Porous Stainless Steel Substrate Research Articles

The Influence of Process Equipment on the Properties of Suspension Plasma Sprayed Yttria-Stabilized Zirconia Coatings

Suspension plasma-sprayed YSZ coatings were deposited at lab-scale and production-type facilities to investigate the effect of process equipment on coating properties. The target application for these coatings is solid oxide fuel cell (SOFC) electrolytes; hence, dense microstructures with low permeability values were preferred. Both facilities had the same torch but different suspension feeding systems, torch robots, and substrate holders. The lab-scale facility had higher torch-substrate relative speeds compared with the production-type facility. On porous stainless steel substrates, permeabilities and microstructures were comparable for coatings from both facilities, and no segmentation cracks were observed. Coating permeability was further reduced by increasing substrate temperatures during deposition or reducing suspension feed rates. On SOFC cathode substrates, coatings made in the production-type facility had higher permeabilities and more segmentation cracks compared with coatings made in the lab-scale facility. Increased cracking in coatings from the production-type facility was likely caused mainly by its lower torch-substrate relative speed.

PdAu membranes supported on top of vacuum-assisted ZrO2-modified porous stainless steel substrates

To enable the formation of defect-free PdAu composites by electroless plating, the vacuum-assisted ZrO2-modified method was optimized on top of porous stainless steel disks. Both the ZrO2-modified supports and the PdAu synthesized membranes were characterized by XRD (X-ray diffraction), SEM (scanning electron microscopy), EDS (energy dispersive X-ray analysis) and XPS (X-ray photoelectron spectroscopy). SEM cross-section results showed that dense, continuous, defect-free PdAu films were deposited on top of the ZrO2-modified PSS disks, and the EDS data indicated that no significant concentration gradient was present on the thickness. At 400°C and 100kPa, the pure hydrogen permeation flux for a 10μm thick PdAu membrane was about 0.14mols−1m−2 and the H2/N2 ideal selectivity was higher than 10,000.

Residual stresses in suspension plasma sprayed electrolytes in metal-supported solid oxide fuel cell half cells

Solid oxide fuel cells (SOFCs) efficiently convert chemical energy into electrical energy with fuel flexibility and low emissions. Plasma spraying has emerged as a fabrication technique for metal-supported SOFCs. Residual stresses in suspension plasma sprayed (SPS) yttria-stabilized zirconia (YSZ) electrolytes fabricated with various processing parameters and substrates were analyzed by X-ray diffraction. The temperature dependence of the residual stresses was also evaluated. The electrolyte residual stresses varied with both processing conditions and substrate characteristics, and ranged from 35 to 91 MPa. The change in stresses agreed well with the observed microstructural changes arising from the use of different processing conditions and substrates. The electrolytes fabricated using torch power and stand-off distance of 133 kW and 90 mm exhibited the highest residual stress due to the their relatively dense microstructure with low level of vertical cracking compared to electrolytes made with the other spray conditions. As these electrolytes were heated from room temperature to 750 °C, residual stresses decreased from 91 to 39 MPa. The decrease is due to changes in Young’s modulus and to thermal expansion mismatch between the layers, and possibly also due to the formation of additional microcracks or creep of the porous stainless steel substrate.

Fabrication of H2-permeable palladium membranes based on pencil-coated porous stainless steel substrate

The increasing utilizations of hydrogen energy have greatly promoted the demand on H2-permeable palladium membranes, particularly those supported on porous stainless steel (PSS). A macroporous stainless steel tube was employed as substrate material, and its surface was modified by pencil coating. The palladium membrane was successfully fabricated via electroless plating. Before plating, the Pencil/PSS substrate was simply activated by an immersion in PdCl2−HCl solution, where the PSS and the graphite layer served as anode and cathode, respectively, yielding palladium seeds on the Pencil/PSS surface through galvanic cell reaction. During electroless plating, a peeling of the palladium layer occurred, but this problem can be solved by introduction of a suction treatment, and the resulting Pd/Pencil/PSS membrane was found to be permeable and stable.

