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 particles was determined by XRD using monochromatic Cu Kα
radiation. The Fourier transform infrared spectroscopy (FTIR)
measurements were performed by SHIMADZU FTIR-8400. The
morphology, size distribution and shape of the as-prepared particles
were observed by TEM using JEOL-JSM-2100 at an acceleration
voltage of 200 kV. N2 adsorption–desorption isotherm curve was
measured using a volumetric gas analyzer (Counter SA 3100) at 77 K,
with the sample being activated by evacuating in vacuum at 523 K for
2 h. The BET (Brunauer–Emmett–Teller) equation was used to give
specific surface area from the nitrogen adsorption data. The pore
volume and diameter were evaluated from the desorption branch of
isotherm based on the BJH (Barrett–Joyner–Halenda) model