Doping with copper is studied in a series of double perovskite-type GdBa0.5Sr0.5Co2-xCuxO5+δ, candidate oxygen electrode materials for reversible Solid Oxide Cells. Obtained by a sol-gel method, the material with x = 1.15, having the highest amount of the introduced Cu (lowest Co content) is selected, and systematically evaluated regarding physicochemical characteristics, as well as chemical stability with La0.8Sr0.2Ga0.8Mg0.2O3-δ and Ce0.9Gd0.1O2-δ solid electrolytes. Promising electrochemical performance is obtained if this compound is used to manufacture oxygen electrodes, with the recorded low polarization resistance of 0.144 Ω cm2 at 700 °C, and 0.020 Ω cm2 at 850 °C. Also, the anode-supported laboratory cell is found to deliver over 725 mW cm-2 power density at 850 °C, and shows good performance in the electrolyzer mode.
The effect of Cu addition on crystal structure, compressive properties and shape-memory effect of Ni50Mn25Ga25−xCux alloys was studied. With increasing Cu content, the type of crystal structure evolves following a sequence: L21 → 10M → 2M → 2M+γ. Addition of Cu significantly improves room temperature ductility. In polycrystalline Ni50Mn25Ga17Cu8 alloy, a full recoverable strain equal to 7 pct was achieved. High martensitic transformation temperature and large shape-memory effect makes this material potential candidate in high-temperature shape-memory applications.
In this paper, we report on mechanical properties observed during bending experiments conducted on quinary Ni–Mn–Ga–Co–Cu melt-spun ribbons. Depending on the ribbon’s side to which force is applied, different mechanical response is noted. Substantially larger mechanical instabilities are observed when force is applied to the “free side” than to the “wheel side” of ribbons. When force is applied to the latter, much lower force fluctuations are recorded and the amplitude of the force–displacement response remains within the experimental resolution limit. It is also shown that the character of the force–displacement curve changes upon cycling; mainly by decreasing the maximum force and mechanical hysteresis. These results are important for materials design and optimization of the magnetic field-induced bending effect recently shown in Ni–Mn–Ga-based melt-spun ribbons.
Phase transformations over a nanocrystalline iron catalyst in the nitriding process were carried out at 350 °C and under atmospheric pressure. The process was conducted under conditions of changing nitriding potential both during the nitriding and reduction of iron nitrides. These processes were monitored by measuring the magnetic permeability and changes of mass and reaction gas composition. Four stages of nitriding were observed and ascribed to the following general schematic reactions:The measurements of magnetic permeability revealed that the magnetic properties of the investigated samples strongly depended on the nitriding degree and can be described with linear equations of two variables. For γ′-Fe 4 N, the value of magnetic permeability was 1.280 times larger than for the iron catalyst, while for ε-Fe x N, it was more than 3 times smaller. However, in the case of the smallest nanocrystallites both in the process of iron nitriding and reduction of iron nitrides, the magnetic permeability did not change with the nitriding degree. It was also claimed that the composition of iron nitrides, concentrations of nitrogen in iron nitrides, and the magnetic permeability depend on the direction of the reaction (nitriding or reduction). A hysteresis phenomenon was observed.
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