Relationship Between Particle and Plasma Properties and Coating Characteristics of Samaria-Doped Ceria Prepared by Atmospheric Plasma Spraying for Use in Solid Oxide Fuel Cells

Samaria-doped ceria (SDC) has become a promising material for the fabrication of high-performance, intermediate-temperature solid oxide fuel cells (SOFCs). In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were measured and correlated to the resulting microstructures of SDC coatings fabricated using atmospheric plasma spraying, a manufacturing technique with the capability of producing full cells in minutes. Plasmas containing argon, nitrogen and hydrogen led to particle surface temperatures higher than those in plasmas containing only argon and nitrogen. A threshold temperature for the successful deposition of SDC on porous stainless steel substrates was calculated to be 2570 °C. Coating porosity was found to be linked to average particle temperature, suggesting that plasma conditions leading to lower particle temperatures may be most suitable for fabricating porous SOFC electrode layers.

Permeation efficiency of Pd–Ag membrane modules with porous stainless steel substrates

It is generally regarded that the permeation of hydrogen through palladium or palladium alloy membranes follows the “solution–diffusion” mechanism, which can be described by Sieverts’ Law. The hydrogen permeability of actual membrane modules usually differ from those predicted from Sieverts’ Law due to the influence of substrate and some other factors. An efficiency (or efficiency factor) has been introduced by many researchers to denote the difference between the actual permeability and those predicted from Sieverts’ Law. Extensive experiments were carried out in an electrically heated vessel to study the hydrogen permeation flux and permeation efficiency of Pd–Ag membrane modules with porous stainless steel substrates. The influence of operation conditions on the membrane permeation flux and efficiency was examined. It was observed that the hydrogen permeation flux through the module increased by increasing the temperature and hydrogen pressure in the vessel, while the permeation efficiency increased by increasing the hydrogen pressure in the vessel side and decreasing the membrane temperature. The permeation efficiency was correlated to the vessel temperature (T) and hydrogen pressure difference (PH0.5−PL0.5) for the conditions studied.

Preparation, characterization and microstructural optimization of a thin γ-alumina membrane on a porous stainless steel substrate

► A mesoporous γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates. ► γ-Al 2 O 3 membrane was potential for CO 2 separation at high pressure test conditions. ► Thus, it was required to provide the membrane layer with more strength. ► α-Alumina substrate was substituted with porous stainless steel. ► A stainless steel supported α-Al 2 O 3 membrane with better properties was synthesized. In this work, a supported mesoporous (MEP) γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates by sol–gel dip coating process. In the following, the preparation of a novel metallic–ceramic composite membrane was studied, which incorporated desirable properties of both ceramic membrane and porous metallic substrate. For this purpose, mesoporous alumina membrane layer was developed on a porous 316L stainless steel substrate. The substrate was prepared by loose powder sintering and modified by soaking–rolling and fast drying method. The prepared membranes were characterized using scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and N 2 -adsorption/desorption measurements (BET analyses). The results revealed that a defect-free γ-alumina membrane with 2.1 nm average pore size can be produced. Permeation tests with N 2 gas revealed that the stainless steel substrate had 40 times more permeability than conventionally used alumina support. Additionally, single gas permeation of γ-alumina membrane for CO 2 and N 2 was compared. It was observed that CO 2 could be separated from N 2 by the MEP γ-Al 2 O 3 membrane in high pressure permeation condition, where stainless steel presents superior mechanical strength than alumina as a substrate.

Optimization and characterization of electroless co-deposited PdRu membranes: Effect of the plating variables on morphology

PdRu films were successfully synthesized on top of non-porous stainless steel supports by electroless co-deposition. The effect of synthesis variables on morphology, substrate adherence, bulk and surface composition was studied. The microstructure and morphology of the samples were analyzed by X-ray diffraction and scanning electron microscopy. Homogeneous and defect-free PdRu films were obtained employing baths at low pH, moderate to high agitation speeds, high concentration of hydrazine, using EDTA as a stabilizer and temperatures near 50 °C. Films characterized by X-ray photoelectron spectroscopy showed Pd segregation after annealing the sample at 400 °C in H 2 (5%)/Ar in the load-lock chamber of the spectrometer. The optimized conditions were employed to synthesize a PdRu composite membrane on top of a tubular porous stainless steel substrate (0.1 μm grade). Hydrogen permeation was measured over a 350–450 °C temperature range and a trans-membrane pressure up to 100 kPa. The PdRu membrane showed good performance with a hydrogen permeability of 6.5 × 10 −9 mol m −1 s −1 Pa −0.5 and a selectivity higher than 1700.

