Hi again,
This is the second abstract for a paper presented at the same meeting as
listed in Dust part 1. The number for this paper is 641.
I hope some of you can use this info. Thank you for your time.
D. A. Douthit
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Corrosion and Protection of Metals in the Presence of
Submicron Dust Particles
R.E.Lobnig 1* ,
R.P.Frankenthal 1 , C.A.Jankoski 1 , D.J.Siconolfi 1 ,J.D.Sinclair 1 ,
M.Unger 2 , M.Statmann 2
* Present Address: University of Applied Sciences
Esslingen, Germany
1 Lucent Technologies Bell Labs Innovations, Murray
Hill, N.J., USA
2 Erlangen University, Erlangen, Germany
To evaluate the effect of environmental interaction
on the reliability of electronics, the components of
the environment that need to be considered are: (1)
corrosive gases derived primarily from fossil fuel
combustion; (2) coarse particles (>1 m) formed by
erosion of soil and minerals or flaking of biological
materials; and (3) fine particles (<1 m) produced
from corrosive gases through chemical and physical
processes that occur in the atmosphere.
In recent years, ionic contamination from fine particles has
been a common cause of field failures. The
increased use of forced-air cooling, brought on by
increasing power densities in electronics, has caused
up to a 100-fold increase in the deposition rate of
fine particles to critical component surfaces. In many
urban indoor environments, the mass concentration
of these particles and their arrival rate at surfaces are
comparable to the mass concentration and arrival
rate of corrosive gases. Fine particles play the
decisive role in the corrosion of electronics because
of their higher concentration indoors (due to low
filtration efficiencies for fine particles) and because
of their greater content of soluble ions compared to
coarse particles.
In this talk, laboratory simulations of the effect of
fine dust particles on the corrosion of copper,
aluminum and zinc will be presented. To simulate
the composition of real dust, ammonium sulfate,
acid ammonium sulfate or sodium chloride were
deposited onto the metal surfaces and the corrosion
behavior was followed by several experimental
techniques. SEM with EDX, XPS, X-ray diffraction,
AFM, metallography, and ion chromatography were
used as ex-situ techniques to characterize corrosion
products. Additionally, some techniques were used
in-situ: XRD, pH-measurements, AFM, FT-IR in the
reflection-absorpbion mode, and scanning Kelvin
probe studies.
The corrosion products are compared to those found
in natural patinas. The corrosion mechanisms will be
discussed and compared for copper, aluminum and
zinc. For all three metals and ionic contaminants, the
corrosion rates increase with increasing relative
humidity of the air. The corrosion rates increase in
the sequence Al < Cu < Zn.
For Al and Cu, major corrosion is only
observed at humidities above the critical relative
humidity (CRH) of the salt deposits. However, even
below the CRH an accelerated growth of surface
corrosion products can be detected by XPS in the
presence of dust particles. For zinc, major reaction
with the particle deposit is already observed below
the CRH of the ionic contaminants. Data suggest
that this difference between zinc and aluminum or
copper can be attributed to the presence of basic zinc
carbonate on the surface, which absorbs sufficient
water at an RH above 60% to make electrochemical
reactions possible. At the CRH, reaction occurs
faster than at lower RH and the corrosion products
spread over large areas of the sample, in contrast to
aluminum and copper. Above the CRH, droplets are
formed on the particle deposits on all three metals,
facilitating electrochemical reactions.
The effect of the amount of deposited
(NH4)2SO4-particeles on the corrosion of copper at
RH > CRH will be discussed. With larger amounts
of particles deposits (up to 13 mg/cm2) Cu2O is
formed as the major corrosion product at 373 K. At
300 K only minor amounts of Cu2O are formed.
After longer exposure times the initial droplets dry
out, and the basic copper sulfate Cu4(SO4)(OH)6H2O
(posnjakite) forms as first solid corrosion products,
which is later converted to Cu3(SO4)(OH)4 (antlerite)
or Cu4(SO4)(OH)6 (brochantite) . The bulk copper is
pitted up to 100 um depth. With smaller amounts of
particle deposits (1-3 g/cm2), the initial solid
corrosion product posnjakite is converted to Cu2O
(cuprite), that is, the Cu2+of the basic copper sulfate
is reduced to Cu+.
Benzotriazole (BTA) is a common corrosion
inhibitor for copper. BTA-copper surface layers
were shown to be effective corrosion inhibitors for
(NH4)2SO4-particle induced corrosion for low
amounts of particle deposits (1-3 g/cm2). The
thickness the surface oxide layer after 12 weeks of
exposure did not exceed 5 nm. However, for high
amounts of particles (a few mg/cm2), similar
amounts of the same corrosion products were
observed as without a BTA-pretreatment.
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