Zirconia Hollow Fiber Research Articles

Fabrication of a Novel Catalyst Reactor with Improved Strength and Catalytic Performance Used for Automotive Exhaust Treatment

Yttria-stabilized zirconia hollow fibers (YSZ-HFs) containing radial wall microchannels with one end opening on the inner surface were prepared, and robust reactor modules of YSZ-HFs for automotive emission were prepared by bundling fibers with cement glue. 100% open-cell ratio and the unique microstructure of the YSZ-HFs catalytic reactor facilitated deposition of LaMnO3 three-way catalysts. Compared with the commonly used cordierite (2MgO-2Al2O3-5SiO2) honeycombs (CHs), the YSZ-HFs improved the reducibility and sintering resistance of the attached catalyst film. Higher effective conversion of CO and NO was found in the YSZ-HFs samples in comparison to the CHs samples. Moreover, the YSZ-HFs samples achieving higher flexural strength (∼135 MPa) can better preserve the mechanical properties and the integrity of the catalyst film after 200 thermal shock cycles at 900 °C, due to the small thermal mismatch between the YSZ-HFs and the catalysts, as well as the intrinsic merit of zirconia.

Hydrothermal ageing of tetragonal zirconia porous membranes: Effect of thermal residual stresses on the phase stability

Yttria-stabilized tetragonal zirconia hollow fiber membranes were aged in aqueous solution for investigating effect of porosity and residual stress on hydrothermal ageing. The monoclinic phase was evaluated by XRD and confocal micro-Raman spectra, to be ≤ 5.0 vol% and ≤ 60 vol% even after 100 h ageing, respectively. It is the first time to clarify the hydrothermal ageing mechanism of highly porous zirconia membranes. Highest monoclinic phase amount occurred at the interface transition regions of the aged samples, which suggested that the thermal residual stress can noticeably promote the monoclinic phase growth rate of the grain boundaries.

Batch-scale preparation of hollow fiber supported CHA zeolite membranes and module for solvents dehydration

CHA zeolite membranes have been successfully synthesized on thin yttria-stabilized zirconia (YSZ) hollow fiber (HF) substrates by secondary growth method. Prior to membrane synthesis, the outer surface of YSZ hollow fibers were planted with ball-milled submicron CHA zeolite seeds. Extensive investigations on batch-scale preparation of CHA zeolite membranes were carried out in terms of seeding method. Uniform and continuous seed layers were achieved by vacuum seeding with the addition of colloidal silica in seed suspension, which resulted in high reproducibility HF CHA zeolite membranes at crystallization temperature of 160 °C for 20 h. The membranes showed average water permeation flux of ca. 8.0 kg m−2 h−1 with separation factor of ca. 2500 in 90 wt% ethanol/water mixture at 75 °C. A HF CHA zeolite membrane module was fabricated for multi-cycle dehydration of iso-propanol/water mixture and acetic acid/isopropanol/water mixtures at 75 °C with high stability for over 100 h.

Preparation and characterization of high performance CHA zeolite membranes from clear solution

CHA zeolite membranes with Si/Al ratio of 2–3 have been successfully synthesized on the outer surface of yttria-stabilized zirconia (YSZ) hollow fibers from clear solution for the first time. The influence of synthesis parameters, such as precursor alkalinity, crystallization time and temperature, on the morphologies and dehydration performance of CHA zeolite membrane, were extensively investigated. Pervaporation (PV) results indicated that the separation performances of obtained CHA membranes were strongly influenced by the morphology of the membranes. The optimal synthesis condition was 140°C for 16h in the precursor of 22 SiO2: 1 Al2O3: 15 K2O: 1 Na2O: 4400 H2O. The as-synthesized membranes composed of flake-like grains exhibited a water permeation flux of 13.3kgm−2h−1 with separation factor of 6000 for the PV dehydration of 90wt% ethanol/water mixture at 75°C. The long-term (>550h) acid resistance of the as-synthesized CHA zeolite membranes ensures them the most promising candidate for PV dehydration of organic solvents containing acids.

Novel Organic-Dehydration Membranes Prepared from Zirconium Metal-Organic Frameworks

Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well-intergrown UiO-66 metal-organic framework membranes fabricated on prestructured yttria-stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m−2 h−1 and excellent separation factor (>45 000) for separating water from i-butanol (next-generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.

