analysis of the corrosion protection of intercept technology licensed
metal substrate storage product
Intercept Technology is a Lucent Technologies patented and licensed polymer
process. The Technology has been licensed, manufactured, distributed,
and sold by our licensees since 1991. In order to ensure the highest quality
production, and manufacture of Intercept products are maintained, samples
of production materials are regularly retained and tested. These checks,
coupled with periodic inspections and updated improvements in formulations
create a technically advanced product. Periodically, final products are
laboratory tested for static and/or corrosion protection performance.
Coin storage systems are designed to protect copper, silver and their
alloys from tarnishing. These metals are commonplace in the electronic
equipment Lucent Technologies manufactures. Therefore, it is beneficial
for Lucent Technologies Bell Labs to test their performance of such systems
so as to expand our information base in the matter of the atmospheric
corrosion protection of electronic materials. This report describes such
a test for corrosion protection and its results.
Storage systems for coinage have been tested for corrosion protection
from atmospheric trace sulfur gases. Intercept Technology significantly
outperformed non-Intercept Technology systems.
and their alloys have been degraded from atmospheric gases from the moment
they were purified and polished more than 5,000 years ago(1).
The most abundant corrosive gas is oxygen. Upon exposure to oxygen copper
forms an oxide film of Cu2O, which, is semitransparent, and self limiting.
This oxide grows to approximately 15Å in one hour to an upper limit
of approximately 2 NM at 20° C(2).
Typical copper degradation occurs when sulfur and water vapor are deposited
on the metal surfaces. Liquid water, sufficient to form an acidic condensate
slurry with sulfur, occurs at relative humidity levels greater than 60%.
This slurry penetrates and breaks protective oxide interstitial grain
boundary bonds. Eventually, sulfur and copper ions form copper sulfide,
which, mix into the oxide, and form directly on the copper surfaces. In
very thin layers an overall darkening will occur at thicknesses as low
as 10 nm(3). Typically, experiments
used to mimic these natural occurring processes utilize water and a corrosive
gas. We have chosen this proven method to evaluate product performance.
The gas we wish to use as a catalyst for the test is hydrogen sulfide.
It is abundant in the atmosphere. It has a natural vapor pressure of 292
psi at STP, is colorless, and it has an affinity for reacting with copper
having a chemical stoichiometry favoring a Cu reaction as does carbonyl
sulfide and three to four times more than So2(4).
of 4 ppm were used in experiments. These have been found to provide an
increase in exposure concentration that follows a linear relationship
with total exposure as shown by Graedel et al(5).
Generation of the atmospheres and exposure chamber was similar to previous
work using a variable length, low pressure permeation tube capped on one
end, and connected to a variable pressure regulated H2S(6)
lecture bottle of technical grade H2S. Continuous monitoring of hydrogen
sulfide (H2S) concentrations were made by a Thermo Electron Model 43 Pulsed
Florescence monitor with precursory catalysis on H2S by platinum reduction.
Temperature measurements were made by a Fluke Model 16 digital thermometer,
and humidity by an EXTECH model 10 humidity meter. The test chamber dimensions
are 450 x 600 x 600 cm., with a construction of 0.64 cm thick clear polycarbonate.
The chamber has two slotted shelves, and incorporates a cross feed gas
flow system to ensure linear gas concentration exposures. The air supply
line was filtered with an oil separator, an activated charcoal cartridge,
and a 0.5 micron particulate filter. A continuous feed water drip maintained
the bubbler at 10 cm of water. The water supply was deionized and triple
filtered. Air flow through the chamber was maintained at 10 liters per
minute. This flow provided the 162 liter chamber with one volume exchange
per 16.2 minutes. Following the 90th percentile gas flow rule, calculations
show a complete air exchange occurs at ten times a volume exchange. Therefore
the chamber is completely refreshed every 2 hours 42 minutes.
Coin samples consisted of 1964 to 1980 pennies which all have a composition
of 95% Cu, 5% Zn and, 1964 to 1979 nickels with a composition of 75% Cu
and 25% Ni.
