Stability of NiO cathode modified by ZnO additive for molten carbonate fuel cell

The preparation and subsequent oxidation of nickel cathodes modified by impregnation with zinc oxide (ZnO) were evaluated by surface and bulk analysis. The ZnO impregnated cathodes showed the similar porosity, pore size distribution and morphology as the reference nickel cathode. The stability tests of ZnO impregnated NiO cathodes in the eutectic molten Li/K carbonates showed that the ZnO additive could dramatically reduce the solubility of NiO in the melts under the standard cathode condition. The mechanism of ZnO additive on the solubility reduction of NiO cathode in the melts was also proposed in this paper. ZnO/NiO materials could be alternative cathode materials for molten carbonate fuel cells.     

Compression temperature and binder ratio on a process for fabrication of open-celled porous Ti

This study was performed to investigate the fabrication of open-celled porous Ti by space holder using spherical polymer balls, and to evaluate the effect of temperature and binder ratio in the compression process. In compression condition of 80 °C, the open cellular structure consisted of continuously connected Ti struts with pore fraction above 85% and with the pores distributed homogeneously with nominal diameters between 200 μm and 400 μm. The large stress of 700 MPa applied to the acryl balls, containing the Ti feedstock, were not crushed, because the uniaxal stress applied to the acryl balls was transferred into the pseudo-hydrostatic stress state. A compression temperature of 90 °C caused the agglomeration of Ti feedstock and penetration of Ti powders into the inner part of acryl balls by softening. The thinner struts were gradually developed with increase of binder ratio due to increase of deformation.     

Electrophoretic technique for hydrothermal synthesis of NaA zeolite membranes on porous α-Al2O3 supports

Uniform and dense NaA zeolite membranes were prepared on the α-Al₂O₃ support by electrophoretic technique. The membrane morphology and membrane thickness were investigated by XRD, SEM and pervaporation properties for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. Under the action of the applied electric field, the negatively charged zeolite particles could migrate to the support surface homogenously and rapidly, forming uniform and dense membranes in a short time. High quality NaA zeolite membrane, with a separation factor (water/isopropanol) of 3281 and a flux of 1.24 kg/m² h, could be prepared by electrophoretic technique with the electrical potential of 1 V. The formation mechanism of zeolite membrane in the electric field is discussed.     

Fabrication of porous TiO2 nanofiber and its photocatalytic activity

Porous TiO₂-based nanofiber was fabricated via a combined electrospinning and alkali-dissolution method. TiO₂/SiO₂ composite nanofiber was firstly prepared by electrospinning and sintering, and then silica was leached out with alkaline solution from the bulk of TiO₂/SiO₂ composite nanofiber to produce porous microstructure. The thermal decomposition and phase structure of the composite nanofiber precursor was investigated with TG/DSC and XRD, and optimal sintering temperature was obtained. SEM-EDX and FT-IR characterization show that most silica can be dissolved out from the composite nanofiber and thus porous nanofiber with excellent microstructure can be spontaneously formed. The effect of composite nanofiber composition on porous microstructure was studied, and it is found that the composite nanofiber with 20wt% silica can produce better porous microstructure compared to those with 10wt% and 30wt% silica. Meanwhile, porous TiO₂ nanofiber with 20wt% silica shows higher degradation efficiency to Congo Red.     

Enhanced accumulation and visible light-assisted degradation of azo dyes in poly(allylamine hydrochloride)-modified mesoporous silica spheres

A new route for the economic and efficient treatment of azo dye pollutants is reported, in which surface-modified organic-inorganic hybrid mesoporous silica (MS) spheres were chosen as microreactors for the accumulation and subsequent photodegradation of pollutants in defined regions. The surface-modified silica materials were prepared by anchoring the polycationic species such as poly(allylamine hydrochloride) on MS spheres via a simple wet impregnation method. The as-synthesized spheres with well-defined porous structures exhibited 15 times of accumulating capacity for orange II and Congo red compared to that of the pure MS spheres. Diffuse reflectance UV-vis spectroscopy and confocal laser scanning microscopy demonstrated that the accumulated orange II and CR in defined MS spheres were rapidly degraded in the presence of Fenton reagent under visible radiation. Kinetics analysis in recycling degradation showed that the as-synthesized materials might be utilized as environment-friendly preconcentrators/microreactors for the remediation of dye wastewater.     

