• Journal of the Korean institute of surface engineering
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• v.46 no.5
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• pp.187-191
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• 2013

Niobium nitride (NbN) films were deposited on AISI 304 stainless steels by inductively coupled plasma (ICP) assisted dc magnetron sputtering method at different ICP powers, and the effects of ICP power on the phase formation, mechanical and chemical properties of the films were investigated. X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (FESEM) were used to analyze the crystal structure and micro-knoop hardness was used to measure the hardness of the films. Also, 3-D mechanical profiler and a ball-on-disk wear tester were used to measure the thickness of the films and to estimate wear characteristics, respectively. The thickness of the films decreased but their hardness increased with increasing ICP power, and it was confirmed that only cubic ${\delta}$-NbN(200) remained at high ICP power. At lower ICP powers, a mixture of the hexagonal ${\delta}^{\prime}$-NbN and cubic ${\delta}$-NbN phases was obtained in the films and the hardness decreased. The corrosion potential value increased gradually with increasing ICP power, but the changes of ICP power did not significantly influence the overall corrosion resistance.

• Korean Journal of Metals and Materials
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• v.46 no.7
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• pp.458-463
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• 2008

High purity Fe thin films were prepared by the ion beam deposition method with $^{56}Fe^{+}$ions on the Si substrate at the room temperature. The Fe thin films were deposited at the ion energy of 50 eV and 100 eV. Microstructural properties were investigated on the atomic scale using high-resolution transmission electron microscopy (HRTEM). It was found that the Fe thin film obtained with the energy of 50 eV having an excellent corrosion resistance consists of the amorphous layer of ~15 nm in thickness and the bcc crystalline layer of about 30 nm in grain size, while the thin film obtained with the energy of 100 eV having a poor corrosion resistance consists of little amorphous layer and the defective crystalline layer. Furthermore the crystal structures and arrangements of the oxide layers formed on the Fe thin films were analyzed by processing of the HRTEM images. It was concluded that the corrosion behavior of Fe thin films relates to the surface morphology and the crystalline structure as well as the degree of purification.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.6
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• pp.480-486
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• 2021

Magnetoelectric (ME) composite is composed of a piezoelectric material and a magnetostrictive material. Among various ME structures, 2-2 type layered ME composites are anticipated to be used as high-sensitivity magnetic field sensors and energy harvesting devices especially operating at its resonance modes. Rosen type piezoelectric transducer using piezoelectric material is known to amplify a small electrical input voltage to a large electrical output voltage. The output voltage of these Rosen type piezoelectric transducers can be further enhanced by modifying them into ME composite structures. Herein, we fabricated Rosen type ME composites by sandwiching Rosen type PMN-PZT single crystal between two Ni layers and studied their ME coupling. However, the voltage step-up ratio at the resonance frequency was found to be smaller than the value calculated with α_ME value. The ATILA FEA (Finite Elements Analysis) simulation results showed that the position of the nodal point was changed with the presence of a magnetostrictive layer. Thus, while designing a Rosen type ME composite with high performance in a resonant driving situation, it is necessary to optimize the position of the nodal point by optimizing the thickness or length of the magnetostrictive layer.

• Journal of Environmental Science International
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• v.28 no.6
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• pp.561-570
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• 2019

A zeolitic material (Z-Y2) was synthesized from Coal Fly Ash (CFA) using a fusion/hydrothermal method under low-alkali condition (NaOH/CFA = 0.6). The adsorption performance of the prepared zeolite was evaluated by monitoring its removal efficiencies for Sr and Cs ions, which are well-known as significant radionuclides in liquid radioactive waste. The XRD (X-ray diffraction) patterns of the synthesized Z-Y2 indicated that a Na-A type zeolite was formed from raw coal fly ash. The SEM (scanning electron microscope) images also showed that a cubic crystal structure of size $1{\sim}3{\mu}m$ was formed on its surface. In the adsorption kinetic analysis, the adsorption of Sr and Cs ions on Z-Y2 fitted the pseudo-second-order kinetic model well, instead of the pseudo-first-order kinetic model. The second-order kinetic rate constant ($k_2$) was determined to be $0.0614g/mmol{\cdot}min$ for Sr and $1.8172g/mmol{\cdot}min$ for Cs. The adsorption equilibria of Sr and Cs ions on Z-Y2 were fitted successfully by Langmuir model. The maximum adsorption capacity ($q_m$) of Sr and Cs was calculated as 1.6846 mmol/g and 1.2055 mmol/g, respectively. The maximum desorption capacity ($q_{dm}$) of the Na ions estimated via the Langmuir desorption model was 2.4196 mmol/g for Sr and 2.1870 mmol/g for Cs. The molar ratio of the desorption/adsorption capacity ($q_{dm}/q_m$) was determined to be 1.44 for Na/Sr and 1.81 for Na/Cs, indicating that the amounts of desorbed Na ions and adsorbed Sr and Cs ions did not yield an equimolar ratio when using Z-Y2.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.605-609
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• 2011

