Vitas Valincius

Carbon and Nickel Oxide/Carbon Composites as Electrodes for Supercapacitors

The carbon and nickel oxide/carbon composite electrodes were prepared by plasma jet and magnetron sputtering techniques. The investigations were performed to evaluate the influence of the Ar/C2H2 ratio on the specific capacitance values of carbon and NiO/carbon electrodes. The obtained electrodes were investigated by scanning electron microscopy, Raman scattering spectroscopy (RS), and X-ray diffraction techniques. The surface of the carbon electrodes became less porous and more homogenous with increasing Ar/C2H2. The RS results indicated that the fraction of the sp2 carbon sites increased with increasing Ar/C2H2 ratio. The increase of the Ar/C2H2 ratio increased the capacitance values from 0.73 up to 3.6 F/g. Meanwhile, after the deposition of the nickel oxide on the carbon, the capacitance increased ten and more times and varied in the range of 7.6–86.1 F/g.

Preparation of catalytic coatings for heterogeneous catalysts employing atmospheric pressure non-equilibrium plasma

Abstract Well-adhered CuO and Cr 2 O 3 supported catalytic coatings with highly developed surface, excellent thermal and mechanical stability and high catalytic activity were prepared employing atmospheric pressure plasma spray technology. A system consisting of a linear DC plasma torch with a hot Hf cathode and cooling copper anode has been used. A temperature range of 2800–3500 K has been established as optimal. Coatings were analyzed by X-ray diffraction (XRD) structural patterns, scanning electron microscopy (SEM) and Brunauer–Emmet–Teller (BET) method analysis, as well as a catalytic combustion behavior study. The catalytic activity towards carbon monoxide (CO) oxidation was tested in the range 400–700 K.

Investigation of sewage sludge treatment using air plasma assisted gasification

This study presents an experimental investigation of downdraft gasification process coupled with a secondary thermal plasma reactor in order to perform experimental investigations of sewage sludge gasification, and compare process parameters running the system with and without the secondary thermal plasma reactor. The experimental investigation were performed with non-pelletized mixture of dried sewage sludge and wood pellets. To estimate the process performance, the composition of the producer gas, tars, particle matter, producer gas and char yield were measured at the exit of the gasification and plasma reactor. The research revealed the distribution of selected metals and chlorine in the process products and examined a possible formation of hexachlorobenzene. It determined that the plasma assisted processing of gaseous products changes the composition of the tars and the producer gas, mostly by destruction of hydrocarbon species, such as methane, acetylene, ethane or propane. Plasma processing of the producer gas reduces their calorific value but increases the gas yield and the total produced energy amount. The presented technology demonstrated capability both for applying to reduce the accumulation of the sewage sludge and production of substitute gas for drying of sewage sludge and electrical power.

Nitriding of an austenitic stainless steel in plasma torch at atmospheric pressure

Experiments with a nitrogen torch at atmospheric pressure have been performed in order to identify the role of surface processes in the mechanism of nitrogen transport during nitriding of stainless steel AISI 304. Unusually thick (∼175 μm) layers of supersaturated N solid-solution f.c.c. phase have been obtained for 10 min at 450 °C. Samples treated at 550 °C have a radically different structure. The scanning electron microscopy (SEM) surface and cross-sectional micrographs reveal that surface topography is an indicator of the degree of modification occurring in the nitrided layer. Surface vacancies generated by surface instabilities move deeply into the bulk at elevated temperatures and form a highly defective layer with pores and microcracks. The transport of nitrogen in austenitic stainless steel is driven by the fluxes of matrix atoms directed to stabilize surface instabilities. Nitrogen depth profiles simulated on the basis of a model with a surface-atom relocation process and activation energy of 1.15 eV, and including balanced fluxes of atoms in the bulk for relaxation of surface energy, are in qualitative agreement with experimental results.

The investigation of solid slag obtained by neutralization of sewage sludge.

The purpose of this research is to investigate the feasibility of utilizing the slag collected after gasification of organic fuel combined with sewage sludge. The residue left after gasification process is likely usable as raw material for production of supercondensers. The sewage sludge neutralization system consists of a dosing system (fuel tank), gasifier, plasma reactor, electrostatic filter, and heat exchangers. For the gasification process, dried solid sewage is supplied in proportion of 70% to biomass 30% by weight. The slag is collected in a specially designed chamber beneath the gasifier. A scanning electron microscope (SEM) was used to evaluate surface morphology of the samples. Elemental analysis of the sewage sludge slag was performed using the energy-dispersive spectroscopy (EDS) method, which showed different solid-state elements contained in the porous structure of the solid phase: carbon 29%, aluminum 26%, potassium 20%, chlorine 1%, and others. The specific surface area of the sewage sludge slag is 6.15 m2/g as the BET analysis shows. In order to use the slag as a secondary raw material, detailed analysis of the structure and properties is necessary for a decision on whether the slag left after gasification of sewage sludge is suitable for any further usages. Initial results indicate that the slag may be used for production of electrodes for supercapacitors. Implications: Every year thousands of tons of sewage sludge are formed in Lithuania. Sewage sludge consists of organic and inorganic compounds. Partial combustion, plasma decomposition, and other methods are used to neutralize the sewage sludge. The incineration of sewage sludge results in generation of solid-phase slag. In this paper the material structure and composition of a solid slag (formed during neutralization of sewage sludge) is considered. Also, the impact the ambient temperature on structure and composition of solid slag is analyzed.

