Entrapped air bubble is one of the main defects in slurry processing of ceramics. For preventing bubble occurrence or removing them efficiently, an improved knowledge of bubble behaviors in slurries is indispensable. In this paper, effects of particle characteristics, solid loading and dispersant concentration on bubble content in aqueous alumina slurries were studied experimentally. The results showed that the characteristics of initial powders, i.e. particle size distribution and shape, significantly affected the bubble content in slurries. The bubble contents were drastically enhanced by smaller and irregular particles with a higher specific surface area. Moreover, the bubble contents were also greatly increased with increasing solid loadings, and this influence was more pronounced for the particles with a higher specific surface area. No noticeable change in bubble content was resulted from varying the dispersant concentration. A new parameter, solid surface area per unit volume of slurry has been introduced to interpret these effects of powders. It is found that the bubble content shows a parabolic increase as a function of the parameter.

抄録全体を表示

Our previous investigation showed that a random array of fine silver particles formed on sheet glass works as a frequency-selective screen that reflects near-infrared rays and transmits radio waves. In order to improve its screening efficiency, we investigated the use of AlN and TiO₂ films with relative dielectric constants of 4.0 and 5.7, respectively, deposited on sheet glass. It was found that for both substrate films resonance reflection occurred at longer wavelengths and the irregular reflectance was lower than for a glass substrate. In particular, the array on the TiO₂ film showed a very low value of irregular reflectance and high values of shielding effect and visible light transmittance. These results suggest that a system in which a two-dimensional random array of fine silver particles is fixed on a dielectric film deposited on sheet glass can be applied as a solar control glass, which suppresses near-infrared rays and admits radio waves into a room.

抄録全体を表示

ZrO₂ gel film was prepared by spin-coating of Zr sol from Zr-n-propoxide, n-propanol, acetylacetone, water and nitric acid, on various substrates such as polycrystalline Al₂O₃, and single crystals of Al₂O₃, SrTiO₃, 8 mol% Y₂O₃ doped ZrO₂ (YSZ) and MgO. The dried-gel film on Al₂O₃ substrate was transformed to cubic ZrN single phase with bright gold-color by a new carbothermal nitridation method, in which the thin film was covered with a porous graphite crucible to realize a strong reducing atmosphere was fired in flowing nitrogen gas at a fairly high temperatures above 1673 K. The ZrN thin film thus obtained was characterized by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM) observation, reflection spectra.

抄録全体を表示

The fluorescence of two divalent europium-activated oxonitridoaluminosilicates, namely SrSi₅AlO₂N₇ and SrSiAl₂O₃N₂, is reported in this work. The powder sample was synthesized by sintering at 1800°C (SrSi₅AlO₂N₇) or 1600°C (SrSiAl₂O₃N₂) for 2 h under 0.5 MPa N₂. A single broadband blue-green emission is observed for both SrSi₅AlO₂N₇ : Eu²⁺ and SrSiAl₂O₃N₂ : Eu²⁺ at room temperature under ultraviolet excitation. The short-wavelength fluorescence is attributed to the weak crystal-field strength as a result of long distances between the activator ion and ligand anions. The effect of the Eu²⁺ concentration on the emission intensity and CIE chromaticity coordinations of both samples is presented.

抄録全体を表示

An 800 nm-SiC powder (75 vol%) was mixed with a 30 nm-SiC powder (25 vol%) in a 0.05-0.3 M-Y(NO₃)₃ solution containing an Al₂O₃ powder of median size 0.2 μm at pH 5 to distribute homogeneously the sintering additives (Al₂O₃+ yttrium ions) around the SiC particles. In a 20 vol% SiC suspension, the network structure of negatively charged SiC particles was formed by the heterocoagulation through the positively charged Al₂O₃ and yttrium ions. Addition of polyacrylic acid increased the dispersibility of colloidal SiC particles and the amount of yttrium ion fixed to the SiC surfaces owing to the electrostatic interaction among negatively charged polymer, yttrium ions and SiC surfaces. The aqueous suspension of the SiC (800 nm SiC 75%-30 nm SiC 25%)-Al₂O₃ (1.2 vol%)-Y³⁺ ions (1.2-3.2 vol% Y₂O₃) system was consolidated by casting in a gypsum mold and formed green compacts of 36-38% theoretical density. These SiC compacts were hot-pressed to relative density 96.8-100% at 1950°C in an Ar atmosphere. The addition of 30 nm-SiC to 800 nm-SiC decreased the grain size and flaw size of the hot-pressed SiC and improved the flexural strength and fracture toughness. The dense SiC with 2.0 μm of average grain size, prepared from the mixed powder system, showed the following excellent mechanical properties: average four-point flexural strength of 812 MPa, fracture toughness of 6.0 MPa•m^1/2 and Vickers hardness of 18-20 GPa.

