• Journal of Powder Materials
• /
• v.30 no.4
• /
• pp.324-331
• /
• 2023

Lithium (Li) is a key resource driving the rapid growth of the electric vehicle industry globally, with demand and prices continually on the rise. To address the limited reserves of major lithium sources such as rock and brine, research is underway on seawater Li extraction using electrodialysis and Li-ion selective membranes. Lithium lanthanum titanate (LLTO), an oxide solid electrolyte for all-solid-state batteries, is a promising Li-ion selective membrane. An important factor in enhancing its performance is employing the powder synthesis process. In this study, the LLTO powder is prepared using two synthesis methods: sol-gel reaction (SGR) and solid-state reaction (SSR). Additionally, the powder size and uniformity are compared, which are indices related to membrane performance. X-ray diffraction and scanning electron microscopy are employed for determining characterization, with crystallite size analysis through the full width at half maximum parameter for the powders prepared using the two synthetic methods. The findings reveal that the powder SGR-synthesized powder exhibits smaller and more uniform characteristics (0.68 times smaller crystal size) than its SSR counterpart. This discovery lays the groundwork for optimizing the powder manufacturing process of LLTO membranes, making them more suitable for various applications, including manufacturing high-performance membranes or mass production of membranes.

• Journal of the Korea Institute of Building Construction
• /
• v.23 no.3
• /
• pp.231-240
• /
• 2023

In this research, our goal was to explore the potential use of cement mortar augmented with liquid red mud. To facilitate this, we neutralized liquid red mud(LR) - exhibiting a pH of 10-12 - using sulfuric acid to yield sulfuric acid neutralized red mud(SR). We then evaluated the flow, setting time, and compressive strength of the cement mortar combined with liquid red mud, while also performing a thorough examination of its chemical properties through X-ray diffraction(XRD) and scanning electron microscopy(SEM). The flow tests indicated a decrease in flow values for both MS-LR and MS-SR in comparison to the Plain. Analogously, the setting time for MS-LR and MS-SR was found to be abbreviated when juxtaposed with the Plain. With regards to compressive strength, MS-LR demonstrated a surge in strength at the 1-day mark, while MS-SR displayed a diminution at the 1-day and 3-day timepoints compared to the Plain. XRD analysis illustrated that after 28 days, the XRD patterns of Plain and MS-SR bore significant resemblance, though a new peak was detected in MS-LR. SEM imagery highlighted that the microstructures of Plain and MS-SR were alike, but MS-LR manifested a distinct microstructure, characterized by a finely fibrous formation. Based on these observations, we infer that the replacement of cement mortar with liquid red mud neutralized with sulfuric acid contributes to a noticeable enhancement in strength, thereby verifying its suitability for this application.

• Journal of Convergence for Information Technology
• /
• v.12 no.2
• /
• pp.134-141
• /
• 2022

To improve the performance of aluminum-air batteries, it is very important to understand the effect of electrolytes on the electrochemical properties of electrodes. In this study, the effects of electrolyte cations on the electrochemical redox reactions proceeding at the negative and positive electrodes were investigated using electrolytes having the same anion but different cations such as NaCl, LiCl, CaCl₂, and ZnCl₂. It was confirmed by discharge test, scanning electron microscopy and X-ray diffraction analysis that electrolyte cations affect the discharge potential and specific capacity of the electrode. Precipitates were formed on the surface of the positive electrode by Ca²⁺ and Zn²⁺ ions, resulting in degradation of the performance of the positive electrode. In addition, Ca²⁺ ions passivated the negative electrode and accelerated the performance degradation. This suggests that the positive ions of the electrolyte have different effects on the electrochemical performance of the positive and negative electrodes.

• Korean Chemical Engineering Research
• /
• v.61 no.3
• /
• pp.419-425
• /
• 2023

This paper presents the research results of analyzing the high-temperature corrosion characteristics of three currently commercialized heat exchanger tube materials under actual operating conditions of a biomass power plant. In order to precisely analyze the high-temperature corrosion characteristics of these materials, a high-temperature corrosion evaluation device was installed in the power plant equipment, which allows for adjusting the surface temperature of the heat exchanger tubes. Experiments were conducted for approximately 300 hours under various temperature and operating conditions. In this study, the commercialized heat exchanger tube materials used were SA213T12, SA213T22, and SA213T91 alloys. In order to objectively analyze the high-temperature corrosion characteristics of each material, an international standard-based process to remove corrosion products was applied to obtain the weight change of the specimens, and the average thickness loss and corrosion rate were derived. Thus, the high-temperature corrosion results for each condition were quantitatively compared and analyzed. In addition, in order to increase the reliability of the high-temperature corrosion evaluation method introduced in this study, the surface and cross-sectional corrosion of the specimens were confirmed by using scanning electron microscopy and energy-dispersive X-ray analysis. Based on these analysis results, it was found that the corrosion resistance of the commercial heat exchanger materials increases as the content of chrome and nickel in the composition increases. Additionally, it was found that the corrosion phenomenon is rapidly accelerated as the surface temperature increases. Finally, the replacement period (lifetime) of the heat exchanger tubes under each condition could be inferred through this study.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.2
• /
• pp.130-137
• /
• 2023

