S. Morooka

Preparation of γ-alumina thin membrane by sol-gel processing and its characterization by gas permeation

Abstractγ-alumina porous membranes without pinholes or cracks were prepared by the sol-gel process. The boehmite sol obtained from hydrolysation of aluminium isopropoxide was applied to the inner surface of a porous supporting tube by a dipping procedure. The effects of sol concentration and the repetition number of dipping-drying-firing procedure on the membrane performance were investigated by scanning electron microscopy, X-ray diffraction and the Brunauer-Emmett-Teller method in connection with the micro-structure of the membrane. Gas permeation measurements were also conducted. The gas permeation through the thin membranes is well explained by Knudsens flow, indicating the pores are controlled finely and homogeneously.

Separation of hydrogen from an H2-H2O-HBr system with an SiO2 membrane formed in macropores of an α-alumina support tube

Abstract A porous α-alumina tube of 2.5 mm o.d. and 1.9 mm i.d. was used as the support of a silica membrane used for hydrogen separation at high temperature. The pore structures of the tube were as follows: size distribution, 110–180 nm; average size 150 nm; and porosity, 0.4–0.55. Macropores of the tube were plugged with silica formed by thermal decomposition of tetraethylorthosilicate at 600 °C. To improve the step coverage of the deposition in residual pinholes, the reactant was continuously evacuated through the porous wall of the support. The hydrogen permeation of the membrane formed was of the order of 10 −8 mol m −2 s −1 Pa −1 at 600 °C, while the nitrogen permeance was below 10 −11 mol m −2 s −1 Pa −1 . The membrane was applied to separate hydrogen in the presence of HBr and abundant steam at 200–400 °C in a thermochemical water decomposition process (UT-3 process). The permeance of H 2 from the H 2 -H 2 O-HBr mixture was nearly the same as obtained with pure H 2 and that of H 2 O was smaller than the detection limit in the present study, 10 −10 mol m −2 s −1 Pa −1 . This means that the permselectivity of hydrogen to water was at least 100. HBr molecules could not permeate the membrane because of their large size and the permeance was below 10 −12 mol m −2 s −1 Pa −1 . The membrane was durable in the H 2 -H 2 O-HBr atmosphere at 400 °C.

Development of supported thin palladium membrane and application to enhancement of propane aromatization on Ga-silicate catalyst

Palladium acetate was sublimed at reduced pressure at 400°C and was evacuated through the porous wall of an α-alumina support tube. A thin palladium membrane was thus formed in the macropores due to chemical vapor deposition. The palladium membrane showed a hydrogen permeance of 10 -6 mol/m 2 .s.Pa and a hydrogen/nitrogen permselectivity higher than 1000. Further, gallium-silicate catalyst (Si/Ga = 40) was synthesized via an alkoxide method, and the membrane was coaxially fixed in a tubular reactor in which the catalyst particles were packed. Aromatization of propane was performed at 500-600°C, and the hydrogen evolved was continuously removed from the system. Propane conversion and aromatics selectivity were increased by decreasing hydrogen partial pressure by the installation of the membrane.

Effect of substrate pretreatment on diamond deposition in a microwave plasma

The evolution of substrate surface at an early stage of diamond formation in a microwave plasma was studied with a high-resolution scanning electron microscope. Changes in the shape, size and population of diamond particles at the same points were observed at prescribed time intervals. The substrate used was a mirror-polished Si (100) plate which was ultrasonically pretreated with diamond, c-BN or α-Al2O3 powders prior to the deposition. The pretreatment introduced fragments of the abrasives as well as many scratches on the substrate surface. When the diamond and c-BN abrasive were used, diamond was formed on the surface of abrasive residues. With α-Al2O3 abrasive powder, on the other hand, residues vanished in the plasma and no deposition was observed. These results suggest that the deposition site of diamond from the vapour phase is dependent on the type of abrasive powder used for substrate pretreatment.

Heteroepitaxial growth of diamond on c-BN in a microwave plasma

Abstract Diamond was synthesized heteroepitaxially on single-crystal cubic boron nitride (c-BN) by microwave plasma-assisted chemical vapour deposition from a gas mixture of methane and hydrogen. Diamond films formed were characterized by Raman spectroscopy, and their morphology and microstructure were investigated by scanning electron microscopy. The heteroepitaxial nucleation and growth of diamond were confirmed on the (100) and (111) planes of c-BN. The boron-terminating (111) plane was most efficient for the formation of a textured diamond film. The epitaxy on the (100) plane was achieved in a narrow range of reaction conditions, and no oriented deposits were observed on the nitrogen-terminating (111) plane.

