The tribological behavior of W–S–C films in pin-on-disk testing at elevated temperature

W–S–C films were deposited by magnetron sputtering in an Ar atmosphere with a Ti interlayer. A carbon target with several pellets of WS₂ incrusted in the zone of the preferential erosion was used. The number of pellets was changed to modify the carbon content in the films, which varied from 29 up to 70 at%. Doping W–S films with carbon led to a substantial increase of the hardness in the range 4–10 GPa; the maximum of hardness was obtained for coatings with the carbon content of 40 at%. X-ray diffraction (XRD) patterns showed that there was a loss of crystallinity with the increase of the carbon content in the film.The coatings were tested by pin-on-disk from room temperature (RT) up to 400 °C. At RT, the friction coefficient was in the range 0.2–0.30. At temperatures higher than 100 °C, the friction is below 0.05 for all compositions. The tribological behavior of the coatings with increasing temperatures depended on the films carbon content. For low-carbon content up to 40%, the wear rate was almost independent of the temperature up to 300 °C, while it increased dramatically in the case of the coatings with high-carbon content. In general, the limiting temperature for W–S–C coatings is 400 °C.     

Study of fluorine contamination on MgO(100) surfaces

The fluorine contamination on MgO(100) surfaces is studied using Electron Stimulated Desorption (ESD) and Auger Electron Spectroscopy (AES). While Ar⁺ ion sputtering is very effective to clean the carbon contamination on the surface, the fluorine content does not significantly decrease. Thermal treatments of the sample considerably increase the F surface concentration due to its diffusion from the bulk to the surface. Heating the sample at 700 K simultaneously with H₂O exposure produces a decrease in the fluorine signal. The ion kinetic energy distribution of the F⁺ ion shows two peaks at 2.4 and 5 eV. The threshold energy of the F⁺ ion desorption is at 60 eV.     

Transmission electron microscopy study of carbon nanophases produced by ion beam implantation

The formation of carbon nanocrystals, produced by ion implantation of carbon ions into fused SiO₂ substrates, followed by 1 h thermal annealing at 1000 °C, in an Ar + 5% H atmosphere has been studied. Combined high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) have been employed for structural characterization of carbon nanophases embedded in the quartz substrate. The dependence of grain size and sample morphology of the carbon nanophases on implantation dose was studied. The carbon nanocrystals formed by the implantation for a dose of 1 × 10¹⁶ C/cm² at 320 keV have been identified as a mixture of c-diamond nanophase and a modified diamond nanophase known as n-diamond. For a higher implantation dose, 5 × 10¹⁶ C/cm², besides n-diamond, another solid carbon nanophase was observed, with a structure known as i-carbon. Following the highest implantation dose 1 × 10¹⁷ C/cm² the sample contained the i-carbon nanophase only. A least-square refinement of SAED patterns was employed for the calculation of unit-cell parameters of identified carbon nanophases.     

Role of PVD oxide coatings on HK40 cast steel during short and long exposure to C-rich atmospheres

The role of Cr/Cr oxide thin film coatings on HK40 steel substrates during exposure to C-rich atmospheres was investigated. The coatings were produced via reactive magnetron sputtering as an alternative method to protect these materials against metal dusting. Coated and uncoated substrates were exposed at 1073 K to an Ar + CH₄ atmosphere with residual oxygen for 10, 30, 60 min and 50 h. Analysis of the products formed on both samples indicated that attack in the uncoated samples involves both C and O from the atmosphere together with Cr, Fe, and Ni outward diffusion in which the dendritic structure plays an important role. The presence of even a residual amount of oxygen in the carburizing atmosphere had a remarkable effect on the corrosion mechanism in these samples as well. In the coated samples, the Cr/Cr oxide film minimized internal alloy attack not only by limiting carbon ingress, but also minimizing the role of oxygen and outward Cr (Fe and Ni) diffusion from the alloy.     

