Fibrous Aluminum Research Articles

Dual-active-component assembly catalyst based continuous flow system for organic reactions with high processing rate

Designing and fabricating suitable packing catalyst with high activity and low flow resistance for continuous flow system is highly desirable but remains a grand challenge. Here we report a facile one-pot strategy to synthesize a dual-active-component assembly catalyst (DACAC) with N-doped holey graphene (NHG) anchored single-atom Pd (Pd1) self-assembled on fibrous aluminum silicate cluster (FASC) skeleton. The resultant Pd1/NHG–FASC DACAC possesses dual-active-components (i.e., Pd atoms and NHG) and hierarchical architecture and can be easily integrated into a fixed-bed platform to construct a catalytic continuous flow system. This fixed-bed system based on the assembly catalyst architecture effectively drives continuous flow reactions with excellent catalytic efficiency for nitroarene reduction and phenylboronic acid oxidative hydroxylation reactions. The processing rate for catalytic reduction of 4-nitrophenol is 1.5 × 10–3 mmol·mg−1·min−1, which is much higher than that of other previously reported packing catalysts based fixed-bed systems. The activity enhancement strategy of dual-active-component provides a new approach to design highly efficient catalytic materials.

Simulation of Phase Change Material Absorbers for Passive Cooling of Solar Systems

One of the main challenges that face the reliable use of photovoltaic solar systems in hot arid regions is the prevailing high temperatures during the day. To overcome this issue, Phase Change Materials (PCM) are used for passive cooling providing different options to attain sufficient thermal management solutions for different applications. Passive cooling can be achieved by adjusting a heat sink to the solar PV module. This can be realized by attaching a PCM layer or sensible heat storage to the backside of PV panels. Few studies have reported on simplified modeling and numerical procedures using the apparent heat capacity formulation and volume averaging technique as a robust approach to solving such sophisticated problems with minimal computational efforts, high accuracy, and in a short period of time. However, there is still a need to bridge the large-scale gap between the macroscale within the PCM layer, with a moving melting front, and the length scale of PV modules. Hence, this work focuses on modeling and simulating PCM-Matrix Absorbers (PCM-MA) that consist of fibrous aluminum cellular structure filled with PCM for passive thermal management of PV panels using apparent heat capacity formulation and homogenization based on volume averaging technique. COMSOL Multiphysics FEM software was used for the numerical simulation of the phase change problem by using a Smoothed Heaviside step function to overcome the singularity of PCM challenge that arises with sharp melting temperatures. To validate the proposed model, it has been compared with a benchmark analytical solution for an ice melting problem, i.e., the Stefan problem, in a semi-finite slab, i.e., Neumann’s solution under the same assumptions and boundary conditions. The specific characteristics of phase change and evolution of melting front with time, heat capacity change with the temperature at different times, and with locations along the slab height are presented. As the phase change is modeled to take place over a mushy region, i.e., a narrow temperature interval rather than a sharp melting point, the results show a good coincidence of the heat capacity profile and its peak at different times and locations. The validated model can be used for the optimization of PCM-MA for any specific geographical location and other applications such as the passive cooling of buildings with PCM integrated with the outer envelope. To this end, the results of the simulation in this work are shown to be in agreement with those obtained from the analytical solution.

N-Doped holey graphene assembled on fibrous aluminum silicate for efficient carbocatalysis in fixed-bed systems

A fixed-bed based catalytic system is ideal for a green organic synthesis process, benefitting from the advantages of easy product purification, simple operation, and convenient catalyst recycling.

Continuous flow reduction of organic dyes over Pd-Fe alloy based fibrous catalyst in a fixed-bed system

Continuous flow chemistry has been considered as a green technology for modern catalytic industry as it not only improves the manufacture efficiency but also facilitates the sustainability. Herein we report a facile method for synthesizing bimetallic Pd-Fe alloy nanoparticles catalysts anchored on N doped carbon (NC) functionalized fibrous aluminium silicate fibers (ASFs). The as-prepared ASF@NC/PdFe catalytic fibers are packed into a column to construct a fixed-bed system, which exhibits excellent treatment capacity and durability for continuous catalytic hydrogenation of organic dyes. Typically, the flow rate of the fixed-bed is high up to 200 mL/min for 4-nitrophenol and methylene blue reduction, which is one of the most efficient fixed-bed catalytic systems. The catalytic turnover frequency is calculated to be as high as 59.6 min−1 due to the enhanced synergetic effect of Pd and Fe. Furthermore, only slight loss of activity for the fixed-bed is observed even after nine successive catalytic cycles.

