Research

14 pages, 6336 KiB

Open AccessArticle

Electrochemical Properties of Super Austenite Stainless Steel with Temperature in a Green Death Solution

by Hyun-Kyu Hwang and Seong-Jong Kim

Coatings 2023, 13(1), 130; https://doi.org/10.3390/coatings13010130 - 10 Jan 2023

Cited by 1 | Viewed by 1030

In this investigation, potentiodynamic polarization experiments were conducted on UNS S31603 and UNS N08367 in a modified green death solution, which simulates the environment of a desulfurization device (scrubber), using temperature as a variable. A Tafel analysis showed that the corrosion current density [...] Read more.

In this investigation, potentiodynamic polarization experiments were conducted on UNS S31603 and UNS N08367 in a modified green death solution, which simulates the environment of a desulfurization device (scrubber), using temperature as a variable. A Tafel analysis showed that the corrosion current density of UNS S31603 at the highest temperature (90 °C) was approximately 4.5 times higher than that of UNS N83067. A surface analysis using a scanning electron microscope revealed that pitting and intergranular corrosion occurred simultaneously in UNS S31603, whereas UNS N83067 exhibited a stronger tendency toward intergranular corrosion. After electrochemical experiments, the corrosion rates according to maximum damage depth were compared with the corrosion rates according to corrosion current density; the relationships between the two values were expressed as α values. The α values of UNS N08367 were higher than those of UNS S31603, indicating that the local damage rate of UNS N08367 was higher. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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13 pages, 2302 KiB

Open AccessArticle

Investigation of Electrochemical Characteristics and Interfacial Contact Resistance of TiN-Coated Titanium as Bipolar Plate in Polymer Electrolyte Membrane Fuel Cell

by Ho-Seong Heo and Seong-Jong Kim

Coatings 2023, 13(1), 123; https://doi.org/10.3390/coatings13010123 - 09 Jan 2023

Cited by 3 | Viewed by 2024

Abstract

In this research, titanium nitride (TiN) was applied to grade 1 titanium as a bipolar plate for a proton exchange membrane fuel cell (PEMFC). The TiN was deposited by the arc ion plating method (AIP) to investigate the electrochemical characteristics of the anode [...] Read more.

In this research, titanium nitride (TiN) was applied to grade 1 titanium as a bipolar plate for a proton exchange membrane fuel cell (PEMFC). The TiN was deposited by the arc ion plating method (AIP) to investigate the electrochemical characteristics of the anode and cathode environments in the PEMFC. The corrosion experiments were conducted in an aqueous solution of pH 3 (H₂SO₄ + 0.1 ppm HF, 80 °C) determined by the Department of Energy (DoE). The hydrogen gas and air were bubbled to simulate the anode and cathode environments. The potentiodynamic polarization experiment showed that there was no active peak. The potentiostatic experiment showed that the current densities of the TiN-coated specimens were less than 1 μA/cm² in both the anode and cathode. As a result of observing the surface with an SEM before and after the potentiostatic experiment, only pinholes generated during the coating process were observed, and no corrosion damage was observed. Furthermore, electrochemical impedance spectroscopy (EIS) analysis showed that the coated specimens had a higher charge transfer resistance than the titanium substrate. In the case of interfacial contact resistance (ICR), the TiN-coated specimen displayed lower resistance than the titanium substrate and satisfied the DoE technical target of less than 10 mΩ·cm² at 140 N/cm². Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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17 pages, 5652 KiB

Open AccessArticle

Electrochemical Characteristics with NaCl Concentrations on Stainless Steels of Metallic Bipolar Plates for PEMFCs

by Dong-Ho Shin and Seong-Jong Kim

Coatings 2023, 13(1), 109; https://doi.org/10.3390/coatings13010109 - 07 Jan 2023

Cited by 1 | Viewed by 1225

Abstract

Stainless steel, which is used in metallic bipolar plates, is generally known to have excellent corrosion resistance, which is achieved by forming oxide films. However, localized corrosion occurs when the oxide films are destroyed by pH and chloride ions. Particularly, since the operating [...] Read more.

