Porous Metal Fiber Research Articles

An investigation of hollow NiCrAl metal fiber porous material for high-temperature sealing

Porous metal fiber materials are a type of low-density material promising for functional and structural applications. Unlike traditional metal fiber porous materials, this study developed a novel hollow metal fiber porous material based on carbon fibers. Nickel was electroplated on the surface of the chopped carbon fiber, then the carbon core was removed by wet hydrogen sintering, and finally, Cr and Al were infiltrated by gas phase alloying to obtain the finished product. SEM showed that its internal structure was connected by metal fibers interlaced and overlapped to form a three-dimensional network porous structure. TEM and XRD proved that Ni (fcc) is the main phase of the material, and the addition of Cr and Al elements causes Ni lattice distortion. The compressive strength of the material at 900 °C is 4.44 MPa. In addition, the material's strength decreases with the heat treatment temperature increasing. The thermal conductivity of the NiCrAl porous material increases with the temperature, which is 0.143 W/(m·K) at room temperature and 0.416 W/(m·K) at 900 ℃. TG analyses showed that the NiCrAl porous material possessed excellent high-temperature and oxidation-resistance properties. Quartz lamp heating tests showed that the material had good thermal insulation, as the temperature dropped by about 230 °C after passing through the material. The average permeability of the material at room temperature is 5.46 e-6D. This metal fiber porous material has both the inherent properties of metal and the functional properties of porous materials such as lightweight, high-temperature resistance, heat insulation, etc. It is a promising high-temperature sealing material.

Heat Transfer Experiment on the Air Side of a Radiator Using Sintered Porous Metal Fiber

Heat Transfer Experiment on the Air Side of a Radiator Using Sintered Porous Metal Fiber

Fabrication of porous metal fiber sintered sheet as a flow field for proton exchange membrane fuel cell

To improve the diffusion performance of reactive gas, a porous copper fiber sintered sheet (PCFSS) was fabricated and used as the flow field for proton exchange membrane fuel cell (PEMFC). The pressure and flow velocity distribution of the reaction gas in the PCFSS was firstly compared with the serpentine flow field by using the Fluent simulation software. Our results showed that the superiority of PCFSS in the uniformity of gas diffusion was observed. The total resistance of PEMFC with PCFSS in different porosities was obtained. And the advantages of PCFSS in electronic transmission were found by comparing with the serpentine flow field. Besides, the influences of different operating conditions and different porosities of porous flow fields on the performance of PEMFC were experimentally investigated. With the cell temperature of 70 °C as well as the humidification temperature of 60 °C, a PEMFC with PCFSS of 70% porosity exhibited better performance.

Preparing a novel gradient porous metal fiber sintered felt with better manufacturability for hydrogen production via methanol steam reforming

The porous copper fiber sintered felts with gradient porosity structure (gradient PCFSFs) as catalyst supports is beneficial for heat and mass transfer for methanol steam reforming (MSR). However, the previously developed gradient PCFSF based on the velocity distribution introduces curved interface between different porosity portions, making the mold pressing method for its preparation more sensitive to tiny process changes. To improve its manufacturability, a novel gradient PCFSF with planar interface (PCFSF-SLR) is proposed in this paper by fabrication with multi-step mold pressing and solid phase sintering method using cutting copper fibers. Furthermore, MSR experiments under different gas hourly space velocities and reaction temperatures are conducted to verify the characteristics of PCFSF-SLR loaded with Cu/Zn/Al/Zr catalyst. The results have shown that the reaction characteristics of the PCFSF-SLR were similar to those with curved interfaces, and PCFSF-SLRs with a middle portion porosity of 0.9 have better hydrogen production performance and lower carbon monoxide concentration. More importantly, the results indicated that the methanol conversion and hydrogen flow rate of the gradient PCFSF with planar interface and porosity of 0.7-0.9-0.8 were close or even almost the same with that of the best gradient PCFSFs with curved interface and porosities of 0.7-0.9-0.8 and 0.8-0.9-0.7. Therefore, the proposed PCFSF-SLR provides a superior alternative to gradient PCFSFs with better manufacturability.

