• 한국대기환경학회지
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• 제20권3호
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• pp.411-419
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• 2004

Titania particles are widely used as a photocatalyst to treat various contaminants in air and water. Titania particles were formed by vapor-phase oxidation of titanium tetraisopropoxide (TTIP) in a tube furnace between 773 and 1,273 K. The effect of process variables such as furnace temperature, flow rate of carrier air, and flow rate of sheath air on powder size and phase characteristics was investigated using a scanning mobility particle sizer (SMPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The size distribution of synthesized titania particles was characterized with mode diameter and peak concentration. The mode diameter ranging from 20 to 80 nm decreased with increasing flow rates of sheath air and carrier air, and increased with increasing furnace temperature. The peak concentration increased with increasing flow rates of sheath air and carrier air The best synthetic condition for high production rate can be derived from the experimental data set represented by mode diameter and peak concentration. The crystal structure of synthesized titania particles was found to be anatase phase, ensuring high photocatalytic potential.

• 한국주조공학회지
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• 제15권3호
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• pp.283-290
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• 1995

Molybdenum ingot of 50mm in diameter were obtained from sintered Mo bars by EB drip melting technique. Macroscopic observation of EB remelted ingot indicates that coarse and columnar grains grow in the direction parallel to ingot pulling direction. This can be explained by slow solidification (3mm/min), large temperature gradient and heat flow to this direction. The orientation of columnar structure was found to be <110>, <200> and <211> by the analysis of X-ray diffraction patterns. The contents of typical metallic impurities in Mo sintered bar are 1.2ppm Cr, 3ppm Fe, 44ppm Zr, 150ppm W. Most of metallic impurities were reduced below the order of ppm except zirconium and tungsten by the selective evaporation. In the removal of nonmetallic impurities, oxygen and carbon impurities were lowered from 120 to 6ppm and from 157 to 106ppm, respectively, after first melting. Although the purification effect was not significant with the number of remelting, Vickers hardness was reduced from 217 to 195 and 184 in sequence with increasing the number of remelting.

• 대한치과기공학회지
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• 제14권1호
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• pp.23-43
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• 1992

Corrosion characteristics of four commerial gold-based dental alloys(C-1; Au75%, Ag13.9%, Pd3%, Cu & etc.,8.1%, C-2 ;Au 52.08, Ag 24%, Pd 5%, Cu & etc.,18.92, C-3 ; Au 53%, Ag 22%, Pd 5%, Pt 3% Cu & etc.,17%, C-4 ; Au 53%, Pd4, Pt1.5%, Ag & Cu & etc.,41.5%) and four experimental ternary Au-Ag-Cu alloys(E-1 ; Au 50%, Ag 30%, Cu 20%, E-2 ; Au 50%, Ag 20%, Cu 30%, E-3 ; Au 50%, Ag 10%, Cu 40%, E-4 ; Au 50%, Ag 40%, Cu 10%) were investigated by potentiodynamic polarization analysis and the structure was examined by optical microscope and SEM. All corrosion testing was conducted in 1% NaCl solution. The main results are as follows : 1. The corrosion resistence of commercial alloys was decreased in the order of C-1, C-3, C-4, C-2. C-2. 2. The E-1 and E-3 ternary alloys exhibits the higher corrosion resistence than E-2 and E-4 alloys. 3. The cast microstructure of alloys reveals dendrite morphology which shows the significant microsegregation caused by the difference in the diffusion rate between liquid and solid. 4. It is found that the surface corrosion products were mainly AgCl by X-ray diffraction results.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집
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• pp.1-6
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• 2004

In this paper author describe the undoped and $Co^{2+}$ (0.5mole%)doped $Cd_4GeS_6$ single crystals were grown by the chemical transporting reaction(CTR) method using high purity(6N) Cd, $GeS_2$, S elements. It was found from the analysis of X-ray diffraction that the undoped and $Co^{2+}$(0.5mole%) doped $Cd_{4}GeS_{6}$ compounds have a monoclinic structure in space grop Cc. The optical energy band gap was direct band gap and temperature dependence of optical energy gap was fitted well to Varshni equation. Impurity optical absorption peaks due to the doped cobalt in the $Cd_4GeS_6:Co^{2+}$ single crystal were observed at 3593cm-1, 5048cm-1, 5901cm-1, 7322cm-1, 12834cm-1, 13250cm-1, 14250cm-1，and 14975cm-1 at 11.3K.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 영호남 합동 학술대회 및 춘계학술대회 논문집 센서 박막 기술교육
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• pp.27-30
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• 2006

In this paper, the undoped and Co-doped $Zn_4SnSe_6$ single crystals grown by the chemical transporting reaction(CTR) method using iodine as a transporting agent are investigated. For the crystal growth, the temperature gradient of the CTR furnace was kept at $680^{\circ}C$ for the source zone and at $780^{\circ}C$ for the growth zone for 7days. It was found from the analysis of x-ray diffraction that the $Zn_4SnSe_6$ and $Zn_4SnSe_6Co^{2+}$ compounds have a monoclinic structure. The direct optical energy band gap of the $Zn_4SnSe_6$ and $Zn_4SnSe_6Co^{2+}$ single crystals at 300K were found to be 2.146eV and 2.042eV.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1594-1596
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• 1997