Stainless steel, which is used in metallic bipolar plates, is generally known to have excellent corrosion resistance, which is achieved by forming oxide films. However, localized corrosion occurs when the oxide films are destroyed by pH and chloride ions. Particularly, since the operating condition of polymer electrolyte membrane fuel cells (PEMFCs) is strongly acidic, the reduced stability of the oxide films leads to the corrosion of the stainless steel. In this research, the electrochemical characteristics of 304L and 316L stainless steels were investigated in an accelerating solution that simulated the cathode condition of PEMFCs with chloride concentrations. Results under all experimental conditions showed that the corrosion current density of 304L stainless steel was at least four times higher than that of 316L stainless steel. Maximum damage depth was measured at 6.136 μm and 9.192 μm for 304L stainless steel and 3.403 μm and 5.631 μm for 316L stainless steel for chloride concentrations of 0 and 1000 ppm, respectively. Furthermore, 304L and 316L stainless steels were found to have uniform and localized corrosion, respectively. The differences in the electrochemical characteristics of 304L and 316L stainless steel are considered to be due to the molybdenum contained in the chemical composition of 316L stainless steel. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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13 pages, 4698 KiB

Open AccessArticle

Hierarchical Porous Carbon Fibers Synthesized by Solution-Plasma-Generated Soot Deposition and Their CO₂ Adsorption Capacity

by Andres Eduardo Romero Valenzuela, Chayanaphat Chokradjaroen, Satita Thiangtham and Nagahiro Saito

Coatings 2022, 12(11), 1620; https://doi.org/10.3390/coatings12111620 - 26 Oct 2022

Cited by 1 | Viewed by 1346

Abstract

Global warming caused by CO₂ emissions is a major environmental problem. Thus, the development of materials with innovative architectures that approach the CO₂ problem is a necessity. In this study, hierarchical porous carbon fibers (HCFs) were synthesized by a chemical deposition [...] Read more.

Global warming caused by CO₂ emissions is a major environmental problem. Thus, the development of materials with innovative architectures that approach the CO₂ problem is a necessity. In this study, hierarchical porous carbon fibers (HCFs) were synthesized by a chemical deposition process that operates at 400 °C and uses solution-plasma-generated soot (PGS) as a carbon precursor. Subsequently, the CO₂ adsorption capacity of the synthesized material was evaluated. The HCFs showed enhanced surface areas and networks of micropores and mesopores. Moreover, the HCFs were post treated by metal etching and KOH activation. The post treated HCFs achieved a CO₂ uptake of 0.8 mmol g⁻¹ at 273 K, which was superior to the simultaneously produced solution plasma carbon (SPC), which has a CO₂ uptake of 0.2 mmol g⁻¹. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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16 pages, 2534 KiB

Open AccessArticle

Plasma–Solution Junction for the Formation of Carbon Material

by Jiangqi Niu, Chayanaphat Chokradjaroen, Yasuyuki Sawada, Xiaoyang Wang and Nagahiro Saito

Coatings 2022, 12(11), 1607; https://doi.org/10.3390/coatings12111607 - 22 Oct 2022

Cited by 2 | Viewed by 1428

Abstract

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs [...] Read more.

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs to be urgently explored to achieve the modulation of the SPP. Here, to address the knowledge gap, we experimentally determined the physical parameters of the spital distribution in the plasma phase, plasma–gas phase, and gas–liquid phase of the SPP by the Langmuir probe system with modification. Based on the assumption that plasma can act similarly to semiconductors with the Fermi level above the vacuum level, an energy band diagram of the plasma–solution junction could be proposed for the first time. It was observed that the Fermi level of the organic molecule could determine the magnitude of electron temperature in plasma, i.e., benzene produced the highest electron temperature, followed by phenol, toluene, and aniline. Finally, we found that the electron temperature at the interface could induce quenching, leading to the formation of multilayer large-size-domain carbon products. It provided significant evidence for achieving nonequilibrium plasma modulation of carbon nanomaterial synthesis. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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17 pages, 5990 KiB

Open AccessArticle

Amine-Modified Small Pore Mesoporous Silica as Potential Adsorbent for Zn Removal from Plating Wastewater

by Vanpaseuth Phouthavong, Jae-Hyeok Park, Tatsuo Nishihama, Shuhei Yoshida, Takeshi Hagio, Yuki Kamimoto and Ryoichi Ichino

Coatings 2022, 12(9), 1258; https://doi.org/10.3390/coatings12091258 - 28 Aug 2022

Cited by 1 | Viewed by 1454

Abstract

The removal of Zn from wastewater generated from the Zn-based electroplating manufacturing process is essential because the regulation limit of Zn concentration in wastewater is becoming stricter in Japan. However, achieving this through conventional methods is difficult, especially for small and medium enterprises [...] Read more.

