Surface Review and Letters

Deposition of phosphate conversion coating using electrochemical methods have many advantages such as low phosphating temperature, low energy cost and good properties of fabricated coating and in recent times increasingly employed for deposition of phosphate coating. Deposition mechanism of coating which is fabricated using electrochemical methods is different from those obtained by conventional chemical methods, consequently, the properties of electrophosphate coating is also different from those conventional phosphate coating. In this paper, recent understanding of deposition mechanism of electrophosphate coating is reviewed. The microstructure, composition, thickness and corrosion behavior of electrophosphate coatings and effect of different factors of those properties were also reviewed.

Facing the challenge of low energy density of conventional electric double layer supercapacitors, researchers have long been focusing on the development of novel pseudocapacitive electrode materials with higher energy densities. Since capacitive charge storage reaction mostly occurs on the interface of electrode and electrolyte, the interface chemistry determines the achievable power and energy densities of a supercapacitor. Consequently, understanding of surface–interface reaction mechanism is a key towards efficient design of high-performance supercapacitor electrode materials. In this paper, we have reviewed the recent advances in the understanding of surfaces–interfaces in the system of pseudocapacitive supercapacitors. With significant research advancements in the understanding of surface–interface of supercapacitors, novel colloidal electrode materials with improved surface–interface structures have been developed in our previous work, which have the potential to deliver both high energy and power densities. This review aims to provide an in-depth analysis on the surface–interface control approaches to improve the energy and power densities of supercapacitors.

This work presents the influence of changing Ar:N₂ gas ratio on the growth and properties of InAlN films. InAlN films were deposited on $p$-type Si(111) substrates by using magnetron co-sputtering method in 6:12, 10:10, 12:8 and 12:6 Ar:N₂ mixtures at 300${}^{\circ }$C. The surface, structural, electrical and optical properties of the deposited films were evaluated at different Ar:N₂ ratios. The grain size and film thickness were increased by increasing the Ar flow with respect to N₂. Structural characterization by X-ray diffraction (XRD) revealed an improvement in the crystalline quality of the $c$-axis-oriented InAlN film by adjusting the Ar:N₂ ratio to 12:8, however no diffraction peak corresponding to InAlN was detected at 6:12 Ar:N₂ mixture. The surface roughness of InAlN film exhibited an increasing trend whereas the electrical resistivity of the film was decreased by increasing the Ar:N₂ ratio. The bandgap of InAlN film was calculated from the optical reflectance spectra and it was found to change by changing the Ar:N₂ gas ratio. The analysis of results from this work shows that the InAlN film with improved physical properties can be obtained through reactive magnetron co-sputtering method by adjusting the Ar:N₂mixture to 12:8.

Plasma surface alloying (PSA) technique was employed with nickel as incident ions to prepare the TiNi/Ti₂Ni alloyed layer on surface of Ti6Al4V. High-temperature friction and wear performance of TiNi/Ti₂Ni alloyed layer and the Ti6Al4V substrate were evaluated at 500${}^{\circ }$C. The results indicated that the TiNi/Ti₂Ni alloyed layer exhibited superior high-temperature wear performance. The variations of friction coefficient were the same rule but wear rate was lower compared to Ti6Al4V substrate. The wear mechanism of TiNi/Ti₂Ni alloyed layer was mainly slight abrasion and the Ti6Al4V substrate showed abrasion and oxidation wear. The friction coefficient of the TiNi/Ti₂Ni alloyed layer decreased from 0.90 to 0.50 with the increase of temperature from room temperature to 500${}^{\circ }$C.

In this work, the static corrosion behaviors of Fe(Al), and 20 wt.% Al₂O₃/Fe(Al) composites with and without 4 wt.% Cr produced by mechanical alloying (MA) and plasma activated sintering (PAS) were investigated. The results showed that the main corrosion failure mode was pitting, and Fe(Al) had higher static corrosion resistance than those of Al₂O₃/Fe(Al) composites. The second phase Al₂O₃ addition resulted in an increase in phase interface and a large difference of the electron density between the Fe(Al) matrix and Al₂O₃ reinforcement. All these made the phase interface become the corrosion weaknesses. With 4 wt.% Cr addition, the static corrosion weight loss rate reduced by about 20% because Cr element could improve the stability of Al₂O₃ passivation film on the composite surface.

