• Journal of the Korean Crystal Growth and Crystal Technology
• /
• 제14권4호
• /
• pp.129-134
• /
• 2004

In this study, we investigated the effect of a nitrogen atom on the amorphization of V-Fe alloy through solid-gas reaction during mechanical alloying (MA). MA by planetary ball mill of $V_{70}Fe_{30}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed after 160 hours of ball milling in this case. The DSC spectrum for the mechanically alloyed ($V_{70}Fe$_{30}$)_{0.89}N_{0.11}$ powders exhibits a sharp exothermic peak due to crystallization at about $600^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was also observed through X-ray and neutron diffractions. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is selectively situated at a center of the polyhedron formed by V atoms.

• Bulletin of the Korean Chemical Society
• /
• 제34권9호
• /
• pp.2769-2773
• /
• 2013

Red phosphors $Ca_{(1-1.5x)}Eu_xWO_4$ and $Ca_{(1-2x)}Eu^_xNa_xWO_4$ were synthesized with various concentrations x of $Eu^{3+}$ ions by using a solid-state reaction method. The crystal structure of the red phosphors were found to be a tetragonal scheelite structure with space group $I4_1/a$. X-ray diffraction (XRD) results show the (112) main diffraction peak centered at $2{\theta}=28.71^{\circ}$, and indicate that there is no basic structural deformation caused by the vacancies ${V_{Ca}}^{{\prime}{\prime}}$ or the $Eu^{3+}$ (and $Na^+$) ions in the host crystals. Densities of $Ca_{(1-1.5x)}Eu_xWO_4$ were measured on a (helium) gas pycnometer. Comparative results between the experimental and theoretical densities reveal that $Eu^{3+}$ (and $Na^+$) ions replace the $Ca^{2+}$ ions in the host $CaWO_4$. Also, the photoluminescence (PL) emission and photoluminescence excitation (PLE) spectra show the optical properties of trivalent $Eu^{3+}$ ions, not of divalent $Eu^{2+}$. Raman spectra exhibit that, without showing any difference before and after the doping of activators to the host material $CaWO_4$, all the gerade normal modes occur at the identical frequencies with the same shapes and weaker intensities after the substitution. However, the FT-IR spectra show that some of the ungerade normal modes have shifted positions and different shapes, caused by different masses of $Eu^{3+}$ ions (or $Na^+$ ions, or ${V_{Ca}}^{{\prime}{\prime}}$ vacancies) from $Ca^{2+}$.

• Applied Chemistry for Engineering
• /
• 제8권5호
• /
• pp.729-736
• /
• 1997

For the recovery of industrial waste heat, a chemical heat transformer based on the reversible reaction between metal chlorides and ammonia gas was designed and a pilot scale unit of 1 kW-1hr was developed. A static calculation, which determined the amount of reacting materials and operating condition of system, and dynamic simulations were performed for the optimal design. The temperature and output power of generator in the system were varying with the amount of salt and heat exchange area. Optimum conditions such as the amount of salt-graphite, apparent density and size of mechanical unit were determined by the dynamic simulation for the system. According to the operating cycle of 4 stages, experimental results of temperature and output power were well agreed with the simulation values. This chemical heat transformer is turned out to be a very promising system for recovery of industrial waste heat because of its effective feature of lifting temperature.

• Journal of the Korean Chemical Society
• /
• 제46권2호
• /
• pp.164-168
• /
• 2002

SrGa$_2$S$_4$ : Eu is a green emitting phosphor which is applied for field emission display, and cathodoluminescence. Conventionally, SrGa$_2$S$_4$ : Eu is synthesized by solid state reaction, in which a mixture of SrCO$_3$, Ga$_2$O$_3$, and Eu$_2$O$_3$ is fired at high temperatures under flowing H$_2$S and Ar gases. In this study,SrGa$_2$S$_4$ : Eu phosphor is synthesized by using a decomposition method, where SrS, Eu complex, and Ga com-plex are used. The advantage of this method is that toxic H$_2$S gas and Ar gas are not used. The synthetic con-ditions and luminescent properties of SrGa$_2$S$_4$ : Eu phosphor are also investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• 제10권4호
• /
• pp.292-296
• /
• 2000

Mechenochemical reaction by planetary type ball mill is applied to prepare $Sm_2$$Fe_{17}$$N_{x}$ permanent magnet powders. Starting from pure samarium and iron powders, the formation process of hard magnetic $Sm_2$$Fe_{17}$$N_{x}$ phase by ball milling and a subsequent solid state reaction were studied. At as-milled stage powders were found to consist of amorphous Sm-Fe and $\alpha$-Fe phases in all composition of $Sm_2$$Fe_{100-x}$(x = 11, 13, 15). The dependence of starting composition of elemental powder on the formation of Sm-Fe intermetallic compound was investigated by heat treatment of as-milled powders. When Sm concentration was 15 at%, heat-treated powder consists of mostly $Sm_2$$Fe_{17}$$N_{x}$single phase. For synthesizing of hard magnetic $Sm_2$$Fe_{17}$$N_{x}$ compound, additional nitriding treatment was carried out under $N_2$gas atmosphere at $450^{\circ}C$. The increase in the coercivity and remanence was parallel to the nitrogen content which increased drastically at first and then gradually as the nitriding time was extended. The ball-milled Sm-Fe-N powders were expected to be prospective materials for synthesizing of permanent magnet with high performance.

