Characterization of Al2O3-TiO2 nano porous solar absorbers derived via MAO/sol-gel hybrid process

Micro arc oxidation combined with sol-gel process was used to develop solar selective absorber systems for the first time. Phase structure and chemical composition of the layers were studied by XRD and XPS techniques. The layers consisted of anatase, rutile, α-alumina, γ-alumina, and Al₂TiO₅ phases with varying fractions with the growth conditions. SEM and AFM investigations revealed a porous structure (pore size: 60-550 nm) with a rough surface where pore size and surface roughness increased with the applied voltage. Solar absorption and emission coefficients were measured using UV-Vis-NIR and IR spectrophotometry. In spite of being so thin, the fabricated samples revealed a high solar absorptivity of α = 0.99 and low thermal emissivity of ε = 0.06. A formation mechanism was proposed based on the electrochemical foundations as well.     

Development of nano CeO2-incorporated high performance hot-dip zinc coating

Nano CeO₂ composite has been synthesized and explored as an effective activator for enhancing galvanic performance of hot-dip zinc coatings. The pre-treatment conditions and bath composition were optimized based on preliminary test results. Particle size of the CeO₂ was characterized by XRD and TEM analyses. Various electrochemical techniques such as OCP decay measurements, Anodic polarization, Salt spray analysis and Electrochemical Impedance Spectroscopy (EIS) were adopted to evaluate galvanic performance of the CeO₂-incorporated coatings. The coating incorporated with an optimum amount of CeO₂, i.e. 0.1%, exhibited best galvanic performance. The incorporation of CeO₂ caused significant improvement in galvanic and other physical characteristics of the coatings. It also resulted in lowering of the alloying reaction between zinc and iron, but enhanced barrier protection of the interior layers.     

Quantification of metallic coating failure on carbon fiber reinforced plastics using acoustic emission

Carbon fiber reinforced plastic substrates were subsequently coated with an electrochemically applied nickel and an electroplated copper layer. The coating-substrate system was loaded in four-point bending and the acoustic emission from coating failure was recorded during loading. The acoustic emission signals were analyzed using pattern recognition and frequency analysis techniques. This approach yields three distinguishable types of acoustic emission signals, which are correlated to three different failure mechanisms: i) nickel cracking ii) copper cracking and iii) delamination between the two coating layers. To confirm the correlation between the types of acoustic emission signals and the respective failure mechanisms and to assess the validity of the acoustic emission method to describe mechanical failure, the micro-mechanical fracture energies released during mechanical loading were calculated based on microscopic measurements of the crack progress utilizing scanning electron microscopy and scanning acoustic microscopy. These energies were compared to the associated acoustic emission signals energy for each failure mechanism. We found the calculated micro-mechanical energy values to be proportional to the measured accumulated acoustic emission energy of the associated acoustic emission signal type. We conclude that the reported failure classification method offers the possibility to compare fracture toughness values in multilayered coatings with multiple failure types, derived solely from acoustic emission energies.     

The growth of carbon coating layers on iron particles and the effect of alloying the iron with silicon

Magnetic fine particles of metallic Fe coated with graphitic carbon layers were synthesized by annealing Fe₂O₃ particles with carbon powders at 1673 K in nitrogen atmosphere. For comparison, SiC was added to Fe₂O₃. X-ray diffraction measurement showed that the lattice constants of Fe changed depending on the Si contents. Mössbauer spectroscopy confirmed that Fe-Si alloys were formed by the Si addition and that the iron carbide disappeared. Electron microscope images revealed that the thickness of carbon coating layers increased from 24 nm to 36 nm as a result of the Si addition. Soaking tests showed that the corrosion resistance of the carbon-coated Fe particles was improved by the addition of Si. The results suggest that Si caused C to leave the Fe cores and move to the surface to form a carbon coating.     

Effects of nickel coating thickness on electric properties of nickel/carbon hybrid fibers

In this work, nickel/carbon hybrid fibers were prepared by the electrolytic plating on carbon fibers in order to improve electric conductivity of the carbon fibers; the effects of nickel content and coating thickness on the electric conductivity of the fibers were studied. The structural properties and surface morphologies of the hybrid fibers were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electric conductivity of the fibers was measured using a 4-point probe method. As for experimental results, it was observed that the electric conductivity of the nickel/carbon hybrid fibers was dramatically increased in the presence of metallic nickel particles, with the best result in the condition of over 0.75 μm of the thickness due to the minimization of the inner pores.     

