Papers by Author: Atsushi Nakahira

Abstract: Zeolite is a microporous aluminosilicate material with uniform pore size of less than 2 nm and chemical, mechanical, and thermal stability. In general zeolite is synthesized from silica, alumina, mineralizer (alkali metal hydroxide and fluoride) and water. Recently it has been reported that various zeolites is synthesized from soda-lime glass, slag and coal fly ash as silica and alumina source. On the other hand, the production volume of various kinds of high-quality glass which are utilized for high-tech products such as liquid crystal displays and plasma displays is rapidly increasing. The purpose in this study is to synthesize a zeolite from crushed aluminoborosilicate glasses which is used as LCD panels glass substrate. According to the XRD analysis, it was found that the synthesized sample had zeolite related structure. And the results of SEM observation of the products suggest that the zeolite structure was obtained as well as XRD results. It was thought that zeolite was successfully synthesized from the glass by this synthetic processing.

Abstract: Nano-sized BaTiO3 powders with narrow size distribution and the high tetragonality were attempted to synthesize by the rotary-hydrothermal process in water system, using two kinds of commercial anatase-type TiO2 (ST21/ST01) with different particle size and Ba(OH)2. The rotary-hydrothermal syntheses were done with the rotary-speed of 20 revolutions per minute at 523 K for 24 h. Highly- and mono-dispersed BaTiO3 powders were successfully synthesized by applying the rotary-hydrothermal process. For rotary-hydrothermal synthesis, it was found that the average size, tetragonality, and quality of the BaTiO3 particle strongly depended on the particle size of the starting material. In the case of using ST01 as a starting material, BaTiO3 nano-powders mainly composed of coarse-faceted particles (average particle size = ca.100 nm) with the tetragonal phase and very little lattice defects were successfully synthesized.

Abstract: In this study, the synthesis of the bulky and dense mesoporous silica such as FSM was attempted by a hydrothermal hot-pressing (HHP) with a surfactant as a template and a subsequent calcination. According to TEM observation, the dense bulks obtained by HHP had a hexagonal mesopore structure. Also, these dense FSM bulks possessed high specific surface areas. Furthermore, Ag-supported dense FSM bulks were successfully synthesized by HHP with Ag salt and a subsequent calcination in H2. Thus, this HHP method is useful for synthesizing dense bulks and simultaneous supporting novel metals such as Ag on bulky FSM.

Abstract: In this study, morphology control of ZnO was performed by a wet chemical processing without templates at room temperature. In special, the effect of aging time and pH of this wet processing on ZnO morphologies was in detail investigated. As a result, products composed of a single phase of ZnO with a unique morphology like a hollow tube were obtained. Then, it was found that an aging process played an important role on controlling morphology of ZnO during this wet chemical process. Furthermore, it was found that this hollow-tubular ZnO had a high transparency.

Abstract: In our previous study, we reported that a metastable phase with high Ca/P molar ratio appeared in the temperature range from 700 οC to 800οC
The purpose of this study is to investigate the crystallographic relationship between the metastable phase and HAp matrix. Ca-def HAp was annealed at 500-1000' ο C in air. High-resolution transmission electron microscopic (HRTEM) observations were performed along the [010], [110] and [001] zone axes in order to investigate the structure of the metastable phase. From HRTEM images and results of the analysis of selected area electron diffraction patterns along [010], [110] and [001] zone axes, the lattice constants of the metastable phase were analyzed into a=2.86nm, b=0.94nm, and c=0.69nm of an orthorhombic crystals system.

Abstract: In this study, porous hydroxyapatite (HAp) bodies were prepared by the simple process. We fabricated porous fibers consisting of polyacrylonitrile (PAN) and HAp by an extrusion method of the mixture of PAN and HAp in dimethylformamide (DMF) solution. Fibers obtained by this extrusion method were chopped and molded. Subsequently, these compactions from chopped fibers consisting of HAp and PAN were sintered at various temperatures in air atmosphere. The sintered HAp bodies had high porosity and a number of pores with diameter some hundreds μm. These porous HAp bodies can be used as a scaffold in the body.

Abstract: In this study, the synthesis of nanotubular titanate was attempted though heat-treatment in an oil bath (non-hydrothermal treatment), heat-treatment with stirring in an oil bath (non-hydrothermal treatment), or hydrothermal treatment for metal Ti in NaOH aqueous solution systems. Obtained products were characterized by various methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results suggested that products obtained by both hydrothermal treatment and heat-treatment in an oil bath with and without stirring could be identified as H2Ti4O9
H2O. From TEM observations, however, various morphologies for products obtained by these treatments were confirmed. Therefore, it was considered that morphologies of these products strongly depended on synthesis conditions.

Abstract: Synthesis of bulky Y-zeolite was attempted by a hydrothermal hot-pressing (HHP) method. These bulky products synthesized under hydrothermal conditions were identified as Y-zeolite single phase. Especially, bulky Y-zeolite having translucency, high density and large surface area was obtained by HHP treatment at 423K for 2h with 17wt% of 5M-NaOH solution. This solidified zeolite like single-crystal was considered to be made by dissolution and precipitation mechanism. High-density bulky zeolites can be expected as novel molecular sieves and catalysts with high activity.

Abstract: By the usage of the hydrolysis of Ti alkoxide, various types of TiO2 were obtained through the addition of catalyst (HCl, NH4OH, and CH3COONH4) and some additives into Ti alkoxide solution at room temperature. In special, the effect of two additives, diethylene glycol (DEG) and hexamethylphospheric triamide (HMPA), on hydrolysis behaviors and microstructure with various catalyst for hydrolysis of Ti-tetraisopropoxide was in detail investigated. In case of TiO2 powder with HMPA as an additive, the crystallinity of TiO2 except with NH4OH as a catalyst decreased in XRD patterns, compared to those of products with no additive and with DEG as an additive. The addition of HMPA prohibited the growth of TiO2 and led to fine TiO2 with the average particle size of approximately 10nm.

Abstract: 12 mol%CeO2 based composites were fabricated by a pressureless sintering technique and post-HIP treatments. The mixture of 12CeO2-ZrO2/3Y2O3-ZrO2 (= 80 wt%/20 wt%) powders from various methods were prepared by a ball milling technique and consequently sintered at 1400
in air atmosphere and post-HIP treatment at 1350
. The 12Ce-ZrO2/Y-ZrO2 composites sintered from mixture of 12CeO2-ZrO2 powder and 3Y2O3-ZrO2 powders possessed the high strength over 1300 MPa and also high fracture toughness over 11 MPam1/2. Furthermore, the significant inhibition of the ZrO2 phase transformation of tetragonal to monoclinic phase under an aqueous hydrothermal condition at 150
was obtained for these 12Ce-ZrO2/Y-ZrO2 composites prepared from this method. Microstructural observation was in detail performed by TEM and EDS.