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Dirk Hegemann – One of the best experts on this subject based on the ideXlab platform.

  • Macroscopic control of Plasma polymerization processes
    Pure and Applied Chemistry, 2008
    Co-Authors: Dirk Hegemann


    Plasma polymerization covers a broad range of Plasma deposits from soft to hard coatings. Nanoscale coatings are formed within a dry and eco-friendly process on different substrate materials and structures. To gain a deeper insight into Plasma polymerization, a macroscopic approach using the concept of chemical quasi-equilibria might be useful. Following this macroscopic approach, the reaction parameter power input per gas flow W/F, which represents the specific energy invested per particle within the Active Plasma Zone, solely determines the mass deposition rate. Hence, Plasma polymerization can be described by measuring the deposited mass and examining the power input and gas flow which con- tributes to it. Thus, the control, investigation, and up-scaling of Plasma polymerization processes are enabled. Different examples are given to make use of the macroscopic ap- proach.

  • Macroscopic Description of Plasma Polymerization
    Plasma Processes and Polymers, 2007
    Co-Authors: Dirk Hegemann, Mohammad Mokbul Hossain, Enrico Körner, Dawn J. Balazs


    Industrial applications based on Plasma polymerization require reliable processes that can be transferred to production-scale reactors. To enable an inexpensive access to control Plasma deposition processes, macroscopic kinetics were investigated to describe Plasma polymerization, which is based on the concept of chemical quasi-equilibrium. The evaluation of deposition rates was carried out in order to obtain the apparent activation energy for a specific process. Influencing factors, such as substrate temperature, energetic particles, reactor geometry, Plasma expansion, pressure, monomer, carrier/reActive gas, power modulation, and Plasma source were thoroughly examined. The obtained activation energy was correlated to the Plasma-chemical processes, such as dissociation and radical formation, which are taking place within the Active Plasma Zone. Since these processes are also contributing to the film growth, the activation energy was used for the scale-up of Plasma polymerization processes.

  • Influence of pressure on an asymmetric, radio frequency discharge with methane
    Thin Solid Films, 2006
    Co-Authors: Dirk Hegemann


    Abstract Recently, we reported about the influence of flow on deposition rates within an asymmetric, radio frequency (RF) discharge with methane. The Plasma expansion of the unconfined discharge was found to contribute strongly to the energy consumed by the film-forming particles. To enhance this macroscopic approach to Plasma polymerization by simple evaluation of the deposition rates this work considers the pressure as external parameter. Also pressure was found to influence the expansion of the Plasma Zone in front of the RF-driven electrode. The introduction of geometrical factors describing the reactor and the Plasma geometry enables the identification of the energy consumed within the Active Plasma Zone that solely determines the deposition rates and the activation energy for CH4 discharges. This concept helps to understand Plasma polymerization processes such as the transition from a volume- to a corner-dominated discharge as well as comparison and scale-up of reactors.

J. Ráhel’ – One of the best experts on this subject based on the ideXlab platform.

  • Effect of DCSBD Plasma treatment distance on surface characteristics of wood and thermally modified wood
    Wood Science and Technology, 2020
    Co-Authors: R. Talviste, Oleksandr Galmiz, Monika Stupavská, J. Ráhel’


    This study focused on Plasma treatment of European beech ( Fagus sylvatica ) and heat-treated European beech surfaces with varying distance from the planar electrode of the diffuse coplanar surface barrier discharge. In addition to the treatment in the air, Plasma treatment was also carried out in O_2, CO_2, N_2 and Ar atmospheres. Treatment was differentiated between treatment in the Active Plasma Zone and in the so-called Plasma afterglow region. Air Plasma treatment in the Active Plasma Zone led to the well-known improvement of surface wettability of polar liquids due to increased polar part of surface free energy. Treatment in Plasma afterglow region caused the wettability decline of polar liquids and caused a more hydrophobic surface. The phenomenon was primarily present for air Plasma treatment. Oxygen-to-carbon ratio measured by X-ray photoelectron spectroscopy did not change with the treatment in air Plasma afterglow. Based on additional tests with pure cellulose paper and based on findings in previous studies, the reason for increased hydrophobicity was suggested to be degradation of hemicelluloses on the wood surface.

Rah Richard Engeln – One of the best experts on this subject based on the ideXlab platform.

  • CO and byproduct formation during CO2 reduction in dielectric barrier discharges
    Journal of Applied Physics, 2014
    Co-Authors: F. Brehmer, S Stefan Welzel, Van De Mcm Richard Sanden, Rah Richard Engeln


    The dissociation of CO2 and the formation of CO, O3, and O2 were studied in a dielectric barrier discharge (DBD) at atmospheric pressure by means of ex-situ infrared absorption spectroscopy. CO mixing ratios of 0.1%–4.4% were determined for specific injected energies between 0.1 and 20 eV per molecule (0.3–70 kJ/l). A lower limit of the gas temperature of 320–480 K was estimated from the wall temperature of the quartz reactor as measured with an infrared camera. The formation of CO in the DBD could be described as function of the total number of transferred charges during the residence time of the gas in the Active Plasma Zone. An almost stoichiometric CO:O2 ratio of 2:1 was observed along with a strongly temperature dependent O3 production up to 0.075%. Although the ideal range for an efficient CO2 dissociation in Plasmas of 1 eV per molecule for the specific injected energy was covered, the energy efficiency remained below 5% for all conditions. The present results indicate a reaction mechanism which is…