Enhanced performance of Fe2O3 doped yttria stabilized zirconia hollow fiber membranes for water treatment

Fe2O3 powders were introduced as sintering aid to fabricate yttria-stabilized zirconia (YSZ) hollow fiber membranes using a combined wet-spinning and post-sintering method. The obtained Fe2O3-YSZ hollow fiber membranes show enhanced performance for water treatment with fine crystal structure in terms of bending strength and pure water permeability. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and thermogravimetric analysis (TGA) along with mechanical tests were employed to investigate the structural evolution in the sintering process and the effect of Fe2O3. It is suggested that the Fe2O3 dopants dissolve into YSZ at elevated temperatures, providing defect sites and vacancies for fast ion migration, favoring for densification and grain growth of the YSZ, which yields dense microstructures of fine crystallites at relatively low sintering temperature. The Fe2O3-YSZ hollow fiber membranes sintered at 1150°C show a 3-fold increase of the permeate flux of pure water (F) (743Lm−2h−1) along with comparable bending strength (152MPa) compared to pure YSZ membranes. This modified method can reduce sintering costs and therefore fabrication costs which should pave the way for scale-up production for ceramic hollow fiber membranes.

Growth of carbon nanofibers/tubes by an in-situ polymerization route without metal-catalyst

An in-situ pyrolytic and polymerizable method was investigated to grow carbon nano-fibers/tubes (CNF/CNT) without metal-catalysts. The 3 mol % yttria-stabilized zirconia hollow fiber membranes (3YSZ-HFM) were used as supports for growing the CNF/CNT. The polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were used as polymer binders and carbon sources. The as-grown CNF (formed at 1250 °C/4h) had diameters of 50–100 nm and lengths of 1–50 μm, and the length gradually decreased along radial direction of the supports. The as-grown CNT (formed at 1450 °C/4h) were shorter and larger in diameter. A novel solid-state transformation mechanism was proposed, in which the carbon black particles (CB) were the carbonized products of PES/PVP, then the CB grew into the CNF/CNT. Thermal stresses originated from sintering of CB itself and 3YSZ particles were believed to be the driving forces that promoting the CNT/CNF nucleation and growth. The thermal stresses of the pure 3YSZ-HFM and 3YSZ/(CNF/CNT)-HFM were theoretically and experimentally discussed base on linear elastic thoery and Raman spectroscopy.

Microstructure evolution and properties of YSZ hollow fiber microfiltration membranes prepared at different suspension solid content for water treatment

Yttria-stabilized zirconia (YSZ) hollow fiber ceramic membranes for microfiltration applications were prepared by the phase inversion and sintering technique. The influence of suspension solid content on the rheological behavior of suspension, and the microstructure and properties of the hollow fiber membranes were investigated. With the addition of YSZ powder, the viscosity of the spinning suspension increased obviously, and the rheological behavior of the suspension changed from Newtonian fluid into thinning behavior fluid. The increment of suspension viscosity upon the YSZ content led to a more porous inner surface, larger inner finger-like pores extending outward, and reduced outer finger-like layer for the prepared hollow fiber membrane. When the YSZ content was increased to 65%, a double-layer structure mostly consisting of outer sponge-like layer and inner finger-like structure layer was formed. The pure water flux of the hollow fiber membrane decreased with the increment of YSZ content, while the bending strength showed obvious enhancement. The prepared membranes showed good oil/water separation performance, and steady permeate flux of more than 0.85 m3/(m2 h bar) and high oil rejection rate of 99.2–99.7% were attained. Transmembrane resistance analysis indicated that the membranes prepared at 50 and 65% YSZ content had different dominant fouling mechanism in oil/water separation process.

