• Proceedings of the KIEE Conference
• /
• 1999.07d
• /
• pp.1642-1644
• /
• 1999

This paper provides the results of dielectric properties for aged or controlled lightening arresters. The aged lightening arresters were used for five years in distribution line. The leakage current of lightening arresters and elements was measured to confirm whether the lightening arrester was deteriorated or not. The microstructure was also investigated to determine the size of grain and grain boundary. The dielectric properties of aged lightening arresters were compared to those of controlled lightening arresters. The dielectric constant and the tan${\delta}$ of aged lightening arrester were larger than those of controlled one, resulting from accelerated aging due to the thin grain boundary.

• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.16-20
• /
• 2002

Semiconducting (Ba.Sr)TiO$_3$ceramic device, which shows the PTCR effect, has been usually used as a current limiter. In this case, the device should endure the condition under the high electric field. In this study, the dynamic electrical properties of the PTCR device under high voltage has been evaluated. Two different formulated powders were used and the sintered bodies exhibited the different grain size and porosity. The wide range of characterization such as complex impedance spectroscopy, microstructure, I-V characteristics and voltage dependence of resistivity of the samples were performed. The PTCR effect of the specimen containing coarse grains was very sensitively dependent on the AC electric field, showing that it was inversely pro-portional to the grain boundary potential barrier. The withstanding voltage was proportional to the potential barrier of grain boundary.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.05b
• /
• pp.66-71
• /
• 1998

A study of treatment effects on laser surface melted Ni-base alloy 600, especially on precipitation behavior ad chemical composition changes on the grain boundary were conducted with microscopic equipments. Long-term aging treatment at 40$0^{\circ}C$ caused no considerable effects on the grain boundary properties. Cr-rich M$_2$$_3$C$_{6}$ and Cr$_{7}$C$_3$ carbides were precipitated and the resultant Cr depletion below 12 wt pct on some high angle grain boundaries was occurred by heat treatment at $600^{\circ}C$ for 24 hours. These results can imply that the resistance of intergranular stress corrosion cracking of heat treated alloy 600 might not be changed considerably in comparion with the as-LSM one.e.e.

• Journal of the Korean Society for Heat Treatment
• /
• v.11 no.4
• /
• pp.324-332
• /
• 1998

The grain growth characteristics of dual-phase (${\alpha}+{\gamma}$) containing high Cr-steel have investigate using ${\alpha}$-, ${\gamma}$-single phases and (${\alpha}+{\gamma}$)dual-phase of 12%Cr Steel. The heat treatment has performed at $1000-1200^{\circ}C$ for 1-100hr. The results are as follows : 1) The grain growth rate in (${\alpha}+{\gamma}$) dual phase was substantially slower than that of single grain. 2) The relation between mean grain radius $\bar{{\gamma}}$ and annealing time t is, in general, described as following equation : $$(\bar{{\gamma}})^n-(\bar{{\gamma}_o})^n=K_n{\cdot}t{\cdots}{\cdots}(1)$$ i) In the case of single phase of high Cr steel, Eq.(1) is described as $(\bar{{\gamma}})^2-(\bar{{\gamma}_o})^2=K_2{\cdot}t$ and the grain growth is controlled by boundary migration. ii) In dual phase, the grain growth needs diffusion of alloying elements because the chemical composition of ${\alpha}$- and ${\gamma}$- phases differs from each other. When the volume fraction of ${\alpha}$-, ${\gamma}$-phase was almost equal and ${\gamma}$-phase in the case of 80 and $90%{\gamma}$. Eq.(1) is described as $(\bar{{\gamma}})^3-(\bar{{\gamma}_o})^3=K_3{\cdot}t$ because the grain growth is controlled by volume diffusion iii) In the case of ${\gamma}$-rich phase (80 and $90%{\gamma}$), the grain growth of minor phase (10 and $20%{\alpha}$) is described as $(\bar{{\gamma}})^4-(\bar{{\gamma}_o})^4=K_4{\cdot}t$ because the boundary diffusion is predominent rather than volume diffusion.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10b
• /
• pp.123-126
• /
• 2003

A high strength aluminum alloy bolt (A7050, T7 temper treatment) has been developed by the authors. The bolt has a small grain size in the whole area of the bolt because of the large equivalent strain followed by thermo-mechanical treatment. As the bolt made of A 7050 has a risk of stress corrosion cracking, each grain should be strengthened the grain inside than the grain boundary in order to improve the stress corrosion cracking resistance. It has been confirmed that the nano-indentation hardness at each grain inside increased with the increasing equivalent strain by thermo-mechanical treatment processing.

