radiation damage in resins and composites

Dave EvansAdvanced Cryogenic Materials Ltd

(davidevans276@btinternet.com)

Radiation Damage in Resins and Composites

1

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The author consents to the photographic, audio and video recording of this lecture at the CERN Accelerator School. The term “lecture” includes any material incorporated therein including but not limited to text, images and references.

The author hereby grants CERN a royalty-free license to use his image and name as well as the recordings mentioned above, in order to broadcast them online to all registered students and to post them without any further processing on the CAS website.

The author hereby confirms that the content of the lecture does not infringe the copyright, intellectual property or privacy rights of any third party. The author has cited and credited any third-party contribution in accordance with applicable professional standards and legislation in matters of attribution.

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2

Outline

Ø Radiation Units and TypesØ Interaction of Radiation with materialsØ Classification of Plastics Materials

Ø Thermoplastics and ThermosetsØ Structure and Materials Selection Ø Effects of Radiation

Ø Mechanical, gas evolution, dimensional changes?Ø Irradiation Under Load Ø Electrical properties

3

Radiation Units

Ø The S.I. unit of absorbed dose is the Gray (Gy)Ø An energy equivalent of one Joule absorbed in one

Kilogram Ø Non SI Unit – Rad; 1 Rad = 10-5 J/g = 10-2 Gy Ø 1 eV = 1.602 x 10-19 Joules ; 1 MeV = 1.602 x 10-13

Joules

Ø barn: Unit of area (10-28 m2 ) used in measurement of nuclear cross-sections

4

Radiation Types

ØNeutrons - particles with energy but no charge

ØElectromagnetic radiation such as g-rays

ØCharged particles - such as protons, electrons and a-particles (He2+)

5

Interaction of Radiation With Polymers

High energy particles lose energy and transfer it to polymer by:

Ø Ionisation - breaking chemical bondsØ Excitation -Separation of orbital electronsØ Nuclear Displacement Reactions - mainly fast

neutrons - leads also to ionisationØ Nuclear Transformation - Mainly slow neutronsØ Scattering and Emission

Ø Absorbed energy is degraded and appears as heatØ Energy deposition is characterised by LET

6

Linear Energy Transfer

Ø Rate of energy loss of a particle depends only on it's speed and charge and not on it's mass.

Ø Protons and alpha particles will react in a similar manner to electrons of the same velocity and charge.

Ø Difference in mass means that the penetration of a 20 MeV proton is comparable with that of a 10 keV electron.

Ø Since the LET is increased as the particle is slowed, uniform radiation conditions, apply only if the specimen is considerably thinner than the range of the incident particle.

Ø7

Fast Neutrons - 1

Ø Fast Neutrons are intensely damaging

Ø Major result is production of fast protons

Ø Energy transfer to other atoms may break chemical bonds

Ø Re-coiled neutron may still have sufficient energy to break more bonds

8

Fast Neutrons 2

Ø Ø Deposit Energy by collisionsØ Et = 4 x M (E Cos 2 q)

(M+1)2

Nucleus MassEnergy

Transfer (%)Hydrogen 1 100

Carbon 12 28Nitrogen 14 25Oxygen 16 22

9

Slow Neutrons

Ø Most elements have larger capture x - section for slow neutrons than for fast - result is nuclear transformation reactions:

Ø After capture nucleus may be unstable: (capture X-section of hydrogen 80 barns)H(1) (n,g)D(2) N(14) (n,p) C(14)2.2 MeV g 0.66 MeV proton

B(10) (n,a) Li(7) (B capture X-Section 700 barns)Boron gains 1 amu and loses 4 (a high energy alpha

particle) - a net loss 3 amu

10

Methane – A Special Case

Ø Hydrogen rich compound most efficient way to “slow” neutrons

Ø Methane (CH4) often used as a ‘moderator’; fast neutron irradiation leads to hydrogen gas and ‘wax’ like substance –eventually carbon!

