[en] Biodegradable magnesium alloys have attracted much attention in recent years due to their potential applications in cardiovascular stents and bone implants. However, their inadequate corrosion resistance in the physiological environment is a major obstacle limiting wider application. In this work, a niobium nitride (NbN) film is deposited on Mg-Y-RE alloy (WE43) by reactive magnetron sputtering to improve the corrosion resistance. The structure of the nitride film is determined by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy. The corrosion behavior of the uncoated and NbN-coated WE43 is evaluated in simulated body fluids by electrochemical impedance spectroscopy, polarization tests, and immersion tests. The surface morphology of the samples before and after the immersion tests is examined by scanning electron microscopy to assess the degree of corrosion. Our results indicate that the corrosion resistance is improved by the corrosion-resistant nitride film and the reasons are discussed. - Highlights: • Niobium nitride is deposited on magnesium alloy by reactive magnetron sputtering. • Niobium nitride enhances the corrosion resistance in simulated body fluids. • Corrosion products contain mainly Mg, O, and P

[en] Highlights: • Carbon, as a biocompatible benign element, was implanted into Mg. • A protective amorphous carbon layer was formed after implantation. • Treated sample exhibits good corrosion resistance in two solutions. - Abstract: The corrosion resistance of magnesium-based biomaterials is critical to clinical applications. In this work, carbon as a biocompatible and benign nonmetallic element with high chemical inertness is implanted into pure magnesium to improve the corrosion behavior. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), and Raman scattering reveal the formation of an amorphous carbon layer after ion implantation. Electrochemical studies demonstrate remarkable improvement in the corrosion resistance of magnesium in simulated body fluids (SBF) and Dulbecco’s Modified Eagle Medium (DMEM)

[en] One type of 100 kV repetitive fast trigger generator based on Tesla transformer and PFL is developed. The generator has characteristic of good reliability and compact construction. The factors which influence the system jitter are theoretically analyzed and improved methods are proposed. The design and numerical simulation of Tesla transformer are described, The experimental results show that the trigger generator can output 100 kV at 40 Ω matched load with a duration of 4 ns (FWHM) and 0.5 ns rise time, the overall jitter is less than 10 ns at 50 Hz repetitive frequency. (authors)

[en] Plasma immersion ion implantation (PIII) is conducted to improve the intrinsically poor corrosion properties of biodegradable AZ31 magnesium alloy in the physiological environment. Carbon dioxide is implanted into the samples and X-ray photoelectron spectroscopy and scanning electron microscopy are used to characterize the materials. The corrosion properties are systematically studied by potentiodynamic polarization tests in two simulated physiological environments, namely simulated body fluids and cell culture medium. The plasma-implanted materials exhibit a lower initial corrosion rate. Being a gaseous ion PIII technique, conformal ion implantation into an object with a complex shape such as an orthopedic implant can be easily accomplished and CO₂ PIII is a potential method to improve the biological properties of magnesium and its alloys in clinical applications.

[en] An investigation of 45 soil samples collected from the surface soil around a municipal solid waste incinerator, in northeast China, was performed to understand the status of metallic contamination in the soil. Methods such as inverse distance weighting, pollution index, potential ecological risk, and statistical analysis were used to investigate metallic contamination in soils around municipal solid waste incineration sites. Both grade II and background concentrations were employed as reference standards to evaluate the levels of metallic contamination in soils. The results revealed that the metal concentrations and contamination levels were both the highest near the centre of the MSWI and decreased away from the centre of the MSWI. The source identification results demonstrated that the MSWI, natural sources and complicated sources represented the three primary sources, accounting for 59.08 %, 11.17 %, and 10.43 % of the contamination, respectively. The most heavily polluted samples were located to the south of the MSWI. When the grade II values were used as references, the metals in soils, except for Cd, Zn, and Cu in some samples, exhibited low contamination levels and ecological risks. Soils were polluted by the metals to various degrees based on the background reference values. Additionally, the potential ecological risk analysis further suggested that the study area was at considerable risk, especially for Cd pollution. These results are critical for protecting the environment in the vicinity of a MSWI and providing basic data for policy-makers to formulate viable regulations in the future.

