– development and research of DC plasma sources for a wide range of applications;
– research of processes and phenomena taking place in discharge channels, exhaust plasma jets and flows;
– plasma and high-temperature gas flows diagnostics and development of diagnostics measures;
– interaction of plasma jets and substances in various plasma-technological processes;
– research and implementation of plasma neutralization process of extra hazardous substances;
– synthesis and characterization of catalytic and tribological coatings in plasma ambient;
– research on thermal and heterogeneous processes nearcatalytic surface immersed in the reacting flow of combustion products;
– formation and modification of constructional material surfaces in plasma;
– synthesis and characterization of micro and nano dispersed granules and mineral fiber from hardly melted materials and investigation of properties;
– generation of water vapour plasma and its application for fuel conversion and neutralization of hazardous waste.
Researchers of Laboratory of Plasma Processing have over 40 years experience working in different fields of development, scientific research and application of atmospheric and reduced pressure plasma and are able successfully simulate new plasma technologies, using plasma equipment, designed in the Laboratory. Different composition gas and its mixtures are used for plasma jets formation. Laboratory contains pilot production technological equipment, which is used to change and modify mechanical, tribological, chemical and optical properties of layers of different material surfaces. Constant updating of technical base, development and disposal of available analytic equipment enables to perform research of plasma sources, diagnostics of plasma flows and jets, analysis of gas dynamic characteristics and heat-mass exchange.
Under the basis of acquired knowledge, Laboratory of Plasma Processing is carrying out the following researches:
Development of plasma sources and research of plasma jet
Laboratory of Plasma Processing develops novel plasma generators up to 200 kW of capacity and improves the construction of the existing ones. Recently a novel water vapour plasma generator has been developed. Its thermal and operational characteristics were generalized on the basis of the similarity theory and a variety of processes occurring in the reactive discharge chamber. This allows determining stable operating regime when electric arc heats the overheated water vapour under different pressures. The obtained results show that the generator is suitable for the realization of various processes in the reactive arc zone and may be used for the conversion of solid, liquid, organic and inorganic materials into gas.
Laboratory continues carrying out the investigations of heat transfer in plasmatron reactive arc zone, electric arc strength variation in laminar and turbulent arc, the impact of various factors on the characteristics of plasma flows and jets, impact of radiation in the presence of different plasma forming gases. Operating conditions of linear electric gas arc heaters and plasma chemical reactors have been examined as well as their operating characteristics and new methods for their application in plasma equipment.
Diagnostics of plasma and high-temperature jets
Formation of high-temperature and plasma jet, its dynamics and heat exchange characteristics in the channels of different configuration and heat exchanger cells and elements are investigated in the Laboratory. Plasma diagnostics is available by numerical and experimental methods. A numerical research of heated gas jet in the channel was performed applying hydrodynamics software Fluent. It was used to solve full Navier-Stokes and energy equations based on the dynamic k-ε model for the fluid jet. However, the numerical research becomes especially difficult when multiphase jets are running and the solid particles are injected into the jet. This is because of specific plasma properties; therefore, numerical research of two-phase plasma jets are performed applying software package Jets & Poudres, adjusted to model plasma jets. Yet, if the task is not considerably simplified, numerical research methods become impossible to use for multiphase plasma jets; thus, the experimental method is given the priority in the Laboratory. It was used to solve full Navier-Stokes and energy equations based on the dynamic model for the fluid jet. However, the numerical research becomes especially difficult when multiphase jets are running and the solid particles are injected into the jet. This is because of specific plasma properties; therefore, numerical research of two-phase plasma jets are performed applying software package , adjusted to model plasma jets. Yet, if the task is not considerably simplified, numerical research methods become impossible to use for multiphase plasma jets; thus, the experimental method is given the priority in the Laboratory.
Recently, non-contact methods have been widely applied for plasma diagnostics in the Laboratory. One of them is optical spectroscopy method; its main analytical device is an optical spectrometer AOS-4. It is an optical system for rapid measurements, that may be used for the investigation of gas emission spectra peaks in a wavelength range of 250–800 nm. The system is used also for the examination of plasma element composition and emission spectra.
