Erdem, Özge

In this paper, the advantages and disadvantages of using B powder and C encapsulated B powder as a precursor during the production process of MgB2 with the addition of pyrene (C16H10) were investigated. Two MgB2 bulk samples with the addition of 10 wt % C16H10 of 1 g MgB2 were produced by the in-situ method using B powder and C encapsulated B powder. The C encapsulated B powder as a precursor was prepared by adding 10% C16H10 as a C source. From XRD and SEM analysis, a greater increase in MgO phase and a greater decrease in a-lattice parameter were observed for the sample produced with B, compared to the sample produced with C encapsulated B. The curves of critical current density (Jc) at 5 K showed a similar character for both samples. The Jc values at 5 K in self field were respectively obtained as 1.52 × 105 A/cm2 and 1.90 × 105 A/cm2 for the samples produced by B and C encapsulated B. The decrement ratio of in-field Jc at 20 K was less affected by increasing magnetic field for the sample produced using C encapsulated B due to the relatively higher increase in the irreversibility field (Hirr) and the upper critical magnetic field (Hc2) values. The Jc values at 20 K and 3 T were respectively determined as 1.49 × 104 A/cm2 and 1.93 × 104 A/cm2 for the samples produced with B and C encapsulated B.

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Erdem, Özge

The effect of ball milling on the microstructure and some superconducting parameters such as flux pinning force (Fp) and critical current density (Jc) of the oleic acid (C18H34O2) added MgB2 bulk samples produced by two different methods, was analysed in this article. In the first method, ball milling was applied to the samples produced by using boron (B) powders coated with carbon (C) released from oleic acid. In the second method, oleic acid was mixed with magnesium (Mg) and B powders at the same time and then the same ball milling process used in the first method was applied to the powder mixture. The structural, magnetic and electrical properties of the produced samples were analysed. The results showed that ball milling process enhances the homogeneity of the structure, decreases the grain size and improves the grain connectivity of MgB2. Also, C substitution into MgB2 lattice resulting in an increase in electron scattering and disorders, enhances after ball milling process. It supplies a significant increase in Jc at high fields and causes a slightly decrease in transition temperature (Tc), especially for the samples produced by using the first method. Because the first method supports the ball milling effect on the homogenous dispersion of oleic acid addition in the MgB2 structure and the C entrance to MgB2 lattice, acting as pinning centres, the best Jc and Fp values at high fields was obtained for the produced samples with second method.

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