Yasumasa Takao

Microstructure of alumina compact body made by slip casting

Abstract An attempt was made to understand the structural changes and particle-packing behavior of compacted alumina (α-Al 2 O 3 ) made by slip casting. Packing structure of powder particles was examined in alumina compact made by slip casting with the crossed polarized light microscope in the transmission mode. Anisotropic structure was present in the specimen. A repeated change of color was noted with the rotation of the specimen at every 45° increments in the cross-section of compact cut parallel to the flow direction of water in the casting process. The alumina particles were aligned with the longest axis normal to the flow direction. The center of the cross-section showed a rather disordered packing structure. Isotropic optical property was noted in the specimen cut perpendicular to the flow direction. Isotropic microstructure was found in all directions of the compact made by the spontaneous drying process, in which less apt water flow occurred during drying. The development of anisotropic structure was insensitive to the dispersing state of particles in the slurry.

Processing defects and their relevance to strength in alumina ceramics made by slip casting

Abstract Al2O3 made by slip casting inherently contained the elongated and the spherical shaped defects. The pores of elongated shape were formed through the liquid flow during the casting process, since they were found in all slip cast specimens and not found in the spontaneously dried specimen where no rigorous flow of water happened. The formation of these defects was insensitive to the slurry properties. The origin of spherical pores was likely due to the entrapped air bubbles during de-airing procedure. Their removal by de-airing was easy for a dispersed slurry having a low viscosity, but difficult for a flocculated slurry of high viscosity. The Weibulls plots for the flexural strengths are essentially the same in the region of high strengths. Specimens made from the flocculated slurry contain a higher concentration of the spherical pores, and some of the resultant specimens have low strength. The lower strength of those ceramics has been ascribed to more detrimental defects, i.e. the spherical ones.

Application of pure silica gel as cation-exchange stationary phase in lon chromatography with indirect photometric detection for common mono-and divalent cations using aromatic monoamines as eluents

SummaryA pure silica gel (Pia Seed 5S-60-SIL), synthesized by the hydrolysis of pure tetraethoxysilane [Si(OCH2CH3)4], was applied as a cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono-and divalent cations (Li+, Na+, NH4+, K+, Mg2+, and Ca2+) using various protonated aromatic monoamines (tyramine [4-(2-aminethyl) phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine) as eluet ions. When using 0.75 mM tyramine-0.25 mM oxalic acid-1.5 mM 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) at pH 5.0 as the eluent, excellent simultaneous separation and highly sensitive detection at 275 nm for these mono-and divalent cations were achieved on the Pia Seed 5S-60-SIL column (150×4.6 mm I.D.) in 20 min.

Simultaneous separation of common mono- and divalent cations on a calcinated silica gel column by ion chromatography with indirect photometric detection and aromatic monoamines–oxalic acid, containing crown ethers, used as eluent

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as a cation-exchange stationary phase in ion chromatography with indirect photometric detection (IC-IPD) for the separation of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out using various aromatic monoamines [tyramine [4-(2-aminoethyl)phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine] as eluents. When using these amines as eluents, the peak resolution between these mono- and divalent cations was not quite satisfactory and the peak shapes of NH4+ and K+ were largely destroyed on the SMBSG B-5 silica gel column. Hence, the application of SMBSG B-5 silica gel calcinated at 200, 400, 600, 800 and 1000 degrees C for 5 h in the IC-IPD was carried out. The peak shapes of the monovalent cations were greatly improved with increasing calcination temperature and, as a result, symmetrical peaks of these mono- and divalent cations were obtained on the SMBSG B-5 silica gel calcinated at 1000 degrees C as the stationary phase. In contrast, the peak resolution between these mono- and divalent cations was not improved. Therefore, crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] were added to the eluent for the complete separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection at 275 nm were achieved in 25 min on a column (150x4.6 mm I.D.) packed with SMBSG B-5 silica gel calcinated at 1000 degrees C by elution with 0.75 mM tyramine-0.25 mM oxalic acid at pH 5.0 containing either 1.0 mM 18-crown-6 or 10 mM 15-crown-5.