Low-temperature plasma coating of electroluminescence particles with silicon nitride film

A Si3N4 thin film was deposited on ZnS phosphor particles of 18μm diameter in a silane-nitrogen radio-frequency (r.f.) plasma at 310–330 K. The particles were frequently shaken to maintain contact with plasma gas. The film deposited was characterized by X-ray photoelectron spectroscopy XPS, Fourier-transformed infrared spectroscopy and high-resolution scanning electron microscopy (SEM). The Si/N ratio of the film was about 1.25, and little change in the infrared spectrum was observed following the exposure in the ambient air for 10 days. The performance of the film as a diffusion barrier was evaluated by monitoring the lifetime of electroluminescence (EL). A film as thin as 50–60 nm could cover the EL powder without pinholes, and successfully protected the phosphor from water vapour.

High-resolution scanning electron microscopy study on the early stage of diamond synthesis by microwave-plasma chemical vapour deposition

Scratches of a few nm have a strong relationship to the nucleation for the diamond synthesis by MPCVD. The population density of the nuclei formed in the early stage was as high as that of scratches, but only a small portion of the nuclei contributed to the diamond film formation

Synthesis of phosphorus-doped homoepitaxial diamond by microwave plasma-assisted chemical vapor deposition using triethylphosphine as the dopant

Abstract Triethylphosphine [TEP, P(C2H5)3] was used as a dopant for homoepitaxial (100) and (111) phosphorus-doped diamond films. which were formed by microwave plasma-assisted chemical vapor deposition using CH4 as the carbon source. The growth rate of TEP-doped (100) diamond increased with increasing atomic ratio of phosphorus to carbon in the gas phase, from 300 nm h−1 at 0 ppm to 800 nm h−1 at 10 000 ppm at 850 C. TEP-doped (100) diamond films deposited at temperatures below 850 C were smooth and homoepitaxial, whereas those deposited above 950 C as well as the TEP-doped (111) films formed at 750–1050 C were polycrystalline. Phosphorus was found to be uniformly incorporated into the diamond film, as evidenced by secondary ion mass spectrometry. The Hall conductivity of the TEP-doped films remained low.

Promotion of nitrogen removal during coal pyrolysis by using iron catalyst impregnated by solvent swelling method

Publisher Summary This chapter discusses two organometallic iron precursors––ferric acetate and ferrocene––which are impregnated into three coals of different ranks swollen in polar organic solvents. The iron-impregnated coals are subjected to slow atmospheric pyrolysis. The effect of the incorporated iron species on the fate of nitrogen is quantitatively examined. Nitrogen evolved as hydrogen cyanide (HCN), ammonia (NH 3 ), and tar in the initial pyrolysis period is the primary contributor to NO x generated in following combustion stage. Thus, the selective conversion of coal nitrogen into N 2 in the pyrolysis stage is effective for suppressing NO x emission. The selective increase of N 2 is balanced by the reduction of nitrogen evolved as HCN, tar, and that fixed in char. Iron catalyst precursors is located in micropores prior to pyrolysis to contact the coal matrix at molecular level for promoting pyrolytic removal of coal nitrogen. Brown coals contain much carboxyl groups as cation exchange sites. Iron (Fe 3+ ) ions are easily incorporated into the coal matrix through ion exchange.

Flash co-pyrolysis of coal retaining depolymerized polyethylene as radical donor

Publisher Summary This chapter describes the flash copyrolysis of coal retaining depolymerized polyethylene as radical donor. Flash pyrolysis is an attractive coal conversion process for the production of useful chemicals, such as benzene and naphthalane derivatives. These light aromatics are generated by the vapor-phase secondary pyrolysis of tar that is produced in the primary pyrolysis stage. To increase the yield of the tar that is the precursor of light aromatics, decomposition of the macromolecular network of coal is enhanced in the primary pyrolysis. Rapid donation of hydrogen and hydrocarbon radicals to fragment radicals of coal molecules is essential both to promote tar evolution and to suppress char formation. Polypropylene and polyethylene coated on the surface of a brown coal increased the tar yield by 5–12 wt% on the daf-coal basis by donating hydrogen and hydrocarbon radicals under atmospheric pressure. The promotion of tar formation is strongly dependent on the contact between coal and polyolefin. The swollen coals are physically incorporated with depolymerized polyethylene (DPE) and are subjected to flash pyrolysis with a Curie point pyrolyzer and an entrained-flow pyrolyzer.