g.giunchi - international workshop on "thin films applied to superconductiviting rf"...
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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
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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
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Reactive Liquid Infiltration (RLI) process
International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 4October 10, 2006
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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
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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
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MgB2 Bulk
International Workshop on "Thin films applied to superconductiviting RF" Legnaro (PD)-Italy 7October 10, 2006
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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