• Proceedings of the KIEE Conference
• /
• 1997.07d
• /
• pp.1430-1432
• /
• 1997

A solar cell conversion effiency was degraded by grain boundary effect in polycrystalline silicon. To reduce these effects of the grain boundaries, we investigated various influencing factors such as preferential chemical etching of grain boundaries, grid design, transparent conductive thin film, and top metallization along grain boundaries. Pretreatment in $N_2$ atmosphere and gettering by $POCl_3$ and Al were performed to obtain polycrystalline silicon of the reduced defect density. Structural, electrical, and optical properties of solar cells were characterized. Improved conversion efficiencies of solar cell were obtained by a combination of Al diffusion into grain boundaries on rear side, fine grid finger, top Yb metal grid on Cr thin film of $200{\AA}$ and buried contact metallization along grain boundaries.

• Electrical & Electronic Materials
• /
• v.9 no.4
• /
• pp.396-403
• /
• 1996

In this paper, the (S $r_{0.85}$.C $a_{0.15}$)Ti $O_{3}$ of paraelectric grain boundary layer (GBL) ceramics were fabricated, and the analysis of microstructuye and the thermally stimulated current(TSC) were investigated for understanding effects of GBL's interfacial phenomenon on variations of electrical properties. As a result, the three peaks of .alpha., .alpha. and .betha. were obtained at the temperature of -20 [.deg. C], 20[.deg. C] and 80[.deg. C], respectively. The origins of these peaks are that the .alpha. peak observed at -20[.deg. C] looks like to be ascribed to the ionization excitation from donor level in the grain, and the .alpha.' peak observed at 20[.deg. C] appears to show up by detrap of the trapped carrier of border between the oxidation layer and the grain, and the .betha. peak observed at 80[.deg. C] seems to be resulted from hopping conduction of existing carrier in the trap site of the border between the oxidation and second phase. and second phase.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.4
• /
• pp.197-204
• /
• 2003

Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 mm cell size, whereas 1:1.45 in 4 mm cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171.1 MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 mm cell size. And in 4mm cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores, It is thought to be main reason for lower flexural strength of 1.0 wt%C core.

• Nuclear Engineering and Technology
• /
• v.53 no.5
• /
• pp.1587-1592
• /
• 2021

The effects of the symmetrical tilt Σ5 (310) <001> grain boundary (GB) on the evolution of radiation-induced point defects in pure δ-plutonium (Pu) were studied by Molecular dynamics (MD) simulations. The evolution of radiation-induced point defects was obtained when primary knock-on atom (PKA) was respectively set as -15 Å and 15 Å far from the GB and the number of residual defects was obtained as the distance from PKA to GB was changed. According to the results, compared with vacancies, interstitial atoms were more easily absorbed by GB. In addition, the formation energy of point defects was also calculated. The results showed that there was almost no difference for the formation energy of vacancies in the all matrix. However, the formation energy of interstitial atoms close to the GB was lower than that in the other bulk regions.

• Journal of the Korean Ceramic Society
• /
• v.35 no.4
• /
• pp.347-354
• /
• 1998

Densification and grain growth behaviors of ITO ceramics were investigated as a function of TiO2 ad-ditions. TiO2 addition led to inhibition of the grain growth and promotion of the densification of ITO ceram-ics. From the microstructure observation it was found that the crack-like voids which were formed in pure ITO specimens decreased with increase of TiO2 additon. The grain growth exponent(n) was measur-ed to be 4 for pure ITO 3 for TiO2-doped ITO specimens respectively. It was supposed that the grain boun-dary migration of pure ITO ceramics was controlled by the pores which were moved by surface diffusion. On the contrary the grain boundary migration of TiO2-doped ITO specimens was depressed by solute drag effect. The activation energies for grain growth were measured to be 1013 kJ/mol for pure ITO ceramics and 460kJ/mol for TiO2-doped ITO specimens respectively.