• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.626-634
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• 1995

The SiC-porcelain powder mixtures containing 51.9wt% SiC are produced as by-products from the surface abrasion process of porcelain cores. This raw powders were used as starting materials for the synthesis of SiC containing ceramics. The specimen, which was fired at 135$0^{\circ}C$ from raw powders, had SiC, $Al_{2}O_{3}$, , cristobalite, mullite as crystalline phases, and the fractured microstructure showed dispersed SiC crystalline particles almost wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts wetted with glassy matrix and spherical pores. Although the oxidation of SiC containing powder compacts started at the range of 600~80$0^{\circ}C$ form the analysis of weight gain, the presence of $SiO_{2}$ crystallien phase and cristobalite was confirmed at 100$0^{\circ}C$ by XRD analysis. Mullitization of specimens was accelerated by preheating before the final firing. The specimen sintered at 135$0^{\circ}C$ after 100$0^{\circ}C$ preheating consisted of SiC, cristobalite, mullite as crystalline phases, and revealed 2.24g/$cm^{3}$ bulk density, 11.73% water adsorption, porous microstructure with small amount of glassy phase. SiC contents of specimens, which was 51.9 wt% in the raw powders, reduced to 37~22 wt% after firing at 135$0^{\circ}C$ depending on the preheating condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.995-999
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• 2007

The lead zirconate titanate (PZT) powders were synthesized to make the piezoelectric ceramics in low temperature as low as $900^{\circ}C$. To investigate the influence of additives on sintering of PZT, two kinds of sintering aids were made as follows; $wB_2O_3-xBi_2O_3-zCuO$and LiBiO2-CuO. The sintering aid, $1{\sim}3$ wt.% $LiBiO_2-CuO$, was added into these PZT powders and the specimens were fired at temperature in the range of $800{\sim}1200^{\circ}C$. The highest density was shown in the specimen with 1 wt.% $LiBiO_2-CuO$ as additive at temperature of $900^{\circ}C$. The sintered specimen were analyzed by X-ray diffraction(XRD) and scanning electron microscopy (SEM) was utilized to observe the microstructure, especially the densified morphology of specimens. In the XRD pattern, the well-crystallized PZT phase could be obtained in consequence of firing at $900^{\circ}C$. The scanning electron microscopy(SEM) was utilized to observe the structure of specimens after firing at $900^{\circ}C$. The densified perovskite structure of $PbZrTiO_3$ could be obtained by sintering at temperature as low as $900^{\circ}C$. The high sinterability of PZT ceramics was attributed to the low formation temperature of the liquid phase of additives.

• Applied Chemistry for Engineering
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• v.31 no.6
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• pp.646-652
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• 2020

In this study, an NH3-selective catalytic reduction (SCR) experiment was performed to control NOx in the temperature range of 200~500 ℃. The reaction activity experiment was conducted by varying the firing temperature of Sb/TiO2 when using V/Sb/TiO2 composite as a catalyst. As a result, when the sintering temperature of Sb/TiO2 was 600 ℃, the efficiency was the best, and it was confirmed that the NOx conversion rate was close to 80% at the reaction temperature of 250 ℃. H2-temperature programmed reduction (TPR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses were employed to derive the cause of the activity enhancement when prepared at different firing temperatures as described above. As a result, when the sintering temperature of Sb/TiO2, which showed an excellent activity, was prepared at 600 ℃, it was confirmed that VSbO4 was generated. This indicates that the non-stoichiometric species of V increased, resulting in the excellent NOx conversion rate of V/Sb/TiO2.