Sound absorption performance of porous metal fiber materials with different structures

Porous metal fiber materials (PMFMs) with gradient structure for the thickness above 10 mm can be used widely in the field of noise controlling because of excellent sound absorption coefficient. But, how does the sound absorption coefficient of PMFMs with the thickness below 3 mm? In the paper, green felts of 316L stainless steel fibers with fibers diameters of 8–20 μm were used to manufacture the PMFMs (the thickness of 2–3 mm) with different structures by the sintering process at the vacuum condition. Sound absorption coefficients of the PMFMs were measured in the 4206 two-microphone impedance tube with the sound wave frequency ranging from 50 Hz to 6400 Hz. The results show that the sound absorption coefficient of the PMFMs with gradient structure is largely affected by the interface between different layers. Furthermore, although the thickness of PMFMs is only 2 mm or 3 mm, the average sound absorption coefficient of gradient structure is much higher than that of single-layer structure at the same thickness.

Laser sintering and laser parameters optimization for porous foam microchannel reactor

Porous foam microchannel reactor can effectively improve the reaction efficiency of Methanol reforming hydrogen production. Currently, porous foam microchannel reactors are primarily formed by the solid phase and liquid phase sintering techniques which generally require the metal fiber sheet of semi-finished products sinter at 800-1000℃ temperature conditions for 30–60 minutes. In this paper, a method of laser-sintered porous metal fiber sintering plate is proposed. Compared with the traditional methods, laser sintering technology has the advantages of shorter sintering time and retaining the surface microstructure which is more conducive to the adhesion of the catalyst. The effects of laser power, scanning rate, scanning distance, and scanning path on the sintering effect were also studied and analyzed. The results show that the porosity of copper fiber laser sintering sheets can reach 80% by laser sintering. When the laser sintering parameters for I=60A, f=20Hz, h=6.5ms, v=15mm/s, under the condition of variable speed sintering can achieve the best mechanical properties.

Robust Superhydrophobic Polytetrafluoroethylene Nanofibrous Coating Fabricated by Self-Assembly and Its Application for Oil/Water Separation

A novel and facile method is developed to fabricate polytetrafluoroethylene (PTFE) nanofibrous coating on both flat surface and curved micro metal fibers via self-assembly technique. The process starts from PTFE nanoparticles as building blocks and utilizes electrostatic interaction as self-assembly driving force followed by molecular rearrangement through thermal aging treatment. The formation process of nanofibers from nanoparticles was experimentally investigated and its mechanism was discussed in detail. As-prepared PTFE nanofibrous coating presented ultrathin morphology with high uniformity and outstanding chemical stability. Porous metal fiber sintered felt (PMFSF) coated with nanofibers exhibited superhydrophobic and superoleophilic properties and could separate various oil/water mixtures with high efficiency and good reusability. The coated PMFSF also presented excellent anticorrosion. Overall, the self-assembling fabrication method presented in this paper is simple, cost-efficient, productive, an...

3D stochastic modeling, simulation and analysis of effective thermal conductivity in fibrous media

This paper develops a 3D stochastic model to describe porous metal fiber sintered sheet (PMFSS), which is a non-woven fiber mat composed of curved and partial overlapped sintered fibers. Firstly, single fibers of PMFSS are modeled based on morphology information involving curvature and orientation extracted from the actual structure employing the 3D micro-CT imaging. Secondly, since fibers are partially overlapped at sintered joints (fiber to fiber overlapping section) during sheet formation process, a graphics processing unit (GPU) accelerated force biased simulation is introduced, which turns the arbitrarily overlapped single fibers into partially overlapped ones, for the sake of making the virtual geometry more realistic. Finally, fibrous geometries resembling the microstructure of PMFSS with various porosities are established and further imported into the STAR-CCM+ CFD package (CD-adapco, London) to study the effective thermal conductivity. Results illustrate that the numerical effective thermal conductivity of PMFSS agrees well with the experimental results in the in-plane direction. Besides, the sensitiveness of effective thermal conductivity due to structural anisotropy is also verified.

