[SI-LIST] Re: Metal to Metal Question
- From: jrbarnes@xxxxxxxxxxx
- To: dave_hoover@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Thu, 11 Oct 2001 15:24:40 -0400
Dave,
Here are two excerpts from part 1 of my article, "Designing Electronic =
Equipment
for ESD Immunity," to help you. This appeared in the July 2001 Print=
ed
Circuit Design magazine (vol. 18 no. 7, pp. 18-26) and can be downlo=
aded from
http://www.pcdmag.com/story/OEG20010928S0122
B3. Choose shield materials, fastener materials, and gasket materials =
to
minimize corrosion-- see Table 2:
* Parts that will be in contact should have electromotive forces =
(EMF's)
within 0.75V of each other; within 0.25V if they will be used i=
n a salt-
spray environment.
* The anodic (positive) part should be larger than the cathodic (=
negative)
part.
Table 2: Galvanic Series
electromotive force (EMF), Resistivity
Material Volts Nano-ohm-meters=
---------------------- ------------------------------ ---------------=
--------
(anodic, corrodes)
Magnesium +2.37V 42
Magnesium alloys 50-175
Aluminum +1.66V 27
Zinc +0.76V 60
Galvanized steel 100-197
Aluminum alloys 27-86
Chromium +0.74V 132
Cadmium +0.40V 73
Mild steel +0.44V 100-197
Iron +0.44V 101
Tin-lead solder 145-195
Stainless steel (active) 560-780
Lead +0.13V 206
Tin +0.14V 126
Nickel +0.25V 69
Brass 61-110
Beryllium copper 29-115
Copper -0.34V 17.2
Bronze 91-212
Monel 510-614
Silver solder 22-172
Stainless steel (passive) 560-780
Titanium alloys 482-1700
Silver -0.80V 16
Titanium +1.63V 540
Gold -1.50V 22
(cathodic, passive)
Notes:
1. Some authors define the electromotive force as the oxidation potent=
ial, and
some as the reduction potential,
which are exact opposites. I followed the scheme used in the C=
RC
Handbook of Chemistry and Physics,
78th ed (1997-1998), pages 8-20 to 8-30. The Standard Hydrogen El=
ectrode
is defined as exactly 0V.
2. The electromotive force for alloys depends on the alloying elements=
and
their exact proportions, thus they can
take a range of values. Table 2 shows the approximate center of =
the range
of electromotive forces reported
in the references below.
3. Titanium is a wierdo. Clean titanium surfaces are almost as active=
as
aluminum. But titanium very quickly
grows an tough oxide film that passivates the surface and protect=
s it from
further corrosion, making it almost
as passive as gold.
My books and other source materials for the article are at home, but so=
me of the
sources I used to compile this table were:
[1] AFSC Design Handbook 1-4 Electromagnetic Compatibility. July 15,
1987. (Design notes 5D2, 5D3, 5F6)
[2] Designing for Immunity to Pulsed EMI. Keytek Instrument Corp.,
Wilmington, MA, 1990.
[14] ASM International, Metals Handbook 9th edition Volume 13 Corrosion=
.
ASM International, Metals Park, OH, 1987.
[16] Barnes, John R., Electronic System Design: Interference and Noise=
Control Techniques. Prentice-Hall, Englewood Cliffs, NJ, 1987.
[17] Boxleitner, Warren, Electrostatic Discharge and Electronic Equipme=
nt-- A
Practical Guide for Designing to Prevent ESD Problems. IEEE Press, New=
York,
1989.
[21] Chomerics, EMI Shielding for Military/Aerospace Electronics, 1998.=
(download from http://www.chomerics.com/)
[39] Kimmel, William D, and Gerke, Daryl D., Electromagnetic Compatibil=
ity in
Medical Equipment. IEEE Press and Interpharm Press, Piscataway, NY, 19=
95.
[44] Lide, David R., and Frederikse, H. P. R., CRC Handbook of Chemistr=
y and
Physics, 78th ed. CRC Press, New York, 1997-1998. (pages 8-20 to 8-30=
)
[49] Mardiguian, Michel, Grounding and Bonding Volume 2. Interference
Control Technologies, Gainesville, VA, 1988.
[51] McAteer, Owen J., Electrostatic Discharge Control. McGraw-Hill, N=
ew
York, 1990. (section 12.12, pages 339-340)
[59] Ott, Henry W., Noise Reduction Techniques in Electronic Systems, 2=
nd
ed. John Wiley & Sons, New York, 1988.
