• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.431-439
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• 2021

This research work aims to investigate the effect of the aerobic bacterium, Pseudomonas aeruginosa on the mechanical and electrochemical properties of the 316L stainless steel and α-brass. These properties of both the alloys were determined after 7 days of exposure to the controlled and inoculated media at 37℃. The microstructural and electrochemical test results revealed the deleterious effects of Pseudomonas aeruginosa. After exposure to the inoculated medium, the scanning electron microscopy (SEM) results showed the larger pitting and formation of relatively dense biofilm on α-brass compared to 316L stainless steel. The tensile strength and hardness of 316L stainless steel were slightly affected after exposure to the controlled and inoculated media. After exposure to the controlled medium and inoculated media, the tensile strength of the α-brass was least affected but a significant decrease in the hardness (from 165 HV to 124 HV) was observed due to the severe attack induced by the Pseudomonas aeruginosa. Similarly, the open-circuit potential of the 316L stainless steel in the inoculated medium was measured to be less active (-410 mV vs Ag/AgCl) than α-brass (-550 mV vs Ag/AgCl). In the inoculated medium, potentiodynamic polarization curves confirmed the severe attack of Pseudomonas aeruginosa on α-brass (7.15 × 10^-2 mm/year) compared to 316L stainless steel which registered a corrosion rate of 5.14 × 10^-4 mm/year.

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.237-253
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• 2022

The methyl 2-(1,3-dithietan -2- ylidene)-3-oxobutanoate (MDYO) and 2-(1,3-dithietan-2-ylidene) cyclohexane -1,3-dione (DYCD) were synthesized and tested at various concentrations as corrosion inhibitors for 316L stainless steel in 1 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface analysis techniques (SEM / EDX and Raman spectroscopy) and Functional Density Theory (DFT) was also used to calculate quantum parameters. The obtained results indicated that the inhibition efficiency of MDYO and DYCD increases with their concentration, and the highest value of corrosion inhibition efficiency was determined in the range of concentrations investigated (0.01 × 10^-3 - 10^-3 M). Polarization curves (Tafel extrapolation) showed that both compounds act as mixed-type inhibitors in 1M HCl solutions. Electrochemical impedance spectra (Nyquist plots) are characterized by a capacitive loop observed at high frequencies, and another small inductive loop near low frequencies. The thermodynamic data of adsorption of the two compounds on the stainless steel surface and the activation energies were determined and then discussed. Analysis of experimental results shows that MDYO and DYCD inhibitors adsorb to the metal surface according to the Langmuir model and the mechanism of adsorption of both inhibitors involves physisorption. SEM-EDX results confirm the existence of an inhibitor protective film on the stainless steel surface. The results derived from theoretical calculations supported the experimental observation.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.45.1-45.1
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• 2021

The polarization degree as a function of phase angle (the Sun-target-observer's angle), so-called the polarimetric phase curves (PPC), have provided priceless information on asteroids' albedos since B. Lyot (1929). Succeeding experimental works in 1970s have confirmed the Umow law: There is a universal and strong correlation between the albedo and the PPC slope (slope of the tangential line at the zero of the PPC at phase angle ~ 20 degrees). Experiments in 1990s (ref [1]), on the other hand, have demonstrated that the negative branch of PPC is dependent on the size parameter (X ~ π * particle-size / wavelength), especially when X <~5. The change in particle size changed the minimum polarization degree, location of the minimum, and the width of the negative branch (called the inversion angle). From polarimetry[2] and spectroscopy[3], large asteroids are expected to be covered with fine (<~ 10 ㎛ size) particles due to the gravity. The size parameters are X ~ 30 at the optical wavelength (λ ~ 0.5 ㎛) and X ~ 10 in near-infrared (J, H, Ks bands; λ ~ 1.2-2.2 ㎛), if the representative particle size of 5 ㎛ is considered. Accordingly, the near-infrared polarimetry has a great potential to validate the idea in ref[1]. We conducted near-infrared photopolarimetry of the large asteroid (4) Vesta using the Nishiharima Infrared Camera (NIC) at Nishi-Harima Astronomical Observatory (NHAO). NIC allows simultaneous polarimetric measurements in J, H, and Ks bands, and thus the change of PPC is obtained for three different size parameters. As a result, we found a signature of the change in the negative branch in the PPC of asteroid (4) Vesta. We will introduce our observation and the results and give an interpretation of the regolith on Vesta.

