• Journal of the Korean Ceramic Society
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• v.18 no.1
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• pp.27-34
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• 1981

The phase separation of low-alkali borosilicate glass with the composition of $6.25Na_2O$.$18.75B_2O_3$.$75.00SiO_2$(mole%) substituting $Li_2O$ for $Na_2O$ was studied. The phase separation in the temperature range of transformation was examined with various heating temperatures and soaking times. Durability to water, thermal expansion and specific density of the specimen were investigated and the microstructure of the separated phase was also observed by transmission electron micrograph techniques. The maximum alkali extraction result with the best phase separation effect was obtained when $Na_2O$ of the base glass was replaced with $1.88Li_2O$ (mole %) and electron micrograph of carbon film replica of $1.88Li_2O$$4.37Na_2O$.$18.75B_2O_3$.$75.00SiO_2$ (mole %) glass showed that the glass consisted of homogeneous two phases. The minimum specific density was shown with the specimen treated at 57$0^{\circ}C$ and it was also shown that the longer the treating time the lower the specific density. The apparent activation energies of approximately 45 kcal/mole by the alkali extraction and 43kcal/mole by the thermal expansion method were derived from the Arrhenius plots, respectively.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.4
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• pp.511-520
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• 2010

In general, spot welding is used at no welding rod or flux for the process, low welding point temperature compared to arc welding, short heating time, less damage to the parent material, and low deformation and residual stress, relatively. Also, because of the pressurization effect, better mechanical qualities of the welding parts are obtained. Therefore, in various fields of industry its rapid operation speed can make mass production possible such as motor industry. In FEM analysis for the spot welding process, it is effective to use simple modeling rather than complicated one because of its numerous number of spots and reduction of analysis time. Therefore, this study provides with not only simplification of modeling analysis by using beam component composition of structure without re-compositing the spot welding point mesh but also modeling analysis of which property of fracture strength is reflected. In addition complete spot welding model is examined at rectangular post shape (hat shape) by impact test, compared the results, and verified its validity. As a result, it is possible to optimize the welding position and to recognize the strength of structure and the proposed equal distance model shows the effect of welding point reduction and improvement of stiffness.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.5
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• pp.434-439
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• 2008

Silver pastes as the outer electrodes have been prepared using Pb-free glass frits with different content of $Bi_2O_3$ and the effects of glass composition on the degradation behaviors of the Ag electrodes were investigated using the change of adhesion between Ag electrode and alumina substrate with thermal cycle stress. Low adhesion and high surface resistance were observed in Ag electrode using glass frit with a $Bi_2O_3$ content of 60 wt%, owing to the open microstructure formed at the firing temperature of $600^{\circ}C$. When the $Bi_2O_3$ was increased to 80 wt% in the glass frit, the Ag electrodes had a dense microstructure with high adhesion and a low surface resistance. Delamination of the Ag electrodes was a major failure mode under thermal cycle stress and this was attributed to residual stress due to the thermal expansion mismatch between the Ag electrode and the alumina substrate.

• Tribology and Lubricants
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• v.25 no.1
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• pp.7-12
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• 2009

Coating brittle intermetallic compounds on metal can enlarge the range of their use. It is found that intermetallic compound coating layers made by only combustion synthesis in an electric furnace have porous multi-phase structures containing several intermediate phases, even though the coating layers show good wear resistance. In this study, dense $Ni_{3}Al$ single phase layer corresponding to the initial composition of the mixed powder is coated on two different ferrous materials by the diffusing treatment after combustion synthesis. After- ward, sliding wear behaviors of the coating layer are evaluated in comparison with that of the coating layer with porous multi-phase structure made by only combustion synthesis. As a result, the wear properties of the coating layer composed of dense $Ni_{3}Al$ single phase are considerably improved at the range of low sliding speed com- pared with that of the coating layer with porous multi-phase structure, particularly in the running-in wear region. This is attributed to the fact that wear of the coating layer is progressed by shearing as a sequence of adhesion, not by occurring of pitting on the worn surface due to having dense structure without pores.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1109-1115
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• 2010

ZnO thin films were deposited on Si(100) substrates at low temperatures ($44^{\circ}C{\sim}210^{\circ}C$) by atomic layer deposition using DEZn (diethyl zinc) and water as precursors. The film thickness was measured by ellipsometry calibrated with cross-sectional TEM. The phase formation, microstructure evolution, UV-absorbance, and chemical composition changes were examined by XRD, SEM, AFM, TEM, UV-VIS-NIR, and AES, respectively. A uniform amorphous ZnO layer was formed even at $44^{\circ}C$ while stable crystallized ZnO films were deposited above $90^{\circ}C$. All the samples showed uniform surface roughness below 3 nm. Fully crystallized ZnO layers with a band-gap of 3.37 eV without carbon impurities can be formed at substrate temperatures of less than $90^{\circ}C$.