Latest Research on the Development of High-Quality Aluminum-Oxide Ceramics (Review). Part 2. Synthesis and Sintering of Nanopowders, Sol-Gel and Other Methods of Producing Finely Disperse and Fibrous Aluminum Oxide

Russian dissertations on aluminum oxide ceramic and methods of producing it covering the period from 2000 to present are reviewed. Attention is focused primarily on fine structural ceramic. Part 2 of this review includes synthesis of nanopowders of aluminum oxide and their use for sintering, the sol-gel method of producing Al2O3, and other methods of synthesizing finely disperse and fibrous Al2O3 for corundum ceramic.

Heat Transfer and Pressure Loss Characteristics of a Channel Flow with Fibrous Aluminum Layer

Heat Transfer and Pressure Loss Characteristics of a Channel Flow with Fibrous Aluminum Layer

Ultrafine Particle (UFP) Exposures in an Aluminium Smelter: Soderberg vs. Prebake Potrooms

The objectives of this work were to evaluate ultrafine particle (UFP) exposures during aluminium smelting in Soderberg and prebake potrooms. Particle concentrations were monitored using the P-Trak 8525 and aerosol particle size distributions were monitored with the electrical low pressure impactor (ELPI). UFP samples were analyzed for chemical composition by transmission electron microscopy (TEM). Workers who accomplished tasks in the Soderberg cell environment were more exposed to UFP than those who worked in the prebake; however, the specific task of anode shift in the prebake process was an important source of UFPs. More than 92 % and 98 % of particles had aerodynamic diameters less than 98 nm in the Soderberg and prebake processes, respectively. TEM/EDS analysis suggests that workers are exposed to short fibrous aluminium particles with a nanometric aerodynamic diameter. Overall, this study suggests that occupational hygiene practices aimed at evaluating UFP exposures should include monitoring of the particle number concentration, monitoring of the particle size distribution, and characterization of the nanoscale fraction of the aerosol.

Effect of dehydration on porous structure of monolithic aerogels based on fibrous aluminum oxyhydroxide

Aluminum oxide monolithic aerogels (PMAOs) with specific surfaces of up to 400 m2/g and densities of up to 0.004 g/cm3 were obtained by the direct oxidation of metallic aluminum by water vapors. Studies of the obtained aerogels using the methods of scanning and transmission electron microscopy showed that a freshly prepared aerogel represents the amorphous structure from alumina fibrous with a diameter of about 5 nm. Parameters of a porous aerogel structure were determined from the isotherms of adsorption of nitrogen vapors at 77 K. It is shown that the specific surface area decreases by 50% upon the dehydration of aerogel by temperature pretreatment at 900°C until the phase transition temperature is reached. At the same time, heat treatment at temperatures above 1200°C results in a phase transition at which significant contraction of structure occurs and the specific surface area decreases to 20 m2/g. The number of primary adsorption centers was obtained from comparative plots of water vapor adsorption. It was found that preliminary dehydration only slightly affects the number of primary centers of water adsorption.

Experimental investigation of initial and subsequent yield surfaces for laminated metal matrix composites

The aim of this work is to construct yield surfaces to describe initial yielding and characterize hardening behavior of a highly anisotropic material. A methodology for constructing yield surfaces for isotropic materials using axial–torsion loading is extended to highly anisotropic materials. The technique uses a sensitive definition of yielding based on permanent strain rather than offset strain, and enables multiple yield points and multiple yield surfaces to be conducted on a single specimen. A target value of 20 × 10 −6 is used for Al 2O 3 fiber reinforced aluminum laminates having a fiber volume fraction of 0.55. Sixteen radial probes are used to define the yield locus in the axial–shear stress plane. Initial yield surfaces for [0 4], [90 4], and [0/90] 2 fibrous aluminum laminates are well described by ellipses in the axial–shear stress plane having aspect ratios of 10, 2.5, and 3.3, respectively. For reference, the aspect ratio of the Mises ellipse for an isotropic material is 1.73. Initial yield surfaces do not have a tension–compression asymmetry. Four overload profiles (plus, ex, hourglass, and zee) are applied to characterize hardening of a [0/90] 2 laminate by constructing 30 subsequent yield surfaces. Parameters to describe the center and axes of an ellipse are regressed to the yield points. The results clearly indicate that kinematic hardening dominates so that material state evolution can be described by tracking the center of the yield locus. For a nonproportional overload of ( σ, τ) = (500, 70) MPa, the center of the yield locus translated to ( σ, τ) = (430, 37) MPa and the ellipse major axis was only 110 MPa.

Influence of the structure of polytetrafluoroethylene-based nanocomposites on their tribotechnical characteristics

Results of investigation of the influence of the structure of nanocomposites based on polytetrafluoroethylene and fibrous aluminum- and magnesium-oxide nanopowders on their tribotechnical characteristics are presented. The basic regularities of structure formation in the studied polymer composite materials are established. The interrelation between the supramolecular composite structure and the nanofiller chemical nature, phase composition, and concentration is investigated. The structural transformations in the composites agrees well with the changes in their physicomechanical and tribotechnical characteristics. The most perfect supramolecular structure, which is characterized by the formation of uniformly shaped and sized spherulites evenly distributed in the matrix volume, corresponds to the best deformation-strength characteristics of the material and to decrease in its friction coefficient and wear.

