| Summary: | 碩士 === 東海大學 === 應用物理學系 === 105 === The oxidation had always been a challenge in producing metal and alloy nanoparticles. In this research, unoxidized rare earth nanoparticles (Tb and Dy) and high entropy alloy (TiVNbMoTa) nanoparticles had been successfully prepared by flash vaporization method in liquid.
Both Tb and Dy nanoparticles were fabricated by electrical discharge machining (EDM) and laser ablation in liquid (LAL). In process, the samples were rapidly evaporated by momentary high energy, and then rapidly cooled in working liquid (octane) to be the nanoparticles. The suspended nanoparticles would be coated with collodion during dry process. Both the lattice structure (by TEM) and the component analysis (by EDS) showed that no significant oxidation can be found in these rare earth nanoparticles. The particle size of EDM process was about 10 nm; and LAL process was about 7 nm, which was smaller than EDM process and the size distribution was more uniform.
High entropy alloy (TiVNbMoTa) was produced by arc melting method, and that was single BCC phase. The high entropy alloy nanoparticles were fabricated by LAL process, which was using three different laser power parameters in deionized water. The average particle size was about 14-16 nm. The EDS result showed that the constituent of nanoparticles were similar to the bulk, because the flash vaporization method was an effective way to maintain the component. From the TEM observation can be found that the high entropy alloy nanoparticles were mostly amorphous in this method, and crystal structure changed from amorphous to crystal by modifying laser power parameter. The reason might be that the flash vaporization method in liquid has a high cooling rate, so that the samples composed of amorphous. These amorphous had the opportunity been changed to crystal by laser irradiation heat treatment.
In general, the samples fabricated by two series flash vaporization method in liquid were very tiny (less than 20 nm). The reason might be due to the liquid process had a high cooling rate, so that the samples were difficult to growth after solidification into the nucleus.
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