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Comparison of Diffusion Coefficients in Initial Stages of Mutual Diffusion in Layered Structures Carbon/Ferrite and Carbon/Austenite for Chosen Alloys
Čermák, Jiří ; Král, Lubomír
Coefficients of mutual carbon diffusion were measured at initial stages of diffusion for surface thin layer of carbon/ferrite and carbon surface layer/austenite. The aim of the study was to compare the diffusion characteristics obtained at the present strongly non-equilibrium case with those known for carbon mutual diffusion in cases where the carbon concentration does not exceed the solubility limit in the respective substrate. The second goal was to judge, whether the carbon diffusivity is determined by the structure of the substrate matrix (BCC or FCC). As examples of ferrite substrate, pure Fe and chromium steel P91 were chosen, as an example of austenite substrate, AISI316 was taken. It was obtained that – similar to nearequilibrium case – the carbon diffusion measured close to interface C/austenite is significantly lower compared to carbon diffusion near the C/ferrite. Values of carbon diffusion coefficients in cases C/Fe and C/P91 are close one to another. All carbon diffusion coefficients are much lower than those, reported for near-equilibrium conditions; they approach values measured in carbides.
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Analysis of technical indicators on foreign exchange market
Čermák, Jakub ; Musílek, Petr (advisor) ; Veselá, Jitka (referee)
The goal of this diploma work is aplication of technical analysis indicators, especially trend indicators and oscillators. Analysis was made for period of 5 years back on one title from foreign exchange market. Analysis indentifies whether are indicators more profitable than benchmark in the long term. Analysis also examine whether combination of indicators earn more, than indicators themselves.
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Synthesis, structure, and opto-electronic properties of organic dies on diamond
Rezek, Bohuslav ; Čermák, Jan ; Ukraintsev, Egor ; Hubík, Pavel ; Mareš, Jiří J. ; Ledinský, Martin ; Fejfar, Antonín ; Kočka, Jan ; Kromka, Alexander
We prepare a thin-film heterojunction of polypyrrole (Ppy) on hydrogen-terminated diamond by electro-polymerization from solution. We combine advanced scanning techniques (AFM, KFM, micro-Raman) to characterize microscopic structural, chemical, and opto-electronic properties of such system.
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Measurement of Carbon Diffusion Coeficient - Calibration of Sputter Depth
Král, Lubomír ; Čermák, Jiří
Depth profiling mode of MiniSIMS device was applied to diffusion measurement. Calibration of crater depth was done using shearing interference microscope Zeiss Epival Interphako (ZEI) and confocal mikroskope Olympus LEXT OLS3100 with atomic force microscopy (AFM) modul. The ZEI uses one of the classical interferometric measuring methods. Generally this method leads to results with considerable experimental error. AFM is a very high-resolution type of scanning probe microscopy, with typical resolution of the order of fractions of nanometers, which is more than 1000 times better than the optical diffraction limit. However, the results taken by ZEI were in agreement with much more precise results of surface profiling achieved by AFM. It was found, at given experimental conditions (Fe-rich matrix, Ga + primary ions, 5 kV/3nA, DWT=1), that the sputter rate is some 0.3 nm per a single sputter scan of the crater area (50x50 µm). This depth calibration with SIMS technique can be applied to the study of carbon diffusion in BCC iron as an example. Special technique was developed, which avoids radio-tracer measurements with C-14. Obtained results are lower than the extrapolated values, which may be due to limited solubility of carbon in iron.
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Hydrogen Storage Capacity of Mg/Mg2Ni Eutectic Doped with Elements from Groups XIII and XIV
Čermák, Jiří ; Král, Lubomír
In the present paper, the chemical composition of Mg-8.5 at.% Ni-2.7at.%X alloys (X – elements of the 13th and 14th groups) as prospective hydrogen storage was investigated. Experimental alloys were studied in three states: (i) after stabilization anneal, (ii) after stabilization anneal and hydrogen charging, and (iii) after stabilization anneal, hydrogen charging and hydrogen desorption. It was ascertained that a ratio of concentration of X in two principal phases – Mg2NiH4(-X) and MgH2(-X) – was a decreasing function of the ionization potential of X. The stronger the preference of X for Mg2NiH4-X phase, the higher the hydrogen storage capacity of Mg-Ni-X alloy was. For X = In, the hydrogen storage capacity was slightly higher than the capacity of an un-alloyed binary eutectic Mg-Ni alloy.
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Improvement of Hydrogen Desorption Characteristics of Eutectic Mg/Mg2NiH4 and Mg2NiH4 by In addition
Čermák, Jiří ; Král, Lubomír
Mg-xNi alloys are known as perspective hydrogen storage materials [1,2]. Hydrogen storage capacity and hydrogen desorption rate of binary alloys Mg-Ni are, however, still unsatisfactory and therefore, improvements are sought, e.g., by introduction of a proper catalyst [3]. As candidate elements, transition metals [4] are often used that attract bonding valence electrons and, hence, destabilize the hydrides. However, also elements with weaker bond to H than that of Mg, or even non-hydride forming elements show a beneficial effect upon the hydrogen desorption rate [5,6]. The present investigation continues our previous work [7,8]. Here we investigate the resistance of eutectic Mg/Mg2Ni against the poisoning by residual air and possible ways how to improve the hydrogen desorption kinetics of Mg2NiH4 by doping. As dopants, elements of the 13th and the 14th group were tested that do not form stable hydrides.
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