Liquid-phase Infiltration Research Articles

Synchrotron X-ray studies of model SOFC cathodes, part II: Porous powder cathodes

Infiltrated La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) sintered porous powder cathodes for solid oxide fuel cells have been investigated by synchrotron ultra-small angle x-ray scattering (USAXS). We demonstrated that atomic layer deposition (ALD) is the method for a uniform coating and liquid-phase infiltration for growing nanoscale particles on the porous LSCF surfaces. The MnO infiltrate, grown by ALD, forms a conformal layer with a uniform thickness throughout the pores evidenced by USAXS thickness fringes. The La0.6Sr0.4CoO3 (LSC) and La2Zr2O7 (LZO) infiltrates, grown by liquid-phase infiltration, were found to form nanoscale particles on the surfaces of LSCF particles resulting in increased surface areas. Impedance measurements suggest that the catalytic property of LSC infiltrate, not the increased surface area of LZO, is important for increasing oxygen reduction activities.

Enhancing Anodic Catalytic Activity at High Fuel Utilization By Infiltration of Ni Nanoparticles

The performance of SOFCs degrades with increasing fuel utilization, since the fuel oxidation reaction faces increased competition for the three-phase-boundary (TPB) sites in the anode from adsorbed water vapor species. Introduction of addition TPB sites by infiltration of Ni nanoparticles into the anode is an effective way to alleviate this problem. Both liquid and vapor phase infiltration of Ni nanoparticles into commercially available Ni/YSZ cermet anodes have been explored. The microstructure of the anode has been examined by µ-CT and FIB/SEM 3-D reconstructions. The cells have been electrochemically characterized by I-V and EIS techniques in a temperature range of 600°C-800°C. The infiltrated Ni nanoparticles have been characterized by image analysis of SEM micrographs from fracture cross-sections, before and after electrochemical testing. The effect of the nanoparticles on cell electrochemical performance as a function of temperature and anode input water vapor content, the stability of the nanoparticles, as well as the thermodynamics of vapor phase infiltration of Ni will be presented.

Enhancing Anodic Catalytic Activity at High Fuel Utilization By Infiltration of Ni Nanoparticles

The performance of SOFCs degrades with increasing fuel utilization, since the fuel oxidation reaction faces increased competition for the triple-phase-boundary (TPB) sites in the anode from adsorbed water vapor species. Introduction of addition TPB sites by infiltration of Ni nanoparticles into the anode is an effective way to alleviate this problem. Both liquid and vapor phase infiltration of Ni nanoparticles into commercially available Ni/YSZ cermet anodes have been explored. The microstructure of the anode before infiltration has been examined by FIB/SEM 3-D reconstruction to quantify the TPB length. Infiltrated and un-infiltrated cells have been electrochemically characterized by I-V and electrochemical impedance spectroscopy (EIS) techniques in a temperature range of 600°C-800°C at varying water vapor partials pressures. The infiltrated Ni nanoparticles have been characterized by image analysis of SEM micrographs from fracture cross-sections, before and after electrochemical testing. The effects of the nanoparticles on cell electrochemical performance as a function of temperature and anode input water vapor content, the stability of the nanoparticles, as well as the thermodynamics of vapor phase infiltration of Ni are presented.

Limited infiltration due to reactive sintering of nano-Sm2O3 with preforms—its effect on (Y, Sm)Ba2Cu3O7−δ superconductors

