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ABSTRACT: Four kinds of porous mullite ceramics, named lotus ceramics because of the similarity of their microstructure with lotus roots, were prepared by an extrusion method using rayon fibers of four different diameters (8.1, 9.6, 16.8 and 37.6 mm) as the pore formers. The physicochemical properties of these samples were characterized to test their applicability for the generation of microbubbles. The lotus ceramic samples contained pores of 9.4, 10, 15.6 and 30 mm size and porosities of 45–48%. SEM micrographs confirmed that the cylindrical pores were oriented unidirectionally along the extrusion direction and the degree of alignment was greater with larger fiber diameter. The permeability for gaseous CO 2 increased with increasing pore size from 3 Â 10 À 13 to 8 Â 10 À 13 m 2 . The four lotus ceramic samples, a commercial air stone (72 mm) and two simple tubes (1000 and 3500 mm) were used to generate microbubbles in water under ambient conditions from a gas mixture of CO 2 and air. It was found that the bubble size could be decreased with bubblers of smaller pore size. In the bubble size measurements for pure CO 2 and air, the air bubbles were larger than the CO 2 bubbles due to partial dissolution of CO 2 into the water during bubbling. In order to generate smaller size bubbles using porous ceramic bubblers, the liquid must penetrate through the pores of the lotus ceramics before the gas is introduced into the system.
Ceramics International 01/2013; 39:1443-1449. · 1.75 Impact Factor
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ABSTRACT: The effect of additives on paste rheology was investigated for preparation of porous ceramics with unidirectionally aligned
cylindrical pores. Ammonium poly-carboxylic acid (APA) used as a dispersant and it was adsorbed on alumina powder surface.
The adsorption isotherm of APA was fitted by Langmuir equation. The saturated monolayer adsorption was 5.9 mg/g. The apparent
viscosity became a minimum at 0.8 mass % of APA corresponding to 71.2 mPa⋅s. This APA amount of 5.6 mg/g, is in good agreement
with the observed APA amount. Since the nylon 66 fibers (0–35 vol. %) mixed with the alumina powder have a strong interaction
with each other, they became twisted and agglomerated. This agglomeration increased with increasing fiber content but decreased
by adding oleic acid. The pastes with added oleic acid were capable of being extruded at higher pressure. The obtained porous
alumina ceramics showed highly oriented cylindrical pores parallel to the extrusion direction. The pore orientation was higher
in the oleic acid added pastes than those without oleic acid. The added nylon 66 fibers are mostly converted to pores while
maintaining the original shape after sintering. The pore size distribution of the obtained porous ceramics measured by mercury
porosimetry method showed a peak at about 4 μm which is apparently smaller than that observed in the SEM photographs and the
obtained result is considered to be corresponding to the necks formed by fiber contacts.
Journal of Porous Materials 04/2012; 13(3):269-273. · 1.24 Impact Factor
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ABSTRACT: The decomposition mechanism of manganese-containing 10 mol% Sc 2 O 3 and 1 mol% CeO 2 co-doped ZrO 2 (10Sc1CeSZ) electrolyte during long-term operation of a cathode-supported tubular-type solid oxide fuel cell (SOFC) was investigated. With Fe 2 O 3 , TiO 2 , Na 2 CO 3 , and MgO applied respectively on an electrolyte sur-face, cell operation tests were conducted at 1000 °C for 270 h. Additionally, an annealing test using manganese-containing 10Sc1CeSZ pellets was conducted under a fuel atmosphere to clarify the influence of p(O 2) distribution in the electrolyte. After operation or annealing, samples were analyzed using SEM/EDX and Raman spectroscopy. Decomposition occurred on the electrolyte surface where Fe 2 O 3 or TiO 2 had been applied, but it did not occur on annealed pellet surfaces. Because reactive products containing manganese ox-ides were detected on surfaces to which Fe 2 O 3 or TiO 2 had been applied, results revealed that decomposition of this type requires a nucleation site of Mn 3 O 4 precipitation and a high-p(O 2) region near the electrolyte sur-face. On the surface with Na 2 CO 3 or MgO, the grain boundaries were particularly damaged. Pellet surfaces were also damaged. Results suggest that the electrolyte surface decomposition caused by manganese oxide precipitation is a new phenomenon that can be regarded as different from decomposition caused by an alkali metal such as Na 2 CO 3 .
Solid State Ionics 01/2012; 224:6-14. · 2.65 Impact Factor
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ABSTRACT: A six-rayed star-like nanostructure was prepared by a combination of colloidal self-assembly, thermal sintering and chemical etching, which enables the tuning of both size of the particles and neck diameter. In this nanostructure, six nanotips are arrayed in a symmetric and planar arrangement on a spherical particle. Localized surface plasmon resonance characteristics were also clarified.