Elaboration, by tape casting, and thermal characterization of a solid oxide fuel half-cell for low temperature applications

In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cell (SOFC) down to about 700 °C. In this respect, materials with a high ionic conduction at intermediate temperature have to be found and the processes to elaborate fuel cells, using these new materials, have to be developed.Apatite materials (La_10−xSr_x(SiO₄)₆O_2±δ) are attractive candidates for solid electrolyte working at intermediate temperature. The ceramic powder was produced by solid state reaction and was tape cast to obtain green sheets.Concerning the cathode, a perovskite oxide (La_1−xSr_xMn_1−yCo_yO_3−δ) has been chosen. The perovskite powder was also shaped by tape casting with the introduction of a pore forming agent (corn-starch) to obtain the required porosity in the sintered cathode.The co-firing of the electrolyte/cathode half-cell in air at 1400 °C-2 h gives a flat sample with a dense apatite (98.2%), a 42.7% porous cathode and neither delamination nor chemical reactivity between electrolyte and cathode materials.The dimensional behaviour of the electrolyte material is stable for an oxygen partial pressure ranging from 10⁻¹⁰ to 0.21 atmosphere, from room temperature to 700 °C. The thermal expansion coefficients of the electrolyte and cathode materials are rather close (Δα = 2.8 × 10⁻⁶ K⁻¹) under air.     

Layered H2K2Nb6O17 exfoliation promoted by n-butylamine

We have been exploring experimental conditions to achieve the exfoliation of the layered niobate phase K₄Nb₆O₁₇ using alkyl amines. In this work, the exfoliation process of the niobate acidic form H₂K₂Nb₆O₁₇ was evaluated in aqueous solution media using n-butylamine. Different amine/H⁺-niobate molar ratios were used and for each one, two fractions were isolated: one that corresponds to the deposited solid (or sediment) and the second one that consists of an aqueous colloidal dispersion. Fractions were characterized by X-ray powder diffraction, electronic absorption spectroscopy and, scanning and transmission electron microscopies. It was observed that the hexaniobate exfoliation is very dependent on the amine/H⁺-niobate molar ratio utilized. The highest amount of exfoliated niobate particles was achieved by using a butylamine/H⁺-niobate molar ratio around 0.5. High molar ratios promote the intercalation preferred to the delamination, indicating that the interlayer region saturation precludes the hexaniobate sheets exfoliation. TEM images of delaminated sample showed nanosized particles with flat and tubular morphologies.     

Synthesis of size-tunable mesoporous anatase titania spheres by a template-free method

A facile route was presented to fabricate mesoporous anatase titania spheres at low temperature; the titania precursor sphere was prepared through a template-free process and then treated by the boiling water. X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were adopted to characterize the morphology and crystal structure of the products. The adsorption properties and photocatalytic activities were also investigated. The results indicated that the porous structure and anatase nanocrystals were gradually formed from the surface to the interior of the titania precursor spheres with increasing treatment time. Moreover, there was little change in the size of the spheres during boiling water treatment, thus the size of the mesoporous anatase titania spheres could be easily tailored by controlling the diameter of precursor spheres. The as-prepared product showed excellent adsorption capacity and photocatalytic activity than the commercial P25 due to its high specific surface area.     

Kinetics of gas phase reduction of nickel chloride in preparation for nickel nanoparticles

We investigated the chemical kinetics of NiCl₂ reduction to apply to the synthesis of nickel nanoparticles in a tubular furnace reactor. The conversion of NiCl₂ increased monotonically with reaction temperature up to 99% at 950 °C, and in turn, the rate constant of the reaction increased from 78 to 286 with an increase in the temperature from 800 to 950 °C. The reaction rate was estimated to be the first order with respect to chloride concentration, and the rate constant obeyed the Arrhenius law, of which the activation energy and pre-exponential factor were 103.79 kJ/mol and 7.34 × 10⁶ min⁻¹, respectively. Taking advantage of the kinetics, we synthesized crystalline nickel nanoparticles with average primary particle size ranging from 31 to 106 nm by systematically controlling the reactor temperature and chloride concentration.     