[70] White, Donald R. J., A Handbook Series on Electromagnetic Interfer=
ence
and Compatibility Volume 3: EMI Control Methods and Techniques. Don Wh=
ite
Consultants, Germantown, MD, 1973.
[71] Williams, Tim, EMC for Product Designers. Newnes, Oxford, England=
,
1996.
[72] Williams, Tim, and Armstrong, Keith, EMC for Systems and
Installations. Newnes, Boston, 2000. (Section 10.2.2, pages 257-261)
[79] Department of Defense, Military Standard Corrosion Prevention and
Deterioration Control in Electronic Components and Assemblies,
MIL-STD-1250A, 29 June 1992. (download from http://www.dodssp.daps.mil=
/)
[80] Department of Defense, Military Standard Dissimilar Metals,
MIL-STD-889B, 7 July 1976. (download from
http://astimage.daps.dla.mil/docimages/0000/32/77/36032.PD5)
[80a] Department of Defense, Military Standard Grounding, Bonding and
Shielding Design Practices, MIL-STD-1857(EL), 30 June 1976. (download =
from
http://www.dodssp.daps.mil/)
[97] Ministry of Defence, "Metals and Corrosion Guide," Defence Standar=
d
02-738, Aug. 1992. (download from http://www.dstan.mod.uk/)
[99a] "A Galvanic Series of Certain Metals and Alloys Arranged In Order=
of
Corrosivity". (download from http://www.stusteel.com/galvseri.htm)
[107a] "Corrosion". (download from
http://www.gordonengland.co.uk/xcorrosion.htm
[107b] "Corrosion". (download from
http://www.er6.eng.ohio-state.edu/~SOBOYEJO/lecture18.html)
[107c] "Corrosion". (download from
http://www.cda.org.uk/megab2/elecapps/earthing/sec111.htm
[107d] "Corrosion Information". (download from
http://ccfast.com/ccfcorrosion.html)
[107e] "corrosion potentials graph". (download from
http://www.problemsolved.com/reference_library/HVAC_water/corrosion/
corrosion_potentials.htm)
[108] "Corrosion Potentials in Flowing Seawater". (download from
http://corrosion-doctors.org/Aircraft/galvseri-fig.htm)
[108a] "Corrosion susceptibility of metals". (download from
http://myhome.shinbiro.com/~dddgr/cu10.htm)
[108b] "Corrosion problems associated with stainless steel 4-1". (down=
load
from http://www.mcnallyinstitute.com/04-html/4-1.html)
[129] "Galvanic Compatibility". (download from
http://corrosion-doctors.org/Aircraft/galvseri-compat.htm)
[129a] "Galvanic Corrosion". (download from
http://corrosion.ksc.nasa.gov/html/galcorr.htm)
[130] "Galvanic Corrosion Potential". (download from
http://www.pemnet.com/design_information/galvanic.html)
[131] "Galvanic Series", 2000. (download from
http://www.corrosionsource.com/handbook/galv_series.htm)
[131a] "Galvanic Series: Corrosion Potentials in Flowing Seawater, (V v=
s SCE
Half-Cell Reference Electrode). (download from
http://www.corrprev.org.au/Galvanic.htm)
[131b] "Galvanic Series in Seawater". (download from
http://corrosion-doctors.org/Aircraft/galvseri-sea.htm)
[131b] "Galvanic series in sea-water at 10?C". (download from
http://www.alu-info.dk/Html/alulib/modul/A00106.htm)
[132] "Galvanic Series of Metals and Alloys". (download from
http://www.mcnallyinstitute.com/Charts/galvanic-series.html)
[132a] "galvanic series of metals and alloys". (download from
http://www.problemsolved.com/reference_library/HVAC_water/corrosion/
corrosion_galvanic_series.htm)
[133] "Galvanic Series of Metals in Sea Water". (download from
http://dixdesign.com/galvanic.htm)
[455] Erb, Lee, "Corrosion Control- Galvanic Table", Aug. 1997. (downl=
oad from
http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm)
[589] Groshart, Earl, "Corrosion Control in EMI Design," Electromagneti=
c
Compatibility 1977, Zurich, Switzerland, June 28-30, 1977, pp. 229-232.=
[970] Pennisi, Mario S., "Why Apply a Coating-- Corrosion?". (download=
from
http://www.ifinishing.com/Library/pennisi/corrosion.html)
John Barnes Advisory Enginee=
r
Lexmark International
=
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