抄録全体を表示

Lanthanum-doped hollow alumina particles (A-E) were made by the emulsion combustion method (ECM). Powder characteristics and three-way catalytic performance were evaluated and compared with those of precipitation-made alumina (A-P). The A-E powder was gamma alumina and 40 m²/g in specific surface area (SSA). The unique hollow structure resulted in a broad peak at 130 nm in the pore size distribution and a large pore volume (3.0 cm³/g) with pore diameters of >20 nm. The A-E powder primarily maintained its shape, crystalline phase and SSA up to 1200°C, indicating high thermal stability. Conversion of total hydrocarbon (THC) started at higher temperatures for the Rh-loaded A-E pellets (Rh/A-E) than for Rh-loaded A-P pellets (Rh/A-P) because of the low dispersion of Rh for Rh/A-E. However, a gradient of the THC conversion-temperature curve was higher for Rh/A-E than for Rh/A-P. The large pore volume can promote good gas accessibility inside the pellets for Rh/A-E, resulting in the high gradient of the THC conversion-temperature curve and thus the high activity at high temperatures where gas diffusion is likely to determine the conversion efficiency. The conversion-temperature curves of CO and NO_X showed primarily similar behavior to the THC ones.

抄録全体を表示

Nano-dots array whose diameter and interval were approximately 200 nm and 750 nm, respectively, were made parallel to the atomic step edges on sapphire wafers by focused ion beam (FIB) system. Upon annealing a bunched multi-steps structure formed at regularintervals and straight because the steps were pinned at the nano-dots. The step heights andterrace widths were approximately 2.0 nm, 700 nm in off-angle 0.15° and 10.0 nm, 350 nm in off-angle 1.0°, respectively.

抄録全体を表示

Long persistent phosphor Sr₂MgSi₂O₇: Eu, Dy thin film was prepared by a sol-gel method. The phosphor showed bright blue-green long-lasting afterglow. The afterglow property of sol-gel derived sample was comparable to that of samples prepared by solid state reaction.

抄録全体を表示

Fine leucite powder with an average diameter of 0.2 μm was fabricated by the low-temperature synthesis method for leucite using natural mineral potash feldspar as the major raw material, followed by ball milling. A sintered leucite body with a 99.0% relative density was obtained by heating the leucite powder cylindrical pellet at 1250°C for 1 h. The mechanical properties of this dense leucite body were determined. The bending strength, fracture toughness, elastic modulus and Vickers hardness of the body were 173 MPa, 2.3 MPa•m^1/2, 63 GPa and 5.3 GPa, respectively.

抄録全体を表示

Al₂O₃ slurries with low viscosity and thixotropic properties which is suitable for slip casting were prepared within a short period of time by adopting wet jet milling process. The viscosity of wet jet milled slurry was about 6 mPa•s and remained unchanged for long time, while the viscosity of ball milled slurry rapidly increased with time and reached a maximum value. The FWHM of (113) XRD peak was the same before and after milling indicating no change in crystal structure by the process of milling. Particle size distribution of wet jet milled slurry corresponded to that of the ball milled slurry. However, wet jet milled slurry had low re-flocculation properties and high packing density (more than 60%) than ball milled slurry. We also found that the Al₂O₃ particles after ball milling yielded many hydroxy groups on the surface as compared with the raw materials and wet jet milled particles.

抄録全体を表示

Green body fabricated by slip casting using wet jet milled slurry, which had low viscosity and low re-flocculation property, had very high relative density and showed very small shrinkage during sintering. The square of the thickness of green bodies was proportional to casting time indicating slip casting was implemented well. The relative density of the green body prepared by wet jet milled slurry was 67%, markedly higher than that of ball milled slurry (58%). After sintering, the compacts prepared by wet jet milled and ball milled slurry had a similar relative density of 99%. The linear shrinkages of the sintered bodies prepared by wet jet milled and ball milled slurry were 11.5 and 16.8%, respectively.

抄録全体を表示

Homogeneous hydroxyapatite nanocrystals which have aspect ratio with more than four were synthesized by hydrothermal method. X-ray fluorescence analysis revealed that the Ca/P ratio of hydroxyapatite nanocrystals was maintaining start composition. The protein adsorption properties and bacteria-resistant of hydroxyapatite nanocrystals were investigated. The protein adsorption properties of hydroxyapatite nanocrystals were improvement after the hydrothermal treatment. Bacteria-resistant behavior of hydroxyapatite nanocrystals was not observed, however, multiplication of bacteria was not observed, either.

抄録全体を表示