United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-85/048 July 1985
Project Summary
Development and Evaluation
of an Instantaneous
Atmospheric Corrosion Rate
Monitor
F. Mansfeld, S. L. Jeanjaquet, M. W. Kendig, and D. K. Roe
A research program has been carried
out in which a new instantaneous at-
mospheric corrosion rate monitor
(ACRM) has been developed and evalu-
ated, and equipment that will allow the
use of many sensors in an economical
way in outdoor exposures has been
constructed. The ACRM was tested in
flow chambers in which relative humid-
ity and gaseous and paniculate pollu-
tant levels can be controlled. A rela-
tively inexpensive electronics system
for control of the ACRM and measure-
ment of atmospheric corrosion rates
was designed and built. Calibration of
deterioration rates of various metallic
and nonmetallic materials with the re-
sponse of the ACRMs attached to these
materials was carried out under con-
trolled environmental conditions using
this system.
This Project Summary was devel-
oped by EPA's Atmospheric Sciences
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Since atmospheric corrosion can be
assumed to be an electrochemical pro-
cess, it is quite logical to use electro-
chemical techniques to monitor atmo-
spheric corrosion phenomena. These
techniques have the following impor-
tant advantages: atmospheric corrosion
behavior can be monitored continu-
ously and correlations can be estab-
lished with atmospheric parameters
that are recorded at the same location.
The development of corrosion sensors
for atmospheric corrosion studies has
been relatively slow compared to appli-
cation of corrosion sensors to other cor-
rosion phenomena. The approach of
several groups that have been using
electrochemical sensors in atmospheric
corrosion research has been reviewed
recently. The main activities have been
in Canada, where Sereda developed a
concept to monitor the time-of-wetness,
tw; in Scandinavia, where Kucera and
Haagenrud have applied electrochemi-
cal sensors to measure tw and atmo-
spheric corrosion rates; in the USSR,
where Mikhailovskii and co-workers are
carrying out an extensive program in at-
mospheric corrosion research; and in
the United States, where the principal
investigator of this project and his co-
workers have carried out systematic at-
mospheric corrosion research using
electrochemical techniques. In the latter
studies, the atmospheric corrosion
monitor (ACM), which is an electro-
chemical sensor, has been used to mon-
itor tw and atmospheric corrosion rates
in outdoor exposure and laboratory
studies. Most recently, a detailed statis-
tical analysis has been carried out in
which the factors that affect the re-
sponse of ACMs and the reproducibility
of ACM data have been determined.
These factors included environmental
parameters such as relative
(RH), tw and S02 concentration, he&
the metal used to assemble an ACM,
location in the test cell, and aging in out-
door exposure.
-------
The new atmospheric corrosion rate
monitor (ACRM), which was developed
and tested in this program, is based on
Sereda's concept, which is the basis for
the American Society for Testing Mate-
rials (ASTM) G84 Standard Practice for
Measuring the Time-of-Wetness on Sur-
faces Exposed to Wetting Conditions as
in Atmospheric Corrosion Testing. The
geometry of this sensor promises a
much faster response to rapidly chang-
ing atmospheric conditions than the
more bulky ACMs. While the ASTM doc-
ument describes only the approach to
measuring tw, the present effort has fo-
cussed on using the same sensor to de-
termine atmospheric corrosion rates,
which can be used to determine the cor-
rosivity of test sites; to follow corrosion
episodes such as acid rain; and to give
an indirect measure of the corrosion be-
havior of different construction materi-
als. The new ACRM is a two-electrode
system with zinc electrodes, which can
be attached to the metal of interest. The
tw would be a by-product of corrosion
rate measurements in outdoor expo-
sure, since corrosion activity occurs
only during tw.
Atmospheric corrosion sensors can
be designed as galvanic cells such as
Cu/Zn, or Cu/steel; or as one-metal, two-
electrode cells such as steel/steel, or
Zn/Zn. Both approaches have been used
at the Rockwell International Science
Center. In the present program, a Zn/Zn
sensor was used to which a 30 mV po-
tentiostatic pulse was applied. In this
case, in principle the corrosion current
density, icorr, can be calculated from the
Stern-Geary equation:
B __2baXl30__
Rp" - 2.3 AE x A K '30
where
ba an . R _ AE x A
= TT-^ and Rn -•
21
30
(D
Corrosion rates are calculated from icorr
by using Faraday's law for zinc. Applica-
tion of Eq. (1) requires knowledge of the
factor B, which depends on the anodic
Tafel slope ba in the case of diffusion
control of the cathodic reaction (bc-»*).
