• Corrosion Science and Technology
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• 제10권6호
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• pp.212-217
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• 2011

In this study, corrosion characteristics of TiN and ZrN film on the abutment screw by arc-ion plating were investigated using a potentiodynamic anodic polarization test in deaerated 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The surface morphologies of the coating layers before and after corrosion test were investigated by a field-emission scanning electron microscope (FE-SEM) and a energy dispersive x-ray spectroscopy (EDS). The surfaces of the TiN and ZrN coated abutment screws showed the smooth surfaces without mechanical defects like scratches which can be formed during the manufacturing process, compared with those of the non-coated abutment screw. The corrosion and passive current densities of TiN and ZrN coated abutment screws were lower than those of the non-coated abutment screw.

• Corrosion Science and Technology
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• 제19권2호
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• pp.89-99
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• 2020

The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion pit.

• 한국재료학회지
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• 제25권6호
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• pp.293-299
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• 2015

In this study, nitrogen ions were implanted into STS 316L austenitic stainless steel by plasma immersion ion implantation (PIII) to improve the corrosion resistance. The implantation of nitrogen ions was performed with bias voltages of -5, -10, -15, and -20 kV. The implantation time was 240 min and the implantation temperature was kept at room temperature. With nitrogen implantation, the corrosion resistance of 316 L improved in comparison with that of the bare steel. The effects of nitrogen ion implantation on the electrochemical corrosion behavior of the specimen were investigated by the potentiodynamic polarization test, which was conducted in a 0.5 M $H_2SO_4$ solution at $70^{\circ}C$. The phase evolution and texture caused by the nitrogen ion implantation were analyzed by an X-ray diffractometer. It was demonstrated that the samples implanted at lower bias voltages, i.e., 5 kV and 10 kV, showed an expanded austenite phase, ${\gamma}_N$, and strong (111) texture morphology. Those samples exhibited a better corrosion resistance.

• 한국표면공학회지
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• 제48권6호
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• pp.269-274
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• 2015

In this experiment, post-nitriding treatment was performed at $400^{\circ}C$ on AISI 316 stainless steel which was plasma carburized previously at $430^{\circ}C$ for 15 hours. Plasma nitriding was implemented on AISI 316 stainless steel at various gas compositions (25% $N_2$, 50% $N_2$ and 75% $N_2$) for 4 hours. Additionally, during post nitriding Ar gas was used with $H_2$ and $N_2$ to observe the improvement of surface properties. After treatment, the behavior of the hybrid layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. Meanwhile, it was found that the surface hardness increased with increasing the nitrogen gas content. Also small percentage of Ar gas was introduced in the post nitriding process which improved the hardness of the hardened layer but reduced the corrosion resistance compared with the carburized sample. The experiment revealed that AISI 316L stainless steel showed better hardness and excellent corrosion resistance compared with the carburized sample, when 75% $N_2$ gas was used during the post nitriding treatment. Also addition of Ar gas during post nitriding treatment degraded the corrosion resistance of the sample compared with the carburized sample.

• 한국표면공학회지
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• 제44권2호
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• pp.44-49
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• 2011

The films formed on AZ31B magnesium alloy were prepared from alkaline solution composed of potassium permanganate and sodium hydroxide. The immersion tests were carried out at the different concentration of sodium hydroxide and pre-treatment method in 5 minute. The morphology and the phase composition of the film were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior of the film in 5.0% NaCl solution was evaluated using potentiodyanmic polarization. Open circuit potential in developing film was examined with time. The thin and transparent film was mainly composed of MgO and $Mg(OH)_2$. The film with the best corrosion resistance was obtained at $70^{\circ}C$ bath temperature, 1.6 M concentration of sodium hydroxide and chemical pre-treatment.

• 한국전기전자재료학회논문지
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• 제22권1호
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• pp.29-34
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• 2009

PLZT thin films were deposited on platinized silicon (Pt/$TiSiO_2$/Si) substrate by RF magnetron sputtering. A $TiO_2$ buffer layer was fabricated, prior to deposition of PLZT films. the layer was strongly affected the crystallographic orientation of the PLZT films. X-ray diffraction was performed on the films to study the crystallization of the films as various substrate temperatures (Ts). According to increasing Ts, preferred orientation of films was changed (110) plane to (111) plane. The ferroelectric, dielectric and electrical properties of the films were also investigated in detail as increased substrate temperatures. The PLZT films deposited at $400^{\circ}C$ showed good ferroelectric properties with the remnant polarization of $15.8{\mu}C/cm^2$ and leakage current of $5.4{\times}10^{-9}\;A/cm^2$.

