Jung-Pil Noh

Phase transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys

Transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys have been investigated by means of differential scanning calorimetry (DSC) measurements, X-ray diffraction, electron microscopy, tensile tests and wire drawing tests. Mo addition to a Ti-Ni binary alloy induced the R phase transformation, and consequently Ti-Ni-Mo alloys showed two stage transformation, i.e., from the B2(cubic) parent phase to the R(rhombohedral) phase, and then from the R phase to B19′(monoclinic) phase. In the thermo-mechanically treated 51Ti-48.3Ni-0.7Mo alloy, reverse transformation temperature, Af, kept constant, irrespective of thermo-mechanical treatment conditions, while it changed in the thermo-mechanically treated 51Ti-49Ni and 51Ti-48.5Ni-0.5Mo alloys. Mo addition to Ti-Ni binary alloy decreased wire drawing stress. Wire drawing stress decreased with raising intermediate annealing temperature monotonously when the annealing treatment was made in vacuum. When the annealing treatment was made in air, however, it decreased with raising annealing temperature up to 923 K, and then increased. Optimum intermediate annealing temperature of Ti-Ni-Mo alloys for wire drawing was 823 K, above which a thick oxide film which reduced the drawability of the alloys was formed on the surface of alloy wires.

Patterned Si thin film electrodes for enhancing structural stability

A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.

Mechanical properties of Cu matrix composite fabricated by extrusion process

Abstract Carbon nanotube (CNT) was applied in various fields for its superior electrical, mechanical and thermal characteristics. After composites were fabricated by extrusion process using ball-milled Cu–CNT powders, mechanical properties of Cu–CNT composites according to CNT fraction were reviewed. CNT (1%, 5% and 10%), Cu ( d =100 nm), zirconia balls (90 g) and ethanol (20 mL) were mixed and dispersed for 5 h at a speed of 500 r/min using a planetary ball mill. A billet ( d =50 mm, length=100 mm) was made with Cu, and the composite powders were filled up into billet using the uni-axial press. In the extrusion process, after the billet was heated at 880 °C for 1 h, specimens were produced in the shape of a round bar using the billet by applying a load of 200 t. The composite powders were measured for particle size by particle size distribution equipment. Then the specimen surface fabricated by extrusion was observed by SEM. Mechanical properties measured by the indentation equipment increased with increasing CNT content. The yield strength, tensile strength and hardness of the Cu–CNTs composites can be obviously improved.

Structural and Electrochemical Properties of Lithium Nickel Oxide Thin Films

LiNiO2 thin films were fabricated by RF magnetron sputtering. The microstructure of the films was determined by X-ray diffraction and field-emission scanning electron microscopy. The electrochemical properties were investigated with a battery cycler using coin-type half-cells. The LiNiO2 thin films annealed below 500°C had the surface carbonate. The results suggest that surface carbonate interrupted the Li intercalation and deintercalation during charge/discharge. Although the annealing process enhanced the crystallization of LiNiO2, the capacity did not increase. When the annealing temperature was increased to 600°C, the FeCrNiO4 oxide phase was generated and the discharge capacity decreased due to an oxygen deficiency in the LiNiO2 thin film. The ZrO2-coated LiNiO2 thin film provided an improved discharge capacity compared to bare LiNiO2 thin film suggesting that the improved electrochemical characteristic may be attributed to the inhibition of surface carbonate by ZrO2 coating layer.

Surface Modification of Graphene Nanoparticles by Acid Treatment and Grinding Process.

Surface modification is necessary to decrease graphenes (GN) stacking process and increase its advantageous properties. In this study, the effects of acid treatment and grinding processes on the structural integrity of GN have been studied. Morphological and structural characteristics of modified GN were investigated by field emission scanning electron microscopy, transmission electron microscopy, gas Pycnometer, particle size analyzer, X-ray diffractometer, UV-Vis spectroscopy and thermal conductivity measurement system which expose some strong evidences of the effects of purification and grinding process on GN nanoparticles in order to get GN based better nanofluid dispersed in water which gives 1.66% and 3.38% enhancement of thermal conductivity at 20 °C and at 40 °C respectively compared to that of DW in this experiment.

Phase Stability and Properties of Ti-Nb-Zr Thin Films and Their Dependence on Zr Addition

Ternary Ti-Nb-Zr alloys were prepared by a magnetron sputtering method with porous structures observed in some of them. In bulk, in order to control the porous structure, a space holder (NH4HCO3) is used in the sintering method. However, in the present work, we show that the porous structure is also dependent on alloy composition. The results from Young’s modulus tests confirm that these alloys obey d-electrons alloy theory. However, the Young’s modulus of ternary thin films (≈80–95 GPa) is lower than that for binary alloys (≈108–123 GPa). The depth recovery ratio of ternary Ti-Nb-Zr thin films is also higher than that for binary β-Ti-(25.9–34.2)Nb thin film alloys.

