• Corrosion Science and Technology
• /
• v.20 no.4
• /
• pp.196-203
• /
• 2021

To improve corrosion resistance and reduce the hydrogen uptake of 22MnB5, up to 5% Mg was added to the AlSi coating of 22MnB5. After hot-stamping and electrocoating were done on the metallic-coated specimen, the surface characteristics of the steel, hydrogen uptake content, and corrosion resistance were examined by transmittance electron microscopy, thermal desorption spectrometry, cyclic corrosion testing, and electrochemical impedance spectroscopy. Mg was investigated as MgO on the surface layer after hot-stamping while it existed as Mg₂Si before hot-stamping. The total hydrogen content of 22MnB5 was decreased along with the Mg content. However, there was no difference at 0.2 wt% or more. When a small amount of Mg was added, the coating corrosion resistance was decreased, but when it was added at around 1.0 wt%, the greatest corrosion resistance increase was seen. However, when 3 wt% or more was added excessively, the corrosion resistance was decreased. MgO on the surface was considered to suppress H uptake by the AlSi melting solution and increase the barrier effect of the coating.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2016.10a
• /
• pp.74-75
• /
• 2016

Various types of microstrip antennas can be used for many applications in wireless communication systems. In this paper, we studied a design method for a broadband dual-fed stacked microstrip patch antenna. The impedance bandwidth is improved by adjusting the sizes of main radiating patch and parasitic patch, the distance between the patches, the length of inset feed line, etc. The antenna is designed by simulation for an operation in the frequency range of 2.3-2.7 GHz, and the antenna characteristics such as return loss, gain, radiation patterns are examined.

• Journal of Electrochemical Science and Technology
• /
• v.10 no.2
• /
• pp.159-169
• /
• 2019

The activated carbon materials were prepared from waste biomass by ultrasonic assisted chemical activation method (UCA), ultrasonic assisted physical activation method (UPA) and Manganese nitrogen doped carbon (Mn/N-C). The XRD result shows the turbostatic (fully disordered) structure. The cyclic voltammetry test was done at 50 mV/s using 1M sodium sulfate and the values of specific capacitance were found to be 93, 100 and 115 F/g for UCA, UPA and Mn/N-C respectively. The power density values for the samples UCA, UPA and Mn/N-C were found to be 46.04, 87.97 and 131.42 W/kg respectively. The electrochemical impedance spectroscopy was done at low frequency between 1 to 10 kHz. The Nyquist plot gives the resistant characteristics of the materials due to diffusional resistance at the electrode-electrolyte interface. The Energy Dispersive X-Ray Spectroscopyanalysis (EDAX) analysis showed that the percentage doping of nitrogen and manganese were 3.53 wt% and 9.44 wt% respectively. It is observed from the experiment Mn/N-C doped carbon show good physical and electrochemical properties.

• Korean Journal of Metals and Materials
• /
• v.47 no.9
• /
• pp.558-566
• /
• 2009

The alloying effect of a small amount of nickel on low alloy steel for application to flue gas desulfurization(FGD) systems was studied. The structural characteristics of the rust layer were investigated by scanning electron microscopy(SEM). The electrochemical properties were examined by means of potentiostatic polarization test, potentiodynamic polarization test, and electrochemical impedance spectroscopy(EIS) in a modified green death solution of 16.9 vol.% $H_2SO_4$+0.35 vol.% HCl at $60^{\circ}C$ and an acid rain solution of $6.25{\times}10^{-5}M\;H_2SO_4+5.5{\times}10^{-3}M\;NaCl$ at room temperature. It was found that as the amount of nickel increased, the corrosion rate increased in the modified green death solution, which seemed to result from micro-galvanic corrosion between NiS and alloy matrix. In acid rain solution, the corrosion rate decreased as the amount of nickel increased due to the repulsive force of $NiFe_2O_4$ rust against $Cl^-$ ions by electronegativity.

• Composites Research
• /
• v.34 no.6
• /
• pp.373-379
• /
• 2021

A series of novel PBI/SrTiO₃ nanocomposite membranes composed of polybenzimidazole (PBI) and strontium titanate (SrTiO₃) with a perovskite structure were fabricated with various concentrations of SrTiO₃ through a solution casting method. Various characterization techniques such as proton nuclear magnetic resonance, thermogravimetric analysis, atomic force microscopy (AFM) and AC impedance spectroscopy were used to investigate the chemical structure, thermal, phosphate absorption and morphological properties, and proton conductivity of the fabricated nanocomposite membranes. The optimized PBI/SrTiO₃-8 polymer nanocomposite membrane containing 8wt% of SrTiO₃ showed a higher proton conductivity of 7.95 × 10^-2 S/cm at 160℃ compared to other nanocomposite membranes. The PBI/SrTiO₃-8 composite membrane also showed higher thermal stability compared to pristine PBI. In addition, the roughness change of the polymer composite membrane was also investigated by AFM. Based on these results, nanocomposite membranes based on perovskite structures are expected to be considered as potential candidates for high-temperature PEM fuel cell applications.

