International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 1October 10, 2006

G.Giunchi -

MgB2 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)

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

G.Giunchi -

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 3October 10, 2006

G.Giunchi -

Reactive Liquid Infiltration (RLI) process

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 4October 10, 2006

G.Giunchi -

Mg metal, in block form, and B powders (either crystal. oramorphous) are inserted in a SS container and sealed

MgB powders

MgB2

After reaction :The B space results completely occupied by the MgB2 and the Mg space remains almost free of products

“In situ” process :

High density (~2.4 g/cm3) MgB2 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)

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 5October 10, 2006

G.Giunchi -

Driving forces for the RLI process

Volume reduction (molar): Mg + 2 B (23.2 cm3) MgB2 (17. 5 cm3)

Mg diffusivity in B species :

Mg atoms enters in the -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 6October 10, 2006

G.Giunchi -

MgB2 Bulk

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 7October 10, 2006

G.Giunchi -

Morphologies of bulk MgB2 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

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 8October 10, 2006

G.Giunchi -

XRD of MgB2 materials by RLI from crystalline B

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70

2 theta

cps

= MgB2

= Mg = Mg2B25

Mg2B25 / MgB2 = K * (2/12.5 )m with K = 4.152 , m = - 1.626Mg / MgB2 = L*(2/0 )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 9October 10, 2006

G.Giunchi -

Typical composition (at%)

MgB2 Mg2B25 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: MgB2, Mg2B25, Mg

Mg2B25

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

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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 11October 10, 2006

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Mg2B25: disposition of the Mg atoms

b)

a)

B4(83%) - Mg(F)(17%) substitution d(Mg-Mg) > 4 Å

-rhombohedral Boron Mg2B25

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 12October 10, 2006

G.Giunchi -

0

5000

10000

15000

20000

25000

0 0.5 1 1.5 2 2.5

E (keV)

cps

#6#7#8

Calibration of the fluorescence microanalysis

(B/Mg)at = * (B/Mg)XRF

= 16.903 ; = 0.5

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 13October 10, 2006

G.Giunchi -

MgB2 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

Mg2B25 mol% 1.6 24.2 - 20.6 0.33 1.9 -

MgB2 (#199/74,micron size grains)

0

500

1000

1500

2000

2500

3000

3500

4000

0 10 20 30 40 50 60 70

2 teta

cps

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 14October 10, 2006

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Infiltration features at lower temperatures

T36 10' -pwd esterna

0

100

200

300

400

0 10 20 30 40 50 60

2 theta

cp

s

Mg2B25

-boronStainless

Steel

Mainly -Rhombohedral boron

Mg upper level

Modified boron (mainly Mg2 B25)

Mg

t36 - 10' pwd interna

0

50

100

150

200

250

0 10 20 30 40 50 60

2 theta

cps

Mg2B25 -boron

T = 710°C

time = 10’

B

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 15October 10, 2006

G.Giunchi -

MgB2 rod, made by RLI

a) 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 16October 10, 2006

G.Giunchi -

The Reactive Liquid infiltration technique

Maximize internal pressure on the Boron

Manage the container expansion( about 3% linear)

Boron

Steel

Mg

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

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Infiltration of micron size B powders

Macro porous sampleobtained 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 18October 10, 2006

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Technology to produce large MgB2 bulk objects

MgB2

Mg

B

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 19October 10, 2006

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Bulk MgB2 typical manufacts made by RLI

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 20October 10, 2006

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Bulk MgB2 manufacts obtained by RLI

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 21October 10, 2006

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Mechanical behaviour of bulk MgB2 by RLI

AB

C

Vickers Hardness (GPa)

KIC

(MPa m1/2)

A 33 4.8

B 20 6.9

C 8 13.8

E= 167 GPa

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 22October 10, 2006

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MgB2 bulk

superconducting properties

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 23October 10, 2006

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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)

MgB2 Bulk : magneto-optical analysis

The magnetic field is completely excluded, even in presence of the sample granularity

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

G.Giunchi -

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 25October 10, 2006

G.Giunchi -

Superconductive properties of bulk MgB2 by RLI

AC susceptibility

Magnetization loop

DC resistivity

RF Surface resistance

Large Grains

Medium Grains

Micro Grains

Micro Grains

+ SiC(10%)

Large Grains

MicroGrains

0.0E+00

2.0E-06

4.0E-06

6.0E-06

8.0E-06

1.0E-05

1.2E-05

1.4E-05

30 35 40 45 50

T (K)

Re

sis

tiv

ity

(O

hm

cm

)

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 26October 10, 2006

G.Giunchi -

Thermal stability limits for MgB2

0.01

0.1

1

10

100

0 5 10 15 20 25 30 35 40

T (K)

L (

mm

)

B=0T

B=1T

B=2T

B=3T

0Jc2 L2 < 12 C (Tc-T)

Thermal stability of the bulk MgB2

Limitation on the thickness

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 27October 10, 2006

G.Giunchi -

Hirr,Hc2 evaluation from resistivity measurements

0.0E+00

5.0E-07

1.0E-06

1.5E-06

2.0E-06

2.5E-06

3.0E-06

3.5E-06

0 10 20 30 40 50 60

T(K)

Rh

o (

Oh

m c

m)

H=5T

H=2.5T

H=1T

H=0T

Bulk MgB2 with microsize grains

0.E+00

1.E-06

2.E-06

3.E-06

4.E-06

5.E-06

6.E-06

7.E-06

0 10 20 30 40 50 60

T (K)

Rh

o (

Oh

m c

m)

H=5TH=2TH=1TH=0T

Bulk MgB2 with large grains(#199/05)

= Perspective applicative area for undoped materials

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 28October 10, 2006

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Critical current density vs Magnetic field

Bulk MgB2 : Micro Grains

Grains size dependenceBulk MgB2 (magnetic measurements at T= 20K)

100

1000

10000

100000

1000000

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

oH (T)

J c (

A/c

m2 )

Micro grains (< 5 micron)

Medium grains(<40micron)+ C

Large grains (<100 micron)

International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 29October 10, 2006

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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 30October 10, 2006

G.Giunchi -

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 31October 10, 2006

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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 32October 10, 2006

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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 bulk superconductors