The removal of Zn from wastewater generated from the Zn-based electroplating manufacturing process is essential because the regulation limit of Zn concentration in wastewater is becoming stricter in Japan. However, achieving this through conventional methods is difficult, especially for small and medium enterprises in the plating industry. Therefore, a suitable Zn-removal method with a low cost but high performance and Zn selectivity is required. The application of adsorbents is one possible solution. Mesoporous silica (MS) is a well-known adsorbent with controllable pore size, high specific surface area (SSA), high acid resistance, and ease of surface modification. In this study, we modified the surfaces of MSs with different initial pore sizes by amino groups and investigated their Zn removal performances. The effect of pore size on amine modification using (3-aminopropyl)triethoxysilane and on adsorption performance in a single system was investigated along with Zn adsorption selectivity in the Zn–Ni binary system. Amine-modified MS prepared from MS with an initial pore size of 1.9 nm showed drastically lower performance compared to those prepared from MS with an initial pore size larger than 2.8 nm. Zn-selectivity in the Zn–Ni binary system, containing equal amounts of Zn and Ni, was found to reach a maximum of 21.6 when modifying MS with an initial pore size of 2.8 nm. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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9 pages, 3725 KiB

Open AccessArticle

Influence of Plasma Surface Treatment of Polyimide on the Microstructure of Aluminum Thin Films

by Eiichi Kondoh

Coatings 2022, 12(3), 334; https://doi.org/10.3390/coatings12030334 - 03 Mar 2022

Cited by 4 | Viewed by 1863

Abstract

The effects of plasma treatment of polyimide substrates on the texture and grain size distribution of aluminum thin films were studied. Oxygen-argon plasma treatment increased the average grain size and enhanced the (111) film texture. For short oxygen-argon plasma treatment times, the deposited [...] Read more.

The effects of plasma treatment of polyimide substrates on the texture and grain size distribution of aluminum thin films were studied. Oxygen-argon plasma treatment increased the average grain size and enhanced the (111) film texture. For short oxygen-argon plasma treatment times, the deposited Al films showed a (111) texture with a bimodal grain structure and even a {111}<11

\bar{2}

> type in-plane texture. The preferential nucleation and grain growth of (111) grains are discussed in terms of the interface energy anisotropy. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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12 pages, 9086 KiB

Open AccessArticle

Effect of Ammonia Addition on the Growth of an AlO(OH) Film during Steam Coating Process

by Naotaka Itano, So Yoon Lee and Ai Serizawa

Coatings 2022, 12(2), 262; https://doi.org/10.3390/coatings12020262 - 16 Feb 2022

Viewed by 2156

Abstract

Al alloys possess excellent physical and mechanical properties, such as low density, high specific strength, and good ductility. However, their low corrosion resistance limits their use in corrosive environments. The steam coating process has attracted considerable attention as a new coating technology that [...] Read more.

Al alloys possess excellent physical and mechanical properties, such as low density, high specific strength, and good ductility. However, their low corrosion resistance limits their use in corrosive environments. The steam coating process has attracted considerable attention as a new coating technology that can improve the corrosion resistance of Al alloys. This surface treatment technology uses steam to form a corrosion-resistant film on Al alloys. However, a decrease in the processing time, which can result in a lower cost, is needed for the practical application of the steam coating process. In this study, an Al-Mg-Si alloy is used as the base material, and ammonia is added to the steam source to increase the film formation rate. By adding ammonia (0.5 mol/L) to the steam source, the rate constant, K, for film formation increases 1.82 times compared to that of the pure-water-only treatment. Field emission scanning electron micrographs of the film surface confirms that the crystal morphologies of the crystals change from rectangular to parallelepiped shape with increasing process time by ammonia addition. Furthermore, X-ray diffraction patterns show that AlO(OH) crystals are successfully synthesized without byproducts, even when ammonia is added. Full article

(This article belongs to the Special Issue Science and Engineering of Coating)

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