured at high temperature. It is found that Fe‐C droplet easily slids down on coke because of small falling angle, and the falling angle of actual pig iron is even smaller, while those droplets adhere to a graphite substrate. The carbon in iron has only a small effect on the static contact angle with coke, but has a great influence on the falling angle. From the viewpoint of the roughness of coke surface, the variation of static contact angle and falling angle is discussed.