Structure and corrosion resistance of nickel coatings containing tungsten and silicon powders

Ni + W + Si coatings were prepared by nickel deposition from a bath containing a suspension of tungsten and silicon powders. These coatings were obtained at galvanostatic conditions, at the current density of j_dep = − 0.100 A cm^− 2 and at the temperature of 338 K. For determination of the influence of phase composition and surface morphology of these coatings on changes in the corrosion resistance, these coatings were modified in an argon atmosphere by thermal treatment at 1373 K during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. The chemical composition of the coatings was determined by EDS and phase composition investigations were conducted by X-ray diffraction. It was found that the as-deposited coatings consist of a three-phase structure, i.e., nickel, tungsten and silicon. The phase composition for the Ni + W + Si coatings after thermal treatment is markedly different. The main peaks corresponding to Ni and W coexist with the new phases: NiW, NiWSi and a solid solution of W in Ni.Electrochemical corrosion resistance investigations were carried out in 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found that the Ni + W + Si coatings after thermal treatment are more corrosion resistant in alkaline solution than the as-deposited coatings. The reasons for this are a reduction in the amount of free nickel and tungsten, the presence of new phases (in particular polymetallic silicides), and a decrease of the active surface area of the coatings after thermal treatment.     

In–Ga–Zn–O thin film transistor with HfO2 gate insulator prepared using various O2/(Ar + O2) gas ratios

We have investigated the effect of the deposition of an HfO₂ thin film as a gate insulator with different O₂/(Ar + O₂) gas ratios using RF magnetron sputtering. The HfO₂ thin film affected the device performance of amorphous indium–gallium–zinc oxide transistors. The performance of the fabricated transistors improved monotonously with increasing O₂/(Ar + O₂) gas ratio: at a ratio of 0.35, the field effect mobility of the amorphous InGaZnO thin film transistors was improved to 7.54 cm²/(V s). Compared to those prepared with an O₂/(Ar + O₂) gas ratio of 0.05, the field effect mobility of the amorphous InGaZnO thin film transistors was increased to 1.64 cm²/(V s) at a ratio of 0.35. This enhancement in the field effect mobility was attributed to the reduction of the root mean square roughness of the gate insulator layer, which might result from the trap states and surface scattering of the gate insulator layer at the lower O₂/(Ar + O₂) gas ratio.     

Preparation of carbon coated LiMnPO4 powders by a combination of spray pyrolysis with dry ball-milling followed by heat treatment

Nanostructured LiMnPO₄ particles could be successfully synthesized by an ultrasonic spray pyrolysis method from the precursor solution; LiNO₃, Mn(NO₃)₂·6H₂O and H₃PO₄ were stoichiometrically dissolved into distilled water. The X-ray diffraction analysis showed that the as-prepared powders which had the desired olivine structure without any impurity phase could be obtained in the reactor temperatures ranging from 500 to 800 °C. Carbon coated LiMnPO₄ could be prepared from the as-prepared powders by a dry ball-milling followed by heat treatment for 4 h in a N₂ + 3% H₂ atmosphere. Transmission Electron Microscopy observation confirmed that a carbon layer was formed on the surface of LiMnPO₄ particles, which aimed to enhance the electronic conductivity of the material as well as inhibit the agglomeration during annealing. The carbon coated LiMnPO₄ was used as cathode active materials for lithium-ion batteries, and electrochemical performance was investigated using the Li|1 M LiClO₄ in EC:DEC = 1:1|LiMnPO₄ cells at room temperature and 55 °C. At a charge/discharge rate of 0.05 C, the cell exhibited first discharge capacities of 70 mAh g^?1 at room temperature and 140 mAh g^?1 at 55 °C. Moreover, it showed excellent cycleability even at elevated temperature and a high charge/discharge rate of 2 C.     