An X-series high-speed optical camera RedLake Motion Pro X4 with CMOS (Complementary Metal Oxide Semiconductor) sensor is used for multiphase plasma flow visualization and determination of some dynamic characteristics. The camera enables high-speed recording of images in 100 ns interval and also observation of very rapidly moving objects. A high-speed optical camera MotionPro X4 is used in the Laboratory.
Formation of constructional material surface layers by plasma technologies
Synthesis of coatings in plasma flows
Plasma spray technology, developed in the Laboratory, was applied for catalytic, tribological and protective coatings formation as well as for solid ceramic coatings, which are employed for improving the operational characteristics of constructional material surface layers in mechanics, chemistry, energy and medicine. These coatings accelerate the corrosion resistance up to 102–103 times, significantly diminish the friction coefficient and reduce the mechanical wear. The use of plasma technology decreases the demand for expensive constructional materials since their large amounts are replaced by cheap materials covered with different thickness coatings.
Having integrated a non- equilibrium atmospheric pressure plasma jet with non- equilibrium temperature components into the equipment presented in Fig., the activated and synthesized materials acquire different energies before reaching the treated surface. Necessary conditions for certain chemical reactions to combine into blocks in both plasma jet and the substratum surface are created. This enables the synthesis of g phase Al2O3 coatings with highly developed active surface, which is especially relevant in the formation of catalytic coatings. The surface area of the coating was further enlarged by heating it in a certain temperature.
In the fields of science and production, a worldwide attention has recently been given to the renewable energy technologies, hydrogen energy, programmes of fuel synthesis and saving, issues related to the reduction of environmental pollution and their solution. All these areas require special purpose and composition catalysts that are used in approximately 70% of chemical reactions carried out worldwide. The production of the up-to-date catalytic reactors is a time and finance consuming chemical process performed by precipitating platinum group metals. For this reason, the reactors are expensive, their ceramic substrates are non-durable and the meshes often melt and block the reactors due to poor thermal conductivity. In the new generation of catalytic neutralizers, a metal substrate is substituted for ceramic one and the noble metals are replaced by cheaper metal oxides, zeolites and other materials that are successfully used as effective catalysts.
The mass and heat transfer processes taking place in the catalytic reactors made of coatings were examined using the equipment for studying catalyst coating characteristics developed in the Laboratory. Gas with CO concentrations, characteristic of internal-combustion engine, is emitted and the temperature necessary for catalytic oxidation of the pollutant is reached when the propane-butane gas combustion products mix with an oxidant in the air.
For the purpose of the work, the methodology for the research of dynamic and thermal characteristics of gas in the boundary layer zone was developed; the equipment and facilities for examining the jet structure were assembled. The distribution of velocity, temperature and substance concentration of the reactive gas next to the catalytic wall and the heat-mass exchange coefficients of the jet and the wall were established.
On the basis of oxide catalytic coatings, formed employing plasma method, catalytic reactors efficiently reducing the emission of CO, SO2, NOx, HC and other pollutants have been developed. By the catalytic combustion behaviour these reactors are very similar to the ones composed of noble metals. The work related to this issue is continued in accordance with the project of Baltic Sea Region Programme 2007–2013. Presently an innovative efficient catalyst for sulphur compounds oxidation is being developed on the basis of TiO2.
Carbon derivative coatings
Technological modification of surface layers of constructional materials by forming multifunctional coatings is widely applied in engineering. One of the possibilities of using plasma technology is the synthesis of plasma polymers, i.e. thin membranes precipitated by plasma method that may be applied in a wide range of fields: microelectronics, medicine, biotechnologies, semiconductors manufacturing, etc. Plasma polymers are usually synthesized in a vacuum, but their structures are not thoroughly studied yet. Due to the low price and good mechanical properties (resistance to corrosion, toughness, small autonomous mass, slight irrigation angle), hydro, halocarbon polymers and hydrogenated carbon membranes or their groups compete with the best up-to-date materials and melts. Taking into consideration the situation in the field of plasma polymer synthesis and research, it should be noted that plasma polymerization process requires more detailed knowledge, especially about the influence of coating parameters on the obtained plasma polymer properties and the stability of their time and temperature. One of the plasma polymer groups is innovative materials composed of plasma polymers mixed with metals or ceramics. Such composite materials form a new class of coatings, made of composites and non-composites, and are characterized a variety of electric, optical and mechanical properties. The developed plasma polymers are mostly used as solid and protective coatings. The application of carbon derivatives for polymer synthesis is currently expanding.
