Materials for fusion applications
- Interaction of materials with plasma, relevant for thermonuclear fusion, is studied in cooperation with the Tokamak department of IPP in the COMPASS tokamak. These studies have focused for example on erosion properties of materials used for tokamak's first wall under variable plasma conditions. Furthermore, other properties, such as thermal shock resistance and effects of long-time exposure, can be simulated using laboratory plasma and high-energetic beams (e.g. photons, ions, electrons,...).
- Technology of plasma spraying is used for fabrication of tungsten-based coatings. For this purpose, water-stabilized and hybrid plasma torches are used. The process of plasma spraying is continually optimized to obtain the highest thermal conductivity of the coatings, their adhesion to the substrate and thermal-shock resistivity. Experiments which aim at modification of coatings microstructure (in-flight oxidation protection, surface remelting, etc.) are carried out in our laboratory as well.
- Other materials for fusion applications are prepared from powders by Spark Plasma Sintering (SPS) technology, which is highly reproducible and allows to combine broad spectrum of powders to tailor materials properties. One of the advantages of SPS is very short sintering time which suppresses grain growth, e.g. while sintering of nanometric tungsten powders. It is also possible to mix ceramic and metallic powders to prepare oxide dispersion-strengthened (ODS) tungsten alloys.
- Main partners: Forschungszentrum Jülich, Max Planck Institute of Plasma Physics (Garching, D), Dutch Institute for Fundamental Energy Research (Eindhoven, NL), Institute of Plasma Physics and Laser Microfusion (Warsaw, Poland), Research Centre Řež a.s. (Řež, CZ)
Fabrication of special coatings (thick & large-area coatings, functionally-graded materials)
- Plasma spraying belongs to thermal spraying methods and is characterized by using a plasma jet (generated by plasma torch) for melting and acceleration of powder feedstock material. At our department, we use the unique technology of water stabilization of plasma. In principle, water wall is created by a water vortex inside the plasma torch and it protects the inner parts of the torch from the plasma (in conventional industrially used plasma torches, inert gas is used for that purpose). Our solution with water stabilization allows us to obtain plasma with extremely high enthalpy while being cost-effective. Water stabilized plasma torches have high deposition rate of powders which makes them exceptional for deposition of thick coatings (several millimeters) and large-area coatings (limiting factor is usually the size of the spray booth) in a rather short time. By changes in the feedstock powders, functionally graded materials (FGMs) and layered composites can be prepared.
- Frequently deposited materials ion our department include: ceramics (Al2O3, TiO2, ZrO2, ZrSiO4, …), metals (steel, pure metals and various alloys based on W, Cu, Ni, Al, …), composites, natural materials (silicates, garnets, basalts, …) and special materials (titanates, carbides, aluminides, selected alloys with eutectic composition, …).
- Main partners: Czech Technical University in Prague, various industrial partners.
- At our department, we prepare nanomaterials using two different approaches; traditional approach is based on sintering of nanometric powders using SPS technology which ensures maintaining of nanometric grain size by very short sintering time. The other approach is based on plasma deposition of amorphous coatings and their subsequent heat-treatment; this patented method creates composite structure of uniformly distributed nanograins embedded in an amorphous matrix.
- Main partner: Faculty of Mathematics and Physics, Charles University in Prague
Mechanical properties and failure analysis of thermal spray coatings
- Microstructure of plasma sprayed (and generally thermally sprayed) coatings is significantly different from the microstructure of bulk materials prepared by conventional methods. The main difference is the presence of high amount of boundaries in the form of micro- and macro-cracks, pores, inter-phase boundaries (e.g. substrate-coating, oxides, …). The aim of research in the field of thermal spray materials is to take the advantage of these micro-structural “defects” to enhance functional properties of the deposited coatings. It has been shown, for example, that a loose structure of ceramic coatings increases their resistance of the coatings to deformation (strain tolerance) and thermal shocks, which is critical for their utilization as thermal barrier coatings in gas turbines and other dynamically-loaded systems.
- We also perform fractographic analysis of thermal spray coatings, i.e. study of initiation and growth of cracks under various conditions of simulated and real-service load. Fractographic analysis of thermal spray coatings is very specific because the fractographic knowledge from conventional materials is not directly transferable. The main reason of this incompatibility is a different interaction of the crack with the surrounding material and the fact that coatings are primarily used as protective barriers under extreme service conditions (e.g. high temperature, variable mechanical load, corrosive environment, abrasion, …). Moreover, in the real service all these factors are usually combined together which makes the fractographic analysis even more complicated.
- Main partners: Czech Technical University in Prague, University West (Sweden), Stony Brook University (USA)
Structure and phase composition
- Description, understanding and possible exploitations of changes in the structure and phase composition after the materials' interaction with plasma are among the key issues addressed at our department. We study the feasibility of various mechanisms for stabilization of phase composition. The processes of oxidation and corrosion are of significant interest as well. The in-flight oxidation and other processes which are underway during particle’s confinement in plasma are studied mainly via spraying into liquid baths (particle quenching).
- Main partner: Fraunhofer IWS (Dresden, Germany)
- Photocatalysis is a surface reaction activated by ultra-violet or visible light, which leads to decomposition of complex molecules, typically organic materials, to simple inorganic substances like water, CO, CO2 and O2. The goal is to remove toxic substances from polluted air or water by a energy-efficient photocatalyst. In this respect, we concentrate on plasma spraying of titanium dioxide doped with Al, N, Fe, Ba, which is a very promising photocatalyst because of its band gap structure. The main benefit of plasma sprayed photocatalytic materials is the potential to deposit them onto large areas and/or complex shapes, together with their large specific surface area.
- Main partner: Institute of Inorganic Chemistry CAS
- Dielectrics polarize in the presence of electrical field and offer the possibility of energy preservation without its alteration. Commonly, they are manufactured by sintering of oxide ceramics and their field of application are dominantly electrical parts such as capacitors, sensors and isolating parts for environments with high current densities, high temperatures or in the presence of chemically aggressive substances.
- We focus on thermal spraying of dielectric materials and test their performance in alternating current, high temperatures and in dependence on their microstructure, phase composition and chemical purity. Thermal spraying by its inherent technological variability broadens the possibilities of dielectrics manufacturing. In several notable cases, there are fundamental differences between structure and behaviour of sintered and thermally sprayed dielectrics, e. g. shifts in temperatures of phase transformations, origination of amorphous phases, and creation of composite or functionally graded materials.
- Analogical approaches are followed for thermally sprayed ferroelectric and piezoelectric materials. In this respect, perovskite materials such as CaTiO3, BaTiO3, MgTiO3, PbTiO3-ZrTiO3 (PZT) or mixture of Al2O3-TiO2 and both synthetic and natural silicates were studied.
- Main partner: Czech Technical University in Prague