Preform optimized infiltration growth process (POIGP) is employed to fabricate mixed rare earth (Y, Sm)Ba2Cu3O7−δ superconductors of high performance. POIGP creates wide range of pinning centres and also enables nano-particle additions to stable Y2BaCuO5 (Y-211) preforms. Nano-Sm2O3 particles (30–50 nm) were introduced in 0, 10, 20 and 30 wt.%, homogenously and without agglomeration, into the Y-211 preforms and the corresponding composites YBCO-Ar, YSm-10, YSm-20 and YSm-30 are fabricated. Though all the samples were processed in argon atmosphere to suppress the formation of solid solutions with Sm at Ba site, the effort was successful only in the YSm-20 sample, as seen from sharp diamagnetic transition and XRD studies. Magnetic property measurements were carried out on samples which showed strong (00l) texture, but were not necessarily single crystalline since no seed was used in the experiments. The calculated critical current densities (Jc) are thus reflective of the values in the basal plane, in the most favourable direction. The final composites revealed YSm-20 to exhibit better Jc with substantial flux pinning up to 9 T, at 77 K. Detailed examination of microstructures and field dependence of Jc reveal that the addition of nano-particles is not always rewarding and can lead to reactive sintering of Y-211 and limit the extent of liquid phase inflow into preforms. This not only can lead to incomplete reaction leaving larger 211 particles in the matrix, but can also shift the composition of liquid phase such that it promotes the formation of undesired solid solutions in IG processed REBCO as seen in YSm-30. The effect of various factors like open porosity in the preform, the ease of liquid phase infiltration and the liquid phase composition on the residual 211 size in the composites, suppression of RE/Ba solid solutions, and the resultant Jc versus H curves is discussed.

Effect of synthesis method on the morphological and electrochemical characteristics of sulfur/MWCNT composite cathode

Sulfur-multi-walled carbon nanotube composites were synthesized via two different strategies of a simple ball-milling process (S/MWCNT-1) and a two-step procedure of liquid-phase infiltration and melt diffusion (S/MWCNT-2). The influence of preparation method on the structure of the composite materials was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). As compared to the S/MWCNT-1 composite, the sulfur in the S/MWCNT-2 composite was highly dispersed and partially embedded into the pores and hollow tubes of carbon nanotubes, leading to suppress the shuttle mechanism and therefore improve the discharge capacity and the cycle stability. The S/MWCNT-2 composite showed an initial discharge capacity of 866mAhg−1 and a capacity retention of 69% after 50cycles at 0.5C rate, much higher than S/MWCNT-1 composite. The impact of morphology of the composite electrodes on the electrochemical performance was further investigated by electrochemical impedance spectroscopy (EIS) and SEM techniques. Compared with the S/MWCNT-1 composite, the S/MWCNT-2 cathode well maintained its homogeneous and porous morphology after 50cycles and a less formation of passive layer on the cathode surface was observed.

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g−1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.

Numerical modeling of liquid-phase infiltration in the process of sintering ceramic composites

The paper presents a numerical model for infiltration of porous preforms of ceramic materials in the process of sintering. The mathematical model of infiltration is based on the Richards equation and Van Genuchten formulas describing permeability properties of the porous structure and the infiltrant. A finite-element method and stable implicit finite-difference time scheme are applied for discretization of the Richards equation. Based on the outcome of solving test problems, a comparison of the numerical results with the results obtained by other researchers and with the experimental data, the numerical model has been proved adequate. The paper provides some findings of computer modeling of infiltration of liquid silicon into porous silicon carbide preforms of various geometries and dimensions.

A new solder matrix nano polymer composite for thermal management applications

The increasing integration of microelectronics, raising the need for effective heat dissipation, requires new and improved composite materials technologies. For both thermal interface and die attach materials, a major challenge is to combine low thermal resistance joints with sufficient thermomechanical decoupling and reliability. In this paper, we present the fabrication and characterisation of a new type of solder matrix nano polymer composite (SMNPC) aiming to address these challenges. The SMNPC is fabricated into preforms by liquid-phase infiltration of a Sn–Ag–Cu matrix into a silver nanoparticle coated electrospun polyimide fibre mesh. The composite is demonstrated to possess high heat transfer capability, close to that of a direct soldered interface, lower elastic modulus compared to pure Sn–Ag–Cu alloy, and reliable thermomechanical performance during thermal cycling. Taken together, the results indicate that the developed SMNPC can be a useful composite alternative compared to conventional solders and polymer matrix materials for thermal management applications.