Factor A is the area of one of the two
electrodes. For an anodic Tafel slope of
ba = 60 mV, AE = 30 mV, A = 1 cm2, one
obtains k=1.75. Since B can change
with environmental conditions and with
time and because its exact value is often
unknown for a given application, a theo-
retical value is often used for B (or k) in
Eq. (1). Theoretical values of B range
from 6.5 mVto 52.1 MV, although 13 mV
to 26 mV seems to be most common.
The electrochemical measurement car-
ried out here, therefore, is basically a
determination of the polarization resis-
tance Rp.
In this work, the ACRM was devel-
oped and tested in laboratory facilities
in which temperature, RH, and gaseous
and paniculate pollutant levels can be
controlled. A relatively inexpensive
electronics system for data logging and
control of the sensors (ACRMDL) was
developed and tested; whether the cor-
rosion sensor response can be used as
a proxy for the atmospheric corrosion
behavior of a variety of materials such
as galvanized steel, weathering steel,
marble, and latex- or oil-base house
paints was also determined.
The New Atmospheric Corro-
sion Rate Monitor
The design of the new miniature
ACRM is based on the sensor used by
Sereda, which is now the basis of the
ASTM Standard Practice G84. The
ACRM's advantage is its small size,
which makes possible attaching it to a
material of interest and monitoring tw
for this material in its microclimate and
determining a (indirect) measure of the
instantaneous corrosion rate of this ma-
terial. Since the sensor output only re-
flects the corrosion rate of this material,
in this case zinc, conversion factors
have to be established to calculate cor-
rosion rates for other materials. An al-
ternative approach would be to calcu-
late a corrosivity index for a given
microclimate based on the ACRM corro-
sion rate data.
Design of the ACRM and Mea-
surement Principle
The design of the ACRM is shown
schematically in Fig. 1. An important im-
provement over Sereda's original de-
sign is the use of solid zinc instead of
zinc-plated copper; this avoids the
problem of porosity of the zinc layer
after extended exposure periods and
accelerated corrosion due to the Zn/Cu
couple, which would also cause errors
in the measurement. The thickness of
the zinc sensor used in this project is
0.05 mm; it is bonded to an 0.25 mm
thick epoxy laminate board. The sensor
"fingers" are 7.8 mm long, 0.6 mm
wide, and are spaced 0.2 mm apart
(Fig. 1). The active part of the sensor
measures 19 mm x 12.3 mm, and the
remainder is used for connection of the
current amplifier, capacitors, and leads,
which connect the sensor to the control
unit.
The measurement principle is differ-
ent from that of Sereda, who used a gal-
vanic Zn/Au or Cu/Au couple to measure
tw. In the present approach, the polariza-
tion resistance technique is used to
measure instantaneous corrosion rates.
Figure 1 shows the electronic circuit for
measurement of the current flow that
results from application of a ±30-mV
pulse. This potential pulse is produced
by the D/A card in the multiprogrammer
of the computerized system, which con-
trols the experiment. The potential
pulse is applied between the INPUT and
COMMON terminals of the sensor, as
shown in Fig. 1. The current, I, is deter-
mined from the output, V, of the ampli-
fier as I = V/Rm, where Rm is the measur-
ing resistor. The polarity of the applied
30 mV step is changed after 2 min. Se-
quential measurement of the currents
on as many as eight sensors are made
during each pulse by using relay cards
in the multiprogrammer; the output
from the relay cards is measured by an
A/D. The current-time curves are stored
on cassettes for later analysis.
Response to Variations in Envi-
ronmental Conditions
Effect of Pretreatment and Ex-
posure to Single Pollutants on
ACRM Response
Research at this laboratory and at oth-
ers has shown that the chemical nature
of the corrosion product layer has a
great influence on the critical RH level at
which condensation occurs. Therefore,
tw is strongly affected by the chemistry
of the corrosion product layer, and one
can assume that the corrosion rate and
its changes with time also depend on
this chemistry. Thus, evaluating the ef-
fects of different pretreatments on sen-
sor response and stability was neces-
sary.
