Masaki Daimon

Preparation of Lead Zirconate Titanate Thin Film by Hydrothermal Method

A hydrothermal method for preparing thin films of crystalline PZT was developed by controlling the rates of nucleation and crystal growth. This method consisted of two steps of hydrothermal reaction. The first step (nucleation process) was that in which the TiO2 substrate reacted with the mixed solution of Pb and Zr to form PZT and/or PZ nuclei on the surface. Subsequently, the crystal growth of PZT was promoted as the next hydrothermal step (crystal growth process) by the reaction of the mixed solution of Pb, Zr and Ti. From the experimental results of PZT powder preparation, the conditions of the nucleation and crystal growth process were determined as at 150°C for 24 h and at 120°C for 48 h, respectively. It was verified that the thin films consisted of PZT polycrystals and showed ferroelectric properties.

Fabrication of Barium Titanate/Strontium Titanate Artificial Superlattice by Atomic Layer Epitaxy

Epitaxial growth of BaTiO3, SrTiO3 and their superlattices was carried out by the alternating evaporation method using an atomic-layer-epitaxy control system for molecular beam epitaxy (MBE). Stable and reproducible control of the chemical composition was achieved by layer-by-layer growth with this system. Both BaTiO3 and SrTiO3 were grown epitaxially on SrTiO3 substrates, and clear oscillations of reflection high-energy electron diffraction (RHEED) intensity were observed, corresponding to the alternating depositions of BaO and TiO2 in BaTiO3 growth. The artificial superlattice with the structure of [(BaTiO3)5/(SrTiO3)5]7 was fabricated, and the X-ray diffraction (XRD) pattern of the superlattice was simulated by a step model. Diffraction angles of satellite peaks and the shape of Laue peaks in XRD patterns were consistent with those calculated, indicating that the designed structure was fabricated in the superlattice.

EFFECT OF PARTICLE SIZE DISTRIBUTION OF FLY ASH-CEMENT SYSTEM ON THE FLUIDITY OF CEMENT PASTES

Abstract This paper investigates the effect of particle size distribution of fly ash–cement system on the fluidity of the cement pastes using class F fly ash collected from the hopper attached to an electrostatic precipitator when the burning conditions and types of coal are changed at a coal-fired power plant. The unburned carbon content of fly ashes used in the experiment is less than 1.5%. To prevent the unburned carbon in fly ashes from affecting the fluidity of the pastes, polycarboxylic acid plasticizer with more saturation amount is added into the pastes for experimentation. The particle size distribution of fly ash–cement system is analyzed using n value of Rosin–Rammler function and the n value is derived with a nonlinear least squares fitting method. As the result, it is shown that the fluidity increases as the particle size distribution becomes wider, i.e., as n value gets smaller.

Characterization of fly ash directly collected from electrostatic precipitator

Abstract Class-F fly ash was obtained from different hoppers at progressively farther distances from the boiler. Examinations showed that the ash collected from the farthest hopper tended to have finer particle size, greater density, lower carbon content, and higher glass content. When the boiler is operated at full load (600 MW) the glass content increased compared to half load (300 MW), but the Blaine specific surface area and carbon content decreased. Pozzolanic reactivity at 40°C is related to the fineness of the fly ash but the glass content has no significant influence on reactivity. There was a negative correlation between carbon content and the apparent viscosity of cement paste with fly ashes and 1.6% added superplasticizer.

Mechanism of Diffuse Phase Transition in Relaxor Ferroelectrics

Dielectric properties of lead magnesium niobate (PMN) and Ta-bearing strontium barium niobate (SBNT) were measured as a function of temperature, and the crystal structure of PMN was refined by the Rietveld analysis method. The results of structure refinement indicate that the volume of polar microregions (PMR) increases with decreasing temperature. The dielectric properties of PMN and SBNT are well explained by an advanced theory of dielectric dispersion. The anomalous behavior in dielectric permittivity (e) observed on the low temperature side of T m, the temperature of e maximum, is explained by simple dielectric relaxation, while on the high-temperature side of T m is explained by the volume increase of PMR. It is concluded that these is no phase transition around T m, and the diffuse phase transition is an overlapping phenomenon of volume increase of PMR, freezing process of fluctuating dipoles in PMR and dielectric dispersion around the measuring frequrncy. A model of diffuse phase transition and relaxor ferroelectrics is proposed. The difference between normal ferroelectrics and relaxor ferroelectrics is discussed from the viewpoints of spreading of soft-mode phonons and disorder in the crystals.

