• Journal of Powder Materials
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• v.16 no.6
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• pp.396-402
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• 2009

Tantalum nitrides ($Ta_3N_5$) have been developed to substitute the Cd based pigments for non-toxic red pigment. Various doping elements were doped to reduce the amount of high price Tantalum element used and preserve the red color tonality. Doping elements were added in the synthesizing process of precursor of amorphous tantalum oxides and then Tantalum nitrides doped with various elements were obtained by ammonolysis process. The average particle size of final nitrides with secondary phases was larger than the nitride without the secondary phases. Also secondary phases reduced the red color tonality of final products. On the other hand, final nitrides without secondary phase had orthorhombic crystal system and presented good red color. In other words, in the case of nitrides without secondary phases, doping elements made a solid solution of tantalum nitride. In this context, doping process controlled the ionic state of nitrides and the amount of oxygen/nitrogen in final nitrides affected the color tonality.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.309-313
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• 2013

Silicon carbide (SiC) has recently drawn an enormous industrial interest because of its useful mechanical properties such as thermal resistance, abrasion resistance and thermal conductivity at high temperature. Especially, high purity SiC is applicable to the fields of power semiconductor and lighting emitting diode (LED). In this work, high purity carbon powders as raw material for high purity SiC were prepared by a RF induction thermal plasma. Dodecane ($C_{12}H_{26}$) as hydrocarbon liquid precursor has been utilized for synthesis of high purity carbon powders. It is found that the filtercollected carbon powders showed smaller particle size (10~20 nm) and low crystallinity compared to the reactor-collected carbon powders. The purities of reactor-collected and filter-collected carbon powders were 99.9997 % (5N7) and 99.9993 % (5N3), respectively. In addition, the impurities of carbon powders synthesized by RF induction thermal plasma were mainly originated from the surrounding environment.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.74-80
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• 2009

Electrospinning process is the useful and unique method to produce nanofibers from metal precursor and polymer solution by controlled viscosity. In this study, the NiZn ferrite nanofibers were prepared by electrospinning with a aqueous metal salts/polymer solution that contained polyvinyl pyrrolidone and Fe (III) chloride, Ni (II) acetate tetrahydrate and zinc acetate dihydrate in N,N-dimethylformamide. The applied electric field and spurting rate for spinning conditions were 10 kV, 2 ml/h, respectively. The obtained fibers were treated at $250^{\circ}C$ for 1 h to remove the polymer. Finally, the NiZn ferrite fibers were calcined at $600^{\circ}C$ for 3 h and annealed at $900{\sim}1200^{\circ}C$ in air. By tuning the viscosity of batch solution before electrospinning, we were able to control the microstructure of NiZn ferrite fiber in the range of $150{\sim}500\;nm$ at 770 cP. The primary particle size in $600^{\circ}C$ calcined ferrite fiber was about 10 nm. The properties of those NiZn ferrite fibers were determined from X-ray diffraction analysis, electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, thermal analysis, and magnetic measurement.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.627-632
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• 2010

In this paper the effect of the structure, particle size, morphology of nanofibers and nanoparticles for the electrochemical characteristics of $Li_4Ti_5O_{12}$ was investigated. The $H_2Ti_2O_5{\cdot}H_2O$ synthesized in hydrothermal treatment from a NaOH treatment on $TiO_2$ by ion exchange processing with HCl solutions. After the $Li_4Ti_5O_{12}$ nanofibers synthesized in hydrothermal treatment of $H_2Ti_2O_5{\cdot}H_2O$ and $LiOH{\cdot}H_2O$. The hydrogen titanate precursor prepared by ion exchange processing with 0.1~0.3M HCl solutions and the final products calcined at $350^{\circ}C{\sim}400^{\circ}C$. The $Li_4Ti_5O_{12}$ nanofibers showed well reversibility during the insertion and extraction of Li, good cycle performance, high capacity and low electrochemical reaction resistance than nanoparticles. also c-rate exhibited a discharge capacity of 172 mAh/g at 0.2C and 115mAh/g at 5C, which is the 77%, 67% of that obtained in the process charged, discharged at 0.2C.

• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.156-161
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• 2014

Gallium oxide ($Ga_2O_3$) powders were synthesized using a precipitation method and a polymerized complex method. TG-DSC, SEM, and XRD were performed to investigate the phase and morphology of the $Ga_2O_3$. In situ high-temperature XRD analysis revealed the crystal structure of $Ga_2O_3$ at different temperatures. The $Ga_2O_3$ obtained using the precipitation method and polymerized complex method were generally spherical-shaped particles and their average particle size was approximately 80 nm and $1{\mu}m$, respectively. The crystal structure of the $Ga_2O_3$ prepared by the precipitation method was changed from rhombohedral to monoclinic at $700^{\circ}C$, while monoclinic $Ga_2O_3$ was obtained directly from the precursor by the polymerized complex method.

