Carbon-based materials exhibit unique properties driven by the many different bonding configurations available to the
element carbon. Many of them proved to be compatible with inorganic and/or biologic systems and might be considered
as useful materials in medicine and biology. The carbon nanoparticles existing in environment are an important factor on
healthy, either by their toxicity or by interaction with pathogen microorganisms, Carbon black is nowadays one of the
additive most widely used to make composites and the applicability of nanocarbon-based composites depends on how
well its properties can be manipulated. The activation of carbon materials improves their functional properties and
depends on their structure. Through the variation of the experimental parameters, the method of laser-induced pyrolysis
allows obtaining carbon nanoparticles with different morphologies providing useful functional properties. The focus is to
drive these materials into a regime where they can naturally interface with the surrounding matter. With other words, the
goal of the work is to investigate how to modulate, through laser induced pyrolysis, the characteristics of carbon
nanopowders in order to achieve functional properties claimed by specific applications.
Because of their quantum-scale dimensions, nanoparticles exhibit properties different from those of the bulk. As a result
of their unique properties, numerous efforts have been made to disperse nanoparticles in polymers to enhance or modify
their structural and magnetic properties. A new in situ synthesis method was used to incorporate small iron nanoparticles
into a polyoxocarbosilane polymer matrix. Nano-magnetic iron-based composites were obtained by a one-step procedure
consisting of the IR laser co-pyrolysis of a sensitized (with ethylene) gaseous mixture containing gaseous iron
pentacarbonyl and hexamethyldisiloxane in argon. The simultaneously occurring formation of iron from iron
pentacarbonyl and that of organosilicon polymer from hexamethyldisiloxane yield iron nanoparticles surrounded by an
organosilicon polymer shell. The particles become superficially oxidized in the atmosphere. They were characterized by
Raman analysis, electron microscopy and magnetic measurements. The properties of the nanocomposite particles depend
on the experimental synthesis parameters such as flow rates of precursors, total pressure and laser power. Magnetization
curves, exchange bias Hex at T = 5 K and AC susceptibility were studied in the temperature range 5-400 K. It was found
that the nanocomposite should be in a ferromagnetic blocked state with a minor superparamagnetic contribution of the
smallest nanoparticles.
Carbon-made materials have been the field of major discoveries with the identification of new phases, which have
stimulated a huge effort to understand their properties. Laser pyrolysis of hydrocarbons is based on a high temperature
C/H/O/... system of well-established composition and allows obtaining carbon nanostructures from the almost
amorphous carbon and particles with a turbostratic structure up to those characterized by a high degree of curvature. The
variation of the gas composition and experimental parameters controls the final particle morphology providing useful
functional properties. Gas-phase hydrocarbons were used either in resonant or non-resonant laser pyrolysis processes.
The formation of different nanostructures is related to the presence of heteroatom in the reactants. Focusing, in the
context of necessary presence of this heteroatom in the gas composition, on the present questions concerning the rational
synthesis of nanostructures with controlled dimensionality, size and potentially properties, the work presents some
significant changes in soot morphology produced by the variation of the experimental parameters and these, sometimes
unavoidable, heterogeneous atoms.
Multiphase composite nanoparticles presenting core-shell structures have been investigated by performing a detailed correlation between their synthesis parameters and the structural and magnetic properties. Basically in all the experiments iron pentacarbonyl as iron precursor and ethylene as laser energy transfer agent and as a secondary carbon source have been used. The capability of the synthesis technique to form nanocomposite particles by varying laser power density, inlet geometry, pressure in reactor chamber and gas precursors' ratio was tested. The results proved that the laser
pyrolysis can produce particles between 4 and 10 nm diameters. Their sizes may vary according to the reactor pressure and gas flows but their size distributions remain sharp as long as an optimized geometry of the reactor is used. As a second step, the structure and magnetic properties were studied by different techniques such as TEM, HREM, SAED, XRD, FT-IR and Raman spectroscopy. The investigations reveal that, depending on the input parameters, some samples exhibit a nanocomposite structure consisting of iron / iron carbides (Fe3C or Fe2C5) core wrapped in a shell of amorphous or turbostratic carbon. The different magnetic phase identification was performed using Mossbauer spectroscopy and thermo-magnetic analysis.
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