Efficient and stable electrocatalyst for hydrogen evolution reaction prepared by hybrid technique in surface engineering: Electrochemical and magnetron sputtering methods

Developing low-cost, stable, and robust electrocatalysts is significant for high effective hydrogen evolution reaction (HER). In this work, a coating system with Cu₂O/NiMoCu on stainless steel (SS) is employed as a highly active and stable catalyst for HER in acidic solutions. Electrochemical measurements for as-designed system on SS show a low onset overpotential, small Tafel slope of ～32 mV/decade and long-term durability over 7 days of HER operation. To further inspections of electrocatalytic behavior of as-prepared system in HER, the EIS measurements are performed at several overpotentials and temperatures. It is found that high hydrogen evolution activity and stability of Cu₂O/NiMoCu hybrid is likely due to special morphology of Cu₂O which result in large number of active sites for hydrogen adsorption, and a synergetic effect giving electronic structure suitable for the HER.     

Integration of fiber-optic sensors in measuring machines

In last years, optical metrology due to its capability in miniaturization and sensitivity became the primary solution in measurement of complex geometries and fragile pieces. Here, we propose a promising approach to perform highly accurate distance measurements using low-coherence fiber-optic sensors for quality inspection of nozzle orifices in fuel injection systems. In this effort, we develop an adaptive image processing algorithm in MATLAB and install the necessary hardware on a form tester to accelerate and simplify the aligning process. As a result, the repeatability of measurements is one order of magnitude improved while the standard deviation is almost 60% reduced.     

MoSx-Ta composite coatings on steel by d.c magnetron sputtering

Sputter-deposited MoS₂ films have been often used as dry lubricant in various industrial fields, such as space application and much attention has been paid to reduction of friction coefficient and improvement of mechanical properties in recent decades. One way to achieve this is to deposit a MoS₂ film doped with another metal. The MoS_x-metal films were found to be denser, more adhesive and more oxidation-resistant than pure MoS₂. In this study, MoS_x-Ta composite films were synthesized by Electron Cyclotron Resonance microwave source enhanced DC sputtering with different target powers. The effects of doping Ta on mechanical properties of MoS_x-Ta films were investigated. The morphology and structure of films were investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The microhardness was evaluated using microhardness test instrument, and the adhesion strengths were obtained using a scratch tester. The results showed that the S/Mo ratio was influenced by the dc sputtering target power. Typical MoS₂ (100) (103) (002) orientations were present in pure MoS_x films, but disappeared with the increase in doped Ta, with the S/Mo content ratios decreasing from 1.52 to 0.84, and the hardness increasing from 3.55 to 15.23 GPa. The roughness and surface topography, friction coefficient and adhesion were significantly affected by the Ta, Mo and S content. The content of doped Ta plays a dominant role on the change in the Mo/S ratio, thereby influencing the mechanical and tribological properties of the MoS_x-Ta composite films.     

Polyaniline-lignosulfonate/epoxy coating for corrosion protection of AA2024-T3

Corrosion protection arising from epoxy coatings incorporating lignosulfonate-doped polyaniline (Pani-LGS) upon AA2024-T3 was studied in 0.6 M NaCl. Synthesized Pani-LGS particles were investigated using TEM, FTIR, TGA and conductivity, whilst coatings were also physically examined using SEM. The coating performance was studied using a combination of potentiodynamic polarisation, EIS, FTIR spectroscopy and X-ray photoelectron spectroscopy. The performance of Pani-LGS/epoxy blends is discussed more generally, with tests revealing that on exposure to 0.6 M NaCl solution for 30 days, a 5 wt% Pani-LGS/epoxy coating resulted in low levels of corrosion. A mechanism for the postulated mode of corrosion protection is presented.     

Structural and thermal properties of boron nitride nanoparticles

In the present study, our main motivation was to investigate the structural and thermal stability of BN nanoparticles (B_1.0N_0.9-NPs) produced by spray-pyrolysis (SP) of borazine at 1400 °C by thermogravimetric experiments and X-ray diffraction. We observed that B_1.0N_0.9-NPs are relatively stable in air below 850 °C in which only oxidation of the NP surface proceeded. Above 850 °C, the powders started to strongly react with air due to bulk oxidation. Under nitrogen, they appeared to be less stable than plate-like BN synthesized from borazine at 1400 °C through conventional pyrolysis. This is related to the low degree of crystallization of B_1.0N_0.9-NPs that clearly affects their stability. Using a post-pyrolysis treatment at 1400 °C, B_1.0N_0.9-NPs remained stable up to 1600 °C similarly to plate-like BN. However, above 1600 °C, a relatively fast weight loss occurred for B_1.0N_0.9-NPs, whereas plate-like BN remained stable up to 1800 °C. This indicated that their lower size also affects their high temperature thermal behavior.     

