• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.150-155
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• 2014

In aprevious study, the mutual interaction between $Fe_2O_3$ and $TiO_2$ was found to influence the color of celadon glaze. Celadon samples were prepared with varying concentrations of $TiO_2$ at a fixed level of $Fe_2O_3$. The electronic states of Fe and Ti were analyzed by M$\ddot{o}$ssbauer spectroscopy and electron spin-resonance spectroscopy, respectively. These results were examined with the celadon colors measured according to CIELAB values. This study revealed that an increase of $Ti^{3+}$ in the glassy phase decreased the $Fe^{2+}/Fe^{3+}$ ratio, resulting in a color change of the celadon samples in the GY and Y groups. The maximum reflectance wavelength was shifted from 505 nm to 610 nm with an increase in the $TiO_2$ concentration.

• Archives of Pharmacal Research
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• v.24 no.4
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• pp.355-359
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• 2001

A novel HPLC method with electrochemical detection has been developed for the determination of recombinant human epidermal growth factor (rhEGF) in pharmaceutical products. rhEGF was separated from other components in formulation on a reversed-phase C18 column with 24% acetonitrile in 0.1 M phosphate buffer (pH 4.75). The optimum electrochemical oxidation of EGF was obtained at 0.85 V vs. Ag/AgCl in a glassy carbon working electrode due to electroactive tyrosine, tryptophan, methionine, and arginine residues. The quantitation range was from 1.0 to 200 ng of rhEGF with the linear correlation coefficient greater than 0.999. The method was successfully applied for the quantitation of rhEGF in a pharmaceutical preparation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.3
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• pp.339-352
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• 2021

Legacy waste from the decommissioned A-1 nuclear power plant in the Slovak Republic is scheduled for immobilisation within a tailored alkali borosilicate glass formulation, as part of ongoing site cleanup. The aqueous durability and characterisation of a simulant glass wasteform for Chrompik III legacy waste, was investigated, including dissolution experiments up to 112 days (90℃, ASTM Type 1 water). The wasteform was an amorphous, light green glassy product, with no observed phase separation or crystalline inclusions. Aqueous leach testing revealed a suitably durable product over the timescale investigated, comparing positively to other simulant nuclear waste glasses and vitreous products tested under similar conditions. Iron and titanium rich precipitates were observed to form at the surface of monolithic samples during leaching, with the formation of an alkali deficient alteration layer behind these at later ages. Overall this glass appears to perform well, and in line with expectations for this chemistry, although longer-term testing would be required to predict overall durability. This work will contribute to developing confidence in the disposability of vitrified Chrompik legacy wastes.

• Conservation and Restoration of Cultural Heritage
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• v.1 no.1
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• pp.9-22
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• 2012

The most widely excavated iron artifacts used as weapons or farm tools from central southern regions of Korea were subjects of non-metallic inclusion analysis through metallographic examination, microhardness measurement, and scanning electron microscopy with energy dispersive X-ray spectroscopy. Through metallographic interpretation and study of the analyzed results, the steel manufacturing and iron smelting using heat processing in the iron artifacts excavated from the central southern region of the ancient Korean peninsula was studied, and the analysis of the non-metallic inclusions mixed within the metallic structures was interpreted as the ternary phase diagram of the oxide to infer the type of iron ores for the iron products and the temperature of the furnace used to smelt them. Most of the ancient forged iron artifacts showed $Al_2O_3/SiO_2$ with high $SiO_2$ contents and relatively low $Al_2O_3$ contents for iron ore, indicating t hat for $Al_2O_3$ below 5%, it is presumed that magnetic iron ores were reduced to bloom iron (sponge iron) with direct-reduction process for production. The temperature for extraction of wustite for $Al_2O_3$ below 1% was found to be $1,020{\sim}1,050^{\circ}C$. Considering the oxide ternary constitutional diagram of glassy inclusions, the steel-manufacturing temperature was presumed to have been near $1,150{\sim}1,280^{\circ}C$ in most cases, and minimum melting temperature of casting iron part excavated in Daeseong-ri. Gyeonggi was near $1,400^{\circ}C$, and it is thought that hypoeutectic cast iron of about 2.3% carbon was casted and fragility of cast iron was improved by decarburizing in solid state.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.149-159
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• 2002

In the entrained flow gasifiers, the slag viscosity is an important parameter determining the operation conditions. The slag viscosities of 9 coals, which were selected and tested as possible gasification feedstock in Korea, were measured in a high temperature slag viscometer under gasification conditions. The type and size of crystalline phases that were known to affect the slag viscosity behavior were also determined. The slag samples were obtained from the IEA dry-feed gasifier. The slags of Alaska Usibelli, Curragh, Kideco, Adaro, Denisovsky, Baiduri and Drayton coals showed the behavior of crystalline slags, while those of Datong and Cypurus glassy slags. When a recommended minimum operating temperature was arbitrarily defined as $T_{1000}$poise/+$50^{\circ}C$ for glassy slags and $T_{cv}$ +$50^{\circ}C$ for crystalline slags, the Drayton slag required the lowest temperature, while Denisovsky slag required the highest. All the slags contained C $r_2$ $O_3$ from the refractory. The crystalline slags with $T_{cv}$ at around 132$0^{\circ}C$ contained large anorthites as the major crystalline phase that would have caused the rapid inrease in viscosity. Denisovsky slag contained many pores which were formed by $O_2$ from F $e_{x}$O reduction..

