Robert Kultzow TRFA 2005 November 15, 2005
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Transcript of Robert Kultzow TRFA 2005 November 15, 2005
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Robert KultzowRobert Kultzow
TRFA 2005TRFA 2005
November 15, 2005November 15, 2005
Epoxy Systems For Below Zero Degrees CelsiusEpoxy Systems For Below Zero Degrees Celsius
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Features of Epoxy ResinsFeatures of Epoxy Resins• High mechanical strength • Outstanding dielectric
characteristics• Excellent adhesive
properties• Great Chemical resistance• Phenomenal thermal
endurance
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Performance at Lower Performance at Lower Operating TemperaturesOperating Temperatures
• Speed and effectiveness of cure
• Fracture toughness
• Thermal Expansion characteristics
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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
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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
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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
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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
-
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Thermal Shock Specimen
Epoxy
Steel Bolt
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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.
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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
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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.
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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)
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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
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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.
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Core-Shell Morphology
Core: Elastomer, high energy absorption
Shell: Thermoplastic, good matrix adhesion
New Development:Shell crosslinked
Particle size < 1 m
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Testing Crack Resistance
15034. 3
Specimen for Crack Test
Diverses03/risspey2.ds4
filled epoxy
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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
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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
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ConclusionsEpoxies noted for:
Excellent mechanical strengthOutstanding dielectric propertiesExcellent chemical resistance
Increased usage in medium and high voltageapplications where subject to hostileenvironments
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ConclusionsDifferent approaches are available to formulatorsto improve toughness critical in low temperatureapplications
• Matrix flexibilization• Multiphase toughening