Author: H.Kim†, J.Choi, S.Park, T.Eom, K.M.Roh* and J.Kim*Title: Influence of vacancies on the stability and mechanical properties of V2AlC: Guidelines for etching MAX phases via ab initio calculationsJournal: Ceramics InternationalYear: 2024Impact factor: 5.2Abstract:This study focuses on the ideal etching of defective MAX phases in a mechanical exfoliation process to produce vanadium-based MXenes. Two-dimensional MXenes exhibit high structural stability and excellent electrical conductivity, and can be applied as electrode materials. Mechanical exfoliation can be facilitated by modifying the vacancy in the V2AlC MAX phase, which makes etching challenging. We report the effects of M (vanadium), A (aluminum), and X (carbon) vacancies on the mechanical behavior of V2AlC via ab initio calculations. To this end, the anisotropic mechanical properties and strain–stress curves were calculated for MAX phases with different vacancies (x = 0.08, which corresponds to 8.33 at.%). The presence of vanadium vacancies significantly deteriorated the structural and mechanical properties compared to those of aluminum and carbon vacancies. Thus, it was confirmed that vanadium vacancies had a significant effect on the mechanical exfoliation of the MAX phases. These findings provide further insights into the design of MXenes.
Author: S.Lee†, J.Choi, Y.Chung, J.Kim*, S. Moon* and S.Lee*Title: Understanding the catalytic mechanism of calcium compounds for enhancing crystallinity in carbon fiberJournal: Chemical Engineering JournalYear: 2024Impact factor: 15.1Abstract:Graphitized carbon fibers are attractive materials because of their high tensile modulus and thermal and electrical conductivities. These attributes derive from their crystalline structures that develop during heat treatments of up to 3000 °C. Despite the costly thermal processes, there is a structural limit for achieving these sought-after properties for polyacrylonitrile-based carbon fibers. Herein, the preparation of polyacrylonitrile-based carbon fibers with highly developed microstructures via calcium-assisted thermal treatments of up to 2700 °C is reported. Carbon fibers hydrothermally immersed in a solution of calcium carbonate were heat-treated and their chemical structures traced to investigate the calcium-assisted catalytic graphitization mechanism. Graphitic structures appeared at 1400 °C, accompanied by intermediate complexes of carbon and calcium on the carbon fibers surfaces. Further heat treatment of the calcium compounds at 1600 °C to incorporate carbon fibers resulted in an interlayer spacing of 0.3360 nm, which was unachievable solely through heat treatment at 2700 °C. In addition, the achieved tensile modulus and electrical conductivity of 480 GPa and 1.7 × 103 S/cm, respectively, were significantly higher than those of pure carbon fibers. The calcium ions penetrating the internal structure of the carbon fibers aligned the non-uniform graphene structure and developed the graphite structure of the carbon fibers by acting as catalysts, even at low temperatures.
Author: H.Nam†, H.Lee†, H.Kim, J.Lee* and J.Kim*Title: Precipitation strengthening of Cu–Ni–Si-based alloys: Experimental and computational insightsJournal: Journal of Materials Research and TechnologyYear: 2023Impact factor: 6.4Abstract:The effects of interfacial energy on precipitation behavior and physical properties of Cu–Ni–Si–(Co) alloys were investigated. The Cu–1.3Ni–0.3Si and Cu–1.3Ni–0.6Si–1.0Co alloys (in weight %) were prepared by combined cold-rolling and aging processes. The addition of Co promoted the formation of (Ni,Co)2Si by replacing Ni with Co in Ni2Si. Ab initio calculations demonstrated that the small addition of Co considerably reduced the interfacial energy between the Cu matrix and (Ni,Co)2Si, which effectively decreased the activation energy for precipitation. As a result, the precipitation of fine rod-shaped (Ni,Co)2Si was accelerated during the aging process and the number density of the precipitates increased up to 9.0 × 1010 cm−2. The nano-scale (Ni,Co)2Si precipitates with an average size of 13.5 nm strengthened the alloy properly through the Orowan mechanism without much loss of electrical conductivity. The maximum hardness and electrical conductivity were 220 Hv and 51 % International Annealed Copper Standard, respectively, for the Cu–1.3Ni–0.6Si–1.0Co alloy aged for 4 h at 420 °C.
Author: H.Kim†, M.Kim†, J.Kim , and J.Kim*Title: Enhancing the hydrogen storage properties of (Ti, M)C1−x materials (M = W, Mg, Ni, and Al) depends on the carbon vacancies: Potential for the recycling of scrapsJournal: International Journal of Refractory Metals and Hard MaterialsYear: 2024Impact factor: 3.6Abstract:New energy storage systems and recycling schemes are required to solve the increasing environmental and energy problems. Owing to the increasing cost of raw materials, scraps need to be recycled. Carbides can be used as hydrogen storage materials; however, their mechanical properties remain unclear. To fabricate high-quality carbides from scraps as potential candidates for hydrogen storage materials, it is necessary to understand the mechanical properties of the carbides when absorbing hydrogen atoms. In this study, we evaluated the thermodynamic stabilities, mechanical properties, and electronic structures of (Ti, M)C1-x materials (M = W, Mg, Ni, and Al, x = 0-1. The effects of the carbon vacancies were examined using density functional theory calculations. Based on the results, the TiC0.625 composition was stable at ambient temperature and pressure. Titanium carbides have shown potential for use in hydrogen storage applications at 0≤ x ≤ 0.375, as the hardness decreases rapidly when x ≥ 0.375. In addition, the results indicate that (Ti, Al)C should mainly be used in the target hydrogen storage materials at a composition below x = 0.25. These findings support the design of hydrogen storage materials based on recycled carbides.�=0–1
대한금속재료학회 추계학술대회에서 과제관련 발표가 있었습니다.폐내화물 재활용 공정인 용융염전해에 사용되는 불활성전극 조성설계 주제로 교수님께서 발표해주셨습니다.
여러 지식들을 쌓고 배울 수 있는 시간이었습니다. 구두발표를 해주신 명재오빠, 포스터 발표를 해주신 효경언니, 준영오빠 정말 고생하셨습니다!
국제학회에 참여해 다양한 국적의 연구자 분들과 교류할 수 있는 특별한 시간이었습니다.구두발표를 하신 효경언니와 포스터 발표를 해주신 CMD 일원들 모두 고생하셨습니다!
8월 5일~6일, CMD 멤버들이 강원도 동해시 묵호에 하계 엠티를 다녀왔습니다!다같이 즐겁게 해수욕도 하고,바나나보트까지 타면서 바다에서 알찬 시간을 보냈습니다마지막으로 숙소에 돌아와서 맛있는 고기와 여러 음식들을 먹으며 CMDL 엠티를 마무리했습니다.교수님 덕분에 학생들끼리 좋은 시간을 보내며 단합심과 친목을 다질 수 있었습니다.앞으로도 CMDL 일원들끼리 서로 도우며 즐거운 랩 생활을 해나가도록 하겠습니다!