Chemical Communications 12/2011; 48(11):1668-70. · 6.17 Impact Factor
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ABSTRACT: Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.
Science and Technology of Advanced Materials 10/2011; 12(6):064701. · 3.51 Impact Factor
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ABSTRACT: Four patterned surfaces with hydrophilic areas of different sizes were prepared using photolithography with a smooth octadecyltrimethoxysilane (ODS) hydrophobic coating. The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. The sliding angle and contact angle hysteresis of the water droplets increased concomitantly with increasing pattern size. The increase of the contact line distortion between defects at the receding side plays an important role in this trend. The droplet sliding velocity also increased concomitantly with increasing pattern size. This trend was simulated by a simple flow model. The contribution of the interface between the ODS region and the hydrophilic area was deduced from this trend. This study demonstrated the different size dependency of the chemical surface defects for sliding behavior between the critical moment at which a droplet slides down and the period when a droplet is sliding.
Langmuir 06/2011; 27(11):7307-13. · 4.19 Impact Factor
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ABSTRACT: Particle self-assembly was affected by various factors. A theoretical formula using particle concentration, water evaporation rates, and withdrawal rates of substrate during evaporation-driven self-assembly had already reported: However, it showed a lack of evidence for large-size particles (more than diameter 2,106 nm). Here, we suggest optimum fabrication conditions for large-size (3.0-μm dia.) particle monolayer on a horizontally-set glass substrate by the evaporation-driven self-assembly. Two parameters, the volumes of used suspension and the meniscus angles between the suspension and the substrate, were examined. The experimental formula was also constructed by developing the reported formula.
Molecular Crystals and Liquid Crystals 05/2011; 539(1):33/[373]-39/[379]. · 0.58 Impact Factor
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ABSTRACT: In this paper, thermal fusion of polymer spherical particles was examined to prepare ring structures on a solid substrate. Polystyrene particles (200 nm diameter) were two-dimensionally arrayed by an evaporation-driven method. The self-assembled structures, i.e., two-dimensional colloidal crystals, were kept under 50°C for 20 minutes. Three peeling methods were tried after the thermal fusion treatment: manual peeling, peeling by polydimethylsiloxane adhesion and mechanical peeling. We show that using these peeling methods we were able to obtain the ring structures as well as other interesting structures.
Molecular Crystals and Liquid Crystals 05/2011; 539(1):266/[606]-274/[614]. · 0.58 Impact Factor
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ABSTRACT: A batch method was used to investigate the uptake of heavy metal cations and anions by the compounds in the CaTiO(3)-CaFeO(2.5) system, in which a series of oxygen vacancies was systematically introduced into a perovskite structure as the x-value of Ca(Fe(x)Ti(1-x))O(3-x/2) was increased. Samples of CaTiO(3), CaFe(0.1)Ti(0.9)O(2.95), CaFe(0.5)Ti(0.5)O(2.75), CaFe(0.67)Ti(0.33)O(2.67) and CaFeO(2.5) were prepared by solid mixing (SM), co-precipitation (CP) and gel evaporation (GE) methods. The resulting samples were calcined at temperatures between 400 and 1000 °C. The target crystalline phases differed according to the preparation method, but in most cases were formed at 700-800 °C. The Ni(2+) sorption isotherms of all the samples were fitted better by the Langmuir model than by the Freundlich model, while in the case of H(2)PO(4)(-) sorption isotherms, these were better fitted by the latter model. The uptake ability increased with increasing x value of the samples. The maximum values for the saturated sorption of Ni(2+) (Q(0)(Ni(2+)) = 2.83 mmol/g) and H(2)PO(4)(-) (K(F)(H(2)PO(4)(-)) = 2.95 mmol/g) were achieved for x = 1 (i.e. CaFeO(2.5)) sample.
Journal of hazardous materials 01/2011; 185(2-3):1390-7. · 4.14 Impact Factor
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ABSTRACT: Mechanisms for decomposition of 10 mol% Sc 2 O 3 and 1 mol% CeO 2 co-doped ZrO 2 (10Sc1CeSZ) electrolytes of a cathode-supported tubular-type SOFC during the long term operation for ≥ 100 h have been investigated by analyzing SEM, Raman spectroscopy and XPS of decomposed samples and also by additional examination for the effects of impurities (MnO 2 , Al 2 O 3 and Si) on the decomposition of electrolyte. The valence of manganese at the decomposed parts in the fuel side was found to become higher after the long term operation. This leads to the driving force for the decomposition of 10Sc1CeSZ into two phases by the large oxygen potential gradi-ent developed on the surface in the fuel side. The kinetic factors for formation of new phases are considered to be as follows; the Si component in the fuel can be a trigger to form MnSiO 3 which worked at the nucleation points, and the valence changes of manganese in the electrolyte proceed the decomposition cycles consisting of two phase separation in the zirconia, pulverization of manganese-rich phase and detachment of zirconia-based oxides.
