Aleš Hendrych

Size distributions of nanoparticles from magnetotactic bacteria as signatures of biologically controlled mineralization

Abstract This paper addresses the problem of magnetite nanoparticle size distributions in magnetotactic bacteria. The methods described in the paper can be used to determine the origin of natural magnetite nanoparticle samples. We analyzed 36 histograms related to bacterial, inorganic, and biomimetic nanoparticle sizes. Using statistical software we concluded that the size of the nanoparticles in cultured magnetotactic bacteria follows an extreme value distribution. Magnetite in uncultured samples can be treated as a two-component mixture containing extreme value and/or log-normally distributed nanoparticles. Analysis of the time-dependent formation of bacterial magnetite revealed that the magnetite size distribution transforms from the initial log-normal (young bacterial culture) through normal-like toward the extreme value distribution (evolved culture). It seems that at a certain moment during bacterial magnetite formation, the bacterial system starts to behave as a closed system. The closing of the system must be followed by another unknown process, because restriction of the nutrient supply into magnetosomes is insufficient for the generation of the extreme value distribution. Based on our analysis, approximately 50% of the magnetite particles in the martian meteorite ALH 84001 follow an extreme value distribution

Influence of Magnetostriction on Cross-Sectional Magnetic Properties in Bilayered Ribbons

This paper is devoted to the surface and cross-sectional microstructural and magneto-optical investigations of the bilayered (BL) CoFeCrSiB-based ribbon of dissimilar Co/Fe content in the layers and to the comparison with the CoSiB/FeSiB ribbon, both prepared by planar flow casting. It is shown that the interface properties are strongly influenced by chemical compositions of the layers and mainly by the magnetostriction coefficients. This results in different magnetic domain patterns in the layers and across the interlayer and their changes with applied magnetic field intensity. While in the BL sample of a similar layer composition, the magnetic domains concentrate inside the layers, at the sample with completely different layer composition, the domains cross the interlayer.

Stress-Strain Behaviour Simulation of Vanadium Microalloyed Steel with the Internal Defects During two Different Heating Strategies

This paper is focused on the explanation of a linkage between two different heating strategies and a grow of the internal casting defects, that are already present in continuously cast blooms made from vanadium micro-alloyed Cr-Mo steel. Internal defects initiation and propagation can be associated to unsuitable casting and heating conditions. Small casting voids surrounded by ferrite-bainite network enriched by carbides forming elements produce perfect conditions for crack grow during the bloom straightening, heating in the soaking pit and/or heat treatment. Moreover, we simulated the stress-strain behaviour of continuously cast round bloom during heating in soaking pit using the FEM software. It is shown that optimized heating strategy led to significantly lower rates of the plastic strain as a crucial value for the crack propagation.

Magnetic Domain Patterns in Bilayered Ribbons Studied by Magnetic Force Microscopy and Magneto-Optical Kerr Microscopy

The magnetic domain patterns of amorphous bilayered FeSiB/FeNbSiB and FeNbCuSiB/CoSiB ribbons are observed and analysed using the magneto-optical Kerr microscopy (MOKM) and magnetic force microscopy (MFM). Both microscopic techniques are highly sensitive to the sample surface; possibility of Kerr microscopy to visualize the domains separately in both layers is achieved by focusing the laser spot on the ribbon cross section. Wide curved domains as well as fine fingerprint domains were detected at the surface of ribbons due to presence of local stresses coming from the preparation process. With respect to high lateral resolution of MFM and its out-of-plane magnetization sensitivity, the perpendicularly magnetized crossed stripe domain patterns can be selected as well. Coiling of the ribbons on the half-round-end sample holder is often used to induce and control the magnetic anisotropy of these alloys. Changes in the magnetic domain structure at the outer-coiled surface and its dependence on the sign of magnetostriction coefficient are discussed in detail. Finally, the MFM images in the presence of external in-plane magnetic field up to ±40 kA/m are shown.

Low-cost method of the highly porous iron sintering

This paper reports a study of low-cost method relating to the preparation of well defined porous iron-based materials. We employed the technique where the impressed iron oxide powder is sintered. We changed the specific volume fraction of sodium chloride as a primary pore forming additive to achieve the total porosity up to 70 % and effective/total porosity rate in a ratio of 0.89 with interconnected pores. The investigations of physical properties with respect to the particle size distribution, powder morphology, density, volume contraction and both effective and total porosity were carried out by laser diffraction (LD), pycnometric measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy. Porous iron sintered electrodes represent a suitable alternative to the expensive nickel electrodes. K e y w o r d s: iron, sodium chloride, sintering, porosity, surface topography