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MgB 2 bulk formation by Magnesium Infiltration in Boron

MgB 2 bulk formation by Magnesium Infiltration in Boron G.Giunchi( a ),G.Ripamonti( a ),E.Perini( a ), T.Cavallin( b ),E.Bassani( b ) a EDISON SpA, Divisione R&D , Foro Buonaparte 31, 20121 Milano (Italy) b CNR-IENI Sezione di Lecco, Corso Promessi Sposi 29, 23100 Lecco (Italy). Outline.

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MgB 2 bulk formation by Magnesium Infiltration in Boron

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  1. MgB2 bulk formation by Magnesium Infiltration in Boron G.Giunchi(a),G.Ripamonti(a),E.Perini(a), T.Cavallin(b),E.Bassani(b) aEDISON SpA, Divisione R&D , Foro Buonaparte 31, 20121 Milano (Italy) b CNR-IENI Sezione di Lecco, Corso Promessi Sposi 29, 23100 Lecco (Italy) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  2. Outline • MgB2 by Reactive Liquid Infiltration (RLI): a new sintering route • Superconductor phase microstructure • Bulk preparation process : several key parameters • Mechanical properties • Superconducting properties • Comparison with other HTS bulks • Future applications • Conclusions International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  3. Reactive Liquid Infiltration (RLI) process International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  4. Reactive Liquid Infiltration (RLI) (EDISON Spa,Italy - Pending patents) “In situ” process : After reaction : The B space results completely occupied by the MgB2 and the Mg space remains almost free of products NO external pressure Mg metal, in block form, and B powders (either crystal. or amorphous) are inserted in a SS container and sealed High density (~2.4 g/cm3) MgB2 and near net shape manufacts Moderate thermal treatments: (800÷900 °C x 0.5÷3 h) The morphology of the product is related to the grain size of the B powders The liquid infiltration proceeds several cm in deepness and is almost gravity independent International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  5. Volume reduction (molar): Mg + 2 B (23.2 cm3)MgB2(17.5 cm3) Driving forces for the RLI process • Mg diffusivity in B species : Mg atoms enters in the b-rhombohedral structure of boron (A boron-rich magnesium boride phase, Mg2 B25, 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

  6. MgB2 Bulk International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  7. Morphologies of bulk MgB2 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

  8. XRD of MgB2 materials by RLI from crystalline B Mg2B25 / MgB2 = K * (S2/S12.5 )m with K = 4.152 , m = - 1.626 Mg / MgB2 = L*(S2/S0 )n with L = 2.47, n = - 1.923 G.Giunchi, C. Orecchia, L.Malpezzi, N. Masciocchi, Physica C433, 182 (2006) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  9. The internal grain structure MgB2, Mg2B25, Mg A composite structure made by 3 crystalline phases: Typical composition (at%) MgB2 Mg2B25 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

  10. AFM analysis inside a crystalline MgB2 grain Contact mode picture Friction mode picture International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  11. b) a) Mg2B25: disposition of the Mg atoms b-rhombohedral Boron Mg2B25 B4(83%) - Mg(F)(17%) substitution d(Mg-Mg) > 4 Å International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  12. Calibration of the fluorescence microanalysis (B/Mg)at = a * (B/Mg)XRF b a = 16.903 ; b = 0.5 International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  13. MgB2 by micron size B grains International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  14. Infiltration features at lower temperatures Rhombohedral boron Mainly b - Stainless Steel B T= 710°C time = 10’ Mg upper level Modified boron (mainly Mg2 B25) Mg International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  15. MgB2 rod, made by RLI • Stainless steel container for Mg and B reactants • b) Resulting MgB2 bars , cut from the cylinder International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

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

  17. Infiltration of micron size B powders Macro poroussample obtained by mixing B powders and Mg chips Two layer disposition of B powderto promote difficult Mg infiltration International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  18. Technology to produce large MgB2 bulk objects MgB2 International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  19. Bulk MgB2 typical manufacts made by RLI International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  20. Bulk MgB2 manufacts obtained by RLI International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  21. Mechanical behaviour of bulk MgB2 by RLI E= 167 GPa C B A International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  22. MgB2 bulk superconducting properties International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  23. MgB2 Bulk : magneto-optical analysis The magnetic field is completely excluded, even in presence of the sample granularity optical image (50x) 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

  24. MgB2 Bulk magneto-optical observation the trapped magnetic field magneto-optical image trapped field distribution induced currents (50x) Zero Field Cooling , observations at B=0 and T=35 K, after application of a field B=13.5 mT (Gozzelino et ., PHIL. MAG. B, 82 ,1-11 JAN 2002) International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  25. Superconductive properties of bulk MgB2 by RLI AC susceptibility DC resistivity Micro Grains + SiC(10%) Large Grains MicroGrains RF Surface resistance Magnetization loop Large Grains Medium Grains Micro Grains International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  26. Thermal stability of the bulk MgB2 Limitation on the thickness m0Jc2 L2 < 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

  27. Hirr,Hc2 evaluation from resistivity measurements = Perspective applicativearea for undoped materials International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  28. Critical current density vs Magnetic field Bulk MgB2 : Micro Grains Grains size dependence International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

  29. Microwave Resonant Cavity Resonant Mode TE011 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

  30. Differences of bulk MgB2 with respect to MT-YBCO MgB2 has: • 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

  31. Bulk MgB2 applications up to 30K Magnetic shielding (space application, measurement systems) Permanent magnet (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

  32. Conclusions • The bulk MgB2, produced by RLI, is a high density superconducting material with good critical current density, in spite of the composite morphology • The transport and magnetic superconducting properties are suitable for high power applications, like current leads, magnetic shielding systems, magnets for power applications (motors,FCL,magnetic separation, bearings,RF cavity filters) • The MgB2 is almost ready for applications at intermediate temperatures (20 – 30K), if an economical and reliable cooling system is available • The high potentiality of the MgB2 is based on the low prospectic cost of the raw materials and of the manufacturing process for large pieces, compared with the other HTc bulksuperconductors International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy

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