Papers by Keyword: Porous Film

Abstract: The efficiency of a thermoelectric device depends on material properties through the figure of merit, Z = σS²/κ, where σ, S, and κ are electrical conductivity, Seebeck coefficient, and thermal conductivity, respectively. To maximize the thermoelectric figure of merit of a material, high electrical conductivity, high Seebeck coefficient, and low thermal conductivity are required. This work has focused on the synthesis of a mesoporous titania films for its application in thermoelectric generation. The mesoporous titania film was synthesized with titanium tetraisopropoxide. The triblock copolymer, Pluronic P-123 (EO₂₀ PO ₇₀EO ₂₀) was used as surfactant in 1-propanol. As a result, an improvement of electrical conductivity and reduced annealing with a lowering of thermal conductivity by distributions of pores were found to be effective to enhance the thermoelectric property.

Abstract: We introduce the concept of functional microchannel lining. As an example, we describe the composition and structure of a Ni-Al intermetallic layer lining the inner wall of the microchannel produced by a powder-metallurgical process utilizing microscopic reactive infiltration and/or diffusion. The Ni-Al lining layer is a thick film consists of multiple sub-layers and has a peculiar porous structure, in which long and thin micropores had grown along the thickness direction of the film. In our experiment, a nickel-powder compact containing shaped aluminum wire was sintered at temperatures between the melting points of nickel and aluminum. Molten aluminum migrated into the surrounding nickel powder and reacted with nickel, and thus a microchannel and a Ni-Al intermetallic lining layer were produced. In this process, nickel powder composed the device body, and the aluminum wire gave the shape of the microchannel and act as the aluminum source for the lining layer. Metallographical examinations revealed that both aluminum concentration and voidage in the Ni-Al lining layer show a graded distribution along the thickness direction of the layer. Such a porous structure is appropriate for a catalyst support used for high-temperature reactions.

Abstract: To obtain porous TiO2 film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO2 film was fabricated by dip-coating method on quartz glass substrates using this sol. The TiO2 films were calcined at 500-900 °C. The photocatalytic activities of the films were evaluated by examining decomposition of methylene blue in aqueous solution under UV light irradiation. The photocatalytic activity of the porous TiO2 film showed a different tendency according to the irradiation wavelength of UV light. The activity of the film evaluated under UV light irradiation with a wavelength of 254 nm was not affected a great deal by the clacination temperature. In the case of UV light irradiation with a wavelength of 365 nm, the activity of the film increased with increasing calcination temperature and that of the film calcined at 800 °C was the highest.

Abstract: To obtain porous and thick TiO2 film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO2 film was fabricated by dip-coating technique on quartz glass substrates using this sol. The TiO2 films were calcined at 500-700 °C. The photocatalytic activity of the films was evaluated by examining decomposition of methylene blue in aqueous solution under UV light irradiation. The TiO2 film prepared from the sol with trehalose was more active than TiO2 film prepared from the sol without trehalose. The trehalose addition to the dip-coating solution was effective in improving the photocatalytic activity of the TiO2 film.

Abstract: Well-ordered 2-dimensional (2D) hexagonal and 3-dimensional (3D) cubic mesoporous silicon oxide thin films prepared using triblock Poly(ethylene oxide)-Poly(Propylene oxide)-Poly(ethylene oxide) copolymer species (P123, F127) as the structure-directing agents, are studied by positron beam analysis in parallel with X-ray reflection measurements. It is observed that in the two films with equivalent porosity and pore size (normal to the film surface direction), the shape of mesopores considerably affects positron annihilation behavior. The narrowed positron annihilation Doppler broadening in the 2D hexagonal mesoporous film may suggest a higher positronium formation probability there, owing to a larger effective open volume area originated from the extension of pore channels parallel to the film substrate.

Abstract: A sol-gel process was used to prepare polyimide-silica hybrid films from the polyimide precursors and TEOS in N,N- dimethyl acetamide, then the hybrid film was treated with hydrofluoric acid to remove the dispersed silica particles, leaving pores with diameters between 80nm to 1µm, depending on the size of silica particles. The structure and dielectric constant of the hybrid and porous films were characterized by FTIR,SEM. The porous films displayed relatively low dielectric constant compared to the hybrid polyimide-silica films.

Abstract: To obtain porous TiO2 film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO2 film was fabricated by dip-coating technique on glass substrates using this solution. The TiO2 film was calcined at 500 °C. The maximum thickness of the film by one–run dip-coating was ca. 740 nm. The film was composed of nanosized particle and pore. The porosity of the TiO2 film was increased by the addition of trehalose dihydrate to the sol. The porous TiO2 films were calcined at various temperatures. The effects of the calcination temperature on the microstructure of the porous TiO2 film were investigated. The porous film prepared from sol containing trehalose still kept the porous structure for calcination at 950 °C. The phase transition temperature from anatase to rutile of the film was shifted from 650 to 700 °C by trehalose addition to the sol.

Abstract: To fabricate porous and thick alumina films, we prepared an aqueous alumina hydroxide sol containing trehalose. The alumina films were deposited by dip-coating technique on glass substrates and heating at 500 °C. The maximum thickness of the film obtained by one-run dip-coating using the sol containing trehalose was over 1000 nm. The film was an aggregate of alumina particles with a diameter of 20-40 nm and pores were interstices between the particles. The porosity of alumina film can be controlled in the range of 48-65 % by changing trehalose concentration in the dip-coating solution.

Abstract: To obtain porous alumina films, the precursor sol was prepared by hydrolysis of Al isopropoxide and then mixing with poly(ethylene glycol) (PEG). The porous alumina films were fabricated by dip-coating technique on glass substrates and heating at 500 °C. The film was composed of nano sized particles (30-50 nm). The maximum thickness of the film prepared by one-run dip-coating was ca. 1000 nm. The film had humidity-sensitive electrical resistance at room temperature.