Cyclohexene을 첨가한 PIP 공정 사용 Cf/SiC 복합재의 고밀도화

탄소섬유강화 SiC기지상 복합재는 우수한 산화저항성과 우수한 열충격저항성을 가진다. 그리고 이런 특성들은 탄소섬유강화복합재가 고온구조재로서 응용케하였다. 본 연구에서는 <TEX>$C_f/SiC$</TEX> 복합재가 전구체 함침과 액상 함침이 동반된 열분해공정, Cyclohexene을 사용한 화학기상 경화공정을 통해 제조되었다. 최종 제조된 <TEX>$C_f/SiC$</TEX> 복합재는 5회 함침을 통해 <TEX>$0.43g/cm^3$</TEX> 밀도를 갖는 탄소섬유 프리폼에서 <TEX>$1.76g/cm^3$</TEX>의 밀도값을 나타내고 있다. 그리고 산화저항성 특성면에서 <TEX>$C_f/SiC$</TEX> 복합재의 무게가 공기중 <TEX>$1400^{\circ}C$</TEX>에서 6시간 유지 후에 81%가 남았다. 결과적으로 Cyclohexene을 사용한 화학기상 경화공정은 효과적으로 높은 치밀화와 증가된 산화저항성을 보이고 있다. Carbon fiber-reinforced SiC matrix composites have good oxidation resistance and thermal shock resistance. These properties have allowed the composites to be applied to high-temperature structures. In this study, <TEX>$C_f/SiC$</TEX> composites were fabricated via precursor infiltration and pyrolysis (PIP) process, including liquid phase infiltration and chemical vapor curing using cyclohexene. The final <TEX>$C_f/SiC$</TEX> composites, which have gone through the PIP process five times, showed a density of <TEX>$1.79g/cm^3$</TEX>, as compared to a density of <TEX>$0.43g/cm^3$</TEX> for pre-densified bare carbon fiber preform. As for the oxidation resistance characteristics, the weight of <TEX>$C_f/SiC$</TEX> composite was maintained at 81% at <TEX>$1400^{\circ}C$</TEX> in air for 6 hours. Chemical vapor curing (CVC) using cyclohexene has shown to be an effective method to achieve high densification, leading to increased oxidation resistance.

Microstructure and tensile properties of nickel-based superalloy K417G bonded using transient liquid-phase infiltration

Nickel-based superalloy K417G samples with 2.2mm gap are bonded by transient liquid-phase infiltration (TLI). The microstructure and tensile properties of TLI joint have been investigated. The results show that the nonuniform microstructure is obtained in the TLI joints. The voids, Cr5B3 borides and (Cr, W)B borides are presented in the TLI region. The no isothermal solidification of the transient TLI joint leads to the formation of Cr5B3 borides. The tensile properties of TLI joint samples are lower than that of base sample, especially the ductility. The observation of fracture surfaces show that the Cr5B3 borides are the main cause, which leads to the decrease of ductility. The Cr5B3 borides can act as the crack initiation and also accelerate the propagation of cracks during the deformation.

In situ X-ray studies of film cathodes for solid oxide fuel cells

Synchrotron-based X-ray techniques have been used to study in situ the structural and chemical changes of film cathodes during half-cell operations. The X-ray techniques used include X-ray reflectivity (XR), total-reflection X-ray fluorescence (TXRF), high-resolution diffraction (HRD), ultra-small angle X-ray scattering (USAXS). The epitaxial thin film model cathodes for XR, TXRF, and HRD measurements are made by pulse laser deposition and porous film cathodes for USAX measurements are made by screen printing technique. The experimental results reviewed here include A-site and B-site segregations, lattice expansion, oxidation-state changes during cell operations and liquid-phase infiltration and coarsening of cathode to electrolyte backbone.

Tungsten Hydroxide /Porous Silicon Composite Fabricated by the Liquid Phase Infiltration

not Available.

