• Korean Journal of Materials Research
• /
• v.5 no.2
• /
• pp.151-156
• /
• 1995

Low temperature firing $(Ba, Sr)TiO_{3}$ dielectrics were successfully prepared with lead based glass and those electrical properties were investigated. Different amount of PbO content glass materials were added to dielectrics to investigate the sinterability and its dielectric properties. Also, various compositions of ceramic capacitors were prepared to applicate in multilayer ceramic capacitors. A large amount of experiment has been done with various Pb contented glasses and different sintering temperatures. The sintering temperature of $(Ba,Sr)TiO_{3}$can be reduced from $1350^{\circ}C$to as low as $1050^{\circ}C$ with 4wt% addition of $PbO-ZnO-B_{2}O_{2}$ glass materials. Its dielectric constant at room temperature was up to 8100 with low dielectric loss, 0.005. This ceramic capacitor showed fully fired microstructures with its grain size of 1-3$\mu \textrm{m}$. The sintered body which was sintered at $1150^{\circ}C$ for 2hr with 4wt% $PbO-ZnO-B_{2}O_{2}$ glass material addition satisfied the Z5U specification of the EIAS.

• Restorative Dentistry and Endodontics
• /
• v.8 no.1
• /
• pp.89-96
• /
• 1982

The purpose of this study is to identify the phases of four different types, low-copper lathe cut (Type II, class 1) and spherical (Type II, class 2) amalgam alloys which are made by Caulk company and high copper Dispersalloy (Type II, class 3) made by Johnson & Johnson and Tytin (Type I, class 2) made by S.S. White and to determine the Vickers hardness number on the individual phase and four different types of dental amalgam. After each amalgam alloy and Hg measured exactly by the balance was triturated by the mechanical amalgamator (De Trey), the triturated mass was inserted into the cylindrical metal mold which was 4 mm in diameter and 12mm in height and was pressed by the Instron Universal Testing machine (Model 1125) at the speed of 1mm/minute with 143$kg/cm^2$ according to the A.D.A. Specification No. 1. The Specimen removed from the mold, mounted and stored in the room temperature for 7 days. The speciman was polished with the emery paper from #220 to #1200 and finally on the polishing cloth with 0.3 and 0.05 um $Al_2O_3$ powder suspended in water. And then each specimen was etched by Allan's method and washed with Sodium Bisulfinite for 30 seconds. Finally differentiation and metallography on each phase were obtained by using metallographical microscope (Versamet, Union) and microhardness was obtained by using microhardness tester (MVH-2, Torsee). The results were as follows: 1. In the low-copper amalgam, the ${\gamma}$, ${\gamma}_1$ and ${\gamma}_2$ phase were observed and in the high-copper amalgam, the ${\gamma}$, ${\gamma}_1$. ${\epsilon}$ and ${\eta}$ phases were observed but ${\gamma}_2$ phase was not observed. 2. Among the microhardness of each amalgam phase measured under pressing a vickers diamond indenter with 2.0gm load for 30 seconds, e phase has the highest V.H.N (314 ${\pm}$ 20), and in low-copper amalgam 12 phase has the lowest V.H.N. (29${\pm}$1) and ${\eta}$ phase which was observed in high-copper amalgam has 230${\pm}$13 V.H.N and this phase is considerd to contribute to strengthen the handness in amalgam. 3. The V.H.N. measured under pressing a Vickers diamond indenter with 300.0gm load for 30 seconds in low-copper amalgam was lower than that of high-copper amalgam.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.8
• /
• pp.765-770
• /
• 2017

GTD111 DS of nickel base superalloy has been used for gas turbine blades. In this study, low cycle fatigue test was conducted on the GTD111 DS alloy by setting conditions similar to the real operating environment. The low cycle fatigue tests were conducted at room temperature, $760^{\circ}C$, $870^{\circ}C$, and various strain amplitudes. Test results showed that fatigue life decreased with increasing total strain amplitude. Cyclic hardening response was observed at room temperature and $760^{\circ}C$; however, tests conducted at $870^{\circ}C$ showed cyclic softening response. Stress relaxation was observed at $870^{\circ}C$ because creep effects occurred from holding time. A relationship between fatigue life and total strain range was obtained from the Coffin-Manson method. The fratography using a SEM was carried out at the crack initiation and propagation regions.

