Yong Jun Wu

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.

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.

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.

Change in the compositional distribution in perovskite solid solutions during the sintering by SPS

Abstract As an application of characteristic of spark plasma sintering (SPS) method, which can produce highly sintered material with almost no change in compositional distribution, sintered materials that consist of different compositions were prepared. Perovskite three component system, x Pb(Zn 1/3 Nb 2/3 )O 3 – y PbZrO 3 –(1− x − y )PbTiO 3 , exhibits a very sharp pyroelectric peak at phase transition temperature between F RL and F RH phases. When a mixture of calcined materials having different compositions of this system was sintered by SPS, the compositional distribution in the starting mixture was almost maintained. The sintered material exhibited high pyroelectric coefficient over a wide temperature range.

Compositional fluctuation and dielectric properties of Pb(Zr0.3Ti0.7)O3 ceramics prepared by spark plasma sintering

Abstract The microstructure, compositional fluctuation and dielectric properties of Pb(Zr 0.3 Ti 0.7 )O 3 ceramics prepared by spark plasma sintering (SPS) and heat treatment were investigated. The sample heat-treated for 1 h had a large compositional fluctuation, which decreased significantly with increasing heat treatment time up to 2 h and thereafter decreased slightly. It was found that the dielectric constant of above ceramics strongly depended on the compositional fluctuation. Specially, a linear relation between the peak width at two-third maximum dielectric constant of dielectric constant-temperature peak and the compositional fluctuation was observed.

Sandwiched BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 ceramics prepared by spark plasma sintering

Abstract Spark plasma sintering (SPS) combined with heat treatment was investigated to prepare laminated ceramics from compositions having quite different sintering temperatures. Although the optimal sintering temperature of BaNd2Ti4O12 (BNT) ceramics was much higher than that of Bi4Ti3O12 (BIT) ceramics, sandwiched BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 (BNT/BIT/BNT) composite ceramics were successfully prepared with this new method. The results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the BNT layers and the BIT layer were well bonded and no significant diffusion between them was observed. The temperature coefficient of dielectric constant of the laminated ceramic was found to be much smaller than that of BNT ceramic.