• Journal of Powder Materials
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• v.23 no.4
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• pp.311-316
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• 2016

$Ni(OH)_2$ hollow spheres have been prepared by solvent displacement crystallization using a micro-injection device, and the effect of process parameters such as concentration and the relative ratio of the injection speed of the precursor solution, which is an aqueous solution of $NiSO_4{\cdot}6H_2O$, to isopropyl alcohol of displacement solvent have been investigated. The crystal phases after NaOH treatment are in the ${\beta}-phase$ for all process parameters. A higher concentration of $NiSO_4{\cdot}6H_2O$ aqueous solution is injected by a micro-injection device and bigger $Ni(OH)_2$ hollow spheres with a narrower particle size distribution are formed. The crystallinity and hardness of the as-obtained powder are so poor that hydrothermal treatment of the as-obtained $Ni(OH)_2$ at $120^{\circ}C$ for 24 h in distilled water is performed in order to greatly improve the crystallinity. It is thought that a relative ratio of the injection speed of $NiSO_4{\cdot}6H_2O$ to that of isopropyl alcohol of at least more than 1 is preferable to synthesize Ni(OH)2 hollow spheres. It is confirmed that this solution-based process is very effective in synthesizing ceramic hollow spheres by simple adjustment of the process parameters such as the concentration and the injection speed.

• Journal of Powder Materials
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• v.27 no.3
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• pp.233-240
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• 2020

Nano-sized ZnSe particles are successfully synthesized in an aqueous solution at room temperature using sodium borohydride (NaBH₄) and thioglycolic acid (TGA) as the reducing agent and stabilizer, respectively. The effects of the mass ratio of the reducing agent to Se, stabilizer concentration, and stirring time on the synthesis of the ZnSe nanoparticles are evaluated. The light absorption/emission properties of the synthesized nanoparticles are characterized using ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and particle size analyzer (PSA) techniques. At least one mass ratio (NaBH4/Se) of the reducing agent should be added to produce ZnSe nanoparticles finer than 10 nm and to absorb UV-vis light shorter than the ZnSe bulk absorption wavelength of 460 nm. As the ratio of the reducing agent increases, the absorption wavelengths in the UV-vis curves are blue-shifted. Stirring in the atmosphere acts as a deterrent to the reduction reaction and formation of nanoparticles, but if not stirred in the atmosphere, the result is on par with synthesis in a nitrogen atmosphere. The stabilizer, TGA, has an impact on the Zn precursor synthesis. The fabricated nanoparticles exhibit excellent photo-absorption/discharge characteristics, suggesting that ZnSe nanoparticles can be alloyed without the need for organic solutions or high-temperature environments.

• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.422-426
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• 1991

In order to synthesize high-purity alpha alumina fine powder, the aluminum hydroxide and ammonium aluminum sulfate(alum) precursor were prepared from natural alumino-silicate(halloysite). The thermal decomposition mechenism for both precursors was elucidated by DTA/TG, XRD and IR analysis. The microstructure, specific surface area and purity of ${\alpha}-Al_2O_3$ were characterized by SEM, and BET analysis. The particle size of ${\alpha}-Al_2O_3$ was determined to be ${\phi}$ = 0.1∼0.5 ${\mu}$m. However, the specific surface area for the alum derived ${\alpha}-Al_2O_3$(89.0 m$^2$/g) was extremely higher than that for the aluminum hydroxide derived one(7.3 m$^2$/g).

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.325-330
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• 2007

High porous AlO(OH) gel is used in precursor of ceramic material, coating material and porous catalyst. For use of these, not only physiochemical control for particle morphology, pore characteristic and peptization but also studies of synthetic method for preparation of high porous AlO(OH) gel were required. In this study, high porous AlO(OH) gel was prepared through the aging and filtration process of aluminum hydroxides gel precipitated by the hydrolysis reaction of $Na_2CO_3$ solution and $Al_2(SO_4)_3$ and $Na_2SO_4$ mixed solution. In this process, optimum synthetic condition of AlO(OH) gel having excellent pore volume as studying the effect of hydrolysis pH on gel precipitates has been studied. Hydrolysis pH brought about numerous changes on crystal morphology, surface area, pore volume and pore size. Physiochemical properties of gel were investigated as using XRD, TEM, TG/DTA, FT-IR and $N_2$ BET method.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.351-356
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• 2014

A spherical $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was $1,100^{\circ}C$. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the $4f^65d{\rightarrow}4f^7$ electronic transitions of $Eu^{2+}$. The critical quenching-concentration of $Eu^{2+}$ in the synthesized $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor was 5 mol%. A phosphor-converted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.