Thermal Evolution Of The “Mouse Fur” Of Fibrous Aluminium Oxide/Hydroxide Formed On Amalgamated Aluminium Upon Reaction With Moist Air

Nano-fibres of amorphous aluminium oxide/hydroxide have been obtained via reaction of amalgamated aluminium with moist air. Thermal transformation of the as prepared sample was followed by X-ray powder diffraction and electron microscopy techniques. Crystallisation of γ -Al2O3 nanocrystals inside the amorphous fibres starts at 400 °C and the maximum crystal size is achieved at 700 - 800 °C. The fibrous transition alumina matrix transforms into a sponge-like morphology between 800 and 900 °C. Annealing at higher temperature results in the condensation into large globular α-Al2O3 crystals. The entire γ - to α-Al2O3 transformation occurs via two consecutive steps of coalescence and explosive character, respectively. The direct contact between transition alumina crystals governs the transformation. The presence of some other transition alumina is inferred from high resolution electron microscopy studies, and antiphase boundaries in {111} of the spinel type structure for γ -Al2O3 obviously determine the crystallographic path between them

Solidification microstructure affecting ductility in semi-solid-cast products

The semi-solid process produces globular instead of dendritic alpha phase and extraordinarily fine fibrous aluminum–silicon eutectic structure, which apparently enables exceptionally high ductility, even when casting copper-containing and secondary alloys that would normally have limited ductility. Contrary to the experience with liquid cast products of the same alloys, semi-solid products can be given a T-5 heat treatment without loss of ductility, a significant advantage in terms of dimensional controls and treatment costs. This paper will describe solidification events that lead to the unique alpha aluminum, eutectic aluminum–silicon and secondary phase structures of semi-solid products and provide evidence to date that it is these unique characteristics that are responsible for exceptional ductility, especially in the T-5 temper.

나노 및 마이크로 알루미늄의 가수분해에 의한 알루미늄 수산화물의 형성

A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than <TEX>$10\;{\mu}m$</TEX> in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.

Amorphous Aluminum Hydroxide Formed at the Earliest Weathering Stages of K-Feldspar

AbstractWeathering products formed on the surface of K-feldspar in Yakushima Island, Japan were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). XRD confirmed that the weathering products were composed mainly of gibbsite and halloysite. SEM, TEM and EDX clearly showed formation of amorphous aluminum hydroxide exhibiting 2 distinct habits: 1) curled fibrous or circular forms less than 0.02 μm in diameter; and 2) a spherical habit less than 1.0 μm in diameter. The fibrous aluminum hydroxide exhibited curled fibrous forms or circular forms less than 0.02 μm in diameter and gave a diffuse electron diffraction halo. EDX indicated that the material consisted mainly of Al and very small amounts of Si and Fe. The spherical aluminum hydroxide also gave similar EDX and electron diffraction characteristics to the fibrous material. These fibrous and spherical aluminum hydroxides must be formed as a metastable phase in the earliest weathering stages, and transformed into a stable phase of gibbsite and halloysite as the reaction proceeded.

On the evaluation of fibrous particles in remote ambient air

Nuclepore filters were used for sampling fibrous particles in ambient air. The fiber counting and fiber size measurements were done by means of SEM-methods. One square mm of the filter surface containing ambient air particles was photographed and all fiber-like particles on this surface were counted and measured. The number of fibers, distribution of fiber lengths and diameters and the estimated fiber aerodynamic diameters were plotted. The specific identification of asbestos fibers was made by electron microprobe analysis. Certain elements such as Si, Fe, Mg, Al, Mn, Ca, and Na as well as ratios such as Fe/Si, Mg/Si proved to be approximative identification factors for ambient asbestos. Many other inorganic fibrous particles were found in the urban atmosphere as well as in the atmosphere of remote regions. Fibrous gypsum, fibrous ammonium sulfates, fibrous aluminium silicates, fibrious mica, and quartz were identified among these particles. Even in remote ambient air, relatively high concentrations of fibrous particles (10 3−10 4 m −3; nanogram region) could be measured, although the concentrations of asbestos fibers were usually smaller than 10 2 m −3 (picogram region).

The influence of fibrous aluminium nitride on the strength of sintered AIN-Y 2O : Komeya, K. and Inoue, H. Transactions and Journal of the British Ceramic Society, Vol 70, No 3, pp 107–113 (1971)

The influence of fibrous aluminium nitride on the strength of sintered AIN-Y 2O : Komeya, K. and Inoue, H. Transactions and Journal of the British Ceramic Society, Vol 70, No 3, pp 107–113 (1971)