Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publisher：Materials  

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al–Ti–Cu–Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al–Ti–Cu–Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8–5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

DOI： 10.3390/ma17020304

Web of Science

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

An attention to a Li ion battery for electric vehicles has been attracted, but there are two huge problems: a short mileage and slow charging speed. Therefore, it is required to improve the specific capacity and electrical conductivity of the carbon material used for an anode and a conductive agent. To solve these problems, this study organized correlation analysis with descriptor vectors by collecting experimental properties including capacity and conductivity from 21 various types of carbon materials. Focusing on the flux of Li ion, it was found that the capacity was dependent on the intercalation of Li ions, which lead to propose the correlation equation based on the Hill equation. Furthermore, the intercalation occurred at the edge of basal plane lead an increase of the width of the gap between two graphene layers, followed by a diffusion through the basal plane, finally the expanded gap recovered its original width. Also, it was found that the variables which are sensitive to the conductivity are largely dependent on the defects and especially the number of graphene layers around the surface, which proposed a correlation equation that can predict the capacity and conductivity. To validate these functions, we checked the effectiveness of it with both experimental data from 27 previous studies and statistical method. As a result, it was confirmed enough to predict them. Finally, a candidate structure for improving the battery performance was proposed, thus our study aims to guide the exploration of electrode materials for LIBs.

DOI： 10.1016/j.carbon.2023.118479

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Though expensive platinum (Pt) is used as catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), insufficient durability remains as a bottleneck for commercialization of PEFCs. Improving both catalytic performance and durability by graphene encapsulation is an attractive strategy to solve this problem. In this study, graphene-encapsulated PtFe core-shell catalyst is synthesized with dimethyl formamide (DMF) and a pair of Pt and Fe electrodes without using any metal salts by utilizing the solution plasma (SP) process. TEM and EELS results show synthesized PtFe nanoparticles are encapsulated with close to single-layered highly crystallized graphene. Although commercial Pt/C showed significant performance degradation (ECSA −33%, MA −68%) after 50,000 cycles of accelerated durability test (ADT), PtFe core-shell catalyst shows remarkably improved durability (ECSA −13%, MA −19%) while graphene shell clearly remains. The improved durability is more prominent in the single cell test, the decrease in maximum power density after 6000 cycles of ADT was significantly lower as −1.2%, compared to that of Pt/C (−52.1%). This study introduces a novel and attractive catalyst synthesis process by the SP method followed by heat treatments and suggests graphene encapsulation can improve long-term durability of catalyst while maintaining ORR activity.

DOI： 10.1016/j.jpowsour.2023.233419

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems were prepared by mechanical alloying in oxygen-lean atmosphere followed by spark plasma sintering. The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems which were sintered at 750 °C after 16 h milling showed the highest hardness of 509 and 947 HV with low densities of 2.9 and 3.9 g/cm3, respectively. The decrease in particle size and uniform dispersion of elements through optimization of the MA process induced the formation of uniform composite microstructure after SPS. Moreover, the addition of the fourth element, Cu, showed a significant impact on the improvement in hardness. This result was explained from the perspective of the microstructure and the electronic nature of elements. Our results provide a facile method for synthesizing oxide/metal composites from elemental powders without a separate oxidation process. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1557/s43578-023-01137-z

Web of Science

Scopus

Event date： 2023.3

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：知の拠点あいち