Effect of temperature on deposition of LaPO4 coatings produced by ultrasonic-based coating process on steel substrates

High-adhesion LaPO₄ coatings were fabricated on steel substrates at temperatures of 150-400 °C after a 10 min treatment using an ultrasonic-based coating process. The principle underlying this process is the collision of ultrasonically accelerated hard balls with the substrate surface that is covered by loosely adhered LaPO₄ particles. The repeated substrate-to-ball collisions flatten the precoated LaPO₄ particles, bond them together and cold weld them to the substrate. The coating thickness, roughness and structure were found to depend on the substrate temperature. The LaPO₄ coatings produced at temperatures ranging from 150 to 250 °C exhibited a granular and porous structure. The treatment at temperatures higher than 300 °C enabled the production of rather dense coatings.     

The production of a multi-walled carbon nanotube/hexamethylene diisocyanate nanocomposite coating on copper by electrophoretic deposition

A multi-walled carbon nanotube (MWCNT)/hexamethylene diisocyanate (HDI) composite coating with excellent microstructural homogeneity was produced on copper substrate from aqueous suspensions using electrophoretic deposition (EPD). The concentrations of different additives were optimized to obtain stable suspensions of MWCNT. At the optimum EPD condition, a coating of thickness 170 μm was obtained at voltage of 30 V and deposition time of 3 min with well dispersed MWCNT in the polymer matrix. The deposit yield increased linearly with deposition time. The adhesive strength of the MWCNT/HDI composite coating was assessed qualitatively by peel test. The composite coated specimen showed greater resistance to corrosion in the chloride containing environment with inhibiting efficiency 96.65%. The mechanism for adhered coating is due to better wetting of HDI on copper substrate followed by acid-base reaction between metal hydroxide and polymeric resin. The potential application of the nanocomposite coatings could be protecting copper based metallic structure in marine environment.     

Fabrication and application of nano/microcrystalline composite diamond coated drawing dies using alternative carbon sources

Nano/microcrystalline composite diamond films were deposited on the holes of WC-6%Co drawing dies by a two-step procedure using alternative carbon sources, i.e., methane for the microcrystalline diamond (MCD) layer and acetone for the nanocrystalline diamond (NCD) layer. Moreover, the monolayer methane-MCD and acetone-NCD coated drawing dies were fabricated as comparisons. The adhesion and wear rates of the diamond coated drawing dies were also tested by an inner hole polishing apparatus. Compared with mono-layer diamond coated drawing die, the composite diamond coated one exhibits better comprehensive performance, including higher adhesive strength and better wear resistance than the NCD one, and smoother surface (R_a=65.3 nm) than the MCD one (R_a=95.6 nm) after polishing at the same time. Compared with the NCD coated drawing die, the working lifetime of the composite diamond coated one is increased by nearly 20 times.     

Improvement of the electrochemical performance of LiMn2O4 cathode active material by lithium borosilicate (LBS) surface coating for lithium-ion batteries

The LBS coating on the surface of spinel LiMn₂O₄ powder was carried out using the solid-state method, followed by heating at 425 °C for 5 h in air. The powder X-ray diffraction pattern of the LBS-coated spinel LiMn₂O₄ showed that the LBS coating medium was not incorporated in the spinel bulk structure. The SEM result showed that the LBS coating particles were homogeneously distributed on the surface of the LiMn₂O₄ powder particles. The effect of the lithium borosilicate (LBS) coating on the charge-discharge cycling performance of spinel powder (LiMn₂O₄) was studied in the range of 3.5-4.5 V at 1C. The electrochemical results showed that LBS-coated spinel exhibited a more stable cycle performance than bare spinel. The capacity retention of LBS-coated spinel was more than 93.3% after 70 cycles at room temperature, which was maintained at 71.6% after 70 cycles at 55 °C. The improvement of electrochemical performance may be attributed to suppression of Mn²⁺ dissolution into the electrolyte via the LBS glass layer.     