[en] Highlights: • Grinding speed has an important influence on surface morphology. • The influence of grinding speed on subsurface damage can not be ignored. • The Si-II phase is found in the subsurface damage layer. • Residual stresses are mainly distributed in the subsurface damage layer. Understanding the damage mechanism of silicon under interfacial shear is vital as it can provide insights for the ultra-precision low damage machining. In this work, the nano-grinding process of single crystal silicon was studied by molecular dynamics (MD) simulations, the damage mechanism of single crystal silicon were analyzed in details under different grinding speeds. The results show that the maximum height of the grinding chip does not always increase with the increase of the grinding speed. When the speed exceeds 150 m/s, more atoms will flow to both sides of the groove. During grinding, the workpiece changes from cubic diamond structure to non-diamond structure and a small amount of hexagonal diamond structure. The Si-II phase was found in the subsurface damage layer. Residual stresses are mainly distributed in the subsurface damage layer (SDL) and do not always show compressive or tensile stresses as the depth increases. This investigation may shed light on the damage mechanism of silicon from an atomic perspective.

[en] A series of nickel-based materials doping with bismuth element were synthesized by a sol–gel method and investigated as efficient electrocatalysts for methanol electrooxidation in alkaline environment. The physicochemical properties of the materials were well characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TG), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical measurements illustrated that the introduction of bismuth element can enhance the catalytic activity of NiO catalyst for methanol oxidation reaction. The current density of Ni₁₀₀Bi₁ nano-oxides increased by 30% compared with NiO in 1 M NaOH with 1 M CH₃OH solution. The prepared materials exhibited favorable stability for methanol oxidation. Thus, Ni₁₀₀Bi₁ nano-oxides appear to be a promising catalyst for methanol oxidation reaction (MOR).

[en] Boron carbide is an extremely hard material extensively used in the industry. In this study, carbon-coated B₄C nanoparticles were synthesized through a one-step synthesis method using high-temperature firing cheap and readily available raw materials, namely, boric acid and sucrose. X-ray diffraction and Raman spectra analysis indicated the formation of B₄C, and high-resolution transmission electron spectroscopy revealed that the carbon-coated B₄C nanoparticles exhibited regular B₄C-C core-hell structure with an average particle diameter of around 100 nm. This method is simple and time-saving, and can be adopted for the large-scale production of the core-shell nanoparticle. Directly using these core-shell structural nanoparticles as precursor, high-performance B₄C/C ceramics with hardness reaching 34 GPa, fracture toughness reaching 3.3 MPa m^1/2 were synthesized. This study has important implications in developing high-performance B₄C ceramics.

[en] Highlights: • A model with defects was built. • The mechanism of initial defects on the subsurface damage was elucidated. • The structural evolution of diamond in CMP process was investigated. • The large initial defects impact the quality of machined surface. • Stress concentration appears at the defect edge. Surface defects of materials will deteriorate their mechanical properties and limit the applications. Understanding the effect of surface defects on machining performance remains a challenge. Therefore, it is of paramount significance to insight into the structural evolution and subsurface damage induced by defects. Herein, we construct a polishing model with initial defects to make the simulation more realistic, and elucidate the effects of initial defects on the subsurface damage and structure evolution via ReaxFF molecular dynamics simulations. Simulation results show that the structural evolution starts from defect edge, and the substrate with initial defects will produce more amorphous damage layers compared with the ideal substrate. The thickness of the amorphous damage layer is roughly the same as the depth of the initial defects. Moreover, smaller pit defects have a little effect on the surface morphology. Nevertheless, larger pit defects will cause poor surface quality and more severe subsurface damage. Our simulation results are of significance for further understanding the influence of initial defects on subsequent machining quality and subsurface damage, and provide theoretical support for the processing of diamond from an atomic perspective.

[en] The development of photoelectric devices for high integration and miniaturization in the semiconductor industry can be pushed forward by the thriving research of two-dimensional layered metal dichalcogenides (2D-LMDs). SnS₂ nanosheets have an evident photoresponse to both ultraviolet and partial visible light, but only with a fair photoelectric performance limited by their atomic-layer thickness. Here, we report a convenient and simple method to dramatically enhance the electrical and photoelectric performance of the SnS₂ flake. By integrating SnS₂ with Au plasmonic nanostructures, the photocurrent (I _ph) increased by over 20 times. The corresponding responsivity (R), light gain (G), and detectivity (D*) have been improved by ∼2200%, 2200% and 600%, respectively. The responsivity and detectivity of the Au NPs-SnS₂ field-effect transistor (FET) at 532 nm are 1125.9 A W⁻¹ and 2.12 × 10¹¹ Jones. Though atomically thin, the hybrid SnS₂ photodetector, benefiting from local surface plasmonic resonance, achieves an excellent photoelectric performance that is not usually possible with a pristine SnS₂-only device. (paper)