Transformation from hollow carbon octahedra to compressed octahedra and their use in lithium-ion batteries

Hollow carbon octahedra with an average size of 300 nm and a shell thickness of 2.5 nm were prepared by a reaction starting from ferrocene and Mg(CH₃COO)₂·4H₂O at 700 °C for 10 h. They became compressed and turned into deflated balloon-like octahedra when the reaction time was increased to 16 h. It was proposed that the gas pressure generated during the reaction process induced the transformation from broken carbon hollow octahedra into deflated balloon-like compressed octahedra. X-ray powder diffraction and Raman spectroscopy indicate that the as-obtained carbon products possess a graphitic structure and high-resolution transmission electron microscopy images indicate that they have low crystallinity. Their application as an electrode shows reversible capacity of 353 mAh g^?1 after 100 cycles in the charge/discharge experiments of secondary lithium ion batteries.     

Effect of carbon content and calcination temperature on the electrochemical performance of lithium iron phosphate/carbon composites as cathode materials for lithium-ion batteries

Lithium iron phosphate/carbon (LiFePO₄/C) composites were prepared by a convenient method with water-soluble phenol-formaldehyde resin as the carbon precursor. The morphology, crystalline structure, thermal stability, and composition of as-prepared LiFePO₄/C composites were investigated by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectrometry. Their electrochemical performance was examined based on cyclic voltammogram with a LAND battery testing system while the effect of carbon content and calcination temperature was highlighted. Results show that carbon content and calcination temperature dramatically influence the discharge capacities and rate performance of LiFePO₄/C composites. The optimal calcination temperature is 700 °C, and the optimal carbon content (mass fraction) is 8.7%. The LiFePO₄/C composite prepared under the optimal conditions exhibits an initial room temperature discharge capacity of 150.2 mA h g^?1 at a 0.2 C rate and a constant discharge capacity of about 105.7 mA h g^?1 at a 20.0 C rate after 50 cycles, showing promising potential as a novel cathode material for lithium ion batteries.     

Platinum deposition from hydrogen-ion beam irradiated solid precursor

We report a particular method of Pt/glassy carbon (GC) surface formation, based on a 15 keV H^+/? ion beam irradiation of thin H₂PtCl₆ × nH₂O layer placed over the GC surface. Hydrogen-ion beam irradiation provided an excellent adherence of Pt deposit, unlike to any other Pt-deposition method. Furthermore, the morphology and electrochemical activity of GC/Pt catalyst obtained at the fluence of 5 × 10¹⁷ cm^? 2 was found to be sensitive to the sign of charge of hydrogen ions. The electrochemical activity of such obtained Pt/GC surface toward oxygen reduction and ethanol oxidation was compared with the activity of the Pt deposits obtained by other more common reduction procedures.     

Synthesis of nanosize BPO4 under microwave irradiation

Nanosize BPO₄ was synthesized using H₃BO₃ and H₃PO₄ (85%) as raw materials under microwave irradiation. This reaction was performed at powers lower than 640 W and irradiation time ranging from 2.5 min to 5 min, which were only a fraction of the time required for conventional synthetic procedures. The structure of the as-prepared BPO₄ is analogous to that of a high cristobalite. The particle sizes of the samples irradiated at 640 and 400 W range from 40 nm to 90 nm and 30 nm to 60 nm, respectively. The effects of different conditions on the experimental outcome are also discussed.     

Production of TiC reinforced-aluminum composites with the addition of elemental carbon

TiC reinforced Al matrix composites were produced by the additions of elemental carbon to both Al + 4%Ti and Al + 5%Ti alloys. It is shown that the microstructure, phase composition as well as fracture behavior of the composites produced are controlled by the processing parameters, such as temperature, amount of excess carbon and duration. Composite microstructure subjected to 1300 °C for 15 min includes only TiC particles where the fracture occurs in a ductile manner whilst composites subjected to 1200 °C for 30 min contain Al₃Ti and TiC particles which show mixed mode of fracture behavior where Al₃Ti particles resulted in brittle fracture due to their coarser size.     

