Size determination of superconducting MgB₂powder from magnetization curve, image analysis and surface area measurements

Abstract

The present article reports a method for the average grain size evaluation of superconducting nanoparticles through their magnetic properties. The use of SQUID magnetometry to determine the average MgBB 2 particle size was investigated and the results compared with those achieved through other techniques. In particular the data obtained from zero field cooled magnetization measurement as function of the temperature were compared with the results obtained by scanning electron microscopy and Brunauer-Emmett-Teller techniques. The particle magnetization was measured by a commercial SQUID magnetometer in magnetic field (1 mT) and temperatures ranging from 5 to 50 K dispersing the powders in a grease medium. The grain size is obtained by fitting the data taking into account the Ginzburg-Landau temperature dependence of the London penetration depth. Variations on typical modeling parameters were explored in order to gain a better picture of the average grain size and the effectiveness of various measurement techniques. We find that it is possible to use the magnetization measurements to determine the average grain size even if the SEM image analysis allows extracting more information about the grain size distribution. Furthermore a Matlab routine has been developed in order to get automatic analysis of SEM images.

Nano-sized boron synthesis process towards the large scale production

“…Statistical analysis on SEM images confirms an average grains size of 80 nm in agreement with analysis of previous paper [15]. The morphological aspect of pure MgB 2 is given in Fig.…”

“…Then, using the standard synthesis procedure [10] the very fine grain size of B (80 nm) has been lost and MgB 2 particles size was increased 10 times in size. The statistical analysis given an average grain size of 600 nm, in good agreement with results reported in [15] both for pure and Si-doped ex-situ powder. Fig.…”

Method for the production of pure and C-doped nanoboron powders tailored for superconductive applications

“…The second column reports the surface area (S) measured by BET. In the next columns are reported the < d > values, calculated by using the formula < d ≥ 6/(ρ * S) and assuming a spherical shape for the B particles [29], in order to have a direct comparison with the SEM image analysis. The third column shows the < d > value taking into account the theoretical density 2.45 g cm −3 .…”

Synthesis Temperature Effects on Ex-Situ Manufactured MgB2 Wires Useful For Power Applications

“…Pellets of the different MgB2 powders were prepared by compression for SEM imaging, in order to investigate grainsize distribution and morphology. Grain size distribution have also been investigated from m(T) measurements on dispersed powders [20]. This is a new method for grain-size evaluation, more accurate respect SEM analysis because it takes in account whole sample and not a statistical count of a small portion of pelletized sample.…”