Jungwoo Kim

Aqueous Corrosion Behavior of Weathering Steel and Carbon Steel in Acid-Chloride Environments

Abstract Aqueous corrosion characteristics of carbon steel and weathering steel in aerated acid-chloride solutions were studied by using immersion weight loss tests, crevice corrosion tests, electr...

Effect of thermal treatment on the chemical resistance of polydimethylsiloxane for microfluidic devices

We investigated the use of thermally treated polydimethylsiloxane (PDMS) for chemically-resistant microchannels. When the PDMS underwent the thermal treatment at 300 °C, swelling was reduced and the surface of the PDMS microfluidic channel endured well in the extracting media such as dichloromethane. Furthermore, despite the small decrease in size after thermal treatment, both the channel shape and transparency were maintained without showing fluid leakage. The thermally treated PDMS had more hydrophilic properties compared to the untreated PDMS. A single step post-casting process described in this work does not require complex chemical treatments or introduction of foreign materials to the host PDMS substrate, thus expanding the application area of PDMS-based microfluidics.

Wear-corrosion of cast iron thermal spray coating on Al alloy for automotive components

For the modification of an automotive cylinder block, two types of water-atomized cast iron powders were deposited onto an aluminum alloy substrate by atmospheric DC plasma spraying. The wear-corrosion characteristics of the coatings were investigated by means of a wear test and EIS. The pre-annealed and graphitized coating improved the wear-corrosion resistance in a deaerated 0.5M H2SO4 solution.

Influence of cathodic protection on the lifetime extension of painted steel structures

For corrosion to occur on a coated metal surface, an electrochemical double layer must be established. Hence, the adhesion between the substrate and the coating must be weakened to enable a separate thin layer of water to be formed at the interface from water that has permeated the coating. To prevent the failure of a painted coating, we applied a cathodic protection method. This method has been controversial for a few years because cathodic protection can induce cathodic delamination of the entire surface, especially near the anode, and also because it is not effective on a not-wetted surface from the anode. We therefore evaluated the efficiency of cathodic protection for 700 days in an atmospheric environment and performed surface observation, AC impedance measurements and corrosion tests. In the case of a noncathodic protected painted steel specimen, blisters formed after 100 days and grew in number for the remainder of the test. However, cathodic protection of the painted steel increased the coating resistance and extended the lifetime of the coating. According to our calculation with the BEASY program, the thickness of the water film under a rain condition barely influenced the protection potential. The high voltage of the cathodic protection and the subsequent cathodic delamination caused the paint to peel off near the anode. Hence, the protection voltage should be controlled in accordance with changes to the environmental condition.

Improved electroluminescence of quantum dot light-emitting diodes enabled by a partial ligand exchange with benzenethiol.

In this study, benzenethiol ligands were applied to the surface of CdSe@ZnS core@shell quantum dots (QDs) and their effect on the performance of quantum dot light-emitting diodes (QD-LEDs) was investigated. Conventional long-chained oleic acid (OA) and trioctylphosphine (TOP) capping ligands were partially replaced by short-chained benzenethiol ligands in order to increase the stability of QDs during purification and also improve the electroluminescence performance of QD-LEDs. The quantum yield of the QD solution was increased from 41% to 84% by the benzenethiol ligand exchange. The mobility of the QD films with benzenethiol ligands approximately doubled to 2.42 × 10(-5) cm(2) V(-1) s(-1) from 1.19 × 10(-5) cm(2) V(-1) s(-1) compared to the device consisting of OA/TOP-capped QDs, and an approximately 1.8-fold improvement was achieved over QD-LEDs fabricated with bezenethiol ligand-exchanged QDs with respect to the maximum luminance and current efficiency. The turn-on voltage decreased by about -0.6 V through shifting the energy level of the QDs with benzenethiol ligands compared to conventional OA and TOP ligands.