This study analyzed the effect of mixing order on the flowability, compressive strength, and flexural strength of cement composites reinforced with polyvinyl alcohol(PVA) fibers and multi-walled carbon nanotubes(MWCNTs). The experimental results showed that the addition of CNTs significantly reduced the flowability, and the flowability was considerably affected by the mixing order when CNTs were added. The compressive strength was most effectively improved when water and CNTs solution were mixed first before adding PVA fibers, and the flexural strength was highest when water and CNTs solution were mixed with PVA fibers after dry mixing. However, there was no clear correlation between the flexural toughness and the mixing order. In addition, scanning electron microscopy(SEM) image analysis was conducted to analyze the microstructure. The SEM images showed that CNTs were randomly dispersed through the specimens and contributed to the strength improvement, but the effect of the mixing order was not clearly observed. The main results of this study are expected to be useful for evaluations of workability and material performance of PVA fiber-reinforced cement composites with CNTs.

• Journal of the Korean Society for Heat Treatment
• /
• v.36 no.4
• /
• pp.198-205
• /
• 2023

We investigated the effects of Al and Mg on the microstructure and hardness of the coating layer of galvanized steel sheets, by thermodynamic calculations, X-ray diffraction, scanning electron microscopy, and Vickers hardness tests of Zn-0.2Al, Zn-6Al-2Mg, and Zn-10Al-5Mg coating layers. Regardless of the alloy composition of the galvanizing bath, a Fe-Al layer was observed between the coating layer and steel sheet. The Zn-0.2Al coating layer consists of major h.c.p. Zn phase and minor f.c.c. Al phase. The fraction of f.c.c. Al phase (containing a significant amount of Zn) of the coating layer increases with increasing the chemical composition of Al of the galvanizing bath. The h.c.p. MgZn₂ phase was formed in the Al/Mg-containing Zn-6Al-2Mg and Zn-10Al-5Mg coating layers, forming Zn-Al-MgZn₂ eutectic microstructure. The primary MgZn₂ phase was additionally formed in the Zn-10Al-5Mg coating layers containing high concentrations of Al and Mg. The Vickers hardness values of Zn-0.2Al, Zn-6Al-2Mg, and Zn-10Al-5Mg coating layers were 59.1 ± 1.2 HV, 161.2 ± 5.7 HV, and 215.5 ± 40.3 HV, respectively. The addition of Al and Mg increased the hardness of the coating layer by increasing the fraction of the Al phase (containing Zn) and MgZn₂ intermetallic compound, which were harder than the Zn phase.

• Analytical Science and Technology
• /
• v.22 no.6
• /
• pp.464-470
• /
• 2009

For the investigation of the oxidation behavior for titanium metal at various temperatures, titanium specimens were heated for 2 hours in the range of $300{\sim}1000^{\circ}C$, individually. And then X-ray diffraction(XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic analyses were carried out. At $300^{\circ}C$, infrared absorption bands on the surface of the titanium specimen were shown in a spectrum by the oxygen uptake of titanium metal(hexagonal). At increased temperature, not only infrared absorption bands but also X-ray diffraction peaks for the titanium oxide were grown and shifted to low wave number ($cm^{-1}$) and angle($^{\circ}$) due to the more oxygen diffusion into titanium metal. At $700^{\circ}C$, $Ti_3O$ (hexagonal phase) was identified by X-ray diffractometer. $TiO_2$ (rutile, tetragonal phase) layer was produced on the surface of the specimen below $1{\mu}m$ in thickness at $600^{\circ}C$, and grown about $2{\mu}m$ at $700^{\circ}C$ and with $110{\mu}m$ in thickness at $1000^{\circ}C$. Above $900^{\circ}C$, (110) plane of the crystal on the surface of rutile-$TiO_2$ layer was grown.

