Potters Industries Inc. an affiliate of PQ Corporation Potters Conductives Potters Conductives Solving the Galvanic Corrosion Issue In EMI Shielding Harry Fuerhaupter Potters Industries Inc. Research & Development Center 280 Cedar Grove Road, Conshohocken, PA 19428 TEL: 610-651-4780 EMAIL: [email protected]www.pottersbeads.com
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Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
Conductives
Solving the Galvanic Corrosion IssueIn EMI Shielding
Harry FuerhaupterPotters Industries Inc.
Research & Development Center280 Cedar Grove Road, Conshohocken, PA 19428
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesOutline
• What is galvanic corrosion• Basic preventative measures• Specific problem with conductive gaskets• Unique behavior of conductive fillers• New conductive filler for low aluminum corrosion
Potters Industries Inc.an affiliate of PQ Corporation Potters
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesUniform corrosion
• Diagram of zinc in acidZn2+
H+
H+
H+
H2
H+
e-
e-
Zinc
Hydrochloric Acid Solution
Cl- H+
Cl-
Zn Zn2+ + 2 e –
2 H+ + 2 e – H2
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesGalvanic Corrosion
• When two dissimilar metals contact each other in a corrosive environment, the less corrosion-resistant metal experiences more corrosion than when it is not in contact with the other metal.
Steel bolt in steel plate Brass bolt in steel plate
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesGalvanic corrosion
• Diagram of zinc/steel in acidZn2+
H+
H+
H+
H2
H+ Cl-
H+Cl-e-
e-
Hydrochloric Acid SolutionH+
H+
H+H2
e-
e-
Zn2+Zinc
Steel
Zn Zn2+ + 2 e –
2 H+ + 2 e – H2
Fe Fe2+ + 2 e –
- 0.763 V
- 0.440 V
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesGalvanic Corrosion
• The greater the difference in corrosion potential between two metals is, the greater the galvanic corrosion effect is.
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesWC-Aluminum Corrosion Testing
Aluminum Corrosion in Salt Spray
1
10
100
1000
0 200 400 600
Hours of Exposure
Wei
ght L
oss
(mg)
WC-Aluminum
Ag/AluminumNi-Graphite
WC-Aluminum causes significantly less galvanic corrosion on aluminum than nickel/graphite and silver/aluminum
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesWC-Aluminum in Fluorosilicone Gasket
0.1
1
10
100
66 68 70 72 74 76Filler (wt%)
Volu
me
Res
istiv
ity (Ω
-cm
)
60
65
70
75
80
85
90
Har
dnes
s (S
hore
A)
Resistivity Aged Resistivity Hardness
Aging = 48 hours at 200C
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesWC-Aluminum Shielding Effectiveness
Shielding Effectiveness
0
20
40
60
80
100
120
140
30MHz
40 60 80 100 200 400 600 800 1GHz
2 4 6 8 10
Frequency
SE (d
B)
WC-Aluminum has excellent shielding effectiveness between 30MHz and 10 GHz
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesTheory of shielding at 1 Ω-cm
• Porous materials with relatively high volume resistivity have shown shielding capability– Nickel-loaded black rice husk: 80 dB @ 30 MHz to 60 dB @ 1.5 GHz
Journal of Materials Science, 39 (2004), pp. 6209 - 6214– Carbonized wood ceramic: 50 dB from 30 MHz to 1 GHz
Journal of Porous Materials, 4 (1997), pp. 269 – 275
Aluminum
WC
Pore
A C
DB
Pore
Potters Industries Inc.an affiliate of PQ Corporation Potters
• WC-Aluminum filler materials have the right combination of properties to meet the challenges of corrosive environments.
• Some environments where WC-Aluminum could offer improved EMI gasket performance include:– High salt environments - marine– Outdoor enclosures exposed to various weather– High sulfur environments, such as exposure to fuel vapors– Strong chemical exposure, such as bleach for disinfection– Large thermal variations, e.g. aerospace and automotive
• Since WC-Aluminum contains no silver, the cost is closer to nickel-graphite.
Potters Industries Inc.an affiliate of PQ Corporation Potters
ConductivesPotters
ConductivesAdditional considerations• Blending WC-Aluminum and Ag/Aluminum