• Corrosion Science and Technology
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• v.20 no.6
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• pp.347-360
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• 2021

Currently, the demand for eco-friendly energy sources is high, which has prompted research on polymer electrolyte membrane fuel cells. Both aluminum alloys and nickel alloys, which are commonly considered as materials of bipolar plates in fuel cells, oxide layers formed on the metal surface have excellent corrosion resistance. In this research, the electrochemical characteristics of 6061-T6 aluminum alloy and Inconel 600 were investigated with chloride concentrations in an acid environment that simulated the cathode condition of the PEMFC. After potentiodynamic polarization experiments, Tafel analysis and surface analysis were performed. Inconel 600 presented remarkably good corrosion resistance under all test conditions. The corrosion current density of 6061-T6 aluminum alloy was significantly higher than that of Inconel 600 under all test conditions. Also, 6061-T6 aluminum alloy and Inconel 600 presented uniform corrosion and intergranular corrosion, respectively. The Ni, Cr, and Fe, which are the main chemical compositions of Inconel 600, are higher than Al in the electromotive force series. And a double oxide film of NiO-Cr₂O₃, which is more stable than Al₂O₃, is formed. Thus, the corrosion resistance of Inconel 600 is better.

• Journal of the Korean Ceramic Society
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• v.50 no.1
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• pp.63-69
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• 2013

Negative-temperature coefficient (NTC) thermistors based on nickel manganite spinel ($NiMn_2O_4$) are widely used for many applications, such as sensors and temperature compensators, due to their good thermistor characteristics and stabilities. However, to achieve thermistors with a high NTC B constant, which is an important figure of merit pertaining to the degree of temperature sensitivity, the activation energy should be high such that high resistivity at ambient temperatures results. To obtain a high B constant and low resistivity, Al and Si modified spinel structured $Ni_{0.6}Si_{0.2}Al_{0.6}Mn_{1.6}O_4$ hybrid thick films with the conducting metal oxide of $LaNiO_3$ were fabricated on a glass substrate by aerosol deposition at room temperature (RT). The NTC-$LaNiO_3$ hybrid thick films showed resistivity as low as < $100k{\Omega}\;cm$ at $90^{\circ}C$, which is one or two orders of magnitude lower than that of the monolithic NTC films, while retaining a high B constant of $NiMn_2O_4$ of over 5500 K when 20 wt% $LaNiO_3$ was added without a post-thermal treatment. These phenomena are explained by the percolation threshold mechanism.

• Journal of the Korean Electrochemical Society
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• v.4 no.4
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• pp.146-151
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• 2001

The Frumkin adsorption isotherm of the over-potentially deposited hydrogen (OPD H) for the cathodic $H_2$ evolution reaction (HER) at the poly-Ni|0.05M KOH aqueous electrolyte interface has been studied using the phase-shift method. The behavior of the phase shift $(0^{\circ}\leq{\phi}\leq90^{\circ})$ for the optimum intermediate frequency corresponds well to that of the fractional surface coverage $(1\geq{\theta}\geq0)$ at the interface. The phase-shift method, i.e., the Phase-shift profile $(-{\phi}\;vs.\;E)$ for the optimum intermediate frequency, can be used as a new method to estimate the Frumkin adsorption isotherm $(\theta\;vs.\;E)$ of the OPD H for the cathodic HER at the interface. At the poly-Ni|0.05M KOH aqueous electrolyte interface, the rate (r) of change of the standard free energy of the OPD H with $\theta$, the interaction parameter (g) for the Frumkin adsorption isotherm, the equilibrium constant (K) for the OPD H with $\theta$, and the standard free energy $({\Delta}G_{\theta})$ of the OPD H with ${\theta}$ are $24.8kJ mol^{-1},\;10,\;5.9\times10^{-6}{\leq}K{\leq}0.13,\;and\;5.1\leq{\Delta}G_{\theta}\leq29.8kJ\;mol^{-1}$. The electrode kinetic parameters $(r,\;g,\;K,\;{\Delta}G_{\theta})$ depend strongly on ${\theta} (0{\leq}{\theta}{\leq}1)$.

