Gil Ho Hwang

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode.

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.

Performance Degradation of TiN-and TiC-deposited AISI316 bipolar plates for proton exchange membrane fuel cells

TiN and TiC were deposited on AISI316 bipolar plates for proton exchange membrane fuel cells (PEMFCs) and their effects on the corrosion resistance and overall cell performance were investigated. TiN with a Ti interlayer and TiC with a Ti interlayer were deposited on AISI316 bipolar plates by hollow cathode discharge (HCD) ion plating. The electrochemical behavior of the metallic bipolar plates was examined using a potentiodynamic method, an electrochemical impedance spectroscopy (EIS), and a single cell test. These results revealed that the TiN and TiC coatings considerably improved the corrosion resistance of AISI316. However, the TiN-deposited AISI316 bipolar plates showed a better cell performance than the TiC-deposited AISI316 bipolar plates. The differences in the cell performance stemmed from the differences in the ohmic resistance and charge transfer resistance.

Effect of Cu on the surface hardness of Ni−B coating for the strengthening of the Cu surface

In this paper, the effect of Cu on the decrease of the surface hardness of a Ni−B layer electrolessly coated was investigated. Ni3B crystallized at approximately 300 °C was decomposed to metallic Ni and free B after annealing above 500 °C. The metallic Ni formed a solid solution with Cu and the free B diffused to the surface. The free B diffusing to the surface formed the oxide B2O3 after it was annealed in an Ar atmosphere and was volatilized after it was annealed in an H2 atmosphere. However, decomposition of the Ni3B was not observed in Ni−B alloy powders without Cu. Therefore, it was concluded that the decomposition of Ni3B by Cu decreased the surface hardness of the Ni−B coating and strengthened the surface of Cu.

Fabrication of a probe needle using a tubular cathode by electrochemical etching

To fabricate a probe needle, a tubular cathode was applied by electrochemical etching. A tungsten wire was used as an anode, and a stainless steel tube was used as a cathode, respectively. The stainless steel tube was partially immersed into a sodium hydroxide solution. After the tungsten wire was aligned at the center of the stainless steel tube, electricity was supplied from an external power source. During the experiment, the level of solution that was inside the stainless steel tube rose higher than that of the outer solution of the stainless steel tube, due to bubbles generated on the inner surface of the stainless steel tube, and the inner solution increased in volume. Using this process, the length of the probe needle tapering could be controlled without using a vertical loading system or controller.

Pre-annealing effect of electroless Ni−B deposit as a diffusion barrier for electroplated Cu electrodes

Ni−B film of 1 μm thickness was electrolessly deposited on an electroplated Cu bus electrode. The film, which encapsulates the Cu bus electrodes, prevents Cu oxidation and serves as a diffusion barrier against Cu contamination of the transparent dielectric layer in a plasma display during the firing process at 580 °C. The microstructure of theas-deposited barrier film was amorphous phase and crystallized to Ni and Ni3B after annealing at 300 °C. The good barrier properties observed here can be explained by Ni3B precipitates at the grain boundaries acting as a fast diffusion path via pre-annealing at 300 °C before the firing process at 580 °C.

Effect of the Palladium Mid-Layer on the Cyclic Oxidation of Platinum Aluminide Bond Coating

Platinum/Palladium modified aluminide coatings prepared by aluminide pack cementation on the nickel base superalloy Inconnel 738. The platinum/palladium modified aluminide coating of cyclic oxidation behavior at 1200°C was investigated by TGA, XRD and SEM/EDS. Platinum/Palladium modified aluminide coatings showed better cyclic oxidation resistance than Platinum modified aluminide coating and palladium modified aluminide coating compared. Pt and Pd alloy played an enough role in alumina stabilization and in delaying the degradation of β-phase.

Fabrication and Characterization of Al-Fe Coating for the Wet-Seal Area of Separator for Molten Carbonate Fuel Cells (MCFC) by the Laminating of Al Foil

The separator of the molten carbonate fuel cells (MCFC) has the major corrosion problems, especially wet-seal area, because this part contacts directly with the corrosive molten carbonate electrolyte. For the protection of the wet-seal area, aluminization method is developed recently. Coated aluminum reacts with the molten carbonate and forms the LiAlO2 having high corrosion resistance, high melting point, no electrical conductivity and no dissolution in molten carbonate. In this study, 50㎛ thickness aluminum foil was applied to form the Al-Fe coating layer on the AISI316L by using the laminating method. Laminating of aluminum foil on AISI 316L was performed at 630°C for 5h in Ar atmosphere using a jig and diffusion heat treatment was carried out at 700°C, 750°C and 800°C for 3h in Ar atmosphere respectively. This method simplified the existing complicated process and has a great advantage of low-cost mass production compared to other methods like PVD, CVD and spray coating.

Effects of Deformation on Atmospheric Corrosion of Galvanized Steel

The effects of deformation on corrosion behavior of galvanized steel were investigated. Accelerated corrosion test was conducted under the conditions of 30oC and 90% relative humidity with flowing 200ppm sulfur dioxide gas for five weeks. Surface morphologies and corrosion products were analyzed by SEM/EDS and XRD. The corrosion products were composed of hydrates of ZnSO4. And corrosion rates of each part, bottom, bended and wall, were increased with growing strain due to surface damage and enlargement of naked surface for corrosion.

Surface Strengthening of Polymer Micromold Using Electroless Ni-P Deposition

In this work, we made micromolds using SU-8 photoresist and adopted electroless Ni-P deposition, well known as a hard coating material, to improve the rigidity and durability of SU-8 micromolds. After a micromold using SU-8 was defined by conventional lithography, Ni-P layer was electrolessly deposited on SU-8. By means of electroless Ni-P deposition, it was possible to increase the hardness of a micromold as much as about 17 times. In addition, it will be able to make various sized micromolds with one photomask by regulating the thickness of Ni-P layer.