Impermeability of graphene and its applications

This review discusses the genesis of impermeability in graphene and its extraordinary applications in fluid-encasement for wet electron-microscopy, selective gas-permeation, nanopore-bio-diffusion, and barrier coating against rusting and environmental hazards. As the thinnest material, graphene is composed of sp² hybridized carbon atoms linked to one another in a 2D honeycomb lattice with high electron-density in its aromatic rings, which blocks-off all molecules. This phenomena, in combination with its strong structure (C–C bond energy = 4.9 eV and intrinsic strength = 43 N/m) makes graphene the most impermeable membrane (thinnest membrane that is impermeable). Apart from the applications mentioned above, graphene coatings have enabled fundamental studies on chemical processes and fluid structures. For example, graphene can allow electron imaging of nanocrystal nucleation process and water-lattice-structure due to its impermeability. Along with being the strongest, most conductive, and optically-absorbing material (∼2.3% optical absorbance), graphene’s impermeability opens a wide range of exciting opportunities.     

Nanocrystalline diamond synthesized from C60

A bulk sample of nanocrystalline cubic diamond with crystallite sizes of 5–12 nm was synthesised from fullerene C₆₀ at 20(1) GPa and 2000 °C using a multi-anvil apparatus. The new material is at least as hard as single crystal diamond. It was found that nanocrystalline diamond at high temperature and ambient pressure kinetically is more stable with respect to graphitisation than usual diamonds.     

Fabrication of microwave exfoliated graphite oxide reinforced thermoplastic polyurethane nanocomposites: Effects of filler on morphology,mechanical, thermal and conductive properties

Different formulations of microwave-exfoliated graphite oxide (MEGO) based thermoplastic polyurethane (TPU) nanocomposites were successfully prepared via melt blending followed by injection molding. The spectroscopic study indicated that a strong interfacial interaction had developed between the MEGO and the TPU matrix. The microscopic observations showed that the MEGO layers were homogeneously dispersed throughout the TPU matrix. Thermal analysis indicated that the glass transition temperatures (T_g) of the nanocomposites increased with increasing MEGO content and their thermal stability improved in comparison with pure TPU matrix. The mechanical properties of nanocomposites improved substantially by the incorporation of MEGO into the TPU matrix. Electrical conductivity test indicated that a conductivity of 10⁻⁴ S cm⁻¹ was achieved in the nanocomposite containing only 4.0 wt.% of MEGO.     

The corrosion resistance of 316L stainless steel coated with a silane hybrid nanocomposite coating

The present work aims at evaluating the corrosion resistance of 316L stainless steel pre-treated with an organic–inorganic silane hybrid coating. The latter was prepared via a sol–gel process using 3-glycidoxypropyl-trimethoxysilane as a precursor and bisphenol A as a cross-linking agent. The corrosion resistance of the pre-treated substrates was evaluated by neutral salt spray tests, linear sweep voltammetry and electrochemical impedance spectroscopy techniques during immersion in a 3.5% NaCl solution. In addition, the effect of the drying method as an effective parameter on the microscopic features of the hybrid coatings was studied using Fourier transform infrared spectroscopy and scanning electron microscopy. Results show that the silane hybrid coatings provide a good coverage and an additional corrosion protection of the 316L substrate.     

Effect of carbon content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Four series of Mo₂FeB₂ based cermets with different carbon contents were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured. The free carbon present in the green compact significantly decreased the grain size; however, a high carbon content resulted in the formation of graphite phase and Fe₃C phase. An increasing carbon content promoted the dissolution of Mo in the binder phase. In addition, the binder phase varied from ferrite to martensite with increasing carbon content. The highest hardness was found for the cermets with 0.5 wt.% carbon addition, whereas the cermets without carbon addition exhibited the maximum TRS and fracture toughness.