Kazuo Yamana

Mesoporous materials prepared using coal fly ash as the silicon and aluminium source

Coal fly ash was converted into two types of porous materials, MCM-41 and SBA-15 (both of hexagonal structure), using the supernatant of the fly ash. It was found that most of the Si and Al components in the fly ash could be effectively transformed into mesoporous materials, depending on the hydrothermal conditions, and that fusion is essential. Investigation by 29Si and 27Al MAS NMR demonstrated that fusion plays an important role in enhancing the hydrothermal conditions for synthesis of these materials. A high concentration of Na ions in the supernatant of the fused fly ash was not found to be critical in the formation of Al-MCM-41 when prepared under controlled pH conditions. Pyridine adsorption experiments on Al-MCM-41 prepared from coal fly ash revealed the presence of Bronsted and Lewis acid sites. It was also found that the catalytic activity in the cumene cracking reaction is linked only to the accessible aluminium, and not to the total incorporated aluminium present in the Al-MCM-41.

Observations of the Ferroelastic Domain Structure of MP5O14 (M: La-Tb) by means of Scanning Tunneling Microscope, Electron Spin Resonance and X-Ray Diffraction.

The ferroelasticity of rare earth pentaphosphate, MP5O14 (M: La-Tb) belonging to the species mmmF2/m is studied by scanning tunneling microscope (STM), electron spin resonance (ESR) and X-ray diffraction. The temperature dependence (from room temperature to 180°C) of ferroelastic domain structure and monoclinic β angle of EuP5O14 was obtained by STM and X-ray diffraction (ω scan technique). The spin Hamiltonian parameters of LaP5O14:Cr3+ at 150°C in the para phase obtained from the ESR spectra are gx= gy= gz=1.97, D = 0.45 cm-1 and E = 0.05 cm-1. The principal axes of one of the Cr3+ paramagnetic centers are given by the Eulerian angles =15°, θ=90° and ψ= 0°.

XPS Study of Surface Cation Segregation in Mullite/Zirconia Composites

We have investigated thermally induced cation surface segregation in mullite/zirconia composites with zirconia content ranging from 0% to 100% using x-ray photoelectron spectroscopy (XPS). As a result of thermal annealing at 1000 °C, slight surface Si enrichment with respect to Al was found in the pure mullite sample (0% zirconia). In contrast to the mullite sample, surface segregation in Si, Na, Al and Y was observed in the pure zirconia sample. The segregation behaviour of all the composite samples (10-90 mass% zirconia) is dominated by the zirconia phase. For samples with 10-100 mass% zirconia, segregation leads to the formation of silicates and sodium oxides at the surface.

Electrical resistances and deformation of yttria-stabilized cubic zirconia with alumina

Abstract The effect of addition of alumina to cubic zirconia was investigated in order to explore the possibility of plastic deformation in cubic phase materials and to examine its influence on the electrical conductivity. Zirconia powders with additives of 5.5 mol% yttria and 1, 5, 10 and 20 wt% alumina were made by coprecipitation. Without alumina the grain size increased to about 2 μm after sintering at 1450°C, but only to 0.5 μm for the material with 5 wt% alumina additives. The latter showed a large deformation in spite of the presence of the cubic phase. The frequency dispersion measurements of cubic zirconia with 5.5 mol% Y 2 O 3 added together with additives of 0, 3, 5, 7 and 10 wt% alumina were analyzed using the brick layer model. Two overlapping arcs in cubic zirconia with 5 wt% alumina were observed in the impedance results obtained at 400°C. The arc on the high-frequency side is referred to as the bulk resistance. The other one is related to the grain boundaries. The size of this second arc is dependent on the alumina content. The diameter is large for samples containing no alumina. With increasing alumina content, the size of this arc passes through a minimum at 5 wt% and increases slightly with increasing alumina content.

Impact of grain boundaries on properties of mullite as a solid electrolyte

Abstract Basic properties of muUite such as chemical composition, phase stability, crystalline structure and microstructure are briefly reviewed. Effect of impurities, resulting in the formation of grain boundary glassy precipitates on high temperature properties such as mechanical properties and ionic conductivity is considered. Properties of mullite which is free of the glassy phase are analyzed as an ionic conductor for high temperature oxygen sensors. Electromotive force (EMF) of an oxygen concentration cell, based on mullite (which is free of impurities or involving an excess of silica) as an oxygen conductor, indicates that the electronic conductivity component at high temperatures assumes negligible values especially at very low oxygen activities (below 5ppm).

Atomic Force Microscopy Observation of Ferroelastic Domain Boundary in GdP5O14

The surface structure of GdP 5 O 14 (gadolinium pentaphosphate) with a ferroelastic domain boundary is investigated by AFM (atomic force microscopy) at room temperature in air. The AFM data are obtained for a 1500-nm-square area (400×400 data points) on the (100) surface of the sample. The domain boundary is observed as a zigzag pattern about 300 nm in width. The contour map of the surface shows a unique surface structure in which hollows are aligned along the domain boundary; the hollows have a width of about 600 nm and a depth of 2 nm. If the surface image indicates a strain originating from the domain boundary structure, the thickness of the ferroelastic domain wall of GdP 5 O 14 is estimated to be about 0.6 µm at room temperature.

Study on the utilization of fly ash as raw material for architectonic tile

In order to utilize fly ashes of Mongolian fourth and Tsuruga Power Plants as ceramics raw material, the green body of tile was prepared by using the methods Dr. blade. The sintering of tile performed at temperature 1000–1400°C and mullite formation process was conducted above 1250°C. Water absorption, shrinkage and bending strength of tile were corresponded to Japan industrial standard (JIS). Most of phase composition of tile is mullite and crystobalite.

Synthesis and characterization of Al-MCM-48 type materials using coal fly ash

Supernatant of the coal fly ash solution was used to prepare aluminum containing MCM-48 (Al-MCM-48). It was found that most of the Si and Al components in the fly ash could be effectively transformed into MCM-48 when a surfactant mixture containing cationic cetyltetramethylammonium bromide, CTMABr and tetraoxyethylene dodecyl ether, C 12 (EO) 4 were used as templates. Alkali fusion was found to be necessary as it improves the hydrothermal condition for synthesis of the mesoporous materials. High degree of aluminum incorporation into the tetrahedral positions was revealed when Al-MCM-48 was prepared under controlled pH condition.