Oxygen separation from air using Ba0.95La0.05FeO3−δ membranes fitted with porous La1−xSrxFeO3−δ layers

Selective oxygen separation from air was performed using perovskite-type oxide membranes made of Ba_0.95La_0.05FeO_3−δ. We demonstrated that surface modification of Ba_0.95La_0.05FeO_3−δ membranes with La_1−xSr_xFeO_3−δ catalyst layers led to an increase in oxygen permeation fluxes at 700–930 °C. We studied the effects of oxygen vacancy amounts, surface area, particles size, surface treatment of La_1−xSr_xFeO_3−δ on the oxygen permeability of the membranes fitted with La_1−xSr_xFeO_3−δ catalyst layers. Among the catalyst layers tested, the membranes fitted with La_0.9Sr_0.1FeO_3−δ (x=0.1) showed the highest oxygen permeation flux probably because of its higher porosity and uniform morphology without open voids, which would increase the number of surface reaction sites. The obtained results suggest the feasibility of further upgrading the membrane performance by using surface catalyst layers having a homogeneous morphology and a different composition from that of the mother membrane.     

Temperature field and residual stress analysis of multilayer pyroelectric thin film

The two-dimensional finite element model was built for the multilayer pyroelectric thin film. The temperature field and residual stress were simulated. The results show that porous silica film as a thermal-insulation layer and a reasonable model structure are effective for decreasing the heat loss. The silicon substrate and pyroelectric thin film that influence the temperature variation rate in pyroelectric thin film are also discussed. The annealing temperature and model structure have significant influence on residual stresses of pyroelectric thin film. The residual stresses increase rapidly with the increase of annealing temperature. The scanning electron microscopy (SEM) is employed to investigate the morphology of the pyroelectric thin film. The results show that the pyroelectric thin film annealed at 750 °C has a crack structure.     

Review of perovskite ceramic synthesis and membrane preparation methods

In the 25 years since the first report of mixed ionic and electronic conducting ceramics, perovskite membranes underwent both research and development phases, with the latest works entering pilot trials for oxygen separation from air. During this time a number of perovskite synthesis methods were investigated from the original solid state chemistry through the more advanced and well established sol–gel route via the Pechinni method. The advances in synthesis methods were possible due to the desirable full incorporation of cations into the A and B-sites of perovskites with a general ABO₃ structure. In terms of membrane manufacturing, perovskite hollow fibres attracted a major research effort due to small membrane thickness and high fluxes. This led to a number of investigations by doping with other cations or by surface modification, all aiming at increasing oxygen fluxes. Recently, advanced ceramic processing by tape casting has led to the preparation of very thin dense films either on porous supports or as monoliths containing internal porous regions. All these developments in perovskite synthesis and membrane preparation methods, together with other types of methods requiring special equipment are addressed in this review, including an analysis of the state of the art. Finally, future challenges are discussed in terms of competing technologies and potential industrial design directions of perovskite membranes for oxygen separation from air.     

Usability of electrophoretic deposition for additive manufacturing of ceramics

The potential of electrophoretic deposition of ceramic particles for additive manufacturing of 3D structures is investigated. A custom-made test setup is constructed using a hollow electrode for the supply of a ceramic suspension and a tip c electrode for focused deposition of particles on the surface of a membrane. Parameters like voltage, electrode distance, suspension flow rate, etc. are systematically varied to study their impact on the deposition yield and the morphology of the deposited structures. Experimental work is supported by computer simulations on the electrical field distribution within the electrode area. Although detrimental phenomena like electrohydrodynamic effects occur, we have shown that the technique offers opportunities for future 3D printing of ceramics.     

Growth and structural characteristics of perovskite-wurtzite oxide ceramics thin films

Wurtzite ZnO thin films were grown on single-crystal perovskite SrTiO₃(STO) (1 0 0) substrates at various temperatures. The ZnO/STO thin films thus formed exhibit a preferred (1 1 0)-orientation at a growth temperature of 600-700 °C. A high growth temperature enhances not only the (1 1 0)-texture of ZnO/STO thin films but also the crystalline quality of the film. (La_0.7Sr_0.3)MnO₃ (LSMO) thin films were subsequently grown on ZnO(1 1 0)/STO(1 0 0) substrates with various thicknesses, and were polycrystalline. A thicker LSMO film has a stronger (0 0 l)-preferred orientation than the thinner one. The lattice distortion of LSMO decreases as the LSMO thickness increases. Magnetization vs. temperature curves show that both crystalline quality and lattice distortion influence the magnetic properties of LSMO thin films. The physical properties of the manganite oxide can be modulated by forming a heterostructure with wurtzite ZnO.     