We study on the oxygen behavior of $V_2O_5/TiO_2$ catalysts in the $NH_3$-selective catalytic reduction (SCR) prepared by the ball milling processing. There are not any changes in crystal structure and surface area of the $TiO_2$ catalyst by ball milling, but the maximal reduction temperature decreased in $H_2$-temperature programmed reduction (TPR) analysis. Experimental observations with various concentrations of oxygen indicate that all catalysts showed a very low NOx conversion rate in the absence of oxygen and the reactivity of ball milled catalyst higher depending on the oxygen. It is occurred because the degree of participation of atmospheric oxygen and lattice oxygen is great than that of the not-milled catalyst.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.345-349
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• 1988

The polycrystalline powder of (CaLa) (MgMo)$O_6$ has been prepared at $1350^{\circ}C$ in $H_2/H_2O$ and $N_2$ flowing atmosphere. The powder X-ray diffraction pattern indicates that (CaLa) (MgMo)$O_6$ has a monoclinic perovskite structure with the lattice constants $a_0=b_0=7.901(1){\AA}$, $c =7.875(1){\AA}\;and\;{\gamma}=89^{\circ}$16'(1'), which can be reduced to orthorhombic unit cell, a = 5.551(1) ${\AA}$, b = 5.622(1) ${\AA}$ and c = 7.875(1) ${\AA}$. The infrared spectrum shows two strong absorption bands with their maxima at 590($ν_3$) and 380($ν_4$) cm, which are attributed to $2T_{1u}$ modes indicating the existence of highly charged molybdenum octahedron $MoO_6$ in the crystal lattice. According to the magnetic susceptibility measurement, the compound follows the Curie-Weiss law below room temperature with the effective magnetic moment 1.83(1)$_{{\mu}B}$, which is well consistent with that of spin only value (1.73 $_{\mu}_B$) for $Mo^{5+}$ with $4d^1$-electronic configuration within the limit of experimental error. From the thermogravimetric analysis, it has been confirmed that (CaLa) (MgMo)$O_6$ decomposes gradually into $CaMoO_4,\;MoO_3,\;MgO,\;La_2O_3$ and unidentified phases due to the oxidation of $Mo^{5+}$ to $Mo^{6+}$.

• Oral Biology Research
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• v.42 no.4
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• pp.187-197
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• 2018

Chemical agents such as minocycline (MC) and citric acid (CA) were suggested in the treatment of contaminated implant surface. In this study, MC-HCl treatment was performed to enhance surface characteristics of titanium alloy surface. The purpose of this study was to assess the characteristics and the biocompatibility of Ti-6Al-4V surface treated by MC. Alpha-beta titanium alloy (Ti-6Al-4V) samples were prepared and they were divided into 6 groups according to chemical concentration and treatment time. These groups include 1) group I, non-treated smooth titanium alloy; 2) group II, MC 1.5 mg/mL for 1 hour; 3) group III, MC 1.5 mg/mL for 24 hours; 4) group IV, MC 15 mg/mL for 10 minutes; 5) group V, MC 100 mg/mL for 5 minutes; 6) group VI, pH1 CA for 3 minutes. The analysis of the surface characteristics of MC-treated titanium alloy was executed using scanning electron microscopy, roughness test, and X-ray photoelectron spectroscopy (XPS). Cell adhesion and MTT assay was done using MC3T3 cell. Titanium surfaces treated with MC indicated a more smoothened surface microstructure. For group II and III, the new peaks of rutile TiO2 were found. Group II and V have more basic group of Ti-OH form in XPS. In MTT assay, all MC-treated groups showed significantly higher cell viability compared to control. The surface roughness, crystal structure, surface hydrophilicity, cell viability of smooth titanium surface was improved by MC treatment. Compared with the control experiment and CA-treated group, smooth titanium surface treated with MC showed improved surface characteristics and cell biocompatibility.