• Journal of Conservation Science
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• v.37 no.2
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• pp.77-89
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• 2021

In this study, materials and color formation techniques were assessed for black potteries excavated from the Janghyeon-dong, Jungsan-dong and Gyodong-ri sites during the Proto-Three Kingdoms period in Ulsan, Korea. Although the black potteries were black superficially, the inner cores were either black or reddish yellow. Microscopy analysis identified that body clay was used for reddish iron oxide rich soils with quartz, alkali feldspar and mica, along with grains of myrmechite texture. Additionally, as marginal differences exist in the contents of SiO₂, Fe₂O₃ and CaO, the composition of the host rock and clay distributed around the sites was affected. Thus, we can deduce that pottery was made by soiling at a short distance. Raman spectroscopy results revealed that the black layer of the black pottery was used as amorphous combustion carbon. In addition, as a transparent layer of brown lacquer was observed on the substrate that was in contact with the surface layer, the black layer of the pottery induced black color development by a combination of combustion carbon and lacquer. Based on the mineral composition and microtexture of the body clay, the firing temperature of the potteries seemed to range from 750 to 850℃, whereas the lacquer layer was pyrolyzed at 468℃ by thermal analysis. Therefore, a combined layer of combustion carbon and lacquer, which formed the black color, was painted after the body clay was fired.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.795-800
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• 2009

In this study, the $CO_2$ removal characteristics of the Vortex tube type absorbtion apparatus were investigated to enhance the compactness of $CO_2$ absorption process and to reduce the amount of absorbing solution of the $CO_2$ separation process. The Vortex tube with the diameter of 17 mm and the length of 250mm was introduced in the experimental apparatus to treat $20Nm^3/hr$ of $CO_2$ containing flue gas. The flue gases for experiments containing 11~13 vol% of $CO_2$ were supplied from the coal-firing CFBC power plant with 12 ton/hr of steam producing capacity. The mixed solutions of 20 wt% of MEA as base solution with the adding solutions like HMDA, AMP and KOH were used as absorbents. The experiments were executed under the various conditions like the absorbing solution concentrations in the range of 20 to 50 wt%, the flow rate of $CO_2$ containing flue gases in the range of 6 to $15Nm^3/hr$ and the flow rate of absorbing solution in the range of 1.0 to 3.0 l/min. As a results, the $CO_2$ removal efficiency of mixed absorbent of 20 wt% of MEA with HMDA was remarkable. From this study, we concluded that the efficient separation of $CO_2$ from flue gases using the features of the Vortex tube type absorbing unit for gas/liquid contact and the separation of gas/liquid be possible. But more works are needed to increase the $CO_2$ removal efficiency of Vortex tube process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.2
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• pp.87-90
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• 2002

$LiCoO_{2}$ powders were synthesized at various temperatures using lithium hydroxide and cobalt hydroxide as precursors prepared by precipitation process and freeze-drying. In this study, the$LiCoO_{2}$ samples were synthesized via a solid state reaction with various LiOH concentration between 10 % and 30 % excess. And $LiCoO_{2}$powders were calcined at 600~$800^{\circ}C$ in a short time. Measurements of XRD and SEM were performed to characterize the properties of the prepared materials. The effect of amount of Li ions on the structural change in powder has been examined using the XRD analysis. For the not added excess of LiOH, CoOOH phase presented in the XRD pattern of $LiCoO_{2}$ due to loss of Li ions during firing. The morphology and particle size of the powders were examined using SEM. The obtained powders are high temperature-$LiCoO_{2}$HT-LiCoO$_{2}$) and homogeneous with the range of grain size in the order of hundreds of nanometers. The effects of variation of LiOH concentration on the structural change in powder were investigated using the Rietveld analysis. As an analysis result, c/a is constant by 4.99 on all occasions. Finally, the structure of HT-$LiCoO_{2}$ was simulated by the commercial software $Creius^{2}$(Molecular Simulations, Inc.) from the results of Rietveld analysis.

• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.19-27
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• 2015

Permissible soil concentrations for explosives (i.e., TNT and RDX) and heavy metals (i.e., Cu, Zn, Pb, and As) heve been derived from human risk and ecotoxicity, respectively. For TNT and RDX, human risk based-permissible soil concentrations were determined as 460 mg-TNT/kg-soil and 260 mg-RDX/kg-soil. Ecotoxicity based-permissible soil concentrations for Cu and Zn were determined from species sensitivity distribution (SSD) and uncertainty factor of 1 to 5, yielding 18.0-40.0 mg-Cu/kg-soil and 46.0-100 mg-Zn/kg-soil. For Pb and As, ecotoxicity data were not enough to establish SSD so that a deterministic method was used, generating 13.8-30.8 mg-Pb/kg-soil and 2.10-4.60 mg-As/kg-soil. It is worth noting that the methodology used to derive permissible concentrations in soil can differ depending on ecotoxicity data availability and socio-economic situations, which results in different permissible concentrations. The permissible concentrations presented in this study have been derived from conservative assumptions for exposure parameters, and thus should be considered as soil standards. In the light of remediation and pollution management of a site of interest, the site-specific and receptor-specific permissible soil concentrations should be derived considering potential receptors, current and future land use, background concentrations, and socio-economic consultation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.10
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• pp.754-759
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• 2013

Aluminum oxide($Al_2O_3$) film deposited by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surfaces. Since $Al_2O_3$ has fixed negative charge, it forms effective surface passivation by field effect passivation on the rear side in p-type silicon solar cell. However, $Al_2O_3$ layer formed by ALD process needs very long process time, which is not applicable in mass production of silicon solar cells. In this paper, plasma-assisted ALD(PA-ALD) was applied to form $Al_2O_3$ to reduce the process time. $Al_2O_3$ synthesized by ALD on c-Si (100) wafers contains a very thin interfacial $SiO_2$ layer, which was confirmed by FTIR and TEM. To improve passivation quality of $Al_2O_3$ layer, the deposition temperature was changed in range of $150{\sim}350^{\circ}C$, then the annealing temperature and time were varied. As a result, the silicon wafer with aluminum oxide film formed in $250^{\circ}C$, $400^{\circ}C$ and 10 min for the deposition temperature, the annealing temperature and time, respectively, showed the best lifetime of 1.6ms. We also observed blistering with nanometer size during firing of $Al_2O_3$ deposited on p-type silicon.

• Journal of Conservation Science
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• v.8 no.1 s.11
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• pp.10-15
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• 1999

The chemical compositions and microstructure of the punch'ong excavated from Bokwangri, Kangnung were investigated by the scanning electron microscope (SEM) with an energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), and dilatometer. The compositions of body were $SiO_2(73-78\%),\;Al_2O_3(13-16\%)$, $RO{\cdot}R_2O(4-5\%,\;R=Ca,\;Mg,\;Na,\;K),\;R_xO_y(3-6\%,\;R=Fe,Ti)$ in weight ratio, which were higher silica and flux $(RO{\cdot}R_2O)$ but lower alumina. Owing to the high content$(21-30\%)$ of calcium oxide the glaze is considered lime type. Firing temperature range for the ceramic was presumed to about $1150^{\circ}C$.

• Journal of Biomedical Engineering Research
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• v.32 no.1
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• pp.55-60
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• 2011

Although sound intensity is considered as one of important factors in auditory processing, its neural mechanism in auditory neurons with limited dynamic range of firing rates is still unclear. In this study, we examined the effect of sound intensity adaptation on the change of glucose metabolism in a rat brain using [F-18] micro positron emission tomography (PET) neuroimaging technique. In the experiment, broadband white noise sound was given for 30 minutes after the [F-18]FDG injection in order to explore the functional adaptation of rat brain into the sound intensity levels. Nine rats were scanned with four different sound intensity levels: 40 dB, 60 dB, 80 dB, 100 dB sound pressure level (SPL) for four weeks. When glucose uptake during the adaptation of a high intensity sound level (100 dB SPL) was compared with that during adaptation to a low intensity level (40 dB SPL) in the experiment, the former induced a greater uptake at bilateral cochlear nucleus, superior olivary complexes and inferior colliculi in the auditory pathway. Expectedly, the metabolic activity in those areas linearly increased as the sound intensity level increased. In contrast, significant decrease interestingly occurred in the bilateral auditory cortices: The activities of auditory cortex proportionally decreased with higher sound intensities. It may reflect that the auditory cortex actively down-regulates neural activities when the sound gets louder.