Innovative fabrication of PZT pillar arrays by a colloidal approach

An innovative approach for fabricating pillar arrays for ultrasonic transducer applications is disclosed. It involves the preparation of concentrated piezoelectric lead zirconate titanate (PZT) suspensions in aqueous solutions of epoxy resin and its polymerization upon adding a polyamine based hardener. Zeta potential and rheological measurements revealed that 1 wt.% dispersant, 20 wt.% of epoxy resin and a hardener/epoxy resin ratio of 0.275 mL g⁻¹, were the optimized contents to obtain strong PZT samples with high green strength (35.21 ± 0.39 MPa). Excellent ellipsoidal and semi-circle shaped pillar arrays presenting lateral dimensions lower than 10 μm and 100 μm height were successfully achieved. The organics burning off was conducted at 500 °C for 2 h at a heating rate of 1 °C min⁻¹. Sintering was then carried out in the same heating cycle at 1200 °C for 1 h. The microstructures of the green and sintered ceramics were homogeneous and no large defects could be detected.     

Tape-cast asymmetric membranes for hydrogen separation

Ceramic hydrogen separation membrane is a promising technology for obtaining pure hydrogen in a wide range of processes including power generation with pre-combustion CO₂ capture, water-gas shift, methane reforming, etc. This work presents for the first time the production of cer-cer asymmetrical composite membranes. BaCe_0.65Zr_0.20Y_0.15O_3-δ (BCZY) supported BCZY- Gd_0.2Ce_0.8O_2-δ (GDC) membranes were produced by tape casting. Three different sintering aid incorporation methods were investigated to enhance the final density of the BCZY-GDC layer. The optimization of the whole process leads to produce planar crack-free asymmetrical proton conductive membranes with Ø=12 mm, constituted by a porous 350 µm thick BCZY substrate with an open porosity of 48%, and a 20 µm thick gas tight BCZY-GDC layer.     

Piezoelectric and dielectric characteristics of lead-free BNKLBT ceramic thick film and multilayered piezoelectric actuators

Lead-free piezoelectric 0.885(Bi_0.5Na_0.5)TiO₃–0.05(Bi_0.5K_0.5)TiO₃–0.015(Bi_0.5Li_0.5)TiO₃ 0.05BaTiO₃ ceramics (abbreviated as BNKLBT-1.5) were prepared by a conventional mixed oxide method. The composition has a piezoelectric d₃₃ constant of 154 × 10⁻¹² C/N, an electromechanical coupling coefficient k_t of 0.519, a relatively low dissipation factor (tan δ = 1.6%) at 1 kHz. BNKLBT-1.5 multilayered actuators have been fabricated using a roll-casting technique. Each single layer has dimensions of 9.0 mm × 9.0 mm × 0.2 mm. Four multilayer actuators with 5, 10, 15 and 20 layers have been fabricated. Their capacitance and displacement under an a.c. field were measured. The capacitance measured at 1 kHz is 9.64 nF, 14.69 nF, 25.36 nF, 32.59 nF and the displacement measured at 5 kHz is 867 pm/V, 1331 pm/V, 2060 pm/V, 2442 pm/V, respectively.     

High performance BaCe0.8Y0.2O3−a (BCY) hollow fibre membranes for hydrogen permeation

