• Journal of the Korean earth science society
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• v.35 no.5
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• pp.305-312
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• 2014

A number of coated grains (spherical to elongated ones in shape) were collected from a small stream, Dijon, France. They were characterized by typical concentric lamination surrounding broken twigs, and were thus identified as concentric precipitation on plant twigs. Within carbonate coatings of the plant twigs, two morphological groups including, eukaryotic green algae (Vaucheria sp.) and cyanobacteria (Scytonema sp. and Rivularia sp.) were detected, which form carbonate crystals that are surrounding their filaments. The filaments could have triggered carbonate precipitation by photosynthetic removal of $CO_2$ causing the increase of alkalinity of the water, and by supporting their sheaths as nucleation sites. Such encrusted twigs were found from 70 meters downstream, in which temperature and pH were measured as $11.1^{\circ}C$ and 8.18, respectively. These water chemistries ($11.1^{\circ}C$ and pH 8.18), with the aid of microbial photosynthesis, were likely to provide a suitable condition for carbonate precipitation on the twigs.

• Journal of the Korean Vacuum Society
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• v.8 no.3A
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• pp.224-230
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• 1999

$SrBi_{2x}Ta_2O_9$ (SBT) thin films were prepared on platinized silicon substrates by MOD process, and their ferroelectric and leakage current characteristics were investigated. The grain size of the MOD derived SBT films increased with increasing the BI/Ta mole ration. Although the SBT films with x of 0.8~1.2 were composed of the equiaxed grains, the elongated grains were also observed for the SBT films with x of 1.4 and 1.6. The SBT film with x of 1.2 exhibited the optimum ferroelectric properties of 2PR : 9.79 $\muC/\textrm{cm}^2$ and Ec : 24.2kV/cm at applied voltage of 5V. The leakage current density of the SBT films increased with increasing the BI/Ta mole ratio. With post annealing process, 2Pr and $E_c$of the SBT film with x of 1.2 increases 11.3 $\muC/\textrm{cm}^2$ and 39.6kV/cm, respectively. decrement of the leakage current density by post annealing process increased remarkably with increasing the Bi/ta mole ratio, and the SBT film with x=1.6 exhibited the lowest leakage current density after post annealing process.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.229-235
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• 2014

In this paper, the effects of precipitates and Mn-solute atoms on the recrystallization behavior of an Al-Mn alloy was studied using micro-Vickers hardness, electrical conductivity measurements and optical microscopy. Various thermo-mechanical processes were designed to investigate the different morphologies, and the solute concentration, of Mn in the matrix. The results indicate that the recrystallization temperature, $T_R$ and time, $t_R$, are influenced by the amount of M-solute atoms in the matrix, and that the recrystallization microstructure is influenced by the amount of precipitates. Recrystallization in the Slow-Cooling specimen was rapid due to its low concentration of Mn-solute atoms, and the crystal-grain size was the smallest due to finely distributed precipitates. However, in the case of the No-Holding specimen, elongated grains were observed at the low annealing temperature and the largest recrystallized grains were observed at the high annealing temperatures (compared with Slow-Cooling and Base specimens) due to the high Mn-solute atoms in the matrix.

• Journal of Powder Materials
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• v.17 no.5
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• pp.365-372
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• 2010

The evolution of sinterability, microstructure and mechanical properties for the spark plasma sintered(SPS) Ti from commercial pure titanium(CP-Ti) was studied. The densification of titanium with 200 mesh and 400 mesh pass powder was achieved by SPS at $750{\sim}1100^{\circ}C$ under 10 MPa pressure and the flowing $H_2$+Ar mixed gas atmosphere. The microstructure of Ti sintered up to $800^{\circ}C$ consisted of equiaxed grains. In contrast, the growth of large elongated grains was shown in sintered bodies at $900^{\circ}C$ with the 400 mesh pass powder and the lamella grains microstructure had been developed by increasing sintering temperature. The Vickers hardness of 240~270 HV and biaxial strength of 320~340 MPa were found for the specimen prepared at $950^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.911-916
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• 1998

