Revised April 1970
INQUIRY INTO THE ECONOMIC EFFECTS
OF AIR POLLUTION ON ELECTRICAL CONTACTS
Prepared for:
DIVISION OF ECONOMIC EFFECTS RESEARCH
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
1033 WADE AVENUE
RALEIGH, NORTH CAROLINA 27605
Attention: MR. JAMES B. UPHAM
CONTRACT PH-22-68-35
STANFORD RESEARCH INSTITUTE
Menlo Park, California 94025 • U.S.A.
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VII
VIII
CONTENTS
'\
-I
INTRODUCTION
. . . . .
.. . .. .
. . . . . .
. . . . .
. . . . .
II
SCOPE
. . . . . . . . .
. . . .
. . . . .
. . . .
III
SUMMARY
. . . .
. . . .
. . . . . .
IV
INFORMATION SOURCES
.......
. . . . .
. . . . .
A.
B.
Literature Search
. . . . .
. . . .
. . . . . . .
Direct Personal Communication
. . . .
. . . .
C.
Problem Analyses.
. . . . . . . . . . . . .
. . . .
. . . .
. . . .
. . . .
V
THE ELECTRICAL CONTACT CONTAMINATION PROBLEM
. . . . .
. . . . . . .
. . . . . .
VI
SIGNIFICANT AIR POLLUTANTS
. . . . .
. . . . .
A.
B.
Sulfur Gases. . .
. . . . . . .
. . . . . .
Organic Gases
. . . . . .
. . . . .
C.
Particulate Pollutants. . . .
. . . . . . . . .
ECONOMIC EFFECTS. . . . . .
. . . . . . .
. . . .
AIR POLLUTION EFFECTS ON HIGH VOLTAGE POWER TRANSMISSION. . .
ACKNOWLEDGMENTS
. . . .
. . . .
. . . . .
. . . . .
APPENDIX A:
ANNOTATED BIBLIOGRAPHY
. '. . . . . . . . . . .
APPENDIX B:
PERSONAL CONTACTS. . . . .
. . . .
. . . . . . .
APPENDIX C:
GENERAL ELECTRICAL CONTACT AND CONTAMINATION
FLASHOVER BIBLIOGRAPHY. . . . . . . . . . .
i
. . . .
. . . . .
. . . .
. . . . .
. . . . .
. . . . .
. . . . A-I
. . . B-1
. . . . . C-l
1
3
7
11
11
13
14
15
19
19
21
23
25
29
30
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I
INTRODUCTION
A significant part of the total cost of air pollution is directly
related to the effects of air pollution on materials.
The National Air
Pollution Control Administration wishes to analyze this cost, and one
of the areas of particular interest is the effect of air pollution on
electrical contacts.
These devices have a special importance because
they are components of extensive communications, computer, and instru-
mentation systems.
The highest degree of reliability and performance
is required from electrical contacts to obtain satisfactory overall
operation in these systems.
The specific goal of this study was to survey, identify, and docu-
ment problems of economic significance caused by air pollution in the
utilization and operation of electrical contacts and other electrical
devices.
If air pollution does cause problems, they were to be de-
termined and analyzed by searching the literature, by consulting with
experts in the field of electrical contact technology, and by consulta-
tion with electrical engineers, manufacturers of electrical contacts,
and users of electrical devices.
1
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II
SCOPE
Contaminants from sources other than air pollution affect electrical
contacts and produce the same or similar deleterious effects; therefore,
it is important to define the term "air pollution."
For the purpose of
this report, air pollution is considered to be contamination from ex-
ternal sources, and will include only airborne pollutants whose source
is outside the building that houses the electrical contacts.
Electrical contacts are conductor pairs that may carry an electrical
current when their separable surfaces are in contact.
Contacts are used
in switches, relays, connectors, potentiometers, and commutators.
Switches
are used to interrupt the flow of current in an electrical circuit.
A
relay is a switch operated by an electromechanical device such as a so-
lenoid.
A connector is usually a multiple-contact device permitting the
separation of equipment from power sources or from other equipment.
A
potentiometer, which consists of a contact sliding on a resistive element,
is used to vary the flow of current.
Finally, a commutator is a disc or
cylinder consisting of metal contact segments separated by insulation;
a brush contact rides on the segments, making contact with them sequen-
tially as the disc or cylinder rotates.
Contacts are made from a wide variety of materials by a number of
techniques. Common materials are precious metals (gold, platinum, palla-
dium, silver), refractory metals (tungsten, molybdenum), and base metals
(copper, tin, lead, zinc, aluminum). Occasionally metals are used in
the pure state, but more often combinations of metals are used.
A con-
tact may be made of a single material, or may be a two-layer structure
having bonded or electroplated gold or palladium on a base metal sub-
strate.
Electroplated contacts are probably the best compromise between
cost and performance.
From the standpoint of contamination, contacts must be differen-
tiated according to the magnitude of the current and voltage being
swi tched.
Switching in low-power circuits (millivolts and microamperes)
is easily interrupted by thin insulating surface films on contacts.
Air
pollution-caused films of this type result in poor performance with base
3
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metal contacts.
Therefore, in low-power circuits, contact materials
considered resistant to the formation of surface films are usually used.
Computers, communications equipment, and electronic instrumentation ex-
tensively employ low-power switching.
Although insula~ing films are troublesome in low-power switching,
they generally do not present a problem at higher power levels because
the films undergo dielectric breakdown at higher voltage.
Much greater
amounts of contact contamination are necessary to affect operation under
these conditions.
In any assessment of air pollution effects on contacts, it is im-
portant to consider the natural surface conditions of various contact'
metals.
For example, an atomically clean copper surface, upon exposure
to unpolluted air, immediately forms a layer of oxide several molecules
thick.
This layer continues to grow but at a progressively slower rate.
Hydrogen sulfide, which is a very minor component of the atmosphere,
will react with copper to form sulfide in the surface layer.
Carbonate
from C02 may also be included in the surface layer. The background
atmospheric aerosol is composed of silica and metal oxides, ammonium
sulfate, sodium chloride, anq other salts and organic material.
This
material adds to the surface layer both by deposition and by acceler-
ating corrosive attack.
Other base metals will behave in a similar
manner when exposed to unpolluted air.
All contacts exposed to both
unpolluted air and polluted air will show increasing contact resistance
with time.
The effect of air pollution on contact resistance behavior
is therefore one of degree, not of kind.
Precious metal contacts will
resist corrosive attack but they will, of course, acquire particulate
deposits.
While air pollution effects on electrical contacts are the principal
interest in this study, significant air pollution effects on any other
components of electrical or electronic systems were also of interest.
One such area which appears to have economic significance is the effect
of air pollution on contamination flashover at the insulators in high
voltage transmission systems.
Although not called for in the work state-
ment, it was mutually agreed by the technical representative and the
4
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author that this effect should be investigated.
Contamination flashover
can be caused by sea salt, natural dust, and other natural particulate
material, but air pollution adds significantly to this problem.
5
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III
SUMMARY
Prevention of contact failure in low voltage contacts is the largest
problem area in which air pollution effects on electrical contacts are
involved.
Millions of low voltage contacts are used in computer and in-
strumentation circuits and some provision must be made to ensure their
reliable and continued operation.
The sulfur gases are primarily re-
sponsible for the deleterious effect of air pollution on these contacts.
More money is spent in the protection of low voltage contacts against the
effects of sulfur gases than in all the other problem areas combined.
Protection of low voltage contacts against sulfur gases takes two
forms.
First, air conditioning and air purification equipment are used
to minimize or eliminate sulfur gas effects on contacts.
All computer
systems and most instrumentation systems now include air conditioning,
and some of these systems have high efficiency particulate and activated-
charcoal filter combinatidns added.
The total cost of this
air con-
ditioning and purification equipment for 1968 in the United States was
about $250,000,000.
The fraction of this cost assignable to air pollution
is somewhat arbitrary as the air conditioning would have been provided in
the absence of air pollution.
A tenth of the air conditioning-purification
cost, or $25,000,000, is a conservative estimate of the fraction charge-
able to control of air pollution effects.
The second kind of protection of contacts against sulfur gases is
precious metal plating.
The estimated value of gold and platinum used
in electrical contacts in the United States in 1968 was $140,000,000.
Of this total amount, according to industry estimates, only about 15%,
or $20,000,000, was used to combat air pollution. The larger fraction
(85%) of precious metal was used to counteract specific contaminants
from sources other than air pollution.
The use of precious metals in electrical contacts should be reduced
in the near future as new operational and design techniques are now being
developed that will give base metal contacts satisfactory performance
characteristics in hostile environments.
Palladium is used in many elec-
trical contact applications; it is corrosion-resistant and has excellent
7
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wear properties.
However, it is also a polymerization catalyst for many
organic compounds.
Hydrocarbon vapors present in the air around contacts
will polymerize on palladium and palladium alloy surfaces forming insu-
lating films and loose powder.
In telephone switching relays this material
is referred to as "frictional" polymer as its formation is greatly accel-
erated by rubbing or wiping during contact operation.
Large amounts of
this polymer on contact surfaces cause high resistance failure.
The com-
munications industry has chosen to meet this problem by removing hydro-
carbon vapor from the local environment rather than discontinue use of
palladium.
Palladium contacts, which may age several months or years before being
called upon to operate, present a special problem.
During any part of the
stand-by interval, exposure to hydrocarbon vapors may cause a polymer film
to form and grow.
A contact so coated is liable to fail during its first
operation.
Another palladium contact-polymer problem involves accelerated con-
tact erosion due to "contact activation" of arcing contacts.
The organic
material is carbonized by arc heating and the carbon layer increases the
arcing intensity which leads to erosion damage.
The communications industry has used gold on silver in some contact
applications.
When exposed to hydrogen sulfide, the silver sulfide formed
may migrate through microscopic pores in the gold electroplate and foul
the gold contact surface with an adherent silver sulfide film.
Another problem area in air pollution effects on electrical devices,
not related to electrical contact problems, is that of "contamination
flashover" across the insulators of high transmission lines.
Particulate
deposition on insulators combined with humid conditions or fog can even-
tually cause flashover.
Contamination from natural particulate is the
primary source of trouble but pollutants play an important secondary role.
Contamination flashover is prevented by periodic washing with high pressure
water.
Costs reported by U.S. power companies indicate that they spend
about $4,000,000 a year on insulator washing to prevent air pollution
effects.
8
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At the present time air pollution costs related to electrical devices
are unnecessarily high because in most of the problem areas, two or more
effective countermeasures are being applied simultaneously.
This over-
reaction is a response to the reliability problem in electrical contacts
which became serious and troublesome a few years ago.
Thus, while the cost relating to problems caused by air pollution in
the use of electrical devices for 1968 in the United States is estimated
to be about $50,000,000, more selective use of the most efficient measures
to eliminate air pollution effects could have reduced this cost.
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IV
INFOR~iATION SOURCES
A.
Literature Search
The search for literature on air pollution effects on electrical
contacts and contamination flashover was approached from several direc-
tions to ensure thorough coverage.