Novel light-weight, high-performance anode-supported microtubular solid oxide fuel cells with an active anode functional layer

Influence of the air-gap, the distance from the tube-in-orifice spinneret to the upper surface of the external coagulant bath during the extrusion/phase-inversion process, on the microstructure of nickel – yttria-stabilized zirconia (Ni–YSZ) hollow fibers has been systematically studied. When the air-gap is 0 cm, the obtained Ni–YSZ hollow fiber has a sandwich microstructure. However, when the air-gap is increased to 15 cm, a bi-layer Ni–YSZ hollow fiber consisting of a thin layer with small pores and a thick support with highly porous fingerlike macrovoids has been achieved. The output power density of microtubular solid oxide fuel cells (MT-SOFCs) with a cell configuration of Ni–YSZ/YSZ/YSZ–LSM increases from 594 mW cm−2 for the cells with the Ni–YSZ anode of sandwich microstructure to 832 mW cm−2 for the cells with the Ni–YSZ anode of bi-layer microstructure at 750 °C, implying that to achieve the same output power density, the weight of the cells with the bi-layer anode support can be reduced to 41.5% compared with that of the cells with the sandwich anode support. Thermal-cycling test shows no obvious degradation on the open-circuit-voltage (OCV), indicating that the MT-SOFCs have robust resistance to thermal cycling.

Microstructure tailoring of the nickel oxide-Yttria-stabilized zirconia hollow fibers toward high-performance microtubular solid oxide fuel cells.

NiO-yttria-stabilized zirconia (YSZ) hollow fiber anode support with different microstructures was prepared using a phase-inversion method. The effect of the solid loading of the phase-inversion suspensions on the microstructure development of the NiO-YSZ anode support was investigated. Solid loading in the suspension was found to have an important influence on the microstructure of the NiO-YSZ anode support and viscosity-related viscous fingering mechanism can be adopted to explain the pore formation mechanism of the as-prepared hollow fibers. NiO-YSZ anode-supported microtubular solid oxide fuel cells (SOFCs) with different anode microstructures were fabricated and tested, and the correlation between the anode support microstructures, porosity, gas permeability, electrical conductivity, and the cell electrochemical performance was discussed. Microtubular SOFCs with a cell configuration of Ni-YSZ/YSZ/YSZ-LSM (LSM = (La(0.8)Sr(0.2))(0.95)MnO(3-x)) and optimized anode microstructure show cell output power density of 833.9 mW cm(-2) at 750 °C using humidified H2 as fuel and ambient air as oxidant.

Preparation and characterization of high-flux T-type zeolite membranes supported on YSZ hollow fibers

T-type zeolite membranes were prepared on thin yttria-stabilized zirconia (YSZ) hollow fiber substrates by secondary growth method. Prior to membrane synthesis, the outer surface of YSZ hollow fibers were planted with T-type zeolite seeds. Extensive investigation on membrane synthesis was carried out in terms of seeding method, synthesis temperature, crystallization time and precursor composition. High-quality hollow fiber T-type zeolite membranes were synthesized at 100°C for 40h using milk-like aluminosilicate gel (SiO2:Al2O3:Na2O:K2O:H2O=1:0.05:0.26:0.09:17 in mol) as a synthesis precursor. The as-synthesized membranes via the seeding approach of rubbing had well-intergrown zeolite layers with a thickness of ~12μm, which displayed high permeation flux for dehydration of organics. Typically, a water permeation flux of 7.36kgm−2h−1 with separation factor of >10,000 was obtained for dehydration of 90wt% isopropanol solution at 75°C. The membrane synthesis via the seeding approach of vacuum-coating could produce hollow fiber T-type zeolite membranes in batch scale. High acid resistance for the membrane material was confirmed by dehydration of propanal solution with pH~4. Moreover, hollow fiber membrane modules with ca. 0.1m2 membrane area were fabricated and assembled for propanal dehydration to evaluate the technical feasibility.

Phase Inversion and Electrophoretic Deposition Processes for Fabrication of Micro-Tubular Hollow Fiber SOFCs

