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Design of nuclear ceramic materials with enhanced thermal conductivity
Roleček, Jakub ; Katovský, Karel (referee) ; Salamon, David (advisor)
Oxid uraničitý (UO2) je v současnosti nejčastěji používaným materiálem jakožto palivo v komerčních jaderných reaktorech. Největší nevýhodou UO2 je jeho velmi nízká tepelná vodivost, a protože se při štěpení UO2 v jaderném reaktoru vytváří velké množství tepla, vzniká v UO2 peletě velký teplotní gradient. Tento teplotní gradient způsobuje vznik velkého tepelného napětí uvnitř pelety, což následně vede k tvorbě trhlin. Tyto trhliny napomáhají k šíření štěpných plynů při vysoké míře vyhoření paliva. Tvorba trhlin a zvýšený vývin štěpného plynu posléze vede ke značnému snížení odolnosti jaderného paliva. Tato práce se zabývá problematikou zvyšování tepelné vodivosti jaderného paliva na modelu materiálu (CeO2). V této práci jsou studovány podobnosti chování CeO2 a UO2 při konvenčním slinováním a při „spark plasma sintering.“ Způsob jak zvýšit tepelnou vodivost použitý v této práci je včlenění vysoce tepelně vodivého materiálu, karbidu křemíku (SiC), do struktury CeO2 pelet. Od karbidu křemíku je očekáváno, že zvýší tok tepla z jádra pelety, a tím zvýší tepelnou vodivost CeO2. V této práci je také porovnávána podobnost chování SiC v CeO2 matrici s chováním SiC v UO2, které bylo popsáno v literatuře.
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THERMAL AND MECHANICAL PROPERTIES OF TUNGSTEN COMPACTS PREPARED BY SPS
Nevrlá, Barbara ; Vilémová, Monika ; Matějíček, Jiří
Tungsten is a promising candidate material for use in the tokamak device aimed at future production of nuclear fusion power. Here, tungsten is intended for the application in the part called first wall,with the function of a heat-resistant plasma facing armor.In the present work,two fractions of tungsten powder (2 and 4 μm) were used to prepare two consolidated samples by spark plasma sintering (SPS),using a combination of pressure,temperature and electric power.This sintering technique produces samples of near theoretical density which is positive for the application.Tungsten compacts were then studied to determine some basic thermal and mechanical properties, namely thermal conductivity using the laser-flash method and hardness by Vickers test.The measurements were focused on thermal conductivity of the compacts because high thermal conductivity is crucial for the material of tokamak first wall,loaded by high heat flux from the plasma.High hardness is desirable for good resistance
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Silicon carbide for chemical application prepared by SPS method
Brožek, Vlastimil ; Kubatík, Tomáš František ; Vilémová, Monika ; Mušálek, Radek ; Mastný, L.
Silicon carbide discovered more than 121 years ago has a wide usage in the mechanical engineering industry as well as in electrical engineering.It is an excellent abrasive medium as well as a construction material with high resistance to mechanical and chemical deterioration.Under standard condition, silicon carbide has no melting point (decomposes at 2700 °C – principle used for industrial production of silicon),thus the bulk form must be prepared in a composite form with a metallic, ceramic or polymer binder. This method is suitable for tailoring of mechanical properties; nevertheless,it does not produce SiC form applicable for laboratory purposes.Binder-free sintering of SiC is practically impossible, despite decreased chemical resistivity of the produced material. Pure SiC is insoluble in all acids except hydrofluoric acid.Reaction of SiC with HF is enabled only due to residual SiO2 created during the industrial production.However, SiO2 located between the planes of growth of SiC
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Composites of titanium carbide with scandium matrix
Brožek, Vlastimil ; Pala, Zdeněk ; Vilémová, Monika ; Kubatík, Tomáš František ; Mušálek, Radek ; Nevrlá, Barbara ; Mastný, L.
First reference about existence of ultrahard composite in the TiC-ScCx system was made by G.V. Samsonov in the year 1962. Further research performed on ICT Prague and University of Vienna proved a discrepancy in the structure and stoichiometry of scandium carbide. Analogously to cubic carbides and nitrides of 3rd period metals, Scandium was also expected to have extreme hardness, high chemical stability and to enable solid solution formation (Vegard rule) with controlled regulation of physical parameters. Higher hardness of the cubic carbides is related to the decrease of lattice parameter, thus is was expected that smaller atomic radius of Sc in TixSc1-xC solid solution will lead to increase in hardness. However it was discovered that scandium carbide differs chemically as well as structurally, e.g. Sc15C19 is hydrolyzed and the product of the reaction is hydrogen, allylen and other hydrocarbons. Due to high price of Sc compounds, CVD and PVD layers of TiAlN or TiScAlN on sintered
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Preparation of multiphase materials with spark plasma sintering
Mušálek, Radek ; Dlabáček, Zdeněk ; Vilémová, Monika ; Pala, Zdeněk ; Matějíček, Jiří ; Chráska, Tomáš
Spark plasma sintering (SPS), also called Field Assisted Sintering Technique (FAST), represents a novel method of preparation of sintered materials from powders. The main advantage of the SPS method is a high achievable heat rate (>200 °C/min) and high sintering temperatures (up to 2200 °C in our laboratory). Combination of high heating rate, rather high pressures (up to 80 MPa) and electric field fluctuations leads to an effective sintering and significant reduction of sintering time for both coarse-grained and nanocrystalline powders. Composite materials may be easily obtained by mixing or layering of different powders. The paper will introduce several examples of multiphase materials sintered by SPS at our institute and the establishment of procedures for routine testing of sub-sized specimens.
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Application of SPS technology for preparation of high-tech materials
Mušálek, Radek
Spark Plasma Sintering (SPS) is a modern technology, which allows sintering of powder materials in the variable electric field (also FAST technology – Field Assisted Sintering Technique). Heating rate in the range of hundreds °C/minute, high pressure and sintering temperature (more than 2000 °C) enables for example sintering of materials with high melting point or nanometric powders without growth of grain size in the sintered body.
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