In general, material was included
if it pertained directly to electrical contact phenomena or to the eco-
nomics of air pollution of electrical contacts.
Initially it was decided
that formal coverage of abstracts and indexes would extend back to 1960,
and that general literature on corrosion and oxidation would not be
covered.
These limitations were set because:
(1)
Air pollution problems
of ten or twenty years ago were apt to be quite different than they are
today and much of the old literature would not be applicable, and (2) the
general literature on corrosion and oxidation was so extensive that cover-
ing all of it for a few references pertaining to electrical contacts was
prohibitive and inefficient.
Rather, it was felt that extensive coverage
of citations quoted by key authors would uncover specific corrosion and
oxidation references, and would provide any older work that was still
useful.
This proved to be the case.
The various approaches taken to uncover pertinent literature were
the following:
1)
A list of more than twenty authors active in the electrical
contact field was established on the basis of the frequency
of appearance in Electrical and Electronic Abstracts and
Applied Science and Technology for the period from 1960 to
1968, and an author search was made for each one covering
several literature sources.
2)
A list of companies producing electrical ~ontacts, or active
in research on electrical contacts, was also established.
Searching by company was done for those literature sources
which contained corporate author indexes.
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3)
Formal abstracting and indexing journals were surveyed and con-
siderable thought was given to choosing all the subject headings
that applied to pollution of electrical contacts.
If there were
cross references leading out of the chosen headings these were
investigated to see whether additional information would be found
at the new headings.
Subject headings change from source to
source but, in general, we covered such headings as Air Pollu-
tion, Capacitors, Commutators, Contacts, Corrosion (for specific
entries only), Flashover, Insulators, Electrical Motors, Elec-
trical Switchgear, Electric Signals, Slip Rings, Coatings (for
specific entries only), Finishes, Oxidation (for specific entries
only), Dust, Sulfides, Copper, Gold, Nickel, Palladium, Platinum,
and Pollution. The specific abstracting and indexing journals
covered were:
- Electrical and Electronics Abstracts, 1960 - May 1968
- Applied Science and Technology, 1960 - July 1968
- Chemical Abstracts, 1957 - July 15, 1968
- Battelle Technical Review, 1967 - Aug. 1968
- Science Citation Index, 1964 - 2nd Quarter 1968
- ASTM Review of Metal Literature, 1960 - 1967
- Current Contents, 1968
- Business Periodical Index, July 1966 - Dec. 1968
- TAB, STAR and Nuclear Science Abstracts were searched
for authors and corporate authors but subject searching
and searching by contract number was done by computer
by the agencies themselves.
4)
Custom searches were made by DDC, NASA, and AEC by subject as
listed above, personal author, corporate author, and contract
number.
5)
The bibliographies of reprints obtained were checked for more
pertinent literature references.
If titles were not available,
we frequently ordered a reprint of the reference cited in order
to check the subject content.
Literally thousands of references
were considered in this manner.
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6)
The tables-of-contents of current journals were covered for three
to six months back in order to pick up material that might have
been missed by abstract journals.
7)
Science Citation Index was covered for several key papers.
This
source allows one to go forward in time as well as backward, and
therefore uncovers recent work and new workers in the field.
8)
Most of the Holm Seminars on Electrical Contacts were obtained
and scanned for pertinent information, as were the International
Research Symposia on Electrical Contacts and the CIGRE conferences.
References, by author, title, publication, and date, considered per-
tinent, were alphabetized according to author and entered in reference
notebooks.
These references were then procured from our library or from
outside sources for screening.
The articles that were selected as per-
tinent after screening were copied, and those reprints entered in a set
of reprint notebooks.
The reference notebooks served as a record of what literature had
been covered and ordered, and they were mainly used for order records and
to avoid duplication.
The reprint notebooks were organized by author and
chronologically under each author.
This provided a brief survey of each
author's work and quickly pinpointed work that was missing.
The reprints
were read and further screened, and those considered most pertinent to the
subject were included in the Annotated Bibliography (Appendix A).
The re-
maining references are listed in the General Bibliography (Appendix C).
B.
Direct Personal Communication
Companies manufacturing electrical contacts, relays, switches, and
connectors; companies manufacturing electrical and electronic instruments;
companies using electrical contacts; and electrical power companies were
considered as sources of current industrial information concerning air
pollution effects on electrical contacts and high voltage power trans-
mission.
Technical or research people in these companies were contacted
by telephone or letter.
Site visits were then made to those people who
had a related problem or pertinent information concerning a related prob-
lem.
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In addition, the 1968 Holm Seminar on Electric Contact Phenomena was
attended and discussions were held with a number of people there.
C.
Problem Analyses
Most of the information leading to the identification and analysis
of the important problem areas was obtained from the technical people
contacted.
The literature was then used to fill in the technical details,
background, and to provide documentation in the analysis of these problems.
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v
THE ELECTRICAL CONTACT CONTAMINATION PROBLEM
Electrical contacts can be classified into three groups: light duty
contacts required to transmit low voltage and negligible power, contacts
carrying moderate currents at moderate voltages, and contacts required
to perform heavy duties.
The operating problems of heavy duty contacts
involve erosive and mechanical wear associated with arcing and large
forces in contact closure.
Heavy duty contacts are essentially immune
to contamination.
Light duty contacts, on the other hand, are extremely
susceptible to contamination.
Very thin films or very small foreign
particles can prevent electrical contact when voltages and closing forces
are small, Fedorov and Zakirov (1964), and Forster and Gebauer (1960).
From the point of view of electrical contact technology, contamina-
tion by air pollution is a minor part of the total contamination problem.
The total contamination problem is, however, severe, with many facets.
Sources of contamination from within the immediate environment constitute
a much greater threat to reliable contact performance than air pollution.
Bloomberg and Campbell (1961), Fairweather (1953, 1960, and 1962),
Freudiger (1960), Kaufman et ale (1960), and Mahler (1960) have all ex-
amined the details of contact contamination.
Wire insulation, plastic
components, paints, adhesives, and solder fluxes can release hydrocarbon
vapors and corrosive gases.
Other contaminants, such as oil droplets or
dirt particles, can be introduced at the time of manufacture or cleaning
or assembly, Egan (1968) and Lish (1960).
These problems of contamination from local sources occur in all low
voltage electrical contact systems, including hermetically sealed contacts,
Hyde (1964), Keller (1964), and Chaiken (1961).
Sealing relays in an inert
atmosphere, unfortunately, does not always give successful protection to
contact surfaces because it is so difficult to co~pletely exclude internal
sources
of contamination, Van Auken et ale (1967).
Contacts in moderate duty service show much less sensitivity to con-
taminants than low voltage contacts, but in the case of palladium contacts
frictional polymer buildup can be troublesome in atmospheres contaminated
with hydrocarbon vapors, Holm (1967) page 117.
15
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There is a very extensive continuing effort by industry to improve
all of the aspects of contact technology using all of the available
scientific and engineering resources,
Several annual national and inter-
national conferences dedicated either wholly or partially to research and
development of electrical contacts are held annually,
These include the
Holm Seminar on Electric Contacts, the International Symposium on Elec-
tric Contact Phenomena, the Electronic Components Symposium, the Annual
Symposium on Reliability, and the National Conference on Electromagnetic
Relays,
Two very important factors in contact contamination are humidity and
temperature,
High humidity plus high temperature makes a corrosive en-
vironment in the absence of pollutants,
In the presence of pOllutants,
humidity is a critical factor, for even high pollution level corrosion
rates are very slow at low relative humidities,
Thus, in the control of
air pollution effects on electrical contacts, it is very important to
control the humidity and temperature of the local environment, Evans
(1948-1960), Bowcott and Cleaver (1962).
High humidity can promote galvanic corrosion under some conditions
but this problem is generally not severe in contact application, Frant
(1961).
The only contact application in which high humidity may be desirable
is in the use of carbon brushes in commutator rings.
The water vapor has
the role of lubricant and decreases wear, but even here moderate humidities
are adequate, Elsey et aI, (1954), Moberly (1956),
The kinds of metals used in electrical contacts and their pertinent
properties as related to type of contact operation were summarized neatly
by Flatau (1967) in the following table. Blake (1958, 1961) and Chiarenzell:
(1966 and 1967) also have reported the results of comparative real time and
accelerated corrosion tests of the various metals used in electrical con-
tacts.
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Table I
CONTACT PROPERTIES OF METALS AND ALLOYS
I I Palladium Platinum I ""~I Silver- Silver- Silver- Silver- I Platinum-
Contact Silver Gold Copper Copper Palladium Tungsten RheDium Nickel Cadmium Gold Gold-
Material (72-98%) (20-50 %) (5-20%) Oxide Alloys Silver
(5-15%) (6-69-25 %)
Contact I
Resistance
I
I Very Low 1 Moderate I Very Low I Moderate I
Low Low Low
Tendency To:
Nil Below
Oxidise Nil 400.C Nil Nil High
Sulphide
T arDish High Nil Nil Nil High
Form
Polmyer
Deposi t Nil High Moderate Low Nil
Weld on
Closure Moderate Low Nil High High
ResiStance To:
I-' Arc
'I Erosion Moderate Moderate Good Poor Poor
Abrasion Poor Moderate High Poor Poor
Material Some -I
Transfer Some Some Low High
Available in
aU Shape! Yes Yes Yes No Yes
Ve~ Very
Coat Low Low Hig High Low
Remarka Associated Usually
insulalols used as
must be coating
chosen or overlay
wi[h cart
to guard
against
Silver
m~f.ar9~n ---
Low High Low Low
Nil Moderate Nil High High High Nil Low Nil
Nil High Low Nil Nil High High Nil Nil
Some Nil Nil Nil Nil Nil Moderate
Low Nil Nil Low Nil Low Low
Good to
Moderate High High Good Good Moderate .\\odcratc
Good High High High Moderate High High
Some Nil Nil Low Low Low Low
Yes No No Yes No No Yes
Low Nil
Nil Low
Poor Good
High High
Some Some
No Yes
Ve~
Hig Low
Used ..
coating
only
I Moderate I Moderate I Moderate I
I I Moderate I Very Moderate I High I High
Low High Moderate
Corrodes Oxides are Alloying
in the unstable clements
presence and low Pt,Ni,Si,
of some resistance Co or Ai.
organic
matcria18
- From:
G. Flatau, Reliable contacts and connections in the telecommunications plant.
Inst. Elec. Engr. Trans. (Australia), EE-3(1), 59-67 (Mar. 1967).
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VI
SIGNIFICANT AIR POLLUTANTS
A.
Sulfur Gases
Much more money is spent combatting the effect of S02 and H2S from
air pollution on low voltage electrical contacts than all the other air
pollution effects on electrical devices combined.
As always, the picture
is complicated by a number of factors.
First, it is difficult to make
a quantitative separation between natural H2S and pollution H2S; and
second, the presence and concentrations of other atmospheric components,
not necessarily pollutants, have a profound influence on the corrosive
potential of the sulfur gases.