Although the plasma coating formation process in the atmospheric pressure has been widely used for a long time, it is not fully investigated in terms of physics. It is claimed that the chemical, physical and mechanical properties of the coating as well as its composition and structure are affected by about 50 factors. The prevailing ones are the following: composition of starting materials, materials introduced in plasma jet, dislocation, construction of plasmatron, working characteristics, distance from plasmatron to substrate, temperature, pressure and the type of working gas. Presently a great deal of attention is directed towards developing solid carbon coatings of various composition and properties on different surfaces (steel, Al2O3, quartz glass, etc.) and investigating their properties by available methods.
To carry out the mentioned work, two plasma systems for synthesis of solid ceramic and diamond coatings were developed. They are equipped with modified plasma generators that supply non-equilibrium plasma jet. The systems operate at the atmospheric and reduced pressure of gas, such as nitrogen, argon, hydrogen, acetylene, propane-butane and their mixtures. The coatings on the surfaces of stainless steel, quartz glass and silicon, obtained during the process of synthesis, are characterized by good properties of adhesion. The SEM, XRD, IR and Raman spectroscopy methods were applied for determining the following factors: the coatings surface structure, the size, shape and composition of their particles, their dependence on the composition of gas, constituting and transporting plasma, as well as the place and means of gas introduction into the plasmatron. It was noticed that all spectra of IR photoconductance and reflection have relations common to CHx, OH, CO, CO2 and C=C groups.
Following the performed research, the synthesis of supercondenser electrode coatings was realized and carbon derivative coatings were obtained by developing them in the atmospheric-pressure plasma in argon/acetylene ambient. The electrical characteristics of the coatings enable increasing the capacity of supercondensers presently used in practice.
Research on interaction of plasma jet and materials
For the purpose of production of high-temperature fibre with especially small diameter, reprocessing of hazardous substances, formation of various coatings and synthesis of new materials, the interaction of electric arc and plasma jet with dispersed materials is analysed. Physical, chemical and mechanical properties of obtained materials are determined.
The plasma processing efficiency depends on the nature of chemical reactions, the value of plasma ambient temperature and velocity, the pressure of material in high temperature zone, etc. The surfaces formed employing plasma method are obtained by laminating many dispersed particles, which before the collision with the solid surface must be partly alloyed and plastic. Thus, their shape and structure in the coating is very different. The interaction of particles and plasma jet during contact is defined by flow, deformation, and cooling processes, whereas the variety of fundamental results of particle interaction with plasma jet is manifested by their principal parameters, that is, velocity, temperature and concentrations. It has been determined that parameters of material particles with the same dispersity and composition are very different in the cross-section of coated substrate. In reality, these parameters are non-stationary during the contact. Their functions of distribution are determined by the flow and the formation of two-phase jet conditions in the initial region of the jet. The distribution of injected particles in the plasma jet along different directions usually becomes anisotropic. These processes describe the structure and features of the produced final product.
Melting of ceramic materials and synthesis of high-temperature metal oxide fibre
Traditional technology and equipment presently used to produce mineral fibre require continuous operation process, complex and expensive alloying furnaces and insulation materials. The quality and composition of fibre produced traditionally are also limited by the melting-point of raw materials; therefore, this method is not suitable for the production of high-temperature thermal insulation fibre, which is more and more often used in various fields.
Plasma technology is the only alternative to obtain a high quality high-temperature fibre. Melting and stringing ceramic materials and forming mineral fibre, an experimental plasma device with 70–90 kW capacity plasma generator has been developed at the Laboratory of Plasma Processing. It enables to form a splint from dispersed particles, using air as plasma forming gas and auxiliary (Ar, N2, propane-butane) gas mixtures.
