• Journal of Powder Materials
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• v.22 no.4
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• pp.266-270
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• 2015

The synthesis of NiTi alloy powders by hydrogen reduction and dehydrogenation process of NiO and $TiH_2$ powder mixtures is investigated. Mixtures of NiO and $TiH_2$ powders are prepared by simple mixing for 1 h or ball milling for 24 h. Simple-mixed mixture shows that fine NiO particles are homogeneously coated on the surface of $TiH_2$ powders, whereas ball milled one exhibits the morphology with mixing of fine NiO and $TiH_2$ particles. Thermogravimetric analysis in hydrogen atmosphere reveals that the NiO and $TiH_2$ phase are changed to metallic Ni and Ti in the temperature range of 260 to $290^{\circ}C$ and 553 to $639^{\circ}C$, respectively. In the simple-mixed powders by heat-up to $700^{\circ}C$, agglomerates with solid particles and solidified liquid phase are observed, and the size of agglomerates is increased at $1000^{\circ}C$. From the XRD analysis, the presence of liquid phase is explained by the formation and melting of $NiTi_2$ inter-metallic compound due to an exothermic reaction between Ni and Ti. The simple-mixed powders, heated to $1000^{\circ}C$, lead to the formation of NiTi phase but additional Ni-, Ti-rich and Ti-oxide phases. In contrast, the microstructure of ball-milled powders is characterized by the neck-grown particles, forming $Ni_3Ti$, Ti-oxide and unreacted Ni phase.

• Journal of Powder Materials
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• v.24 no.4
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• pp.279-284
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• 2017

The formation mechanism and photocatalytic properties of a multiwalled carbon nanotube (MWCNT)/$TiO_2$-based nanotube (TNTs) composite are investigated. The CNT/TNT composite is synthesized via a solution chemical route. It is confirmed that this 1-D nanotube composite has a core-shell nanotubular structure, where the TNT surrounds the CNT core. The photocatalytic activity investigated based on the methylene blue degradation test is superior to that of with pure TNT. The CNTs play two important roles in enhancing the photocatalytic activity. One is to act as a template to form the core-shell structure while titanate nanosheets are converted into nanotubes. The other is to act as an electron reservoir that facilitates charge separation and electron transfer from the TNT, thus decreasing the electron-hole recombination efficiency.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.33-36
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• 2014

This study was aimed at synthesizing and characterizing cerium-doped titania. Cerium-doped anatase titania powders were prepared by sol-gel process, with ammonium (IV) nitrate and titanium (IV) butoxide as the raw materials. The characteristics of pure $TiO_2$ and cerium-doped $TiO_2$ were investigated by XRD, TG/DTA, FE-SEM, and UV-vis spectroscopy. The results of this study show that anatase type of $TiO_2$ was obtained in as-prepared and calcined $TiO_2$ and Ce-$TiO_2$ powder. A DTA curve was also observed as the crystallization temperature decreased with increasing cerium contents. We found that the crystallite size of the obtained anatase particles decreased from 55 nm to 25 nm and the particle size decreased with increasing cerium contents. Moreover, UV-vis spectra showed that anatase titania powders with various cerium contents effectively extend the light absorption properties to the visible region.

• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1378-1386
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• 1994

The characteristic of calcined BaTiO3 powder and sintered PTC ceramics was investigated varing with calcination temperature and time of BaTiO(C2O4)2.4H2O synthesized from BaCl2.2H2O, TiCl4, oxalic acid and ethanol by oxalic acid method. When the particle size was less than 0.1 ${\mu}{\textrm}{m}$ by controlling calcination temperature and time, the resistance at room temperature was measured very high (above M{{{{ OMEGA }}). However, when the calcined particle sizes ranged from 0.2 to 0.3 ${\mu}{\textrm}{m}$, the resistance was 100 {{{{ OMEGA }} (After sintering, the grain size was 10~30 ${\mu}{\textrm}{m}$ homogeneously with the addition of dopant in sintering, the resistivity, resistance, $\alpha$ value and jumped to were 110{{{{ OMEGA }}.cm, 24$^{\circ}C$/% and 106{{{{ OMEGA }}, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.1
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• pp.24-30
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• 2003

The preparation of $PbTiO_3$ powder was carried out using the oxide starting material by hydrothermal method. The powder of a crystalline phase with perovskite structure was synthesized. The optimum conditions for the preparation of powder were as follows; hydrothermal solvent; 8M-KOH or 8M-NaOH, reaction temperature; 250~$270^{\circ}C$, run time; 10 h. The ,shape of synthesized powders were well developed crystalline faces with specific surface area of about 2.3 $\textrm m^2$/g in KOH solution and about 5.0 $\textrm m^2$/g in NaOH solution. The cell parameters of powder were a = 3.90$\AA$, c = 4.14 $\AA$ and cell volume was 57.30 $\AA^3$. The cell ratio (c/a) of powder was the same as the theoretical ratio with c/a = 1.06 and the phase transition temperature(Tc) of the powders was about $470^{\circ}C$.

