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High Performance Sm-Co Magnets for Critical Application
Jinfang Liu, Ph.D.V.P. of Technology and Engineering
Electron Energy Corporation924 Links Ave, Landisville, PA 17538, USA
Phone: 717-898-2294E-mail: [email protected]
Sm-Co Magnets Overview
Properties of Sm-Co Magnets
Temperature Compensated Magnets
Ultra High Temperature Magnets
Applications
Future Trend
OUTLINE
1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
50
40
30
20
10
0
(BH
)max (M
GO
e)
(BH)m
ax(kJ/m
3)
400
320
240
160
80
0KS Steel
MK SteelAlnico
Alnico
Hard Ferrite
SmCo5
Sm(Co,Fe,Cu,Zr)z
Nd-Fe-B
1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
50
40
30
20
10
0
(BH
)max (M
GO
e)
(BH)m
ax(kJ/m
3)
400
320
240
160
80
0KS Steel
MK SteelAlnico
Alnico
Hard Ferrite
SmCo5
Sm(Co,Fe,Cu,Zr)z
Nd-Fe-B
History of Permanent Magnets
Nd-Fe-B MagnetsNd-Fe-B Magnets
Sm-Co MagnetSm-Co Magnet
Strontium FerriteStrontium Ferrite
Barium FerriteBarium Ferrite
Permanent Magnets
Permanent Magnets
Bonded Magnets(Rubber/Plastic)
Bonded Magnets(Rubber/Plastic)
Metal Magnets
Metal Magnets
Ferrite MagnetsFerrite Magnets
RE MagnetsRE Magnets
Alnico MagnetsAlnico Magnets
Bonded Ferrite MagnetsBonded Ferrite Magnets
Bonded RE MagnetsBonded RE Magnets
SmCo 1:5SmCo 1:5
SmCo 2:17SmCo 2:17
Other MagnetsOther Magnets
Permanent Magnets
Sm-Co Magnets Overview
Sm-Co Magnets
SmCo5 type
Sm2 Co17 type
Conventional Sm-Co 2:17 grades
High energy Sm-Co 2:17 magnets
Sm-Co 2:17 TC materials
Conventional Sm-Co 1:5 grades
Sm-Co 1:5 TC materials
High temperature magnets
EEC2:17-31EEC2:17-29
EEC2:17-27EEC2:17-24
T400, T500, T550
EEC1:5TC-15EEC1:5-13EEC1:5TC-9
EEC1:5-18
EEC2:17TC-18EEC2:17TC-16EEC2:17TC-15
TC: temperature compensated
Typical energy product (BH)max , of selected commercial magnets:
Sintered Nd-Fe-B magnets: up to 52 MGOe
Sintered Sm-Co magnets: up to 32 MGOe
Isotropic bonded Nd-Fe-B magnets: up to 10 MGOe
Sintered ceramic magnets: up to 4 MGOe
Cast Alnico magnets: up to 9 MGOe
Magnetic Properties ComparisonMagnetic Properties Comparison
We have NdFeB, why do we still need Sm-Co?
We can provide a long list of the benefit of Nd-Fe-B, such as high (BH)max
at RT, less expensive.
But Sm-Co has:
Superior high temperature magnetic properties (with maximum application temperature up to 550oC)
Excellent corrosion resistance
Very good radiation resistance
Small reversible temperature coefficients of residual induction, Br
Nd-Fe-B vs. Sm-Co
15 20 25 30 35 40 45 50
100
200
300
400
500
600
Max
imum
Ope
ratin
g Te
mpe
ratu
re (o C
)
Maximum Energy Product (MGOe)
Sm-Co Based Magnets
Nd-Fe-B Based Magnets
Typical Manufacturing Process for Sintered Sm-Co Magnets
Magnetizing & Testing
Ball milling or Jet milling To ~ 2-5 μm
Sintering, Solution and Heat treatment
Pressing
Grinding, lapping, honing, Or wire EDM
Machining
Raw Materials Sm, Co, Fe,Cu, Zr (2:17)
Sm, Co (1:5)
Crushing to <500 μm
Induction Melting
Temperature-Compensated Permanent Magnets
What is it?
A family of magnets that has almost zero reversible temperature coefficient (RTC) of residual induction.
What is the definition of RTC?
Reversible temperature coefficient
Br changes with temperature
Some applications , such as gyro and TWTs, require stable Br over a wide temperature range
The reversible temperature coefficient of Br is defined as:
α
=
To address above requirements, EEC developed temperature compensated magnets with the reversible temperature coefficient of Br close to zero
ΔBrBr ΔT
1X 100%
Temperature-Compensated Permanent Magnets
4πM (at 10 kOe) vs. temperature for RE(Co,Fe,Cu,Zr)7.4
magnetic compounds.
Source: C. Chen et al.. J. Applied Physics 91 (10) 8483-8485 (2002)
Sm
Tb
Dy Gd
TmErHo
How Do we accomplish Temperature compensation?