Electrochemical hydrogen storage of NdMg12–Ni composites modified with carbon nanotubes and BN particles

In this work, the electrochemical performance of NdMg₁₂–Ni composite electrode in alkaline solution and the effect of the surface modification with carbon nanotubes (CNTs) and boron nitride (BN) particles on the NdMg₁₂–Ni composite were investigated. The NdMg₁₂ alloy was synthesized by a salt-cover-melting and a subsequent quenching process. The NdMg₁₂–Ni–BN and NdMg₁₂–Ni–CNTs composites were prepared by ball-milling NdMg₁₂ alloy, Ni powders and CNTs or BN particles. It is found that CNTs or BN particles are mainly attached onto the surface of the NdMg₁₂–Ni composite after the ball-milling process. The electrochemical experiment results indicate that the NdMg₁₂–Ni composites modified with CNTs or BN particles have the improved electrochemical performance. In particular, the NdMg₁₂–Ni–5 wt.% CNTs and NdMg₁₂–Ni–3 wt.% BN composites have the higher initial discharge capacity of 416.6 mAh/g and 442.9 mAh/g, respectively, larger than the original NdMg₁₂–Ni composite. The large amount of grain boundaries and crystalline defects, induced during the ball-milling process, can accelerate the bulk hydrogen diffusion and provide more surface active sites for the electrochemical reaction of the composites. However, the cycle stability of the composites modified by CNTs or BN particles is still not satisfactory for the practical application.     

Ti6Al4V钛合金表面Al2O3颗粒改性微弧氧化涂层制备及性能

微弧氧化技术是一门新的表面处理技术,在很多领域有着广泛的应用前景,但其结构受限于电解液成分。本文通过在磷酸盐电解液中加入Al2O3陶瓷颗粒,使得在Ti6Al4V钛合金表面的微弧氧化涂层结构和性能得到改性。涂层的结构和性能通过扫描电镜和XRD衍射仪进行表征和测试,涂层的抗高温氧化性能和热震性能通过高温热循环氧化试验和热震试验进行测试。结果表明,通过在电解液中添加Al2O3陶瓷颗粒,涂层由Al2TiO5 and TiO2组成,涂层更为致密,表现出更为优异的抗高温氧化和热震性能。电解液中游动的Al2O3陶瓷颗粒在微弧氧化过程中被吸入到样品表面并进入涂层,涂层的结构和性能得到改性。     

The growth of single Fe2B phase on low carbon steel via phase homogenization in electrochemical boriding (PHEB)

In this study, we introduce a new electrochemical boriding method that results in the formation of a single-phase Fe₂B layer on low carbon steel substrates. Although FeB phase is much harder and more common than Fe₂B in all types of boriding operations, it has very poor fracture toughness; hence, it can fracture or delaminate easily from the surface under high normal or tangential loading. We call the new method “phase homogenization in electrochemical boriding” (PHEB), in which carbon steel samples undergo electrochemical boriding for about 15 min at 950 °C in a molten electrolyte consisting of 90% borax and 10% sodium carbonate, then after the electrical power to the electrodes is stopped, the samples are left in the bath for an additional 45 min without any polarization. The typical current density during the electrochemical boriding is about 200 mA/cm². The total original thickness of the resultant boride layer after 15 min boriding was about 60 μm (consisting of 20 μm FeB layer and 40 μm Fe₂B layer); however, during the additional phase homogenization period of 45 min, the thickness of the boride layer increased to 75 μm and consisted of only Fe₂B phase, as confirmed by glancing-angle x-ray diffraction and scanning electron microscopy in backscattering mode. The microscopic characterization of the boride layers revealed a dense, homogeneous, thick boride layer with microhardness of about 16 GPa. The fracture behavior and adhesion of the boride layer were evaluated by the Daimler-Benz Rockwell C test and found to be excellent, i.e., consistent with an HF1 rating.     

以MOFs为前驱体制备二维碳带/Al2O3及氮掺杂碳带/Al2O3去除高氟废水

以2D-MOFs为前驱体,采用溶剂热法合成铝基金属有机骨架MIL-53(Al),采用煅烧法合成2D碳带/Al2O3.为了解氟在碳带/Al2O3和氮掺杂碳带/Al2O3上的吸附行为,对吸附参数如pH、液固比、吸附动力学、吸附热力学和阴离子竞争等进行研究.碳带/Al2O3对氟的吸附为化学吸附和多层吸附;而氮掺杂碳带/Al2...     

Study of magnetic field assisted mechanochemical polishing process for inner surface of Si3N4 ceramic components: Finishing characteristics under wet finishing using distilled water

This study discusses the finishing characteristics of a magnetic field assisted mechanochemical polishing process using Cr₂O₃ abrasive mixed with magnetic particles in the case of wet finishing using distilled water, which was proposed for internal finishing of Si₃N₄ fine ceramic tubes. It was clarified that a highly accurate finishing can be achieved more efficiently in the case of wet finishing using distilled water compared with dry finishing. Moreover, those conditions necessary to achieve high efficiency finishing are discussed.