• Journal of Electrochemical Science and Technology
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• v.2 no.3
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• pp.180-185
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• 2011

The layered lithium-manganese oxide ($Li_2MnO_3$) as a cathode material of lithium ion secondary batteries was prepared and characterized the physico-chemical and electrochemical properties. The morphological and structural changes of MnO(OH) and $Li_2MnO_3$ are closely connected to the changes of electrochemical properties. The crystallinity of $Li_2MnO_3$ is enhanced as the annealing temperature increase, but its capacity is reduced due to the easier structural changes of less crystalline $Li_2MnO_3$ than highly crystalline one. Moreover, the addition of buffer material such as MnO(OH) into cathode causes to reduce the morphological and structural changes of layered $Li_2MnO_3$ and increase the discharge capacity and cycleability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.217-220
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• 1995

By substituting Cd$\^$2+/ into both A-site and B-site in PNN-PZ-PT ternary perovskite material, it is possible to determine the effects of the substitution site of Cd$\^$2+/ on sintering behavior. Sintering was performed in the temperature range from 1000$^{\circ}C$ to 1300$^{\circ}C$. The substitution site of Cd$\^$2+/ is identified by XPS spectra. Although Cd$\^$2+/ is substituted into both A-site and B-site in PNN-PZ-PT, Cd$\^$2+/ prefers A-site to B-site. The density is influenced by substitution site of Cd$\^$2+/. If Cd$\^$2+/ replaces Pv$\^$2+/, weight gain is observed during sinterig process. On the contrary, if Cd$\^$2+/ replaces Ni$\^$2+/, weight loss is promoted during sintering. From these weight changes, it is believed that Cd$\^$2+/ changes the bonding strength between B-site cation and oxygen of octahedron in perovskite structure. The changes of lattice parameters as a function of Cd$\^$2+/ content were consistent with those of the bonding strength. The densities of A-site-doped compositions were higher than those of B-site-doped composition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.751-756
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• 2010

Ultrasonic nonlinearity is very sensitive to changes in material properties. This paper describes the study of the correlation between heat treatment and ultrasonic nonlinearity by taking nonlinear factors into consideration. A modified formula was proposed for ultrasonic velocity. This formula indicated that the changes occurring in nonlinearity during heat treatments cause changes in the ultrasonic velocity. The experimental results show that the relative nonlinearity parameters calculated from the modified ultrasonic velocities and the ratio of amplitudes of the second harmonic and fundamental wave are in good agreement. The experimental results prove that heat treatment can result in changes in material nonlinearity. Moreover, the relative nonlinearity parameter calculated from the modified velocity formula is has a large value. Since this parameter has high sensitivity to changes in nonlinearity, it can be used to represent the relative nonlinearity change calculated in this study by using the modified formula for ultrasonic velocity.

• The Journal of Advanced Prosthodontics
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• v.6 no.6
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• pp.427-433
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• 2014

PURPOSE. Surface color is one of the main criteria to obtain an ideal esthetic. Many factors such as the type of the material, surface specifications, number of firings, firing temperature and thickness of the porcelain are all important to provide an unchanged surface color in dental ceramics. The aim of this study was to evaluate the color changes in dental ceramics according to the material type and glazing methods, during the multiple firings. MATERIALS AND METHODS. Three different types of dental ceramics (IPS Classical metal ceramic, Empress Esthetic and Empress 2 ceramics) were used in the study. Porcelains were evaluated under five main groups according to glaze and natural glaze methods. Color changes (${\Delta}E$) and changes in color parameters (${\Delta}L$, ${\Delta}a$, ${\Delta}b$) were determined using colorimeter during the control, the first, third, fifth, and seventh firings. The statistical analysis of the results was performed using ANOVA and Tukey test. RESULTS. The color changes which occurred upon material-method-firing interaction were statistically significant (P<.05). ${\Delta}E$, ${\Delta}L$, ${\Delta}a$ and ${\Delta}b$ values also demonstrated a negative trend. The MC-G group was less affected in terms of color changes compared to other groups. In all-ceramic specimens, the surface color was significantly affected by multiple firings. CONCLUSION. Firing detrimentally affected the structure of the porcelain surface and hence caused fading of the color and prominence of yellow and red characters. Compressible all-ceramics were remarkably affected by repeated firings due to their crystalline structure.

