Colloidal Suspensions of Platinum Group Metal Nanoparticles (Pt,Pd, Rh) Synthesized by Dielectric Barrier Discharge Plasma (DBD)

Atmospheric‐pressure plasmas produced by dielectric barrier discharge can be used to grow nanoparticles from aqueous solutions containing ions from the platinum group metals (PGM: Pt, Pd, and Rh). The technology could also be applied to recover PGM from waste solutions. In plasma electrochemistry, PGM solutions act as a liquid electrode, and a counter electrode located near the surface of the liquid is used to generate the plasma (e.g., hydrogen, argon). The treatment synthesizes nanoparticles within minutes, which can be separated from the treated solutions. In the present study, small concentrations of PGM ions (1 × 10⁻³m ) are recuperated from aqueous solutions containing chloride ions. The efficiency of the process is quantified by elemental analysis, and the size of the colloids, measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Very high recovery yields are found for palladium (>99%), as well as for rhodium (>75%) and for platinum (>51%). Plasma electrochemistry is a very efficient and rapid process to recuperate PGM ions from water solutions (faster than conventional electrowinning) such as industrial waste, acid leach, and related effluents. The very fine and surfactant‐free nanoparticles could find promising applications as industrial and automotive catalysts.     

Comparative Plasma Chemical Reaction Studies of CH4/Ar and C2Hm/Ar (m = 2,4,6) Gas Mixtures in a Dielectric Barrier Discharge

Plasma chemical reactions in CH4/Ar and C₂H_m/Ar (m = 2, 4, 6) gas mixtures in a dielectric barrier discharge at medium pressure (300 mbar) have been investigated. From mass spectrometry the production of H₂ and formation of larger hydrocarbons such as C_nH_m with up to n = 12 is inferred. Hydrogen release is most pronounced for CH₄ and C₂H₆ gas mixtures. Fourier Transform InfraRed (FTIR) spectroscopy reveals the formation of substituted alkane (sp³), alkene (sp²), and alkyne (sp) groups from the individual gases which are used in this work. Abundant formation of acetylene occurs from C₂H₄ and to a lesser extent from C₂H₆ and CH₄ precursor gases. The main reaction pathway of acetylene leads to the formation of large molecules via C₄H₂ and, eventually, to nano‐size particles. The experimental results are in reasonable agreement with simulations which predict a pronounced electron temperature and gas pressure dependency. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of a non-thermal plasma torch in streamer mode and its effect on polyvinyl chloride and silicone rubber surfaces

In this study, a non-thermal plasma torch in steamer mode was characterized to apply for surface modification in ambient air. The plasma source is a central rod-ring configuration based on DBD operation. Mixture of Ar/air gases was passed through the hollow Copper rod. A home-built high voltage generator at 18.8 kHz was employed to ignite the plasma. Electrical features of plasma torch were studied and different regions of plasma were examined using optical emission spectroscopy to explore the reactive species that result in efficient treatment. The surfaces of polyvinyl chloride (PVC) and silicone rubber (SIR) films were treated by the cold plasma torch. Contact angle measurement shows the improvement of surface hydrophilicity and wettability. Analysis revealed that the surface energy of the films increases indicating their activation after plasma treatment. This process is attributed to increasing the polar component of the surface energy.     

三电极共面介质阻挡放电的放电特性及诱导气流实验研究

等离子体流动控制激励器由于其响应速度快、激励频带宽、能量损耗低、可靠性强的优势,在航空航天领域的主动流动控制等方面得到了广泛应用.文章提出了一种新型的等离子体气动激励器——三电极共面介质阻挡放电激励器,研究了该激励器电极结构对放电特性和诱导气流速度的影响,并与传统共面介质阻挡放电和沿面介质阻挡放电激励器进行了比较.结果表明:（1）随着激励电压的提高,高压电极和地电极之间先出现了丝状放电并逐渐延伸到第三电极;（2）随着第三电极与高压电极之间的距离增大,诱导气流速率从2.4 m/s下降到0 m/s,而第三电极宽度的变动对诱导气流速度影响可忽略不计;（3）相同外部条件下,该激励器诱导的气流速度小于沿面介质阻挡放电激励器,但高于共面介质阻挡放电激励器.