Transcript Document

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
Performance at Lower
Operating Temperatures
• Speed and
effectiveness of cure
• Fracture toughness
• Thermal Expansion
characteristics
Uses of Epoxies at Lower
Temperatures and Cryogenic
Conditions
• Nuclear physics apparatus
• Super conducting devices comprised of
magnets and transformers
• Magnetic imaging devices
Pathways to Development of a
Cryogenic System
Epoxy Resin Sytem
<Title>
Inorganic Fillers
Lower CTE
Chemical Modification of Matrix
Reinforced Fibers
High strength parallel to fiber direction Limits stresses between metal inserts and epoxy
Final Cryogenic Epoxy System
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
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
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
12,325
40,555
29,435
4,640
23,200
_
391,000
1,044,000
1,102,000
101,500
1,059,000
-
Barcol Hardness
Flexural strength, psi
@ 298°K
@ 77°K
@ 4.2°K
Flexural modulus, psi
@ 298°K
@ 77°K
@ 4.2°K
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.
Low Temperature Curing
Property
Amine A
Phenalkamine
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
• Phenalkamines excellent for low
temperature curing
• POPDA – gives
excellent properties
• Accelerators such as
benzyl alcohol,
salicylic acid, and
dimethylaminopropylamine
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
• 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 crackarresting micro-phases
such as fillers, short
fibers, micro-voids,
glass beads,
thermoplastics, and
rubbers
• Matrix flexibilization
•
Material
•
•
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
•
•
•
•
•
•
•
G1c[J/m2]
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.
Core-Shell Morphology
Particle size < 1 m
Core: Elastomer, high energy absorption
Shell: Thermoplastic, good matrix adhesion
New Development:
Shell crosslinked
Testing Crack Resistance
S
p
e
c
im
e
nfo
rC
ra
c
kT
e
30. 0
fille
de
p
ste
Thermal Cycle Soak Test
Temperature Profile for Hexagonal Crack Test
24 h
20
10
Temperature [°C]
0
0
10
20
30
40
50
60
70
80
90
100
-10
-20
-30
-40
-50
-60
hours [h]
2h
diverses03/temptest.grf
Results of Soak Testing
Toughened
Tg = 115-120°C
KIC = 2.4-2.6
100
80
60
40
20
0
Standard
Tg = 115-120°C
KIC = 1.7-1.9
I
H
+140
+25
0
-20
-40
Temperature [°C]
-50
-60
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
Conclusions
Different approaches are available to formulators
to improve toughness critical in low temperature
applications
• Matrix flexibilization
• Multiphase toughening