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  • Küçük Resim
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    Formation of high-field pinning centers in superconducting MgB2 wires by using high hot isostatic pressure process
    (Springer, 2017) Gajda, Daniel; Morawski, Andrzej; Zaleski, Andrzej Janusz; Akdoğan, Mustafa; Yetiş, Hakan; Karaboğa, Fırat; Belenli, İbrahim
    This paper demonstrates the effects of hot isostatic pressure (HIP) on the structure and transport critical parameters of in situ MgB2 wires without a barrier. Our results show that only HIP and nano-boron allow the formation of more high-field pinning centers, which lead to the increase in critical current density (J (c)) at high applied magnetic fields. Nano-boron and annealing at a low pressure increase the J (c) in the low magnetic field. This indicates that nano-particles create more high-field pinning centers. In addition, the results show that nano-boron improves the connection between the grains. Scanning electron microscope results show that HIP increases the reaction rate between Mg and B, density, and homogeneity of the MgB2 material. Additionally, HIP allows to create a structure with small grains and voids and eliminates the significance of the number of voids. High isostatic pressure allows to obtain high J (c) of 10 A/mm(2) (at 4.2 K) in 10 T and increases irreversible magnetic field (B (irr)) and upper critical field (B (c2)). Measurements show that these wires have high critical temperature of 37 K.
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    Influence of amorphous boron grain size, high ısostatic pressure, annealing temperature, and filling density of unreacted material on structure, critical parameters, n-value, and engineering critical current density in MgB2 wires
    (MDPI, 2021) Gajda, Daniel; Zaleski, Andrzej Janusz; Morawski, Andrzej; Malecka, Malgorzata; Akdoğan, Mustafa; Karaboğa, Fırat; Avcı, Doğan; Yetiş, Hakan; Belenli, İbrahim
    Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (B-irr), critical temperature (T-c), upper magnetic field (B-c2), engineered critical current density (J(ec)), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on B-irr, T-c, B-c2, J(ec), and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest B-irr, T-c, B-c2, J(ec), and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.
  • Küçük Resim
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    The influence of HIP process on critical parameters of MgB2/Fe wires with big boron grains and without barriers
    (Elsevier Science Sa, 2016) Gajda, Daniel; Morawski, Andrzej; Zaleski, Andrzej Janusz; Akdoğan, Mustafa; Yetiş, Hakan; Karaboğa, Fırat; Belenli, İbrahim
    We show transport results of the critical temperature (T-c), irreversible magnetic field (B-irr), upper critical field (B-c2), critical current density (J(c)) and the pinning force (F-p) for undoped MgB2 wires without barriers. The results of SEM show that the hot isostatic pressure process increases the density and uniformity of MgB2 materials. Hot isostatic pressure allows for obtaining small grains and increasing the number of connections between the grains, accelerated reaction rate and limits the diffusion of Fe atoms into MgB2 material from the adjacent sheath. The pressure of 1.1 GPa increases T-c quite significantly in high magnetic field range of 6-12 T, improves the B-irr and B-c2 and increase the J(c) at 4.2 K and 20 K of about three times. Our results may be important for this field since many MgB2 wires are made from big grains of boron greater than 1 mu m. Moreover, our research can be important for the production of MgB2 wires for the International Thermonuclear Experimental Reactor with boron B-11. (C) 2016 Elsevier B.V. All rights reserved.
  • Küçük Resim
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    The significant influence of packing density of unreacted Mg+2B mixture and heat treatment conditions on some of critical parameters for MgB2/Fe wires
    (Elseiver Science SA, 2021) Gajda, Daniel; Zaleski, Andrzej Janusz; Morawski, Andrzej; Czujko‬, ‪Tomasz; Avcı, Doğan; Karaboğa, Fırat; Akdoğan, Mustafa; Yetiş, Hakan; Belenli, İbrahim
    Our research show that the higher packing density of the unreacted material (Mg +2B) by 8%, especially for Mg in the solid state, allows to eliminate the large number of large voids (20 mu m), improves the homogeneity and density of the MgB2 superconducting material, allows to obtain a greater number and longer lengths of connections between MgB2 grains, eliminates the formation of the intermetallic phase (iron borides), allows to obtain MgB2 grains of a uniform size and shape, increase irreversible magnetic field (Birr), critical temperature (T-c) and upper magnetic field (B-c2). Research show that spherical grains significantly reduce the number of inter-grain connections in the material with low and high density of unreacted material and allows to obtain the more superconducting phase. Research shows that MgB2 grains with a plate-like and rectangular shape allow to obtain more connections between the grains. Studies show that thermal treatment under high iso-static pressure does not allow to obtain the large amount of superconducting phase for the unreacted material of low density. Moreover, studies show that the high packing density of unreacted material and thermal treatment under high isostatic pressures (0.8 GPa and 1.1 GPa) allow to obtain a large amount of superconducting phase even for Mg in the solid state. Additionally, studies points that heat treatment under medium isostatic pressure (0.3 GPa) significantly reduce B-irr and B-c2. Our results are important for long superconducting wires made by using the powder-in-tube (PIT) technique. Because they indicate that the higher packing density of the unreacted material (Mg +2B) will allow to obtain a the superconducting material with greater homogeneity and density, and improve the critical parameters e.g. coils. (C) 2021 Elsevier B.V. All rights reserved.