Cheap ceramic materials (quartz sand, dolomite, clay, aluminum oxide, industrial ceramic waste, etc.) as raw materials are used for producing heat resistant ceramic fibre. After conducting experimental and numerical research it was determined that dynamic and energetic characteristics of plasma jet have major impact on the fibre process of ceramic materials. Since melting temperature of ceramic materials reaches 2500 K, the temperature of plasma jet inflowing into the reactor should be 2500–3000 K, whereas velocity – 700–1000 m/s in order to completely alloy and fibre ceramic dispersed particles. The average mass plasma het temperature and velocity along reactor channel length evenly reduces and changes at the end, respectively, 14 and 10%, not taking into account plasma generator operating regimes. This enables to easily regulate plasma jet parameters in the reactor discharge. After getting acquainted with the mechanism of ceramic fibre formation in plasma-chemical reactor it was determined that particles melting occurs in the reactor channel, whereas formation of fibre elements, which occurs 4–10 ms, – behind the reactor limits. After blowing raw material dispersed materials in to the reactor, heat exchange occurs not only between plasma jet and reactor walls but also among dispersed particles, which has impact on the reduction of plasma jet temperature. It was investigated that heat exchange of plasma jet and dispersed particles are more intensive depending on the concentration of particles in the jet. With increase of mass cold dispersed particles concentration in plasma jet from 6 to 24%, the heat flow into the reactor wall reduces from 6 to 31% due to intensive flow heat release to particles.
Plasma jet velocity is one the basic factors conditioning the quality of ceramic fibre since with the increase of plasma jet (60%) velocity discharged from the reactor the developed fibre yield increases by 5%, whereas the fibre diameter comprising the splint and granular amount in it reduces.
The derived splint is irreplaceable in the production of muffle furnaces, MHD generators and blast-furnaces, and due to splendid sound isolating properties – for sound isolation s well. The ceramic splint can also be relevant in the manufacturing of different filtrating materials, also as constructional, concrete solidifying material, whereas certain composition ceramic splint may serve as a catalyst.
Water vapour plasma technology
The application of water vapour plasma for various needs of energy, environmental protection and industry areas spreads worldwide. When the temperature is high (4000–5000 K), water vapour mass enthalpy is about 6 times greater than air enthalpy. This suggests that heating water vapour requires 6 times greater capacity than the same amount of air mass jets; therefore, the produced energy of the jet is much greater than of other gas plasma energies used up to now. At high temperature water vapour decomposes into oxygen, hydrogen and their compounds, which react in plasma-chemical reactions. Decomposing waste of different types with plasma method, due to its unique properties it is characterized as environmentally extremely friendly process. Plasma pyrolysis of organic waste is applied in two cases, when it is necessary to utilize extremely hazardous waste (for example, chlorine organic pesticides) or plasma-chemical processing of organic waste with the aim to derive valuable materials. Using water vapour operating plasmatron due to plasma it is possible to derive valuable gas enriched with hydrogen and CO, the so called synthetic gas.
Extremely rapid chemical processes occur in water vapour plasma, when reactive elements H and O are formed. Due to this flow property, hydrocarbons introduced into water vapour plasma are decomposed very efficiently. This technology may be applied for decomposition of waste and environmentally hazardous materials or turn them into synthetic gas during the conversion.
The first experiments of organic materials’ decomposition were carried out. Hydrocarbon gas was chosen to perform the conversion and they were introduced into the plasma-chemical reactor. Propane gas (C3H8) was chosen for decomposition as an initial sample since it encompasses active carbon and hydrogen, when decomposing it in the water vapour environment the exhaust of hazardous materials in to the environment is avoided. The propane conversion in the water vapour plasma environment is endothermal reaction (498 kJ mol-1) :
C3H8 + 3H2O ® 7H2 + 3CO.
After performing primary conversion research and analysis of reaction products using gas chromatograph and summarizing the results it was determined that at different water vapour and propane relation the formed hydrogen amount is always higher than 60%.