The sensors were pretreated with
1 mM NaCI, 1 mM CaCI2, deionized
water, or were untreated. Pretreatment
following cleaning in ethanol consisted
of application of a known volume of de-
ionized water, 1 mM NaCI, or 1 mM
CaCl2 to which a small amount of alco-
hol had been added to improve wet-
tability. One set of sensors was not pre-
treated after cleaning. The liquids
placed on the surface of the sensors
-------
Cm
Hh
ACRM-r-
Out
-Vs + Vs
Figure 1. Design of ACRM and electronic circuit.
were allowed to dry out, and the sen-
sors were kept overnight at 45% RH.
They were then exposed to an RH cycle
of 65%-80%-95%-80%-65% RH for 1 h
each.
The responses of eight ACRMs to RH
after pretreatment with CaCI2 were pro-
nounced and were fairly similar be-
tween sensors. Similar results were ob-
served for the NaCI pretreatment. For
deionized water pretreatment and for
no pretreatment, the current flow was
very low and was often below the detec-
tion limit of the system. This set of data
was taken, therefore, as a qualitative in-
dication of the necessity of an effective,
reproducible pretreatment.
Table 1 explains the test sequence for
a test series in which the effect of sensor
pretreatment and the nature of pollu-
tants were evaluated. For each subset of
this series, eight ACRMs were pre-
treated according to the four possibili-
ties la-d and then were subjected to the
sequence under II in Table 1. Two sen-
sors (e.g.. No. 1 and 2) were coated with
carbonaceous particulate matter (CPM)
to an extent equivalent to 0.5 yr expo-
sure in an urban environment. These
two sensors and two additional sensors
(e.g., No. 3 and 4) were then exposed to
2 h at 90% Rh, and Rp values were con-
tinuously determined. As shown in Fig.
2a, the S02 level was increased to
1 ppm for 1 h each (step II.2). The S02
was then turned off and after another
hour at 90% RH, the RH was reduced to
65% overnight. The next morning, two
Table 1. Test Schedule
I. Effect of Pretreatment
a. dist. H2O
b. NaCI (1 mM)
c. CaC\2 (1 mM)
d. None
Cycle RH - 65-80-95% and back, 1 h each.
II. Effect of Pollutants
7. Sensors No. 1, 2 with pretreatment
a, + carbonaceous particulate matter.
Sensors No. 3, 4 with pretreatment a,
RH = 90%, 2 h.
2. (Sp2) = hi^-low^stepwise to hi, 1 h
each.
3. RH = 90% for 1 h, followed by
RH = 65% overnight.
4. Add sensors No. 5, 6, Rh = 90% for
1h.
5. Repeat 2 and 3 for NO2.
6. Add sensors No. 7, 8, RH = 90% for
1 h.
7. Repeat 2 and 3 for O3.
Same for pretreatments b. -d. (sensors
No. 9-32).
Particulate matter is applied only in
Step 7.
additional sensors (e.g.. No. 5 and 6)
were added to the test cell and the cycle
was repeated for NO2 (steps II.4 and II.5)
(see Fig. 2b). On the last day, the pollu-
tant was 03. The design of this test se-
ries was such that sensors No. 1-4 were
exposed sequentially to SO2, NO2, and
03; sensors No. 5 and 6 were exposed
to N02 and 03; and sensors No. 7 and 8
were exposed only to 03. A comparison
of the corrosion behavior of sensors No. 1
and 2 with sensors No. 3 and 4 should
allow an estimate of the effect of CPM
on the corrosion behavior.
Sulfur dioxide has a strong effect on
the corrosion rate of the zinc sensor.
The Rp decreased almost immediately
when the S02 level was increased to
1 ppm. This effect is not due to in-
creased conductivity of the surface elec-
trolyte because an almost instanta-
neous increase of Rp results when the
S02 level is decreased to 0.1 ppm. Nitro-
gen dioxide also affects corrosion rates.
No clear change of Rp with 03 level can
be detected. Similar behavior was ob-
served for the NaCI pretreatment. For
deionized water pretreatment, the cur-
rent flow was very low and was often
under the detection limit of the system.