Ø Hydrogen gas from hydrogen abstractionØ ESR measurements show H* & C*H3 in solid methane at 4K

after irradiation at that temperatureØ Under similar conditions H* NOT detected in PE or other

polymersØ Activated atoms lead to polymer formation and ultimately

carbonization

11

Neutron Fluence and Dose Conversion –Energy Deposited (1st Collision)

1.E-18

1.E-17

1.E-16

1.E-15

1.E-14

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07Neutron Energy (eV)

Gy/

n/m

^2

N (capture)TotalHOC

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 12

Polymer Structures(radiation Resistance is related to

structure & Composition)

13

Relative atomic Sizes (Approximately)!

Hydrogen Carbon OxygenMethyl Group

Chlorine

Benzene nucleus

14

Some Thermoplastics

Ø Poly(ethylene) Poly(propylene)

Ø Poly(vinyl chloride)

15

Another Common Thermoplastics Material

16

More Complex Plastics Materials

17

Di-Functional Resins

Ø Typical commercial DGEBA, average value for n = 0.15

CH2 CH CH2

O

NCH2 CH CH2

O

Diglycidyl Aniline

C CH2 CH CH2

O

OCH2CH CH2

O

O

n

CH3

CH3

CH2 CH CH2

OH

C

CH3

CH3

O O

DGEBA

18

Epoxy Novolak Resins

CH2 CH CH2

O

2 O

n

CH2

CH2 CH CH

O

O

CH2

CH2 CH CH

O

O 2

Commercial EPN Resin (n= 0.4 avg) when n = 0, Resin is (pure) DGEBF

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 19

Tri-Functional Epoxy Resins

CH2 CH CH2

O

CH2 CH CH2

O

N

O

CH2 CH CH2

O

Low viscosity - brittle when cured

20

Tetra Functional Resins

H

H

N C

CH2-CH-CH2

O

CH2-CH-CH2

O

N

CH2-CH-CH2

O

CH2-CH-CH2

O

DETGDM

TGDM

H

H

C2H5

C2H5

N C

CH2-CH-CH2

O

CH2-CH-CH2

O

N

CH2-CH-CH2

O

CH2-CH-CH2

O

21

Cyanate Ester ResinTwo Reactive Groups(Di-Functional)

CH3

O CCH2-CH-CH2

O

CH2-CH-CH2

O

O

CH3

CH3

O C O

H

C NN C

Cyanate Ester Monomer (AroCy L-10)

DGEBA shown pure for clarity

Dave Evans – ACM Ltd – CEREN Accelerator School – Radiation Damage 22

Cyanate Ester – Ring Formation

CH3

O C O

H

C NN C

Dicyanate monomer

C

C C

N N

NOO

O Cyan. Est O NC

N OC Cyan. EstCyan. Est O NC

Trimerization

Triazine Ring

Totally cross-linked – leads to Radiation / Thermal Stability and High Tg

23

Solid Aromatic Amines

CH NH2NH2 2 DDM (MDA) (Suspected carcinogen)

S

O

O

NH2NH2DDS

24

Aromatic Amines - Liquids

3

C2H5NH2

C2H5

CH3

NH2

NH2

NH2

CH3

SCH

CH3S

DMTD Hardener AHEW 53.5

DETD Hardener AHEW 44.5

25

Anhydride Hardeners

CH CH

C CHCH3

CH2

CH2C

C

O

O

O

MNA 5 methyl 1,4 endomethylene cyclohexanoic anhydride CH CH

C CHCH3

CH

CHC

C

O

O

O

CH2

MTHPAmethyl tetra hydro phthalic anhydride

26

Results & Test Methodology

Mechanical Changes in Materials

27

Radiation Stability of Various Plastics Materials

0

5

10

15

20

25

30

PTFE

FEP

Butyl Rubber

Si Rubber

PVC

P/E

PETP

Neoprene

EVA

Halar

PP/XPE

EPR/EPDM

G10

G11

PI (Kapton

Material

Usea

ble

Rang

e (M

Gy)