Experimental Study on Characteristics of Grinded Graphene Nanofluids with Surfactants

In earlier studies, much research has focused on increasing the efficiency of heat exchanger fields. Therefore, in this study, graphene nanofluid was fabricated for use as a heat transfer medium for a heat exchanger. Graphene has excellent electrical conductivity, mechanical properties, and heat transfer properties. It is expected that the heat transfer efficiency will be improved by fabricating the nanofluid. However, graphene is prone to sedimentation, because of its cohesion due to van der Waals binding force. In this experiment, a nanofluid was fabricated with enhanced dispersibility by surfactant and the ball-milling process. The zeta potential, absorbance, and thermal conductivity of the nanofluid were measured. As a result, when using the ratio of 2:1 (graphene:sodium dodecyl sulfate (SDS)), a higher thermal conductivity was obtained than in other conditions.

Effect of Substrate Roughness on Adhesion and Structural Properties of Ti–Ni Shape Memory Alloy Thin Film

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Forced Convective Heat Transfer of Aqueous Al2O3 Nanofluid Through Shell and Tube Heat Exchanger.

This study presents the forced convective heat transfer of a nanofluid consisting of distilled water and different weight concentrations (1 wt% and 2 wt%) of Al2O3 nanoparticles flowing in a vertical shell and tube heat exchanger under counter flow and laminar flow regime with certain constant heat flaxes (at 20 °C, 30 °C, 40 °C and 50 °C). The Al2O3 nanoparticles of about 50 nm diameter are used in the present study. Stability of aqueous Al2O3 nanofluids, TEM, thermal conductivity, temperature differences, heat transfer rate, T-Q diagrams, LMTD and convective heat transfer coefficient are investigated experimentally. Experimental results emphasize the substantial enhancement of heat transfer due to the Al2O3 nanoparticles presence in the nanofluid. Heat transfer rate for distilled water and aqueous nanofluids are calculated after getting an efficient setup which shows 19.25% and 35.82% enhancement of heat transfer rate of 1 wt% and 2 wt% aqueous Al2O3 nanofluids as compared to that of distilled water. Finally, the analysis shows that though there are 27.33% and 59.08% enhancement of 1 wt% Al2O3 and 2 wt% Al2O3 respectively as compared to that of distilled water at 30 °C, convective heat transfer coefficient decreases with increasing heat flux of heated fluid in this experimental setup.

Vibration Signal Analysis by Defect Type of Heat Exchanger

The dynamic characteristic was changed due to Youngs modulus when the temperature of the heat exchanger changed. The case is often destroyed due to the heat exchanger tube, such as SCC occurs. Therefore, there is a need to predict using the FEM model. In this paper measured the vibration signal to Crack type of tubes the tube was classified attributes for each defect. And by conducting the Modal Test at the room temperature stated by using a dynamic characteristic of the hold and the predicted flow rate were compared Tube room temperature state and the dynamic characteristics of the operation state. In addition, when driving through the eigenvalue analysis, the changes in the eigenvalues component defect by types, also with respect to the heat exchanger by analyzing approached by Frequency analysis. Introduction There are many kinds of machine facility failures. Especially, leakage of heat exchanger, boiler and pressure vessel are common examples of failures. Leakage of tube that is used for boiler and heat exchanger, it seemed to have diversities on causes such as internal pressure, corrosion, erosion, external impact as well as types. But usually these failures are fixed immediately depends on types of system and it must be kept as operating status due to system protection or economic reason. If failures such as tube leakage occurs and causes are possible to be found out by external signal that provides critical information to operator for deciding operation mode such as reduced rated operation, idle operation and emergency shutdown. Recently, many diagnosis techniques by using vibration signal has been researched. This research use faulty tubes that happened by different causes and controllable flux such as supply amount and leaked amount to measure released vibration signal. Also it figures out characteristics of the signal by temperature. Therefore, this research had experiments that similar to real field by using faulty pipe in heat exchanger and get vibration signal that occurs. Also it analyzes frequency correlation to have characteristics of signal due to fault or normal status. Experiment Equipment and Model Research Model that the molten carbonate required equipment is a heat exchanger of a fuel cell system, the horizontal direction of the diameter compared to the pitch of the pipe value (T / D) was 1.8, and the vertical direction to tube diameter value of contrast pitch (P / D) is 4.5 be. Inlet and outlet of the Cold Side has been fixed to the manifold, Hot Side inlet is the value of square Flange, the fluid moves around the tube at the rate of average 13 meters / s. The heat exchanger was supported by a wire, Figure 1 was set as shown. Gave the temperature to the temperature change by installing the temperature control on the inlet to determine the signal characteristic of the amount of leakage, using the valve provided in the outlet was adjusted to leakage.