• Economic and Environmental Geology
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• v.50 no.2
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• pp.105-116
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• 2017

The purpose of this study is to provide the information on genesis of obsidian occurring in the southwestern part of Ulleung Island, Korea, and to discuss its implications for volcanic activity through volcanological and mineralogical properties of obsidian. Obsidian occurs locally at the lower part of the Gombawi welded tuff, showing various complex textures and flow banding. Though obsidian is mostly homogeneous, it is closely associated with alkali feldspar phenocrysts, reddish tuff, and greyish trachyte fragments. The obsidian occurs as wavy, lenticular blocks or lamination composed of fragments. Cooling fractures developed on obsidian glass are characterized by perlitic cracks, orbicular or spherical cracks, indicating that obsidian rapidly quenched to form an amorphous silica-rich phase. It is evident that hydration took place preferentially at the outer rim relative to the core of obsidian, forming alteration rinds. The glassy matrix of obsidian includes euhedral alkali feldspars, diopside, biotite, ilmenite, and iron oxides. Microlites in glassy obsidian are composed mainly of alkali feldspars and ilmenite. Quantitative analysis by EPMA on the obsidian glass part shows trachytic composition with high iron content of 3 wt.%. Accordingly, obsidian formed with complex textures under a rapid cooling condition on surface ground, with slight rheomorphism. Such results might be induced by collapse of lava dome or caldera, which produced the block-and-ash flow deposit and the transportation into valley while keeping high temperatures.

• Journal of Powder Materials
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• v.9 no.6
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Journal of Welding and Joining
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• v.28 no.6
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• pp.35-39
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• 2010

Generally, ceramic material is very difficult to machine due to high strength and hardness. However, ceramic material can be machined at high temperature by plastic flow as metallic material due to the deterioration of the grain boundary glassy phase. Recently, a new method was developed to execute cutting process with CBN cutting tool by local heating of surface with laser. There are various parameters in LAM because it is a complex process with laser treatment and machining. During laser assisted machining, high power results in reducing of cutting force and increasing tool life, but excessive power brings oxidation of the surface. The effect of laser power, feed rate, cutting depth and etc. were investigated on the life of cutting tool. Chips were observed to find out suitable machining conditions. Chips of SSN had more flow-types than HIPSN. It means SSN is easier to machining. The life of cutting tool was increased with increasing laser power and decreasing feed rate and cutting depth.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.276-285
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• 2003

In the undercooled melt of $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy, the solidification behavior including nucleation and growth of crystals at the micrometer level has been observed in-situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy specimens were cooled from the liquid state to glass transition temperature. 575 K, at various cooling late under a helium gas flow. According to the cooling rate, the morphologies of the solidification front are changed among various types, irregular jog like front, columnar dendritic front, cellular grain, star like shape jog and fine grain, etc. The velocities of the solid-liquid interface are measured to be $10^{-5}{\sim}10^{-8}$ m/s which are at least two orders higher than the theoretical crystal growth rates. Combining the morphologies observed in terms of cooling rates and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy. The continuous cooling transformation (CCT) diagram was constructed from solidification onset time at various linear cooling conditions with different rate. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.5 K/s, which is in agreement with the previous calorimetric findings.

• Nano
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• v.13 no.11
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• pp.1850134.1-1850134.10
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• 2018

Increasing active sites and enhancing electric conductivity are critical factors to improve sensing performance toward phenol. Herein, Ni nanoparticle was successfully anchored on acidified multiwalled carbon nanotube (a-MWCNT) surface by electroless plating technique to avoid Ni nanoparticle agglomeration and guarantee high conductivity. The crystal structure, phase composition and surface morphology were characterized by XRD, SEM and TEM measurement. The as-prepared Ni/a-MWCNT nanohybrid was immobilized onto glassy carbon electrode (GCE) surface for constructing phenol sensor. The phenol sensing performance indicated that Ni/a-MWCNT/GCE exhibited an amazing detection performance with rapid response time of 4 s, a relatively wide detection range from 0.01 mM to 0.48 mM, a detection limit of $7.07{\mu}M$ and high sensitivity of $566.2{\mu}A\;mM^{-1}\;cm^{-2}$. The superior selectivity, reproducibility, stability and applicability in real sample of Ni/a-MWCNT/GCE endowed it with potential application in discharged wastewater.