The most important of these components
is water vapor; however, oxidants, particulate metal oxides, and organic
droplets that settle on the contact surfaces all tend to promote sulfur
gas corrosion by producing sulfuric acid or acid salts held in intimate
contact with the surface.
During the past 20 years, a great deal of effort has been directed
into the study of the mechanisms of sulfur gas attack on metal surfaces,
including specific studies of electrical contact systems; silver, copper,
gold plated copper, gold plated copper with nickel diffusion barrier,
and many other surfaces, Phillips (1962), Halstrdm (1961), and Snowball
et ale (1967).
Campbell (1965) and Campbell and Thomas (1968) have studied the
mechanisms and rates of tarnishing and corrosion of copper and silver
over a period of many years.
They have found that copper tarnishes much
more rapidly than silver in atmospheres containing H2S.
It reacts with
very dry H2S, silver does not. Silver is unreactive to S02 even at high
humidity, but copper reacts rapidly. A dry atmosphere containing both
H2S and S02 causes rapid reaction with both copper and silver.
All of this suggested that free sulfur vapor is the silver tarnish
component of the atmosphere and that it is produced by the reaction
2 H2S + S02 ~ 3 S + H20
or
2 H2S + 02 (in presence of water vapor) ~ 2 S + 2 H20
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This hypothesis was confirmed by passing New York City air through
pumice soaked in lead acetate, then over a silver surface. Any H2S was
completely removed by the lead acetate, but the silver tarnished at the
same rate as untreated air.
Campbell and Thomas (1968) also investigated the nature of the films
produced on copper and silver in polluted air.
The copper corrosion film
was composed of CuS with a small amount of CuO. As the film grew, the
CuS/CuO ratio remained constant. Silver tarnish was found to be AgS with
a trace of Ag2S04.
Abbott (1968) has also studied copper and silver tarnishing in the
laboratory. He added H2S, S02' and also sulfur vapor at realistic pol-
lutant concentration (1-100 ppb) to a synthetic air, 80% N2' 20% 02.
Water vapor was added to produce different relative humidities to a maxi-
mum of 90%.
The growth of Ag2S followed a linear rate law to film thickness of
at least 0.2 micron. Analysis of the film material on silver and copper,
tarnished with H2S or S, revealed that Ag2S and CuS were the principal
products. CuO was found in the Cu tarnish and traces of Ag2S04 were found
in the Ag2S.
One effect that has produced serious contact problems was first re-
cognized and studied by Egan and Mendizza (1960) and Frant (1960).
Where
contacts containing silver under gold or silver solder leads to gold con-
tacts are exposed to a tarnishing atmosphere, the Ag2S formed will creep
through pores in the gold plating and across boundaries onto gold surfaces.
Silver sulfide adheres more strongly to gold than to silver, Antler (1966),
Keil (1963), and Harding (1960).
Antler, Barte, and Brumbein (1967) have evaluated gold plated contacts
for corrosion resistance, and have shown that smoothness of the substrate
surface is very important, as is a diffusion barrier underplate between
the substrate and the gold film.
They also showed that pore blocking
corrosion inhibitors used with compatible lubricants help in the isola-
tion of the base metal substrate with a minimum thickness of gold plate,
Krumbein and Antler (1967).
20
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Paraffin and polyphenol ethers have shown promise as lubricants for
gold plated contacts, according to Antler (1967) and Chiarenzelli (1966).
The corrosiveness of urban atmospheres toward many metals has greater
dependence on sulfur dioxide concentration and humidity than any other
factor.
Lodge and Havlik (1960) and Lodge and Frank (1962) developed a
method of determining atmospheric corrosivity by measuring the amount of
attack on thin evaporated metal films.
As there are no direct experimental studies of real air pollution
effects on electrical contacts, field studies of nonferrous metal cor-
rosion are probably the best available means of assessing air pollution
of base metal contacts without further experimental studies.
Using zinc
as a typical nonferrous metal, the American Society for Testing Materials
made a comparison of the corrosiveness of various rural, urban, and marine
atmospheres in hot, moderate, and cold climates (Larrabee, 1961).
The
comparison was made by measuring the weight loss occurring to 4-by-6-inch
zinc specimens after exposure for one year.
State College, Pa., was taken
as a standard rural (clean) atmosphere.
Industrial atmospheres in Newark,
N.J., Bayonne, N.J., and London, England, produced 2 to 4 times the zinc
corrosion that occurred at State College, but probably the most signifi-
cant finding was the wide local differences found, which appeared to be
dependent on the sample location relative to the major pollution sources.
B.
Organic Gases
The most important air pollution effect on electrical contacts re-
lating to organic gases is the "frictional" polymer formation on sliding
or wiping palladium contacts.
The so-called "frictional" polymer was first studied and identified
by Hermance and Egan (1958).
Telephone switching relays using palladium
contacts were noticed to be subject to transient closure failures.
When
this occurred, a dark brownish deposit was always found on the contacts.
A study of the formation mechanism and composition of the material re-
vealed that it was formed from organic vapors, it was entirely organic,
and its formation rate was proportional to the number of cycles of contact
21
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operation or the amount of rubbing or wiping of the contact surface.
Hermance and Egan showed that organic vapors were the reacting species
and that a polymerization reaction was catalyzed by the palladium and
strongly promoted by the rubbing action between the contacts.
They also found that a small amount of polymer was beneficial, as
wear was reduced without greatly changing the electrical conductivity.
The phenomenon of organic polymer formation has been intensively
and extensively studied during the past decade.
In addition to Hermance
and Egan (1958) and Chaiken (1961), Campbell and Lee (1962) have investi-
gated various aspects of the problem.
Palladium and other platinum family
metals are surface catalysts for this reaction, which proceeds slowly on
static surfaces and is greatly accelerated by the rubbing or wiping action
of operating contacts, Mader (1966), and Fairweather (1966).
In operational practice the hydrocarbon vapor is usually produced by
outgassing of insulation and other plastic components in the electrical
system and only a very small part of polymer formation on telephone relay
contacts can be attributed to air pollution.
During the course of investigation of the frictional polymer problem
a number of possible solutions have been suggested.
Chaikin (1963) noted
that lead and iodine compounds inhibited polymer formation.
Gold is a
poor polymer producer and alloying palladium with gold greatly decreases
the formation of polymer.
Ruthenium (Ru) appears to be an inhibitor.
In
a discussion concerning polymer inhibition by Ru, W. DOherty, of Microdot
in South Pasadena, California, reported a recent claim that 4% Ru in Pd
completely inhibits polymer formation.
A second minor organic gas effect occurs with medium voltage contacts.
Hydrocarbon vapor is carbonized by arc heating during relay operation and
the carbon layer produced intensifies and changes the character of the
contact arc, W. E. Campbell (1962), Germer and Smith (1957 and 1958).
This effect is called "contact activation." The deposited carbon lowers
the minimum arcing potential and greatly increases arcing time per opera-
tion and thus leads to greatly increased erosion damage to the contact
surfaces.
22
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Here again, the fraction of erosion failures due to general atmos-
pheric organic gases is small, as outgassing of insulation and other
plastic components cause most of the contact activation problems.
C.
Particulate Pollutants
The effects of particulate material from air pollution on electrical
contacts are almost entirely chemical.
In urban areas the atmospheric
aerosol contains corrosive components, Keefer (1957), Maddock et al. (1957),
and Williamson et al. (1956).
In addition, this material is usually an
excellent adsorbent of corrosive gases and water vapor while suspended as
an aerosol and also after deposition.
Chiarenzelli (1963), in studying
the effect of particulate pollutants on electrical contacts, analyzed the
material collected in one New York location over a considerable period of
time on a fiberglass filter.
He found ferric chloride to be the main
corrosive component.
Other analyses of collected particulate from the
New York area show sulfate as the major anion, with iron and ammonium as
the main cations plus significant fractions of magnesium, lead, titanium,
vanadium, and copper.
This material is hygroscopic and mildly corrosive
to copper at 60% relative humidity, at 80% it is severely corrosive to
copper.
Several investigators over the past several years have reported
that the New York aerosol causes nickel "fogging."
This is believed to
be due to a catalytic oxidation reaction at the surface, producing a
nickel sulfate-nickel hydroxide film,
Pacific Bell Telephone had a particular pollution problem in Los
Angeles a few years ago when their wire spring relays started breaking
in large numbers.
Upon investigation it was learned that the ammonium
nitrate in the Los Angeles aerosol, upon settling on the wire springs,
caused stress corrosion cracking at humidities higher than 50%.
The
copper-zinc-nickel alloy used at the time was uniquely affected by the
combustion of high nitrate dust and high humidity.
Bell Telephone
changed its wire spring alloy composition and also installed high ef-
ficiency filters on the air intakes of exchanges having the old wire
springs, Hermance (1966), McKinney and Hermance (1967).
23
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VII ECONOMIC EFFECTS
There are three classes of low voltage contacts on the basis of mode
of operation:
(1) static connectors, (2) sliding contacts, and (3) relays.
\Vhile each of these kinds of contacts has its own problems of operational
design and of wear, they all have the common major problem of high contact
resistance caused by surface film, Solov'yeva (1964), and Freudiger (1962).
In critical contact application, surface films thicker than 10 angstroms
may affect reliability, films of 100 angstroms are completely insulating
to contacts operating at less than one volt, Baker (1964).
For the last four or five years, most of the electrical contacts and
connector manufacturers have taken the attitude that for low voltage con-
tacts and connectors, where thin tarnish or corrosion films pose a real
threat to contact or connector reliability, thick gold or palladium plate
was the answer, Fairweather et al. (1962), Angus (1962), Shtremberg and
Gayevskaya (1964), and Chaston (1967). So the trend has been to gold plate
contact with 100 to 200 microinches of gold, Ball et al. (1968) and the
consumption of gold in the U.S. has increased rather sharply from 500,000
ounces in 1963 to 2,000,000 ounces in 1968.
The value of the gold and
platinum metals (mostly palladium) used in electrical contacts in 1968
was almost $140,000,000 (estimated from Annual Report of the Secretary of
the Treasury, 1967). Even with this recent large increase in use, most
of the precious metal was used to minimize the effect of local contami.-
nation from sources other than air pollution.
Only 10 to 20% was used
to combat air pollution, according to an estimate made by V. G. Mooradian
while discussing the use of precious metals in contacts with the author.
Thus, the precious metal cost attributable to air pollution in the U.S.
for 1968 was about $20,000,000.
The electrical contact industry is actively seeking new solutions to
the contamination and corrosion problems.
At least some of the research
and development people involved believe that, in spite of increasing air
pollution, low voltage contacts made of base metal can be made to perform
at desired levels of reliability by utilizing proper design concepts.
25
-------
One such approach involving high pressure electrical contacts has been
suggested by King (1967).
By the simple expedient of optimum mating and
surface design, and the use of relatively high closing pressures, he has
demonstrated that base metal contacts can be operated in polluted atmos-
pheres without excessive wear by penetrating the corrosion film with each
contact closure.
The use of computers and sophisticated electronic control systems in
the U.S. has expanded at a rate of about 30% per year for the past three
years.