• Korean Journal of Materials Research
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• v.32 no.6
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• pp.287-292
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• 2022

Magnesium-antimonide is a well-known zintl phase thermoelectric material with low band gap energy, earth-abundance and characteristic electron-crystal phonon-glass properties. The nominal composition Mg_3.8-xZn_xSb₂ (0.00 ≤ x ≤ 0.02) was synthesized by controlled melting and subsequent vacuum hot pressing method. To investigate phase development and surface morphology during the process, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out. It should be noted that an additional 16 at. % Mg must be added to the system to compensate for Mg loss during the melting process. This study evaluated the thermoelectric properties of the material in terms of Seebeck coefficient, electrical conductivity and thermal conductivity from the low to high temperature regime. The results demonstrated that substituting Zn at Mg sites increased electrical conductivity without significantly affecting the Seebeck coefficient. The maximal dimensionless figure of merit achieved was 0.30 for x = 0.01 at 855 K which is 30% greater than the intrinsic value. Electronic flow properties were also evaluated and discussed to explain the carrier transport mechanism involved in the thermoelectric properties of this alloy system.

• Korean Journal of Soil Science and Fertilizer
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• v.22 no.1
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• pp.61-66
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• 1989

Plants were exposed to different sub-optimal growth temperature regimes for hardening or sprayed with abscisic acid (ABA) before being placed at $10^{\circ}C$ for three days. Comparisons were made with non-treated plants for plant survival, photosynthetic activities and fatty acids composition of phospholipids. The level of endogenous ABA of the hardened seedlings was compared with that in control and ABA sprayed-seedlings. The results of the above experiment were summarized as follows: 1. Compared to non-treated plants, the hardening and ABA treatment resulted in higher plant survival rate and better seedling growth following earlier transplanting. The low temperature hardening which gradually increased the duration of the low temperature treatment at 2-day intervals was more effective than the controled temperature hardening which gradually decreased the temperature from $25^{\circ}C$ to $20^{\circ}C$ and $15^{\circ}C$. 2. The photosynthetic activities of rice leaves after 3-day exposure to $10^{\circ}C$ were higher in hardened and ABA sprayed seedlings than in non-treated plants. The root activities after low temperature treatment were also higher in hardened and ABA sprayed seedlings than in control. 3. Fatty acids of phospholipids in rice plants such as stearic acid and oleic acid were decreased and the highly unsaturated fatty acids, linoleic acid and lenolenic acid were increased by hardening or ABA treatments. It is assumed that the increase of cold tolerance in these plants was due to the higher ratio of unsaturated to saturated fatty acids. Respectively, the ratio was 1.86, 1.97 and 1.80 in plants given controled temperature hardening, the low temperature hardening and ABA treatments. While in control plants, it was 1.17. 4. ABA content in rice seedling given the low temperature hardening treatment was 67.2 ng/g F.W which was approximately twice that of non-treated control, which was 33.9 ng/f F. W., in contrast, the ABA content of the ABA treated seedlings was 91.7 ng/g F. W.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.1-26
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• 1994