Solid State Ionics 01/2011; 204-205:120-128. · 2.65 Impact Factor
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ABSTRACT: Dew condensation effects on the wettability of rough and smooth coatings of two fluoroalkylsilanes (FAS3 and FAS17) were investigated by controlling the temperature. Contact angles of the coatings decreased concomitantly with decreasing surface temperature. Inflection points in the temperature dependence of contact angles were observed at the dew point. They were attributable to the change of the interfacial free energy of the solid-gas interface by water adsorption. The contact angle decrease suggested a mode transition from Cassie to Wenzel on the rough surface, and resulted from the surface wettability change and the increase of the condensation amount of water. The contact angle change by increasing temperature from -6 degrees C revealed that the Wenzel mode is more stable than Cassie's mode.
Langmuir 08/2010; 26(16):13305-9. · 4.19 Impact Factor
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ABSTRACT: The effect of various factors on the photodecomposition of methylene blue (MB) by iron oxides calcined at various temperatures in various concentrations of oxalate solutions was investigated by illuminating with UV, visible and solar radiation. Iron oxides were prepared by a gel evaporation method and calcined at 200-700 degrees C. XRD showed that the as-synthesized iron oxides were amorphous, but formed maghemite (gamma-Fe(2)O(3)) at 200-400 degrees C and hematite (alpha-Fe(2)O(3)) at > or =500 degrees C. The effect of the various iron oxides, their contents, the oxalate concentration and wavelength of the light source (UV, visible and solar) were all found to strongly influence MB photodecomposition. The optimal contents of the iron oxides increased greatly from 25 to 2000 mg/L at higher calcining temperatures. The MB photodecomposition rate at each optimal iron oxide content was related to the calcining temperature in the order 700 degrees C<uncalcined<500 degrees C<400 degrees C<300 degrees C. The MB degradation was confirmed to occur by visible light illumination. Excellent photodecomposition was found at pH 2-5, but the photodegradation decreased greatly at pH>6, consistent with the presence of iron-oxalate complexes. A much higher concentration of hydroxyl radicals was generated in the present system compared with those from a commercial TiO(2) (ST-01), as determined by the coumarin method. Since this process does not require the addition of hydrogen peroxide and shows good efficiency even under solar light, it is an economically viable method for pre-treating and/or decolorizing wastewaters containing dyes.
Water Research 02/2010; 44(9):2876-84. · 4.86 Impact Factor
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ABSTRACT: The evaporation behavior of microliter (2.0 microL) and subnanoliter (0.8 nL) scale water droplets was investigated on two smooth hydrophobic and hydrophilic fluoroalkylsilane coatings prepared using chemical vapor deposition. The contact angle was constant in the second stage of evaporation for a 2.0 microL droplet on the hydrophobic coating, but it was slightly decreased in the case of a 0.8 nL droplet. The contact angle decreased gradually in the same stage of evaporation for a 2.0 microL droplet on the hydrophilic coating, but it was almost constant for a 0.8 nL droplet. These differences in evaporation behavior are expected to originate from the differences of their magnitudes and signs of line tension.
Langmuir 09/2009; 25(20):11998-2001. · 4.19 Impact Factor
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ABSTRACT: Mg-Al-ascorbic acid (ASA)-layered double hydroxides (ASA-LDHs) with Mg/Al=3 were synthesized by ion-exchange, coprecipitation and reconstruction methods. Composites with sodium oleate (SOA)/ASA-LDH were prepared by an ion-exchange method using various concentrations of SOA solutions. The (003) basal spacing of the ASA-LDHs changed from 0.76nm in the CO(3)-LDH to 0.78 and 0.86nm after intercalation of the ASA ions and these basal spacings are in good agreement with models based on the assumption as mono layers and double layers of ASA ions in the LDH interlayers, respectively. The amounts of ASA in the LDHs prepared by the reconstruction method were higher than those by the ion-exchange and coprecipitation methods. In the preparation of composites of SOA/ASA-LDH, an ion-exchange method was more suitable than a reconstruction method to cause surface sorption of the SOA molecules with maintaining intercalated ASA ions in the LDH interlayers. The acid-resistant properties of the composites of SOA/ASA-LDH were found to be much higher than for the pure ASA-LDH and mixture of CO(3)-LDH and ASA. The surfaces of the LDH particles in the composites are, thus, mostly covered with sorbed SOA molecules and they are good candidates as drug delivery materials for intestines through the stomach.