In this work, BaCe_0.8Y_0.2O_3−α (BCY) perovskite hollow fibre membranes were fabricated by a phase inversion and sintering method. BCY powder was prepared by the sol–gel technique using ethylenediaminetetraacetic acid (EDTA) and citric acid as the complexing agents. Gel calcination was carried out at high temperature to form the desired crystal structure. The qualified BCY hollow fibre membranes could not be achieved even the sintering was carried out at temperatures up to 1550^oC due to the poor densification behavior of the BCY material. The addition of sintering aid (1 wt% Co₂O₃) inside BCY powder as the membrane starting material significantly improved the densification process, leading to the formation of gas-tight BCY hollow fibres. The optimum sintering temperature of BCY hollow fibre membrane was 1400 °C to achieve the best mechanical strength. H₂ permeation through the BCY hollow fibre membranes was carried out between 700 and 1050 °C using 25% H₂–He mixture as feed gas and N₂ as sweep gas, respectively. For comparison purpose, the disk-shaped BCY membrane with a thickness of 1 mm was also prepared. The measured H₂ permeation flux through the BCY hollow fibres reached up to 0.38 mL cm⁻² min⁻¹ at 1050 °C strikingly contrasting to the low values of less than 0.01 mL cm⁻² min⁻¹ from the disk-shaped membrane. After the permeation test, the microstructure of BCY hollow fibre membrane was still maintained well without signals of membrane disintegration or peeling off.     

Growth-temperature-dependent microstructure and ferromagnetic properties of perovskite manganite-based heterostructures

Oxide heterostructures composed of ferromagnetic La_0.7Ba_0.3MnO₃ (LBMO) spacers and paramagnetic LaNiO₃ (LNO) spacers were grown on SrTiO₃ (0 0 1) substrates at various substrate temperatures. The X-ray diffraction (XRD) patterns confirm the formation of the heterostructure at a growth temperatures of 400–600 °C. A high substrate temperature of 700 °C caused serious atomic intermixing between the LBMO and the LNO spacers of the heterostructure, further degrading the crystalline quality of the heterostructure. The ferromagnetic LBMO spacer in the heterostructure is under biaxial compressive stress. The XRD results reveal that the lattice of the heterostructure was elongated parallel to the c-axis at a growth temperature of 400–600 °C. Experiments that involve XRD, atomic force microscopy and X-ray photoelectron spectroscopy provide structural information on the designed heterostructures. The observed magnetization characteristics of the heterostructures show that lattice strain and the quality of the surface and the interface of heterostructures affect the Curie temperature of the manganite layers.     

Annealing-induced changes in the nanoscale electrical homogeneity of bismuth ferrite dielectric thin films

In this study, we investigated the effects of forming gas (7% H₂ + 93% Ar) annealing (FGA) and recovery annealing (RA) in ambient oxygen on the structure and electrical properties of BiFeO₃ (BFO) thin films. X-ray diffraction results indicate that BFO remains in the perovskite phase following FGA. However, the spatial distribution of current maps obtained by conductive atomic force microscopy shows that FGA-treated BFO thin films are less electrically insulating than those without prepared thermal annealing. Recovery annealing improves the structural and chemical homogeneity of the FGA-treated films, thereby increasing the electrical resistance of the films.     

Fabrication of novel superhydrophilic and underwater superoleophobic hierarchically structured ceramic membrane and its separation performance of oily wastewater

Hierarchically engineered asymmetric ceramic membrane is successfully fabricated, and special wettability is endowed to the membrane by introducing superhydrophilic and underwater superoleophobic silica nanoparticles through dip-coating technology onto the active separation layer. Effect of reaction temperature on the wettability of the silica nanoparticles is discussed. It has been found that the hydrophilicity of the silica increases with increasing the temperature and superhydrophilicity can be obtained when the temperature reaches to 60 °C. Underwater oil contact measurements are performed using a series of oils and it turns out the as-prepared material bear excellent oil repellency towards various oil droplets. Separation performance of the membrane for oily wastewater treatment was investigated. It has been revealed that the as-prepared membrane can successfully separate the oil contaminated wastewater within one step under a small applied pressure (0.1 MPa) with oil rejection coefficient R>99.95%, indicating an extremely high separation efficiency.     

Preparation of photocatalytic TiO2 coatings by gel-dipping with polysaccharides

Commercial tiles are being produced in vast quantities. The main properties of tiles are well established but there is an increasing interest in producing ceramics with tailored-properties and advanced functionalities. One way of adding value to commercial tiles is to deposit a photocatalytic coating to obtain ‘smart’ tiles for environmental reasons, e.g. for the (photo) degradation of organic pollutants in air or in a liquid. Here, we show the manufacture of ‘smart’ tiles by formation of TiO₂ coatings onto commercial tiles by a colloidal processing route based on the immersion of the substrate into a homogeneous aqueous ceramic suspension and its consolidation by agar thermogelation. The effect of the processing parameters (withdrawal rate, solid loading and gelling agent content) and the grain size on the photocatalytic activity of the final coated tiles is reported and discussed. Final coatings properties depend on the viscosity of the suspension, particle size, withdrawal rate, solid loading and gelling agent content, and hence, this dependence affects the photocatalytic activity of the coatings.     

