Fabrication of conductive porous alumina (CPA) structurally modified with carbon nanotubes (CNT)

A novel binary porous composite nano-carbon networks (NCNs)/alumina, which is denoted as electrically conductive porous alumina (CPA), was structurally modified by carbon nanotubes (CNT) pre-treated with mixed concentrated acids at 60 °C for 6 h in this study. This conductive ceramics (CCs) was fabricated by combination of gelcasting and high temperature reductive sintering (HTRS) in novel atmosphere. CNT pre-treatment leading to the increased hydrophilicity makes it possible to make uniformly dispersed CNT/alumina slurry. And by HTRS in Ar at 1700 °C for 2 h, well-gelled polymer net-paths in green body prepared by gelcasting technology were totally converted to nano-carbon networks (NCNs) without destruction of CNT. NCN with graphitic crystal structure was evaluated by Raman spectroscopy in sintered ceramic body. Moreover, comparing with as-received CNT, the decreased surface defect of detected composite also supported the further graphitization of CNT via HTRS in Ar instead of burning out. With the aid of field-emission scanning electronic microscopy (FE-SEM) observation, the increased alumina grains in sintered ceramic body CNT/NCN/alumina was valid. Moreover, it was demonstrated that there were three components in this composite, which is carbon filler with two different forms (CNT and NCN) and alumina matrix. And these three components CNT covered with Al₂O₃ particles (Al₂O₃/CNT), NCN and alumina grains (alumina) co-exist in four different situations as follows: (a) Al₂O₃/CNT–alumina co-junction, (b) Al₂O₃/CNT–NCN co-junction, (c) Al₂O₃/CNT–alumina–NCN and (d) Al₂O₃/CNT mesh between alumina boundaries. Furthermore, by comparing with binary composite NCN/alumina (CPA), the increased flexural strength of ternary composite CNT/NCN/alumina (CNT/CPA) up to 38 MPa was attributed to the reinforcement CNT acting as elastic bridge in composite.     

Facile fabrication of SiO2/Al2O3 composite microspheres with a simple electrostatic attraction strategy

SiO₂/Al₂O₃ composite microspheres with SiO₂ core/Al₂O₃ shell structure and high surface area were prepared by depositing Al₂O₃ colloid particles on the surface of monodispersed microporous silica microspheres using a simple electrostatic attraction and heterogeneous nucleation strategy, and then calcined at 600 °C for 4 h. The prepared products were characterized with differential thermal analysis and thermogravimetric analysis (DTA/TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). It was found that uniform alumina coating could be deposited on the surface of silica microspheres by adjusting the pH values of the reaction solution to an optimal pH value of about 6.0. The specific surface area and pore volume of the SiO₂/Al₂O₃ composite microspheres calcined at 600 °C were 653 m² g⁻¹ and 0.34 ml g⁻¹, respectively.     

A study of the erosion-corrosion behavior of nano-Cr2O3 particles reinforced Ni-based composite alloying layer in aqueous slurry environment

To investigate the role of nano-Cr₂O₃ particles on the erosion-corrosion behavior of composite alloying layer, a nano-Cr₂O₃ particles reinforced Ni-based composite alloying layer was fabricated onto AISI 316L stainless steel (SS) via a duplex surface treatment, consisting of Ni/nano-Cr₂O₃ predeposited by electric brush plating, and subsequent Ni-Cr-Mo-Cu multi-element surface alloying by a double glow process. The microstructure and composition of composite alloying layer were characterized by means of X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results indicated that the added nano-Cr₂O₃ particles were homogeneously distributed in the alloying layer and didn’t decompose or react with surrounding metal matrix under alloying temperature (1000 °C) condition. A series of electrochemical techniques, including potentiodynamic polarization, open circuit potential (OCP), current response and electrochemical impedance spectroscopy (EIS), was employed to evaluate the corrosion properties of nano-Cr₂O₃ particles reinforced composite alloying layer under various hydrodynamic conditions. Erosion-corrosion tests were conducted in 3.5% NaCl solution plus sand particles with varying concentration (50-150 g/L) at different rotation speeds (600-1100 rpm). To estimate the influence of the nature of different nano-particles on the erosion-corrosion property of composite alloying layer, nano-SiO₂ particles reinforced Ni-based composite alloying layer, single alloying layer and 316L SS was selected as the reference materials for all the corrosion and erosion-corrosion tests.     