Preparation of nanocrystalline bredigite powders with apatite-forming ability by a simple combustion method

Nanocrystalline bredigite (Ca₇MgSi₄O₁₆) powders were synthesized by a simple solution combustion method. Phase pure bredigite powders with particle sizes ranging from 234 to 463 nm could be obtained at a relatively low temperature of 650 °C. The apatite-forming ability of the bredigite powders was examined by soaking them in a stimulated body fluid. The compositional and morphological changes of the powders before and after soaking were analyzed by X-ray diffraction and scanning electron microscopy and the results showed that hydroxyapatite was formed after soaking for 4 days.     

Preparation of porous nickel electrodes for molten carbonate fuel cells by non-aqueous tape casting

The casting behaviour, ultimate tensile strength and the sintering process of tapes consisting of nickel powder, ethanol, po!yvinylbutyral as the binder, polyethylene glycol (molecular weight 200, PEG2) or dibutyl phthalate (DBP) as the plasticizer, and glycerol trioleate as the dispersant agent, were studied. On increasing powder content in the slurry the packing factor of nickel in the green increased, but the ultimate tensile stress and strain to failure decreased. Increasing binder to total binder ratio caused the green density and strain to failure to decrease, but the ultimate tensile stress increased for both PEG2 and DBP. The maximum strain to failure (about 35% for both PEG2 and DBP) in the case of DBP was obtained with an amount of plasticizer lower than that of PEG2. When tapes having different composition were sintered at various temperatures, a linear relation was found between packing factor and fired density, independently of the kind of binder and plasticizer used.     

Effects of surfactants on the microstructure of porous ceramic scaffolds fabricated by foaming for bone tissue engineering

A porous scaffold comprising a β-tricalcium phosphate matrix and bioactive glass powders was fabricated by foaming method and the effects of surfactants as foaming agent on microstructure of scaffolds were investigated. Foaming capacity and foam stability of different surfactants in water firstly were carried out to evaluate their foam properties. The porous structure and pore size distribution of the scaffolds were systematically characterized by scanning electron microscopy (SEM) and an optical microscopy connected to an image analyzer. The results showed that the foam stability of surfactant has more remarkable influence on their microstructure such as pore shape, size and interconnectivity than the foaming ability of one. Porous scaffolds fabricated using nonionic surfactant Tween 80 with large foam stability exhibited higher open and total porosities, and fully interconnected porous structure with a pore size of 750-850 μm.     

Preparation of M metal/alumina-pillared mica composites (M = Cu, Ni) by in situ reduction of interlayer M ions of alumina-pillared fluorine micas

Alumina-pillared fluorine micas form micropores in the interlayer region and exhibit cation exchangeability. Reduction of 3d transition metal cations (Cu²⁺ and Ni²⁺) in the interlayer regions of the cation exchanged alumina-pillared micas was attempted using ethylene glycol or diethylene glycol. The Cu²⁺-exchanged pillared mica led to the formation of a pillared mica composite containing interlayer zero-valence Cu⁰ metal clusters along with Cu⁰ metal fine particles on external surfaces of pillared mica flakes when refluxed in either ethylene glycol or diethylene glycol. Ni²⁺ cations in the interlayer region were also found to be reducible by refluxing in diethylene glycol. The zero-valence metal contained in the refluxed products occurs in three forms: M⁰ clusters in the interlayer region, elongated fine particles sandwiched between silicate layers, and submicron spherical particles on external surfaces of mica crystals. The zero-valence metal/alumina-pillared mica composites thus obtained largely retained the micropore properties of the alumina-pillared micas.     