The gross value of this electronic equipment installed in 1968
was about three billion dollars (U.S. Census Bureau, Annual Survey of
Manufacturers, Value of Shipments of Product Classes 27, 29, 1967).
Reliability of operation of this expensive equipment is obviously of
primary importance, Bryant (1968), Atkinson (1964), and New (1960).
Air
pollution effects on electrical contacts during operation could quickly
jeopardize this all important reliability.
Manufacturers of these systems
attempt to minimize air pollution effects by using precious metal contacts,
and by including air conditioning facilities in the computer system, Wagner
et al. (1961), and Blake (1959).
It is desirable and frequently necessary
to cool and dehumidify the air for these electronic systems even where air
pollution is absent.
Therefore, only a fraction of the $250,000,000 per
year cost of air conditioning equipment can be charged to air pollution.
This includes activated carbon filters and high efficiency fine particle
filters which are used in a few urban areas such as Los Angeles.
It is
our estimate that the cost of air conditioning and purification equipment
assignable to air pollution is about one-tenth of the cost of the air
purification equipment, or $25,000,000.
cost chargeable to air pollution.
This is the largest recognizable
The air pollution costs to high voltage power transmission are essen-
tially embodied in the measures taken to prevent contamination flashover,
. "h t h . "
1.e., 0 was 1ng.
Southern California Edison Company's cost for this
was reported in Electric Light and Power, August 1969, page 43.
The esti-
mated cost at SCE for 1969 is $1,000,000.
As SCE represents about 5% of
the electric power industry, the cost for the entire country can be con-
servatively estimated to be ten times this amount.
Forrest et al. (1960)
26
-------
made an analysis of contamination flashover frequency in terms of sea
salt contamination versus total contamination in the United Kingdom.
This analysis showed 40% of contamination flashovers due to industrial
pollution.
Extrapolating this fraction to the U.S. and using $10,000,000
as an estimated washing cost, the annual cost of air pollution in con-
tamination flashover is about $4,000,000 at the present time.
A more
~
detailed discussion of this problem is contained in the following section.
27
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VIII
AIR POLLUTION EFFECTS ON HIGH VOLTAGE POWER TRANSMISSION
The air pollution problem relating to high voltage power transmis-
sion was included in this evaluation because it appeared to be significant
in connection with the economics of electrical devices.
Insulator flashover in humid and polluted atmospheres is a major
transmission line problem.
This kind of flashover is called contamina-
tion flashover as opposed to flashover caused by atmospheric ionization
during thunderstorms.
The mechanisms involved in producing contamination
flashover are complex and only partially elucidated even though the phe-
nomenon has been studied for many years, Hampton (1964), Ely and Lambeth
(1964), Fujitaka et ale (1968), and Kawai (1968). In recent years the
power companies have gradually increased transmission line voltages from
about 250 kV to as high as 750 kV as their power requirements increased
(Gothberg et al., 1968).
In doing this the contamination flashover prob-
lem has become intrinsically much more severe, and it has been necessary
to improve insulator design continually.
It is known that contamination
flashover occurs when insulator surfaces, which have deposited layers of
material from the atmosphere, are wetted by high humidity, fog, or rain.
Alston and Zoledziowski (1963) have analyzed this phenomenon and shown
that a minimum conductance gradient through the contaminant layer is
required.
Much contamination flashover is caused by deposited sea salt
in regions where salt aerosol concentrations are high.
Silica and silicate
dust are not as liable to cause flashover as salt or certain deliquescent
air pollutants.
In recent years the particulate burden in industrial areas
composed mostly of soot, fly ash, sulfur compounds, coal dust, and cement
dust, adding to the loading on high voltage insulators, has caused con-
tamination flashover to become a severe problem in those areas downwind
of the sources, Ely and Roberts (1968).
In many areas in the northern U.S., calcium chloride is used on high-
ways to remove snow and ice.
During the spring and summer, much of this
CaC12 is picked up by the winds and some of it is deposited on high voltage
insulators to become a particularly troublesome contamination component.
This was reported by M. Kawai in 1968 at the General Electric UHV Labora-
tory in Pittsfield, Massachusetts.
29
-------
A number of methods have been developed to minimize contamination
flashover, Lambeth (1964).
Oil or grease films have been used; silicon
grease was found to be effective but expensive, Lambeth et al. (1966),
Ignacz (1962), and Harris (1954).
The most successful measure appears to
to be "hot washing," i.e., washing the insulators with very high pressure
streams of water without interrupting service, ona preventive schedule,
Last et al. (1966), Gaiennie (1960), and Hill (1947).
Acknowledgments
Miss Elizabeth Feinler and Miss Caroline Arnold made the literature
search for this study.
Dr. Saul W. Chaikin, Micrex Corporation, Mountain
View, California, and Dr. Wilfred W. Campbell, Department of Materials
Engineering, Rensselaer Polytechnic Institute, Troy, New York, were con-
sultants.
30
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APPENDIX A
ANNOTATED BIBLIOGRAPHY
-------
ANNOTATED BIBLIOGRAPHY
Abbott, W. H. and H. R. Ogden. Electrical contact materials in low
~current technology, Battelle Tech. Rev. 14 (3), 17-22 (1965).
Low-current contacts are of prime importance because of their
influence on the reliability of vital electronic systems.
Future improvements will depend on extending the basic knowl-
edge about material properties and contact phenomena. The
causes of failure of various types of contacts and factors
involved in designing materials for improved devices are dis-
cussed.
Abbott, W. H. The mechanism of tarnishing of silver and copper, In:
Electrical Contacts, 1968, Proc. Engineering Seminar on Elec-
trical Contact Phenomena, Illinois Institute of Technology,
Chicago, Ill., Nov. 11-15, 1968, PP. 53-4.
A study was made of the effects of environment on the tarnishing
reactions of high purity silver and copper. The objectives of
the research were (1) to determine the composition of the sur-
face films formed under several environmental conditions, and
(2) to relate film composition and/or structure to contact re-
sistance characteristics.
Alston, L. L. and S. Zoledziowski. Growth of Discharges on polluted
insulation, Proc. Inst. Elec. Engrs. 110 (7), 1260-6 (1963).
The voltage required to maintain local discharges on polluted
insulation may increase with increase in discharge length, and
if this voltage exceeds the supply vOltage, the discharges ex-
tinguish without causing a flashover.
Angus, H. C. Surface films on precious-metal contacts.
Phys. ~~, 58-63 (1962).
A study of incidence and behavior of thin films on platinum metal
surfaces by measuring contact resistance at 1 mg to 5 gm loadings.
Brit. J. Appl.
Antler, M. and J. Gilbert. The effects of air pollution on electric
contacts, J. Air Poll. Cont. Assoc. 13 (9), 405-15+ (1963).
A thorough review of the various effects of air pollution on
contacts including field and laboratory information and an
interpretation of the basic physics and chemistry involved.
Antler, M. Current topics in the surface chemistry of electric contacts,
IEEE Trans. Parts, Mater., Pkg PMP-2 (3), 59-67 (1966).
This paper describes recent work in the science of the separable
electronic pressure contact with emphasis on chemical factors in
performance. The following topics are discussed: growth and
morphology of sulfide tarnish films which creep across the inter-
face between gold plate and silver or copper alloys and degrade
A-I
-------
contact performance; the formation and structure of corrosion
solids on porous gold electroplated contacts, and which originate
in atmospheres polluted with sulfur dioxide or hydroscopic dusts;
new developments in measuring the porosity in precious metal plates;
the critical dependence of the porosity of gold plate on substrate
roughness; and new concepts for developing electronic connectors
with contacts made of base metals.
Antler, M. Current research in the precious metal plating of electric
contacts, Plating 54 (8), 915-22 (1967).
A new method for reducing the corrosion of thin, hence porous,
gold plates on basic metals and underplates (e.g., nickel) is
presented. Organic coatings were developed which do not signi-
ficantly increase the contact resistance of the gold. In addition
to corrosion inhibition, they effectively lubricate contacts, and
so minimize wear-induced porosity of the plate.
Antler, M., S. M. Garte and S. J. Krumbein. Recent studies of
properties of gold plate, In: Electrical Contacts, 1967,
neering Seminar on Electrical Contact Phenomena, Illinois
of Technology, Chicago, Ill., Nov. 6-9, 1967, PP. 79-92.
High reliability contacts with a minimum of gold plate can be pro-
duced by using (1) smooth substrates, (2) an underplate, or system
of underplates, chosen to minimize substrate diffusion and reduce
the intrinsic porosity of the gold plate, (3) pore-blocking corrosion-
inhibitor coatings, and (4) compatible lubricants having a liquid
component.
the contact
Proc. Engi-
Institute
Atkinson, J. E. Environment-resistant connector field reliability report,
IEEE Trans. Reliability R-13 (2), 8-15 (1964).
4 x 108 connector operating hours were logged in 173 commercial jet
airplanes. Connector failure rates averaged one per 106 cycles.
Baker, R. S. Studies of static low voltage contacts at
Laboratories, In: Second International Conference
tacts, Graz, Austria, May 4-6, 1964. 35 PP.
The effect of atmospheric exposure on various electroplated coatings
for possible use in separable static connectors has been studied.
the Bell Telephone
on Electrical Con-
The wear behavior on crossed cylinders and on actual production
equipment plated with various coatings has been measured.
The best protection during atmospheric exposure is provided by
precious metal coatings thick enough to be pore free. A composite
coating of gold-rhodium-nickel has outstanding wear resisting prop-
erties. Hard alloy golds plated from acid baths are also highly
resistant to wear. Soft 24-carat gold and 50% tin-lead coatings
are likely to gall and exhibit a high degree of wear even at light
contact forces; however, the use of lubricants during the wear-in
period can eliminate rapid initial galling.
A-2
-------
Ball, M., F. H. Hardie and E. J. Struckus. Increase connector contact
reliability, Electron. Engr. 27, 82-5 (March 1968).
For aerospace applications the authors recommend gold on nickel
as the contact material with an increase in thickness of the gold
plating from the standard 50 mils to about 150 mils.
Blake, B. E. Some measurements of contact resistance in an accelerating
. air atmosphere, In: Proc. Engineering Seminar on Electrical Contacts,
Pennsylvania State Univ., Univ. Park, Pa., June 1958, pp. 1-6.
The effects on contact resistance of contact material, loading, and
contact shape for crossed-wire contacts of aging in accelerating
atmospheres were studied. Measurements of copper tarnish film
thicknesses were made comparing normal growth rates with accelerated
growth rates.
Blake, B. E. Dry circuit contacts, In: Proc. Engineering Seminar on
Electrical Contacts, Pennsylvania State Univ., Univ. Park, Pa.,
June 1959, pp. 85-94.
The problems of low voltage contact operation are discussed.
Blake, B. E. and M. A. Oliver. Progress report on the activities of
Section G of ASTM Committee B-4, Sub-committee IV, IBM Corp.,
Poughkeepsie, N.Y., June 1961, 35 PP.
Blake, B. E. Summary report of the ASTM Section G contact field tests,
Components Div., IBM Corp., Poughkeepsie, N.Y., 14 PP.
