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Ceramo-metallic materials of the Ti-B-C and Ti-B-N systems
Brožek, V. ; Doležal, J. ; Novák, M. ; Ctibor, Pavel ; Kolman, Blahoslav Jan
Products prepared by the sintering of titanium and boron carbide powder and by the sintering of titanium and boron nitride powder were studied. The sintering was performed at 2,000 °C under the pressure of 6 GPa in a high-pressure apparatus of BELT-type with sufficient holding time to reach thermodynamic equilibrium. The results of chemical and phase composition analyses were compared with thermodynamic prediction of possible reactions in the system. We proved the preferential formation of borides TiB and TiB2 prior to the carbides or nitrides formation. The products, which may be considered Ti-(TiB,TiB2)-TiN or Ti-(TiB,TiB2)-TiC cermets, were analysed in order to determine their microstructure, phase and chemical composition and their influence on mechanical properties such as hardness or elastic modulus. This work precedes similar study which will be performed using the same powders processed by plasma spraying, which enables to stabilize high-temperature phases by rapid cooling.
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Catalysis of Hydrogen De-sorption from MgH2
Čermák, Jiří ; David, Bohumil
Hydrogen is considered to be clean fuel for various energy sources in the near future. One of technical problems in this area is its effective storage. MgH2 is very perspective material whose main advantage is high hydrogen storage capacity (theoretically 7.6 wt. % H2). However, there are negative features of this material as a hydrogen storage medium: before all, it is its poor hydrogen de-sorption kinetics. Therefore, much effort has been devoted in the past to find out possible ways how to enhance the MgH2 de-sorption rate and how to shift this material close to technical applications. It is known that nickel and Mg2Ni enhance hydrogen de-sorption from MgH2. This paper continues our previous works on hydrogen de-sorption from Mg-Ni –based materials. It is devoted to the investigation of separate catalytic effect of Mg2NiH4 and Mg2Ni upon the hydrogen de-sorption from the principal component of the material - MgH2. It was found that catalytic efficiency of Mg2NiH4 is much higher than that of Mg2Ni.
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Corrosion of Nickel Exposed to LiF-NaF Molten Salt
Král, Lubomír ; Čermák, Jiří ; Matal, O. ; Šimo, T. ; Nesvadba, L.
This work is devoted to study of changes of structure and chemical composition in corrosion areas of the chosen candidate alloy, Nickel 201, for components of a LS-VHTR. The material was annealed at 1013K/10h/vacuum and at 1000°C/24h/Ar before corrosion tests. The annealed material was studied after its exposure to the molten mixture of 60 mol. % LiF + 40 mol. % NaF at the temperature of 1013K. The exposition was carried out in a quasidynamic regime, which simulates real circulation of the coolant (a mixture of molten salts) in the piping. The structure of the alloy was studied by SEM. Severe corrosion damage was observed in grain boundaries.
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