HRE/TM: antiparallel
coupling
LRE/TM:
Parallel Coupling
Temperature compensated Sm-Co 2:17 magnets
*RTC: Reversible temperature coefficient
RTC of Br is calculated within the temperature range –50 to +150oC
Grades
2:17-24
(BH)max RTC* of Br Comment
24 MGOe -0.035 %/oC
-0.02 %/oC
-0.001 %/oC
No compSome comp2:17TC-18 18 MGOe
2:17TC-16 16 MGOe Full comp
3
5
7
9
11
13
-200 -150 -100 -50 0 50 100 150 200 250 300 350
Temperature (°C)
Br (
kG)
Sm2 TM17
(Sm,Gd)2 TM17
Gd2 TM17
For comparison, the RTC of Br for Nd-Fe-B magnet is about -0.11%/oC
Temperature compensated RE-Co 1:5 magnets
EEC 1:5TC-15
EEC 1:5TC-13
EEC 1:5TC-9
Grades
EEC 1:5-18
(BH)max RTC* of Br Comment
18 MGOe -0.04 %/oC
-0.03 %/oC
-0.02 %/oC
no compensation
some compensation15 MGOe
13 MGOe some compensation
9 MGOe -0.001 %/oC full compensation
*RTC: Reversible temperature coefficient
Temperature-Compensated Permanent Magnets
Why Do We Need Zero RTC Magnets?
Inertial guidance systems
Traveling wave tubes
Ultra High Temperature MagnetsMaximum operating temperature of conventional Sm-Co
magnets is only up to 300oC
DoD initiated the More Electric Aircraft program, which requires magnets with maximum operating temperature more than 400oC
Funded by Department of Defense, a series of sintered Sm-Co 2:17 magnets with maximum operating temperature as high as 550oC was developed in late 1990s and early 2000s
High intrinsic coercivity Hci at elevated temperatures to resist demagnetization
Low temperature coefficient of Hci
Straight-line demagnetization curves at maximum operating temperatures
Magnets can be made for any specified TM up to 550°C with highest possible (BH)max (TM: Maximum Operating Temperature)
High temperature magnets require surface coating (such as Ni-plating) if used above 400oC continuously.
High temperature magnets still belong to Sm2TM17 type magnet family.
Important Features of Ultra High Temperature Magnets
Comparison of Magnetic Properties
Grades
EEC24-T400
(BH)maxMaximum
Operating Temp
24 MGOe 400 oC500 oC
550 oC
EEC20-T500 20 MGOeEEC16-T550 16 MGOe
EEC2:17-27
EEC2:17-31
27 MGOe31 MGOe
300 oC240 oCSmCo 2:17
magnets
Ultra high temperature magnets
Category
Long-term Thermal Stability at 300°C in Air
0 4000 8000 12000 16000 20000 24000 28000-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1 Year
Magnet Dimensions:1 cm OD x 1 cm THK
2 Years 3 Years
T550C-16MGOe w/coating T550C-16MGOe T500C-20MGOe T400C-24MGOe T330C-27MGOe T250C-31MGOe
Time at 300°C (Hours)
Mag
netic
Irre
vers
ible
Los
ses
(%)
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Corrosion ResistanceSm-Co magnets have excellent corrosion
resistance. No coating is needed to protect parts from corrosion.
Nd-Fe-B magnets require surface coating such as Ni-plating or epoxy coating
OSU Research Reactor at full power (450 kW) during the radiation
experiment
Picture showing sample and thermocouple assembly
Thermocouple0.25 mm x LSample:5mm x 6.25mmHole:0.5mmx3.13mm
Thermocouple0.25 mm x LSample:5mm x 6.25mmHole:0.5mmx3.13mm
(b)
Magnet Samples: φ5 mm x 6.25 mm Hole: φ0.5mm x 3.13 mm
Radiation Effects
Radiation Effects
* Different conditions resulted in different temperatures: 77ºC – filled with Helium and 153ºC – filled with air (with neutron flux = 4 x 1013 neu/cm2 •
s); 266ºC – filled with air (with neutron flux was 2.1 x 1012 neu/cm2 •
s). TL is the localized temperature
The irradiation damage is primarily caused by a radiation-induced thermal effect.
Sm-Co magnets do not have any noticeable changes in magnetic properties, while Nd13
Dy2
Fe77
B8
magnets lost almost 100% of their magnetic flux at a neutron flux of 1016 n/cm 2.