• Journal of Korea Society of Digital Industry and Information Management
• /
• v.18 no.4
• /
• pp.47-54
• /
• 2022

In this paper, MEMS embedded system design implemented the sensor events via analyzing the characteristics that dynamically happened to an abnormal status in power IoT environments in order to guarantee a maintainable operation. We used three kinds of tools in this paper, at first Bluetooth Low Energy (BLE) technology which is a suitable protocol that provides a low data rate, low power consumption, and low-cost sensor applications. Secondly LSM6DSOX, a system-in-module containing a 3-axis digital accelerometer and gyroscope with low-power features for optimal motion. Thirdly BM1422AGMV Digital Magnetometer IC, a 3-axis magnetic sensor with an I2C interface and a magnetic measurable range of ±120 uT, which incorporates magneto-impedance elements to detect the magnetic field when the current flowed in the power devices. The proposed MEMS system was developed based on an nRF5340 System on Chip (SoC), previously compared to the standalone embedded system without bluetooth technology via mobile App. And also, MEMS embedded system with BLE 5.0 technology broadcasted the MEMS system status to Android mobile server. The experiment results enhanced the performance of MEMS system design by combination of sensors, BLE technology and mobile application.

• Journal of Environmental Science International
• /
• v.32 no.1
• /
• pp.25-35
• /
• 2023

The purpose of this study was to determine the optimal sound absorption conditions by comparing the sound absorption characteristics of fresh and air-dried leaves of Quercus glauca, the main species of evergreen broadleaf trees (EBLT) in southern Korea. The sound absorption coefficients (SACs) obtained under 18 conditions were comparatively analyzed. The SAC of air-dried leaves improved significantly with increasing leaf layer thickness. The highest average SAC in the fresh leaf group was 0.617, which was observed under the condition of a leaf specimen size of 0.5 × 0.5 cm² and a leaf layer thickness of 1.75 cm. In a group of air-dried leaves, this was 0.615 under the condition of a leaf specimen size of 0.5 × 0.5 cm² and a leaf layer thickness of 2.50 cm. The maximum value of SAC for each wavelength was observed under the condition of a leaf layer thickness of 2.50 cm consisting of 0.5 × 0.5 cm² leaf specimens, ranging from 1,400 Hz to 1,500 Hz.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2003.05a
• /
• pp.53-53
• /
• 2003

Plasma polymerized organic thin films were deposited on Si(100) glass and metal substrates using thiophene and ethylcyclohexane precursors by PECVD method. In order to compare electrochemical properties of the as-grown thin films, the effects of the RF plasma power in the range of 30~100 W. AFM showed that the polymer films with smooth surface and sharp interface could be grown under various deposition conditions. Impedance analyzer was utilized for the determination of I-V curve for leakage current density and C-V for dielectric constants, respectively. To obtain C-V curve, we used a MIM structure of metal(Al)-insulator(plasma polymerized thin film)-metal(Pt) structure. Al as the electrode was evaporated on the thiophene films that grew on Pt coated silicon substrates, and the dielectric constants of the as-grown films were then calculated from C- V data measured at 1MHz. From the electrical property measurements such as I-V and C-V characteristics, the minimum dielectric constant and the best leakage current of thiophene thin films were obtained to be about 3.22 and $1{\;}{\times}10^{-11}{\;}A/cm^2$. However, in case of ethylcyclohexane thin films, the minimum dielectric constant and the best leakage current were obtained to be about 3.11 and $5{\;}{\times}10^{-12}{\;}A/cm^2$.

• Progress in Superconductivity and Cryogenics
• /
• v.9 no.1
• /
• pp.67-71
• /
• 2007

HTS transformers which have been developed until now had only fundamental structures. Among the auxiliary functions of conventional transformers, voltage regulating is the most important one. For the voltage regulation, conventional transformers are equipped with on load tap changers (OLTCS). In this paper, we describe the possibility of the HTS transformer with OLTC. For the case study, we designed a single phase 33 MVA HTS transformer with OLTC. It is one of three individual HTS transformers which composes a 3 phase, 100 MVA transformer. It is expected to substitute for a 3 phase, 60 MVA conventional transformer in Korea. The parameters of an HTS transformer are varied due to the gap length between primary and secondary windings. The length was decided for the transformer to have the impedance of 12 %. Its size was limited to the one of the conventional transformer. The characteristics of the HTS transformer were analyzed in both case of having OLTC and not.

• Progress in Superconductivity and Cryogenics
• /
• v.8 no.4
• /
• pp.22-25
• /
• 2006

This paper deals with the computation of the current limiting behavior of high-temperature superconducting (HTS) modules for the superconducting fault current limiter (SFCL). The SFCL module consists of a monofilar type BSCCO-2212 tube and a shunt coil made of copper or brass. The shunt coil is connected to the monofilar superconducting tube in parallel. Through analysis of the quench behavior of the monofilar component with shunt coils, it is achieved to drive an equivalent circuit equation from the experimental circuit structure. In order to analyze the quench behavior of the SFCL module, we derived a partial differential equation technique. Inductance of the monofilar component and the impedance of the shunt coil are calculated by Bio-Savart and Ohm's formula, respectively. We computed the quench behavior using the calculated values, and compared the results with experimental results for the quench characteristics of a component. The results of computation and test agreed well each other, and it was concluded that the analytic result could be applied effectively to design of the distribution-level SFCL system.