In order to improve the performance of the Ti6Al4V (TC4) spur gear, a Mo surface modified layer is prepared by the plasma surface metallurgy technique. The element concentration, microstructure and elastoplastic properties are investigated with glow-discharge optical emission spectroscope (GDOES), scanning electron microscope, optical microscope (OM) and nanoindenter. Engaging with 41Cr4 steel gears, the wear resistances of the treated and untreated TC4 spur gears are evaluated through running-in and operation tests performed by a friction and wear tester under lubricated conditions. By finite element analysis, contact stress distributions in the TC4 and 41Cr4 spur gears pair are quantitatively determined. The results indicate that, being compact and uniform, the Mo-modified layer has higher hardness and retains relatively fine plasticity. The wear resistance of the treated TC4 spur gear is improved significantly.

The thermal and mechanical properties of nasopharyngeal airway (NPA) samples are improved by irradiation using 4keV oxygen and nitrogen ion beams with different ion fluences varying from $25\times 10^{17}$ ions/cm² to $65\times 10^{17}$ ions/cm². The thermal stability of NPA medical device increases with increasing nitrogen and oxygen ion fluences. The tensile strength increased from 48MPa for unirradiated sample to 74MPa for samples irradiated with nitrogen and to 58MPa for samples irradiated with oxygen ion, while the elongation at break decreases for irradiated samples. Silver thin films are deposited on NPA medical device samples using 4keV argon ion beam. The XRD spectra demonstrated that silver nanoparticles are deposited on NPA medical device substrate. The effects of Ag thin film on gram-positive and gram-negative bacteria are studied.

In this work we synthesize bamboo charcoal (BC)/ZnO nanocomposite by sol–gel technique. The synthesized BC/ZnO nanocomposite is surface modified by atmospheric air and oxygen plasma to improve the surface functional properties. The structure and morphology of the resultant nanocomposite are analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDAX) and ultraviolet–visible spectroscopy (UV–vis) and its antibacterial behavior is analyzed by the disc diffusion plate technique. We obtained new bonds in FTIR results on BC/ZnO nanocomposite after oxygen plasma treatment. From SEM results we observed there was a plasma etching process that occurred on the resulting BC/ZnO nanocomposite after plasma treatment. Significantly, the antimicrobial behavior also increased after oxygen plasma treatment.

The structural, surface and transport properties of Sn–Ag alloys were investigated by X-ray diffraction (XRD), radial heat flow, energy-dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM) and four-point probe techniques. We observed that the samples had tetragonal crystal symmetry except for the pure Ag sample which had cubic crystal symmetry, and with the addition of Ag the cell parameters increased slightly. Smooth surfaces with a clear grain boundary for the samples were shown on the SEM micrographs. The grain sizes of pure Ag, $\beta$-Sn and the formed Ag₃Sn intermetallic compound phase for Sn–$x$ wt.% Ag [$x=1.5$, 3.5] binary alloys were determined to be 316nm, between 92nm and 80nm and between 36nm and 34nm, respectively. The values of electrical resistivity for pure Sn, pure Ag and Sn–$x$ wt.% Ag [$x=1.5$, 3.5] were obtained to be $22.60\times 10^{-8}$, $62.36\times 10^{-8}$, $23.54\times 10^{-8}$, $24.62\times 10^{-8}$$\mathrm{\Omega }\cdot$m at the temperature range of 300–450K, respectively. Thermal conductivity values of pure Sn and Sn–$x$ wt.% Ag [$x=1.5$, 3.5] binary alloys were found to be 60.60$\pm$3.75, 69.00$\pm$4.27 and 84.60$\pm$5.24W/Km. These values slightly decreased with increasing temperature and increase with increasing of the Ag composition. Additionally, the temperature coefficients of thermal conductivity and electrical resistivity and the Lorenz numbers were calculated.