Catalytic reduction of nitrogen oxides via nanoscopic oxide catalysts within activated carbons at room temperature

Cabin air filters consisting of activated carbon infiltrated with nanoscopic metal oxide particles as catalysts have been investigated for the reduction of nitrogen oxides within motor-car cabins. In that concept, nitrogen dioxide is adsorbed on the activated carbon during operation conditions of the car and then reduced by the catalysts within the pores. The conversion has to take place at ambient temperature during the relatively long standstill periods of motor-cars. In this article we are going to discuss the manufacturing of the adsorbents by “liquid phase infiltration” and their characterization by techniques, such as nitrogen sorption analysis, X-ray diffraction, thermogravimetry, energy dispersive X-ray spectroscopy, and electron microscopy. The new adsorbents were evaluated in repeated breakthrough tests using NO2 (4 ppmV as feed concentration) in humid air as the adsorptive. In the intermittent rest periods of varying duration the volume flow through the fixed bed of adsorbent was stopped. The measured breakthrough curves indicate a catalytic conversion of the nitrogen dioxide in the filter beds.

THE EFFECT OF CeO2 NANOPARTICLE DOPING ON REFINEMENT OF Y-211 PARTICLES IN POIG PROCESSED YBCO COMPOSITES

Doping of non-interacting nanoparticles in YBCO superconductors in order to get fine microstructure defects has been studied. Y-211 inclusion, itself has large potential to create structural defects without affecting Y-123 matrix phase. Nanoparticles of grain refining agent like CeO2/Pt/PtO2 are interesting dopants, especially CeO2 for being cheaper than Pt. POIG process, as is one of the advance processing techniques to get uniform distribution of fine Y-211 particles of the order of 1-2 μm, throughout the YBCO composites. Finer Y-211 particles can drastically increase the pinning centers. Introduction of fine sized CeO2 as grain refining agent to reduce the size of Y-211 particles would create additional pinning centers. In the present work, the effect of CeO2 on Y-211size and distribution in POIG processed YBCO composite was studied. It was observed that with increase in CeO2 content Y-211 particle size decreases below 1μm and even less than 0.5μm for 10 weight percent CeO2 doping. The mechanism for refinement appears to be the formation of BaCeO3 on the surface of Y-211 during liquid phase infiltration that leads to splitting of Y-211 into smaller particles.

Carbon Fiber Reinforced Phosphate Porous Ceramic Composites

Fiber porous ceramics are the excellent candidates for a variety of applications, and thus, their research is a hotspot in recent years. In this study, carbon fiber reinforced phosphate porous ceramics composites were prepared by acupuncture and in-situ solidification vacuum-assisted liquid-phase infiltration method. The tensile strength of composite was tested by universal testing machine, the microstructures of the specimen were observed by scanning electron microscopy while the thermal analysis was detected by Thermo Gravimetric Analyzer. The results show that the carbon fiber reinforced phosphate porous ceramics composites which is prepared by the technology showed above have a pore rate of 63.7%.The tensile strength reached 50.2MPa with an average pore size of at most 50μm.It also has good thermal shock resistance.

Effect of Tetraethoxysilane Infiltration on Properties of 2.5D Quartz Fibers Reinforced Silica

In this study, 2.5 dimensional quartz fibers reinforced fused silica (2.5D SiO2f/SiO2) composites were prepared by in-situ solidification vacuum-assisted liquid-phase infiltration method using Si-sol and tetraethoxysilane. Composites’ tensile strength and compressive strength were tested by universal testing machine, and the microstructures of the specimen were observed by scanning electron microscopy (FEI Sirion 200). The ultimate sintering temperature was chosen by the differential thermal analysis of tetraethoxysilane gel and the effect of sintering temperature on the composites’ tensile strength. Densification behavior, mechanical properties and microstructures of the composites were investigated. The results show that tetraethoxysilane infiltration process is an efficient route for the preparation of SiO2f/SiO2 composites, after two cycles when the weight was no longer increased using Si-Sol infiltration, the density of SiO2f/SiO2 composites increases from 1.63 to 1.74g/cm3, while the tensile strength and compressive strength, respectively, increase from 31.2 to 52.7MPa and 59.0 to 129.7 MPa. And the interface de-bonding and distinct fibers pull-out of the fracture faces show that it is non-brittle fracture. The enhanced mechanism of tetraethoxysilane infiltration was also analyzed in this paper.