• Applied Biological Chemistry
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• v.20 no.3
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• pp.300-309
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• 1977

The information related to the heavy metal pollution in the environment was obtained from studies on the effects of pH, phosphate and soil properties on the adsorption of metal ions (Cd, Cu, Ni, and Zn) by soils. Three soil materials; soil 1 with low CEC (8.2 me/100g) and low organic carbon content (0.34%); soil 2 with high CEC (36.4 me/100g) and low organic carbon content (1.8%) and soil 3 with high CEC (49.9 me/100g) and high organic carbon content (14.7%) were used. Soils were adjusted to several pH's and equilibrated with metal ion mixtures of 4 different concentrations, each having equal equivalents of each metal ion (0.63, 1.88, 3.12 and 4.38 micromoles per one gram soil with and without 10 micromoles of phosphate per one gram soil). Reported here are the results of the equilibrium study on soil I. The rest of the results on soil 2 and soil 3 will be repoted subsequeutly. Generally higher metal ion concentration solution resulted in higher final metal ion concentrations in the equilibrated solution and phosphate had minimal effect except it tended to enhance removal of cadmium and zinc from equilibrated solutions while it tended to decrease the removal of copper and nickel. In soil 1, percentages of added metal ions removed at pH 5.10 were; Cu 97, Ni 69, Cd 63, and Zn 55, while increasing pH to 6.40, they were increased to Cu 90.9, Zn 99, Ni 96, and Cd 92 per As initial metal ion concentration increased, final metal ion concentrations in the equilibrated solution showed a relationship with pH of the system as they fit to the equation $p[M^{++}]=a$ pH+b where $p[M^{++}]=-log$[metal ion concentration in Mol/liter]. The magnitude of pH and soil effects were reflected in slope (a) of the equation, and were different among metal ions and soils. Slopes (a) for metal ions in the aqueous system are all 2. In soil 1 they were; Zn 1.23, Cu 0.99, Ni 0.69 and Cd 0.59 at highest concentration. The adsorption of Cd, Ni, and Zn in soil 1 could be represented by the Iangmuir isotherm. However, construction of the Iangmuir isotherm required the correction for pH differences.

• The korean journal of orthodontics
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• v.41 no.5
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• pp.337-345
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• 2011

Objective: The purpose of this study was to evaluate the effect of force and moment produced by Nickel-titanium wires of different sizes at activation and deactivation according to differing vertical bracket displacement. Methods: Superelastic NiTi wires of 3 different sizes (0.014", 0.016", and 0.016" ${\times}$ 0.022") were tied with elastomeric or 0.009-inch stainless steel ligations in a twin-bracket, 0.018-inch slot. A testing machine recorded the effects of simulated activation of 5 distances from 1 to 5 mm and deactivation of 5 distances from 4 to 0 mm, in increments of 1 mm. Results: Frictional force increased the wire stiffness during loading. Ligation of 0.014-inch NiTi wire with O-ring resulted in a significant increase in the stiffness. On application of orthodontic force for 5 mm of vertical displacement of teeth, the effective displacement in the case of the 0.014", 0.016", and 0.016" ${\times}$ 0.022" NiTi wires was 2 mm, 3 mm, and 4 mm, respectively. Conclusions: Our results showed that movement of teeth with large vertical displacement was ineffective because of excessive friction. This finding might contribute to the understanding of the force system required for effective teeth movement and thereby facilitate the application of the appropriate light wire for leveling and alignment.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.257-268
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• 1998

During cleaning and shaping of narrow and curved canals, it is very difficult or nearly impossible to maintain the original canal shape. Procedural accidents such as, ledge, zipping, perforation, and instrument breakage are frequently occurred and even may lead to failure of endodontic therapy. To prevent these kinds of accidents, various instrumentation techniques and materials have been introduced. Recently some nickel titanium (NiTi) files are introduced and it is reported that These NiTi files created rounder preparations with less transportation than conventional instruments in curved canals. This study compared the change of the canal curvature and procedural accidents after instrumentation produced by stainless steel K-flexo file, and NiTi rotary files (Profile 29 and Quantec 2000). Thirty narrow and curved canals (25-45 degree) of extracted human molars were randomly divided into three groups. In group 1, canals were instrumented using a step-back and watch-winding/pull motion with K-flexo files. In group 2, canals were prepared with Profile 29. Group 3, canals were prepared with Quantec 2000 files. Before and after preparation of canals, periapical radiographs were taken and scanned. The change of canal curvature were measured using Photoshop 4.0 program and the incidence of procedural accidents were also evaluated. The results were as follows: 1. All group showed some loss of canal curvature after instrumentation. 2. Average loss of canal curvature was $6.70{\pm}5.31$ degree for group 1, $3.80{\pm}2.57$ degree for group 2, and $5.40{\pm}4.83$ degree for group 3. All group There was significant change in curvature between before and after instrumentation (p<0.05). But there was no statistical difference amoung 3 groups. 3. In group I, there were no procedural accidents, such as ledging, perforation, or instrument fracture. In group 2, two cases of ledge and one case of instrument fracture were produced Goup 3, each one case of ledge, perforation and instrument fracture were occurred. Whthin the limits of above results, It seems that NiTi rotary instrumentation is not All Mighty and if we use uncarefully, it is more dangerous to produce some procedural accidents than conventional hand files. But more studies should be taken to evaluate the exact effects of NiTi rotary instrumentations.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.672-678
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• 2011