自组装磷化镍纳米片阵列电极的电催化析氢性能研究

可持续发展的清洁氢能源是未来能源发展的方向之一,因而发展高效廉价的析氢材料变得尤为重要。本文首次通过水热和退火的方式制备出自组装磷化镍纳米片阵列结构,并通过SEM和XRD等技术表征这种结构的形貌和组成成分。与众多关于Ni-P纳米材料集中在酸性体系下的析氢电化学研究不同,本文首次通过在碱性条件下稳态极化曲线(LSV)、Tafel极化曲线、电流-时间曲线(i-t)以及交流阻抗曲线探究了其作为电解水析氢纳米电催化电极材料的电化学性能。该材料的电极具有特殊的纳米形貌结构和性质,使其具有更低的析氢反应电位、更大的析氢反应活性和较好的稳定性,具有替代贵金属作为水解析氢材料的潜力。     

Fe2O3 core-NaCo[Fe(CN)6] shell nanoparticles—Synthesis and characterization

A facile precipitation route was developed for the synthesis of cobalt hexacyanoferrate (CoHCF) as a thin shell around cores of nanoparticles of iron(III) oxide, forming nanoparticles of iron(III) oxide@CoHCF (n-Fe₂O₃@NaCo[Fe(CN)₆]). The morphology and structure of the as-prepared n-Fe₂O₃@NaCo[Fe(CN)₆] were characterized by the techniques of electron microscopies, X-ray diffraction measurements, X-ray photoelectron spectroscopy, infrared spectroscopy and thermogravimetry. Carbon composite electrodes of n-Fe₂O₃@NaCo[Fe(CN)₆] were prepared and the electrochemical behavior of the nanoparticles was evaluated using cyclic voltammetry. The redox couples of n-Fe₂O₃@NaCo[Fe(CN)₆] were investigated and the diffusion coefficients of counter cation in the shell of CoHCF were obtained. The effect of size of particles and the structure of CoHCF was also evaluated. n-Fe₂O₃@NaCo[Fe(CN)₆] represented prominent electrocatalytic activity toward the oxidation of some biologically active compounds.     

Preparation of polyimide/Al2O3 composite films as improved solid dielectrics

Considerable demand for solid thin-film dielectrics with high dielectric constants for use in the fabrication of capacitors has been observed. In this study, polyimide (PI)/Al₂O₃ composite films were prepared by incorporating different micron-sized α-Al₂O₃ contents into PI derived from pyromellitic dianyhydride and 4,4′-oxydianiline via ultrasonication. Chemical structure, morphology, dielectric and thermal properties were investigated by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), LCR meter and Perkin Elmer Pyris 6. FTIR spectra showed complete imidization, and all characteristic peaks of the imide groups are observed in PI and PI/Al₂O₃ composite films. XRD patterns revealed that the PI/Al₂O₃ composite exhibits peaks similar to those of α-Al₂O₃, indicating that the crystal structure of α-Al₂O₃ remains unchanged and stable after being doped into the PI matrix. SEM micrographs showed uniform distribution of α-Al₂O₃ particles in the PI matrix. Meanwhile, the dielectric constant, dielectric loss and thermal stability of PI/Al₂O₃ increases with the addition of α-Al₂O₃ content.     

Hydrothermal synthesis of carbon nanotube/cubic Fe3O4 nanocomposite for enhanced performance supercapacitor electrode material

Carbon nanotube/Fe₃O₄ (CNT/Fe₃O₄) nanocomposite with well-dispersed Fe₃O₄ nano-cubes inlaid on the surfaces of carbon nanotubes, was synthesized through an easy and efficient hydrothermal method. The electrochemical behaviors of the nanocomposite were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry in 6 M KOH electrolyte. Results demonstrated that CNT as the supporting material could significantly improve the supercapacitor (SC) performance of the CNT/Fe₃O₄ composite. Comparing with pure Fe₃O₄, the resulting composite exhibited improved specific capacitances of 117.2 F/g at 10 mA/cm² (3 times than that of pure Fe₃O₄), excellent cyclic stability and a maximum energy density of 16.2 Wh/kg. The much improved electrochemical performances could be attributed to the good conductivity of CNTs as well as the anchored Fe₃O₄ particles on the CNTs.     