• Current Photovoltaic Research
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• v.10 no.4
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• pp.101-106
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• 2022

We prepared a CsPbI₂Br solution using Cesium iodide (CsI), Lead (II) bromide (PbBr₂) and Lead (II) iodide (PbI₂) materials into a polar solvent mixture of N,N-dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO). A simple spin coating technique was used for the fabrication of CsPbI₂Br absorber layer in the solution process. In order to prepare uniform coating of absorber film we adopted a hot-air process in assocation with the spin coating. It was confirmed that the thin film manufactured by the hot-air process had a higher absorption rate than that without it, and the optical band gap was measured 1.93 eV. The thin film of absorber was uniformly prepared and revealed the Black α-Cubic crystal phase as proved through X-ray diffraction analysis. Finally, a perovskite solar cell having an n-i-p structure was manufactured with a CsPbI₂Br perovskite absorption layer. From the solar cell, we obtained a power conversion efficiency (PCE) of 5.97% in a forward measurement.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.435-444
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• 2001

WC-( $Ti_{1-x}$ A $l_{x}$) N coatings of constant changing Al concentration were deposited on S45C substrates by high-ionization sputtered PVD method. The Al concentration could be controlled by using evaporation source for Al and fixing the evaporation rate of the metals (i.e, WC- $Ti_{0.86}$A $l_{0.14}$N, WC- $Ti_{0.72}$A $l_{0.28}$N, and WC- $Ti_{0.58}$A $l_{0.42}$N). The corrosion behavior of WC-( $Ti_{1-x}$ A $l_{x}$)N coatings in a deaerated 3.5% NaCl solution was investigated by electrochemical corrosion tests and surface analyses. The measured galvanic corrosion currents between coating and substrate indicated that WC- $Ti_{0.72}$A $l_{0.28}$N coating showed the best resistance of the coating tested. The results of potentiodynamic polarization tests showed that the WC- $Ti_{0.72}$A $l_{0.28}$N coating deposited with 32W/c $m^2$ of Al target revealed higher corrosion resistance. This indicated that the WC- $Ti_{0.72}$A $l_{0.28}$N coating is effective in improving corrosion resistance. In EIS, the WC- $Ti_{0.72}$A $l_{0.28}$N coating showed one time constant loop and increased a polarization resistance of coating ( $R_{coat}$) relative to other samples. Compositional variations of WC-( $Ti_{1-x}$ A $l_{x}$)N coatings were analyzed by EDS and XRD analysis was performed to evaluate the crystal structure and compounds formation behavior. Surface morphologies of the films were observed using SEM and AFM. Scratch test was performed to measure film adhesion strength.strength. adhesion strength.strength.

• Journal of the Korean institute of surface engineering
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• v.56 no.5
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• pp.299-308
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• 2023

In this study, phosphorus (P)-doped nickel cobaltite (P-NiCo₂O₄) and nickel-cobalt layered double hydroxide (P-NiCo-LDH) were synthesized on nickel (Ni) foam as a conductive support using hydrothermal synthesis. The thermal properties, crystal structure, microscopic surface morphology, chemical distribution, electronic state of the constituent elements on the sample surface, and electrical properties of the synthesized P-NiCo₂O₄ and P-NiCo-LDH samples were analyzed using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The P-NiCo₂O₄ electrode exhibited a specific capacitance of 1,129 Fg^-1 at a current density of 1 Ag^-1, while the P-NiCo-LDH electrode displayed a specific capacitance of 1,012 Fg^-1 at a current density of 1 Ag-1. When assessing capacity changes for 3,000 cycles, the P-NiCo₂O₄ electrode exhibited a capacity retention rate of 54%, whereas the P-NiCo-LDH electrode showed a capacity retention rate of 57%.