• Journal of Powder Materials
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• v.24 no.6
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• pp.472-476
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• 2017

Porous W-10 wt% Ti alloys are prepared by freeze-drying a $WO_3-TiH_2$/camphene slurry, using a sintering process. X-ray diffraction analysis of the heat-treated powder in an argon atmosphere shows the $WO_3$ peak of the starting powder and reaction-phase peaks such as $WO_{2.9}$, $WO_2$, and $TiO_2$ peaks. In contrast, a powder mixture heated in a hydrogen atmosphere is composed of the W and TiW phases. The formation of reaction phases that are dependent on the atmosphere is explained by a thermodynamic consideration of the reduction behavior of $WO_3$ and the dehydrogenation reaction of $TiH_2$. To fabricate a porous W-Ti alloy, the camphene slurry is frozen at $-30^{\circ}C$, and pores are generated in the frozen specimens by the sublimation of camphene while drying in air. The green body is hydrogen-reduced and sintered at $1000^{\circ}C$ for 1 h. The sintered sample prepared by freeze-drying the camphene slurry shows large and aligned parallel pores in the camphene growth direction, and small pores in the internal walls of the large pores. The strut between large pores consists of very fine particles with partial necking between them.

• Journal of Powder Materials
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• v.13 no.2 s.55
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• pp.119-123
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• 2006

The grain growth behavior of $0.95Na_{1/2}Bi_{1/2}TiO_{3}-0.05BaTiO_{3}$ (NBT-5BT) has been investigated with respect to the grain shape. The powder compacts of NBT-5BT were sintered at 1200 for various times. The corresponding equilibrium shape was a round-edged cube with flat {100}-faces. Abnormal grains were not observed in the specimens sintered for 1 to 12 h but abnormal grains appeared when sintered for 24 h. Before the formation of abnormal grains, a valley was observed in the measured grain size distribution of NBT-5BT, showing that the grain size distribution was a combination of two unimodal distributions. The present result suggests that the grain growth in NBT-5BT was governed by the growth of facet planes which would occur via 2-dimansional nucleation and growth.

• Journal of the Korean Chemical Society
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• v.55 no.6
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• pp.932-935
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• 2011

Using tetrabutyl titanate as precursor, $Eu^{3+}$ doped $TiO_2$ nano-powder was prepared by sol-gel method, the nature of luminescence of nano-powder was studied. The interaction of chlorpyrifos with $Eu^{3+}$ doped $TiO_2$ was studied by absorption and fluorescence spectroscopy. The results indicated the fluorescence intensity of $Eu^{3+}$ doped $TiO_2$ was quenched by chlorpyrifos and the quenching rate constant ($k_q$) was $1.24{\times}10^{11}\;L/mol{\cdot}s$ according to the Stern-Volmer equation. The dynamics of photoinduced electron transfer from chlorpyrifos to conduction band of $TiO_2$ nanoparticle was observed and the mechanism of electron transfer had been confirmed by the calculation of free energy change (${\Delta}G_{et}$) by applying Rehm-Weller equation as well as energy level diagram. A new rapid method for detection of chlorpyrifos was established according to the fluorescence intensity of $Eu^{3+}$ doped $TiO_2$ was proportional to chlorpyrifos concentration. The range of detection was $5.0{\times}10^{-10}-2.5{\times}10^{-7}mol/L$ and the election limit ($3{\sigma}$) was $3.2{\times}10^{-11}$ mol/L.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.286-287
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• 2006

Barium titanate ($BaTiO_3$) glycolate particles were synthesized at temperature as low as $100^{\circ}C$ through glycothermal reaction by using $Ba(OH)_2{\cdot}8H_2O$ and amorphous titanium hydrous gel as precursors and ethylene glycol as solvent. The particle size and morphology of $BaTiO_3$ glycolate powders can be controlled by varying the reaction conditions such as the reaction temperature and Ba:Ti molar ratio of starting precursors. After glycothermal treatment at $220^{\circ}C$ for 24 h in 1.25:1(Ba:Ti), the average particle size of the $BaTiO_3$ glycolate powder was about 200-400 nm and low agglomeration. $BaTiO_3$ powders were formed by heat-treating the glycolate powder in air at $500-1000^{\circ}C$. As a result, the size of $BaTiO_3$ crystallites changed from around 50-300 nm. It is also demonstrated that the size and shape of $BaTiO_3$ particles investigated as a function of calcination temperature. The $BaTiO_3$ particles obtained from optimum synthesis condition were pressed, sintered and measured for the dielectric property. The $BaTiO_3$ ceramics sintered at $1250^{\circ}C$ for 2 h had 98 % of theoretical density. The ceramics have an average grain size of about $1\;{\mu}m$ and displays the high dielectric constant (~3100) and low dielectric loss (<0.1) at room temperature.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2001.05a
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• pp.138-139
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• 2001

$TiO_2$/UV 고급 산화 공정을 실제 산업 폐수에 적용하였다. 회분식 원통형 반응기에서 T산업 폐수를 광반응시킨 결과 COD 값과 TOC 값이 24시간 경과된 후 95% 이상의 제거 효율을 나타내었다. 광반응에 미치는 인자에 대한 연구에서 $TiO_2$ powder가 0.1 $g/{\ell}$ 에서 8 $g/{\ell}$까지는 투입된 광촉매의 량과 광반응속도가 비례적으로 증가되었으나 10 $g/{\ell}$ 이상에서는 광차폐효과가 나타나 광반응속도가 감소하였으며, UV 광원이 강할수록 광반응 속도는 증가하였고 초기 pH는 광촉매 반응에 영향을 미치지 않음을 알 수 있었다.