Utilization and positive effects of produced CO2 on the performance of a passive direct methanol fuel cell with a composite anode structure

This study investigates the CO2 behavior and its effect on the performance of a passive direct methanol fuel cell (DMFC) by use of visualization method. Different flow field designs are introduced to the anode of the DMFC. The parallel-fence structure and the new composite structure with a sintered porous metal fiber felt (SPMFF) are experimentally compared in terms of the cell performance and mechanisms of reactant and product managements. Results show that the cell based on the composite structure yields the best performance during high-concentration operation. The vertical parallel-fence structure is more suitable at a lower methanol concentration. The visualization tests indicate that the use of a composite structure can help enhance convection due to CO2 self-promoting behavior and also enhance gas storage in the channel to control the methanol concentration. The presence of CO2 helps to restrain methanol crossover, which should be actively controlled to enhance internal convection and thereby improve the cell performance. The use of a composite structure enables the cell to perform stably for continuous operation at a higher methanol concentration. The open-circuit and dynamic characteristics of this composite-structure-based DMFC are also evaluated in this study.

Investigation of transport property of fibrous media: 3D virtual modeling and permeability calculation

Porous Metal Fiber Sintered Sheet (PMFSS) shows a significant potential in the development of high-performance and compact fuel cell. To achieve optimized PMFSS structural design, it is essential to evaluate permeability, i.e., the correlation between fiber structures and the transport property. To perform pre-scale simulation, a method is proposed in this research to construct 3D virtual PMFSS models using morphological features extracted from X-ray images. A length-weighted orientation method is used to evaluate the anisotropy of fiber arrangement in the through-thickness direction, and a numerical model is proposed to evaluate the flow property through the gaps between fibers. Simulation results confirm that the Forchheimer law dominates flow behavior as flow rate rises. Permeability of both the transverse and the parallel flow directions are investigated and the simulation data obtained are compared with results obtained from various sources such as the analytical equations in the literature, numerical calculations based on the Lattice Boltzmann Method (LBM) as well as material testing experiments. It is found in the comparison that the permeability results obtained in this work are consistent with the values predicted by the analytical models of layered fiber arrangement proposed by Spielman and Goren. The proposed method thus provides an efficient way of PMFSS design optimization using virtual models.

Experimental Study on Tensile Properties of a Novel Porous Metal Fiber/Powder Sintered Composite Sheet.

A novel porous metal fiber/powder sintered composite sheet (PMFPSCS) is developed by sintering a mixture of a porous metal fiber sintered sheet (PMFSS) and copper powders with particles of a spherical shape. The characteristics of the PMFPSCS including its microstructure, sintering density and porosity are investigated. A uniaxial tensile test is carried out to study the tensile behaviors of the PMFPSCS. The deformation and failure mechanisms of the PMFSCS are discussed. Experimental results show that the PMFPSCS successively experiences an elastic stage, hardening stage, and fracture stage under tension. The tensile strength of the PMFPSCS is determined by a reticulated skeleton of fibers and reinforcement of copper powders. With the porosity of the PMFSS increasing, the tensile strength of the PMFPSCS decreases, whereas the reinforcement of copper powders increases. At the elastic stage, the structural elastic deformation is dominant, and at the hardening stage, the plastic deformation is composed of the structural deformation and the copper fibers’ plastic deformation. The fracture of the PMFPSCS is mainly caused by the breaking of sintering joints.