Retention behavior of common mono- and divalent cations on calcinated silica gel columns in ion chromatography with conductimetric detection and the use of nitric acid, containing crown ethers, as eluents

Ion chromatographic behavior of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) on columns packed with silica gels (Super Micro Bead Silica Gel B-5, SMBSG B-5) calcinated at 200, 400, 600, 800 and 1000 degrees C for 5 h was investigated using nitric acid containing crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) and 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] as eluent. When using 0.5 mM HNO3 as the eluent, the calcination had almost no effect on the improvement of peak resolution between these mono- and divalent cations. In contrast, when using 0.5 mM HNO3 containing crown ethers as the eluent, with increasing the calcinating temperature, the amount of crown ethers adsorbed on the corresponding calcinated SMBSG B-5 silica gels columns increased and, as a consequence, peak resolution between these mono- and divalent cations was quite improved. Excellent simultaneous separation of these mono- and divalent cations was achieved on column (150x4.6 mm I.D.) packed with the SMBSG B-5 silica gel calcinated at 1000 degrees C by elution with 0.5 mM HNO3 containing either 1.0 mM 18-crown-6 or 5.0 mM 15-crown-5.

Microwave Absorbency Change of Zirconia Powder and Fiber during Vacuum Heating

Stabilized zirconia shows rather high microwave absorbency at room temperature, and the absorbency become higher with increasing temperature. In this study, stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber were subjected for microwave absorption measurements at elevated temperature. Microwave absorption measurements were done by using a system consists of a microwave vector network analyzer, a circular wave-guide fixture and a vacuum furnace. Microwave absorbency was evaluated by the reflection power change from the sample in the circular wave-guide fixture under vacuum heating. Microwave absorbency of stabilized zirconia powder, partially stabilized zirconia powder and zirconia fiber gradually increased with the increase of temperature. We supposed that the increase of microwave absorbency is related to the ionic (oxygen) conduction behavior of stabilized zirconia. Stoichiometric composition ZrO2 powder was also subjected for a measurement to consider the relation between microwave absorbency and ion conduction of zirconia. As the result, stoichiometric composition ZrO2 powder was not absorbed microwave power even when the powder was heated up to 900oC because it isn’t an oxygen ion conductor.

Simultaneous separation of common mono- and divalent cations on an acid-treated silica gel column by ion chromatography with indirect photometric detection and tyramine-oxalic acid, containing 18-crown-6 as eluent

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as cation-exchange stationary phase in ion chromatography with indirect photometric detection for common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out using 0.75 mM tyramine [4-(2-aminoethyl)phenol]-0.25 mM oxalic acid at pH 5.0 as the eluent. Although complete group separation between these mono- and divalent cations was achieved on the SMBSG B-5 column (150x4.6 mm I.D.) in 12 min, peak shapes of NH4+ and K+ were strongly tailed. Hence, the application of SMBSG B-5 silica gel treated with conc. hydrochloric acid at reflux-temperature for 12 h for the simultaneous separation of these cations was carried out. Although the retention volumes of these cations decreased on the acid-treated SMBSG B-5 silica gel column, the peak shapes of NH4+ and K+ were quite improved. Excellent simultaneous separation and highly sensitive detection at 275 nm [detection limits (signal-to-noise ratio of 3 and injection volume of 20 microl), 0.34 microM for Li+, 0.47 microM for Na+, 0.39 microM for NH4+, 0.59 microM for K+, 0.24 microM for Mg2+ and 0.28 microM for Ca2+] were achieved in 15 min on the acid-treated SMBSG B-5 column using 0.5 mM tyramine-0.2 mM oxalic acid-10 mM 18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) at pH 5.5 as the eluent.

Flame Synthesis of Ceramic Particles

We introduce a case study of “high sphericity” and “high uniformity” generated through flame synthesis. Recently, cosmetics need to solve 1) UV-protective effect, 2) transparence, and 3) smooth-textured touch. However, the best recipe and usable evaluation methods are not established. This research is a result combined with a theoretical approach of flame formation process, and a strategic regional alliance of the “AIST” grant venture. A new manufacturing and evaluation method has been commercialized in the forms of a highly original cosmetics and a new evaluation device.

Development of Particulate Unit Operations and Morphology Property Relations of Particulate Products

Some particulate unit operations (apparatus engineering) are developed to control the particle morphology. The innovative aspect of this operation is the correspondence between the necessary material properties and their apparatus optimization. Spherical powders of aluminum oxynitride and aluminum nitride are directly prepared by flame synthesis (in spite of the fact that oxygen serves as an indispensable reactant). Non-oxide powders are commonly non-spherical with a size below the submicrometer scale. The major limiting factors in their synthesis are free energy, reaction temperature, and reaction rate. The innovative aspect of this flame synthesis technology assisted by DC arc plasma concerns the reducing gas composition beyond 1500 K. A chemical equilibrium calculation indicates that the plasma heating compensates the lack of reaction temperature under a low oxygen condition. This burner realizes a high-speed reaction with the help of reactive species in the arcs. We also report the multilayer-coated cosmetic powders with regard to material application, and the powder bed shear force evaluation equipment with regard to apparatus optimization.Copyright