• Restorative Dentistry and Endodontics
• /
• v.45 no.4
• /
• pp.54.1-54.16
• /
• 2020

Objectives: This study aimed to synthesize nanocrystals (NCs) of zinc oxide (ZnO) and calcium ion (Ca²⁺)-doped ZnO with different percentages of calcium oxide (CaO), to evaluate cytotoxicity and to assess the effects of the most promising NCs on cytotoxicity depending on lipopolysaccharide (LPS) stimulation. Materials and Methods: Nanomaterials were synthesized (ZnO and ZnO:xCa, x = 0.7; 1.0; 5.0; 9.0) and characterized using X-ray diffractometry, scanning electron microscopy, and methylene blue degradation. SAOS-2 and RAW 264.7 were treated with NCs, and evaluated for viability using the MTT assay. NCs with lower cytotoxicity were maintained in contact with LPS-stimulated (+LPS) and nonstimulated (-LPS) human dental pulp cells (hDPCs). Cell viability, nitric oxide (NO), and reactive oxygen species (ROS) production were evaluated. Cells kept in culture medium or LPS served as negative and positive controls, respectively. One-way analysis of variance and the Dunnett test (α = 0.05) were used for statistical testing. Results: ZnO:0.7Ca and ZnO:1.0Ca at 10 ㎍/mL were not cytotoxic to SAOS-2 and RAW 264.7. +LPS and -LPS hDPCs treated with ZnO, ZnO:0.7Ca, and ZnO:1.0Ca presented similar NO production to negative control (p > 0.05) and lower production compared to positive control (p < 0.05). All NCs showed reduced ROS production compared with the positive control group both in +LPS and -LPS cells (p < 0.05). Conclusions: NCs were successfully synthesized. ZnO, ZnO:0.7Ca and ZnO:1.0Ca presented the highest percentages of cell viability, decreased ROS and NO production in +LPS cells, and maintenance of NO production at basal levels.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.3
• /
• pp.260-266
• /
• 2023

In recent years, excessive emissions of carbon dioxide(CO₂) have become the cause of global climate change. Consequently, there has been significant research activity aimed at both removing and utilizing CO₂. This study assesses the potential utilization of railway tie concrete waste, generated from railway infrastructure, as a CO₂ absorption material and investigates the physicochemical properties before and after CO₂ absorption to understand the CO₂ removal mechanisms. Railway tie concrete waste primarily consists of Si(26.60 %) and contains 9.82 % of Ca. Compared to samples of Cement and Normal concrete waste, it demonstrated superior potential for use as a CO₂ absorption material, with approximately 98 % of the Ca content participating in CO₂ absorption reactions. Through Thermogravimetric Analysis(TGA) and X-ray Diffraction(XRD) analysis, it was confirmed that the carbonate reaction, where the Ca in railway tie concrete waste converts into CaCO₃ through reaction with CO₂ gas, is the primary mechanism for CO₂ removal. Furthermore, Scanning Electron Microscopy(SEM) analysis revealed the formation of numerous CaCO₃ particles with sizes less than 0.1 ㎛ after the CO₂ absorption reaction. This transformation of large internal voids in the CO₂ absorption material into mesopores resulted in an increase in the specific surface area of the material.

• Korean Journal of Materials Research
• /
• v.33 no.10
• /
• pp.406-413
• /
• 2023

This study used optical and scanning electron microscopy to analyze the surface oxidation phenomenon that accompanies a γ'-precipitate free zone in a directional solidified CM247LC high temperature creep specimen. Surface oxidation occurs on nickel-based superalloy gas turbine blades due to high temperature during use. Among the superalloy components, Al and Cr are greatly affected by diffusion and movement, and Al is a major component of the surface oxidation products. This out-diffusion of Al was accompanied by γ' (Ni₃Al) deficiency in the matrix, and formed a γ'-precipitate free zone at the boundary of the surface oxide layer. Among the components of CM247LC, Cr and Al related to surface oxidation consist of 8 % and 5.6 %, respectively. When Al, the main component of the γ' precipitation phase, diffused out to the surface, a high content of Cr was observed in these PFZs. This is because the PFZ is made of a high Cr γ phase. Surface oxidation of DS CM247LC was observed in high temperature creep specimens, and γ'-rafting occurred due to stress applied to the creep specimens. However, the stress states applied to the grip and gauge length of the creep specimen were different, and accordingly, different γ'-rafting patterns were observed. Such surface oxidation and PFZ and γ'-rafting are shown to affect CM247LC creep lifetime. Mapping the microstructure and composition of major components such as Al and Cr and their role in surface oxidation, revealed in this study, will be utilized in the development of alloys to improve creep life.