• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.525-529
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• 2003

Biotribological properties, such as wear rate and friction coefficient, of 3Y-TZP and Low Temperature Degradation (LTD) free materials were investigated via a ball(SiC)-on-plate sliding wear test to evaluate the relationship between wear mechanism and phase transformation. Wear test was conducted with a sliding speed of 0.035 m/s at room temperature and at 25$0^{\circ}C$ in air under a normal load of 49 N, respectively. Although friction coefficient of 3Y-TZP was the lowest due to the fine grain size, the highest wear loss and rate were observed due to the debris of monoclinic grains introduced during sliding and their values increased drastically with raising temperature. However, the biotribological properties of LTD-free materials were insensitive to temperature due to the inertness of the phase transformation, suggesting that they may be applicable to the biomechanical parts.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.886-891
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• 2008

Contact glow discharge electrolysis(CGDE) is an unconventional electrolysis where plasma is sustained by D.C. glow discharge between an electrode and the surface of electrolyte surrounding it at high voltage. In this study, the behavior of CGDE in NaCl solution and the depolymerization of fucoidan by CGDE were investigated. After onset of CGDE, increase of voltage enhanced Glow discharge which resulted in low current density and low temperature in NaCl electrolyte. From the variation of molecular weight of fucoidan with the reaction time, it was demonstrated that the degradation of fucoidan followed a first-order rate law. Molecular weight of fucoidan treated with CGDE was about 40 times lower compared to initial fucoidan without content decrease of sulfate and fucos.

• The Journal of Advanced Prosthodontics
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• v.1 no.3
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• pp.113-117
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• 2009

STATEMENT OF PROBLEM. Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE. The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS. Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad $S\ddot{a}ckingen$, Germany) were prepared in 40 mm (length) $\times$ 4 mm (width) $\times$ 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and $225^{\circ}C$ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences ($\alpha$= .05). RESULTS. The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below $125^{\circ}C$ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above $150^{\circ}C$, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION. The monoclinic phase started to appear after aging treatment above $100^{\circ}C$. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above $175^{\circ}C$. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.256-260
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• 2015

In this paper, achieved rise temperature distribution about degradation phenomenon of 24 MVA distribution cast resin transformer using CFD(Computational Fluid Dynamics). Usually, life of transformer is depended on temperature distribution of specification region than thermal special quality of transformer interior. Specially, life of transformer by decline of dielectric strength decreases rapidly in case rise by strangeness transformer interior hot spot temperature value permits. Because calculating high-voltage(HV) winding and low-voltage(LV) winding of cast resin transformer and Joule's loss of core for improvement these life, forecasted heat source, and HV winding and LV winding of cast transformer rise temperature distribution of core for supply of electric power and temperature distribution of highest point on the basis of the results. Also, calculated temperature rise limit of cast resin transformer and permission maximum temperature using analysis by electromagnetic heat source. Calculated and forecasted rise temperature distribution by heat source of thermal analysis with calculated result.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.1
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• pp.29-35
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• 2004

The effect of low tempering in a temperature range of $150{\sim}400^{\circ}C$ on corrosion resistance in 420J2 stainless steel austenitized at $1000^{\circ}C$ was investigated by the application of salt spray test, electrochemical pitting test in 3.5% NaCl solution and DL-EPR test for intergranular corrosion in 0.5M $H_2SO_4$+0.01M KSCN solution. In salt spray test, good corrosion resistance was obtained in a tempering temperature range of $150{\sim}250^{\circ}C$. Pitting potential was increased to the tempering temperature of $250^{\circ}C$, but decreased with the increase of temperature up to $400^{\circ}C$ And it was thought that the degradation of pitting corrosion resistance showed at the tempering temperature of around $400^{\circ}C$ was due to the precipitation of $Cr_7C_3$ of $M_7C_3$ type. The degree of sensitization showed increasing tendency with the increase of tempering temperature, and also Cr depletion phenomena were observed in the vicinity of grain boundary.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.6
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• pp.433-439
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• 2011