Upper useable range for PTFE is 1000Gy and for FEP and Butyl Rubber is 20,000 GY

28

Radiation Effects in Resins

Ø Changes in Mechanical properties

Ø Particularly matrix dependent properties such as flexural strength and shear strength

Ø Classification of “Damage”

Ø Radiation induced gas evolution / swelling

Ø Effect of Temperature

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 29

Mechanical Changes 1. Flexural Strength

30

Radiation Effects in Materials (1)(Flexural Strength – Gamma Radiation – RT)

0

50

100

150

200

250

300

350

400

450

500

0.1 1 10 100 1000Radiation Dose (MGy)

Flex

ural

Stre

ngth

(MPa

)

DGA

DGEBAEpoxy Novolak

TGPAPTGDM

Anhydride cured Resins

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage

Rutherford Laboratory Report RHEL/R 200

31

Radiation Effects in Materials (2)(Flexural Strength – Gamma Radiation – RT)

0

50

100

150

200

250

300

350

400

450

500

0.1 1 10 100 1000

Radiation Dose (MGy)

Flex

ural

Stre

ngth

(MPa

)

DGADGEBAEpoxy NovolakTGPAPTGDM

Aromatic Amine Cured

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage

Rutherford Laboratory Report RHEL/R 200

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Radiation Stability and Resin Structure

020406080

100120140160180200

0 1 2 3 4

Number of reactive Groups on Resin

Dos

e to

Red

uce

Stre

ngth

by

25 %

(MGy

)

Acid Anhydride Cured Resin

Aromatic Amine Cured Resin

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 33

Shear Testing

34

Stressful (Working)Lunch

35

Shear Strength Evaluation

Ø Many methods – each has it’s own problemsØ Major Techniques are :

Ø Guillotine – bending & stress concentrations

Ø Short beam shear – variation of 3-point bending test but short span – compression on one face tension on the other

Ø Shear / compression – said to be free of stress concentations – mainly used for adhesive properties

36

ILSS– G10Guillotine Method

0

20

40

60

80

100

120

0.00 0.50 1.00 1.50 2.00

Ratio - Shear Length to Thickness (l/t)

ILSS

(MPa

)

ILSS at 77K

ILSS at 300K

Constant Overlap - 12.7 mm (0.5 inches)

37

Reactor Irradiation at 5K(Short Beam Shear)

0

20

40

60

80

100

120

0.1 1 10 100

Total Dose (Gamma + Neutron) MGy

ILSS

(Sho

rt B

eam)

(MPa

)

DGEBA-AnhydrideTGDM-Aromatic Amine

0.9 E+22 neutrons / m 2̂

1.8 E+22 n/m 2̂

1.5e+201e+20 1e+21

1.5e+21 1e+22

Neutron Fluence (E> 0.1 Mev)

R.P. Reed et al – US ITER Radiation program -sponsored by US Office of Fusion Energy)

38

SBS With and Without Kapton(R.P. Reed et al – US ITER Radiation program - sponsored by US Office of Fusion Energy)

Radiation Dose (n/m2) (Mgy)

ILSS (Mpa) (SBS) No Kapton 0° 90°

ILSS (Mpa) (SBS)

Kapton 0° 90

Ratio UTS/ILSS No Kapton 0° 90°

Ratio UTS/ ILSS

Kapton 0° 90°

0

80

77

81

75

11 4.5

9.3 5.2

5 x 1021

(~25) 44

37

50

45

18 ---

13 ---

1 x 1022

(~50) 31

24

35

27

22 4.8

14 8.0

Tape Wound Samples, partly purified DGEBA – unspecified hardener

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 39

Tests in Shear Compression

Ø Test is ‘free” of stress concentrationsØ Many tests carried out RT and at 4KØ Little data on radiation stable materialsØ No comparison between 4k and RT irradiation (except

for samples with mica barrier) ???Ø For DGEBA cured with Acid Anhydride:

Ø Test at 4K – no irradiation (45 angle) 190 MpaØ Test at 4K irradiated at 4K* (45 angle) 26 MPa* Reactor irradiated 1.8 x 1022 n/m2 (~67 MGy)

40

Gas Evolution & Swelling

41

Radiation – Effectof Temperature

00.05

0.10.150.2

0.250.3

0.350.4

0 100 200 300 400

Temperature (K)

G Va

lue

(micro

moles

/ J

)

Gas evolution from ld polyethylene

8.6 cc/g/MGy (300K)

6.7cc/g/MGy (240K)

Dave Evans - ACM Ltd – CERN Accelerator School – Radiation Damage 42

Gas Evolution & Reactor Irradiation(Evans & Reed, Adv. Cry. Eng. Vol 42, 29 – 35)

Resin Hardener Gas(cc/g/MGy)

DGEBF DETD 0.58DGEBF DMTD 2.32TGPAP DETD 0.58DETGDM DETD 0.91DETGDM DMTD 2.78DGEBA DDM 0.30

For Reference: DGEBF/MTHPA 1.08cc/g/MGy from Reactor Irradiation – polyethylene dosimeter

Dave Evans - ACM Ltd – CERN Accelerator School – Radiation Damage 43

Composition of Radiation Induced Gasses

(Generalised and approximating)

Ø Amine Cured (aliphatic or aromatic):90% hydrogen, 10% carbon monoxide

Ø Acid Anhydride cured:20% hydrogen, 20% carbon monoxide, 60%

carbon dioxide

44

Is Gas Trapped in Bulk Specimens?(Evans & Reed, Adv. Cry. Eng. Vol 42, 29 – 35)

Ø Bulk means ~ 7 mm cube

Material Gas Production Rate Cc’s / g/MGy

True * Bulk**

% Gas Trapped

DGEBF/MTHPA 1.03 0.47 53 DGEBF / DETD 0.58 0.44 24 TGPAP / MTHPA 1.10 0.64 42 TGPAP / DETD 0.58 0.64 0

* Rate from powdered sample ** Rate from 7 x 7 x 7 cubes

Dave Evans – ACM Ltd - CERN Accelerator School – Radiation Damage 45

Swelling & Reactor Irradiation at 5K(Humer et al - Cryogenics, 40 , pp 295-301)

DGEBF / Anhydride

-2

0

2

4

6

8

10

0.1 1 10 100

Calculated Dose (MGy)

Swell

ing %

Thin LaminateThin Sandwich

Thin Tube

1E+21

1.5E+21

1.0E+22

If glass is ~50 vol% - swelling in resin phase is double composite What is stress in composite? (720 MPa if E = 9 GPa)

0.5mm thick specimens

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 46

Swelling and Mass Loss (20 MGy)Reactor Irradiation at 5K – Unfilled Resin

(Evans & Reed, Adv. Cry. Eng. , Vol. 46, pp 211 - 218)

Resin Hardener Change in Properties (%) Diam Length Mass

Mass Change % / MGy

DGEBF MTHPA -0.1 0.0 -0.8 -0.04 EPN MTHPA 0.3 0.0 -1.0 -0.05 DGEBF DETD 0.1 0.2 -0.1 < -0.01 DGEBA DETD 0.0 0.2 -0.1 < -0.01 TGDM DDS 0.0 0.3 -0.1 < -0.01 TGPAP DETD 0.3 0.3 0.0 <-0.01 DGEBA MTHPA -0.1 -0.2 -0.8 -0.04 TGPAP MTHPA 0.5 -0.1 -0.7 -0.04