Laboratory activity in the National Space Programme
In 1981–1989 the researchers of Laboratory of Plasma Processing worked hard by experimenting with various materials, used for producing space shuttle hulls of the former Soviet Union, in plasma jets and flows. The effect of high temperature and velocity to the changes of structure and properties of the given material was investigated, and the tested material was used for the manufacture of the hull for the space shuttle Buran.
Presently for the similar purposes the Laboratory employs analogous plasma equipment with 150 kW capacity. The temperature of plasma jet, flowing from the plasma generator, is 1600–7500 K, while its velocity reaches 150–750 m/s. This creates a possibility to examine the behaviour of various materials in plasma jet, form the surface layers of multi-purposeful constructional materials, develop protective coatings for a vide range of application, having different properties and suitable for rocket engineering and space exploration.
In 2010 the research of material testing and experiments were reinitiated. The research on Novel materials for use in the surface thermal protection system of re-enter space vehicles using low-temperature plasma jet was initiated in cooperation with the Laboratory of Materials Research and Testing under the innovation cheque contract. During the implementation of this study, samples of refractory materials were placed in plasma flow and the impact of high temperature and velocity on the structure and erosion of the materials was investigated. The work in this direction is still continued.
The Events of 2012
ISFV-15 conference, in Minsk, Belorussia. Dr. Viktorija Grigaitienė was granted the Soloukhin nominal award for presented results in the field of flow visualization (photo left).
Mindaugas Milieška defended his doctoral thesis Research of thermal-hydrodynamic processes in plasma by fibreing hardly alloyng ceramic materials (06T).
Projects implemented in the Laboratory
In 2012 together with researchers from Laboratory of Combustion processes new long-term R&D programme Experimental and numerical research of combustion and plasma processes for improvement of energy generation technologies from renewable biofuel and reduction of environment pollution was initiated. The objective of the laboratory is to create water vapour plasma technology designed for conversion of biomass and solid fuel, using numerical and experimental methods to investigate processes occurring during the conversion and identify their regularity patterns. To investigate possibilities and create conditions to employ water vapour plasma generator in the field of development of new environmental technologies.
In 2012 a new scientific work, funded from budget assets, Synthesis of carbon coatings in argon-acetylene and argon-hydrogen-acetylene plasma and investigation of their properties was initiated. Conducting work tasks, applying long-term experience of LEI researchers and available facilities it is aimed at investigating possibilities and conditions for development of new generation carbon coatings. During the project plasma process of formation of amorphous and crystalline solid carbon coatings will be implemented. Supplying various modification additives, there is an objective to investigate their impact on the structure and properties of obtained coatings.
In 2012 researchers of the Laboratory participated in international projects and programs:
• COST CM0903 activity Utilisation of Biomass for Sustainable Fuels and Chemicals (UBIOCHEM) till 2013. In this activity, the researches of the Laboratory are performing an individual project Water Vapour Plasma for Biomass Conversion and Waste Utilization. During its implementation, an entirely new plasma technology, which has not been created before, will be developed for converting organic substances into synthetic gas containing a larger amount of hydrogen. Not only different waste, but also hazardous materials will be processed using water vapour plasma technology. Scientists from 18 European countries participate in this activity. COST CM0903 activity (UBIOCHEM) till 2013. In this activity, the researches of the Laboratory are performing an individual project During its implementation, an entirely new plasma technology, which has not been created before, will be developed for converting organic substances into synthetic gas containing a larger amount of hydrogen. Not only different waste, but also hazardous materials will be processed using water vapour plasma technology. Scientists from 18 European countries participate in this activity.COST CM0903 activity (UBIOCHEM) till 2013. In this activity, the researches of the Laboratory are performing an individual project During its implementation, an entirely new plasma technology, which has not been created before, will be developed for converting organic substances into synthetic gas containing a larger amount of hydrogen. Not only different waste, but also hazardous materials will be processed using water vapour plasma technology. Scientists from 18 European countries participate in this activity.
• 2012 – 2014 Research Council of Lithuania financed scientific group technological development Project Ceramic fibre catalyst formed by plasma technologies for reducing pollution emission. Basic project objective – by employing plasma technology to develop a catalytic ceramic fibre of desired properties, from which to produce metal oxide fibre catalyst of required properties designed for neutralizing environment pollution, to design and produce experimental research equipment of catalytic properties and realize research in real exhaust combustion product flows.