Test pieces of copper, beryllium copper, brass, nickel, tin lead,
silver, palladium, and gold were exposed for 2.2 years at Newark,
N.J., and Kure Beach, N.C.
Bloomberg, J. and W. E. Campbell. Effects of atmospheric contamination
on switching noise, In: Proc. Engineering Seminar on Electrical
Contacts, Pennsylvania State Univ., Univ. Park, Pa., June 11-15,
1961, PP. 95-108.
The effects of humidity on the chemical activity of traces of
corrosive gases was studied in the laboratory.
Bloomberg, J. and W. E. Campbell. Further studies of sliding contact
, noise, In: Proc. Engineering Seminar on Electrical Contacts, Penn-
sylvania State Univ., Univ. Park, Pa., June 11-15, 1961, pp. 109-13.
The above study was extended to include field data.
Bowcott, H. J. and A. J. Cleaver. Corrosion
by their atmospheric environment, Proc.
Supple 22, 559-66 (1962).
of electrical components
Inst. Elec. Engrs. B-I09,
Mechanisms of atmospheric corrosion are first surveyed. Dry con-
ditions are usually harmless except when hydrogen sulphide is
present; above a certain critical humidity, electrochemical cor-
rosion can occur, and is stimulated by gaseous and solid atmospheric
A-3
-------
contaminants such as sulphur dioxide
may be evolved by organic insulating
rosion may be enhanced at bimetallic
applied potential differences exist.
occasionally occurs.
Next, possible effects of corrosion and whisker growth on electrical
components are discussed. Failures may result from disconnections
due to corrosion of wires, prevention of contact and clogging of
moving parts by corrosion products, and from the making of unwanted
contacts by metal whiskers, corrosion products and silver migration.
A list of corrosion cases is then given, classified according to
cause, illustrating some of the corrosion and fault mechanisms. The
more interesting cases are commented on briefly. Finally, preven-
tive measures are covered. The ideal environment is provided by a
hermetically-sealed enclosure containing a dry uncontaminated inert
gas. More practical steps include air purification, adequate ventila-
tion of enclosed equipments, and avoidance of humid conditions and
metal-surface contamination.
and soot. Aggressive vapours
and packing materials. Cor-
contacts or where externally
Metallic 'whisker' growth
Bryant, R., M. H. Bester, and J. McCormick. Reliability of microelectronic
circuit connections, In: Proc. 1968 Annual Symposium on Reliability,
Boston, Mass., Jan. 16-18, 1968, PP. 558-63.
High humidity was found to have an adverse effect on gOld-plated
Kovar/ribbon.
Campbell, W. E. and R. E. Lee, Jr. Polymer formation on sliding metals
in air saturated with organic vapors, ASLE Trans. ~, 91-104 (1962).
A laboratory study of the mechanism of polymer formation, its de-
pendence on metal type and vapor adsorbance.
Campbell, W. E. Atmospheric effects on friction and wear, Machine Design
36 (20), 186+ (1964).
Fundamentals of oxide film formation and gas adsorption.
Campbell, W. E. Factors affecting reliability of
space application, Final Report No. 144, Jet
Pasadena, Calif., PP. 85-136 (1962).
Review of operating and environmental conditions adversely affecting
electrical contact performance.
electrical contacts for
Propulsion Laboratory,
Campbell, W. E. The tarnishing of
neering Seminar on Electrical
June 14-18, 1965, PP. 343-4.
Sulfide formation reaction mechanisms of silver and copper were
investigated.
silver and copper, In: Proc. Engi-
Contacts, Univ. Maine, Orono, Maine,
A-4
-------
Campbell, W. E. and U. B. Thomas. Tarnishing and contamination of metals,
In: Electrical Contacts, 1968, Proc. Engineering Seminar on Elec-
trical Contact Phenomena, Illinois Institute of Technology, Chicago,
Ill., Nov. 11-15, 1968, pp. 233-65.
All of the common contact contaminants were considered, corrosive
gases, organic materials, dust, soot, and macroscopic dirt.
Chaikin, S.W. Mechanics of electrical-contact failure caused by surface
contamination, Electro-Technol. 68, 70-5 (Aug. 1961).
Contamination from fabrication operations (soldering and welding)
and from outgassing of plastic components are difficult to eliminate.
Chaikin, S. W.
electrical
Institute,
Study of effects and control
materials, Final Rept. Proj.
Menlo Park, Calif., June 10,
of surface contaminants on
PU-3145, Stanford Research
1961.
This was primarily a study of outgassing and degradation of polymeric
materials used in insulation.
Chaikin, S. W. Organic contact deposits under rubbing and non-rubbing
conditions, In: Proc. International Research Symposium on Electric
Contact Phenomena, Univ. Maine, Orono, Maine, Nov. 1961, PP. 141-58.
Polymer forms on palladium in the presence of hydrocarbon vapors,
rapidly with rubbing, slowly without rubbing.
Chaston, J. C.
66, 76-7+
Gold and
Surface properties: key to contact selection, Mater. Eng.
(Aug. 1967).
platinum alloys are best choices for light duty contacts.
Chiarenzelli, R. V. Analysis of dust obtained from the equipment used
in the ASTM two-year exposure test in Newark, General Products
Division Development Lab., IBM Corp., Endicott, N.Y., July 1963, 3 pp.
Major components: carbon, ferric chloride; minor components: sulphite,
nickel, zinc, and aluminum ions.
Chiarenzelli, R.
Engineering
June 14-18,
V. Air pollution effects on contact materials, In:
Seminar on Electrical Contacts, Univ~ Maine, Orono,
1965, pp. 65-102.
Proc.
Maine,
Detailed review of laboratory and field studies with a large amount
of contact resistance data.
Chiarenzelli, R. V. and B. C. Henry. Lubricating separable electric con-
tacts and tarnish prevention, Lubrication Eng. 22, 174-80 (May 1966).
Paraffin mixed with polyphenyl ether found to be a good lubricant
and corrosion inhibitor.
A-5
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Chiarenzelli, R. V. and E. L. Joba.
electrical contact materials; a
Assoc. 16 (3), 123-7 (1966).
Gold, palladium, silver, tin, and lead test pieces were exposed for
four months at six industrial sites and contact resistance measure-
ments made.
The effects of air pollution on
field study, J. Air Poll. Cont.
Chiarenzelli, R. V. Tarnishing
3rd International Research
Univ. Maine, Orono, Maine,
studies on contact materials,
Symposium on Electric Contact
June 6-10, 1966, 9 PP.
In: Proc.
Phenomena,
Laboratory corrosion studies were compared with the earlier field
studies.
Chiarenzelli, R. V. Tarnishing studies on contact materials, IEEE Trans.
Parts, Mater., Pkg PMP-3 (3), 89-96 (1967).
The contact properties of gold, silver, copper, and nickel were in-
vestigated. Corrosion film thicknesses were measured, in addition
to contact resistance.
Egan, T. F. and A. Mendizza. Creeping silver sulfide, J. Electrochem.
Soc. 107 (4), 353-4 (1960).
Silver sulfide creep through pores in gold plating and across
boundaries onto gold contact surfaces was shown to be a serious
contact problem.
Egan, T. F. Contamination during manufacture of low energy electrical
contacts, In: Electrical Contacts, 1968, Proc. Engineering Seminar
on Electrical Contact Phenomena, Illinois Institute of Technology,
Chicago, Ill., Nov. 11-15, 1968, PP. 267-8.
Control of contact quality during manufacture is more critical to
the electronics industry than the effects of air pollution.
Elsey, H. M., L. E. Moberly and J. L. Johnson. Air humidity and brush
contact drop: The effect of water vapor, sulfur dioxide, and
hydrogen sulfide, AlEE Trans. Power App. Systems 73, Pt. III-B,
1383-9 (1954).
Carbon brush-copper commutator rings are quite sensitive to humidity.
High S02 and ~S concentrations increase film resistance while present.
Ely, C.H.A. and p. J. Lambeth. Artificial-pollution test for high-voltage
outdoor insulators, Proc. Inst. Elec. Engrs. III (5), 991-9 (1964).
Salt solution fogs were used to set up standard flashover tests.
Ely, C.H.A. and W. J. Roberts. Flashover of polluted h.v. insulators
under switching surges, Proc. Inst. Elec. Engrs. 115 (5), 443 (1968).
Extent of contamination was related to voltage surges.
A-6
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Evans, U. R. Electrical contacts, the effect of atmospheric corrosion,
Metal Ind., 10-13 (July 2, 1948).
Study of the corrosion of nickel and copper by sulfur dioxide and
hydrogen sulfide.
Evans, U. R. The Corrosion and Oxidation of Metals: Scientific
Principles and Practical Applications, St. Martin's Press, Inc.
New York, 1960, PP. 481-535.
Chapter XIII. Atmospheric Corrosion Mechanisms of Base Metal
Corrosion in Air.
Fairweather, A. The behavior of metallic contacts at low voltages in
adverse environments, Proc. Inst. Elec. Engrs. 100 (Pt. 1), 174-82
(1953).
The surfaces of electrical contacts are usually contaminated by
foreign layers. Such layers may consist of dust or grease, or of
films produced by adsorption, tarnishing or corrosion. The applied
voltage is regarded as "low" when it is too small to initiate con-
duction by any process analogous to breakdown. The problem in such
circumstances is to obtain a metal-to-metal contact mechanically.
An attempt is made, for the first time, to describe the behavior of
a closed contact subjected to corrosion, and the closure processes
for a corroded contact, both with and without "wipe."
Fairweather, A. Reliable contacts, In:
Symposium, London, 1960, pp. 45-6.
Surface contamination by corrosion or foreign films is the main
factor controlling contact behavior.
Electronic Equipment Reliability
Fairweather, A., F. Lazenby and A. E. Parker. Long-life low-voltage
contacts, Proc. Inst. Elec. Engrs. B-I09, Supple 22, 567-86 (1962).
The preservation of near-metallic contact, with reasonable contact
forces in adverse environments, usually necessitates the use of
coatings of precious metals such as gold, platinum, palladium or
rhodium. For semi-permanent contacts, the coating requirements are
determined almost entirely by considerations of environmental attack.
For sliding contacts, considerations of mechanical wear are also in-
volved.
Fairweather, A., R. L. Jury, F. Lazenby, A. E. Parker, D. H. Thrift and
L. J. Weight. Massacre, a machine for automatic surface sampling
and automatic contact-resistance evaluation, Proc. Inst. Elec. Engrs.
A-I09, Supple 3, 210-19, 228-30 (1962).
The machine described is automatic: ten loads are available and a
plate two inches square can be tested at a thousand different places,
each observation occupying eight seconds.
A-7
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The test sequence at each place is as follows. A probe is lowered
gently on to the plate, and when stationary, the contact resistance
is measured and classified automatically. The probe is then 'wiped'
and, again when stationary, a similar evaluation is made. This pro-
cedure is repeated for each of seven loads (10, 20, 50, 100, 200,
500 and 1000 g) or until one or other of the two sets of contact re-
sistances falls within a specified range. The remaining three loads
can be applied manually when it is necessary to explore a particular
load interval in detail.