The purpose of this study was to investigate the dissolution components during corrosion of amalgams and to identify surface corrosion products in the modified Fusayama artificial saliva. Four type of amalgam alloys were used: low copper lathe cut amalgam alloy (Cavex 68), low copper spherical amalgam alloy (Caulk Spherical Alloy), high copper admixed amalgam alloy (Dispersalloy) and high copper single composition amalgam alloy (Tytin). Each amalgam alloy and Hg were triturated according to the manufacturer's direction by means of mechanical amalgamator (Capmaster, S.S.White), and then the triturated mass was inserted into the cylindrical metal mold which was 10mm in diameter and 2.0mm in height and condensed with compression of 150kg/$cm^2$ using oil pressor. The specimens were removed from the mold and stored at room temperature for 7 days and cleansed with distiled water for 30 minutes in an ultrasonic cleaner. The specimens were immersed in the modified Fusayama artificial saliva for the periods of 1 month, 3 months and 6 months. The amounts of Hg, Cu, Sn and Zn dissolved from each amalgam specimen immersed in the artificial saliva for the periods of 1 month, 3 months and 6 months were measured using Inductivity Coupled Plasma Atomic Emission Spectrometry (ICPQ-1000, Shimadzu, Japan) and amount of Ag dissolved from amalgam specimen was measured using Atomic Absorption Spectrophotometry (Atomic Absorption/Flame emission spectrophotometer M-670, Shimadzu, Japan). A surface corrosion products of specimens were analysed using Electron Spectroscopy Chemical Analyser (ESCA PHI-558, PERKIN ELMER, U.S.A.). The secondary image and back scattered image of corroded surface of specimens was observed under the SEM, and the corroded surface of specimens was analysed with the EDX. The following results were obtained. 1. The dissolution amount of Cu was the most in high copper admixed amalgam(Dispersalloy) and the least in high copper single composition amalgam(Tytin). 2. Sn and Zn were dissolved during all the experiment periods, and dissolution amounts were decreased as the time elapsed. 3. Initial surface corrosion products were ZnO and SnO. 4. Corrosion of ${\gamma}$ and ${\gamma}_2$ phase in low copper amalgams was observed and Ag-Cu eutectic alloy phase was corroded in low copper spherical amalgam(Caulk Sperical Alloy). 5. Corrosion of ${\gamma}$ and $\eta$' phase in high copper amalgams was observed and Ag-Cu eutectic alloy phase was corroded in high copper admixed amalgam(Dispersalloy). 6. Sn-Cl was produced in the subsurface of low copper amalgams and high copper admixed amalgam.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.2
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• pp.162-167
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• 2024

Fossil fuels have been main energy source to people. However, enormous amount of CO₂ was emitted over the world , resulting in global climate crisis today. Recently, solid oxide electrolyzer cell (SOEC) is getting attention as an effective way for producing H₂, a clean energy resource for the future. Also, SOEC could be applicable to reverse water-gas shift reaction process due to its high-temperature operating condition. Here, SOEC system was utilized for both H₂ production and CO₂ reduction process, allowing product gas composition change by controlling operating conditions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.563-566
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• 2000

The effect of CuO and CuO-B $i_2$ $O_3$ additives on microwave dielectric properties of (P $b_{0.45}$C $a_{0.55}$)[F $e_{0.5}$N $b_{0.5}$)$_{0.9}$S $n_{0.1}$] $O_3$were investigated to decrease the sintering temperature for usage of Low Temperature Co-firing Ceramics (LTCC). The (P $b_{0.45}$C $a_{0.55}$)[F $e_{0.5}$N $b_{0.5}$)$_{0.9}$S $n_{0.1}$] $O_3$ceramics was sintered at 11$65^{\circ}C$. In order to decrease the sintering temperature, CuO and Cuo-B $i_2$ $O_3$ were added in the (Pb,Ca)[(Fe,Nb)Sn] $O_3$ with CuO-B $i_2$ $O_3$. For the addition of 0.4 wt.% CuO, the sintered density and the dielectric constant of the ceramics were revealed the maximum values of the 6.06g/c $m^2$ and 83 respectively and temperature coefficient of resonance frequency ($\tau$$_{f}$) shifted to the positive value. As increasing B $i_2$ $O_3$to the (Pb,Ca)[(Fe,Nb)Sn] $O_3$ with CuO-B $i_2$ $O_3$with 0.2 wt.% CuO, the sintered density, the $\varepsilon$$_{r}$ and the Q was decreased, and $\tau$$_{f}$ was minimized at 0.2 wt.% CuO, and 0.2 wt.% B $i_2$ $O_3$. For this composition, dielectric properties were $\varepsilon$$_{r}$ of 81, Q. $f_{0}$ of 4400 GHz, and $\tau$$_{f}$ of 5 ppm/$^{\circ}C$ at sintering temperature of 100$0^{\circ}C$. the relationship between the microstructure and properties of ceramics was studied by X-ray diffraction(XRD), scanning electron microscopy(SEM).copy(SEM).oscopy(SEM).copy(SEM).EM).