Synthesis and electrocatalytic property of mono-dispersed Ag/Fe3O4 composite micro-sphere

One-step reaction was designed to synthesize mono-dispersed Ag/Fe₃O₄ micro-sphere with different Ag content via a facile and easily controlled hydrothermal method without use of any surfactant. The phases and composition analysis of the as-prepared samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The morphology of the samples was observed by transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FE-SEM). The results revealed that the Ag/Fe₃O₄ composite samples with different Ag content were micro-spheres with almost the identical size of 175 nm or so in diameter. The electrocatalytic activity of the resultant samples modified on a glassy carbon electrode (GCE) for p-nitrophenol reduction in a basic solution was investigated. The results indicated that all the samples exhibited enhanced electrocatalytic activity for p-nitrophenol reduction, and the sample with 3% Ag exhibited the highest electrocatalytic one.     

Characterization of metal-supported Al2O3 thin films by scanning electrochemical microscopy

In this paper, physiochemical properties of amorphous alumina thin films, grown by the metal organic chemical vapour deposition process on the surface of platinum (Pt/Al₂O₃) and stainless steel (SS/Al₂O₃), were investigated in aqueous media. The study was performed by the use of scanning electrochemical microscopy (SECM), which allowed obtaining information on uniformity, topography and chemical stability/reactivity of the alumina coatings with high spatial resolution. In particular, the effects due to local acid, base and fluoride ions attack on alumina layers of thickness of about 250 nm (in the Pt/Al₂O₃ sample) and 1000 nm (in the SS/Al₂O₃ sample) were investigated. In the acid and base attack, high concentrations of H₂SO₄ and KOH were electrogenerated locally by the use of a 25 μm diameter platinum microelectrode. The latter was also used as SECM tip to monitor the chemical effect on the alumina layers. It was found that, regardless of the thickness of the film, alumina provided good resistance against local attack of concentrated H₂SO₄; instead, the film dissolved when subjected to KOH attack. The dissolution rate depended on several experimental parameters, such as SECM-tip to substrate distance, electrolysis time and alumina film thickness. The alumina layer proved also relatively poor resistance to etching in 0.1 M NaF solutions.     

Whiskers of Al2O3 as reinforcement of a powder metallurgical 6061 aluminium matrix composite

An Al-Mg-Si alloy matrix composite reinforced with 10 vol.% of alumina whiskers (Al₂O₃w) has been processed by powder metallurgy and investigated. The Al₂O₃w were produced as single crystal c-axis alpha-alumina fibres at pre-pilot scale via vapour-liquid-solid (VLS) deposition in a cold-wall air-tight furnace with alumina linings. As far as we know, this is the first report of the utilization of whiskers of Al₂O₃ as reinforcing elements for Al alloys. Tensile tests have been performed on the composite at room and high temperatures. Results show that the AA6061 alloy reinforced with the as-produced Al₂O₃ whiskers has remarkably high mechanical properties at room temperature. This is attributed to the high quality of the Al₂O₃ single crystals and to the strong bonding attained between them and the 6061 alloy matrix.     

Preparation and characterization of Nb2O5-Al2O3 composite oxide formed by cathodic electroplating and anodizing

Al foil was coated with niobium oxide by cathodic electroplating and anodized in a neutral boric acid solution to achieve high capacitance in a thin film capacitor. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed the niobium oxide layer on Al to be a hydroxide-rich amorphous phase. The film was crystalline and had stoichiometric stability after annealing at temperatures up to 600 °C followed by anodizing at 500 V, and the specific capacitance of the Nb₂O₅-Al₂O₃ composite oxide was approximately 27% higher than that of Al₂O₃ without a Nb₂O₅ layer. The capacitance was quite stable to the resonance frequency. Overall, the Nb₂O₅-Al₂O₃ composite oxide film is a suitable material for thin film capacitors.     