$LiMn_2O_4$ is prepared by reacting stoichiometric mixture of LiOH $H_2O$ and $MnO_2$ (mole ratio 1 : 2) and calcinating at $800^{\circ}C$ for 24h, 36h, 48h, 60h and 72h. At X-ray diffraction, cathode active materials calcined at $800^{\circ}C$ for 36h. (111)/(311) peak ratio was 0.37. It was that crystal structure is formed very well. In the result of charge/discharge test, when heated at $800^{\circ}C$ for 36h, charge/discharge characteristics of $LiMn_2O_4$ is the best and Super-s-black sort of conductive agent showed well property. Also, AC impedance creased gradually during cycling and stabilized after 10cycle.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3420-3424
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• 2013

The reaction of $LnCl_3{\cdot}7H_2O$ [Ln = La (1), Ce (2)] with salicylic acid (HL) and 1,10-phenanthroline (Phen) at $20^{\circ}C$ in $H_2O$/ethanol gave after work-up and recrystallization two novel lanthanide complexes with general formula $[Ln(Phen)_2(L)_3(HL)]{\cdot}H_2O$. Compounds 1 and 2 were characterized by IR and UV-Vis spectroscopy, TGA, CHN as well as by X-ray analysis. According to these results, compounds 1 and 2 are isostructural and contain $Ln^{3+}$ ions with coordination number nine. Complexes 1 and 2 consist of two Phen, one neutral HL and three L anions (two L anions act as monodentate ligands and the third one is chelating to $Ln^{3+}$). Thermal decomposition led to primary loss of the Phen molecules. Then HL molecules and finally L moieties left the material to give $Ln_2O_3$.

• Elastomers and Composites
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• 제53권2호
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• pp.57-66
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• 2018

Styrene-butadiene rubber (SBR), reinforced with different contents of silica (with or without modification using silane coupling agents), was prepared by a modified sol-gel method involving hydrolyzation of tetraethoxysilane over an acid catalyst. The structures of the as-prepared samples were characterized using various techniques, such as scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The mechanical properties of the as-prepared samples were discussed in detail. The results revealed an increasing of the storage modulus (G') with increase in the silica content without modification. In contrast, G' decreased after modification using silane coupling agents, indicating a reduction in the silica-silica interaction and improved dispersion of silica in the SBR matrix. Both tensile stress and hardness increased with increase in the silica content (with modification) in the SBR matrix, albeit with low values compared to the samples with un-modified silica, except for the case of silica modified using (3-glycidyloxypropyl) trimethoxysilane (GPTS). The latter observation can be attributed to the special structure of GPTS and the effort of oxygen atom lone-pair.

• 한국세라믹학회지
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• 제35권6호
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• pp.559-568
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• 1998

Studies of preparation condition and characteristics of AUC(ammonium uranyl carbonate) were carried out to optimize AUC process with different reactor sizes and precipitation methos. As results four types of precipitates with different chemical compositions and morphologies were obtained from the reaction of {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 } }} with {{{{ {UO }_{2 }( {NO }_{3 }) { }_{2 } }} solution. A phase diagram has been made and crystal structure and chemical composition of each phase have been characterized by using SEM X-ray IR and thermal analysis. It was found that ammonium uranyl carbonate {{{{ {(NH }_{4 }) { }_{4 } {UO }_{2 } {(CO }_{3 }) { }_{3 } }} with monoclinic crystal morphology could be syn-thesized when the mole ratio of in {{{{ {(NH }_{4 }) { }_{2 } {CO }_{3 }/ {UO }_{2 } {(NO }_{3 }) { }_{2 } }} in the solution was higher than 5 Also a mechanism and a precipitating condition on rounding of the AUC particle were examined in the course of the AUC pre-cipitation. The rounding of the AUC particle was possible only by external circulation using pump not by internal circulation using agitator.

• Advances in concrete construction
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• 제4권2호
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• pp.89-105
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• 2016

The post - fire investigation is conducted on a fire-affected reinforced concrete shear wall building to ascertain the level of its strength degradation due to the fire incident. Fire incident took place in a three-storey building made of reinforced concrete shear wall and roof with operating floors made of steel beams and chequered plates. The usage of the building is to handle explosives. Elevated temperature during the fire is estimated to be $350^{\circ}C$ based on visual inspection. Destructive (core extraction) and non-destructive (rebound hammer and ultrasonic pulse velocity) tests are conducted to evaluate the concrete strength. X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) are used for analyzing micro structural changes of the concrete due to fire. Tests are conducted for concrete walls and roof slab on both burnt and unburnt locations. The analysis of test results reveals no significant degradation of the building after the fire which signifies that the structure can be used with full expectancy of performance for the remaining service life. This document can be used as a reference for future forensic investigations of similar fire affected concrete structures.