Mg B 2 bulk formation by Magnesium Infiltration

Mg. B 2 bulk formation by Magnesium Infiltration in Boron G. Giunchi(a), G. Ripamonti(a), E. Perini(a), T. Cavallin(b), E. Bassani(b) EDISON Sp. A, Divisione R&D , Foro Buonaparte 31, 20121 Milano (Italy) b CNR-IENI Sezione di Lecco, Corso Promessi Sposi 29, 23100 Lecco (Italy) a International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 1

Outline Ø Mg. B 2 by Reactive Liquid Infiltration (RLI): a new sintering route Ø Superconductor phase microstructure Ø Bulk preparation process : several key parameters Ø Mechanical properties Ø Superconducting properties Ø Comparison with other HTS bulks Ø Future applications Ø Conclusions International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 2

Reactive Liquid Infiltration (RLI) process International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 3

Reactive Liquid Infiltration (RLI) (EDISON Spa, Italy - Pending patents) “In situ” process : NO external pressure Mg metal, in block form, and B powders (either crystal. or amorphous) are inserted in a SS container and sealed After reaction : The B space results completely occupied by the Mg. B 2 and the Mg space remains almost free of products High density (~2. 4 g/cm 3) Mg. B 2 and near net shape manufacts Moderate thermal treatments: (800÷ 900 °C x 0. 5÷ 3 h) The liquid infiltration proceeds several cm in deepness and is almost gravity independent The morphology of the product is related to the grain size of the B powders International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 4

Driving forces for the RLI process Ø Volume reduction (molar): Mg + 2 B (23. 2 cm 3) Mg. B 2 (17. 5 cm 3) Ø Mg diffusivity in B species : Mg atoms enters in the b-rhombohedral structure of boron (A boron-rich magnesium boride phase, Mg 2 B 25, has been identified as residual impurity phase and structurally resolved by X-ray diffraction) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 5

Mg. B 2 Bulk International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 6

Morphologies of bulk Mg. B 2 obtained by RLI Microcryst. B : “S” grains Cryst. B (<40 mm): “M” grains Cryst. B (<100 mm) : “L” grains Cryst. B(<180 mm) : “XL” grains International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 7

XRD of Mg. B 2 materials by RLI from crystalline B Mg 2 B 25 / Mg. B 2 = K * (S 2/S 12. 5 )m Mg / Mg. B 2 = L*(S 2/S 0 )n with K = 4. 152 , m = - 1. 626 with L = 2. 47, n = - 1. 923 G. Giunchi, C. Orecchia, L. Malpezzi, N. Masciocchi, Physica C 433, 182 (2006) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 8

The internal grain structure A composite structure made by 3 crystalline phases: Mg. B 2, Mg 2 B 25, Mg Typical composition (at%) Mg. B 2 Mg 2 B 25 Mg Grain Interior : 60÷ 70 30÷ 40 - Channels: 95÷ 99 1÷ 5 - Intergrains: 98÷ 99 - 1÷ 2 International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 9

AFM analysis inside a crystalline Mg. B 2 grain Contact mode picture Friction mode picture International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 10

Mg 2 B 25: disposition of the Mg atoms b-rhombohedral Boron Mg 2 B 25 B 4(83%) - Mg(F)(17%) substitution b d(Mg-Mg) > 4 Å ) a ) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 11

Calibration of the fluorescence microanalysis (B/Mg)at = a * (B/Mg)XRF b a = 16. 903 International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy ; b = 0. 5 October 10, 2006 G. Giunchi - 12

Mg. B 2 by micron size B grains Sites 1 2 3 4 5 6 7 (B/Mg)FRX 0. 019 0. 13 0. 014 0. 109 0. 015 0. 02 0. 009 Mg 2 B 25 mol% 1. 6 24. 2 - 20. 6 0. 33 1. 9 - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 13

Infiltration features at lower temperatures Mainly b- Rhombohedral boron Stainless Steel B Mg upper level T = 710°C Modified boron (mainly Mg 2 B 25) time = 10’ Mg International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 14