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

The aim of this work is to investigate the surface characteristics and corrosion behavior of NiTi (50.6 at.% Ni) shape memory alloy coated by a ceramic-like and highly biocompatible material, iridium oxide (IrO₂). IrO₂ coatings were prepared by thermal decomposition of H₂IrCl₆ · 6H₂O precursor solution at the temperature of 300 °C, 400 °C and 500 °C, respectively. The surface morphology and microstructure of the coatings were investigated by scanning electron microscope (SEM) and glancing angle X-ray diffraction (GAXRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the surface elemental composition. Corrosion resistance property of the coated samples was studied in a simulated body fluid at 37 ± 1 °C by electrochemical method. It was found that the morphology and microstructure of the coatings were closely related to the oxidizing temperatures. A relatively smooth, intact and amorphous coating was obtained when the H₂IrCl₆·6H₂O precursor solution (0.03 mol/L) was thermally decomposed at 300 °C for 0.5 h. Compared with the bare NiTi alloy, IrO₂ coated samples exhibited better corrosion resistance behavior to some extent.     

Effects of heat treatment on the microstructure of amorphous boron carbide coating deposited on graphite substrates by chemical vapor deposition

A two-layer boron carbide coating is deposited on a graphite substrate by chemical vapor deposition from a CH₄/BCl₃/H₂ precursor mixture at a low temperature of 950 °C and a reduced pressure of 10 KPa. Coated substrates are annealed at 1600 °C, 1700 °C, 1800 °C, 1900 °C and 2000 °C in high purity argon for 2 h, respectively. Structural evolution of the coatings is explored by electron microscopy and spectroscopy. Results demonstrate that the as-deposited coating is composed of pyrolytic carbon and amorphous boron carbide. A composition gradient of B and C is induced in each deposition. After annealing, B₄C crystallites precipitate out of the amorphous boron carbide and grow to several hundreds nanometers by receiving B and C from boron-doped pyrolytic carbon. Energy-dispersive spectroscopy proves that the crystallization is controlled by element diffusion activated by high temperature annealing, after that a larger concentration gradient of B and C is induced in the coating. Quantified Raman spectrum identifies a graphitization enhancement of pyrolytic carbon. Transmission electron microscopy exhibits an epitaxial growth of B₄C at layer/layer interface of the annealed coatings. Mechanism concerning the structural evolution on the basis of the experimental results is proposed.     

Effect of N2 / Ar gas flow ratio on the deposition of TiN/Ti coatings on NiTi shape memory alloy by PIIID

TiN coating with a thin Ti intermediate layer was deposited on the NiTi shape memory alloy substrate using plasma immersion ion implantation and deposition technique. The effect of nitrogen to argon gas flow ratio on the surface characteristics, chemical composition and mechanical properties of the as-deposited samples were investigated. Atomic force microscopy analysis indicates that all the coatings exhibited island morphology and the average root mean square (RMS) values were determined to be 2.912, 4.152 and 4.227 nm for N₂ / Ar ratios of 1 / 3, 1 / 2 and 2 / 3, respectively. The results of XPS and X-ray diffraction show that the chemical composition, phase composition and preferred orientation of the TiN coating varied significantly with the N₂ / Ar gas ratio. Nanoindentation, scratch and wear tests results demonstrated that coatings deposited with N₂ / Ar = 1 / 2 exhibited the highest hardness and elastic modulus, good adhesion strength and excellent wear resistance.     

