Containerless solidification of Si, Zr, Nb, and Mo by electrostatic levitation

Abstract

Containerless solidification of Si (Tm=1687 K), Zr (Tm=2128 K), Nb (Tm=2750 K), and Mo (Tm=2896 K) has been carried out by the electrostatic levitation (ESL) process in which a bulk sample was electrostatically charged and levitated, then melted by laser irradiation in high vacuum. Multiple cycles of melting–undercooling–recalescence–cooling of Si (23.1 mg), Zr (41.9 mg), Nb (40.4 mg), and Mo (45.7 mg) were reproducibly repeated. Among them, Mo is a refractory material with the highest melting temperature ever containerlessly melted and solidified by electrostatic levitation. The ESL-processed Mo sample showed a thermal dendritic structure throughout the entire surface uniformly without any apparent grain boundaries implying heterogeneous nucleation must have been suppressed due to the containerless condition in the ESL process. The back reflection Laue pattern also revealed a homogeneous quality of the ESL-processed Mo sample.