Yoko Ohba

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.

Hydrothermal Syntheses of Lead Zirconate Titanate Thin Films Fabricated by a Continuous-Supply Autoclave

Crystalline lead zirconate titanate (PZT) films formed hydrothermally in a test-tube autoclave have heterogeneous chemical composition, because the concentration of each ion (Pb, Zr and Ti) in solution cannot be controlled. A continuous-supply autoclave system was used to obtain PZT films with desirable chemical compositions. A solution was sampled from the reactor during the reaction, and the change in concentration of elements was measured. Based on the results, the appropriate composition and concentration were determined. The obtained PZT film has an intermediate layer between the film and titanium substrate. The layer was much thinner than that obtained with a test-tube autoclave.

Carbonation of low heat portland cement paste precured in water for different time

Abstract The carbonation technique was applied to accelerate the hydration of low heat portland cement (LHC). Before carbonation, the demoulded pastes were precured in water for 0, 2, 7, and 21 d, respectively. The results show that procuring time in water strongly influences the carbonation process. The phenolphthalein test indicates that the paste precured in water for a shorter time is more quickly carbonated than that for a longer time. The content of calcium hydroxide increases with increasing the precuring time in water, whereas, the amount of absorbed carbon dioxide changes contrarily. Scanning electron microscope (SEM) observation shows that portlandite always fills up big air bubbles in the paste during procuring in water, and the mercury intrusion porosimetry (MIP) results show that there are less large capillary pores in the paste precured in water for a longer time. It is found that the paste without precuring in water has more carbon dioxide absorption during curing in carbon dioxide atmosphere, and its total pore volume decreases remarkably with an increase in the carbonation time than that precured in water. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) surface area analyses indicate that the carbonate products are vaterite and calcite; CxSHy formed from carbonation has low BET surface area in comparison with that of C-S-H formed from curing in water.