The dominant factor for radiation tolerance is thermal stability, which is related to the following factors:
(1)
Curie temperature of permanent magnets
(2)
Working point of permanent magnet in the system
(3)
Intrinsic coercivity
Radiation Effects
Accelerometers and gyroscopesHigh performance motors and generatorsHigh temperature magnetic bearingsMagnetic couplers and actuatorsHall effect devicesHigh performance pumps and mixersTraveling wave tubes
Applications of Sm-Co magnets
Straight-Line Demagnetization Curves
Application with load line #1: Both magnets are okay to use
Application with load line #2: Only magnet #1 is suitable
Bd1
Magnet #1: Sm-Co
Load line 2
Br
Hc 0
Knee
Load line 1
Bd2
Hd1 Hd2
Br
Hc
Magnet #2: Comparison magnet
Traveling Wave Tube Amplifier (TWTA)
Towed Decoys could improve survivability of current military Aircraft
0.545 T
Axial Field (T)
Position (inch)
Some requirement for magnets: a) Small temperature coefficient of Brb) Straight-line demagnetization curve up to 300oC
Sm-Co Magnet for Ion Propulsion
Some requirements for the magnets:a) High temperature performance up to 300oCb) Good radiation resistance
DEEP SAPCE I
Some requirements for magnets:a) If the application temperature
is below 150oC, Nd-Fe-B magnet is a good choice
b) If it is used in corrosive environment and/or at high temperatures, Sm-Co magnet is a good choice
c) Corrosion resistance should be considered at design stage
Magnetic Coupling Systems
Surface Coupling Systems
Concentric Coupling Systems
Some requirements for magnets:
Straight-line demagnetization curve up 300oC, and the for some up to 500oC
PM-Biased High Temperature Radial Magnetic Bearing
Supported by NASA Glenn Research Center, EEC/TAMU designed and built a PM-biased hybrid high temperature magnetic bearing that can operate at 1000 F
Magnet arc assemblies on the outer diameter of bearing lamination stacks.
Magnet
Demagnetization Curves of T550 High temp magnet
High Temperature PM Biased Magnetic Bearings
0
200
400
600
800
1000
0 5 10 15 20
Current (A)
Force (lbs
4 Load Cells
Dr.Kenny's Prediction using FEA
calculation from circuit model (0.65*Hc)
2 Load Cells
Radial Bearing Force vs. Current at R.T.
• Reasonably good agreement between 3D FEA and 4 Load Cell Data.
• Analytical result at 10 Amps is 7% higher than actual
Sm-Co Magnets for Medical DevicesSome medical devices require autoclave sterilization,
which makes Sm-Co magnets more attractive
Nanocomposite permanent magnets Promises and challenges
Some processes for nanostructured and/or nanocomposite magnetic materials:
(1)
Melt-spinning and annealing (normally isotropic)
(2)
High energy / low energy ball milling
(3)
Sputtering (thin films)
(4)
Electroless
deposition (of soft magnetic layer onto hard magnetic particles)
(5)
Chemical synthesis (nanoparticles)
(6)
………..
Why Nanocomposite
magnets
E. F. Kneller and R. Hawig, IEEE Trans. Mag. MAG 27, 3588 (1991)
Nd2
Fe14
B: δw (hard)
= 4.3 nmSm2
Co17
: δw (hard)
= 8.6 nm
• Challenges: preserve a sufficiently high iHc
and loop squareness.
• This can be only guaranteed if
•
Theoretical micromagnetic
calculations: almost
double (BH)max in nanocomposite
magnets.
• Physical principle: magnetic exchange hardening
Dg (soft)
≤
2 x
δw (hard)
grain size domain wall width
Chemical Synthesis and Consolidation(b) Powder consolidation(a) Chemical synthesis
micelletechnique
silicone oilbubbles
hot-pressing apparatus
RF die-upsetting apparatus
core powder immersed in (FeCl2
+Eth)
NaBH4
+ DI H2
O
specific gravity separation
reaction layer
glycol
sample inside the RF coil
press
dielectricpunches
WC die
localized reaction (micelles)
in-volume reaction
Hard Magnetic Nanoparticles by SurfactantHard Magnetic Nanoparticles by Surfactant--Assisted Ball MillingAssisted Ball Milling
0 2 4 6 8 10 12 140
20
40
60
Cou
nt
Particle size (nm)
PrCo5<d> = 7 nm
Sm2 (Co0.8 Fe0.2 )17PrCo5
●
Anisotropic R-Co nanoparticles were fabricated by high-energy milling in heptane with oleic acid added as a surfactant.
Hot press
Chemically synthesized Fe(B) nanoparticles on Sm2 Co17 particles
Core/Shell Powders and Nanocomposite Magnets by Nanoparticle Coating
-25 -20 -15 -10 -5 0 5 10 15 20-10
-8
-6
-4
-2
0
2
4
6
8
10
SmCo5
SmCo5 / nano-Fecomposite magnet(HP & DU)
4πM
(kG
)
H (kOe)
SmCo5 HEBM 4h + LEBM 5hcoated with Fe nanoparticles SmCo5 / nano-Fe
composite powder
Magnetic properties of composite SmCo5 / nano-Fe magnets
SummarySmCo magnet can operate up to 500oC
Temperature compensated magnets can have a RTC of Br close to zero
SmCo magnets have very good thermal stability, corrosion resistance, and radiation resistance
Nanocomposite is the future?
Thanks for your attention
Contact Information:Jinfang Liu, Ph.D.Vice President of Technology and EngineeringElectron Energy Corporation924 Links Ave, Landisville, PA 17538717-898-2294 (Phone) 717-459-1004 (Direct Line)717-898-0660 (Fax) E-mail: [email protected]