• Restorative Dentistry and Endodontics
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• v.46 no.1
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• pp.6.1-6.10
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• 2021

Objectives: The aim of this study was to evaluate the corrosion resistance of heat-treated (Reciproc and WaveOne) and non-heat-treated (ProTaper and Mtwo) superelastic nickel-titanium endodontic files when immersed in a 5.25% sodium hypochlorite solution. Materials and Methods: Anodic polarization curves were obtained with potential sweeps that began at the open circuit potential or corrosion potential (E_corr). The pitting potential (E_pit) was identified on the anodic polarization curve as the potential at which a sudden increase in current was observed. The micromorphology of the 28 tested files was analyzed before and after the electrochemical assay using scanning electron microscope (SEM). The data were analyzed using 1-way analysis of variance with the post hoc Bonferroni test (for E_corr) and the Student t-test for independent samples (for E_pit). Results: The mean E_corr values were 0.506 V for ProTaper, 0.348 V for Mtwo, 0.542 V for Reciproc, and 0.321 V for WaveOne files. Only WaveOne and Protaper files exhibited pitting corrosion, with E_pit values of 0.879 V and 0.904 V, respectively. On the SEM images of the ProTaper and WaveOne files, cavities suggestive of pitting corrosion were detected. Conclusions: Signs of corrosion were observed in both heat-treated and non-heat-treated files. Of the evaluated files, WaveOne (a heat-treated file) and ProTaper (a non-heat-treated file) exhibited the lowest corrosion resistance.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1422-1432
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• 2014

Convergent all-electron multi-reference configuration-interaction (MRCI) calculations are performed for a lithium dimer with Kaufmann's Rydberg basis functions. A comparison of the results of these calculations with those of the effective core potential/core polarization potential (ECP/CPP) method and experimental data reveals the deficiency of the all-electron ab initio method. The deficiency is related to the mere 51.9% attainment of electron correlation for the ground state. The percent attainment of electron correlation for the first excited state is slightly better than that for the ground state, preventing us from obtaining better agreements with experimental data by means of increasing the size of basis sets. The Kaufmann basis functions are then used with the ECP/CPP method to obtain the accurate convergent potential energy curves for the $^1\prod_u$ states correlated to Li(2p) + Li(2p) and Li(2s) + Li(n = 2, 3, 4). Quantum defect curves (QDCs) calculated for both the $X^2\sum_g$ and 1 $^2\prod_u$ states of the $Li{_2}^+$ ion and the Lu-Fano plot reveal a strong series-series interaction between the two $2snp{\pi}$ and $2pnp{\pi}$ Rydberg series. The QDCs are then used to resolve assignment problems in the literature. The reassignments, performed by Jedrzejewski-Szemek et al., of the dissociation product of the D $^1\prod$ state from (2s+3d) to (2s+3p) and that of the 6 $^1\prod_u$ from (2s+4d) to (2s+4p) are found to be incorrect. It may be more natural to assign their $2snp{\pi}$ Rydberg series as a $2snd{\pi}$ series. The state, assigned as 5p $^1\prod_u$ by Ross et al. and 4d $^1\prod$ by Jedrzejewski-Szemek et al., is assigned as the 7 $^1\prod_u$ state, correlated to the Li(2s) + Li(4f) limit.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.307-311
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• 2011

Solid solutions of the (1-x)$BiFeO_3-xSrTiO_3$ ceramic system (x = 0~0.4) are explored here in attempts to obtain multiferroic properties in these systems. The polarization-electric field hysteresis, magnetization-magnetic field curves, and dielectric properties are also characterized. This solid-solution system shows a crystal structural transition from a noncentrosymmetric (R3c) structure to a centrosymmetric (Pm-3m) structure at 0.3 < x < 0.4. The solid solution ceramic shows unsaturated M-H behavior and low remanent magnetization over the composition region of 0.1 ${\leq}$ x ${\leq}$ 0.3. The $0.7BiFeO_3-0.3SrTiO_3$ system shows the largest value of $M_s$ at 0.17 emu/g and the smallest value of $H_c$ at 1.06 kOe. The P-E hysteresis curves were not saturated under an electric field as high as E = 70 kV/cm. This system is considered to have multiferroic characteristics in the composition range of 0.1 ${\leq}$ x ${\leq}$ 0.3.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1352-1354
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• 1998

$LiNbO_3$ transistor showed relatively stable characteristic, low interface trap density, and large remanent polarization. This paper reports ferroelectric $LiNbO_3$ thin films grown directly on p-type Si(100) substrates by 13.56 MHz rf magnetron sputtering system for FRAM applications. To take advantage of low temperature requirement for growing films, we deposited $LiNbO_3$ films lower than $300 ^{\circ}C$. RTA(Rapid Thermal Anneal) treatment was performed for as-deposited films in an oxygen atmosphere at $600^{\circ}C$ for 60 sec. We learned from X-ray diffraction that the RTA annealed films were changed from amorphous to poly-crystalline $LiNbO_3$ which exhibited (012), (015), and (022) orientations. The I-V characteristics of $LiNbO_3$ films before and after anneal treatment showed that RTA improved the leakage current of films. The leakage current density of films decreased from $10^{-5}$ to $10^{-7} A/cm^2$ at room temperature measurement. Breakdown electric field of the films exhibited higher than 500 kV/cm. The C-V curves showed the clockwise hysteresis represents ferroelectric switching characteristics. From C-V curves, we calculated dielectric constant of thin film $LiNbO_3$ as 27.5 which is close to that of bulk value.