Novel PdAgCu ternary alloy: Hydrogen permeation and surface properties

Dense PdAgCu ternary alloy composite membranes were synthesized by the sequential electroless plating of Pd, Ag and Cu on top of both disk and tubular porous stainless steel substrates. X-ray diffraction and scanning electron microscopy were employed to study the structure and morphology of the tested samples. The hydrogen permeation performance of these membranes was investigated over a 350–450 °C temperature range and a trans-membrane pressure up to 100 kPa. After annealing at 500 °C in hydrogen stream followed by permeation experiments, the alloy layer presented a FCC crystalline phase with a bulk concentration of 68% Pd, 7% Ag and 25% Cu as revealed by EDS. The PdAgCu tubular membrane was found to be stable during more than 300 h on hydrogen stream. The permeabilities of the PdAgCu ternary alloy samples were higher than the permeabilities of the PdCu alloy membranes with a FCC phase. The co-segregation of silver and copper to the membrane surface was observed after hydrogen permeation experiments at high temperature as determined by XPS.

A sol–gel-derived α-Al2O3 crystal interlayer modified 316L porous stainless steel to support TiO2, SiO2, and TiO2–SiO2 hybrid membranes

A homogeneous α-Al2O3 crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al2O3 membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al2O3 membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al2O3 completely transformed into α-Al2O3 and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al2O3 intermediate layer to initially modify its surface. A single α-Al2O3 crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO2, SiO2, and TiO2–SiO2 hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al2O3 crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.

Surface characterization of Pd–Ag composite membranes after annealing at various temperatures

Pd–Ag films (∼24% Ag, 20–26 μm thick) were deposited by sequential electroless plating onto porous tubular stainless steel substrates. Intermediate α- and γ-Al 2O 3 oxide layers were employed to modify the support pore size and to prevent intermetallic diffusion of the stainless steel components into the Pd–Ag layer. The aluminum oxides were applied to the substrate porous system by a vacuum assisted-coating method. Composite membranes annealed at temperatures between 500 and 600 °C were characterized for film structure (XRD), morphology (SEM), bulk and surface component distribution (EDS, XPS), and hydrogen permeance. Pd–Ag alloy formation progressed as annealing temperature was increased to 600 °C. Composition measurements within the Pd–Ag layer revealed preferential segregation of the Ag component to the top surface; this result is consistent with Ag's lower surface free energy. No diffusion of stainless steel components into the Pd–Ag layer was observed, demonstrating the effectiveness of the oxide interdiffusion barrier. Hydrogen permeation tests of membranes annealed at 500 °C displayed high permeability and H 2/N 2 selectivity at operating temperatures between 400 and 450 °C. Permeabilities were higher but selectivities were lower for membranes annealed at 550 °C. This performance deterioration may be related to defects within the Pd–Ag layer caused by growth of dendritic Ag deposits.

Hydrogen permeability of Pd–Ag membrane modules with porous stainless steel substrates

Palladium-based membranes are attractive for their nearly perfect permselectivity to hydrogen. Membrane modules, consisting of a membrane foil, porous stainless steel substrate, test frame and flange were assembled and tested in an electrically heated vessel. Instantaneous hydrogen permeation flux was measured. Influences of operation conditions on the membrane performance were examined. Microstructure and morphology of the membrane surface and the cross-sectional surface of the substrate and membrane foil were characterized by scanning electron microscopy. It was observed that for an operation temperature higher than 755 K, the hydrogen permeation flux through the membrane module with 0.2 μm grade porous 316L stainless steel substrate decayed continuously due to the inter-metallic diffusion between the membrane and the substrate. For a temperature of around 869 K–943 K, a stable hydrogen permeation flux through the membrane module with 0.5 μm grade stainless steel substrate was observed. Pretreatment of the 0.5 μm grade substrate with polishing and etching helped to smooth the membrane foil surface. However, it changed the surface structure of the material and led to a decrease in hydrogen permeability. Under the conditions investigated, the permeation factor of the module increased by raising the hydrogen pressure in the vessel side and decreasing the membrane module temperature. By decreasing the hydrogen exit partial pressure by sweep gas, the membrane module permeation flux increased, while the permeation factor decreased.