The coin samples were degreased with 111 trichloethane, and dried with
gaseous nitrogen. They were then placed in appropriate compartments in
the storage media samples.
Evaluation of the samples was performed with, a LEO 1530 scanning electron
microscope for surface topography, X ray analysis with a Kevex EDXA for
elemental analysis, and a Kodak model 950 digital camera for optical data.
Five types of storage boxes were evaluated:
Album, multipage book with clear plastic covered slot and an outer cover
with Intercept Technology throughout the book.
X Album, similar to 1, different vendor, no Intercept
Y Album, similar to 1, different vendor, no Intercept
Tri Fold, open coin slots: cover folds onto itself. Intercept Technology
Z Tri Fold, open coin slots: cover folds onto itself. No Intercept
books were placed in the test chamber for a 150ppm hour exposure. Previous
work(7) indicated this exposure is
equivalent to average ambient H2S exposure for 10 years. This relationship
of copper sulfide film growth and sulfur gas exposure has been shown to
follow the formula of RCu,i=lCu,i[í]
where RCu,i is the rate of formation of a sulfur-containing
corrosion film on copper by species i, [í] is the atmospheric sulfurous
gas concentration, and lCu,i is the
pseudo-first-order rate constant. For comparative purposes RCu,i
can be approximated for SO2 and CS2
at a total exposure of 100 ppm-h (approximately the total sulfurous gas
exposure that would occur in 10 year in a typical urban environment).
The derived value of í is 4x10-3 nm ppb-h-1
for H2S. A similar relationship exists for silver
and sulfur gases with í being a lower number in that the reaction
efficiency of silver is lower than that of copper(8).
Twelve coins were tested in each album and tri fold. Typical representations
of the exposed coins were selected to evaluate. One nickel and one penny
from each was analyzed.
As observed, the Intercept album and Intercept tri fold performed without
visual degradation. These had Intercept Technology protection. The Sample
X album pennies changed to an overall darker hue, with the nickels shifting
to an even yellow tone. The Sample Y Album pennies sulfided far worse
with additional degradation in the form of blue/black ringing patterns
on the outer edge. The nickel shifted from yellow to a reddish tone. Although
overall corrosion had taken place, corrosion on the Sample Y album coins
were heaviest on the side facing the opening.
The Sample Z tri fold was the worst protector causing the penny to form
a blue/black corrosion film, and the nickel to shift completely yellow/red
with bright but speckled areas of blue. In order to quantify the film
growth and surface chemistry the coins were placed in the scanning electron
microscope for sulfur observation and X-ray analysis for elemental mapping
SEM observations were unremarkable except in areas of surface discontinuities.
For example, where the ear of Lincoln of the Sample Y album penny shows
corrosion occurring at the apex of the raised struck outline of the topography.
This is typical of an altered grain boundary which will exhibit more susceptibility
toward corrosion than the surrounding area as seen in previous work on
the Statue of Liberty restoration(9).
Another significantly altered zone exists on the outer rim areas of all
the coins, shown in figure 3. Sulfide growth is significantly higher than
the surrounding surfaces (8,696). Figure 3 also depicts spot corrosion
(blue spots) were created due to localized increases in time of wetness
most likely caused by anhydrous particulates. These blue areas are indicative
of the formation of hydrated sulfate formations such as posnjakite(10).
The remaining samples did not reveal significant deviations from previous
observations. Further corrosion mapping was deemed unnecessary. Electron
Dispersive X-Ray Analysis (EDXA) was used to obtain an elemental spectrum
of the metal samples. The evaluation scheme took advantage of the EDXA's
ability to digitally record a background elemental spectrum and subtract
that data from another samples response. The resultant data can then be
computed into a ratio of increase of elements in Thousands of Electron
Volts activations (Kev) to corresponding chemical
elements. Since both coins possessed at least 75% Cu the Cu peak was set
as a reference baseline parameter. The La copper
reference peak which is at .93 Kev was used for
reference analysis. The Ka
sulfur peak is used as a corrosivity evaluator. That peak is seen at 0.213
Kev. The analysis started at zero and stopped counting
spectra until 100,000 X-Ray counts accumulated from the La
copper peak. At that time the Ka
sulfur count was recorded. Data analysis was configured to provide a relative
ratio of sulfur accumulation over the base line as reasonably accurate
as possible. The following analysis remains qualitative in nature. This
analysis should not be considered quantitative. Figure 4 plots the results
of the differential scans of the three types of Album Storage Media coins.