Microstructural characterization of a rapidly solidified Al-Sr-Ti alloy

The microstructure of the melt-spun Al-7Sr-3Ti alloy has been characterized using X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The results show the microstructure of the melt-spun Al-7Sr-3Ti alloy is composed of the equilibrium α-Al, Al₄Sr, Al₃Ti and metastable Al₂₃Ti₉, different from that of the ingot-like alloy comprising α-Al, Al₄Sr and Al₃Ti. Moreover, the amount of Al₃Ti is much less than that of Al₄Sr and metastable Al₂₃Ti₉ in the melt-spun alloy. The melting temperature of primary phases and enthalpies of fusion for the melt-spun Al-7Sr-3Ti alloy are lower than those for the ingot-like alloy. The formation mechanism of the microstructure of the melt-spun alloy has also been discussed.     

A facile water-based process for preparation of stabilized Bi nanoparticles

Stabilized bismuth nanoparticles have been prepared by reducing bismuth chloride with hydrazine hydrate in the presence of sodium oleate under a facile water-based process. The obtained samples are investigated by X-ray diffraction, transmission electron microscopy (TEM) and differential thermal analysis and thermogravimetry (DTA/TG). The present results indicate that the bismuth nanoparticles are spherical, small diameter and in a high purity. In addition, measurement of water contact angle indicates that Bi samples are hydrophobic, which gives defense to samples from further oxidation, samples are steady in 6 months without obvious oxidation.     

Fast synthesis and morphology control of lead tungstate microcrystals via a microwave-assisted method

Lead tungstate (PbWO₄) microcrystals with different morphologies, such as tetragonal flowerlike, amygdaloidal, and multiple-lamellar, have been successfully synthesized via a simple microwave-assisted method. Various factors, such as the pH value and the concentration of the cetyltrimethylammonium bromide (CTAB), play an important role in the morphological control of PbWO₄ microcrystals. The products were characterized by the techniques of powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The possible formation mechanisms of PbWO₄ samples of various morphologies were discussed. The luminescence properties of the final products were investigated and the as-prepared PbWO₄ microcrystals showed special room-temperature photoluminescence intensity compared to the solid structures.     

Synthesis and characterization of various zeolites and study of dynamic adsorption of dimethyl methyl phosphate over them

Zeolite-A, MCM-22, Zeolite-X and Erionite were synthesized successfully under hydrothermal conditions and were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area analysis and thermal programmed desorption (TPD). Dynamic adsorption of dimethyl methyl phosphate (DMMP) was carried out on these zeolites. Zeolite-X having high surface area among all four zeolites shows highest adsorption capacity followed by Erionite and MCM-22 where as Zeolite-A shows the least. For all zeolites adsorption was found to be high initially and it then decreases with increase in injected volume. Then desorption pattern was analyzed which shows two types of peaks, sharp peak representing desorption of physisorbed DMMP and a broad peak representing desorption of strongly chemisorbed DMMP.     

Porous alumina/zirconia layered composites with unidirectional pore channels processed using a tertiary-butyl alcohol-based freeze casting

Symmetric three-layer porous alumina/zirconia composites with controlled “designer” pore structure have been prepared by a tertiary-butyl alcohol-based freeze casting and sintering at 1400–1500 °C in air. Unidirectional aligned macropore channels were developed over a long range by controlling the solidification direction of tertiary-butyl alcohol solvent; in this case, they were surrounded by more dense structured walls. In layered composite, the bottom layer consisted of small sized pore channels (∼11 μm in diameter) compared with the middle and the top layer, due to the comparatively rapid velocity of the TBA crystal growth during solidification. The compressive strength (63–376 MPa) of the sintered porous layered composite remarkably increased as the porosity decreased (64–32%).     

Study on the structures and magnetic properties of Ni, Co-Al2O3 electrodeposited nanowire arrays

We report on the direct electrodeposition of nickel and cobalt nanowire arrays within the nanopores of ordered porous alumina films prepared by a two-step anodization. SEM and TEM images reveal that the pore arrays are regularly arranged throughout the alumina film. X-ray diffraction and TEM analysis show that the nickel and cobalt nanowires are single crystalline with highly preferential orientation. The aspect ratio of nanowires is over 300. M-H hysteresis loops determined by VSM indicate that the nanowire arrays obtained possess obvious magnetic anisotropy. Because of proper square ratio and coercivity the nanowire arrays of nickel seem to be more suitable candidates for perpendicular magnetic recording medium than those of cobalt.