A novel combination of a phase inversion process followed by electrophoretic deposition was used to fabricate anode supported micro-tubular hollow fiber solid oxide fuel cells (SOFCs). The phase inversion process was used to produce 240 μm thick 60 wt% NiO - 40 wt% yttria-stabilized zirconia (YSZ) hollow fiber anode precursors with asymmetric porosity. Subsequently, electrophoretic deposition (EPD) was used to apply 40 μm thick, particulate YSZ electrolyte layers onto the un-sintered NiO-YSZ hollow fibers from a YSZ dispersion in ethanol at an applied electric field of ca. 22 kV m−1. The YSZ-coated NiO-YSZ fibers were sintered in a hydrogen atmosphere at 1500°C to produce gastight electrolytes. Two dispersions of YSZ and lanthanum strontium manganite (LSM) particles were then painted consecutively on top of the electrolyte layers, as ‘graded’ LSM-YSZ | LSM cathode precursors that were sintered at 1200°C. When fed with H2 fuel and air, a single such SOFC delivered peak power densities of 0.20, 0.18 and 0.14 W cm−2 during operation at 800, 750 and 700°C, respectively. A lumped parameter model, incorporating calculations of the contact, ohmic, activation and concentration polarization losses, is presented and the means are proposed by which certain potential losses may be obviated.

Development of a High-Performance Micro-Tubular SOFC Based on a Hollow Fiber Support

A new design of micro-tubular solid oxide fuel cell (SOFC) is proposed to improve current collection efficiency from the bore side. The proposed micro-tubular SOFC uses a ceramic hollow fiber as a support component above which functional layers are deposited. The provision of a thin porous layer of a current collector above the cell support makes it possible to collect current from the entire surface of the inner electrode. The thermal-fluid and electrochemical phenomena in the proposed design are studied through computational fluid dynamics (CFD) simulations. The simulation results suggest that due to significantly reduced ohmic losses, the proposed design is able to deliver a superior performance compared to the conventional anode-supported micro-tubular design. Finally, for the realization of the proposed design, the preparation of yttria-stabilized zirconia (YSZ) hollow fibers through an electrophoretic deposition (EPD) method is also discussed.

Preparation and Characterization of Hydrophobic Porous Yttria-stabilized Zir-conia Hollow Fiber for Water Desalination

Porous yttrium-stabilized zirconia (YSZ) hollow fibers with an outer diameter of 1.92 mm, membrane thickness of 0.21 mm were prepared by a combined technique of phase inversion and sintering. The hollow fiber possessed a sandwich structure with long-finger like voids near the inner and outer walls and a thin porous sponge-like layer in the center. The porosity and average pore size of the YSZ hollow fiber were determined to be 54% and 0.56 m, respectively. The surface of the hollow fiber was converted from hydrophilic to hydrophobic by grafting with fluoroalkylsilane (FAS). The as-prepared hydrophobic YSZ hollow fiber exhibited desired water desalination performance operating in the vacuum membrane distillation (VMD). A water flux as high as 48.3 L/(m 2 h) was attained with a salt rejection of over 99.7% by exposing the shell side of the fiber to an aqueous

New Fabrication Techniques for Micro-Tubular Hollow Fiber Solid Oxide Fuel Cells

A novel combination of phase inversion and electrophoretic deposition was used in the fabrication of anode supported micro tubular (hollow fiber) solid oxide fuel cells (MT-HF-SOFCs). The phase inversion process was used to produce ca. 240 μm thick, highly porous 60 wt. % NiO-40 wt. % yttria-stabilised zirconia (YSZ) hollow fiber anode precursors. The electrophoretic deposition process was then used to apply ca. 40 μm thick, particulate YSZ electrolyte layers onto the unsintered NiO-YSZ HFs from an ethanol suspension at an applied electric field of ca. 0.22 kV cm-1. The YSZ-coated NiO-YSZ HFs were sintered at 1500 oC for twelve hours. Dispersions of YSZ-LSM particles were then painted on top of the electrolyte layer, as ‘graded’ YSZ-LSM porous cathode precursors that were sintered at 1200 oC for three hours. The fabrication process was completed by winding silver wire current collectors spirally round the cathodes and through the lumen of the fibers to enable current collection from the anodes. Single MT-HF-SOFCs delivered peak power densities of 0.20, 0.18 and 0.14 W cm-2 at 800, 750 and 700 oC, respectively, with flow rates of 15 cm3 min-1 H2 (97% H2-3% H2O) and 30 cm3 min-1 of air.

