• Journal of Powder Materials
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• v.11 no.6 s.47
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• pp.503-509
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• 2004

Dispersion stabilities and photocatalytic activities of rutile $TiO_{2}$ powders with unique nano-structure synthesized by homogeneous precipitation process at low temperature(HPPLT) have been investigated in the acrylic resin containing fluorostyrene in the range of 0~0.16 mole. Isoelectric point of $TiO_{2}$ in the acrylic resin placed in the neutral region whereas that of $TiO_{2}$ in the water placed in the acidic region, indicating that zeta potential and agglomeration of $TiO_{2}$ powder is strongly dependent on the pH and the type of solvent. To prepare an adhesion, an acrylic resin containing fluorostyrene was synthesized by a radical polymerization. The adhesion of coating layer was increased with increasing fluorostyrene's contents without changing the dispersion stabilities and degrading photocatalytic properties.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1120-1126
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• 2003

Yttrium Aluminum Garnet (YAG) powders were prepared by precipitation of Y hydroxides during milling of alumina powders. The powder calcined at 1200$^{\circ}C$ for 4 h contained a small amount of Yttrium Aluminum Monoclinic (YAM) in addition to YAG. However, phase-pure YAG was obtained in the compact of the milled powder with an average particle size of 0.57 ${\mu}$m at 1300$^{\circ}C$, which is much lower than those (l500∼1600$^{\circ}C$) for a mixed oxide method. The powder was found to exhibit an excellent sinterability regardless of the addition of a sintering aid, SiO$_2$(350 ppm Si). The undoped sample were sintered to a relative density of 98% at l600$^{\circ}C$. In contrast, the addition of SiO$_2$ caused a considerable densification to occur at 1500$^{\circ}C$ and the relative density reached 97.7%. But the sintering aid had little effect on the densification at 1600$^{\circ}C$, showing a similar relative density to the undoped sample.

• Journal of the Korean Chemical Society
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• v.42 no.2
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• pp.220-227
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• 1998

Homogeneous precipitation of $Y^{3+}$ with urea has been studied in order to investigate the effect of urea concentration on the preparation of monodispersed colloidal "Yttrium Hydroxycarbonate $(Y(OH)CO_3 \cdot nH_2O)$". As the initial concentration of urea increased, the mean size of colloidal precipitates decreased, and the rate of precipitation of $Y^{3+}$ increased. When the initial concentration of urea was higher than $4.0 \sim 7.0 M$, precipitates obtained were no more monodispersed colloidal particles, but coagulated big particles; and, although the initial concentration of urea increased over 4.0 M, the rate of precipitation did not increased. It is important to decide the proper initial concentration of urea, because excessive urea can cause the environmental problems such as water pollution.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.6
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• pp.264-271
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• 2007

The inorganic pigments of $Fe_2O_3-CoO-Cr_2O_3-MnO_2$ were synthesized by the co-precipitation method. $FeCl_3,\;CoCl_2,\;CrCl_3\;and\;MnCl_2$ are used for the starting raw materials, and 2 N-KOH for precipitator. $MnCl_2$ is secured with 10 mole%, and 6 composition ratios are used with three ingredients to synthesize the pigments. The samples were calcined at $1350^{\circ}C/1.5h$. The resulting pigments were characterized by using XRD, FT-IR, SEM, and UV spectrophotometer. 6wt% pigments were applied to lime glaze and lime-barium glaze respectively firing at $1260^{\circ}C$ for oxidation atmosphere and $1240^{\circ}C$ for reduction one. The results of color analysis by using UV spectrophotometer showed black, bluish black and dark grayish green.

• Journal of Powder Materials
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• v.22 no.1
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• pp.46-51
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• 2015

A precipitation behavior of nano-oxide particle in Fe-$5Y_2O_3$ alloy powders is studied. The mechanically alloyed Fe-$5Y_2O_3$ powders are pressed at $750^{\circ}C$ for 1h, $850^{\circ}C$ for 1h and $1150^{\circ}C$ for 1h, respectively. The results of Xray diffraction pattern analysis indicate that the $Y_2O_3$ diffraction peak disappear after mechanically alloying process, but $Y_2O_3$ and $YFe_2O_4$ complex oxide precipitates peak are observed in the powders pressed at $1150^{\circ}C$. The differential scanning calorimetry study results reveal that the formation of precipitates occur at around $1054^{\circ}C$. Based on the transmission electron microscopy analysis result, the oxide particles with a composition of Y-Fe-O are found in the Fe-$5Y_2O_3$ alloy powders pressed at 1150oC. It is thus conclude that the mechanically alloyed Fe-$5Y_2O_3$ powders have no precipitates and the oxide particles in the powders are formed by a high temperature heat-treatment.

• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.111-116
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• 1988

Aluminum hydrates were prepared by precipitation method using Al2(SO4)3$.$18H2O as a starting material and NH4OH as precipitation agent. The phases of aluminum hydrate were changed from amorphous aluminum hydrate to pseudo-boehmite of AlOOH form and bayerite, gibbsite, hydragillite and norstrandite of Al(OH)3 form with increasing pH. As pH increased, agglomeration phenomena were reduced. Aluminum hydrates of AlOOH and Al(OH)3 form represented dehydration of structural water near 175$^{\circ}C$ and 385$^{\circ}C$, and 280$^{\circ}C$, respectively. As the ratio of Al(OH)3 to AlOOH increased, specific surface area was reduced.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.3
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• pp.95-100
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• 2016

In this work, tin oxides were obtained by the liquid reduction precipitation method and hydrothermal process using $SnCl_2{\cdot}2H_2O$, $N_2H_4$, and NaOH. Tin oxide crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM). Depending on the molar ratio of the raw materials, tin oxide crystalline with the spherical and rectangular plate-like shape could be obtained, the crystal phase was SnO and $Sn_6O_4(OH)_4$. And the obtained SnO crystals by a hydrothermal reaction showed various shapes, such as, spherical, plate-like and flower-like architectures depending on the temperature conditions.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2543-2551
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• 2020

Calculations of chemical equilibrium for multicomponent aqueous systems of the HyBRID dissolution of magnetite were performed by using the HSC Chemistry. They were done by using a Pitzer-based aqueous solution model with the recipe of raw materials in experiments conducted at KAERI. The change in the amounts of species and ions and the pH values of the solution at equilibrium was observed as functions of temperature and raw amount of CuSO₄. Precipitation of Cu₂O occurred at a large amount of CuSO₄ added to the solution, while no precipitation of Cu(OH)₂ was found at any amounts of CuSO₄. The E-pH diagrams for Cu were constructed at various Cu concentrations to provide the effect of the Cu concentration on the pH values at boundaries where the coexistence of Cu⁺ ion and Cu₂O solid occurred. To prevent Cu⁺ ions from being precipitated to Cu₂O, the raw amount of CuSO₄ should be adjusted so that the pH value of the solution from the equilibrium calculation is less than that from the E-pH diagram. We provided guidelines for the raw amount of CuSO₄ and the pH value of the solution, which prevent the formation of Cu₂O precipitates in the HyBRID dissolution experiments for magnetite.

• Current Applied Physics
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• v.18 no.11
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• pp.1403-1409
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• 2018

In the present study, the $SrMoO_4:Eu^{3+}$ phosphors has been synthesized through hydro-thermal co-precipitation method, and single factor and orthogonal experiment method was adopted to find optimal synthesis condition. It is interesting to note that hydro-thermal temperature is a prominent effect on the luminescent intensity of $SrMoO_4:Eu^{3+}$ red phosphor, followed by co-precipitation temperature, calcining time, and the doping amount of $Eu^{3+}$. The optimal synthesis conditions were obtained: hydro-thermal temperature is $145^{\circ}C$, co-precipitation temperature is $35^{\circ}C$, the calcining time is 2.5 h, and the doping amount of activator $Eu^{3+}$ is 25%. Subsequently, the crystalline particle size, phase composition and morphology of the synthesized phosphors were evaluated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results show that these phosphors possess a scheelite-type tetragonal structure, and the particle size is about $0.2{\mu}m$. Spectroscopic investigations of the synthesized phosphors are carried out with the help of photo-luminescence excitation and emission analysis. The studies reveal that $SrMoO_4:Eu^{3+}$ phosphor efficiently convert radiation of 394 nm-592 and 616 nm for red light, and the luminescence intensity of $SrMoO_4:Eu^{3+}$ phosphors is improved. $SrMoO_4:Eu^{3+}$ phosphors may be a potential application for enhancing the efficiency of white LEDs.

• Applied Chemistry for Engineering
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• v.21 no.4
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• pp.440-444
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• 2010

$SnO_2$ powders were prepared from the calcination of stannic acids precipitated from the aqueous solution of $SnCl_4$ with ammonium nitrate as a precipitator at $90^{\circ}C$. For the comparison of properties, the stannic acids were prepared from the homogeneous precipitation method using urea as a precipitator at the same temperature. The stannic acid from ammonium nitrate at a thermal gravity analysis showed the weight loss until $700^{\circ}C$ and the percentage of total weight loss was 16.5%. The crystallization of stannic acid into $SnO_2$ finished in the calcination at $600^{\circ}C$ for 2 h. The crystallite size of $SnO_2$ increased with the increase of calcination temperature and initial concentration of $SnCl_4$ solution. In case of the same calcination condition, $SnO_2$ prepared from homogeneous precipitation using urea had a relatively smaller crystallite size rather than $SnO_2$ prepared from ammonium nitrate.