Mihail Burdusel

Significant enhancement of the critical current density for cubic BN addition into ex situ spark plasma sintered MgB2

High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN) x , x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature Tc = 38.8 K. The variation of the critical current density Jc with the external magnetic field H for h-BN added sample is almost overlapping the Jc(H) dependence for the pristine MgB2 sample. On the other hand, Jc for the samples added with c-BN is larger at high magnetic fields, while the decrease of Jc at low H is very small. At T = 20 K, a Jc of 102 A cm−2 is determined for the sample with xc-BN = 0.005 at H = 58 kOe, and for the sample with xc-BN = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.

Short Review on Rare Earth and Metalloid Oxide Additions to MgB2 as a Candidate Superconducting Material for Medical Applications

MgB2 is a candidate for the fabrication of magnetic coils used in medical applications. Our review indicate that oxide additions based on the rare earth or metalloid elements show improvement of the MgB2 critical current density (Jc) and the irreversible magnetic field (Hirr) without significantly affecting the critical temperature (Tc) However, the characteristics of the additions and the technological approaches show a strong influence in controlling superconducting properties. Both additions and the technology need a careful and complex optimization in order to enhance the Jc and Hirr.

The Influence of Different Additives on MgB 2 Superconductor Obtained by Ex Situ Spark Plasma Sintering: Pinning Force Aspects

Superconducting samples of MgB2 prepared by ex situ spark plasma sintering were characterized by magnetic measurements emphasizing functional characteristics such as the critical current density J c, the irreversibility field H irr or the product J c(0) · µ0 · H irr, and the pinning-force-related parameters extracted within the universal scaling law and the percolation-based theory. Additions introduced into MgB2 were classified as following: approximately chemically inert (type 1: h-BN, c-BN, and graphene), reactive with formation of MyBz (type 2: RE2O3 with RE being a rare earth element such as Ho, La, or Eu) or MguMv (type 3: Sb, Sb2O3, Bi, Bi2O3, Te, TeO2, Ge, and GeO2), and additives which are source of carbon substituting for boron in the crystal lattice of MgB2 (type 4: fullerene (F), F + c-BN, SiC + Te, Ge2H10C6O7, and B4C). Each group of additives show specific features, but within each group there are differences. When considering the influence of the additive of types 1–3, one has to pay attention also to substitutional x-carbon level which shows a strong influence on the functional and on the pinning-force-related parameters. A general trend is that at low x and high temperatures (>~15 K), samples are in the point pinning region and contribution of the grain boundary pinning is increasing when the additive amount is higher and the temperature is lower. There are also exceptions and within the general trend there are notable differences among the samples. From a practical point of view, additives such as c-BN, Te, Ge2H10C6O7, or B4C are shown to increase high magnetic field functional characteristics such as J c and H irr, while suppression of J c at low magnetic fields is minimized.

Reactive spark plasma sintering of MgB2 in nitrogen atmosphere for the enhancement of the high-field critical current density

High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N2) atmosphere for different heating rates (10, 20 and 100 °C min−1) and compared with reference samples processed in vacuum and Ar. N2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N2 with a heating rate of 100 °C min−1. At 2–35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.

Total Elbow Implant - Computer Assisted Design and Simulation

The elbow total implant is in appearance a simple orthopedic device, with few components and no complex mechanisms. In spite of the reported successful surgical interventions, there are still many medical reports which show that a certain percentage of the implants fails.In our work we conceptually approach a computer assisted design of a Coonrad-Morrey like total elbow implant and simulate the mechanical behavior by finite element analysis, for three different loads (10 N, 50 N, and 100 N). Materials used for simulation were Ti, TiNi and Ti6Al4V for the metallic components, and UHMWPE for bushing polymeric components. Through our results we confirmed the practical observations, namely that the hinge mechanism is an important region where the failures initiates from, as the highest stress is concentrated on the polymeric components.