• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.1
• /
• pp.49-54
• /
• 1998

$BaTiO_3$ fine particles were synthesized by hydrothermal method. $TiO_2$ and $Ba(OH)_2{\cdot}8H_2O$ were used as staring materials, and it was possible to synthesize $BaTiO_3$ fine particles in pure water by using excess $Ba(OH)_2{\cdot}8H_2O$. The shape of synthesized particles are irregular but near spherical, and the particle size depends on the temperature and Ba/Ti atomic ratio.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.11 no.1
• /
• pp.33-37
• /
• 2001

Kaolinite was synthesized through th acid treatment of mixture which consisted of psudoboehmite and colloidal silica in hydrothermal reaction at $213^{\circ}C$ under autogeneous vapor pressure. Crystallization process was characterized by X-ray powder diffraction pattern, IR spectra and Hinckley index was calculated. The synthesis in acidic solution promotes the dissolution of the starting materials and leads to crystallization of kaolinite. The rate of crystallization to kaolinite and stacking defect were found to e affected by kind of anion, acidity and starting materials.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06b
• /
• pp.87-107
• /
• 1996

The fine Co powder with an average particle sie of less than 1$\mu\textrm{m}$ was prepared by hydrothermal reduction with hydrogen from Co(OH)2 slurry obtained by mixing the solutons of CoSO4$.$7H2O and NaOH. A method to control pH of the end solution around neutrality was proposed. The reduction rate was found to be a function of pH, temperature, hydrogen pressure and the amount of catalyst.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.2 no.2
• /
• pp.33-39
• /
• 1992

Calcia stabilized zirconia polycrystal(Ca-TZP) powders were prepared by hydrothermal treatment at $200 ^{\circ}C$ in autoclave. Ca-TZP powders were shown the spherical shape with an average diameter of about 9-13 nm and specific surface area of>$112m^2/g$, and possessed weak agglomerates among the particles.

• Journal of the Korean Ceramic Society
• /
• v.52 no.6
• /
• pp.531-534
• /
• 2015

In this work, we undertake a comparative study of the crystallographic microstructures and photo-catalytic properties of rutile $TiO_2$ nanorods grown on FTO facing up and down by a hydrothermal method. An analysis of the fine structures showed that $TiO_2$ nanorods grown on FTO facing up were mixed with sea urchin and microsphere. These structures induced a vertical orientation of the nanorods on FTO. The saturated photocurrent densities of the $TiO_2$ nanorods grown both up and down were $1.5mA/cm^2$ in the former case, the IPCE was increased to 10% at 300~350 nm. The onset potential (${\fallingdotseq}$ flat band potential) of the nanorods grown on FTO facing up is negatively shifted to a value of -0.31 V. This is caused by an increase in the surface state, in this case the number of oxygen vacancies, and by the formation of $Ti^{3+}$. Therefore, the FTO facing direction is considered as a critical factor during the hydrothermal reaction for $TiO_2$ growth so as to develop an efficient photo-catalytic system.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.3 no.1
• /
• pp.12-17
• /
• 1993

Growth runs of KTP single crystals were carried out by the hydrothermal method. KTP powders used for the crystal growth were prepared as a single phase by the solid state reaction of a stoichiometric mixture of $KH_2PO_4 and TiO_2$ at TEX>$800^{\circ}C$ and subsequently by the hydrothermal treatment at $250^{\circ}C$ 4m KF solution. The most effective solvents for the crystal growth of KTP were KF and K $K_2HPO_4$ solutions. Solubilities of KTP in these solutions were positive over the range $350~450^{\circ}C$.Seed crystals of good quality could be obtained by the horizontal temperature gradient method at temperatures over the range 380~430^{\circ}C$ in these solutions. The hydrothermal conditions for the high growth rates of seed crystals are as follows: growth method; vertical temperature gradient method, solvent; 4m KF or $K_2HPO_4$ solution, temperature region; $400~450^{\circ}C$, pressure region; $1000~1500kg/cm^2$, where solubility of KTP was large enough to proceed the growth. Under such conditions, seed crystals of KTP are grown at a rate of approximately 0.06-0.08mm/day in the direction of the c-axis. Morphologies of grown crystals tended to be bounded by (100), (011) and (201) faces.

