Main research areas of the laboratory:
– 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 of experience working in different fields of development, scientific research and application of atmospheric and reduced pressure plasma and are able to 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 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 field 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–emodel 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.
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 a 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.
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. (on the right), the activated and synthesized materials acquire different energies before reaching the treated surface. Necessary conditions for chemical reactions to combine into blocks in both plasma jet and the substratum surface are created. This enables the synthesis of phase Al2O3 coatings with highly developed active surface, which are 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 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 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 fibre from dispersed particles, using air as plasma forming gas and auxiliary (Ar, N2, propane-butane) gas mixtures.
Water vapour plasma technology
In 2009, the earlier research of the Laboratory was renewed applying water vapour plasma for various needs of energy, environmental protection and industry areas. The advantages of water vapour plasma are obvious: its usage does not form toxic nitrogen oxides that are unwanted in some plasma-technologic processes; moreover, 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. Another reason why the material processed in water vapour plasma may receive much more energy in the same time is that its thermal conduction coefficient is much greater than of other gas plasma. The comparison of water vapour and air volume enthalpies shows that they are rather similar. On the whole, in order to compare the properties of water vapour and air plasma, they have to be compared on the basis of equal mass volume rather than mass jets.
Initial research suggested that upon formation of coatings and granules of various materials, water vapour plasma is especially relevant. If some water vapour (even a small amount) is passed into plasma jet, flowing into plasma-chemical reactor, the output and quality of the end product (e.g. mineral fibre) highly improves. This may be explained by the impact of hydrogen, formed via electrolysis, or dissociated OH group of vapour as well as the influence of more active oxygen, nitrogen or hydrogen atoms on dispersal particles of raw material and melt surface, flowing in the reactor. This is especially important for the formation of organic material coatings (e.g. catalytic) for special purposes. Therefore, it is necessary to explore the impact of water vapour plasma parameters on physical and chemical characteristics of the final product and the formation processes of nano-dispersal structures, microgranules and vapour phase. Further research is directed at the proper investigation of the interaction mechanism of water vapour plasma jet with dispersal particles and jet elements.
Laboratory activity in the National Space Programme
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 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.
Projects implemented in the Laboratory
A state subsidy funded work Identification and Assessment of Prevailing Factors Determining the Synthesis of Inorganic Material Oxides Fibre in Plasma Ambient (2009 – 2010) was completed and defended. Its main objective is to reveal the regularities of various processes during plasma and inorganic material oxides melting and their melts conversion into micro- and nano-structural fibre using numerical and experimental methods. Performing the investigation in reactive gas plasma environment of different composition aims at improving the quality and properties of the mineral fibre being formed. During the implementation of the work, the problem of high-temperature fibre formation was examined in worldwide scientific and technical sources and an experimental dynamic gas device with a plasma generator for special purpose was designed and manufactured.
In the experimental equipment of the Laboratory, the process of plasma spray pyrolysis was implemented and its initial consistency patterns were analysed. It was determined that the interaction of plasma flow and dispersal particles takes about 1 ms and the most rapid particle phase change begins at x/d = (3–8) from the outflow of the exhaust nozzle. The mechanism of plasma pyrolysis process was explored and its impact on the formation process of micro- and nano-dispersal particles was determined. A research of heat exchange process in plasma generator and plasma-chemical reactor during the formation of fibre was carried out. Applying numerical and experimental methods, the dynamic and thermal characteristics of multiphase jet, flowing from the reactor nozzle, and the level of plasma non-equilibrium were determined. The plasma jet emission spectra, providing information about the element composition of plasma flow, were obtained using the optical spectroscopy method. A thin (up to 5 µm diameter) ceramic fiber, which can be used as insulation in thermal equipment, as building material for reinforcing concrete or as a filter for precipitation of ultra-small particles, was produced
In 2011 the researchers of the Laboratory participated in the following international programmes and projects:
– 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.
– Research on carbon nano-derivatives synthesized from non-saturated hydrocarbon plasma No.MIP-59/2010 funded by Research Council of Lithuania and prepared by under the initiative of the researchers. Period of implementation (2010 – 2012). Implemented in cooperation with KTU.
– International project Research on formation regularities and properties of multifunctional metal oxide coatings formed by combined laser-plasma methods carried out under the Lithuanian- Belarus 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.
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 issues. 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 the Baltic Sea region.
PlasTEP project partners
In 2011 two new applications were submitted to the invitation of the National Research Programme Future Energy (2012 – 2014). An application was also submitted for the project of MITA renewable energy programme. An application for EUREKA project Development of water vapour plasma equipment for fuel conversion and treatment of hazardous waste is under preparation. Finally, the Laboratory is also going to prepare an application for the Lithuanian-Swiss research programme.
The personnel of the Laboratory of Plasma Processing consists of 7 scientists with a doctoral degree, 2 young researchers PhD students, 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 (10 papers) and national (4 papers) conferences, 7 articles were published in the ISI indexed journals and 14 articles in the worldwide reviewed publications.