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The Changes in Structure of Steel P91 after Short Annealings
Král, Lubomír ; Čermák, Jiří ; Král, Petr
Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423 °C for 20h and water cooled. After tempering at 673 °C for 2 h, the formation mainly M3C type carbides and after tempering at 873 °C for 2 h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion.
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New Characterisation Approaches for Carbon Ionic Liquid Electrodes (CILES)
Mikysek, T. ; Stočes, M. ; Švancara, I. ; Vytřas, K. ; Ludvík, Jiří
Within this study, some new approaches to characterize the carbon paste mixtures and the respective carbon ionic liquid electrodes (CILEs) are presented and their properties discussed. Particular attention has been paid to the changes of the resistivity, relative to the dependence on composition of the CILE. Three types of carbon ionic liquid pastes were examined, and for the interpretation of experimental data, the results were compared with those of "classic" carbon paste electrode (CPE) based on graphite powder. Some problems connected with homogeneity and stability of carbon pastes are also discussed.
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CARBON DIFFUSION IN CARBON-SUPERSATURATED 9CR-1MO STEEL: ANOMALOUS TEMPERATURE DEPENDENCE OF CARBON DIFFUSIVITY
Čermák, Jiří ; Král, Lubomír
Carbon diffusion was studied in temperature interval 573 - 1073 K in carbon-supersaturated surface layer of 9Cr–1Mo steel P91 and in model Fe-15Cr binary alloy. Extremely low carbon diffusion coefficient D (by 3 orders of magnitude lower than the value D eq in material with equilibrium carbon concentration) was observed in carburized surface region of Fe-15Cr. Similar results were obtained for P91 above the temperature T n ~ 800 K. However, below T n , the values of D measured in P91 increased and approached the value of D eq . It seems that the non-Arrhenius behaviour of P91 steel around T n may be ascribed to the α → α + α’ phase decomposition. Possible effect of nitrogen upon the low-temperature increase in D in P91 steel was excluded.
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Society-wide importance of forest from the carbon sequestration point of view
Pokorný, Radek
Global Climate Change (GCC) has been evoked by anthropogenically elevated CO2 concentration in the atmosphere. The final developmental stadium of the most of terrestrial ecosystems is a forest which consists of long-living plants with ability to capture and sequester atmospheric carbon into plant biomass and soil. Therefore, there are two main possibilities how to mitigate GCC impact on biosphere: i) land-use change to advance ecosystems with high ability and capacity to absorb CO2 from air, and ii) change of the management of existing ecosystems. Forests have high societ-wide importance under the above mentioned context.
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Initial Stage of Mutual Diffusion of Carbide in Iron
Čermák, Jiří ; Král, Lubomír
Initial stage of mutual diffusion close to carbon/iron interface was investigated in the present work. SIMS technique of concentration profiles enabled to study the carbon redistribution in the very early stages, when the diffusion process occurs – at least partly – in regions, where the carbon concentration exceeds the carbon concentration limit. It was observed that carbon diffusion coefficients are much lower under such conditions, than in Fe matrix with equilibrium carbon concentration. The measured carbon diffusion coefficients approached values reported for carbon diffusion in carbides.
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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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Why we identify term ?humus? with ?soil organic matter? in pedology, if it directs us to wrong deductios?
DVOŘÁK, Miroslav
To this day are terminological inaccuracies in subject publications, which direct us to wrong deductions. Therefore I devote oneself to literature search about soil organic matter, in my theses. Separately is split primary organic matter, levels of it´s lability and stable humus. I clarify the term stability and the difference in humus and primary soil organic matter. In this theses were effected analyses acid cambi soil in region Czech Budejovice and acid cambi soil in range of Bohemian Forest ? Kubova Huť. Was quantificated content HK, FK, Cox, humification degree SH, mineralized carbon Cminer, speed constant of biochemical oxidation C, fraction of labile organic substance Ccws, Chws, a CPM. I had compared this data with data, which we keep at one´s disposal from analyses effected twelve years ago. By comparing the real quality of humus in samples A (Kubova Huť) and B (České Budějovice) it stands to reason, that the B sample is superior in quality than sample A. Practice and media very often consider as ?humus? total content of Cox. If this thought should be the true, I would have to consider sample A (with content 9,3% Cox) as a soil with high level of humus and I would expect record returns in it. This conclusion would be real absurd. We can not talk about humus according to Cox content only. It is also necessary to take the primary claims (that the content Chws is an indicator of soil fertility) of some big men in field of pedology (for example Haynes) with a grain of salt. This applies only if soil micro ? edaphon is not decimated somehow. I came to the conclusions, that the final result of the analyses, effected by my thesis supervisor (Kolář) twelve years ago, on practically identical soil samples, are almost exactly the same with my results.
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Kinetics and temperature dependance of cellulose degrading enzymes in the Arctic soils
VAZAČ, Jan
Kinetics and temperature dependance of ?-glucosidase and cellobiosidase was investigated in Arctic soil. These enzymes are key in cellulose degradation, while ?-glucosidase produces the final product of cellulose degradation, the glucose, which si readily available to soil microbes and can influence the CO2 production. The enzymes activities was measured using fluorogenic substrates.
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