• International project Research on formation regularities and properties of multifunctional metal oxide coatings formed by combined laser-plasma methods carried out under the Lithuanian- Belorussian bilateral cooperation programme in the fields of science and technology. The aim of the project is to determine of structure and properties of metal oxide coatings with controlled physical-mechanical and operational characteristics formed by plasma and laser methods.
• National science program Future Energy project ATE02/2012 Research of local fuel thermal decomposition processes by developing efficient and ecological technologies.
• National science program Future Energy project ATE10/2012 Conversion of organic waste in water vapour plasma by reducing environmental pollution.
• In EU support measure Promotion of high international level scientific research project Development of innovative thermal decomposition technology and its application for utilization of waste water sewage (INODUMTECH). A 100 kW power gasification process-technology prototype is to be developed during the project designed to utilize the sewage amounts of wastewater comprised in wastewater treatment enterprises of small Lithuanian towns. The project idea is implemented together with Laboratory of combustion processes, Laboratory of Nuclear Engineering and Laboratory of Heat Equipment Research and Testing.
• Project Dissemination and Fostering of Plasma Based Technological Innovation for Environment in BSR (PlasTEP) of Baltic Sea Region Programme 2007–2013. The main objectives of this project are to develop and use plasma technologies for solving environmental problems.It is also important to develop equivalents that prove the possibility to practically improve air and water quality and to introduce plasma technologies in the field of environmental protection.
Main tasks of the project:
– control and reduction of hazardous material emission;
– application of plasma technologies for the neutralisation of toxic industrial waste;
– reduction of air and water pollution;
– development of environmental technologies clusters in Baltic Sea region;
– promotion of support and investment into novel environmental technologies;
– incorporation of politicians and government representatives into the project activity
– group formation of industrial and scientific partners in the field of environmental protection;
– specialised group formation aiming at reducing NOx and SOx emission, neutralising VOCs compounds) and smells as well as cleaning the water;
– spread of knowledge and environmental technologies in the states of Baltic Sea region.
The personnel of the Laboratory of Plasma Processing consists of 8 scientists with a doctoral degree, 1 young researcher PhD student, 1 junior research assistant and well experienced ancillary personnel: 3 engineers and 2 highly qualified foreman.
Since 2007, the Laboratory has been taking active participation in the activity of Plasma Technology Network of the Baltic countries. Last year the scientific and technical production of the Laboratory was presented in international (13 papers) and national (3 papers) conferences, 6 articles were published in the ISI indexed journals and 2 articles in the worldwide reviewed publications.
Argon plasma jet discharged from constant current linear plasma generator
Arrangement of temperatures in the air plasma jet at speeding 50 mm Al2O3 particle
Composition of argon and water vapour plasma jets discharged from 35 kW plasma generator, identified using spectroscopy method. Water vapour flow G=2 g·s-1
Movement of alloy and granules and mineral splint formation process in supersonic plasma jet, observed by high-speed video camera
Formation of surface layers of construction materials in atmosphere pressure air plasma and examples of prepared products
Catalytic coating (on the left) and its element composition (on the right)
Operating carbon coating synthesis facility generating argon/acetylene plasma
SEM images of carbon coatings derived from argon-hydrogen-acetylene plasma
The impact of dispersed particle on the dropdown of heat flow into the reactor walls D. GD and GO – flows of particles and air
SEM images of zeolite fibre at different plasma flow velocities. 1 – 1600 m/s, 2 – 1500 m/s, 3 – 1200 m/s, 4 – 1000 m/s
Operating water vapour plasma facility designed for decomposition of organic materials
Composition of synthetic gas derived in plasma-chemical reactor at H2O vapour flow 3.51–4.,48×10-3 kg/s, propane flow 0.34×10-3 kg/s
Investigation of behaviour of hardly alloying materials in high temperature zone. On the right – example after the plasma jet impact
Excursion to the Laboratory of Plasma Processing during the open doors day in LEI
Presentation of the results of implemented Future Energy projects at international conference UBIOCHEM-2012
PlasTEP project partners