Dr. Miriana Vadalà
Institut für Materialwissenschaft
University of Duisburg-Essen
- Yttrium oxide freeze-casts: Target materials for radioactive ion beams
Kröll, E. and Vadalà, M. and Schell, J. and Stegemann, S. and Ballof, J. and Rothe, S. and Lupascu, D.C.
Materials 14 (2021)Highly porous yttrium oxide is fabricated as ion beam target material in order to produce radioactive ion beams via the Isotope Separation On Line (ISOL) method. Freeze casting allows the formation of an aligned pore structure in these target materials to improve the isotope release. Aqueous suspensions containing a solid loading of 10, 15, and 20 vol% were solidified with a unidirectional freeze-casting setup. The pore size and pore structure of the yttrium oxide freeze-casts are highly affected by the amount of solid loading. The porosity ranges from 72 to 84% and the crosslinking between the aligned channels increases with increasing solid loading. Thermal aging of the final target materials shows that an operation temperature of 1400◦ C for 96 h has no significant effect on the microstructure. Thermo-mechanical calculation results, based on a FLUKA simulation, are compared to measured compressive strength and forecast the mechanical integrity of the target materials during operation. Even though they were developed for the particular purpose of the production of short-lived radioactive isotopes, the yttria freeze-cast scaffolds can serve multiple other purposes, such as catalyst support frameworks or high-temperature fume filters. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
view abstract 10.3390/ma14112864
- Ice-Templated Poly(vinyl alcohol): Enhanced Strength and Low Thermal Conductivity
Voges, K. and Hübner, C. and Vadalá, M. and Lupascu, D.C.
Macromolecular Materials and Engineering 303 (2018)The freeze-casting technique has been used for a variety of materials to tailor their pore structure. The growing ice crystals act as a template for the subsequent voids present in the body. While it is mostly used for inorganic oxide materials, the method is also applicable to polymers like poly(vinyl alcohol) (PVA). The synthesized materials have an aligned anisotropic pore structure which significantly influences the mechanical behavior and the thermal conductivity. Glutaraldehyde (GA) can be used as a cross-linking agent to reduce the water solubility of the PVA samples. The composition-dependent thermal conductivities are measured, and found to be 0.055–0.078 W m−1 K−1 parallel to the freezing direction and 0.048–0.058 W m−1 K−1 in the transverse direction. The scaffold-like structure resembling the hydroxyapatite structures in bones yields high strength values in the axial direction well exceeding that of common unsupported building insulation materials. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/mame.201800198
- Dense nanopowder composites for thermal insulation
Voges, K. and Vadalá, M. and Lupascu, D.C.
Physica Status Solidi (A) Applications and Materials Science 212 (2015)We show in this paper that composites of mechanical impedance mismatch nanopowders yield competitive thermal insulation values to aerogels. The powders are connected by a polymer matrix assuring mechanical integrity. A simple calculation for the thermal boundary resistance has been conducted based on established models. © 2014 WILEY-VCH Verlag GmbH & Co.
view abstract 10.1002/pssa.201431551
- The effect of annealing on the junction profile of CoFeB/MgO tunnel junctions
He, H. and Zhernenkov, K. and Vadalá, M. and Akdogan, N. and Gorkov, D. and Abrudan, R.M. and Toperverg, B.P. and Zabel, H. and Kubota, H. and Yuasa, S.
Journal of Applied Physics 108 (2010)The tunnelling magnetoresistance of CoFeB/MgO tunnel junctions is exceptionally high, although the electrodes and the barrier are grown at room temperature in the amorphous state. For their functionality annealing steps up to high temperatures are required. We have analyzed in detail the changes in the chemical and magnetization profile upon annealing up to 360°. The multilayers used for this study are similar to those which are used in magnetic tunnel junctions, however with five repeats. In particular, we have used hard non-resonant and soft resonant magnetic x-ray scattering in order to unravel any changes upon annealing. The multilayers exhibit superior structural quality, which hardly changes with annealing. Surprisingly, only little recrystallization of the CoFeB and the MgO layers can be discerned by x-ray diffraction. © 2010 American Institute of Physics.
view abstract 10.1063/1.3483956
synchrotron and neutron radiation