• Geomechanics and Engineering
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• v.17 no.2
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• pp.119-131
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• 2019

Time dependent creep settlements are one of the most important causes of material deteriorations for the huge water structures such as concrete faced rockfill dams (CFRDs). For this reason, performing creep analyses of CFRDs is vital important for monitoring and evaluating of the future and safety of such dams. In this study, it is observed how changes viscoplastic behaviour of a CFR dam depending the time. Ilısu dam that is the longest concrete faced rockfill dam (1775 m) in the world is selected for the three dimensional (3D) analyses. 3D finite difference model of Ilısu dam is modelled using FLAC3D software based on the finite difference method. Two different special creep material models are considered in the numerical analyses. Wipp-creep viscoplastic material model and burger-creep viscoplastic material model were rarely used for the creep analyses of CFRDs in the last are taken into account for the concrete slab and rockfill materials-foundation, respectively. Moreover, interface elements are defined between the concrete slab-rockfill materials and rockfill materials-foundation to provide interaction condition for 3D model. Firstly, dam and foundation are collapsed under its self-weight and static behaviour of the dam is evaluated for the empty reservoir conditions. Then, reservoir water is modelled considering maximum water level of the dam and time-dependent creep analyses are performed for maximum reservoir condition. In this paper, maximum principal stresses, vertical-horizontal displacements and pore pressures that may occur on the dam body surface during 30 years (from 2017 to 2047) are evaluated in detail. According to numerical analyses, empty and maximum reservoir conditions of Ilısu dam are compared with each other in detail. 4 various nodal points are selected under the concrete slab to better seen viscoplastic behaviour changes of the dam and viscoplastic behaviour differences of these points during 30 years are graphically presented. It is clearly seen that horizontal-vertical displacements and principal stresses for maximum reservoir condition are more than the empty reservoir condition of the dam and significant pore pressures are observed during 30 years for maximum reservoir condition. In addition, horizontal-vertical displacements, principal stresses and pore pressures for 4 nodal points obviously increased until a certain time and changes decreased after this time.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.696-701
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• 2005

This paper was investigated the changes of surface properties of high-temperature-vulcanized (HTV) semiconductive silicone rubber due to oxygen plasma discharge. The modifications produced on the silicone rubber surface by oxygen plasma were accessed using Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS), contact angle and Surface Roughness Tester. The results of the chemical analysis Showed that C-H bonds were broken due to plasma discharge and Silica-like bonds (SiOx, x=$3\~4$) increased. It is thought that the above changes lead to the increase of surface energy of high-temperature-vulcanized (HTV) semiconductive silicone rubber also, Surface roughness was increased with cleavage of side-chains and oxidation process, it confirmed change as the SEM. The micromorphology of surface and hydrophobicity due to plasma discharge based on our results were discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05b
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• pp.25-28
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• 2005

This paper was investigated the changes of surface properties of high-temperature-vulcanized(HTV) semiconductive silicone rubber due to oxygen plasma discharge. The modifications produced on the silicone surface by oxygen plasma were accessed using x-ray photoelectron spectroscopy(XPS), contact angle and Scanning Electron Microscope(SEM). The results of the chemical analysis showed that C-H bonds were broken due to plasma discharge and Silica-like bonds (SiOx. x=3~4) increased. It is thought that the above changes lead to the increase of surface energy of high-temperature-vulcanized(HTV) semiconductive silicone rubber. The micromorphology of surface and hydrophobicity due to plasma discharge based on our results were discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.461-464
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• 2005

As the research on the development of the lightweight concrete block by the hydro-thermal synthetic reaction mixed with the calcareous material and bottom ash that is used less among siliceous material, we studied on the physical and chemical characteristics in the changes of hydro-thermal synthetic reaction of lightweight concrete block compounded with the PP fiber to increase flexural toughness and to prevent fragility failure. The results of the experiment are as follow. According to the increase of hydro-thermal synthetic reaction and the fiber content, compressive and flexural strength increased. Despite the changes of the hydro-thermal synthetic reaction time, tobermorite was produced on each of the specimens similarly. However, the phase of tobermorite was changed in accordance with the changes of time. Also, $CaCo_{3}$ appeared on the surface of the 9 hour hardened specimen.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.173-174
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• 2015

This research takes granite stone based floor finishing exposed to concentrated downpouring and observes the material's physical changes, adhesiveness, compressive strength under wet conditions. The results of the experiments shows that elution of sulfide mineral can occur when granite stones are exposed to downpour, but short term exposure shows little physical changes to the material. This indicates that if post maintenance is properly enacted, long term usage of granite stone materials is also possible.

• Magazine of the Korea Concrete Institute
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• v.20 no.2
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• pp.25-36
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• 2008

Seismic design of reinforced concrete flat plate structures is often complicated as it deals with three dimensionality and continuous spans, and mostly material complexity and reinforcement variation. A great degree of uncertainty in such structural and material properties is thus inherent in the RC flat plate systems, and hinders simplification of the design process in terms of slab flexure, unbalanced moment transfer at a slab-column connection, and punching shear. For these reasons, there have been substantial changes and updates in building codes relating to flat plates and slab-column connections over a handful of decades. Also, for the same reason, some of codes never have been revised. As a consequence of nonsimultaneous development of each provision, it tends to confuse structural engineers when using a mixture of all different US code provisions. In this paper, in the step-by-step logical order, seismic design of the RC flat plate systems is re-organized and clarified to make it easier to apply. Furthermore, recent changes or proposed changes are introduced, and are explained as to how it will apply in practice.