Integration of the Rp~Mime curves for
the time when a given pollutant was
present gives the corrosion loss (in sec-
onds per ohm) shown in Table 2. Since
the factor B (Eq. (1)) is not known for the
present experimental conditions, it is
preferable to use the integrated corro-
sion loss as a qualitative measure of the
-------
CaCI2/SO2/RH = 90%
Table 2. Integrated Corrosion Loss (10~3 s/ohm)
012345678
Time (Hr)
(a)
RH = 65%
012345678
Time (Hr) t
RH = 65%
(b)
34567
Time (Hr)
Effect of pollutant nature and
concentration on ACRM re-
sponse (CaClzpretreatment). (a)
SOa. (b) NOt. (c) O»
M
Figure 2.
corrosion effects as shown in Table 2.
Coating with CPM lowers the corrosion
loss for CaCI2 and for NaCI pretreat-
ments (sensor No. 1 and 2 compared
with No. 3 and 4). A comparison of sen-
sors No. 7 and 8 with No. 5 and 6 and
with No. 3 and 4 shows that exposure to
SOa produces a larger corrosion loss
than exposure to N02, while 03 expo-
sure induces the lowest corrosion dam-
age. Pretreatment with NaCI leads to
higher corrosion rates than pretreat-
ment with CaCl2. A comparison of sen-
ACRM No.
PT*
CaCI2
CaCI2
CaCI2
Total
NaCI
NaCI
NaCI
Total
Pollutant
SO2
NO2
03
SO2
NO2
02
1
0.27
0.26
0.10
0.43
0.30
0.55
0.40
1.25
2
0.81
0.24
0.37
1.42
0.72
0.69
0.50
1.91
3
4.89
0.63
0.45
5.97
7.36
3.08
2.56
13.00
4
2.32
0.60
0.63
3.55
6.59
4.59
2.43
13.61
5
0.67
0.20
0.87
3.90
2.47
6.37
6 7
0.38
0. 18 0.08
0.57 0.08
3.34
2.27 2.58
5.61 2.58
8
0.09
0.09
3.38
3.38
*Pretreatment; ACRM No. 1 and 2 coated with CPM
sors No. 3 and 4 with No. 5 and 6 shows
no large effect of prior exposure to SO2
on corrosion losses during exposure to
NO2. Similarly, sensor No. 3-8 show
very similar corrosion losses during ex-
posure to 03, especially for the NaCI
pretreatment. This lack of an effect of
prior exposure to a different pollutant is
somewhat surprising, since the result-
ing changes of surface chemistry would
be expected to also change tw and cor-
rosion rates. However, the short expo-
sure periods that had to be used in the
present tests might have precluded sig-
nificant changes of surface chemistry.
Effect of Exposure to Pollu-
tants, Simulated Dew, and Ul-
traviolet Light Cycles
Eight sensors of different history
were exposed to SO2, NO2, and O3; sen-
sors were cooled and warmed to simu-
late dew and were exposed to ultravio-
let (UV) light during the drying cycles.
The eight sensors were first exposed
to 90% RH for 2 h in the presence of
SO2 + NO2 + O3 at 1 ppm each. The sen-
sors were then cooled for 2 h, which led
to condensation; this was followed by
2 h at room temperature in the presence
of UV light. The pollutant flow was then
stopped. After the first day, the ACRMs
were exposed overnight at an RH of
90%; after the second day, they were
kept at 45% RH. Before the first test, all
eight sensors were put through the RH
cycle.
Cooling of the sensors leads to an al-
most instantaneous drop of Rp and an
increase of corrosion rates (Eq. (1) and
Fig. 3) The Rp increases slightly during
further cooling and decreases again
during warming under UV light. When
UV light is turned on, the RH increases,
and this causes an increase in the flux of
S02 to the surface (lower exit value),
which is consistent with a higher corro-
sion rate. A value of Rp = 1 x 104
ohm-cm2 corresponds to a corrosion
rate of 79 (xm/yr for B = 26 mV (Eq. (1)).
Design and Test of the Data
Logging System
The ACRMDL is used for control of the
ACRMs and for data collection. It incor-
porates a small computer (Radio Shack
TRS80 Model PC-3) programmed in
Basic language, which has sufficient
memory to log 4,608 measurements for
six sensors over a four-day period. A
printer/plotter that is part of the
ACRMDL is used to provide hard copies
of the results as log Rp versus time in
tabular and graphical form. Results may
also be transferred to cassette tape or to
another computer via an RS-232C inter-
face.