Metal (iron and nickel) films have been deposited on soft elastic polydimethylsiloxane (PDMS) substrates by direct current sputtering technique and the impurity induced wrinkling patterns are investigated by using optical microscopy and atomic force microscopy. It is found that the metal films can spontaneously form disordered wrinkles due to the isotropic compressive stress. In the vicinity of film impurities such as extraneous particles, linear defects, cracks and thickness-gradient film edges, the stress field becomes anisotropic owing to symmetry breaking and thus complex wrinkling patterns including straight stripes, herringbones, crossings, labyrinths and their transitions can be observed. The morphological evolutions, structural characteristics and physical mechanisms of the impurity induced wrinkles have been discussed and analyzed based on the continuum elastic theory.

The Fe–Al–Nb alloyed layer was coated on 45 steel by the plasma niobiumizing modification to improve the microstructure and oxidation resistance of Fe–Al coating prepared by hot-dipping aluminum. The alloyed layer growth followed the typical Volmer–Weber mode with the modification time growing (2–4 h), which was carried out at 1073K and pressure of 40Pa. Its surface morphology was compact without any defects, meanwhile, there was a transition layer between the Fe–Al–Nb alloyed layer and the substrate. The mass increase of Fe–Al–Nb specimen after oxidizing at 873, 973 and 1073K for 100h was less than that of the Fe–Al and untreated 45 steel specimen, it owed to the diffusing fully of the Fe, Al and Nb atoms during high-temperature oxidation, forming a compact protective Nb, Al-rich oxidation film on the surface of the Fe–Al–Nb alloyed layer, and the occurrence of the internal oxidation phenomenon between the loose iron oxides layer and the Fe–Al–Nb alloyed layer at 973K for 100h protected the internal coating from further penetration of oxygen. In addition, the Fe₂Nb precipitates and Nb carbides dispersed through the alloyed layer, which were good for improving the strength, creep rupture resistance and inhibiting the Kendal effect at high-temperature.

Enamel glaze was added with glass powders of different sizes and masses and fired into enamel coatings on the surface of low-carbon steel. Acid resistance of the enamel coatings in H₂SO₄ solution was analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and mass loss of acid corrosion. As was discovered in research, the acid corrosion quantity in the enamel coatings decreased with the decrease in the particle size of the glass powder when the particle size of the additive glass powder reduced from 100$\mu$m to 1–2$\mu$m and heated the prepared enamel coatings in the H₂SO₄ solution until 80${}^{\circ }$C and kept for 48h. When the additive amount of the glass powder increased from 5% to 20%, the surface of the enamel coating was smooth and flat with good glossiness and without defects like obvious bubbles and cracks, and the acid corrosion quantity decreased with increase in the additive amount of glass powder, which decreased from 43.24mg/cm${}^2\cdot$d to 4.28mg/cm².d, satisfying the acid-proof performance requirements of industrial enamel coatings.

Due to the biocompatibility, mechanical strength and esthetics properties, titanium–porcelain prosthetic plays an important role in prosthodontics. However, weak bonding strength and considerable thickness of the porcelain restrict its application. Whether we can find a method to increase the bonding strength and reduce the thickness of the porcelain is an acute problem. In this study, ceramic coatings with similar color of nature teeth are fabricated on the surface of pure titanium by micro-arc oxidation (MAO). The colors, thickness and bonding strength of the coatings can be controlled by adding ferrous sulfate into the electrolytes. These new coatings can be used in titanium–porcelain prosthetic to substitute the opaque and dentin porcelain which can enhance the bonding strength and decrease the thickness of the porcelain compared with the conventional technique.

In this work, PVA/Ag nanocomposites films were prepared using solution casting technique, these films were irradiated with Argon ion beam to modify the structure. The main objective of the study is to enhance the optical and electrical properties of the polymer nanocomposites films by irradiation. The conventional characterization techniques such as UV–Visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM) and dielectric measurement are employed to understand the structure–property relations. FTIR analysis of these composite films shows chemical changes and a significant impact on them can be observed after irradiation. After doping, the XRD data shows silver nanoparticles formation in the PVA polymer. The band gap energy of samples is decreased with increases in the concentration of silver nanoparticles and ion beam fluence, which gives clear indication that ion beam irradiation induced defects are formed in the composite systems. The electrical conductivity, dielectric loss ${\epsilon }^{\prime \prime }$ and dielectric constant ${\epsilon }^{\prime }$ are increased with increasing ion beam fluence and Ag dopant concentration.

