Plasma Chemistry and Plasma Processing (v.31, #6)

Plasma Catalytic Oxidation of Stored Benzene in a Cycled Storage-Discharge (CSD) Process: Catalysts, Reactors and Operation Conditions by Hong-Yu Fan; Xiao-Song Li; Chuan Shi; De-Zhi Zhao; Jing-Lin Liu; Yan-Xia Liu; Ai-Min Zhu (799-810).
High energy cost and secondary pollutants formation makes the plasma-based technique impractical. To solve these problems, the effects of different catalysts, reactor configurations and operating conditions on plasma catalytic oxidation of stored benzene in a cycled storage-discharge process were investigated in detail. It is shown that the catalysts and reactor configurations were the main factors affecting the plasma catalytic oxidation of stored benzene. When 0.8 wt% Ag/HZSM-5 catalysts and in-plasma catalytic reactor are used, the stored benzene could be oxidized completely to CO2 in a very short discharge period and almost no secondary pollutant formation is observed. In addition, the relative humidity of air streams at storage stage showed little influence on the plasma catalytic oxidation of stored benzene. When the storage period increased from 1 to 14 h, a small increase of discharge period from 9 to 24 min was required to achieve ~100% conversion of stored benzene to CO2.
Keywords: Plasma catalysis; Benzene removal; Ag/HZSM-5 catalyst; Dielectric barrier discharge (DBD)

To improve application of hydrophobic polymethyl methacrylate intraocular lens (PMMA IOL) in a convenient and continuous way, 2-hydroxyethyl methacrylate (HEMA) was immobilized by dielectric barrier discharge plasma at relatively high pressure. The hydrophilicity and topography of the modified IOL surface were comprehensively evaluated by contact angle and atomic force microscopy, while the surface biocompatibility of the modified IOL was investigated by platelets adhesion and cells proliferation experiments. The results revealed that the hydrophilicity of the HEMA-g-PMMA IOL samples were significantly and permanently improved. Less platelets attachment was observed on the modified IOL, especially in the HEMA2-g-PMMA IOL group (with 1.65 × 10−1 mol/L HEMA concentration), which also suppressed the proliferation of cells.
Keywords: Intraocular lens; Surface modification; DBD plasma; 2-hydroxyethyl methacrylate; Biocompatibility

Instabilities of thermal plasma jets were studied on the basis of analysis of plasma radiation fluctuations recorded by an array of high frequency photodiodes. Characteristic frequencies of jet oscillations were found and spatial distribution of amplitude of plasma fluctuations was determined. The influence of arc current ripple on plasma instabilities was investigated for two types of power supply—classical thyristor controlled unit with the frequency of the current ripple 300 Hz and the rectifier with the high frequency converter and frequency of the current modulation 30 kHz. Generation of boundary layer instability with the current modulation frequency and its harmonics was proved using fast Fourier transform, contour plots and phase portraits. It was found that the character of fluctuations of plasma jet was substantially influenced by current ripple with the frequency or its harmonics close to the frequency of oscillations generated by boundary layer instability.
Keywords: Dc arc jet; Plasma jet oscillations; Boundary layer instability; Frequency spectra

Volatile Compounds Present in Carbon Blacks Produced by Thermal Plasmas by Ramona Pristavita; Ranjan Roy; Blain Moran; Jean-Luc Meunier; Dimitrios Berk (839-850).
Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders, as confirmed by Raman spectroscopy and Thermogravimetric Analysis. A thermal treatment process was developed in order to extract these volatile compounds, which were then identified using a Gas Chromatography—Mass Spectrometry method. The experimental powders were analyzed using Scanning and Transmission Electron Microscopy, X-Ray Diffraction and Raman Spectroscopy before and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties.
Keywords: Nanostructure; Carbon black; Adsorption; Chromatography; Thermal plasma

Carbon Nanoparticle Production by Inductively Coupled Thermal Plasmas: Controlling the Thermal History of Particle Nucleation by Ramona Pristavita; Norma-Yadira Mendoza-Gonzalez; Jean-Luc Meunier; Dimitrios Berk (851-866).
The process control for reproducibility, uniformity, and achievement of desired structures for carbon black generated in thermal plasma devices is studied in this paper through modeling, and correlated with experimental results. A numerical simulation of the flow and energy fields, stream function lines and the quench rates of the plasma gas in a conical shape reactor at different pressures was made. An argon plasma is used with highly diluted methane (0.6–7%) as the carbon precursor. The quench rates were studied in order to observe the flow development and hence the thermal history of particle nucleation. Three pressure cases of 20.7, 55.2 and 101.3 kPa and two plasma powers cases of 10 and 20 kW were studied. The modeling results enabled carbon nanoflakes production in the experimental tests performed on an inductively coupled thermal plasma system. Results indicate a robust process control enabling very little particle morphology variation over this wide range of reactor pressure values and varying plasma power, and a very high reproducibility of the particle morphologies obtained.
Keywords: Carbon black; Conical reactor; CFD modeling; Quench rates; Stream function; Nucleation; Carbon nanoflakes; Carbon nanoparticles

Atmospheric plasma sprayed alumina–titania (Al2O3–13%TiO2), coated on stainless steel (XC18), were characterized. The coating structure and morphology were studied by scanning electron microscopy. Their presented micro cracks, laminar splats. The coatings were studied by X-ray diffraction. The main phase transformation is that of α-Al2O3 into metastable γ-Al2O3. The α-Al2O3 phase is due to the occurrence of partially melted particles Electrochemical behaviours of coatings were mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.01 M [K3Fe(CN)6/K4Fe(CN)6] as a function of process parameters. Also, schematic equivalent circuit was proposed. The results were expected to facilitate the understanding and improvement of the coating behaviours.
Keywords: Plasma spray; Porosity; EIS; Image analysis