• Korean Journal of Materials Research
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• v.23 no.2
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• pp.123-127
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• 2013

The electrolytic reduction of a spent oxide fuel involves liberation of the oxygen in a molten LiCl electrolyte, which is a chemically aggressive environment that is too crosive for typical structural materials. Therefore, it is essential to choose the optimum material for the process equipment for handling a molten salt. In this study, the corrosion behavior of pyro-carbon made by CVD was investigated in a molten LiCl-$Li_2O$ salt under an oxidation atmosphere at $650^{\circ}C$ and $750^{\circ}C$ for 72 hours. Pyro-carbon showed no chemical reactions with the molten salt because of its low wettability between pyro-carbon and the molten salt. As a result of XRD analysis, pyro-carbon exposed to the molten salt showed pure graphite after corrosion tests. As a result of TGA, whereas the coated layer by CVD showed high anti-oxidation, the non-coated layer showed relatively low anti-oxidation. The stable phases in the reactions were $C_{(S)}$, $Li_2CO_{3(S)}$, $LiCl_{(l)}$, $Li_2O$ at $650^{\circ}C$ and $C_{(S)}$, $LiCl_{(l)}$, $Li_2O_{(S)}$ at $750^{\circ}C$. $Li_2CO_{(S)}$ was decomposed at $750^{\circ}C$ into $Li_2O_{(S)}$ and $CO_{2(g)}$.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.128-134
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• 2013

A study on the corrosion behavior of Inconel alloys and Incoloy 800H in molten salt of LiCl-$Li_2O$ was investigated at $650^{\circ}C$ for 24-312 hours in an oxidation atmosphere. The order of the corrosion rate was Inconel 600 < Inconel 601 < Incoloy 800H < Inconel 690. Inconel 600 showed the best performance suggesting that the content of Fe, Cr and Ni are the important factor for corrosion resistance in hot molten salt oxidation conditions. The corrosion products of Inconel 600 and Inconel 601 were $Cr_2O_3$ and $NiFe_2O_4$, In case of Inconel 690, a single layer of $Cr_2O_3$ was formed in the early stage of corrosion and an outer layer of $NiFe_2O_4$ and inner layer of $Cr_2O_3$ were formed with an increase of corrosion time. In the case of Incoloy 800H, $Cr_2O_3$ and $FeCr_2O_4$ were observed. Most of the outer scale of the alloys was observed to be spalled from the results of the SEM analysis and the unspalled scale which adhered to the substrate was composed of three layers. The outer layer, the middle one, and the inner one were Fe, Cr, and Ni-rich, respectively. Inconel 600 showed localized corrosion behavior and Inconel 601, 690 and Incoloy 800H showed uniform corrosion behavior. Ni improves the corrosion resistance and too much Cr and/or Fe content deteriorates the corrosion resistance.

• Elastomers and Composites
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• v.44 no.2
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• pp.98-105
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• 2009

The cochlea of the inner ear has two core components, basilar membrane and hair cells. The basilar membrane disperses incoming sound waves by their frequencies. The hair cells are on the basilar membrane, and they are the sensory receptors generating bioelectric signals. In this paper, a biomimetic technology using ZnO piezoelectric nano-pillar was studied as the part of developing process for artificial cochlea and novel artificial mechanosensory system mimicking human auditory senses. In particular, ZnO piezoelectric nano-pillar was fabricated by both low and high temperature growth methods. ZnO piezoelectric nano-pillars were grown on solid (high temperature growth) and flexible (low temperature growth) substrates. The substrates were patterned prior to ZnO nano-pillar growth so that we can selectively grow ZnO nano-pillar on the substrates. A multi-physical simulation was also conducted to understand the behavior of ZnO nano-pillar. The simulation results show electric potential, von Mises stress, and deformation in the ZnO nano-pillar. Both the experimental and computational works help characterize and optimize ZnO nano-pillar.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.431-437
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• 2001

This research was examined the effect of intercritical heat treatment on the mechanical Properties and retained austenite formation in 0.1C-6.5Mn steels for the development of a high strength high ductility steel. using of transformation induced plasticity due to retained austenite. The stability of retained austenite is very important for the good ductility and it depend on diffusion of carbon and manganese during reverse transformation. It is effective to heat treat at$ 645^{\circ}C$ in order to obtain over 30 vol.% of retained austenite. However, it is more desirable to heat treat at $620^{\circ}C$, considering the volume fraction and mechanical stability of retained austenite. The strength-elongation combination in cold rolled steel sheets after reverse transformed at $620^{\circ}C$ for 1hr was about 4000k9/mm7, but it decreased rapidly with increasing holding time at high temperature due to the decrease of ductility. The addition of 1.1%Si in 0.14C-6.5Mn TRIP steel does not improve the mechanical properties and retained austenite formation.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.393-397
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• 2001