The Solid Particle Erosion Behavior of Carbon/Carbon and Carbon/Phenolic Composite Used in Re-entry Vehicles

Several engineering components made of carbon-based heat-resistant composites are subjected to severe erosive wear. In view of the above, the solid particle erosion behavior of two and four dimensionally reinforced carbon/carbon (C/C) composites as well as that of carbon/phenolic (C/P) composite has been characterized at the ambient temperature. The investigated C/C composites have been produced through a liquid-phase infiltration method followed by hot isostatic pressing, while the C/P composite prepegs have been cured inside an autoclave. The erosion rates of these composites have been determined for two different impact angles and two different impact velocities using silica sand with average particle diameter of 200 μm. The morphologies of as-received and eroded surfaces of test specimens have been examined with the help of scanning electron microscopy to understand the mechanism of material removal. The erosion response, erosion efficiency, and erosion micromechanisms of these composites have been studied in detail. While the erosion resistance of the C/P composite is found to be superior to that of the investigated C/C composites, the four dimensionally reinforced C/C composite have shown the highest erosion efficiency. All the composites have exhibited a semi-ductile erosion response. Their mechanical properties have little correlation with the erosion rates.

INFILTRATION OF MAGNESIUM IN POROUS BORON SKELETONS

The feasibility of the infiltration of molten magnesium into porous boron skeleton was examined. The particle size and crystalline state of starting boron powders as well as the confinement of Mg vapors play an important role in successful infiltration. Magnesium penetrates more readily into porous skeletons formed by large crystalline boron particles than those formed by fine amorphous powders. The infiltration of magnesium mainly occurs via capillary condensation rather than liquid flow. Although the infiltrated microstructures are seemingly very dense, nano-scale structures contain many tiny inter-particle voids due to random packing of MgB 2 grains. This is due to the absence of a liquid phase in final microstructures as a result of transient liquid-phase infiltration.

Biotemplated synthesis of novel porous SiC

Amorphous silicon carbide with unique porous structures was synthesised from three biological templates (egg shell membrane, butterfly wing and sea urchin skeleton) using liquid phase infiltration with polycarbosilane at atmospheric pressure followed by heating to 1000 °C under N 2. The structure and porosity of the preform was largely reproduced in the final material, although with egg shell membrane the cellular structure of the preform was compromised after infiltration and heating. The SiC yield of the final material was linearly correlated with the number of infiltration steps in the case of egg shell membrane and butterfly wing. Infiltration of the sea urchin shell was unsuccessful.

Nanofabrication Process for Highly Ordered Porous Materials by the Liquid Phase Deposition Methods

We have studied a novel technique for the direct synthesis of two-dimensional metal oxide films with highly ordered periodic structure. TiO2 films with highly nano-ordered architectures were directly deposited on substrates at room temperature by the liquid phase infiltration (LPI) method. 2D arrays of several kinds of metal oxide rods with diameters ranging from ca. 100 to 1000 nm are fabricated by filling the holes in a Si wafer. We summarized the various kinds of ordered structured metal oxide thin film with this method and the other techniques which have been reported that a novel soft solution process for the direct synthesis of large-area well-crystallized oxides with 1D-3D ordered periodic structure has been developed based on the LPI method. Metal oxide thin films were deposited directly into the nano-space, and thus the nano-space was completely infiltrated with metal oxide. The LPI process provides a direct fabrication route for metal oxide films with highly ordered structures, enabling nanoscale modification of optical properties of photonic crystals.