2. Experimental
The equipment for producing nanoparticles primarily contains an
arc melting chamber and a collecting system, which was described
elsewhere [10]. The Ca ingot of 15 g with a purity of 99% was kept in
air for about 6 h, and the center part (10× 10 mm2
) was polished to
remove the surface oxide layer. Nanoparticles were produced by arcmelting
this Ca ingot partly covered with an oxide layer in a 70% Ar
and 30% H2 mixture of 0.08 MPa. The flow rate of the circulation gas of
70% Ar and 30% H2 for the collection of nanoparticles was 100 L/min.
The arc current was selected as 90 A. The crystal structure of the