Naofumi Uekawa

Low-temperature synthesis of niobium oxide nanoparticles from peroxo niobic acid sol

A peroxo niobic acid sol was prepared by peptization of the niobic acid precipitate (Nb2O5.nH2O) with a H2O2 aqueous solution. Crystallized Nb2O5 nanoparticles and niobic acid nanoparticles were obtained by heating the peroxo niobic acid sol. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3]=0.3 mol/l) was heated at 348 K for 1 week, Nb2O5 nanoparticles with a diameter of 4.5 nm and a S(BET) of 275 m2/g were obtained. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3]=1 mol/l) was heated at 348 K for 1 week, niobic acid nanoparticles with a diameter of less than 2 nm were obtained. The pore structure and degree of crystallinity of the nanoparticles prepared by heating the peroxo niobic acid sol greatly depended on the concentration of the ammonia solution used for preparing the niobic acid precipitate.

Effect of alkali metal hydroxide on formation processes of zinc oxide crystallites from aqueous solutions containing Zn(OH)42− ions

Aqueous solutions containing Zn(OH)42− ions were prepared by adding 50 ml of 1.5 mol l−1 aqueous alkali metal hydroxide (MOH: M = Li, Na, K, Cs) to 50 ml of 0.1 mol l−1 aqueous zinc nitrate hydrate (Zn(NO3)2·6H2O). Zinc oxide (ZnO) crystallites were obtained by heating aqueous solutions containing Zn(OH)42− ions at ≥348 or 368 K for 3 h. The morphology depended on both of the heating temperature of the Zn(OH)42− aqueous solution and the alkali metal hydroxide used to obtain Zn(OH)42− ions. According to the result of the kinetics of the zinc oxide formation, it was shown that the decomposition of Zn(OH)42− ions on the zinc oxide surface was the rate determining step when NaOH, KOH and CsOH were used to obtain Zn(OH)42− ions. When LiOH was used to obtain Zn(OH)42− ions, the rate determining step was the nucleation of zinc oxide and/or the adsorption of Zn(OH)42− ions.

Nonstoichiometric properties of zinc oxide nanoparticles prepared by decomposition of zinc peroxide

Zinc oxide (ZnO) nanoparticles were obtained by firing the zinc peroxide nanoparticles at more than 473 K for 2 h. The zinc peroxide decomposed at 473 K to form ZnO that contained O22− ions. Furthermore, the ZnO nanoparticles without O22− ions were obtained by decomposition of the zinc peroxide at more than 513 K and the obtained ZnO contained oxygen vacancies. The increase of the unit cell parameter and the decrease of the activation energy for the electronic conduction were observed due to the oxygen vacancy. The ZnO nanoparticles also had lattice strain. The value of Δd/d decreased from 9.1 × 10−3 to 0 when the firing temperature was in the range from 473 K to 773 K.

Eutectic Al2O3-GdAlO3 composite consolidated by combined rapid quenching and spark plasma sintering technique

Abstract A mixture of Al2O3 and GdAlO3 was melted and rapid quenched to produce an amorphous film. Dense eutectic composites were consolidated from ground amorphous powder using both conventional and spark plasma sintering (SPS). Conventional sintering at temperatures above 1600°C for 24 h was required for complete sintering. However, using SPS complete sintering could be obtained at temperatures between 1300 and 1500°C with no soaking. The SPS technique could consolidate ultrafine eutectic structure from rapid quenched amorphous material, whilst conventional sintering was not successful owing to grain growth. A combination of rapid quenching and SPS resulted in an ultrafine eutectic Al2O3–GdAlO3 structure.

Preparation and Nonstoichiometric Property of wide Compositional Fe(III)-doped TiO 2 (anatase)

Fe(III)-doped TiO 2 (anatase) was prepared by the oxidation of Fe x TiS 2 . Two calcination methods were used to oxidize Fe x TiS 2 . In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO 2 (anatase), forming Fe(III)-doped TiO 2 (anatase), in the composition range of 0 ⩽ Fe/Ti ⩽ 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of Fe x TiS 2 . The electronic property and the valence stage of the Fe(III)-doped TiO 2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO 2 (anatase) was decreased by the Fe(III) doping.

Comparative examination of titania nanocrystals synthesized by peroxo titanic acid approach from different precursors

Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV-vis, low temperature N(2) adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl(4) precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO(2) nanoparticles from titanium alkoxide precursor in comparison with those from TiCl(4) precursor.

Spark Plasma Sintering of Transparent PbZrO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 Ceramics

A new method of preparing transparent PbZrO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 (PZ-PT-PZN) ceramics was proposed. This is a multiprocess in which the mixtures of calcined powders were spark plasma sintered for 10 min and then thermally treated for 1 h. Although the sintering time was very short, the densities of the samples prepared by this method were nearly theoretical and the samples were optically transparent. The transparent PZ-PT-PZN ceramics could be promising candidates for applications to areas such as electrooptics and pyrooptics.

Mixed-valence formation in highly oriented Ti-doped iron oxide film

Ti4+-doped α-Fe2O3 films have been prepared by the sol–gel method. The dispersed state of the doped Ti ions in the film was compared with a Ti-doped powder prepared by a coprecipitation method in order to examine homogeneous dispersion effects of the sol–gel method. X-Ray diffraction (XRD) showed the highly oriented structure of the sol–gel-derived Ti-doped α-Fe2O3 films. Ti doping can control the electrical conductivity of the film effectively. X-Ray photoelectron spectroscopy (XPS) valence band spectra evidenced the formation of the mixed valence with Ti doping. The data on electrical conductivity changes with doping indicated a distinct difference of Ti-dopant dispersion in the film and powder. The depth profile of the Ti dopants from the surface was measured with XPS using Ar-ion etching; the Ti dopants are more homogeneously distributed in the sol–gel-derived film than in the powder.

Synthesis of rutile and anatase TiO2 nanoparticles from Ti-peroxy compound aqueous solution with polyols

Ti-peroxy compound was synthesized from Ti(O-iPr) 4 and H 2 O 2 . Anatase and rutile TiO 2 nanoparticles were prepared by heating the Ti-peroxy compound diluted with a polyol aqueous solution at 368 K for 24 h. In this research, ethylene glycol, glycerin, erythritol, and D-mannitol were used as polyols in the diluting solution. The ratio of anatase/rutile of the TiO 2 obtained depended on the polyol concentration in the diluting solution. Furthermore, the polyol concentration at which single-phase anatase could be obtained was lowest when the number of OH groups in the polyol molecule was the highest. With increasing polyol concentration, the obtained TiO 2 nanoparticles showed increasing specific surface area and decreasing particle size.

Characterization of CeO 2 Fine Particles Prepared by the Homogeneous Precipitation Method with a Mixed Solutionof Ethylene Glycol and Polyethylene Glycol

Cerium oxide (CeO 2 ) nanoparticles were obtained by heating a polyethylene glycol (PEG) solution of cerium nitrate hydrate [Ce(NO 3 ) 3 6H 2 O] at 383 K for 3 h. When the PEG, whose molecular weight was 20,000, was used for the preparation, the monodispersed CeO 2 , whose particle size was about 102 nm, was obtained. When the mixture of PEG20,000 and ethylene glycol (EG) was used to prepare the PEG solution of cerium nitrate hydrate, the average particle size increased from 102 nm to 660 nm with an increase in the EG content of the solution. The pore structure in the obtained CeO 2 particles also depended on the weight ratio between EG and PEG20,000.