Solvothermal synthesis of sheet-like Co3O4 and Ag/Co3O4 nanocomposites and their electrocatalysis performances

Precursors of Co₃O₄ and Ag/Co₃O₄ composites with sheet-like shape were synthesized with assistance of ethylene glycol via a solvothermal process. The final samples were obtained by calcining each precursor at 400 °C. The as-prepared samples were identified and characterized by thermogravimetric analysis (TG) and differential thermal gravimetric (DTG) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The Co₃O₄ and Ag/Co₃O₄ composite nanosheets were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol and H₂O₂ reduction respectively in a basic solution. The electrocatalytic results showed that p-nitrophenol could be reduced by pure Co₃O₄ at a large peak current but a rather higher peak potential, and could be reduced effectively by Ag/Co₃O₄ composites at lower potential. Ag/Co₃O₄ composites with 6% Ag displayed the highest electrocatalytic activity for H₂O₂ reduction at the largest peak current and a lower peak potential. The reduction peak potentials of H₂O₂ all reduced a great deal using Ag/Co₃O₄ composite.     

Magnetic and chemical properties investigation of Fe–Ni electrodeposited alloy on titanium substrate at the presence of alumina

Iron-nickel alloys have different applications in electronic systems depending on their magnetic properties. In this research, Iron-nickel alloy and its composite with Al₂O₃ particles were produced by electro wining method using a titanium cathode which is traditionally produced through a melting process (pyrometallurgy). The effect of the processing parameters on the products specification was investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and alternative gradient field magnetometer (AGFM). The produced alloy could be specified as; high saturation magnetization, low coercivity, and low magnetization, and so could be classified in the soft magnetic alloys groups. The best magnetic property of the alloy was obtained at low current density with a coercivity of about 3.10 O_e. SEM images show the cauliflower-like morphology of the product. At the presence of Al₂O₃ nanoparticles in the electrolyte, a well-dispersed particles of alumina in the alloy was observed with a decrease in the magnetization and increase in the coercivity of the alloy. Also, the modified alloy with Al₂O₃ shows better corrosion resistance in NaCl solution.

     

Microstructure and characterization of Ni-Co/Al2O3 composite coatings by pulse reversal electrodeposit

Ni-Co/Al₂O₃ composite coatings were obtained by pulse reversal electrodeposit (PRC) and direct current electrodeposit (DC). The microstructure of the coatings was characterized by means of SEM, XRD and TEM. Hardness, wear resistance and macro residual stress of coatings were also investigated. The results showed that the microstructure and performance of the coatings were significantly affected by the electrodeposit methods and the Al₂O₃ particles content. The PRC composite coatings exhibited compact surface, high hardness and excellent wear resistance. The macro residual stress of PRC composite coatings was lower than that of DC ones. With the increasing of Al₂O₃ particles content, the hardness and wear resistance of the composite coatings increased.     

Influence of SiC, Si3N4 and Al2O3 particles on the structure and properties of electrodeposited Ni

The structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si₃N₄ and Al₂O₃ were compared. A comparison was made with respect to structure, morphology, microhardness and tribological behaviour. The coatings were characterized with optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) technique. The cross-sectional microscopy studies revealed that the particles were uniformly distributed in all the composites. However, a difference in the surface morphology was revealed from SEM studies. The microhardness studies revealed that Si₃N₄ reinforced composite showed higher hardness compared to SiC and Al₂O₃ composite. This was attributed to the reduced crystallite size of Ni — 12 nm compared to 16 nm (SiC) and 23 nm (Al₂O₃) in the composite coating. The tribological performance of these coatings studied using a Pin-on-disk wear tester, revealed that Si₃N₄ reinforced composite exhibited better wear resistance compared to SiC and Al₂O₃ composites. However, no significant variation in the coefficient of friction was observed for all the three composites.     

Refinement of microstructure and improvement of mechanical properties of Al/Al2O3 cast composite by accumulative roll bonding process

Some important problems associated with cast metal matrix composites (MMCs) include non-uniformity of the reinforcement particles, high porosity content, and weak bonding between reinforcement and matrix, which collectively result in low mechanical properties. Accumulative roll bonding (ARB) process was used in this study as a very effective method for refinement of microstructure and improvement of mechanical properties of the cast Al/10 vol.% Al₂O₃ composite. The average particle size of the Al₂O₃ was 3 μm. The results revealed that the microstructure of the composite after eleven cycles of the ARB had an excellent distribution of alumina particles in the aluminum matrix without any noticeable porosity. The results also indicated that the tensile strength and elongation of the composites increased as the number of ARB cycles increased. After eleven ARB cycles tensile strength and elongation values reached 158.1 MPa and 7.8%, which were 2.54 and 2.36 times greater than those of the as-cast MMC, respectively.     