Fairweather, A. and A. E. Parker. Electrical properties of 'natural'
films developed on platinum contacts, Proc. Inst. Elec. Engrs.
113 (4), 581-4 (1966).
First examples of catalytically formed polymer films from hydro-
carbon pollution on non-rubbe~ surfaces.
Fedorov, A. I. and G. Z. Zakirov. Investigation of plug-type connectors
operating with microcurrents at microvolts, In: Sotskov, B. S., et aI,
Electric Contacts, Moscow-Leningrad, 1964, NASA TT F-339, PP. 223-33.
(in Eng.).
In the microvolt signal range, electric contacts may become unstable
due to the appearance of momentary contact potentials.
Flatau, G. Reliable contacts and connections in telecommunication plant,
Inst. Elec. Engrs. Trans. (Australis) EE-3 (1), 59-67 (Mar. 1967).
A general paper reviewing physical factors controlling contact
behavior and the major effects tending to degrade contact behavior.
Forrest, J.S., p. J. Lambeth and D. F. Oakeshott. Research on the per-
formance of high-voltage insulators in polluted atmospheres, Proc.
Inst. Elec. Engrs. A-l07, 172-96 (1960).
A review of the contamination flashover problem.
Forster, D. L. and B. G. Gebauer. Factors in choosing electrical contacts,
Autom. Elec. Tech. J. ~ (7), 252-9 (1965).
Circuit characteristics and environment must be considered in choosing
optimum contacts.
Frant, M. S. Copper sulfide creep on porous electroplate, J. Electrochem.
Soc. 107 (12), 1009-11 (1960).
Silver sulfide creeps over gold, copper sulfide creeps over gold,
palladium, nickel and tin, and this phenomenon must be considered
in selecting contacts.
Frant, M. S. Connectors and galvanic corrosion, Electron. Ind. 20,
112-16 (Dec. 1961).
Aluminum is most susceptible to galvanic corrosion when coupled
with any other metal except tin.
A-8
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Freudiger, E. Investigation of surface contamination on fine silver
contacts, In: Proc. Engineering Seminar on Electrical Contacts,
Pennsylvania State Univ., Univ. Park, Pa., June 1960, PP. 45-51.
The concern here was primarily with dirt and contaminants intro-
duced at time of fabrication.
Freudiger, E. Electrical contact materials, properties and selection,
Electro-Technol. ~ 72-8 (June 1962).
A study of factors influencing contact resistance and contact
degradation.
Fujitaka, S., T. Kawamura, S. Tsurumi, H. Kondo, T. Seta and M. Yamamoto.
- Japanese method of artificial pollution tests on insulators, IEEE
Trans. Power App. Systems PAS-87 (3), 729-35 (1968). .
Describes flashover test developed in Japan involving controlled
spraying of salt solutions of known concentration.
Gaiennie, D. E. Clean insulators with washer 'gun', Elec. World 153,
87 (Mar. 28, 1960).
A truck mounted gun, with 700 psi pump was used to wash insulators
during normal power transmission operation.
Germer, L. H. and J. L. Smith. Activation of electrical contacts by
organic vapors, Bell System Tech. J. 36, 769-812 (May 1957).
This paper defines and describes "activation" of platinum metal
contacts.
Germer, L. H. and J. L. Smith. Organic vapor and relay contacts, Bell
Lab. Record 36, 122-6 (April 1958).
Erosion from contact activation is hermetically sealed relay problem.
Glossbrenner, E. W. Sliding precious metal contacts and electrical noise,
In: Proc. Engineering Seminar on Electrical Contacts, Pennsylvania
State Univ., Univ. Park, Pa., June 1959, pp. 24-30.
The factors controlling electrical noise level in these devices was
discussed.
Gothberg, A. W., A. R. Koerber and C.
of arresters for 500-kV systems,
PAS-87 (3), 703-12 (1968).
E. Zanzie. Contamination testing
IEEE Trans. Power App. Systems
Contamination flashover problems become more severe as transmission
voltages increase.
Halstr~m, H. L. Tarnishing of silver and silver-silicon contacts by
hydrogen sulfide, J. Inst. Metals ~, 144 (1961).
Simple passification of silver surfaces is claimed by oil treatmBnt,
mild soap washing and water rinsing.
A-9
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Hampton, B. F. Flashover mechanism of polluted insulation, Proc. Inst.
Elec. Engrs. III (5), 985-90 (1964).
The voltage gradient of an arc burning in steam is higher than the
voltage gradient of an arc burning in air.
Hara, T. and K. Mano. Thermodynamical studies on the dry corrosion of
several contact materials, Tech. Rept 19, Research Institute of
Electrical Communication, Tohoku Univ., Bendai, Japan, 1967, 28 PP.
Oxidation and sulfurization functions were developed for several
metal and alloy contact materials.
Harding, W. B. The tarnish resistance of gold plating over silver,
Plating 47, 1141-5 (Oct. 1960).
Problem of silver sulfide creep through gold plate pores is
explored.
Harris, H. R. Four measures minimize an unusual case of insulator.con-
tamination, Elec. World 142, 80-3 (July 26, 1954).
Four measures for combating atmospheric contamination of in-
sulators:
1.
Provision of ample insulator surface leakage length
Periodic silicone coating of insulator surfaces
2.
3.
4.
Periodic washing
Reduction of contaminants in the atmosphere through
cooperation with a neighboring plant.
At least one of these, the application of silicone coating, is
believed to be new to the industry.
Hermance, H. W. and T. F. Egan. 'Fingerprinting" relays, Bell Lab.
Record 34 (8), 289-93 (1950).
Plastic replico techniques were used to examine contacts and
identify contaminants.
Hermance, H. W. and T. F. Egan. Organic deposits on precious metal
contacts, Bell System Tech. J. 37 (3), 739-76 (1958).
An amorphous brownish organic deposit was found on non-arcing
palladium contacts. It was shown that this material is produced
when a number of metals, notably those of the palladium and plati-
num groups, are rubbed together in the presence of low concentra-
tions of organic vapors. The deposit is given by a very wide
variety of organic materials, and first involves chemisorption
of the vapor on the metal, followed by frictional activation and
polymerization of the chemisorbed layers to form the visible
accumulation. The use of a gold alloy overlay on the palladium
tends to minimize the growth of the polymer on the contact surface.
A-IO
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Hermance, H. W. Combatting the effects of smog on wire-spring relays,
Bell Lab. Record 44 (2), 48-52 (1966).
Dust in Los Angeles, high in ammonium nitrate content, was found
to cause stress corrosion in the wire springs used in telephone
relays. Countermeasures included use of high efficiency filters
on existing installations and change of wire spring alloy to one
unaffected.
Hill, G. L. Tests and developments in connection with hot-line insulator
washing. AlEE Trans. 66, 1203-16 (1947).
High pressure water and high pressure steam washing methods were
investigated.
Holm, R. and E. Holm. Electric Contacts, Theory and Application,
Springer-Verlag, Inc., New York, 1967.
Standard definitive reference book for electric contacts.
Hosokawa, Y. Abnormal contact erosion of switching relay, NEC Res.
Develop., Nos. 4/5, 10-24 (1963).
The contacts of wire spring relays were found abnormally eroded at
"F" central, only after one year and a half of use. The investiga-
tion into the cause of this erosion was carried out at the central
and in the laboratory. The results showed that the cause of abnormal
erosion of contact is the activation of contact due to the aromatic
hydrocarbon vapor of oily TT wax used for floor polishing and that
the further erosion was stopped by using active carbon filters.
Hyde, N. Electromechanical relays. Part 3.
Electron. Compon. ~ (8), 665-9 (1964).
Factors affecting relay performance are discussed.
The contact problem,
Hyde, N. Electromechanical relays. Part 4. Reliability testing, Electron.
Compon. ~ (10), 865-72 (1964).
General treatment of testing procedures and instrumentation.
Ign~cz, p. Silicone-greasing provides excellent insulator flashover
protection, Power Eng., 56-7 (Oct. 1962).
Kaufman, J. W., H. R. Sutton, A. V. Balchaitis and W. R. Matthias.
Dry-circuit evaluation of mechanical connections, Elec. Manuf.
65 (4), 116-21 (1960).
A summary of the causes of non-conduction in low-level electrical
contacts and the results of environmental tests on two forms of
mechanical-type connectors evaluated from a reliability standpoint
in dry circuits encountered in defense electronic equipment.
A-ll
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Kawai, M. Tests in Japan on the performance of salt-contaminated in-
sulators in natural and artificial humid conditions, Proc. Inst.
Elec. Engrs. 115 (1), 158-68 (1968).
Describes work done in experimental studies to identify the
mechanism of contamination flashover.
Keefer, H. J.
Dust on relay contacts, Bell Lab Record 35, 25-8 (1957).
Dust destroys contact reliability.
necessity.
Air filters are an absolute
Keil, A. G. Some materials problems in electrical contacts, Mater. Res.
Std. 3 (6), 489-91 (1963).
A discussion of silver sulfide creep, contact deformation by arcing
and the resistivity of foreign films.
Keller, A. C. Recent developments in Bell System relays - particularly
sealed contact and miniature relays, Bell System Tech. J. 43 (1),
15-44 (1964).
Important developments are miniaturization, sealed contact relays
using glass-enclosed contacts, and "remanent" type devices. Ferreed
and bipolar ferreed coordinate arrays and individual units are new
and important switching elements. These devices make use of minia-
ture glass-enclosed contacts in combination with "square loop"
magnetic material such as ferrite or certain iron alloys. They are
magnetic "latching" units and are operated or released by short
pulses.
,
'""
King, J. High pressure electrical contacts, In: Proc. 1968 Electronic
components Conference, May 8-10, 1968, PP. 454-8.
Satisfactory performance has been achieved with high pressure con-
tacts of uncoated base metals. These contacts were neither pro-
tected from, nor deliberately exposed to contamination. Variations
of both point and line contact configurations have been evaluated
and their performance falls into predictable patterns. Sufficient
test data has been evaluated and the following conclusions can be
drawn: (1) tarnish films on base metal are penetrable by high
pressure contact indentors without resorting to a wipe motion; (2)
line contact chisels and point contact cones with large included
angles are superior to thin knife-like or needle-like contacts;
(3) relative contact hardness is important in that both indentor
and flat contact target must deform to expose base metal or the
resulting interface will consist of one contact with bare metal
exposed and in direct contact with the insulating tarnished sur-
face of the other contact.
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Krumbein, S. J. and M. Antler. Inhibition of corrosion and wear of gold
plated contacts, Res. Rept. 51, Res. Div., Burndy Corp., Norwalk,
Conn., Jan. 26, 1967, 20 PP.
The increasing reliability requirements for low voltage electric
contacts has led to a search for methods which could make gold
plated surfaces impervious to the effects of atmospheric pollutants.
The susceptibility of. thin gold plate to corrosion is due both to
its inherent porosity and its removal by wear. Because of these
breaks in the plate, pollutants can attack the substrate metal or
underplate to produce insulating corrosion products.
