Development of biomorphic alumina using egg shell membrane as bio-template

Hierarchical interwoven alumina was developed using egg shell membrane as a bio-template. Fibrous network of the egg shell membrane was replicated to form fibrous alumina networks by soaking the membranes in metal salt solution and by subsequent calcination. The synthesis was systematically studied by varying the calcination temperature (400 ? 1200 °C). Morphological features of the developed alumina networks were characterized using electron microscopes and structural investigations were carried out using X-ray diffractometer. Surface features of the hierarchical structures developed were also studied. Calcium and sulfur based compounds got crystallized from egg shell membranes along with alumina. The developed biomorphic networks by virtue of their high surface area and porous properties will be potential candidates for applications in water purification.     

Numerical Study of the Solid Volume Fraction and Pressure Drop of Fibrous Media by Response Surface Methodology

In order to establish a realistic fibrous media structure, internal microscopic cross‐sectional images were taken by scanning electron microscopy and then processed by Matlab. Finally, the 3D models of the fibrous media were reconstructed using Gambit software. The influences of structural parameters of the fibrous media on solid volume fraction and pressure drop were analyzed by response surface methodology, and the internal gas flow fields of the fibrous media were simulated using Ansys Fluent. The simulation results of the pressure drop are in good agreement with the Davies experimental correlation data.     

Molecular simulation study on the colloidal suspension within dilute fibrous media: The effect of particle concentration on partitioning

We investigated the molecular simulations based on the Gibbs ensemble Monte Carlo method, which was previously applied to the colloidal suspensions confined with a narrow pore. The long-range electrostatic interactions between the particle and the adjacent fiber and between pairs of particles are evaluated by adopting the earlier methods. For uncharged cases, the partition coefficient with non-dilute particle concentration decreases with increases in the ratio of particle radius to fiber radius. For charged systems with constant surface charges of both the particle and the fiber, the electrostatic interactions result in a different behavior according to the variations of particle concentration. Note that the particle concentration is associated with the effects of steric exclusion as well as particle-particle interaction. By developing an effective adjusting trial, the particle concentration in the bulk region has been kept as a constant during the simulation. The predicted density profiles of colloids around a fiber indicate that, whether the particles are uncharged or charged, the particle-particle interaction plays a significant role.     

随机排列纤维过滤器颗粒捕集特性的数值研究

结合Matlab软件和数值计算前处理软件Gambit中的Journal文件建立了随机排列纤维过滤器模型,利用计算流体动力学（CFD）技术对4种随机排列纤维过滤器内部气-固两相流动特性进行数值研究,并将数值计算值和经典模型及实验关联式进行了比较。结果表明：利用论文提出的建模方法可以得到与实际纤维过滤器相似的模型。过滤器压力损失的数值计算预测值和实验关联式吻合较好,误差均在2%以内。不同结构过滤器收集效率的数值计算结果和理论模型的趋势基本一致,且不同粒径范围的颗粒收集机理也不同。对于小粒径颗粒（dp〈0.5μm）,主要由布朗扩散起作用,dp〉1.5μm时,惯性碰撞贡献较大,当0.5μm≤dp≤1.5μm时,2种机理作用都较弱。另外,纤维直径和纤维填充密度分布会影响纤维过滤器的过滤性能,论文中,结构1（纤维直径和填充密度沿气流方向减小）的过滤器和结构3（纤维直径和填充密度沿气流方向增加）的收集效率高于结构2（在气流方向上纤维直径减小而填充密度增大）和4（在气流方向上纤维直径增大而填充密度减小）,而压力损失则恰恰相反。结构1在大颗粒的收集上好于结构3,对于小颗粒则正好相反。结构4对于所有类型的颗粒的收集都要好于结构2。     

Entangled structures as high cycle compression springs

Entangled structures, such as steel wool, can be used as inexpensive, high cycle, low stiffness, thin profile compressive springs where uniform pressure on a surface is required particularly in elevated temperature and/or harsh environments. Mechanical compression tests were performed on a variety of steel wool samples to determine the stress–strain curve behavior over high cycles. After initial conditioning cycles, good repeatability can be obtained with hysteresis dependent on strain. The results show a nonlinear behavior over large strains (>10%) and reasonable linear behavior for strains less than 10%. The properties of an entangled structure spring can be selected to achieve the desired stiffness for a particular application.     

