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Epoxy Systems For Below Zero Degrees Celsius. Robert Kultzow TRFA 2005 November 15, 2005. Features of Epoxy Resins. High mechanical strength Outstanding dielectric characteristics Excellent adhesive properties Great Chemical resistance Phenomenal thermal endurance.

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robert kultzow trfa 2005 november 15 2005

Epoxy Systems For Below Zero Degrees Celsius

Robert Kultzow

TRFA 2005

November 15, 2005

features of epoxy resins
Features of Epoxy Resins
  • High mechanical strength
  • Outstanding dielectric characteristics
  • Excellent adhesive properties
  • Great Chemical resistance
  • Phenomenal thermal endurance
performance at lower operating temperatures
Performance at Lower Operating Temperatures
  • Speed and effectiveness of cure
  • Fracture toughness
  • Thermal Expansion characteristics
uses of epoxies at lower temperatures and cryogenic conditions
Uses of Epoxies at Lower Temperatures and Cryogenic Conditions
  • Nuclear physics apparatus
  • Super conducting devices comprised of magnets and transformers
  • Magnetic imaging devices
epoxy systems that exhibit excellent cryogenic performance
System A

100pbw - Modified Bis-A Epoxy

57pbw - Hardener A

10 pbw -Cycloaliphatic Diamine

System B

100pbw – Modified Bis-A Epoxy

15pbw – Hardener A

37pbw – POPDA (High Molecular Weight)

20pbw – POPDA (Low Molecular Weight)

10pbw – Cycloaliphatic Diamine

Epoxy Systems That Exhibit Excellent Cryogenic Performance
properties of a and b cryogenic 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

0.02

0.01

0.041

0.015

Flexural strength, psi

@ 298°K

@ 77°K

@ 4.2°K

12,325

40,555

29,435

4,640

23,200

_

Flexural modulus, psi

@ 298°K

@ 77°K

@ 4.2°K

391,000

1,044,000

1,102,000

101,500

1,059,000

-

Properties of A and B Cryogenic Systems
thermal shock specimen
Thermal Shock Specimen

Steel Bolt

Epoxy

gel 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.

Gel Time vs. Cure Speed
low temperature curing

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

Low Temperature Curing
  • Phenalkamines -excellent for low temperature curing
  • POPDA – gives excellent properties
  • Accelerators such as benzyl alcohol, salicylic acid, and dimethylaminopropyl- amine
cracking of epoxies in structural applications
Cracking of Epoxies in Structural 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 toughness
Fracture 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 concepts
Incorporating crack-arresting micro-phases such as fillers, short fibers, micro-voids, glass beads, thermoplastics, and rubbers

Matrix flexibilization

MaterialG1c[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

Toughening Concepts
core shell toughening
Core-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.
conclusions
Conclusions

Epoxies noted for:

Excellent mechanical strength

Outstanding dielectric properties

Excellent chemical resistance

Increased usage in medium and high voltage

applications where subject to hostile

environments

conclusions1
Conclusions

Different approaches are available to formulators

to improve toughness critical in low temperature

applications

  • Matrix flexibilization
  • Multiphase toughening
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