The mesh was cut into pieces of 42 mm20 mm and rolled up
forming single or multiwall monoliths. This option easily allows
building monoliths with different ratios of external surface area/
monolith volume. The experiments were carried out at atmospheric pressure in a thermobalance (CI Electronics Ltd., UK, model
MK2) operated as a differential CCVD reactor. This experimental
system allows continuous recording of the sample weight and
temperature during all the steps of an experiment. Previous to the
reaction, the monolith was treated with acid to clean the surface.
The metallic monolith, with the desired ratio area/volume, is
placed on the thermobalance basket and then is oxidized and
reduced in situ. After the activation steps, the CCVD reaction with
C2H6/H2/N2mixtures produces the growth of a layer of nanocarbonaceous material over the external surface of the monolith.
From this type of experiments we can calculate not only the NCM
growth rate, but also the kinetics of reduction and reaction stages.
In addition, from the values of the difference between the weights
after oxidation and reduction steps; and the bulk mesh composition can be used to estimate the amount of reduced metal. A typical
composition of the stainless steel mesh 316L is shown inTable 1.
This composition indicates that after the reduction stage, the active
sites for CCVD reaction will be the nanoparticles of Fe and Ni (or
Fe–Ni alloys) segregated to the external surface of the wires after
the activation stages. The operating conditions studied are
presented inTable 2. After reaction, the monolith, as well as the
carbon obtained, was characterized by scanning electronic
microscopy and RAMAN spectroscopy. SEM images were obtained
using a JEOL JSM 6400 instrument. A Horiba Jobin Yvon HR800 UV
model equipped with a CCD (charge coupled device) was used to
get the RAMAN spectra.