Fer the purpose of improving ductility of $Al_3$Ti intermetallic compound has potential to industrial application, we investigated formation behavior of cubic Ll$_2$ structure and effect of Mn addition. Nanocrystalline cubic Ll$_2$Al$_3$Ti intermetallic compound, has 10nm size of grain, was fabricated by mechanical alloying for 20hr at the composition of Al-8Mn-25Ti. Ternary cubic Ll$_2$Al$_3$Ti, added Mn, did not showed phase transformation from Ll$_2$ to D0$_{23}$ or D0$_{22}$ unlike binary cubic Ll$_2$Al$_3$Ti and maintained Ll$_2$ structure.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1138-1145
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• 1998

The sliding wear behavior of Ni-base hardfacing alloy, Deloro 50, was investigated at the contact stresses of 15ksi and 30ksi under the various wear environments. In air at room temperature, Deloro 50 showed lower wear resistance than Stellite 6 even at 15ksi due to the occurrence of severe adhesive wear. This seems to be caused by the lower hardness and work- hardening rate of Deloro 50 than those of Stellite 6. In water at room temperature, Deloro 50 showed as good wear resistance as Stellite 6 at 15ksi. It was considered to be due to that water could effectively prevent metal to metal contact through contacting asperities. However, Deloro 50 showed severe adhesive wear at 30ksi in water at room temperature. It seems to be that the water could not suppress adhesion wear at 30ksi. At $300^{\circ}C$ in air, Deloro 50 exhibited higher wear resistance than Stellite 6 even at 30ksi. It was considered that the oxide glaze layers formed on wear surface during sliding, effectively prevented direct metal-to-metal contacts.

• Journal of Korean Ophthalmic Optics Society
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• v.19 no.4
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• pp.429-434
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• 2014

Purpose: To analyze thermal effect on mechanical properties of domestic commercial polymer-based eyewear frames. Methods: In this study, materials of cellulose acetate, polyamide, epoxy, and polyetherimide were exposed to high or low temperature and were mounted on universal test machine (TO-100-IC) for tensile strength test. Elastic behavior, Young's modulus, maximum displacement, and fatigue were tested with various temperature ($-25^{\circ}C$, $25^{\circ}C$, $60^{\circ}C$). Results: As a result, at room temperature, displacements of materials were changed with increasing impact load. At low temperature ($-25^{\circ}C$), maximum displacements of all specimens were decreased but young's modulus were increased. However, at high temperature, maximum displacements of all specimens were increased but young's modulus were decreased. Conclusions: Degree of displacements due to fatigue behavior was increased following direction of PEI, epoxy, polyamide, acetate. We concluded that commercial polymers used in eyewear frames physical properties were changed differently to exposed temperature.

• Composites Research
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• v.18 no.3
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• pp.21-30
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• 2005

Vacuum hot pressing has been used for the development of titanium metal matrix composites using foil-fiber-foil method. Heterogeneous microstructures prior to and following consolidation have been quantified, and the relations to densification behavior investigated. As shown by the results, dramatic variations of the microstructures including equiaxed $\alpha$, transformed $\beta$ and $ Widmanst\ddot{a}tten$ $\alpha$ are obtained during the process according to the fiber distributions. The dependence of microstructures on the consolidation then has been explained in terms of the change in mechanisms such as grain growth and recrystallization that occur with changing levels of inhomogeneity of deformation. Further, micro-mechanics based constitutive model enabling the evolution of density over time together with the evolutions of microstructure to be predicted has been developed. The mode developed is then implemented into finite element scheme so that practical process simulation has been carried out.

• Elastomers and Composites
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• v.46 no.3
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• pp.231-236
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• 2011

The polyacrylate/multi-walled carbon nanotube (MWNT) composites were prepared and investigated for the application as a counter electrode in solar cell. The electrical conductivity of the composites was increased with increasing MWNT content and with the thickness of the sheet. The surface resistivity value of the composite at 50 wt% loading of MWNT was 0.36 ${\Omega}$/sq. The thermal decomposition temperature of the composites was also increased with the MWNT contents, and the increase of $15^{\circ}C$ was observed at the composite of polyacrylate/MWNT (50/50, w/w). The increase of storage modulus of the composites was observed, especially at the higher temperature compared to polyacrylate. The dimensional change of polyacrylate decreased over $20^{\circ}C$, but that of the composite increased linearly with the temperature. The morphology of the composites stands for the good dispersion of MWNT into the polyacrylate matrix.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.15-21
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• 2008

SiC has an excellent resistance to oxidation and corrosion, high temperature strength and good thermal conductivity. However, it is difficult to density because of its highly covalent bonding characteristics. Hot-press sintering process was applied to fabricate fully densified SiC ceramics with carbon and boron addition as a sintering additive. The addition of carbon improved the mechanical properties of SiC because it could induce a fine and homogeneous microstructure by the suppression of abnormal growth of SiC grain. Also, the addition of carbon could control the phase transformation of SiC. The phase transformation of 6H to 4H increased with sintering temperature but the addition of carbon decreased that kind of phase transformation.