Poly Si TFTs (poly silicon thin film transistors) with p channel those are annealed HT (high temperature) with gate poly crystalline silicon and LT (low temperature) with metal gate electrode were fabricated on quartz substrate using the analyzed data and compared according to the activated grade silicon thin films and the size of device channel. The electrical characteristics of HT poly-Si TFTs increased those are the on current, electron mobility and decrease threshold voltage by the quality of particles of active thin films annealed at high temperature. But the on/off current ratio reduced by increase of the off current depend on the hot carrier applied to high gate voltage. Even though the size of the particles annealed at low temperature are bigger than HT poly-Si TFTs due to defect in the activated grade poly crystal silicon and the grain boundary, the characteristics of LT poly-Si TFTs were investigated deterioration phenomena those are decrease the electric off current, electron mobility and increase threshold voltage. The results of transconductance show that slope depend on the quality of particles and the amplitude depend on the size of the active silicon particles.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.217-220
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• 2009

Conductive adhesives have been investigated for use in microelectronics packaging as a lead-free solder substitute due to their advantages, such as low bonding temperature. However, high resistivity and poor mechanical behavior may be the limiting factors for the development of conductive adhesives. The metal fillers and the polymer resins provide electrical and mechanical interconnections between surface mount device components and a substrate. As metal fillers used in conductive adhesives, silver is the most commonly used due to its high conductivity and the stability. However the cost of conductive adhesives with silver fillers is much higher than usual lead-free solders and silver has poor electro-migration performance. So, copper can be a promising candidate for conductive filler metal due to its low resistivity and low cost, but oxidation causes this metal to lose its conductivity. In this study, electrically conductive adhesives (ECAs) using surface modified copper fillers were developed. Especially, in order to overcome the problem associated with the oxidation of copper, copper particles were coated with silver, and the silver-coated copper was tested as a filler metal. Especially the effect of silver coating on the electrical resistance just after curing and after aging was investigated. As a result, it was found that the electrical resistance of ECA with silver-coated copper filler was clearly lower and more stable than that of ECA with pure copper filler after curing process. And, during high temperature storage test, the degradation rate of electrical resistance for ECA with silver coated copper filler was quite slower than that for ECA with pure copper filler.

• Membrane Journal
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• v.25 no.3
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• pp.223-230
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• 2015

We synthesized novel polyimides with high gas permeability and selectivity for application of gas separation membrane. 2,2-bis(3,4-carboxylphenyl) hexafluoropropane dianhydride (6FDA) and two kinds of amines with high permeability and solubility were used to prepare the novel polymide. 2,4,6-Trimethyl-1,3-phenylenediamine (DAM) was used to improve gas permeability and 4,4-Methylenedianiline was used to improve the gas selectivity respectively. The polyimide copolymers were synthesized by commercial chemical imidization method using Triethylamine and Acetic anhydride and their average molecular weights were over 100,000 g/mol. The glass temperature (Tg) and the thermal degradation temperature were characterized using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The synthesized copolymers showed high Tg over $300^{\circ}C$ and high thermal degradation temperature over $500^{\circ}C$. The gas permeation properties were measured by time-lag equipment. Although general polyimides showed very low gas permeability, synthesized polyimide copolymer showed high $O_2$ permeability of 10.1 barrer with high $O_2/N_2$ selectivity around 5.3. From this result, we confirm that these membranes have possibility to apply to gas separation membrane.

• Journal of the Korean Electrochemical Society
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• v.8 no.4
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• pp.149-154
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• 2005

Fuel cell performance evaluation logic was developed using G-language (LabVIEW) to measure performance stability. Degree of stability and reliability of performance data were improved with averaged value and standard deviation method. Water injection system was introduced and the performance using this method was comparable to that of conventional humidification method. Water injection system has advantage of lowering operation energy consumption, reducing the number of parts needed in humidification, therefore increasing efficiency of fuel cell system. Fuel cell performance was decreased in case of low temperature operation such as sub freezing condition. Air purge method was tested to reduce the water content in cell fixture before sub freezing condition. The performance degradation due to low temperature operation was minimized by air purge method in medium size cell fixture ($25cm^2$) case.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.49-54
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• 2014

Skull Melted 3.2YSZ has good physical properties and does not undergo low temperature degradation. Due to these excellent physical and mechanical properties, Skull Melted 3.2YSZ has been studied for use in dental implants. In this study, a ø2.2mm Initial Twist Drill was made using Skull Melted 3.2YSZ; the drilling characteristics were compared with those of the traditional SUS420J drill. The experimental results indicate that the Skull Melted 3.2YSZ drill requires similar thrust forces and has a slightly higher temperature.