Experimental investigation on the thermal performance of a heat sink filled with porous metal fiber sintered felt/paraffin composite phase change material

Phase change material (PCM)-based heat sinks have the potential to provide reliable thermal management for electronic devices. However, the low thermal conductivity of PCMs hampers their use in large-volume or high-power devices. Embedding a PCM in a porous matrix is an efficient method for enhancing heat dissipation in a passive cooling application. In this study, the copper fibers with ample antler microstructures on their surface were first introduced into the phase change heat transfer enhancement technology. The enhanced heat transfer performance of a PCM embedded in a porous metal fiber sintered felt (PMFSF) was experimentally investigated. Paraffin/PMFSF composite PCM (MF-PCM) was prepared, and three types of heat sinks (filled with MF-PCM, filled with paraffin, and empty) were tested under four power levels. The effect of the porosity was also investigated. It was found that the addition of PMFSF enhanced heat transfer to the PCM, leading to lower heat source temperature. The improvement of heat transfer by MF-PCM is more evident under larger heat flux. Before melting is completed, lower heat source temperature and temperature gradient is achieved for the heat sink with low porosity, while longer duration of temperature control region is achieved in the case of the heat sink with the higher porosity. The time-averaged effective thermal resistance of the heat sink with paraffin is higher than that of the heat sinks with MF-PCM. All these results show the enormous potential of using PMFSF to replace metal foams, thus offering a new porous metal matrix to enhance the thermal conduction of PCMs.

Active multi-scale modeling and gas permeability study of porous metal fiber sintered felt for proton exchange membrane fuel cells

Porous metal fiber sintered felt (PMFSF) is a promising critical component in proton exchange membrane fuel cells, having the ability of simultaneously acting as the flow field plate, gas diffusion layers and also the catalyst layers support, and owing the property of multi-scale surface morphology. A simple multi-scale mathematical method was proposed to actively construct three dimensional models of PMFSF’s microstructure by synthesizing the implicit periodic surface (PS) model and the Weierstrass-Mandelbrot (W-M) fractal geometry. In this method, the PS model described the macro overall fiber shape, and the W-M fractal geometry modeled the micro fractal roughness topography attached. Based on the method, multi-scale fractal PMFSF models were reconstructed according to morphology parameters of physical PMFSFs, and were discretized in ANSYS/ICEM to generate refined mesh for computational fluid dynamics analysis. To verify the validity of the proposed modeling approach, PMFSFs with different porosity and fiber orientation are generated, and then the effects of the fractal surface topography and the fractal parameters such as fractal dimension and height scaling parameter on the gas permeability of PMFSF were investigated. The numeric simulation results show that the influence of the fractal topography on the in-plane and through-plane permeability of PMFSF cannot be ignored, and the permeability of fractal PMFSF models agrees with experimental measurements better. Especially, the results imply that the fractal morphology may have the potential to adjust the anisotropic properties of PMFSFs’ permeability. It is further found that the larger the fractal dimension is and the lower the height scaling parameter is, the better the permeability of PMFSF will be. The synthesis approach and numerical simulation method may facilitate the development of active functional design mode to predict and optimize key characteristics of PMFSF ahead of manufacture.

The Advantages of the Use of Porous Metal Fiber Media in Different Alloys As Gas Diffusion Layer in Various Energy Storage Systems

Large scale energy storage systems are a possible alternative to buffer the variability and the intermittency of electricity generated from renewable sources such as solar and wind. The main requirements of such energy storage systems are high efficiency, good rate capability, long life and low cost. The electrodes in these large energy storage systems like e.g. Electrolysers and Redox Flow batteries are becoming more and more important attributers to the cost and performance drivers in the BOP. As the working environment in the different available system vary significantly, an optimization of the structure and material use in the electrodes is clearly needed. In this study, different metal fiber media which can be used as porous electrode, produced in a variety of different metals and structures were evaluated on the performance drivers needed to achieve an improved energy storage system. The different materials are compared with alternative technologies on a variety of parameters like corrosion resistance, conductivity, permeability, mechanical strength, … and evaluated on the performance in an electrochemical cell. This talk will give an overview on the progress of each of the different drivers.