International journal of pharmaceutics 08/2009; 381(1):34-9. · 2.96 Impact Factor
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ABSTRACT: Evaporation and sliding behaviors of water droplets were investigated on smooth and rough fluoroalkylsilane coatings. The rough coating possesses nanoscale roughness and chemical heterogeneity on its surface. Evaporation behaviors for these two coatings differed when nanoliter-scale droplets were used, although they were nearly identical for microliter-scale droplets. The droplets on the smooth coating exhibit greater sliding acceleration and a larger slipping velocity ratio than those on the rough coating. Both the evaporation behavior of nanoliter-scale droplets and sliding velocity of microliter-scale droplets were affected by nanoscale surface heterogeneity. They are indicators for highly homogeneous smooth silane coatings.
Langmuir 05/2009; 25(10):5417-20. · 4.19 Impact Factor
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ABSTRACT: Activated carbons (AC) impregnated with the hygroscopic salt CaCl2 were synthesized to enhance the amount of water vapor adsorbed at low relative pressure (P/P0). Possible applications for these materials are in adsorption heat pumps and desiccant air conditioners. The ACs were synthesized from tissue paper by chemical activation with K2CO3 and the porous properties were investigated of a number of materials prepared under a variety of activation conditions. The highest specific surface area (SBET) (1820 m2/g) was obtained from the sample prepared with a K2CO3/sample ratio = 1/1 by mass, activated at 900 °C for 2 h under flowing N2 (2 L/min). Impregnation with CaCl2 was performed using 2.4–6.5 M CaCl2 solutions and a solution volume equal to the pore volume of the AC. XPS surface chemical analysis revealed that the impregnated CaCl2 was mostly successfully impregnated into the pores while the surface CaCl2 increased gradually with increasing amount of impregnation. The adsorption of water vapor in the P/P0 range 0.1–0.3 (ΔW0.1–0.3) was dramatically increased by CaCl2 impregnation, the ΔW0.1–0.3 value reaching 0.52 g/g in the sample impregnated with 70 mass% CaCl2; this value is much higher than previously reported ΔW0.1–0.3 values.
Materials Research Bulletin.
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ABSTRACT: A series of geopolymers were prepared with varying ratios of sodium silicate, metakaolinite, NaOH and H2O and their porous properties, water retention and mechanical properties were determined, to develop materials for counteracting heat island effects. Samples were prepared with the molar ratios SiO2:Al2O3:Na2O:H2O of 3.66:1:x:y, where x = 0.92–1.08 and y = 14.2–19.5. The porous and mechanical properties of the geopolymers showed a good correlation with the H2O/Al2O3 ratio (y); an increase in y produced an increase in the pore volume (from 0.26 to 0.46 ml/g), the pore size (from 15 to 390 nm) and the water absorption (from 27.2 to 51.1%). The same increase in y decreased the bulk density (from 1.29 to 0.99 g/cm3), the bending strength (from 14.2 to <5 MPa) and the water retention. Thus, the H2O/Al2O3 ratio is the most important factor for controlling the porous properties of these materials, since geopolymers with higher H2O/Al2O3 ratios are more porous and have higher water absorption rates, making them suitable as materials for surface cooling by water evaporation. Geopolymers with lower H2O/Al2O3 ratios are more suitable for water retention applications, and have the advantage of higher mechanical strength.
Journal of the European Ceramic Society 29(10):1917-1923. · 2.35 Impact Factor
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ABSTRACT: Porous alumina ceramics with unidirectionally oriented pores were prepared using an extrusion method. The paste for extrusion was prepared by mixing alumina and nylon 66 fibers with binder and dispersant. The resulting paste was extruded, dried at room temperature, and after removal of the binder at 600 °C, fired at 1500 °C for 2 h. The pore size in the sintered body, determined from SEM micrographs, was 16 μm, corresponding to the size of the burnt-out nylon 66 fibers. The degree of orientation of the cylindrical pores was evaluated from SEM micrographs to be highly aligned to the extrusion direction. The orientation of the pores decreased with increasing fiber loading because of strong interaction between the fibers. The pore size distribution of the extruded samples showed a peak at 16 μm corresponding to the cylindrical pore diameter and also at 4 and 6 μm corresponding to the pores formed by connection of the fibers.
Journal of the European Ceramic Society 26(12):2213-2217. · 2.35 Impact Factor
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ABSTRACT: Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe2O3 contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm3, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe2O3 and at 15.6 μm in the samples containing Fe2O3; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe2O3 component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe2O3 than in those without Fe2O3, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics.
Journal of the European Ceramic Society 29(12):2491-2497. · 2.35 Impact Factor