The Intercept (Intercept protected) album sulfur counts were zero and
considered baseline. The Sample X album penny was 27x higher in sulfur
and the nickel 19x higher. The Sample Y album penny was 56x higher in
contamination due to sulfur and the nickel 6,176x higher. In the Tri Fold
albums, the penny and nickel samples were at zero for the Intercept album.
Similar to the previous album the Intercept protected coin scan was considered
at the background level. The Sample Z Tri Fold is a commodity storage
media. Sulfur on the penny stored in the Sample Z tri fold was measured
at a ratio of 6,758 and the nickel at a ratio of 7,257.
The evaluation of Intercept Technology encompassed equivalent 10 year
sulfurous atmospheric trace gas corrosion testing followed by optical
evaluation, scanning electron microscopy, and x-ray elemental analysis.
This generic testing and evaluation was designed to demonstrate the protection
ability of material packages in reference to corrosive atmospheric sulfur
trace gases and their reactions with copper, silver, and their alloys.
The test results show the tested Intercept Shield products offer a considerable
increase over other non-Intercept protective products.
1) L. Soto, J.P Faney, T.E. Graedel, and, G.W. Kammlott, "On The
Corrosion of Certain Ancient Chinese Bronze Artifacts", Corrosion
Science, Vol. 23, No. 3, pp. 241-250, 1983.
2) P.A. Skiba, Changes in Reflectivity and Emisivity of Oxide Systems
Subjected to the Influence of Continuous CO2 Laser
Radiation, Zhurnal Prikladoni Spektroskopii, Vol. 37, no. 2, Pages 242-247,
3) J.H. Payer, "Corrosion Processes in the Development of Thin Tarnish
Films", Dept of Materials Science and Engineering, Case Western Univ.,
Cleveland, OH, 1992.
4) T.E. Graedel, J.P. Franey, G.J. Gualtieri, G.W. Kammlott, and D.L.
Malm, "On the Mechanism of Silver and Copper Sulfidation by Atmospheric
H2S and OCS", Corrosion Science, Vol 25, No.
12, pg. 1163-1180, 1985.
5) J.P. Franey, T.E. Graedel, and G.W. Kammlott, "The Sulfiding of
Copper by Trace Amounts of Hydrogen Sulfide", The Journal of the
Electrochemical Society, 158th Meeting, Hollywood, FL, 1980.
6) J.P. Franey, "A Novel System for Atmospheric Corrosion Experiments",
Corrosion Science, Vol. 23, No 1, pg. 1-8, 1983.
7) T.E. Graedel, J.P. Franey, and G.W. Kammlott, "The Corrosion of
Copper by Atmospheric Sulfurous Gases", Corrosion Science, Vol. 23,
No. 11, pg. 1141-1152, 1983.
8) T.E. Graedel, J.P. Franey, and G.W. Kammlott, "The Corrosion of
Silver by Atmosheric Sulfurous Gases", Corrosion Science, Vol 25,
No. 2, pg. 133-143, 1985.
9) J.P. Franey, and M.E. Davis, "Metallographic Studies of the Copper
Patina Formed in the Atmosphere", Corrosion Science, Vol. 27, No.
7 Special Edition, pg. 659-668, 1987.
10) K. Nassau, P.K. Gallagher, A.E. Miller, and T.E. Graedel, "The
Characterization of Patin Components by X-ray Diffraction and Evolved
Gas Analysis", Corrosion Science, Vol 27, No. 7, Special Edition,
pg. 669-684, 1987.