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: jfl@electronenergy.com

Sm-Co Magnets Overview

Properties of Sm-Co Magnets

Temperature Compensated Magnets

Ultra High Temperature Magnets

Applications

Future Trend

OUTLINE

Sm-Co magnets overview

Lancaster County

Electron Energy Corporation

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

Properties of Sm2

TM17

magnets

a b

⊥

EMD //EMD

EMD: Easy magnetization direction

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

Halbach

Structures

Halbach Dipole

Halbach Quadrupole

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

Future Trend

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

Sm-Co or Nd-Fe-B Nanoflakes

Patent pending

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: jfl@electronenergy.com