Mg. B 2 rod, made by RLI a) Stainless steel container for Mg and B reactants b) b) Resulting Mg. B 2 bars , cut from the cylinder International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 15

The Reactive Liquid infiltration technique Ø Maximize internal pressure on the Boron Steel Mg Boron Ø Manage the container expansion( about 3% linear) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 16

Infiltration of micron size B powders Macro porous sample obtained by mixing B powders and Mg chips Two layer disposition of B powder to promote difficult Mg infiltration International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 17

Technology to produce large Mg. B 2 bulk objects Mg. B 2 International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 18

Bulk Mg. B 2 typical manufacts made by RLI International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 19

Bulk Mg. B 2 manufacts obtained by RLI International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 20

Mechanical behaviour of bulk Mg. B 2 by RLI E= 167 GPa C B A B 33 20 KIC (MPa m 1/2) 4. 8 6. 9 C 8 13. 8 Vickers Hardness (GPa) A International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 21

Mg. B 2 bulk superconducting properties International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 22

Mg. B 2 Bulk : magneto-optical analysis The magnetic field is completely excluded, even in presence of the sample granularity optical image (50 x) SEM image magneto-optical image Zero field cooling and observation at B=0. 12 T , at 11 K (Gozzelino et. , PHIL. MAG. B, 82 , 1 -11 JAN 2002) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 23

Mg. B 2 Bulk magneto-optical observation the trapped magnetic field magneto-optical image trapped field distribution induced currents (50 x) Zero Field Cooling , observations at B=0 and T=35 K, after application of a field B=13. 5 m. T (Gozzelino et. , PHIL. MAG. B, 82 , 1 -11 JAN 2002) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 24

Superconductive properties of bulk Mg. B 2 by RLI AC susceptibility DC resistivity Micro Grains + Si. C(10%) Large Grains Micro. Grains RF Surface resistance Magnetization loop Large Grains Medium Grains Micro Grains International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 25

Thermal stability of the bulk Mg. B 2 Limitation on the thickness m 0 Jc 2 L 2 < 12 g C (Tc-T) G. Giunchi, Adv. Cryo. Eng. Trans. of ICMC, vol 52 813 -819 (2006) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 26

Hirr, Hc 2 evaluation from resistivity measurements = Perspective applicative area for undoped materials International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 27

Critical current density vs Magnetic field Bulk Mg. B 2 : Micro Grains size dependence International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 28

Microwave Resonant Cavity Resonant Mode TE 011 at 9755 MHz Q 180. 000 at 4, 2 K 120. 000 at 25 K A. Agliolo Gallito, M. Li Vigni, Y. A. Nefyodov, G. Giunchi (2006) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 29

Differences of bulk Mg. B 2 with respect to MT-YBCO Mg. B 2 has: Ø Ø Ø Ø Ø Lower density Higher mechanical strength Wider range of normal state resistivity No grain boundaries effects More isotropic superconducting properties Adjustable thermal conductivity Larger dimensions of manufacts and lower manufaturing costs Lower Tc Lower flux pinning strength Lower thermal stability at low temperatures International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 30

Bulk Mg. B 2 applications up to 30 K Magnetic shielding Permanent magnet (space application, measurement systems) (levitation systems, bearings, magnetic separation) Current Leads (for superconducting magnets, switches) ? Fault current Limiters (inductive cylinders, resistive meander like or helical stripline) RF devices (cavity filters, antennas) Electrical motors (rotor for reluctance motor, linear syncronous motor) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 31

Conclusions Ø The bulk Mg. B 2, produced by RLI, is a high density superconducting material with good critical current density, in spite of the composite morphology Ø The transport and magnetic superconducting properties are suitable for Ø high power applications, like current leads, magnetic shielding systems, magnets for power applications (motors, FCL, magnetic separation, bearings, RF cavity filters) The Mg. B 2 is almost ready for applications at intermediate temperatures (20 – 30 K), if an economical and reliable cooling system is available Ø The high potentiality of the Mg. B 2 is based on the low prospectic cost of the raw materials and of the manufacturing process for large pieces, compared with the other HTc bulk superconductors International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy October 10, 2006 G. Giunchi - 32