The best methods were the application of a pore blocking inhibitor
and a lubricant coating having a liquid component. They inhibited
corrosion and wear effectively, without significantly increasing
contact resistance compared to untreated samples. These methods
were superior to solid lubricant coatings that have been previously
proposed.
Lambeth, p. J.
(1964).
Preventing pollution flashovers, Elec. Rev. 174, 662-6
A survey of methods in use or being developed to eliminate pollution
flashovers.
Lambeth, p. J., J. S. T. Looms, A. Stalewski and W. G. Todd. Surface
coatings for h.v. insulators in polluted areas, Proc. Inst. Elec.
Engrs. 113 (5), 861-9 (1966).
Petroleum jelly and silicone grease are both effective, but ex-
pensive inhibitors of contamination flashover.
Larrabee, C. p. and O. B. Ellis. Corrosiveness of various atmospheres,
Mater. Res. Std. !, 977 (Dec. 1961).
ASTM report on the relative corrosiveness of the atmosphere at
37 locations in the U.S. with regard to steel and zinc.
Last, F. H., T. H. Pegg, N. Sellers, A. Stalewski and E. B. Whittaker.
Live washing of h.v. insulators in polluted areas, Proc. Inst.
Elec. Engrs. !13 (5), 847-60 (1966).
A review of the effectiveness on live or "hot"
insulators with high pressure water to prevent
flashover.
washing of h.v.
contamination
Lilienfeld, S. and C. E. White. A study of the reaction between
sulfide and silver, J. Am. Chern. Soc. 52, 885-92 (1930).
This paper shows that dryHzS will not attack silver but if
is added to the dry system silver sulfide is formed.
hydrogen
oxygen
A-13
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Lish, E. F. Identification of contact contamination, In: Electrical
Contacts, 1960, Proc. Engineering Seminar on Electrical Contacts,
Pennsylvania State Univ., Univ. Park, Pa., June 1960, PP. 38-43.
Contact contamination has several potential sources. All of the
fabrication assembly and cleaning operations can inadvertently
add contaminants.
Lodge, J. P., Jr. and B. R. Havlik. Evaporated metal films as
of atmospheric pollution, Intern. J. Air Pollution ~ (4),
(1960).
indicators
249-52
Glass slides covered with films of aluminum, iron,
silver were prepared and exposed in the Cincinnati
atmospheric corrosiveness.
Corrosion products were identified by means of X-ray diffraction
and microchemical methods. Corrosion results in an increase in
light transmission by the film, which can be taken as a quanti-
tative measure of corrosion. Preliminary results showed aluminum
to be the most dependable indicator of general atmospheric cor-
rosiveness, although silver appeared specifically sensitive to a
small group of pOllutants, such as halogens, ozone, and sulfur
compounds. Lead corroded so rapidly as to be difficult to inter-
pret while iron was shown to be responsive primarily to relative
humidity. Fair correlations were obtained with independent measures
of pollution level. Some exploratory work was done on the measure-
ment of the electrical resistance of the films.
lead, copper and
area to measure
Lodge, J. p., Jr. and E. R. Frank. Evaporated metal films as indicators
of atmospheric pollution. II. Resistance measurements, Intern. J.
Air Water Pollution ~, 215-21 (1962).
A technique was developed relating corrosive pollution level to
contact resistance.
Maddock, A. J., C. C. Fielding, J. H. Batchelor and A.
effects of dust and force upon certain very light
tacts, Brit. J. Appl. Phys. ~, 471-80 (1957).
Dust was found to cause high contact resistance at very low force
loadings.
H. Jiggins. The
electrical con-
Mader, W. M. Organic free slip ring assemblies - possibility or reality?
Marshall Space Flight Center, Huntsville, Ala., 1966.
Whenever organic material is enclosed in sli~ ring assemblies, there
is a danger of polymer film formation on contact surfaces before the
part is put into operation. This can cause immediate failure when
an attempt is made to use the assembly.
A-14
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Mahler, P. The effects of contamination on relay performance, In: Elec-
trical Contacts, 1960, Proc. Engineering Seminar on Electrical
Contacts, Pennsylvania State Univ., Univ. Park, Pa., June 1960,
pp. 64-6.
The kinds of contaminants were listed
ganic vapors, and moisture, and their
outlined.
- oil, rosin, detergent, or-
actions on contact surfaces
McKinney, N. and H. W. Hermance. Stress corrosion cracking rates of a
nickel-brass alloy under applied potential, Stress Corrosion
Testing, ASTM STP 425, Am. Soc. Testing Mater., 1967, PP. 274-91.
A method was developed to test the susceptibility of nickel-brass
alloys to stress corrosion cracking in the presence of nitrates
or other salts. A wire of the alloy under test was stressed, and
an electrical leakage path was provided to a cathode by the elec-
trolyte being studied. Stresses, potentials, salt concentrations,
relative humidities, and time were varied to evaluate these factors.
McManus, J. J. Improving contact reliability in low-level circuits,
Electro-Technol. 69, 98-101 (May 1962).
Super imposing a 120 v "wetting voltage" signal across low-level
contacts as a means of assuring contact reliability is proposed.
Moberly, L. E. Atmospheric effects on sliding contacts, In: Proc.
Engineering Seminar on Electrical Contacts, Pennsylvania State
Univ., Univ. Park, Pa., June 25-29, 1956, 19 pp.
The effects of moisture, HaS, S02' hydrocarbon vapor, and silicone
vapor on sliding contacts were discussed.
New, A. A. An analysis of failure of components, Radio Electron.
Components !, 193-201 (Feb. 1960).
A detailed examination of the factors causing component failure.
Phillips, V. A.
nucleation
(1962).
Role of defects in evaporated silver films on the
of sulfide "patches", J. Appl. Phys. 33 (2), 712-17
Studied by transmission electron microscopy:
attack points of HaS.
Defect sites were
Pitney, K. E. The ASTM method of test for microcontacts, In: Electrical
/Contacts, 1965, Proc. Engineering Seminar on Electrical Contacts,
Univ. Maine, Orono, Maine, June 14-18, 1965, pp. 293-311.
Use of the ASTM microcontact resistance tester is described.
Rance, V. E. and H. G. Cole. Corrosion of metals by
materials, Inter-service Metallurgical Research
Stationery Office, London, 1958, 25 pp.
A number of metals were enclosed with various plastics and resins for
long test periods, then examined for corrosion damage.
vapours from organic
Council, Her Majesty's
A-15
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~
\V Ridker, R. G. Economic costs of air pollution studies in measurement,
Frederick A. Praeger, 1967, pp. 66-71.
Shtremberg, T. K. and D. V. Gayevskaya. Special features of switching
low level currents and voltages by means of contacts, In: Sotskov,
B.S., et aI, Electric Contacts, Moscow - Leningrad, 1964, NASA
TT-F-339, PP. 276-300. (in Eng.).
Technically, pure gold is recommended as the only satisfactory
contact surface for low level contacts.
Snowball, R. F., J. B. P. Williamson and R.
corrosion of contacting surfaces, IEEE
PMP-3 (3), 82-4 (1967).
The most pressing problem in electric contact testing is to define
the modes by which contacts fail. Until we understand why and by
what mechanism contact spots stop passing electricity between the
mating members, it will be impossible to devise relevant life-
testing procedures. This paper describes an experimental technique
whereby interfaces can be observed during exposure to moist, pol-
luted air and the degradation of contact spots studied in situ.
The reactions that occur are analyzed in terms of the physical
effects of the ingress of reactants into contact joints, and the
resistance changes observed. The distinction between ingress-
limited corrosion and reaction-limited corrosion is introduced,
and the death of contact spots is observed under the microscope.
This technique makes possible the direct observation of the pro-
gressive corrosion of an array of contact spots, and reveals in
detail how the conducting area of each spot is eroded by the
chemical action.
C. Hack. Ingress-limited
Trans. Parts, Mater., Pkg.
Solov'yeva, S. F., I. I. Sigachev, N. A. Surkova and Ye. V. Kogteva.
Contacts of relay-type elements and microswitches which commutate
low level signals, In: Sotskov, B. S., et aI, Electric Contacts,
Moscow - Leningrad, 1964, NASA TT F-339, pp. 301-31. (in Eng.).
A review of the requirements of low level contacts for satisfactory
performance.
Spelman, J. W.
(1968).
Where rhenium is growing, Metal Progr. 93 (2), 103-4+
The chemical and physical properties of rhenium make the metal well
suited for manyJelectrical contact applications.
~
Tripp, J. H. ~na J. B. p. Williamson. A model of mechanical breakup of
films on conductors, In: Proc. 3rd International Research
Symposium on Electric Contact Phenomena, Univ. Maine, Orono,
Maine, June 1966, PP. 71-8. (in Ger.).
Film breakdown is one of the ways to combat air pollution effects
on electrical contacts.
I
A-16
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Turner, H. W. and C. Turner. Contact materials, their properties and
uses, Pt. 2, Elec. Times 152 (8), 277-81 (1967).
A description of aluminum, copper, silver, nickel, tungsten,
molybdenum, and rhenium as contact materials.
Ulsh, H. B. Current ideas in the philosophy of testing electrical
contacts, IEEE Intern. Conv. Record 14 (9), 35-8 (1966).
Environmental test procedures are described.
Van Auken, R. L., W. D. Hensley and S. R. Cole. Totally inorganic
assemblies, an approach to contamination free sliding contacts,
In: Electrical Contacts, 1967, Proc. of the Engineering Seminar
on Electric Contact Phenomena, Illinois Institute of Technology,
Chicago, Ill., Nov. 6-9, 1967, pp. 119-23.
This approach eliminates organic polymer films.
Wagner, R. J., A. E. Sprando, and J. R. Laskie. Reduction of contact
contamination with activated carbon getters, In: 9th National
Conference on Electromagnetic Relays, Natl. Assoc. Relay Manu-
facturers, Oklahoma Institute of Technology, Stillwater, Okla.,
1961, PP. 35-8..
This is probably not as satisfactory as organic-free assemblies.
Williamson, J. B. p., J. A. Greenwood
dust particles on the contact of
560-73 (1956).
and J. Harris. The influence of
solids, Proc. Royal Soc. ~fY
Shows dust to be detrimental to electrical contact operation.
Williamson, J. B. p.
nector surfaces,
(1966).
Recent studies on the physics of electrical con-
IEEE Trans.Parts, Mater., Pkg. PMP-2 (3), 71-5
The manner in which two conductors touch to form an electrical
contact is described, and the influence of the phenomena occurring
at the interface on the engineering properties of the connector
is discussed. In the last ten years, significant advances have
been made in our knowledge of the mechanical, electrical, and
thermal aspects of the contact between surfaces. These have led
to a better understanding of the deterioration processes which
occur naturally in connectors. A new philosophy of the evaluation
and specification of connectors which utilizes these results and
which links the engineering reliability of the device to the basic
science of the interface is discussed.
Wohlers, H. C.