No Change in Young’s Modulus (compression) after Irradiation

10 mm diam x 10 mm long cast and machined resin samples

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage

0.00.0 0.0

47

The Last Word on Swelling

Ø Available data is very confusing – my viewis that swelling doesn’t occur in epoxies or CE at dose levels reported’

Ø WHY – what happens to gas?Ø No new material created – gas is from atoms already

presentØ Molecules possibly ‘trapped’ in area of formation (‘cage

effect’)Ø Gas is ‘in solution’ – does not occupy a separate volume

within resin

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 48

Creep and Radiation

49

The Real World

“---- that some discussion be focussed on integrating the insulation materials results with magnet design and operation issues. In other words, cover more than just insulation properties but also how these impinge on coil fabrication or operation. How do properties measured on small samples relate to properties in large scale impregnated coil cross-sections under multi-dimensional loads, including combined mechanical, thermal and radiation loads ---“ Joe Minervini

(Assistant Director, MIT Plasma Fusion Center)

50

Irradiation at 5K – DGEBF / Anhydride(Evans & Reed Adv. Cry. Eng. Vol 44, 183 - 190 )

Neutron Fluence (E.0.1 MeV

Stress During Irradiation (MPa)

Failure Stress (MPa)

0 (control) 0 172 5 x 1021 0 124 5 x 1021 30 105 1 x 1022 30 92

Dave Evans – ACM Ltd - CERN Accelerator School – Radiation Damage 51

Irradiation at 5K – TGDM / Aromatic Amine(Evans & Reed Adv. Cry. Eng. Vol 44, 183 - 190 )

Neutron Fluence (E.0.1 MeV

Stress During Irradiation (MPa)

Failure Stress (MPa)

0 (control) 0 162 5 x 1021 0 157 5 x 1021 30 139 1 x 1022 30 122

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 52

Creep at 77K of Irradiated Material(Nishiura T et al - Cryogenics, Vol. 35, No. 11, pp 747 – 749)

Creep of Irradiated GRP (5 MGy)

0.00

0.50

1.00

1.50

2.00

2.50

0.00 50.00 100.00 150.00 200.00 250.00 300.00

Time (Minutes)

Cree

p De

flecti

on (m

m)

403 MPa278 MPa

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 53

Creep During Irradiation at 77K(Nishiura T, et al - Cryogenics, Vol. 35, No. 11, pp 747 – 749)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.00 50.00 100.00 150.00 200.00 250.00

T ime (Minutes)

Cree

p De

flect

ion

(mm

) 370 MP a204 MP a

125 MP a

Dose Rate 1.5MGy / Hour

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 54

Creep Rates

Irradiation Conditions

Stress Level (MPa)

Creep Rate (mm/minute)

Pre-Irrad* 278 <5 x 10-5 Pre-Irrad* 403 ~9 x 10-5

During Irrad** 125 1.5 x 10-4

During Irrad** 204 4.5 x 10-4

During Irrad** 370 9.0 x 10-4

* Pre-Irradiated 5 MGY, ** Total during irradiation ~ 6MGy

Dave Evans – ACM Ltd – CEDRN Accelerator School – Radiation Damage 55

A Quick Look at Electrical Properties

56

Electrical Properties and Radiation

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.1 1 10 100

Calculated Dose (MGy at 5K)

Diel

ectr

ic S

tren

gth

(kV/

mm)

Laminate

Sandwich

1 x 1021 n/m2 5 x 1021 n/m2 1 x 1022 n/m2

Dave Evans – ACM Ltd – CERN Accelerator School – Radiation Damage 57

Summary

Ø High functionality promotes radiation stability Ø Aromaticity (resin or hardener) also promotes

stabilityØ Best Epoxies -up to 200 MGy – CE even moreØ Some synergism between irradiation under stressØ Gas volumes and composition related to structureØ Results on swelling are scattered and confusing – on

balance no swelling up to 100 MGyØ No significant change in electrical properties – up to

~ 100 MGy – no apparent relationship with structure

58