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2006, Vol.16, No.5

  • 1.

    Analysis of rutile single crystals grwon by skull melting method

    SEOK, JEONG-WON | Choi Jong Keon | 2006, 16(5) | pp.181~188 | number of Cited : 0
    Abstract PDF
    Rutile single crystals grown by skull melting method were cut paralel and perpendicular to growth axis, and bothsides of the cut wafers (5.5 m×1.0 m) were then polished to be miror surfaces. The black wafers were changed into paleyellow color by annealing in air at 1200 and 1300oC for 3~15 and 10~50 hours, respectively. After annealing, structural and(XRD), FT-IR transmittance spectra, laser Raman spectroscopy (LRS), photoluminescence (PL) and X-ray photoelectronspectroscopy (XPS). These results are analyzed increase of weight in air, decrease of weight in water and specific gravity,shown secondary phase of needle shape, diffusion of oxygen ion and increase of Ti3+. From the above results, we suggest thatthe skull melting method grown rutile single crystals contain defect centers such as Ov,-Ti3+, Ov-Ti3+ interstitials and F+-H+.Key words Rutile, Ov,-Ti3+, Ov-Ti3+ interstitial, F+-H+Skull melting.. .. ... rutile ... .....†.. ........ ..... , .. , 520-714......... , .. , 133-791(2006. 7. 3. .. )(2006. 8. 8. .... )
  • 2.

    Growth and effect of thermal annealing for AgGaSe2 single crystal thin film by not wall epitaxy

    Baek,Seung-Nam | Kwangjoon Hong | 김장복 | 2006, 16(5) | pp.189~197 | number of Cited : 0
    Abstract PDF
    A stoichiometric mixture of evaporating materials for AgGaSe2 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, AgGaSe2 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were 630oC and 420oC, respectively. The temperature dependence of the energy band gap of the AgGaSe2 obtained from the absorption spectra was well described by the Varshni뭩 relation, Eg(T) = 1.9501 eV - (8.79 ?10-4 eV/K)T2/(T + 250 K). After the as-grown AgGaSe2 single crystal thin films was annealed in Ag-, Se-, and Ga-atmospheres, the origin of point defects of AgGaSe2 single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of VAg, VSe, Agint, and Seint obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Ag-atmosphere converted AgGaSe2 single crystal thin films to an optical p-type. Also, we confirmed that Ga in AgGaSe2/GaAs did not form the native defects because Ga in AgGaSe2 single crystal thin films existed in the form of stable bonds.
  • 3.

  • 4.

    Effect of accelerational perturvations on physical vapor transport crystal growth under microgravity environments

    Jeong-Gil Choi | Moo Hyun Kwon | Geug-Tae Kim and 1other persons | 2006, 16(5) | pp.203~209 | number of Cited : 6
    Abstract PDF
    For PB = 50, DT = 10 K, Ar = 5, Pr = 2.36, Le = 0.015, Pe = 1.26, Cv = 1.11, the intensity of solutal convection (solutal Grashof number Grs = 3.44 ?104) is greater than that of thermal convection (thermal Grashof number Grt = 1.81 ?103) by one order of magnitude, which is based on the solutally buoyancy-driven convection due to the disparity in the molecular weights of the component A (Hg2Cl2) and B (He). With increasing the partial pressure of component B from 10 up to 200 Torr, the rate is decreased exponentially. The convective transport decreases with lower g level and is changed to the diffusive mode at 0.1 g0. In other words, for regions in which the g level is 0.1 g0 or less, the diffusion-driven convection results in a parabolic velocity profile and a recirculating cell is not likely to occur. Therefore a gravitational acceleration level of less than 0.1 g0 can be adequate to ensure purely diffusive transport.
  • 5.

    Fabrication of nonequilibrium alloy powders in immiscible Cu-Nb system by mechanical alloying