The experimental data have been
transferred from the ACRMDL to a VAX
11/780 computer for storage and further
processing (analysis, display). This data
transfer is also necessary, since only a
limited amount of data can be stored on
the ACRMDL. It also prevents accidental
loss of data.
To check the operational procedure
for the use of the ACRMDL, a test series
was performed in which RH was kept at
95% for 7 h and was then decreased to
65% overnight. After 1 h at 95% RH, the
base plate of the test cell to which the
sensor was attached was cooled 3°C
versus room temperature, except on the
first day, when it was cooled 4°C. Cool-
ing was maintained for 5 h. Two hours
after the start of the test, S02 was intro-
-------
700
1
i
c
8
|
<0
2 concentration, as
measured at the outlet of the test cell,
dropped due to dissolution of the SO2 in
the surface -electrolyte. Also shown in
Fig. 5 is the RH as calculated from the
temperature of the test cell and the dew
point of the air coming out of the test
cell. The ACRM response (Fig. 5) closely
follows this cycle of environmental con-
ditions. In the first cycle, Rp changes by
a factor of two between the "cool" and
the "warm" condition of the ACRM at-
tached to one of the specimens. Fig-
ure 6 shows an 80-h cycle in the middle
part of the test period. The cyclic re-
sponse of the six ACRMs is clearly seen.
It becomes apparent that sensors No. 1,
2, 5 and 6 show very similar Rp values,
while sensors No. 3 and 4 have higher
values that aj^Tjorepr less the same
for these two^lBMPs. These differ-
ences can be tracjroack to the different
locations of the ACRMs in the test cell.
Sensors No. 1 and 2 were located on the
west wall of the cell, while sensors No. 5
and 6 were on the opposite east wall in
an equivalent position. Sensors No. 3
and 4 were located next to each other
on the south wall. Figure 7 gives a
schematic of the experimental arrange-
ment for test coupons and ACRMs.
Since the air flow came out of the tubes
which were parallel to the east and west
walls, possibly the pollutant and wet air
flow was different for these two walls as
compared to the south wall.
The gradual increase of corrosion
rates with exposure time is reflected in
Fig. 8, in which the average inverse po-
larization resistance and the calculated
reduction in thickness. Ad, for a given
time element (the horizontal bar
through the data of sensor No. 1) are
plotted. For sensors No. 1, 2, 5, and 6,
-------
SO2 (ppm)
i a
Oc
S 2.0
1.6
1.2
0.8.
0.4
Day 3
6 8
t (hours)
fb)
10 12
Figure 4.
Response of four ACRMs with
different pretreatments to
changes in environmental condi-
tions (numbers refer to sensor
nun ^^^^^^
corrosion rates in<^|»t>y about a fac-
tor of 2 to 3, whilt,Jff%nsors No. 3 and
4, this increase is about a factor of 6.
However, for the reasons outlined
above, the corrosion rate at the end of
the test is still much less for these two
sensors than for the other four sensors.
Only the weight loss data for the gal-
vanized steel and the weathering steel
were sufficiently accurate to warrant the
calculation of a conversion factor, CF.
Due to the relatively short exposure
time, the weight loss for the paint and
the marble was very low. Table 3 com-
pares the weight loss, Am, and ACRM
data normalized to the exposed area of
the test coupons or ACRMs. For galva-
nized steel, the average CF of 9.94-10~3
agrees very well with the calculated
value of 8.83-10"3 obtained from the
Stern-Geary equation (Eq. (1)) for zinc
with ba = 60 mV, according to the fol-
lowing equation:
Am(mg/cm2-d) = ^j^ (2)
rip
With Rp = t/81.5 = 32864 ohm-cm2 one
obtains the following:
Am = 2.323-10~2 mg/cm2-d
or
and
0.720 mg/cm2
(3)
CFSG =
0.72
"SG~81.5
= 8.83-10~3 mg-ohm-s"1
(4)
81.5
= 9.94-10-3mg-ohm-s-1 . (5)
For weathering steel, CFexp = 0.138
mg-ohm-s"1. A CFSc calculated in the
Stern-Geary equation for iron as
7.48-10"3 mg-ohm-s~1 does not apply in
this case, since it compares the corro-
sion behavior of iron with that of a zinc
sensor. The corrosion rate of weather-
ing steel decreases with time according
to equation rcorr = at~b, where b = 0.5.