• Korean Chemical Engineering Research
• /
• 제56권6호
• /
• pp.856-863
• /
• 2018

In order to investigate the re-carbonation behaviors of limestones in an oxy-circulating fluidized bed combustor (Oxy-CFBC), the re-carbonation characteristics of domestic 4 different limestone samples were analyzed in a thermogravimetric analyzer (TGA-N1000) with the higher concentration of $CO_2$. Effect of reaction temperature ($600{\sim}900^{\circ}C$) and $CaCO_3$ content (77~95%) of limestones were determined and the mass change of the CaO was observed. Under the temperature of $800^{\circ}C$, the conversion rate increased with increasing reaction temperature. However, the conversion rate decreased with increasing reaction temperature over $800^{\circ}C$. In the case of $CaCO_3$ content, the conversion was remarkably different at $870^{\circ}C$. In addition, reaction rate equations for simulating the re-carbonation of limestone by using gas solid reaction models were proposed in this study.

• Journal of Energy Engineering
• /
• 제20권1호
• /
• pp.36-43
• /
• 2011

Plant biomass has been proposed as an alternative source of petroleum-based chemical compounds. Especially, aromatic chemical compounds can be obtained from lignin by depolymerization processes because the lignin consist of complex aromatic materials. In this study, kraft lignin, the largest emitted substance among several kinds of lignin in Korea, was used as a starting material and was characterized by solid-state $^{13}C$-Muclear Magnetic Resonance($^{13}C$-NMR), Fourier Transform Infrared Spectroscopy(FT-IR), Elemental Analysis(EA). The depolymerization of kraft lignin was studied at water-phenol mixture solvent in near critical region and the experiments were conducted using a batch type reactor. The effects of water-to-phenol ratio and reaction temperature($300-400^{\circ}C$) were investigated to determine the optimum operating conditions. Additionally, the effects of formic acid as a hydrogen-donor solvent instead of $H_2$ gas were examined. The chemical species and quantities in the liquid products were analyzed using gas chromatography-mass spectroscopy(GC-MS), and solid residues(char) were analyzed using FT-IR. GC-MS analysis confirmed that the aromatic chemicals such as anisole, o-cresol(2-methylphenol), p-cresol(4-methylphenol), 2-ethylphenol, 4-ethylphenol, dibenzofuran, 3-methyl cabazole and xanthene were produced when phenol was added in the water as a co-solvent.

• Resources Recycling
• /
• 제15권5호
• /
• pp.47-51
• /
• 2006

The total amount of ash generated from the municipal solid waste incineration(MSWI) in Korea was approximately 420,000 tons in 2005 including 68,000 tons of fly ash. Fly ash from MSWI generally contains high amount of CaO (upto ${\sim}50%$) due to the treatment of flue gas by spraying CaO-base materials. Currently, most of fly ash generated is finally ended up with specially designed landfill sites and only less then 20% of fly ash is recycled. In the present work, preparation of $CaCO_3$ from the MSWI ny ash was studied to promote the fly ash recycling. Fly ash obtained from the dust collector in stoker-type MSWI is used to selectively dissolve CaO by using the sugar solution. Then, $CO_2$ gas was passed through the dissolved solution to pro- duce $CaCO_3$ powder. The optimum conditions for CaO dissolution were solid content 10%, reaction time 15 minutes, sugar concentration $10{\sim}15%\;and\;pH\;10.5{\sim}11.0$. The high grade $CaCO_3$ powder was obtained and the experimental conditions are also discussed.

• Applied Chemistry for Engineering
• /
• 제26권2호
• /
• pp.154-158
• /
• 2015

In this study, the catalytic activity of ${\gamma}-Al_2O_3$ was investigated for the decomposition of $NF_3$. Reactions for $NF_3$ decomposition were carried out in the range of reaction temperature of $330{\sim}730^{\circ}C$ and GHSV of $3,000{\sim}15,000mL/g-cat{\cdot}h$ in a fixed-bed catalytic reactor system. Thermal decomposition of $NF_3$ was also performed in order to compare with the catalytic decomposition of $NF_3$. The conversion of $NF_3$ by the catalytic decomposition at $400^{\circ}C$ was four times higher than that of the thermal decomposition. It was confirmed that the reaction behavior of $NF_3$ over ${\gamma}-Al_2O_3$ exhibited two reaction pathways in the presence of steam. Fluorine in $NF_3$ over ${\gamma}-Al_2O_3$ was chemically absorbed to $AlF_3$ by the gas-solid reaction in the absence of steam. The catalytic decomposition of $NF_3$ occurred by hydrolysis with steam. It was also confirmed by FT-IR analysis that $NF_3$ was completely decomposed to NOx and HF above $500^{\circ}C$.

• Journal of the Korean Society of Food Science and Nutrition
• /
• 제43권1호
• /
• pp.102-109
• /
• 2014

Crab-like flavoring base (CFB) was made from a concentrated snow crab cooker effluent (SCCE) containing five food additives (proline, glycine, arginine, methionine, fructose) using reaction flavor technology (RFT). The volatile flavor compounds in CFB were compared between raw (SCCE) and control (without food additives) samples using solid phase microextraction (SPME) and gas chromatography with mass selective detector. A total of 74 compounds were detected in all samples (30 raw samples, 34 control samples, 55 CFB samples). A total of 22 nitrogen-containing compounds, including 19 pyrazines and 3 pyridines, were formed through RFT and increased 27 times compared to the control. Dimethyl trisulfide and dimethyl disulfide were predominant sulfur-containing compounds that increased through RFT, while aromatic compounds decreased through RFT. Seven compounds, tetramethylpyrazine, 2-ethyl-3,5,6-trimethylpyrazine, 2,3,5-trimethyl-6-(3-methylbutyl)pyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,5-dimethyl-3-(3-methylbutyl)pyrazine, 2-ethyl-3,6-dimethylpyrazine, and 2-decanone potentially have a role in CFB odor by Pearson's correlation analysis.