Robert KultzowRobert Kultzow

TRFA 2005TRFA 2005

November 15, 2005November 15, 2005

Epoxy Systems For Below Zero Degrees CelsiusEpoxy Systems For Below Zero Degrees Celsius

Features of Epoxy ResinsFeatures of Epoxy Resins• High mechanical strength • Outstanding dielectric

characteristics• Excellent adhesive

properties• Great Chemical resistance• Phenomenal thermal

endurance

Performance at Lower Performance at Lower Operating TemperaturesOperating Temperatures

• Speed and effectiveness of cure

• Fracture toughness

• Thermal Expansion characteristics

Uses of Epoxies at Lower Uses of Epoxies at Lower Temperatures and Cryogenic Temperatures and Cryogenic

ConditionsConditions

• Nuclear physics apparatus• Super conducting devices comprised of

magnets and transformers• Magnetic imaging devices

Pathways to Development of a Pathways to Development of a Cryogenic SystemCryogenic System

Epoxy Resin Sytem<Title>

Inorganic FillersLow er CTE

Final Cryogenic Epoxy System

Reinforced FibersHigh strength parallel to fiber direction

Chemical M odification of MatrixLim its stresses between metal inserts and epoxy

Epoxy Systems That Exhibit Epoxy Systems That Exhibit Excellent Cryogenic Excellent Cryogenic

PerformancePerformance• System ASystem A• 100pbw - Modified

Bis-A Epoxy• 57pbw - Hardener A• 10 pbw -

Cycloaliphatic Diamine

• System BSystem B• 100pbw – Modified Bis-A

Epoxy• 15pbw – Hardener A• 37pbw – POPDA (High

Molecular Weight)• 20pbw – POPDA (Low

Molecular Weight)• 10pbw – Cycloaliphatic

Diamine

Properties of A and B Properties of A and B Cryogenic SystemsCryogenic Systems

Property System A System B

Viscosity, cps, 25°C 630 1,000

Gel time, min., 25°C 990 1,200

Barcol Hardness 63.5 45.0

Thermal shock, cycles >25 >25

Impact strength, Nm/mm notch

@ 298°K@ 80°K

  

0.020.01

 

 

0.0410.015

Flexural strength, psi@ 298°K@ 77°K@ 4.2°K

12,32540,55529,435

4,64023,200

_Flexural modulus, psi@ 298°K@ 77°K@ 4.2°K

391,0001,044,0001,102,000

101,5001,059,000

-

Thermal Shock Specimen

Epoxy

Steel Bolt

Gel Time vs. Cure SpeedGel Time vs. Cure Speed

• Gel Time is defined as the required time for a system to make an exothermic state change from liquid to solid.

• Cure speed is the time it takes for a system to actually cross link with itself in order to form a lattice structure.

Low Temperature CuringLow Temperature Curing• Phenalkamines -

excellent for low temperature curing

• POPDA – gives excellent properties

• Accelerators such as benzyl alcohol, salicylic acid, and dimethylaminopropyl- amine

Property Amine A Phenalk- amine

Gel time, min., 25°C

66 50

Pencil Hardness 3H 3H

Cure through time (5°C) >24 hours 16 hours

Direct Impact Test (in/lb) 14 12

Cracking of Epoxies in Cracking of Epoxies in Structural ApplicationsStructural Applications

• Epoxies crack in many electrical apparatus due to sudden changes in temperature.

• Cracks usually start in areas of high stress

• High stress areas include places where a metal or ceramic insert is placed.

Fracture ToughnessFracture Toughness• This is measured by

calculating KIc and GIc of a material.

• The above figure illustrates different modes of fracture testing

• The below figure illustrates a double torsion method used on filled materials

[K1c]2 = E* G1c * (1-ν)

Toughening ConceptsToughening Concepts

• Incorporating crack-arresting micro-phases such as fillers, short fibers, micro-voids, glass beads, thermoplastics, and rubbers

• Matrix flexibilization

• Material G1c[J/m2]

 • Pure metals

1,000,000• Steel

100,000 Titanium alloys 53,000 Aluminum alloys 30,000• Polypropylene 8000• Polyethersulfone 2500• Rubber toughened-epoxy 2000• Polycarbonate 800• Bis-Aepoxy / DDS 250• Marble 20• Window glass 7

Core-shell TougheningCore-shell Toughening• Incorporates a fine

dispersion of soft particles as a second phase within the epoxy matrix

• Such particles, with sizes less than 1 micron have a core structure that absorbs energy and a shell that provides for good adhesion to the epoxy matrix.

 

Core-Shell Morphology

Core: Elastomer, high energy absorption

Shell: Thermoplastic, good matrix adhesion

New Development:Shell crosslinked

Particle size < 1 m

Testing Crack Resistance

15034. 3

Specimen for Crack Test

Diverses03/risspey2.ds4

filled epoxy

Thermal Cycle Soak Test

0 10 20 30 40 50 60 70 80 90 100

-60

-50

-40

-30

-20

-10

0

10

20

Tem

pera

ture

[°C]

hours [h ]

d ive rse s0 3/tem ptes t.g rf

2 h

24 h

Tem perature P rofile for H exagonal C rack Test

Results of Soak Testing

+140 +25 0 -20 -40 -50 -600

20

40

60

80

100

HI

T em perature [°C ]

StandardT g = 115-120°C

K IC = 1.7-1.9

T oughenedT g = 115-120°C

K IC = 2.4-2.6

ConclusionsEpoxies noted for:

Excellent mechanical strengthOutstanding dielectric propertiesExcellent chemical resistance

Increased usage in medium and high voltageapplications where subject to hostileenvironments

ConclusionsDifferent approaches are available to formulatorsto improve toughness critical in low temperatureapplications

• Matrix flexibilization• Multiphase toughening