Bay area
5 PP.
Corrosion aspects of air pollution in the San Francisco
- Electrical contact points, Internal Rept. BAAPCD, 1964
Part of a general assessment of the economic effects of air pol-
lution in the Bay Area.
A-17
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APPENDIX B
PERSONAL CONTACTS
-------
A.
Industrial Visits
These visits were made during the period July 1968 to March 1969.
AMP INC.
Research and Development
Harrisburg, Pa.
Laboratory
Talked with:
Mr. Ryle, Laboratory Manager
Mr. J. H. Whitley
AMP manufactures ~ating connectors, terminals, pin and socket con-
nectors, card reader contacts, and connector assemblies. High current
connectors have no air pollution problems. Low current, low voltage
contacts are gold plated to minimize effects of air pollution and other
deleterious environmental factors. AMP spends about $2,000,000 for gold.
Air conditioning costs in a computer installation amount to about
8% of the total installation costs.
Air pollution effects (particulate fallout) will become more serious
in ultra high voltage power transmission as voltages increase. Working
voltages of 765 KV or higher are expected soon. Effects are contamination
flash-over, radio interference from corona flumes, and current losses from
corona.
ASSOCIATED SPRING CORPO~ATION
Barnes Wallace Division
100 Wallace
Bristol, Connecticut
Talked with:
Mr. Phillip Lombary, Engineer
Mr. James Maker, Chief Metallurgist
Discussed use of gold plating for dry circuits and other ways of
contamination prevention..
BELL LABORATORIES
Holmdel, New Jersey
Talked with:
Mr. Thomas Egan
While the electrical contacts in telephone systems are not as sus-
ceptible to air pollution effects as electrical contacts in some other
lower voltage systems, such as computers, because the telephone network
is so vast and the expected service life of the relay and switching com-
ponents is so great, air pollution effects are of serious concern. A
minimum of 20 years service life is demanded for the electrical contacts
in the system, regardless of operating conditions or environment.
B-1
-------
Bell Telephone prefers palladium to gold in their telephone relays
because the wear properties of palladium in electrical contacts are far
superior to the wear properties of gold. However, the use of palladium
introduces another air pollution type problem, i.e., the formation of
build-up of frictional polymer. If organic vapors are present where
palladium plated contacts are in service, these vapors are catalytically
polymerized by the palladium and a brown deposit of polymer grows on the
contact surface. This brown deposit can cause open circuit failure in
telephone switching by building a thick insulating layer.
The specific problem of silver migration in
was briefly discussed. This effect is primarily
and thus is not closely related to air pollution
contacts.
electrical insulation
dependent upon humidity
effects on electrical
Contact activation caused by carbon residues from organic contaminants
on electrical contacts used in medium and heavy duty relays and-switches
is nearly always a result of air pollution. This condition is undesirable
because it brings on accelerated arc erosion on the contact surface. Plat-
inum metal contacts are especially susceptible to contact activation from
carbonization of frictional polymer, which will form if organic vapors
are present.
'.
BURNDY CORPORATION
Norwalk, Connecticut
Talked with:
Dr. Morton Antler, Deputy Director
Research Division
Burndy is one of the large manufacturers of electrical contacts.
Most of the microcontacts produced by Burndy are gold-plated and the
company, through its research division, has done much valuable research
on the precious metal plating of electrical contacts.
High reliability contacts can be produced with a minimum of gold
plate by using smooth substrates and nonporous underplates chosen to
minimize substrate diffusion through the gold plate.
In the Burndy laboratory at the present time there is the feeling
that gold plate could be eliminated in the manufacture of electrical
contacts should the proper corrosion-inhibiting system be developed for
base metal contacts.
B-2
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RENSSELAER POLYTECHNIC INSTITUTE
Troy, New York
Talked with:
Dr. Wilfred E. Ca~pbell, Consultant
Problems related to acceleration of contact erosion by organic vapors;
corrosive effects of particulate films on contacts; the mechanisms of
silver tarnish; and the general roles of gaseous and particulate pollutants
in contact failure were discussed in detail. Dr. Campbell cited examples
of secondary wear effects of contact exposure to pollutants, both deleterious
and beneficial.
DREXEL INSTITUTE OF TECHNOLOGY
Philadelphia, Pennsylvania
Talked with:
\
Dr. Henry Wohlers, Associate Professor
Environmental Sciences Division
Discussed differences in materials damage among urban air sheds,
specifically differences in metalic corrosion.
ENGELHARD INDUSTRIES
Mallory Division
Newark, New Jersey
Talked with:
Dr. Victor G. Mooradian
The Mallory Division of Engelhard Industries makes precious metal
alloys for industry. They have 500 alloy compositions for electrical
contact application; of these 100 are regularly used. Two hundred of
these alloys contain silver as a major component.
Sulfiding of silver containing electrical contacts can be inhibited
in a number of ways. As much as 25% silver in a gold-silver alloy retains
a sulfur corrosion resistance comparable to that of pure gold. Another
corrosion resistant system is made up of gold diffused on silver. It is
claimed that this combination can be used with as much as 75% silver.
Small amounts of mercury (2 to 3%) diffused into silver reduce the ten-
dency for a silver contact surface to tarnish.
About 10
Industries is
on electrical
to 20% of the business of Mallory Division of Engelhard
based on requirements to eliminate air pollution effects
contacts.
B~
-------
GENERAL ELECTRIC COMPANY
Pittsfield, Massachusetts
Talked with:
Mr. M. Kawai, Research Engineer
Project UHV Facility
Certain types of contamination flashover of high voltage transmis-
sion lines are caused by particulate pollution although a large fraction
of such flashovers are caused by natural particulate accumulations. One
specific pollutant material, which is particularly troublesome, is calcium
chloride in areas where it is used to de-ice highways. Fallout from in-
d ustrial stacks can also cause problems in local areas.
GENERAL ELECTRIC COMPANY
High Voltage Laboratory
Philadelphia, Pennsylvania
Talked with:
Mr. Wendell Starr
Mr. H. O. Schneider
Mr. Roy Anderson
We discussed the problem of the effect of particulate pollution on
high voltage flashover in transmission lines as related to the magnitude
of the line voltage. Problems are severe at ultra high voltages (750 to
1000 KV).
HARVEY HUBBELL, INC.
Bridgeport, Connecticut
Talked with:
Mr. R. M. Murphy, Vice President
Mr. E. R. Carlson, Manager
Advance Design and Development
Hubbell manufactures cold formed parts for electrical contact as-
semblies. Many of their contacts are manufactured from beryllium,
copper, nickel, brass, or bronze, but they will process precious metal
plate parts on a custom basis. Their customers have reported no prob-
lems attributable to air pollution and their feeling is that corrosion
problems are specific and local.
IBM
Durham, North Carolina
Talked with:
Dr. D. M. Preiss, Manager
Materials Laboratory
IBM is interested in attaining essentially perfect performance of
their gold-plated connector boards for a period of at least five years
and they would also like to see an accelerated test method that would
B-4
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accurately foretell the performance characteristics of electrical contact
systems. At present, they use the cycling temperature and humidity test,
the flowers of sulfur test, and the salt spray test for accelerating
corrosion.
ITT CANNON ELECTRIC
Los Angeles, California
Talked with:
Mr. Warren Keating
ITT Cannon Electric manufactures switches, relays, and contact as-
semblies for commercial and communications applications.
A generally used approach to improving contact reliability is in-
creasing the thickness of the gold plate; but where soldered connections
to gold plated contacts are made, the tendency to form a brittle gold-
solder eutectic increases with thickness of the gold plate. Therefore,
recent developments have led toward the use of thinner gold plate on
smoother substrates. The gold plate porosity can be reduced dramatically
by careful substrate surface preparation.
J. M. NEY AND CO.
Bloomfield, Connecticut
Talked with:
Mr. K. E. Pitney, Manager
Electronic Research and Development
The Ney Co. makes contact parts for encoders, potentiometers, gyros,
tape and card readers, and many specialized applications. Most of their
contacts are solid precious metal alloys bonded to rigid plastic support.
The metal is one to three mil thick and the alloy formulations are gener-
ally so nonreactive that air pollution has no effect on contact performance.
LITTON PRECISION PRODUCTS, INC.
Poly-Scientific Division
Blacksburg, Virginia
Talked with:
Mr. Wesley Mader, Vice President-Engineering
This Company makes guidance systems for missiles, launch-stage space
vehicles, ships, and aircraft. Very important components of these systems
are the various integral slip ring assemblies. These assemblies represent
one important type of low load electrical contact. Other high reliability
electrical contact assemblies are also produced.
These components or units are invariably sealed. They are fabricated
by the best procedures known, of the best available materials. The cost
of making these components is justified because they are used in such
critical applications in such valuable and important systems.
B-5
-------
Their one unresolved reliability problem concerns potential electrical
contact failure due to internal environment contaminants, such as solar
flux or polymer produced catalytically from organic vapors. These organic
vapors are the result of outgassing of insulation or other organic com-
ponents in the assembly.
B.
Telephone Contacts
These telephone contacts were made during the period
Augus t 1969.
July 1968 to
AUTO SWAGE PRODUCTS
Shelton, Connecticut
Talked with:
Mr. Robert Burns, Chief Engineer
No air pollution problems recognized, yet they do use gold plate
connectors to order.
IBM
Poughkeepsie, New York
Talked with:
Dr. Robert V. Chiarengelli, Research Engineer
Discussed environmental chamber tests for contact materials and the
advantages and limitations of the flowers of sulfur test.
ITT GENERAL CONTROLS
Glendale, California
Talked with:
Mr. J. Robert Brown, Director of Research
Mr. Brown felt air pollution has no effect on power relays and
switches.
MICRODOT, INC.
South Pasadena, California
Talked with:
Mr. W. Doherty, Engineer
Discussed required cleanliness for contact manufacture.
PACIFIC GAS AND ELECTRIC COMPANY
San Francisco, California
Talked with:
Mr. Richard H. Brainard, Staff Engineer
Discussed contamination flashover in the Bay Area.
B-6
-------
PACIFIC TELEPHONE AND TELEGRAPH COMPANY
Los Angeles, California
Talked with:
~IT. N. G. Reetz, Staff Engineer
Discussed the pollution problems unique to the Los Angeles area,
including frictional polymer formation on palladium contacts and the
corrosive nature of ammonium nitrate.
SOUTHERN CALIFORNIA EDISON POWER COMPANY
Los Angeles,ICalifornia
Talked with:
Mr. W. E. Schroder, Staff Engineer
Discussed the contamination flashover problem and the cost of pre-
ventive measures taken by Southern California Edison Company (not washing).
STANFORQ APPLIED ENGINEERING
Santa Clara, California
Talked with:
Mr. Daniel Munson, Engineer
General discussion of electrical contact contamination.
B-7
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APPENDIX C
GENERAL ELECTRICAL CONTACT AND
CONTAMINATION FLASHOVER BIBLIOGRAPHY
-------
GENERAL ELECTRICAL CONTACT AND CONTAMINATION FLASHOVER BIBLIOGRAPHY
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'- "
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/
C-l
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C-4
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C-5
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