Mechanisms and kinetics of C4AF hydration with gypsum

Abstract The mechanisms and kinetics of early stage C4AF hydration with gypsum was studied by measuring the heat of hydration with a conduction calorimeter. The heat of the reaction was 173 cal/ g-C4AF. The reaction equation was estimated to be C 4 AF + 4 CaSO 4 ·2 H 2 O + 35 1 3 H 2 O → 4 3 C 3 ( A 0.75 , F 0.25 )·3 C S H 31 + 2 3 FH 3 The equation for rate of hydration was ζ = 0.25t as the thickness (ζ) or hydrated C4AF increased from 0 to 0.6 μm.

Quantitative determination of fly ash in the hydrated fly ash - CaSO4·2H2OCa(OH)2 system

Abstract For the quantitative determination of fly ash in hydrated fly ash - CaSO 4 ·2H 2 OCa(OH) 2 system, various kinds of selective dissolution were evaluated using pastes made from a single representative fly ash. Selective dissolution using picric acid-methanol solution was found to be adequate. Selective dissolution using picric acid - methanol + water can also be used, when it is necessary to save time, although rather bigger corrections are needed. Reproducibility of the determination by both methods was found to be satisfactory, as the standard deviation of the measurement was within 0.23 – 0.55%. Several dissolution experiments were also carried out to obtain the basic information related to this technique.

Dispersion mechanisms of Comb-type superplasticizers containing grafted poly(ethylene oxide) chains

This paper discusses the influence of graft chain length and dosage of comb-type superplasticizers on adsorption and dispersion mechanisms, and their subsequent effect on the fluidity of concentrated limestone suspensions. Contrary to the results obtained from interparticle potential calculations, the fluidity of concentrated suspension is improved by the use of comb-type polymers having shorter grafted chain length. The dispersion mechanism of comb-type polymers in a concentrated suspension is evaluated from the perspective of molecular structure, the amount of adsorbed polymer, and the amount of entrapped water in the clusters of CaCO 3 particles. Furthermore, the addition of certain soluble salts, which can effect the concentration of Ca 2+ in liquid phase of CaCO 3 suspensions, has been observed to decrease the adsorption of comb-type polymers on CaCO 3 . Thus, the polymer adsorption process on solid surfaces can be selectively influenced by certain types of ions.

Hydration of low porosity slag-lime pastes

Abstract Slag-lime pastes of low porosity (water/solid ratio of 0.20) were hydrated from 6 hours to 180 days at 20°C. The kinetics and mechanisms of the hydration process were studied from the results obtained in this investigation. The depth of the hydrated layer on the slag particles is found to be thin indicating that the hydration reaction is very slow. The molar compositions of the formed hydrates could also be calculated from the free lime, nonevaporable water and uncombined slag contents. A high lime product (molar C/S+A ratio of 2.5–2.6) is formed during the early stage of the hydration process, then the molar C/S+A ratio drops to a value of 1.5 and finally rises to a value of 1.7 at 180 days. The surface areas and pore volumes of hydrates were determined from water and nitrogen adsorption measurements. For water vapor adsorption, the water molecules in the adsorbed phase seem to be highly oriented in an ordered array. This effect might be associated with the polar character of water molecule, when adsorbed on an ionic surface like high lime hydrate. The results of x-ray diffraction and SEM observations indicate only the formation of ill-cyrstallised hydration products.

MORPHOLOGICAL STUDY ON HYDRATION OF TRICALCIUM SILICATE

Abstract In order to examine the morphology of hydrates in hardened C 3 S paste, the authors performed experiments using a C 3 S sample having a narrow particle size distribution. The hydrate phase in C 3 S paste could be divided into three types which are inner CSH, outer CSH, and Ca(OH) 2 crystal. The latter two make up the outer product, and seem to contribute to the strength of hardened paste.