• Korean Journal of Materials Research
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• v.25 no.6
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• pp.288-292
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• 2015

New lead-free piezoelectric ceramics $0.96[\{Bi_{0.5}(Na_{0.84}K_{0.16})_{0.5}\}_{1-x}La_x(Ti_{1-y}Nb_y)O_3]-0.04SrTiO_3$ (BNKT-ST-LN, where $x=y=0.00{\leq}(x=y){\leq}0.015)$ were synthesized using the conventional solid-state reaction method. Their crystal structure, microstructure, and electrical properties were investigated as a function of the La and Nb (LN) content. The X-ray diffraction patterns revealed the formation of a single-phase perovskite structure for all the LN-modified BNKT-ST ceramics in this study. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature ($T_m$) shifted towards lower temperatures and the curves became more diffuse with an increasing LN content. At the optimum composition (LN 0.005), a maximum value of remnant polarization ($33C/cm^2$) with a relatively low coercive field (22 kV/cm) and high piezoelectric constant (215 pC/N) was observed. These results indicate that the LN co-modified BNKT-ST ceramic system is a promising candidate for lead-free piezoelectric materials.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.62-67
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• 2009

Ti and Ti-alloys have good biocompatibility, appropriate mechanical properties and excellent corrosion resistance. However, the widely used Ti-6Al-4V is found to release toxic ions (Al and V) into the body, leading to undesirable long-term effects. Ti-6Al-4V has much higher elastic modulus (100 GPa) than cortical bone (20 GPa). Therefore, titanium alloys with low elastic modulus have been developed as biomaterials to minimize stress shielding. The electrochemical behavior of surface-modified and MC3T3-E1 cell-cultured Ti-30(Nb,Ta) alloys with low elastic modulus have been investigated using various electrochemical methods. Surfaces of test samples were treated as follows: $0.3{\mu}m$ polished; $25{\mu}m$, $50{\mu}m$ and $125{\mu}m$ sandblasted. Specimen surfaces were cultured with MC3T3-E1 cells for 2 days. Average surface roughness ($R_a$) and morphology of specimens were determined using a surface profilometer, OM, and FE-SEM. Corrosion behavior was investigated using a potentiostat(EG&G PARSTAT 2273), and electrochemical impedance spectroscopy was performed (10 mHz to 100 kHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The microstructures of the Ti-30(Ta,Nb) alloys had a needle-like appearance. The $R_a$ of polished Ti-30Ta and Ti-30Nb alloys was lower than that of the sandblasted Ti alloy. Cultured cells displayed round shapes. For polished alloy samples, cells were well-cultured on all surfaces compared to sandblasted alloy samples. In sandblasted and cell-cultured Ti-30(Nb,Ta) alloy, the pitting potential decreased and passive current density increased as $R_a$ increased. Anodic polarization curves of cell-cultured Ti alloys showed unstable behavior in the passive region compared to non-cell-cultured alloys. From impedance tests of sandblasted and cell-cultured alloys, the polarization resistance decreased as $R_a$ increased, whereas, $R_a$ for cell-cultured Ti alloys increased compared to non-cell-cultured Ti alloys.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.6
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• pp.21-27
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• 1998

Electrical and optical characteristics of ZnS:Mn/ZnS:Tb multilayer TFEL devices were investigated for multi-color electroluminescent display applications. Emission spectra of M $n^{2+}$ and T $b^{3+}$ ions were observed from ZnS:Mn/ZnS:Tb multi-layer TFEL devices, and were very broad from 540 nm to 640 nm. Saturation luminance measured at 155 V was 1025 Cd/$m^2$. C-V, $Q_{t}$ - $V_{p}$ curves showed that the phosphor capacitance ( $C_{p}$ ) and the insulator capacitance ( $C_{i}$ ) were 13.5nF/$\textrm{cm}^2$ and 60 nF/$\textrm{cm}^2$, respectively. Threshold voltage( $V_{thl}$) was shown to decrease from 126 V to 93 V due to the increase of the applied voltage from 155 V to 185 V, which was attributed to the increase of the polarization charge. The equation for the calculation of the threshold voltage as a function of the applied voltage was proposed for the first time. The calculated threshold voltage agreed well with the data obtained from the measurement.t.t.t.