• Korean Journal of Veterinary Research
• /
• v.43 no.2
• /
• pp.289-294
• /
• 2003

This study aimed to determine of osseointegration following dental implantation in the dog mandible using bone scintigraphy. Five mongrel dogs, weighing approximately 8.5 kg and averaging 1.8 years of age, without active periodontal disease were used. During the entire study period, all dogs were fed a soft commercial diet and water ad libitum to minimize functional loading of the implant. Titanium alloy implant systems 10 mm in length and 4 mm in diameter were chosen for insertion. Twelve weeks prior to implantation, the second and third left mandibular premolars in each dog were extracted for the dental implant insertion. Before the dental implantation procedures and 0, 4, 8, and 12 weeks after the insertions, clinical observation, radiography and bone scintigraphy were conducted. The scintigraphy was obtained using a large field of view gamma camera equipped with a paralled-hole, low-energy collimator about 3 hours after intravenous injection of Tc-99m-MDP (8 mCi/dog) to the dogs. There were not inflammation sign after insertion of dental implants on the mandible in dogs. Implants were slightly movable at the first and fourth weeks, and there was no mobility after 8 weeks. Twelve weeks after dental implantation, the bone uptake scintigraphy of peri-implant bone was similar to that of normal alveolar bone, indicating that peri-implant bone was completely regenerated by new bone. In conclusion, we recommend stable implant fixation with alveolar bone for the accurate and safe repair of teeth loot due to decacy, trauma or peridontal disease. Titanium alloy implants were optimal due to their biocompatibility.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.134-134
• /
• 2010

Fuel cell is a device that directly converts chemical energy in the form of a fuel into electrical energy by way of an electrochemical reaction. In the anode for a high temperature fuel cell, nickel or nickel alloy has been used in consideration of the cost, oxidation catalystic ability of hydrogen which is used as fuel, electron conductivity, and high temperature stability in reducing atmosphere. Most MCFC stacks currently operate at an average temperature of $650^{\circ}C$. There is some gains with decreased temperature in MCFC to diminish the electrolyte loss from evaporation and the material corrosion, which could improve the MCFC life. However, operating temperature has a strong related on a number of electrode reaction rates and ohmic losses. Baker et al. reported the effect of temperature (575 to $650^{\circ}C$). The rates of cell voltage loss were 1.4mV/$^{\circ}C$ for a reduction in temperature from 650 to $600^{\circ}C$, and 2.16mV/$^{\circ}C$ for a decrease from 600 to $575^{\circ}C$. The two major contributors responsible for the change in cell voltage with reducing operation temperature are the ohmic polarization and electrode polarization. It appears that in the temperature range of 550 to $650^{\circ}C$, about 1/3 of the total change in cell voltage with decreasing temperature is due to an increase in ohmic polarization, and the electrode polarization at the anode and cathode. In addition, the oxidation reaction of hydrogen on an ordinary nickel alloy anode in MCFC is generally considered to take place in the three phase zone, but anyway the area contributing to this reaction is limited. Therefore, in order to maintain a high performance of the fuel cell, it is necessary to keep this reaction responsible area as wide as possible, that is, it is needed to keep the porosity and specific surface area of the anode at a high level. In this study effective anodes are prepared for low temperature MCFC capable of enhancing the cell performance by using zirconium hydride at least in part of anode material.

• Journal of Hydrogen and New Energy
• /
• v.28 no.1
• /
• pp.9-16
• /
• 2017

Hydrogen forms metal hydrides with some metals and alloys leading to solid-state storage under moderate temperature and pressure that gives them the safety advantage over the gas and liquid storage methods. However, it has disadvantages of slow hydrogen adsorption-desorption time and low thermal conductivity. To improve characteristics of metal hydrides, it is important that activation and thermal conductivity of metal hydrides are improved. In this study, we have been investigated hydrogen storage properties of Hydralloy C among Ti-Mn alloys. Also, the characteristics of activation and thermal conductivity of Hydralloy C were enhanced to improve kinetics of hydrogen adsorption-desorption. As physical activation method, PHEM (planetary high energy mill) was performed in Ar or $H_2$ atmosphere. Hydralloy C was also activated by $TiCl_3$ catalyst. To improve thermal conductivity, various types of ENG (expanded natural graphite) were used. The prepared samples were compacted at pressure of 500 bar. As a result, the activation properties of $H_2$ PHEM treated Hydralloy C was better than the other activation methods. Also, the amounts of hydrogen storage showed up to 1.6 wt%. When flake type ENG was added to Hydralloy C, thermal conductivity and hydrogen storage properties were improved.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.5
• /
• pp.373-382
• /
• 2016