In this work, carbon fibers were electrolessly Ni-plated in order to investigate the effect of metal plating on the electromagnetic shielding effectiveness (EMI-SE) of Ni-coated carbon fibers-reinforced epoxy matrix composites. The surfaces of carbon fibers were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Electric resistance of the composites was tested using a 4-point-probe electric resistivity tester. The EMI-SE of the composites was evaluated by means of the reflection and adsorption methods. From the results, it was found that the EMI-SE of the composites enhanced with increasing Ni plating time and content. In high frequency region, the EMI-SE didn't show further increasing with high Ni content (Ni-CF 10 min) compared to the Ni-CF 5 min sample. In conclusion, Ni content on the carbon fibers can be a key factor to determine the EMI-SE of the composites, but there can be an optimized metal content at a specific electromagnetic frequency region in this system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.226-231
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• 2020

Polyvinyl pyrrolidone nanofibers including nickel, zinc, and iron precursors were fabricated via the electrospinning method. To convert as-spun nanofibers to Ni0.5Zn0.5Fe2O4 oxide nanof ibers which is capable of shielding an electromagnetic wave, heat treatment conditions were optimized. To obtain the heat treatment condition that can exclude amorphous carbon black and secondary crystal phase, samples were taken at each temperature while the calcination process and analyzed. According to the X-ray diffraction (XRD) analysis, the Ni0.5Zn0.5Fe2O4 crystal phase started to appear from 300℃, but it was confirmed through energy dispersive spectroscopy (EDS) analysis that heat treatment of 500℃ or more was required to remove most of the carbon black. When the calcination temperature exceeds 650℃, crystal nuclei starts to grow and the fiber surface condition becomes rough, so it was confirmed that the heat treatment conditions should be selectively determined according to the application field.

• Journal of Powder Materials
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• v.29 no.5
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• pp.411-417
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• 2022

Environmental issues such as global warming due to fossil fuel use are now major worldwide concerns, and interest in renewable and clean energy is growing. Of the various types of renewable energy, green hydrogen energy has recently attracted attention because of its eco-friendly and high-energy density. Electrochemical water splitting is considered a pollution-free means of producing clean hydrogen and oxygen and in large quantities. The development of non-noble electrocatalysts with low cost and high performance in water splitting has also attracted considerable attention. In this study, we successfully synthesized a NiCo₂O₄/NF electrode for an oxygen evolution reaction in alkaline water splitting using a hydrothermal method, which was followed by post-heat treatment. The effects of heat treatment on the electrochemical performance of the electrodes were evaluated under different heat-treatment conditions. The optimized NCO/NF-300 electrode showed an overpotential of 416 mV at a high current density of 50 mA/cm² and a low Tafel slope (49.06 mV dec^-1). It also showed excellent stability (due to the large surface area) and the lowest charge transfer resistance (12.59 Ω). The results suggested that our noble-metal free electrodes have great potential for use in developing alkaline electrolysis systems.

• Journal of the Korean Electrochemical Society
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• v.9 no.3
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• pp.124-131
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• 2006

For commercialization of molten carbonate fuel cell (MCFC), it has some problems to be overcome such as decrease of porosity and thickness of the anode under the operating condition (at $650^{\circ}C$ and working pressure of more than 2 $kg_f/cm^2$). Recently, Ni-Al alloy anode has been proposed to replace the conventional Ni-Cr anode as an alternative material to resist a creep and inhibit the sintering. The objective of this research is to sinter the green sheet of Ni-Al alloy anode during single cell pre-treatment process, which has several advantages like cost down and simplification of manufacturing process. However, the Ni-Al alloy anode prepared with a conventional pre-treatment process showed the phase separation of Ni-Al alloy and formation of micropore(${\leqq}0.4{\mu}m$), resulting in low creep resistance and high electrolyte re-distribution. In order to prevent the Ni-Al alloy anode from phase-separating, nitrogen gas was used in the process of pre-treatment. Introducing the nitrogen, the phase separation from Ni-Al alloy into nickel and alumina was minimized and increased creep resistance. However, there was some micropore formation on the surface of Ni-Al alloy anode during the cell operation due to creation of lithium aluminate. Addition of more amount of electrolyte into a cell, especially at cathode, made the cell performance stable for 2,000 hrs. Consequently, it was possible to make the Ni-Al alloy anode with good creep resistance by the modified in-situ sintering technique.