Molecular and biochemical characterization of Paragonimus westermani tyrosinase

Trematode tyrosinases (TYRs) play a major role in the tanning process during eggshell formation. We investigated the molecular and biochemical features of Paragonimus westermani TYR (PwTYR). The PwTYR cDNA was composed of 1568-bp encompassing a 1422-bp-long open reading frame (474-amino acid polypeptide). A strong phylogenetic relationship with Platyhelminthes and Deuterostomian orthologues was evident. The recombinant PwTYR expressed in prokaryotic cells promptly oxidized diphenol substrates, with a preferential affinity toward ortho-positioned hydroxyl groups. It demonstrated fairly weak activity for monophenol compounds. Diphenol oxidase activity was augmented with an increase of pH from 5.0 to 8.0, while monophenol oxidase activity was highest at an acidic pH and gradually decreased as pH increased. Transcription profile of PwTYR was temporally upregulated along with worm development. PwTYR was specifically localized in vitellocytes and eggs. The results suggested that conversion of tyrosine to L-dihydroxyphenylalanine by PwTYR monophenol oxidase activity might be rate-limiting step during the sclerotization process of P. westermani eggs. The pH-dependent pattern of monophenol and diphenol oxidase activity further proposes that the initial hydroxylation might slowly but steadily progress in acidic secreted vesicles of vitellocytes and the second oxidation process might be rapidly accelerated by neural or weak alkaline pH environments within the ootype.

Effect of indium doping on low-voltage ZnO nanocrystal field-effect transistors with ion-gel gate dielectric

We report the effect of indium (In) doping on the electrical performance of a ZnO nanocrystal-based field-effect transistor of side-gate structure, which was fabricated incorporating a high-capacitance ion gel gate dielectric. Undoped and In-doped ZnO channel layers were formed by spin-coating solutions of dispersed ZnO nanocrystals that included different amounts of In-containing precursor solution. Continuous increase in the amount of In doping solution induced close packing of ZnO nanocrystals with suppressed grain growth and increased carrier concentration, which resulted in the improvement of transistor performance. However, after the optimal In doping level was reached, a slight decrease in channel conductivity was observed, probably due to In-induced scattering and/or the generation of microcracks.

Silicide formation process of Er films with Ta and TaN capping layers.

The phase development and defect formation during the silicidation reaction of sputter-deposited Er films on Si with ∼20-nm-thick Ta and TaN capping layers were examined. TaN capping effectively prevented the oxygen incorporation from the annealing atmosphere, which resulted in complete conversion to the ErSi2-x phase. However, significant oxygen penetration through the Ta capping layer inhibited the ErSi2-x formation, and incurred the growth of several Er-Si-O phases, even consuming the ErSi2-x layer formed earlier. Both samples produced a number of small recessed defects at an early silicidation stage. However, large rectangular or square-shaped surface defects, which were either pitlike or pyramidal depending on the capping layer identity, were developed as the annealing temperature increased. The origin of different defect generation mechanisms was suggested based on the capping layer-dependent silicidation kinetics.

Optical and electrical properties of ZnO nanocrystal thin films passivated by atomic layer deposited Al2O3

While colloidal semiconductor nanocrystal (NC) is preferred for use in solution-based optoelectronic devices, the large number of surface defects associated with its high surface-to-volume ratio degrades the optimal performance of NC-based devices due to the extensive trapping of free carriers available for charge transport. Here, we studied a simple and effective strategy to control the degree of passivation and doping level of solution-deposited ZnO NC films by infilling with ultra-thin Al2O3 using an atomic layer deposition (ALD) technique. According to various spectroscopic, microstructural, and electrical analyses, the ALD-Al2O3 treatment dramatically reduced the number of surface trap states with high ambient stability while simultaneously supplied excess carriers probably via a remote doping mechanism. As a consequence, the field-effect transistors built using the ZnO NC films with ALD-Al2O3 treatment for an optimal number of cycles exhibited significantly enhanced charge transport.