Deposition of SrZrO3 Thin Films Using Liquid Delivery Metal–Organic Chemical Vapor Deposition

Proton-conductive SrZrO3 films were successfully deposited on Pt/SiOx/Si and porous stainless-steel substrates by liquid delivery metal–organic chemical vapor deposition (LD-MOCVD). The as-deposited films deposited on the Pt/SiOx/Si substrate at 600 °C showed good crystallinity and post-annealing at temperatures below 800 °C resulted in improved crystallinity. A 200-nm-thick film deposited on the porous stainless-steel substrate was flat and solid and did not show any gas leakage. We consider this deposition technique to be applicable for the fabrication of a new solid oxide fuel cell structure with intermediate-temperature operation.

Design and synthesis of thin palladium membranes on porous metal substrate for hydrogen extraction

Membrane separation is regarded nowadays as a preferred method for production of purified hydrogen. Palladium (Pd) is an attractive membrane material due to its ability to dissociate molecular hydrogen into atoms. It is usually deposited on the porous substrate that can provide good mechanical support and reduce the thickness of the membrane for maximizing hydrogen permeability. Pd membrane used for hydrogen separation must be thin enough to increase hydrogen flux and reduce cost while remaining thick enough to retain adhesion, attrition resistance and mechanical integrity during high temperature cycles. In this paper, the progress of electroless deposition of Pd around the pore area at surface of porous stainless steel was recorded and a bridge structure that was formed during the membrane deposition around the pore area of the substrate was illustrated. After that, the porous substrate was modified using micro-or nano-size metal or metal oxide particles in order to reduce pore size in the substrate surface. The experimental results obtained from hydrogen permeation through the Pd membranes having the thickness from 400 nm to 18 μm built on both modified and original porous stainless steel substrates demonstrate that these thin membranes are solid and they can be used at the temperature of 550°C and hydrogen pressure difference of 3.447x105 Pa. The proposed processing will allow optimizing the design and fabrication of thin Pd membranes on different porous substrates for hydrogen separation.

In vitro evaluation of osteoblast‐like cells on hydroxyapatite‐coated porous stainless steel implants by synchrotron radiation x‐ray fluorescence

AbstractThe successful application of artificial implants requires osseointegration in the implanted structures. To stimulate bone growth, synthetic hydroxyapatite obtained by the coprecipitation process was coated onto porous stainless steel substrates in order to enhance the biocompatibility and, consequently, mineralization. The substrate of choice was porous 316L stainless steel for its high resistance, mechanical strength and low density due to its foam structure. The aim of the present study was to investigate the biological response of the fabricated implants cultured with MC3T3‐E1 mouse osteoblast‐like cells by analyzing the variation in the elemental concentration, mainly calcium, along with the cellular differentiation and mineralization. By employing synchrotron radiation x‐ray fluorescence spectroscopy (SRXRF), intracellular elemental distribution and concentration could be determined, revealing a clear increase in the total calcium content. This preliminary data suggests that synthetic hydroxyapatite on porous stainless steel substrates might be successfully used for biocompatible medical implants. Copyright © 2009 John Wiley & Sons, Ltd.

High performance metal-supported solid oxide fuel cells fabricated by thermal spray

Metal-supported solid oxide fuel cells (SOFCs) have been fabricated and characterized in this work. The cells consist of porous NiO–SDC as anode, thin SDC as electrolyte, and SSCo as cathode on porous stainless steel substrate. The anode and electrolyte layers were consecutively deposited onto porous metal substrate by thermal spray, using standard industrial thermal spray equipment, operated in an open-air atmosphere. The cathode materials were applied to the as-sprayed half-cells by screen-printing and heat-treated at 800 °C for 2 h. The cell components and performance were examined by scanning electron microscopy (SEM), X-ray diffraction, leakage test, ac impedance and electrochemical polarization at temperatures between 500 and 700 °C. The half-inch button cells exhibit a maximum power density in excess of 0.50 W cm −2 at 600 °C and 0.92 W cm −2 at 700 °C operated with humidified hydrogen fuel, respectively. The half-inch button cell was run at 0.5 A cm −2 at 603 °C for 100 h. The cell voltage decreased from 0.701 to 0.698 V, giving a cell degradation rate of 4.3% kh −1. Impedance analysis indicated that the cell degradation included 4.5% contribution from ohmic loss and 1.4% contribution from electrode polarization. The 5 cm × 5 cm cells were also fabricated under the same conditions and showed a maximum power density of 0.26 W cm −2 at 600 °C and 0.56 W cm −2 at 700 °C with dry hydrogen as fuel, respectively. The impedance analysis showed that the ohmic resistance of the cells was the major polarization loss for all the cells, while both ohmic and electrode polarizations were significantly increased when the operating temperature decreased from 700 to 500 °C. This work demonstrated the feasibility for the fabrication of metal-supported SOFCs with relatively high performance using industrially available deposition techniques. Further optimization of the metal support, electrode materials and microstructure, and deposition process is ongoing.