Experimental Study on the Tensile Property of a Novel Oriented Linear Porous Metal

A novel oriented linear porous metal (OLPM) with high porosity was fabricated through solid-sintering method with cutting copper fibers. In this study, tensile experiments were conducted to investigate the fracture process of the OLPM and the effects of porosity and sintering parameters on the tensile properties. The typical tensile stress-strain plot of this material was obtained based on a large number of tensile test results. The plot can be divided into three stages, namely, initial linear elastic stage, plastic deformation stage, and tensile fracture stage. Based on the results, the fracture mechanism of the OLPM was further studied. Moreover, the porosity and sintering parameters were also varied to investigate their influence on the tensile properties. Tensile strength and plastic deformation were found to decrease with increasing porosity ranging from 70% to 90%. A higher sintering temperature produced a higher tensile strength for the OLPM sintered in the temperature range of 700°C–900°C, but the strength decreased at 1000°C. In addition, the extension of holding time could also slightly affect the tensile strength. Finally, the tensile properties of the OLPM are significantly higher than those of commercial porous metal and porous metal fiber sintered sheet.

Skeleton-based tracing of curved fibers from 3D X-ray microtomographic imaging

A skeleton-based fiber tracing algorithm is described and applied on a specific fibrous material, porous metal fiber sintered sheet (PMFSS), featuring high porosity and curved fibers. The skeleton segments are firstly categorized according to the connectivity of the skeleton paths. Spurious segments like fiber bonds are detected making extensive use of the distance transform (DT) values. Single fibers are then traced and reconstructed by consecutively choosing the connecting skeleton segment pairs that show the most similar orientations and radius. Moreover, to reduce the misconnection due to the tracing orders, a multilevel tracing strategy is proposed. The fibrous network is finally reconstructed by dilating single fibers according to the DT values. Based on the traced single fibers, various morphology information regarding fiber length, radius, orientation, and tortuosity are quantitatively analyzed and compared with our previous results (Wang et al., 2013). Moreover, the number of bonds per fibers are firstly accessed. The methodology described in this paper can be expanded to other fibrous materials with adapted parameters.

Effect of Pore Structure on Performance of Porous Metal Fiber Materials

Abstract The pore structure of porous metal fiber materials is a key factor affecting their performances, so the effects of the pore structure on the performances were analyzed in the paper. Using FeCrAl fiber as starting materials, porous metal materials were prepared by an air flow method and sintering process. The microstructures of sintered samples were observed by a scanning electron microscope (SEM). The tensile strength and air permeability were also tested. The sound absorption coefficients at 90–140 dB with different frequencies from 1000–3000 Hz were measured. In addition, the fractal dimension of the pore structure was calculated by self-developed software which was based on the fractal theory and computer image processing technology. The effects of pore structure on the tensile strength, the sound absorption coefficient and the air permeability were discussed, and the relationships among the tensile strength, the air permeability and the fractal dimension were described. Results show that the tensile strength decreases linearly with the fractal dimension increasing, while the air permeability increases obviously. Additionally, the sound absorption coefficient declines gradually with the fractal dimension increasing at the same sound intensity or frequency.

Uniaxial tensile behavior of porous metal fiber sintered sheet

A novel porous metal fiber sintered sheet (PMFSS) with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.

Effect of characterization of porous metal fiber media on sound absorption coefficient

Porous metal fiber media (PMFM) is a kind of advanced structural and functional material, and it has attracted a wide spread attention owing to excellent sound absorption performance. The sound absorption property of PMFM is mainly influenced by the fiber diameter, the average pore size and thickness of PMFM. In the paper, three stainless steel fibers with the diameters (∅) of 8, 12 and 20 μm were used to make PMFM with the average pore sizes of 10, 20, 30 and 40 μm and the thicknesses of 1, 2 and 3 mm by air-laid and sintering processes. The sound absorption coefficients of PMFM were tested in impedance tube using two-microphone transfer-function method according to ISO 10534-2 and ASTM E1050-98 international standards at room temperature. The results show that when the frequency ranges from 50 Hz to 6,400 Hz in material with the average pore size of 20 μm and the thickness of 3 mm and the fiber diameter of ∅8 μm, the average sound absorption coefficient is the highest.

Получение из металлических волокон пористых и композиционных материалов с высокой эффективностью экранирования

Получение из металлических волокон пористых и композиционных материалов с высокой эффективностью экранирования