This paper investigates the relations between soil organic carbon (SOC) and other physicochemical indices in low hills of Chifeng, Inner Mongolia, and thus to help with soil modification in low hills there. Grey relational analysis and stepwise regression analysis were used to uncover the relations of SOC with total N (TN), pH, available P (AP), available K (AK), and microbial biomass carbon (MBC) under eight land use patterns in a typical small watershed in Chifeng. The eight land uses were Prunus sibirica land, Caragana microphylla land, Populus simonii land, Ulmus pumila land, natural grassland, Pinus Tableulaeformis $\times$ P. sibirica mixed land, secondary forest of natural bush land, and agricultural land. The average SOC contents in the 0–100cm layer in the above eight land use patterns are 7.72, 5.32, 7.40, 6.11, 3.14, 10.26, 17.51 and 5.34g/kg, respectively, indicating significant differences. The relation coefficients of SOC with TN, pH, MBC, AK, and AP are 0.70, 0.66, 0.63, 0.57 and 0.55, respectively, under all land use patterns. SOC contents are significantly different among these land use patterns, and the relation coefficients of SOC with other physicochemical indices rank in the order as: $\mathrm{\text{TN}}>\mathrm{\text{pH}}>\mathrm{\text{MBC}}>\mathrm{\text{AK}}>\mathrm{\text{AP}}$. The optimum regression equation of SOC ($Y)$ with TN ($X_2)$ and pH ($X_5)$ was built: $Y=-6.2698+19.3832X_2+0.0102X_5$, ($R^2=0.85$).

This study employs swelling deformation test for estimating the fractal dimension of salt-modified bentonite soil by measuring the void ratio of montmorillonite ($e_m$) and the effective stress ($p_e$). For the compacted Tsukinuno bentonite, a typical Na-montmorillonite, the fractal dimension is tested by the swelling deformation test conducted in sodium chloride solutions with different concentrations. According to the results, the fractal dimension of the specimens is essentially constant irrespective of the concentration of inundating NaCl solution. The strong correlation of the results from the swelling deformation test with those from the nitrogen adsorption test indicates that the swelling deformation test is an effective laboratory method for testing the fractal dimension of compacted bentonite in salt solution.

In this research paper, in total 212 individual leakage-free Polymethylmethacrylate (PMMA) microfluidic devices are fabricated by maskless lithography, hot embossing lithography and direct bonding technique. The effect of channel aspect ratio on dyed water flow is investigated using these microfluidic devices. Experimental studies show that the dyed water flow is faster on the surface of higher wettability. The effect of capillary pressure on dyed water flow is studied in the fabricated PMMA microfluidic devices. According to the experimental observations, the centrifugal force has prominent effect on the dyed water flow. Also, the effect of bend angle is investigated on the surface-driven capillary flow of water. The polystyrene microparticles have been separated in the microfluidic lab-on-a-chip systems using the investigated flow features. A 100% separation efficiency is achieved in these lab-on-a-chip systems. These microfluidic lab-on-a-chip systems can be used to separate blood cells from human whole blood for further clinical tests. These experimental studies are important in bioengineering applications. The effect of bend angle as channel geometry to control the surface-driven capillary flow is investigated as a novel approach to control the separation time in microfluidic lab-on-a-chip systems. Also, the effect of surface wettability as surface property to control the surface-driven capillary flow is investigated as a novel approach to control the separation time in microfluidic lab-on-a-chip systems.

Microarc oxidation (MAO) composite coatings containing rutile TiO₂ were produced on 2024 aluminum alloy in an electrolyte with nanorutile TiO₂ particles. The microstructure and properties of the composite coatings were analyzed by SEM, EDS, laser confocal microscope, XRD, Vickers hardness tester, scratch test and friction test, respectively. The results showed that the composite coatings consisted of $\gamma$-Al₂O₃, $\alpha$-Al₂O₃, mullite and rutile TiO₂. With increasing concentration of rutile TiO₂ particles in the electrolyte, the compactness of the composite coatings was improved significantly. The abrasion performance of the microarc oxidation composite coatings containing rutile TiO₂ was better than that of MAO coatings without rutile TiO₂.