Impulse Excitation Technique IET as a non-destructive method for determining changes during the gelcasting process

Gelcasting is a good method for obtaining ceramic components with a pre-defined shape. From the point of view of the course of the ceramic casting process, a very important issue is the so-called idle time or gelation time whose measurement is usually based on determining changes in ceramic slurry viscosity by means of rheometers. However, searches are being continued to find methods which would have the least impact on the interactions between ceramic powder particles and the forming polymeric structure and would allow more time range to observe changes in gelcasting process compared to classic measurements of viscosity.In the article, based on measurements on Al₂O₃, ZrO₂ and SiC-based gelcasting systems with various water-soluble acrylic monomers, it has been demonstrated that such requirements may be fulfilled by IET (Impulse Excitation Technique).     

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) (743 L m⁻² h⁻¹) along with comparable bending strength (152 MPa) 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.     

YBa2Cu3O7−x dispersion in iodine acetone for electrophoretic deposition: Surface charging mechanism in a halogenated organic media

Electrophoretic deposition (EPD) performance strongly depends on the particles surface chemistry and the ability to manipulate surface-liquid interfaces. In this study an extensive investigation of YBCO suspension in dry acetone, acetone-water mixtures and acetone-iodine is reported. Chemical instability of YBCO particles determines their colloidal behaviour. Charging mechanism of particles has therefore had to be deeply investigated for complete dispersion understanding. In order to determine the conditions of the YBCO suspension stability, measurements of pH, conductivity, zeta-potential, settling tests, modelling of the particle networks and electrophoretic deposition were done. The influence of the water and iodine concentration, and their role as stabilizers was evaluated. Based on experimental results, pair particle potentials were calculated and then different charging mechanisms of YBCO surfaces in acetone were proposed.     

Effect of nickel doping on structural,optical, electrical and ethanol sensing properties of spray deposited nanostructured ZnO thin films

Undoped and nickel (Ni)-doped ZnO thin films were spray deposited on glass substrates at 523 K using 0.1 M of zinc acetate dihydrate and 0.002–0.01 M of nickel acetate tetrahydrate precursor solutions and subsequently annealed at 723 K. The effect of Ni doping in the structural, morphological, optical and electrical properties of nanostructured ZnO thin film was investigated using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–vis Spectrophotometer and an Electrometer respectively. XRD patterns confirmed the polycrystalline nature of ZnO thin film with hexagonal wurtzite crystal structure and highly oriented along (002) plane. The crystallite size was found to be increased in the range of 15–31 nm as dopant concentration increased. The SEM image revealed the uniformly distributed compact spherical grains and denser in the case of doped ZnO thin films. All the films were highly transparent with average transmittance of 76%. The measured optical band gap was found to be varied from 3.21 to 3.09 eV. The influence of Ni doping in the room temperature ethanol sensing characteristics has also been reported.     

Solubility and aging of lead magnesium niobate in water

Lead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly employed in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, stability of this material in water is not very well known and there is need for a detailed investigation. In this research, solubility of lead magnesium niobate powders in water was determined as a function of solids concentration. The obtained results showed that the amount of cation leaching from the PMN surface depends on the pH value of the suspension and the solids concentration. The Pb²⁺ and Mg²⁺ ion dissolution was very high especially in the acidic pH range. Nevertheless, neither the dissolution mechanism nor the effects of dissolved ions on the stability were the same for those ions. The study provides new aspects on the solubility of perovskite materials which possess more than one soluble cation in their structure.     

Properties of solution-processed MgInZnO semiconductor thin films and photodetectors fabricated at a low temperature using UV-assisted thermal annealing

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10² Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I_light-to-I_dark ratio of 7.7 × 10² and had a photoresponsivity of 5.0 A/W at a bias of 5 V.