Author: A. Iqbal, H. Kim, J. Oh, J. Chae, J. Kim, M. Kim, T. Hassan, Z. Gao, J. Lee, S. Kim, Y. Gogotsi, H. Kwon*, C. Koo*Title: Effect of Substitutional Oxygen on Properties of Ti3C2Tx MXene synthesized from TiO2 PrecursorJournal: Small MethodsYear: 2023Impact factor: 15.367Abstract:MXenes are an emerging class of 2D materials with unique properties including metallic conductivity, mechanical flexibility, and surface tunability, which ensure their utility for diverse applications. However, the synthesis of MXenes with high crystallinity and atomic stoichiometry in a low-cost process is still challenging because of the difficulty in controlling the oxygen substitute in the precursors and final products of MXenes, which limits their academic understanding and practical applications. Here, a novel cost-effective method is reported to synthesize a highly crystalline and stoichiometric Ti3C2Tx MXene with minimum substitutional oxygen impurities by controlling the amount of excess carbon and time of high-energy milling in carbothermal reduction of recycled TiO2 source. The highest used content (2 wt%) of excess-carbon yields TiC with the highest carbon content and minimal oxygen substitutes, which leads to the Ti3AlC2 MAX phase with improved crystallinity and atomic stoichiometry, and finally Ti3C2Tx MXene with the highest electrical conductivity (11738 S cm−1) and superior electromagnetic shielding effectiveness. Additionally, the effects of carbon content and substitutional oxygen on the physical properties of TiC and Ti3AlC2 are elucidated by density-functional-theory calculations. This inexpensive TiO2-based method of synthesizing high-quality Ti3C2Tx MXene can facilitate large-scale production and thus accelerate global research on MXenes.

Author: M. Kim†, J. Kim†, M. Seo, J. Kim*Title: Evolution of a metastable thin film with high-hardness wear resistance for advanced cutting tool applicationJournal: Journal of the American Ceramic SocietyYear: 2022Impact factor: 6.371Abstract:The structure and elastic properties of rocksalt and wurtzite Ti–Al–N ternary solid solutions were investigated using first principles calculations. We also performed an experimental evaluation using the sputtering method to obtain the reliability. The phase transition of (Ti1−xAlx)N solid solutions was occurred at x = 0.5–0.75 for both calculations and experimental results. The bulk modulus of rocksalt and wurtzite solid solutions decreases with increasing Al content. On the other hand, shear moduli and Young's moduli gradually increase with Al content only in rocksalt solid solutions. The theoretical and experimental results indicate that the overall mechanical properties of rocksalt solid solutions are superior to those of wurtzite solid solutions. Therefore, controlling the crystal structure of the Ti–Al–N ternary metastable system was crucial for optimizing the material properties.

Author: H. Kim†, J. Kim, S. Chun, S. Jin, Y-S. Choi, J. Kim*Title: A Study of Thermo-mechanical Properties of (Ti1-xHfx)N Solid Solution of High-strength and Heat-resistant Coated Fabrics for Fire Proximity SuitsJournal: 한국섬유공학회Year: 2022Abstract:We investigated temperature-dependent elastic properties of (Ti1-xHfx)N solid solutions via first principles calculations. The precise convergence tests were performed to obtaining reliable results. Equilibrium structure information of the (Ti1-xHfx)N was in a good agreement with previous results indicated the reliability of the results. The difference between the bulk moduli of TiN and HfN at 0 K and 3000 K is approximately 30 GPa, indicating that the elastic properties are not well maintained at high temperatures. At each temperature, the shear, and Young's moduli of (Ti0.5Hf0.5)N were greater than those of HfN. In addition, (Ti0.5Hf0.5)N maintained its high hardness, which was not significantly affected by temperature. As a result, ternary nitride, such as (Ti0.5Hf0.5)N, is a more promising material for extreme environments than a simple binary system. The results of this study will provide useful information on how to develop new (Ti1-xHfx)N coating materials for fire proximity suits.

대한금속재료학회 전산재료과학 원자력재료/핵연료 심포지엄에서 CMDL 연구실의 석사과정 김효경 학생이 최우수 포스터상을 수상하였습니다.수상한 연구원 구성원 분들을 축하드립니다!