• 한국전기전자재료학회논문지
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• 제16권4호
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• pp.265-271
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• 2003

Ferroelectric lanthanum-substituted Bi$_4$Ti$_3$O$_{12}$(BLT) thin films were fabricated by spin-coating onto a Pt/Ti/SiO$_2$/Si substrate by metalorganic decomposition technique. The grain size in BLT thin films were prepared with controlled by various drying process. The effect of grain size on the crystallization and ferroelectric properties were investigated by x-ray diffraction and field emission scanning electron microscope. The dependence of crystallization and electrical properties are related to the grain size in BLT thin films with different drying temperature. The remanent polarization of BLT thin film increases with the increasing grain size. The value of 2P$_{r}$ and E$_{c}$ of BLT thin film dried at 45$0^{\circ}C$ were 25.9 $\mu$C/$\textrm{cm}^2$ and 85 kV/cm, respectively. The BLT thin film with larger grain size has better fatigue properties. The fatigue properties revealed that small grained film showed more degradation of switching charge than large grained films.lms.s.

• Corrosion Science and Technology
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• 제19권1호
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• pp.8-15
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• 2020

In this paper, the efficiency and the inhibition mechanisms of cobalt salts (cobalt nitrate and cobalt-exchange silica Co/Si) for the corrosion protection of AA2024 were investigated in a neutral aqueous solution by using the electrochemical impedance spectroscopy (EIS) and polarization curves. The experimental measurements suggest that cobalt cation plays a role as a cathodic inhibitor. The efficiency of cobalt cation was important at the concentration range from 0.001 to 0.01 M. The formation of precipitates of oxides/hydroxides of cobalt on the surface at low inhibitor concentration was confirmed by the Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis. EIS measurements were also conducted for the AA2024 surface covered by water-based epoxy coating comprising Co/Si salt. The results obtained from exposure in the electrolyte demonstrated the improvement of the barrier and inhibition properties of the coating exposed in the electrolyte solution for a lengthy time. The SEM/EDS analysis in artificial scribes of the coating after salt spray testing revealed the release of cobalt cations in the coating defect to induce the barrier layer on the exposed AA2024 substrate.

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.99-106
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• 2013

Polyaniline-yttrium trioxide (PAni-$Y_2O_3$) composites were synthesized by the in-situ polymerization of aniline in the presence of $Y_2O_3$ The composite formation and structural changes in these composites were investigated by X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FTIR), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The direct current (DC) electrical conductivity of the order of $0.51{\times}10^{-2}\;S\;cm^{-1}-0.283\;S\;cm^{-1}$ in the temperature range 300 K-473 K indicates semiconducting behavior of the composites. Room temperature AC conductivity and dielectric response of the composites were studied in the frequency range of 10 Hz to 1 MHz. The variation of AC conductivity with frequency obeyed the power law, which decreased with increasing weight percentage (wt %) of $Y_2O_3$. Studies on dielectric properties shows the relaxation contribution coupled by electrode polarization effect. The dielectric constant and dielectric loss in these composites depend on the content of $Y_2O_3$ with a percolation threshold at 20 wt % of $Y_2O_3$ in PAni. Electromagnetic interference shielding effectiveness (EMI SE) of the composites in the frequency range 100 Hz to 2 GHz was in the practically useful range of -12.2 dB to -17.2 dB. The observed electrical and shielding properties were attributed to the interaction of $Y_2O_3$ particles with the PAni molecular chains.

• 한국세라믹학회지
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• 제37권7호
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• pp.665-672
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• 2000

The ferroelectric YMnO3 thin films were prepared by MOD(metal-organic decomposition) method with Y- and Mn-acetylacetonate as starting materials. Thin films were grown on various substrates by spin-coating technique. The crystalline phases of the thin films were identified by X-ray diffractometer as a function of heat-treatment temperature, pH of coating solution and substrate. In addition, the effect of Mn/Y molar ratio(0.8~1.2) on the formation of hexagonal-YMnO3 phase was investigated. In forming highly c-axisoriented hexagonal-YMnO3 single phase, the Pt coated Si substrate was more effective than the bare Si substrate, and the optimum heat-treatment condition was at 82$0^{\circ}C$ for 30 min. Higher Mn/Y molar ratio within 0.8~1.2 and pH of YMnO3 precursor solution within 0.5~2.5 favored formation of ferroelectric hexagonal phase rather than orthorhombic phase. Leakage current density of the hexagonal-YMnO3 thin film formed on Pt(111)/TiO2/SiO2/Si substrate was low enough as 0.4~4.0$\times$10-8(A/$\textrm{cm}^2$) at 5 V and its remanent polarization(Pr), calculated from the P-E hysteresis loop, was 3 nC/$\textrm{cm}^2$.