Development of Pd-based membranes as hydrogen diffusion anodes

Pd-based membranes have been prepared by Pd electroless deposition on porous stainless steel substrate and their structure, composition, morphology and thickness were analyzed by X-ray diffraction (XRD), EDS and scanning electronic microscopy (SEM). The performance of these membranes as hydrogen diffusion electrodes was evaluated in a three-electrode cell in alkaline medium. The activity towards hydrogen oxidation was high at the beginning of the experiment, but it significantly decreased with time. The major cause of this phenomenon has been attributed to the slow entry of hydrogen at the H 2/Pd interface. Even so, the technical feasibility of using these membranes as gas diffusion electrodes (GDE) has been proven.

Spray Pyrolysis Deposition of Electrolyte and Anode for Metal-Supported Solid Oxide Fuel Cell

Metal-supported solid oxide fuel cells (SOFCs) offer many advantages, including increased robustness, improved thermal shock resistance, and decreased cost. However, fabricating metal-supported SOFCs using conventional techniques is both very difficult and very costly. In this study, two processes of spray pyrolysis deposition, pneumatic spray deposition and electrostatic spray deposition, were used to deposit samaria-doped ceria (SDC) electrolytes on different substrates and NiO–SDC anodes on porous stainless steel substrates. A cathode layer was subsequently applied on the electrolyte by stencil printing for electrochemical testing. The test results indicated that the electrolyte had reasonable cell performance, but the topography of the anode needed optimization. It was also discovered that the porous ferritic stainless steel 430 substrate used in this study did not have sufficient oxidation resistance as the substrate of a metal-supported SOFC.

Novel synthesis of a porous stainless steel-supported Knudsen membrane with remarkably high permeability

A stainless steel-supported Knudsen membrane (SKM) with remarkably high permeability was successfully synthesized using only 100 nm-sized colloidal silica sol by means of a dipping–rolling–freezing–fast drying (DRFF) and soaking–rolling–freezing–fast drying (SRFF) method. Hydrogen and nitrogen permeances of the SKM were (6.7–8.2) × 10 −6 and (1.8–2.3) × 10 −6 mol m −2 s −1 Pa −1 with a H 2/N 2 permselectivity of 3.5–3.7, which approaches to a theoretical H 2/N 2 selectivity for the Knudsen diffusion mechanism (3.74). In comparison with a typical mesoporous γ-alumina membrane supported on a porous stainless steel or α-alumina substrate, the SKM had 20 and 5.5 times permeance with almost same H 2/N 2 permselectivity, respectively. Generally, mesoporous materials such as γ-alumina and the M41S family with several nm-sized pores are employed to obtain the Knudsen-dominated permeation characteristics. In this case, a decrease in the gas permeance is inevitable due to deposition of a mesoporous skin layer. However, in the case of the SKM, the Knudsen-dominated permselectivity was extraordinarily obtained through modification of porous stainless steel substrates with the colloidal silica particles having relatively large particle size, because a well-densified layer of the 100 nm-sized colloidal silica could be obtained without formation of defects via the freezing procedure. In addition, the large porosity of the 100 nm-sized colloidal silica layer gave rise to the remarkably high gas permeance.

Spray Pyrolysis Deposition of Electrolyte and Anode for Metal Supported Solid Oxide Fuel Cell

Metal supported solid oxide fuel cells offer many advantages including increased robustness, improved thermal shock resistance and decreased cost. However, fabricating metal- supported solid oxide fuel cells using conventional techniques are either very difficult or very costly. In this study, two processes of spray pyrolysis deposition - pneumatic spray deposition and electrostatic spray deposition were used to deposite samaria doped ceria (SDC) electrolytes on different substrates and deposite NiO-SDC anodes on porous stainless steel substrate. A cathode layer was subsquently applied on the electrolyte by stencil prining for electrochemical testing. The test results indicaed that the electrolyte had reasonable cell performance but the topography of the anode needed optimization.