Filter media properties of mineral fibres produced by plasma spray

ABSTRACT The purpose of this study was to determine the properties of fibrous gas filtration media produced from mineral zeolite. Fibres were generated by direct current plasma spray. The paper characterizes morphology, chemical composition, geometrical structure of elementary fibres, and thermal resistance, as well as the filtration properties of fibre media. The diameter of the produced elementary fibres ranged from 0.17 to 0.90 μm and the length ranged from 0.025 to 5.1 mm. The release of fibres from the media in the air stream was noticed, but it was minimized by hot-pressing the formed fibre mats. The fibres kept their properties up to the temperature of 956°C, while further increase in temperature resulted in the filter media becoming shrunk and brittle. The filtration efficiency of the prepared filter mats ranged from 95.34% to 99.99% for aerosol particles ranging in a size between 0.03 and 10.0 μm. Unprocessed fibre media showed the highest filtration efficiency when filtering aerosol particles smaller than 0.1 µm. Hot-pressed filters were characterized by the highest quality factor values, ranging from 0.021 to 0.064 Pa−1 (average value 0.034 Pa−1).

Water vapor plasma torch for synthesis gas production from organic waste

Plasma technologies have many fields of application, especially for treatment of materials and waste conversion. Water vapor plasma has special properties of high enthalpy and high activity flow. It can be a promising technology for gaseous, liquid and solid waste treatment and production of synthetic hydrogen-rich gas [1,2]. Atmospheric pressure water vapor plasma technology has been realized at Lithuanian Energy Institute, Plasma Processing Laboratory as an alternative to other reforming methods producing synthetic gas. An experimental linear, sectional, direct current arc plasma torch 55-70 kW of power with copper anode was developed and manufactured. The main plasma forming gas is overheated water vapor, produced by 5 bar of pressure steam generator. The operational characteristics of stable work of water vapor plasma torch were established. The flow was heated up to 2000-3000 K of temperature, the fuel conversion process from liquid organic waste, such as toluene and glycerol in plasma-chemical reactor was realized. Hydrogen and carbon monoxide gases (H2+CO) were produced as main products, additionally small amounts of CO2 and CxHy were obtained. The investigations confirmed that the conversion of toluene and glycerol into synthesis gas by means of atmospheric pressure water vapor plasma torch was successful. Liquid waste conversion rate exceed 100%. The main products of thermal plasma treatment are H2 (max. 56.9%) and CO (max. 20.7 %) with relatively high concentrations of CO2 (up to 12.6%). The results will be useful projecting new plasma equipment, designed for the decomposition of biomass and organic waste.

Synthesis of catalytic fibers employing atmospheric pressure arc plasma technology

The principle of non-equilibrium atmospheric pressure arc plasma technology for deposition of high temperature catalytic fibers is considered. CuO and Cr2O3 supported catalytic fiber containing less than 2 μm filaments with excellent thermal and mechanical stability were prepared. A system with linear DC plasma torch cooling step-formed cooper anode was used. The data of this study show that the use of plasma deposition technology has significant consequence in the formation of high thermal resistant catalytic fiber which represents a new approach in the environmental protection area.

Numerical and Experimental Investigation of Two-Phase Plasma Jet during Deposition of Coatings

Atmospheric pressure plasma spraying is widely used to produce various coatings, especially hard ceramic coatings for wear and corrosion protection and thermal barrier function, porous catalytic coatings for environment control and protection, hydrophobic coatings, etc. The plasma spraying process uses a DC electric arc to generate a jet of high temperature ionized plasma gas, which acts as the spraying heat source. The sprayed material, in powder form, is carried into the plasma jet where it is heated, partially or fully melted and propelled towards the substrate. The properties of the produced coating are dependent on the feedstock material, the thermal spray process and application parameters, and post treatment of the coating. However, the influence of flow and particle temperature and velocity on coatings characteristics, its adherence to the substrate, reproducibility of its properties and quality is not clearly established [Fouchais et al., 2006]. Generally, to correlate coating properties to flow parameters and particle in-flight characteristics experimental procedure is used. To monitoring the whole plasma spraying process (plasma jet generation, powder injection, formation of the coating) same techniques, as plasma computer tomography (PCT), particle shape imaging (PST), particle flux imaging (PFI) [Landes, 2006] are used. Such techniques are expensive and complicate for use in industry. Numerical investigations of plasma spray process generally is focused on investigation of heat transfer between plasma jet and surface [Garbero et al., 2006], substrate temperature influence on coatings morphology, adhesion, chemical processes between substrate material and deposited material [Yeh, 2006, Kersten et al., 2001]. In this paper, by means of Jets&Poudres software [Delluc et al., 2003], a numerical simulation of interaction of plasma jet and dispersed particles was investigated. Simulation results were compared with experimental data.