    Lee Chung-Hyo | 2006, 16(5) | pp.210~215 | number of Cited : 0
    Abstract PDF
    Mechanical alloying (MA) by high energy ball mill of pure copper and niobium powders was carried out underthe Ar gas atmosphere. The supersaturated solid solution can be produced in the range up to CuxNb100 x (x = 5-30) by MAsuperconducting transition in the low-temperature specific heat. The Cu30Nb70 samples ball-milled for 120 hrs exhibit only abroad exothermic heat release. The total energy, Ht accumulated during MA for the mixture of Cu30Nb70 powders increasedwith milling time and approached the saturation value of 7.5 kJ/mol after 120 h of miling. It can be seen that the freenergy diference between the supersaturated solid solution and the mixture of Cu30Nb70 powders is estimated to be 7 kJ/mol by Miedema et al. Hence it is thermodynamicaly posible to assume the formation of a supersaturated solid solutionKey words Mechanical alloying, Immiscible Cu-Nb system, Supersaturated solid solution, Total enthalpy, Superconductingtransition... .... .. ... Cu-Nb. ... ... .....†..... ...... , .. , 534-729(2006. 9. 20. .. )(2006. 10. 2. .... ). . . ..... . Cu . Nb ..... ... Ar ... . .... ..... .... ... ...(MA) ... ..... . CuxNb100 x(x = 5-50) ... ..... .. 120.... MA ... .. , Cu. bcc-Nb ....... 30 at% Cu.. .... X. .... , DSC ... . .... ... .. ... .... ..... .. ... . 120.. MA ... Cu30Nb70 ..... ... .. broad. ...... ...... , ..... ...
  • 6.

    Preparation of WO3/TiO2 and V2O5/TiO2 powders and their catalytic performances in the SCR of NOX

    BYEONG WOO LEE | TAE-SUK LEE | Shin Dong-Woo and 1other persons | 2006, 16(5) | pp.216~221 | number of Cited : 1
    Abstract PDF
    An investigation of the influence of WO3 and V2O5 catalysts on the microstructure, phase formation and selective catalytic reduction (SCR) efficiency of the synthesized SCR powders has been carried out. A commercial anatase-TiO2 was used as the catalysts support. For WO3(10 wt%)/TiO2, the W loading to the TiO2 support led to the lower in anatase to rutile transition temperature from 1200oC of TiO2 support to ~900oC. The transition temperature was also lowered to below 650oC in the V2O5 (5 and 10 wt%) added composition. The WO3(10 wt%)/TiO2 SCR powder obtained at 450oC showed near 100 % of NOX conversion efficiency at 350~400oC and for the powder prepared at 650oC the same efficiency was achieved in wider temperature range 300~400oC. The highest NOX conversion efficiency of 100 % was obtained in the V2O5(5 wt%)/TiO2 SCR composition calcined at 650oC in the relatively wider temperature range 250~350oC, while the catalytic efficiency considerably decreased for the V2O5(10 wt%)/TiO2. The lowered conversion efficiency of NOX observed in the V2O5(10 wt%)/TiO2 composition calcined at 650oC was considered to be correlated with the lowered surface area resulting from the increased crystallite growth by highly reactive vanadium loading.
  • 7.

    Enhancement in the physical properties of inorganic pigment layer in the color block by incorporationof a liquid additive

    Dongmyong Lee | Jin-Kon Kim | Cho, Hyun and 5other persons | 2006, 16(5) | pp.222~226 | number of Cited : 0
    Abstract PDF
    Effects of a carboxylated styrene-butadiene-based liquid additive on the microstructure, mechanical strength and decolorization resistance of inorganic pigment layer in the color block have been examined. More dense inorganic pigment layer characterized by lower apparent porosity, lower water absorption and uniform pigment distribution has been achieved by incorporation of a liquid additive. Also significant enhancements in the mechanical strength and decolorization resistance have been observed.
  • 8.

    Analysis of microstructure for glass-ceramics made of silicate glasses containing EAF dust

    KANG SEUNG GU | 김환식 | 2006, 16(5) | pp.227~234 | number of Cited : 2
    Abstract PDF
    Microstructures of fre surface and interior of glass-ceramics obtained by heat treating silicate glass specimencontaining electric arc furnace dust (EAF dust) were observed. The crystallization temperature, Tc of glassy specimen wasmeasured around 850ospecimen was selected as 950oC for 1 hr. Glass specimens containing 50 wt% dust were amorphous, while glass specimenscontaining 70 wt% dust showed spinel crystal peaks in XRD results. In case of glass-ceramic specimens, spinel crystalinephase was appeared with willemite, and willemite crystal peak intensity increased with increasing dust contents. Thefractured surface of glas specimens containing 50 wt% dust was smooth like mirror surface, but that containing 70 wt%dust showed spinel crystals of 10m size in glass matrix. In case of glass-ceramic specimens, ZnO crystal particles of2~5 m size were produced in free surface and glassy phase, spinel and wilemite crystal phases existed in interior. Therewere no crystals in glasses containing 50 wt% dust, while glas containing 70 wt% dust had 14 vol% crystals. Crystalinityof glas-ceramic specimens containing 50 and 70 wt% dust were 19 and 43 %, respectively. When microstructures of glassand glass-ceramic specimens were observed through SEM after TCLP experiment, glass specimens showed flakingphenomenon while glass-ceramic specimens showed a slight corosion evidence without any cracks.Key words