Phase inversion spinning of ultrafine hollow fiber membranes through a single orifice spinneret

This paper reports a new phase inversion spinning method for the preparation of ultrafine hollow fiber membranes through a single orifice spinneret. An oily additive is pre-added in the polymer dope solution as a bore-forming agent. During the rapid solvent extraction and phase separation processes, the oil is pushed by the external solution (coagulant) to the center of the fiber, and thus the hollow fiber membranes can be obtained by washing away the oil. To demonstrate this new method, ultrafine polysulfone and yttria stabilized zirconia hollow fiber membranes were fabricated using a stainless steel syringe tip as a simple orifice spinneret. The fabrication conditions, including the sizes of syringe tips, contents and types of the oily additives were investigated. Gas permeation test indicates the polysulfone hollow fiber membrane had no large defects. The potential benefits of concave surfaces arising from oil droplets in terms of mechanical properties were also discussed.

Microstructure and Performance Investigation of a Solid Oxide Fuel Cells Based on Highly Asymmetric YSZ Microtubular Electrolytes

A combined phase inversion and sintering technique was used to fabricate highly asymmetric yttria-stabilized zirconia (YSZ) hollow fibers with a 1.9 mm external diameter and 210 μm total wall thick...

Highly permeable porous YSZ hollow fiber membrane prepared using ethanol as external coagulant

Highly permeable porous yttria-stabilized zirconia (YSZ) hollow fiber membranes have been developed by a combined phase inversion and sintering technique. Ethanol substituting for usual water was used as the external coagulant in order to prepare YSZ hollow fiber membranes with low trans-membrane resistance. The prepared YSZ hollow fiber membranes show a special asymmetric structure with an outer skin layer, highly porous inner surface and sub-layer composed of long and large finger-like pores. The influences of sintering temperature on the microstructure, porosity and pore size distribution, bending strength and pure water flux were investigated in detail. Results show that YSZ hollow fiber membranes with high permeability and enough bending strength can be prepared using ethanol as the external coagulant and by controlling the sintering temperature. The outer-skinned YSZ hollow fiber membranes show a pure water flux of 2.27–4.30 m 3 m −2 h −1 bar −1 and a bending strength of 154.5–201.7 MPa when sintered between 1350 and 1400 °C. The prepared YSZ hollow fiber membranes are suitable to be used for microfiltration and as support for other composite membranes.

Applications of titania and zirconia hollow fibers in sorptive microextraction of N,N-dimethylacetamide from water sample

The convenient fabrications of titania and zirconia hollow fiber with three-dimensional porous structure using polypropylene hollow fibers as templates were developed. And an analytical method based on enrichment and extraction of analytes in the water sample, hollow fiber sorptive microextraction in combined with gas chromatography has been developed for the rapid analysis of N,N-dimethylacetamide (DMA) in the environmental samples. The results showed that zirconia hollow fiber gave higher extraction performance of DMA than that of titania hollow fiber. The method validations, including linearity, limit of detection, limit of qualification, precision, and repeatability were investigated. Linearity for six-point calibration curve was excellent with zirconia hollow fiber having r 2 value greater than 0.9993 at the linearity range of 0.001–1.0 mg mL −1. In addition, it seems that hollow fiber sorptive extraction is a promising technique for the enrichment and purification of analytes extracted directly from liquid samples without any other pretreatment.

Determination of melamine residues in milk products by zirconia hollow fiber sorptive microextraction and gas chromatography–mass spectrometry

News stories about the contamination of milk with melamine in China emerged on Sept 11, 2008, and the situation has since become an international health scare. In this work, a novel analytical method based on enrichment and pretreatment of analytes in the milk sample, hollow fiber sorptive extraction and gas chromatography–mass spectrometry has been developed for the rapid analysis of melamine in the dairy products. In the proposed method, melamine in the fresh milk was extracted by zirconia hollow fiber, enriching on zirconia coating of the hollow fiber, and then analyzed by GC–MS. The method validations including linearity, limit of detection, limit of qualification, recoveries at three different concentrations, precision, and repeatability were investigated. It was found that the proposed method provided linear range from 0.001 to 1000 μg/mL ( r 2 = 0.9997), low detection limit of 0.001 μg/mL, and preferable recoveries at three different concentrations. The obtained results demonstrated that zirconia hollow fiber combined with GC–MS is a simple, rapid and solvent-free method for the analysis of melamine in the dairy products.