SOFC cathode material of La1.2Sr0.8CoO4±δ with a fibrous morphology: Preparation and electrochemical performance

Using soluble salts as metal-ion sources and polyacrylonitrile (PAN) as a polymer matrix, La_1.2Sr_0.8CoO_4±δ cathode material with a fibrous morphology is prepared by electrostatic spinning, and microstructural characteristic of this material is investigated by field-emission scanning microscopy and X-ray diffraction. Electrochemical performance of the material in solid-oxide fuel cells is then tested. The results demonstrate that phase-pure La_1.2Sr_0.8CoO_4±δ fibrils with tetragonal structure can be prepared from fresh silky precursors using electrospinning after annealing at high temperature. Compared to the conventional cathode material that possesses a plain granular structure, La_1.2Sr_0.8CoO_4±δ fibrils exhibit superior electrochemical performance. At a temperature of 800 °C, the area specific resistance with this fibrous cathode is as low as 0.043 Ω cm², and maximum power density with the corresponding single-cell is 716 mW cm^?2, demonstrating the fast electrode kinetics in the O₂ reduction reaction. Comparatively, the area specific resistance with the plain cathode is 0.062 Ω cm², and the maximum power density with the corresponding single-cell is only 642 mW cm^?2. Under a constant voltage load of 0.6 V at a fixed temperature of 750 °C, the power output from a single-cell with the fiber-structured cathode maintains between 615 mW cm^?2 and 585 mW cm^?2 even after 15 h of running time, showing a slower fading rate and a more stable electrochemical performance than the plain cathode.     

Structure of porous electrodes in polymer electrolyte membrane fuel cells: An optical reconstruction technique

Computing flows and phase transport in porous media requires a physically representative geometric model. We present a simple method of digitizing the structure of fibrous porous media commonly used in polymer electrolyte membrane (PEM) fuel cells, the so-called gas diffusion layer (GDL). Employing an inverted microscope and image recognition software we process images of the GDL surface collected manually at different focal lengths with micrometer accuracy. Processing the series of images allows retrieval of local depths of the salient in-focus structural elements in each of the different images. These elements are then recombined into a depth-map representing the three-dimensional structure of the GDL surface. Superimposition of the in-focus portions of the structural elements distributed throughout the stack of images yields digitized data describing the geometry and structural attributes of the 3D surface of the GDL fibrous material.     

Comparison of Voxel-Based and Mesh-Based CFD Models for Aerosol Deposition on Complex Fibrous Filters

Aerosols represent a health risk since small droplets may enter the respiratory system and cause lung cancer, allergies, or diseases like COVID-19. In this work, an Eulerian-Lagrangian computational fluid dynamics model is used based on a voxel-based (GeoDict) and a mesh-based (StarCCM+) code. For evaluating accuracy and computational time of both models, fractional filtration efficiency and pressure drop are compared to an empirical solution for a single fiber and to experimental results for a complex 3D fibrous filter material. Simulation results of both methods are in good agreement with empirical and measurement results although the complex geometry of the fibers is captured more accurately by the unstructured mesh using the same resolution. Computing times are much faster using the voxel-based code.     

Washcoating of metallic monoliths with a MnCu catalyst for catalytic combustion of volatile organic compounds

A ready-made MnCu catalyst showing a good performance in the combustion of volatile organic compounds has been deposited on FeCrAlloy^® metallic monoliths by means of washcoating. With the aim of depositing a homogeneous and well-adhered layer of catalyst on the monoliths, the effects of a pre-coating with colloidal alumina as a primer, the solid concentration in the slurry, the addition of a stabilizer to the slurry, and the immersions number of the monolith in the slurry were studied. The addition of a stabilizer to the slurry was necessary to prevent sedimentation and to achieve reproducible washcoatings. The pre-coating of the monolith with the primer improved the washcoating adherence obtained with one impregnation but a better adherence did not compensate a lower solid load due to a lower surface roughness. A higher amount of deposited material was obtained with the slurry at 35 wt% making two impregnations. The obtained monoliths showed excellent catalytic activity in the combustion of ethyl acetate and toluene. The activity as well as the surface area and pore volume of each monolith increased with the amount of retained solid.     

Electrospun nanofibrous Ni/LaAlO3 catalysts for syngas production by high temperature methane partial oxidation

Ni/Al₂O₃ catalysts have been widely used for methane reforming while the formation of NiAl₂O₄ with low reducibility reduces catalyst efficiency. La₂O₃ was used to promote the catalytic activity of Ni/Al₂O₃ catalysts through improving Ni dispersion. LaAlO₃ perovskite showed catalytic activity in methane coupling and also used as a catalyst support for methane reforming. This study systematically investigated the effect of La₂O₃ addition into Ni/Al₂O₃ catalysts and found the formation of LaAlO₃ perovskite played an important role, which requires high crystallization temperatures. The thermally-stable structure of nanofibrous catalysts was employed to develop high-performance Ni/LaAlO₃ catalysts. High calcination temperature resulted in the enhanced crystallinity of LaAlO₃ perovskite, improved Ni reducibility and strengthened catalyst/support interaction, which contributed to high catalytic performance during methane partial oxidation. The Ni/LaAlO₃ catalyst calcined at 1100 °C generated a CH₄ conversion of 91.2% during methane partial oxidation with H₂ and CO selectivities of 95.5% and 92.4%, respectively. It is because La₂O₃ addition into Ni/Al₂O₃ promoted Ni reduction via forming LaAlO₃. Therefore, an efficient and thermally-stable fibrous Ni/LaAlO₃ catalyst has been developed for high temperature methane partial oxidation.