Hossein Alimadadi

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Palaeomagnetic measurements of meteorites suggest that, shortly after the birth of the Solar System, the molten metallic cores of many small planetary bodies convected vigorously and were capable of generating magnetic fields. Convection on these bodies is currently thought to have been thermally driven, implying that magnetic activity would have been short-lived. Here we report a time-series palaeomagnetic record derived from nanomagnetic imaging of the Imilac and Esquel pallasite meteorites, a group of meteorites consisting of centimetre-sized metallic and silicate phases. We find a history of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shutdown of the magnetic field as core solidification completed. We demonstrate that magnetic activity driven by progressive solidification of an inner core is consistent with our measured magnetic field characteristics and cooling rates. Solidification-driven convection was probably common among small body cores, and, in contrast to thermally driven convection, will have led to a relatively late (hundreds of millions of years after accretion), long-lasting, intense and widespread epoch of magnetic activity among these bodies in the early Solar System.

Application of Complementary Techniques for Advanced Characterization of White Etching Cracks

Abstract White etching crack (WEC) networks were characterized in heavy loaded bearings for wind turbines. Both conventional techniques as reflected light microscopy and (scanning and transmission) electron microscopy as well as electron backscatter diffraction and ion channelling contrast imaging were applied. The complementary use of the techniques in unravelling the complicated failure mechanisms is explored in the present work.

Dislocation density and Burgers vector population in fiber-textured Ni thin films determined by high- resolution X-ray line profile analysis

Nanocrystalline Ni thin films have been produced by direct current electrodeposition with different additives and current density in order to obtain 〈100〉, 〈111〉 and 〈211〉 major fiber textures. The dislocation density, the Burgers vector population and the coherently scattering domain size distribution are determined by high-resolution X-ray diffraction line profile analysis. The substructure parameters are correlated with the strength of the films by using the combined Taylor and Hall–Petch relations. The convolutional multiple whole profile method is used to obtain the substructure parameters in the different coexisting texture components. A strong variation of the dislocation density is observed as a function of the deposition conditions.

The complementary use of electron backscatter diffraction and ion channelling imaging for the characterization of nanotwins

On the example of electrodeposited nickel films, it is shown that unique information on twins with dimensions on the nanoscale can be obtained by suitable combination of ion channelling imaging and electron backscatter diffraction analysis, whereas both (routine) single techniques cannot meet the requirements for analysis of these films. High‐resolution electron backscatter diffraction is inadequate for full characterization of nanotwins, but image quality maps obtained from electron backscatter diffraction at least yield a qualitative estimation of the location and number of nanotwins. Complementing this information with ion channelling imaging provides more representative insights into the microstructure, because it supplements the quantitative investigation of the number and width of twin lamellae with additional crystallographic orientation analysis provided by EBSD. To this end, two methods for adjusting EBSD data based on ion channelling images are proposed. Thorough selection of the complementary techniques opens future perspectives for the investigation of other challenging samples with nanoscale features in the microstructure.

Columns formed by multiple twinning in nickel layers—An approach of grain boundary engineering by electrodeposition

Complementary microscopic and diffraction based methods revealed a peculiar microstructure of electrodeposited nickel. For the as-deposited layer, thus, without any additional treatment, multiple twinning yields a high population of Σ3n boundaries, which interrupts the network of normal high angle grain boundaries. A peculiar arrangement of Σ3 boundaries forming five-fold junctions is observed. The resulting microstructure meets the requirements for grain boundary engineering. Twinning induced effects on the crystallographic orientation of grains result in one major texture component being a ⟨210⟩ fiber axis and additional minor orientations originating from first and second generation twins of ⟨210⟩, i.e., ⟨542⟩ and ⟨20 2 1⟩.

Polycaprolactone-templated reduced-graphene oxide liquid crystal nanofibers towards biomedical applications

Here, we report a facile method to generate electrically conductive nanofibers by coating and subsequently chemically reducing graphene oxide (GO) liquid crystals on a polycaprolactone (PCL) mat. Ultra large GO sheets obtained are in favor of charge carrier mobility and oriented morphology of the GO coating. We showed that coating the reduced GO (rGO) not only retains the three-dimensional topography, fiber orientation and size of the template PCL, but also makes it electroconductive. Our preliminary in vitro assessments using mesenchymal stem cells revealed no induced cytotoxicity yet increased cellular metabolism on PCL-templated rGO fibers.

Characterization of aluminum and nickel thermochemical diffusion for synthesis of alkaline water electrolysis electrodes

Many of the renewable energy sources, such as wind and solar, are fluctuating daily and seasonally. Hence, load management is of high importance when such energy sources are used [1]. Using the excess electrical power from renewable energy sources to produce hydrogen via water electrolysis, offers new alternatives for load management without emission of greenhouse gases. Water electrolysis constitutes only 4% of global hydrogen production due to its relatively high price, but the other available hydrogen production processes emit CO2 [2]. The increasing legislations towards reducing the CO2 emission worldwide, encourages further development of water electrolysis technologies [1]. Alkaline water electrolysis is the standard large-scale and the most mature technology of water electrolysis. There is a large interest for improving the electrodes in terms of efficiency, durability and cost. We have developed electrodes of high efficiency, durability and stability, by thermo-chemical diffusion of Al-Ni and selective leaching of aluminum [3]. Various electron and ion microscopic characterizations techniques are applied in this study to elucidate on the mechanism of diffusion, formation of new phases and microstructure evolution to optimize the process of the electrode synthesis.