Osamu Sakurai

Preparation of spherical fine ZnO particles by the spray pyrolysis method using ultrasonic atomization techniques

An ultrasonic atomizer was used in the spray pyrolysis method to prepare fine, spherical and uniform ZnO particles. Almost spherical particles were obtained successfully which had a mean particle size of 0.15 μm and had a very narrow particle size distribution. By using alcohol as the solvent, it was found that the particles do not have hollow shell layers which could usually be observed in the spray pyrolysis process by using water as the solvent. The morphology of the ZnO particles was strongly affected by the concentration of the starting solution.

Electrical conductivity of yttria-stabilized zirconia single crystals

The electrical conductivities of YSZ single crystals with various compositions covering FSZ and PSZ regions were measured by a complex impedance method and a four-probe a.c. method. The conductivities changed significantly as a function of composition. A simple conduction model for PSZ showed that the tetragonal phase is a good oxygen ionic conductor having an activation energy for motion of about 0.8 to 0.9 eV. It is promising for low temperature application of a solid state electrolyte.

Particle structure control through intraparticle reactions by spray pyrolysis

Abstract Spray pyrolysis is a droplet–particle conversion process comprising of the evaporation of solvents, precipitation of the solutes, decomposition of the solutes, sintering of the formed phases, etc. Purposive control of the reactions within every droplet or particle makes it possible to control the structure, phase composition and shape of the prepared particles. By introducing reactions into every droplets or precisely controlling the intraparticle reactions, sintering and phase separation, direct preparations of either dense or hollow, single-crystal or layer-structured particles were achieved by spray pyrolysis.

Preparation of dense spherical Ni particles and hollow NiO particles by spray pyrolysis

Dense spherical Ni particles were prepared from nitrate solution by spray pyrolysis in a H2–N2 atmosphere. Hollow NiO particles with rough surfaces were formed first at low temperature and then reduced to Ni by H2 above 300°C. Subsequent intraparticle sintering of the Ni crystallites gave rise to densification of Ni particles as the temperature was raised; most Ni particles became dense above the pyrolysis temperature of 1000°C. However, when a N2 atmosphere was used, hollow NiO particles were formed, which did not densify even at 1200°C due to the lack of sintering. The dense Ni particles obtained were of good crystallinity and good oxidation resistance, especially for those formed at higher pyrolysis temperatures and longer residence times.

Thermal decomposition of basic magnesium carbonates under high-pressure gas atmoshpheres

Abstract Thermal decomposition of basic magnesium carbonates, hydromagnesite 4MgCO 3 ·Mg(OH) 2 ·4H 2 O and nesquehonite MgCO 3 ·3H 2 O, was studied under high-pressure carbon dioxide, nitrogen and argon atmospheres (≤ 50 kg cm −2 ) by high-pressure DTA. The decarbonation was strongly affected by the partial pressure of carbon dioxide. A new decomposition process with a new metastable intermediate was found at high-pressure carbon dioxide atmospheres: hydromagnesite, amorphous dehydrated, amorphous lower carbonate, intermediate, MgCO 3 , MgO. A model was proposed to explain the decomposition mechanism integratedly throughout the various partial pressures of carbon dioxide; the formation of the intermediate governed the decarbonation rate and the crystallization of MgCO 3 from the amorphous lower carbonate at ∼500°C.

Thermogravimetric study on the decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O

Abstract Isothermal and non-isothermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O was studied thermogravimetrically. Decarbonation was strongly influenced by the partial pressure of carbon dioxide. Decarbonation in an argon atmosphere proceeded via an amorphous lower carbonate to MgO. Decarbonation in a carbon dioxide atmosphere was interrupted at ∼460–480°C. This interruption was explained by the formation of a metastable intermediate and the subsequent crystallization of MgCO3, both from the amorphous lower carbonate. This explanation was supported by DTA and power X-ray diffraction analysis of the quenched specimens.

Electrical properties of La-doped SrTiO3 (La: 0.1 to 2.0 at %) single crystals grown by xenon-arc image floating zone method

Lanthanum-doped semiconducting strontium titanate single crystals having various lanthanum contents were grown in an air atmosphere by the xenon-arc image floating zone method. The crystals were characterized by X-ray powder diffraction, EPMA analysis and chemical analysis. Each lanthanum was accompanied by a trivalent titanium ion in the grown crystal. The electrical conductivity of these crystals was measured at 20 to 1150° C, and it was found to increase linearly with increasing lanthanum content. The mobility of the charge carrier was estimated from the concentration of trivalent titanium and the conductivities of the crystals. The mobility in the low temperature region agreed with previous studies. However, a significant difference was found at high temperatures. An error in the temperature dependence in the previous study is responsible for this difference. It is stressed that care is necessary in applying the results of single crystalline studies when discussing high-temperature bulk defect chemistry.

Thermal decomposition of cerussite (PbCO3) in carbon dioxide atmosphere (0–50 ATM)

Abstract The thermal decomposition of cerussite, PbCO 3 , was studied over a wide range of CO 2 pressures (0–50 atm) using high pressure DTA and X-ray powder diffraction. At low CO 2 pressures ( 3 · 2 PbO, but at medium pressures (∼1 atm), two intermediates, PbCO 3 · PbO and PbCO 3 · 2 PbO, were formed. At high pressures (>4 atm), cerussite decomposed to PbO via three intermediates, 2 PbCO 3 · PbO and those given above. As the pressure of CO 2 increased, the temperatures at which the DTA peaks appeared increased, the number of intermediates also increasing. The thermal behaviour is discussed on the basis of the phase diagram of the PbOCO 2 system and also on the temperature-dependence of the decomposition rate.

Isothermal differential scanning calorimetry on an exothermic phenomenon during thermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O

An exothermic phenomenon and a simultaneous rapid evolution of a small amount of carbon dioxide at −500°C during thermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O was studied by isothermal DSCTG in a carbon dioxide atmosphere. It was quantitatively confirmed that the exothermic phenomenon was due to crystallization of MgCO3 from the amorphous phase and that the evolution of carbon dioxide was due to decomposition of the MgCO3 by the heat of crystallization (⋍3.4 kcal mole−1.

Thermal decomposition of hydrocerussite (2 PbCO3 · Pb(OH)2) in carbon dioxide atmosphere (0–50 atm)

Abstract The thermal decomposition of hydrocerussite was studied with TG, high-pressure DTA and powder X-ray diffraction techniques in the P CO 2 range 0–50 atm. The decomposition process was strongly affected by P CO 2 . PbCO 3 , as a new intermediate, was found at carbon dioxide pressures above 1 atm. The results were different from any of the previous studies. The temperatures of all the endothermic processes increased and the formation temperature of PbCO 3 decreased with increasing P CO 2 . The results are discussed by referring to the equilibrium phase diagram of the system PbOCO 2 .