Painting or thermally sprayed metal coating is often used in corrosion protection of steel structures. In recently, duplex coating system which combines thermally sprayed metals with paint is selected as a new generic type of coatings on steel structures under the highly corrosive environments. In this study, the structural steel specimens were surface treated, thermally sprayed with zinc, zinc-15%aluminum alloy, aluminum and aluminum-5%magnesium alloy, and finally sealing or painted with acrylic urethane. And as a reference specimens, steel specimens were painted with acrylic urethane after surface treatment. Circular defects with 1.0, 3.0 and 5.0 mm in diameters and line defect with 2.0 mm width, which reach the steel substrate were created on all specimens. The specimens were exposed into an environmental testing chamber controlled by the ISO 20340, which is a laboratory cyclic accelerated exposure test condition of spraying/UV/low temperature, for up to 175 days. Based on the corrosion tests, corrosion deterioration from the initial defects were evaluated and weathering performance of the specimens are compared.

• Journal of the Korean Vacuum Society
• /
• v.16 no.2
• /
• pp.116-121
• /
• 2007

TiNi shape memory alloy(SMA) was fabricated by PLD(plused laser deposition) using equiatomic TiNi target. Composition and crystallization of TiNi thin films which were fabricated in ambient Ar gas(200m Torr)and vacuum($5{\times}10^{-6}\;Torr$) were investigated. Composition of TiNi thin films was characterized by energy-dispersive X-ray spectrometry (EDXS) and crystallization was confirmed by X-ray diffraction (XRD). The composition of films depends on the distance between target and substrate but does not sensitively depend on the substrate temperature. It is found that the composition of films can be easily controlled when substrate is placed inside plume in ambient Ar gas. It is also found that the in situ crystallization temperature ($ca.\;400^{\circ}C$) in ambient Ar gas is lowered in comparison with that of TiNi film prepared under vacuum. The low crystallization temperature in ambient Ar gas makes it possible to prepare the crystalline TiNi thin film without contamination.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.28 no.5
• /
• pp.407-415
• /
• 2008

The tubes in heat exchanger are typically made from copper alloy, stainless steel, carbon steel, titanium alloy material. type-439 ferritic stainless steel is ferromagnetic material, and furnish higher heat transfer rates than austenitic stainless steels and higher resistance to corrosion-induced flaws. Ferritic stainless steel can typically be found in low-pressure(LP) feedwater heaters and moisture separator reheaters(MSRs). LP feedwater heaters generally utilize thin wall type-439 stainless steel tubing, whereas MSRs typically employ a heavier wall tubing with integral fins. Service-induced damage can occur on the OD(outside diameter) surface of type-439 ferritic stainless steel tubing which is employed for MSRs tubing, and the most typical damage mechanism is vibration-induced tube-to-TSP(tube support plate) wear and fatigue cracking. The wear has been reported that occurs mainly on the OD surface. Accordingly, in this study, we have evaluated the flaw sizing capability of magnetic saturation eddy current technique using magnetic saturation probe and flawed specimen.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.7
• /
• pp.270-276
• /
• 2020

3D printing is an additive manufacturing technology that can produce complex shapes in a single process for a range of materials, such as polymers, ceramics, and metals. Recent 3D printing technology has developed to a level that enables the mass-production through an improvement of the printing speed and the continuous development of applicable materials. In this study, 3D printing technology using a laser was applied to manufacture a heat exchanger for an air compressor in a railway vehicle. First, the optimal design of the heat exchanger was carried out by focusing on weight reduction and compactness as a shape suitable for 3D printing. Based on the design derived, heat exchanger prototypes were made of AlSi10Mg alloy material by applying the SLM technique. Moreover, the manufactured prototypes were attached to an existing air compressor, and the heat exchange performance of the compressed air was tested. The test results of the 3D printed prototypes showed a heat exchange performance of approximately 80% and 85% at low and high-pressure, respectively, compared to the existing heat exchanger. From the 𝓔-NTU method results with an external cooling air condition similar to that of the existing heat exchanger, the calculated heat transfer amount of 3D printed parts showed similar performance compared to the existing heat exchanger. As a result, the 3D printed heat exchanger is lightweight with good performance.