Impact of high dose krypton ion irradiation on corrosion behavior of laser beam welded zircaloy-4

In order to study the effect of krypton ion irradiation on the aqueous corrosion behavior of laser beam welded zircaloy-4 (LBWZr4), the butt weld joint of zircaloy-4 was made by means of a carbon dioxide laser, subsequently the LBWZr4 samples were irradiated with Kr ions using an accelerator at an energy of 300 keV, with a dose range from 1 × 10¹⁵ to 3 × 10¹⁶ ions/cm² at about 150 °C. Three-sweep potentiodynamic polarization measurement was employed to evaluate the aqueous corrosion behavior of Kr-irradiated LBWZr4 in a 0.5 M H₂SO₄ solution. Scanning electron microscopy (SEM) was used to examine the surface topography of the Kr-irradiated LBWZr4 after the potentiodynamic polarization measurement. Transmission electron microscopy was employed to examine the change of microstructures in the irradiated surface. The polarization tests showed that compared with the passive current density of the as-received LBWZr4, the Kr-irradiated LBWZr4 is much lower; however, with the irradiation dose increasing from 1 × 10¹⁵ to 3 × 10¹⁶ ions/cm², the passive current density, closely related to the surface corrosion resistance, increased remarkably. The mechanism of the corrosion behavior transformation was due to the recrystallization of the amorphous phase induced by the lower ion irradiation.     

Nitrogen-doped hollow carbon spheres with enhanced electrochemical capacitive properties

Nitrogen-doped hollow carbon spheres (N-HCS) with uniform size have been synthesized via the hydrothermal method using pyrrole as the precursor. After carbonization at 850 °C, the average diameter of N-HCS is ca. 370 nm with shell thickness of ～15 nm. The electrochemical capacitive behavior of N-HCS was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1.0 M H₂SO₄ aqueous solution. Results show that N-HCS have high specific capacitance (345.2 F g^?1 at 0.2 A g^?1) and high-rate capability with the increase of the scan rate from 10 to 1000 mV s^?1 due to the synergetic effects of the unique hollow nanostructure and the N-doped thin carbon shell. In addition, the capacitance retains 98.1% after 1500 cycles even at a high loading current density of 10 A g^?1.     

Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni–C (graphitic) core–shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores of hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H_c = 138.4 O_e) and good ferromagnetism (M_r/M_s = 0.325).     

An activated microporous carbon prepared from phenol-melamine-formaldehyde resin for lithium ion battery anode

Microporous carbon anode materials were prepared from phenol-melamine-formaldehyde resin by ZnCl₂ and KOH activation. The physicochemical properties of the obtained carbon materials were characterized by scanning electron microscope, X-ray diffraction, Brunauer–Emmett–Teller, and elemental analysis. The electrochemical properties of the microporous carbon as anode materials in lithium ion secondary batteries were evaluated. At a current density of 100 mA g^?1, the carbon without activation shows a first discharge capacity of 515 mAh g^?1. After activation, the capacity improved obviously. The first discharge capacity of the carbon prepared by ZnCl₂ and KOH activation was 1010 and 2085 mAh g^?1, respectively. The reversible capacity of the carbon prepared by KOH activation was still as high as 717 mAh g^?1 after 20 cycles, which was much better than that activated by ZnCl₂. These results demonstrated that it may be a promising candidate as an anode material for lithium ion secondary batteries.     

Effect of different annealing atmospheres on crystallization and corrosion resistance of Al86Ni9La5 amorphous alloy

The effect of different annealing atmospheres (H₂, air, Ar and N₂) on precipitated phases, corrosion resistance and hardness of Al₈₆Ni₉La₅ amorphous alloy was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetry (TG), electrochemistry experiment and microhardness tester. During annealing at 523 K, the primary crystallized fcc-Al is independent on the annealing atmospheres. During annealing at 584 K, the final crystalline phases, i.e. fcc-Al + Al₁₁La₃ + Al₃Ni, are also independent on the different annealing atmospheres. However, during annealing at 523 K, H₂ and air can promote the eutectic crystallization process, and induce the formation of metastable Al₃Ni₂ phase. The promoting effect of different annealing atmospheres is in the order of H₂ > air > Ar > N₂. The microhardness and corrosion resistance in the 3.5 wt.% NaCl solution are improved by annealing in H₂ and air atmospheres. The property promotion caused by annealing process can be ascribed to the formation of nanocrystalline phases, which is possibly helpful to develop the alloy's application in the seawater environment.