• Journal of the Microelectronics and Packaging Society
• /
• v.21 no.4
• /
• pp.45-49
• /
• 2014

In this study, we grew non-polar ZnO nanostructure on (1-102) R-plane sapphire substrates. As for growth method of ZnO, we used hydrothermal synthesis which is known to have the advantages of low cost and easy process. For growth of non-polar, the deposited AZO seed buffer layer with of 80 nm on R-plane sapphire by radio frequency magnetron sputter was annealed by RTA(rapid thermal annealing) in the argon atmosphere. After that, we grew ZnO nanostructure on AZO seed layer by the added hexamethylenetramine (HMT) solution and sodium citrate at $90^{\circ}C$. With two types of additives into solution, we investigated the structures and shapes of ZnO nanorods. Also, we investigate the possibility of formation of 2D non-polar ZnO layer by changing the ratio of two additives. As a result, we could get the non-polar A-plane ZnO layer with well optimized additives' concentrations.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.3
• /
• pp.95-100
• /
• 2006

Synthesis of the non-swelling property micas was carried out by hydrothermal method. In order to artificially induce the diffusion of ions, a rotating system was attached to the hydrothermal apparatus and by adding 0.7 mm zircon beads, synthesis of the non-swelling property micas could be performed in a low temperature area. The hydrothermal conditions for the preparation of micas were a reaction temperature of $260^{\circ}C$, for 72 hrs, using $1K_2O,\;1Al(OH)_3,\;4Mg(OH)_2\;and\;6SiO_2$ as the starting materials and a 8M-KOH solution as the hydrothermal solvent. The micas obtained under these conditions were a plate shape with a size of $2.89{\mu}m$ and showed a whiteness of over 97 %. Also, through the FT-IR analysis, because the absorption peak of the $Mg_3OH$ vibration was observed at approximately $3700cm^{-1}$, it could be known that it was phlogopite of non-swelling property showing the chemical composition of $KMg_3AlSi_3O_{10}(OH)_2$. This result was very consistent with the EDS analysis where O (41.34 %), Mg (3.88 %), Al (11.45 %), Si (17.62 %) and K (25.71%) elements were detected.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.2
• /
• pp.292-300
• /
• 1997

PSZT powders having the particle size of 0.5~5 $\mu\textrm{m}$ with cubic shapes, were prepared by a hydrothermal reaction in the temperature range of 150~$^{\190circ}C$ for a 2 h reaction. Experimental results showed that as the reaction temperature increased, the nucleation and crystal growth were accelerated and the the particle size became larger. However, the particle size became smaller with its narrow distribution as the concentration of a mineralizer (KOH) increased. It was possible to reduce the reaction temperature by increasing mineralizer concentrations. With increase in Zr/Ti ratio, the major crystal phase of synthetic PSZT powders was seen to change from tetragonal phase to rhombohedral phase.

• Applied Chemistry for Engineering
• /
• v.25 no.6
• /
• pp.564-569
• /
• 2014

Zirconia nanoparticles were synthesized by hydrothermal process, and experimental parameters such as reaction temperature, reaction time, kind and concentration of precipitator, kind of precursor were varied. Particle sizes and crystalline phases of each synthesized nanoparticles were analyzed with X-ray diffraction and FE-scanning electron microscope (SEM). The particle size and crystallization of zirconia increased with increasing concentration of precipitator. The growth rate of particle sizes when NaOH as a precipitator was used also increased more than that of KOH. Therefore, the use of KOH rather than NaOH was more effective in the control of particle sizes. An amorphous zirconia nanoparticle was found in 4 h of hydrothermal reaction, but the monoclinic zirconia nanoparticle was found in 8 h and over of hydrothermal reaction, and the width of nanoparticles was slightly slimmed and the length of nanoparticles was slightly extended with increasing reaction time. The smallest particle size was produced at the same synthesis condition when zirconium chloride among the precursors such as zirconium (IV) acetate, zirconium nitrate and zirconium chloride was used.