Controlled Synthesis of β-SiC Nanopowders with Variable Stoichiometry Using Inductively Coupled Plasma

In the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20–40 nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar–H₂ plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methane.     

Cole-Cole plot analysis of dielectric behavior of monoalkyl ethers of polyethylene glycol (CnEm)

The complex permittivity of monoalkyl ether of polyethylene glycol (C_nE_m) was measured at 336.5 K at frequencies from 0.2 to 20 GHz. The number of bonded ethylene glycol units was varied from 1 to 120 to observe the effect of the PEG-chain length on the dielectric permittivity of the whole polymer. The measured real and imaginary parts of complex permittivity of these polymers were studied by the graphical analysis of the Cole-Cole plot as proposed by Havriliak and Negami. This analysis makes us understand that, in the high-frequency region above 9.7 GHz, the Cole-Cole plot of all C_nE_m is located on one single line. This phenomenon implies the same relaxation mechanism of all C_nE_m in this frequency region. It is found that the same relaxation mechanism of the dipoles of the hydroxyl group in n-alcohol contributes to the dipole relaxation of C_nE_m. In the low-frequency region, the arc of the Cole-Cole plot has the same shape as pure PEG, but it is scaled-down linearly following the decrease of the number of PEG units bonded to the n-alkanes. This phenomenon explains the linear contribution of ether dipoles, existing in bonded PEGs, on the complex permittivity of C_nE_m in the low-frequency region.     

Induction Plasma Synthesis of Graphene Nano-flakes with In Situ Investigation of Ar–H2–CH4 Plasma by Optical Emission Spectroscopy

Plasma Chemistry and Plasma Processing - Synthesis process of graphene nano-flakes produced in radio-frequency inductively coupled plasma system by axially injecting CH4 into Ar–H2 plasma is...     

In Situ Treatment of Thermal RF Plasma Processed Nanopowders to Control their Agglomeration and Dispersability

Titanium carbonitride nanoparticles have been produced in an inductively coupled thermal plasma and subsequently modified using a surfactant that has been deposited in situ on their surface in-flight. The surfactant was injected in the reactor while the nanoparticles are still dispersed in the gas phase, allowing the coating of primary particles instead of the corresponding agglomerates. In contrast to naked TiCN nanoparticles, the surfactant coated particles could be readily dispersed in water with a short ultrasonic treatment and built up no large agglomerates as proved by Photon Correlation Spectroscopy measurements. The investigated surfactants seem, however, to undergo a chemical modification and/or a thermal degradation at the surface of the TiCN nanoparticles.