磁控溅射Al掺杂Al2O3薄膜耐蚀性能研究

采用中频电源反应溅射在Si和SS304不锈钢表面制备两种不同成分的Al-O涂层,利用X射线衍射、扫描电镜、纳米压痕仪、电化学工作站和Cu装饰实验对涂层的结构及性能进行了分析。结果表明:室温下制备的涂层,掺Al后沉积速率是纯Al_2O_3的10倍,两种非晶涂层截面无明显的形貌特征,纯Al_2O_3涂层表面有微裂纹存在,掺杂Al的Al_2O_3涂层表现出更为优异的耐腐蚀性能,这与其表面的Al发生钝化氧化反应有关。     

Dielectric and mechanical properties of three-component Al2O3/MWCNTs/polyarylene ether nitrile micro-nanocomposite

Polyarylene ether nitrile (PEN)/multi-walled carbon nanotubes (MWCNTs)/alumina (Al₂O₃) micro-nanocomposite material films were fabricated by uncomplicated and accessible method, overcoming the difficulty of bad interaction between MWCNTs and PEN matrix. Scanning electron microscope revealed that MWCNTs were isolated by Al₂O₃ and realized better dispersion in matrix. Al₂O₃ particles hindered conductive MWCNTs from bridging with each other, working as dielectric obstacle. In addition, the micro-nanocomposite has excellent thermal stability and possesses high performance in dielectric and mechanical. The investigation results showed that the dielectric constant increased to 100.8 (50 Hz), which is 20 times higher than that of pure PEN while the dielectric loss was only 0.1 with 7 wt% MWCNTs loading. Meanwhile, the mechanical property indicated that the composite with 7 wt% MWCNTs loading reached their highest values. In other words, the composite with 7 wt% MWCNTs loading possess excellent mechanical property simultaneously as it reached the percolation threshold.     

多孔Ni-WC复合电极的制备及其在酸性溶液中的电催化析氢性能

目前,关于多孔Ni-WC电极的电催化析氢(HER)性能的报道较少。以多孔海绵镍为基体,采用复合电沉积制备多孔Ni-(WC)x复合电极。运用扫描电镜(SEM)和X射仪线衍射仪(XRD)表征电极的表面形貌和微观结构,通过阴极极化、电化学阻抗(EIS)、循环伏安、计时电流法研究多孔Ni-(WC)x电极在0.5 mol/L H2SO4溶液中的电催化析氢性能。结果表明:与多孔基体Ni电极相比,多孔Ni-(WC)x电极具有较低的析氢过电位、较低的电化学反应阻抗、较小的表观活化能以及较大的交换电流密度;随着镀液中WC浓度的升高,所制备的多孔Ni-(WC)x电极的电催化析氢活性增强,其中Ni-(WC)40电极的表观交换电流密度是多孔Ni基体电极的966.7倍,其表观活化能为5.95 kJ/mol,并具有较好的耐蚀性和析氢稳定性。     

In situ processing and aging behaviour of an aluminium/Al2O3 composite

Reactive sintering involving a displacement reaction between aluminium and CuO powders was applied to fabricate an aluminium based composite. The two powders were mixed in a ball mill and uniaxially pressed before sintering in nitrogen atmosphere at 900 °C. During sintering a displacement reaction between CuO and aluminium occurred, which resulted in in situ synthesis of alumina particles. Differential thermal analysis (DTA), X-ray diffractometry (XRD), optical and scanning electron microscopies were used to investigate the phase and microstructural changes taking place during processing of the composite. Results revealed that no chemical reaction occurred during ball milling and Al₂O₃ phase developed in two stages during sintering of the compact. Below 700 °C, amorphous alumina formed which transformed to crystalline alumina at higher temperature. Aging response of the composite was examined as a function of time in temperature range of 180–220 °C. Composite attained a peak hardness value of 133 H_v after 4 h of aging at 200 °C.