By using {{{{ { { {Y }_{3 }Al }_{5 }O }_{12 } }} (YAG) and SiO2 as sintering additives the effect of the composition of sintering ad-ditives on microstructure and mechanical properties of the hog-pressed and subsequently annealed SiC ma-terials were investigated. Microstructures of sintered and annealed materials were strongly dependent onthe composition of sintering additives. The average diameter and volume fraction of elongated grains in an-nealed materials increased with the SiO2/YAg ratio while the fracture toughness increased with the SiO2/YAg ratio. The average MPa.{{{{ { m}^{1/2 } }} respectively. Typical strength and fracture toughness of an annealed material with SiO2/YAg ra-tionof 0.67 were 371 MPa and 5.6 MPa.{{{{ { m}^{1/2 } }} respectively.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.35-40
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• 2016

Recent developments of Laser metal 3D deposition with wire feeding are reviewed which provide an alternative to powder feeding method. The wire feeding direction, angle and position as well as laser power, wire feeding rate, and deposition speed are found to be key parameters to make quality deposition with high throughput. When compared with the powder feed, the wire feed shows higher material efficiency, higher deposition rate, and smoother surface. Large elongated columnar grains which have epitaxial growth across deposit layers are observed in deposit cross sections. The growth direction is parallel to the thermal gradient during the deposit process. Tensile properties are found to be dependent on the direction due to the anisotropic deposit property. A real-time feedback control is demonstrated to be effective to improve the deposition stability.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.169-177
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• 1999

Different pass strains and rolling temperatures were applied to understand the effects of pass strain and rolling temperature on flow stress and flow strain of AA5083 alloy. The specimens were prepared by conventional casting process followed by hot rolling. Hot torsion tests were conducted at temperature ranges of 350 to 52$0^{\circ}C$ under a strain rate of 1.0/sec. During the process, hot-restoration mechanisms, dynamic recovery(DRV) or dynamic recrystallization (DRX), of the AA5083 alloy were analyzed from the flow curves and deformed microstructures. It was found that while the rolling strain per pass and rolling temperature have little effect on the folw stress, they have significant effect on the failure strain. The DRV was responsible for the hot restoration mechanism of the hot-rolled specimen. heavily elongated grains and small subgrains containing dislocations were obtaned during the hot deformation. This was due to the presence of Al6Mn precipitate in the alloy.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.331-335
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• 1998

R-curve, of three kinds of silicon nitride-based ceramics were measured, using single edge notched beam (SENB) method at room and at elevated temperatures, up to $1200^{\circ}C$. Stable fraacture was seen on ceramic materials with SENB specimens if the machined notch is deep enough, even though the crack resistance did not increase with crack length. Hot pressed silicon nitride did not show the rising R-curve behavior at room temperature, but it showed some rising at $1000^{\circ}C$ and above. Si3N4 reinforced with SiC whiskers showed no rising behavior at room and elevated temperatures, as it has smaller grain size, compare to the monolithic specimen. Gas pressure sintered silicon nitride had very large and elongated grains, and it showed rising R-curve even at room temperature. However, it showed some creep behavior at $1200^{\circ}C$ and the calculated R-curve on this condition did not show a good result. We cannot apply this technique on this condition for obtaining the R-curve.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.193-200
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• 2000

Si$_3$N$_4$powder with 2 wt% $Al_2$O$_3$and 6 wt% $Y_2$O$_3$additives was sintered by the gas pressure sintering (GPS) technique. The unlubricated wear behavior depending on sintering conditions such as sintering temperature, pressure, and sintering time was investigated. When the sintering temperature and time increased, the larger elongated grains were formed and the microstructural heterogeneity increased. When sintering pressure increased, grain growth, however, was impeded. Also, the wear properties depended on microstructure and friction coefficient were related to grain size. Based on the experimental results, the wear properties were associated with initial friction coefficients as well as mechanical properties including fracture toughness and flexural strength.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.230-234
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• 2006

Metal-Induced Crystallization (MIC) of amorphous silicon (a-Si) using aluminum and nickel as catalysts were performed with a variation of metal thickness and temperature. Raman results showed that the crystallization of a-Si depended on the thickness of aluminum while not on nickel. Nickel that forms silicide nodules during annealing simply catalyzed the formation of crystalline silicon (c-Si) while aluminum was consumed and transferred during MIC, which resulted in more complex microstructural characteristics. Crystalline silicons after NIC had elongated shape with a twin along the long axis. Morphological change after Aluminum-Induced Crystallization (AIC) showed more equiaxial grains. The nucleation and growth mechanism of AIC was discussed.