G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 1 October 10, 2006 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, Milano (Italy) b CNR-IENI Sezione di Lecco, Corso Promessi Sposi 29, Lecco (Italy)

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 2 October 10, 2006 Outline  MgB 2 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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 4 October 10, 2006 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 MgB 2 and the Mg space remains almost free of products “In situ” process : High density (~2.4 g/cm 3 ) MgB 2 and near net shape manufacts NO external pressure 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 (EDISON Spa,Italy - Pending patents) Reactive Liquid Infiltration (RLI)

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 5 October 10, 2006 Driving forces for the RLI process  Volume reduction (molar): Mg + 2 B (23.2 cm 3 ) MgB 2 (17. 5 cm 3 )  Mg diffusivity in B species : Mg atoms enters in the  -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)

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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 8 October 10, 2006 XRD of MgB 2 materials by RLI from crystalline B Mg 2 B 25 / MgB 2 = K * (  2 /  12.5 ) m with K = 4.152, m = Mg / MgB 2 = L*(  2 /  0 ) n with L = 2.47, n = G.Giunchi, C. Orecchia, L.Malpezzi, N. Masciocchi, Physica C433, 182 (2006)

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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 11 October 10, 2006 Mg 2 B 25 : disposition of the Mg atoms b)b) a)a) B4(83%) - Mg(F)(17%) substitution d(Mg-Mg) > 4 Å  -rhombohedral Boron Mg 2 B 25

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 12 October 10, 2006 Calibration of the fluorescence microanalysis (B/Mg) at =  * (B/Mg) XRF   = ;  = 0.5

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 13 October 10, 2006 MgB 2 by micron size B grains Sites (B/Mg) FRX Mg 2 B 25 mol%

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

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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 17 October 10, 2006 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

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

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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 21 October 10, 2006 Mechanical behaviour of bulk MgB 2 by RLI A B C Vickers Hardness (GPa) K IC (MPa m 1/2 ) A334.8 B206.9 C813.8 E= 167 GPa

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 23 October 10, 2006 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) MgB 2 Bulk : magneto-optical analysis The magnetic field is completely excluded, even in presence of the sample granularity

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 24 October 10, 2006 MgB 2 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)

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 26 October 10, 2006  0 J c 2 L 2 < 12  C (T c -T) Thermal stability of the bulk MgB 2 Limitation on the thickness G.Giunchi, Adv. Cryo. Eng.Trans. of ICMC, vol (2006)

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 27 October 10, 2006 H irr,H c2 evaluation from resistivity measurements = Perspective applicative area for undoped materials

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

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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 30 October 10, 2006 Differences of bulk MgB 2 with respect to MT-YBCO MgB 2 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

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 31 October 10, 2006 Bulk MgB 2 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) ?

G.Giunchi - International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 32 October 10, 2006 Conclusions  The bulk MgB 2, 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 MgB 2 is almost ready for applications at intermediate temperatures (20 – 30K), if an economical and reliable cooling system is available  The high potentiality of the MgB 2 is based on the low prospectic cost of the raw materials and of the manufacturing process for large pieces, compared with the other HT c bulk superconductors