The experimental CF is, therefore, time-
dependent, considering that in the case
of zinc b = 1.
Summary and Conclusions
A new instantaneous ACRM has been
developed and tested. The response of
the ACRM to single pollutants and com-
binations of SC"2, Os, and NOj; to diur-
nal cycles; and to periods of dew has
been characterized. A data logging sys-
tem - the ACRMDL - has been designed
and tested with the ACRM. The ACMDL
is battery operated and can control up
to six ACRMs simultaneously. The use
of log converters for the recording of
the current transient allows accurate
measurements over four decades.
A number of experiments have been
performed to determine the effects of
sensor pretreatment. No definite effects
could be found in experiments in which
the ACRMs were exposed without for-
mation of liquid layers for short time
periods, although the absence of pre-
treatment produced lower corrosion
losses. The ACRMs showed almost in-
stantaneous changes of Rp when RH
and the pollutant level, especially (SO2),
were changed. When liquid corrosion
layers were formed, especially over
long time periods, the effect of pretreat-
ment was negligible. The sensors are so
sensitive in their response to environ-
mental conditions that a less than opti-
mum placement of some sensors in the
test cell during an exposure test became
quite obvious.
1 -\24
100
•S
tf.
§"
4.2
4.0
312 316 320 324 328
Time (hours) *
332
336
Figure 5. Environmental changes and response of an ACRM.
-------
6.00
5.60
•§ 15.20
.c
§" 4.80
4.40
4.00
ll i l i
3/0 320 330 340 350 360 370 3SO
Time (hours)
6.00
The response of the ACRMs to SO2,
03, and NO2 has been studied as a func-
tion of concentration between 0 and
1 ppm. A very pronounced effect of SC>2
and N02 concentrations was observed,
especially when a liquid electrolyte film
was present on the ACRM surface. The
fact that this effect is reversible shows
that the dissolved pollutant not only
changes the electrolyte conductivity,
but also produces as its main effect a
change in corrosivity.
From the results of the exposure test,
CFs that can be used to convert ACRM
data into corrosion losses of galvanized
steel and weathering steel have been
calculated. It also seems desirable to
obtain CFs in exposure to natural envi-
ronments of different corrosivity to as-
certain the validity of the CFs obtained
in a laboratory test.
The ACRM in its present form that
consists of solid zinc is a very sensitive
sensor for the corrosivity of the atmo-
sphere and its changes and for tw. The
ACRMDL provides a very convenient
way to control the sensor operation and
to collect the corrosion data. Since it is
battery operated, it can be used unat-
tended for long time periods. Data
transfer to a larger computer allows
analysis and display of the ACRM data
in a more detailed manner.
Acknowledgement
Although the research described in
this article has been funded wholly or in
part Jay the U.S. Environmental Protec-
tion Agaru^^uidr€f Contract No.
68-02-3741 to^Kckwell International
Science Center, IT does not necessarily
reflect the views of the Agency and no
official endorsement should be inferred.
The authors acknowledge many helpful
discussions with Project Officer
F. H. Haynie.
4.00 \
370 320 330 340 350 360 370 380
Time (hours)
Figure 6. 80-h test cycle for six ACRMs (numbers refer to sensor numbers).
-------
Cooling \
Outlet
t
Cooling Inlet
1 GS ' ' GS ' ' GS ' '
M
M
Gas Outlet
M + S3
S4
1
^L>
Gas Inlet
Gas flows vertically and towards
GS: Galv. Steel
WS: Weathering Steel
M: Marble
LP: Latex Base House Paint
OP: Oil Base House Paint
22"
Gas Inlet
^ 1 /T\ 1 1
, OP , , OP , , OP , ,
—
_
WS '
WS
wa//
WS
Gas Outlet
LP
LP
t
LP I
•<—
Figure 7. Schematic of ACRM and test coupon location.
100
•§
10 -
100
400
600
t
-------
Table 3. Comparison of Weight Loss and ACRM Data for 31-Day Exposure Test
Galvanized Steel
Weathering Steel
Oil-Base Paint
Latex-Base Paint
Marble
Weight Loss
(mg/cm2)
0.81
11.25
<0.11)
(0.07)
(0.002)
ACRM
(s/fl-cm2)
71.3
90.5
78.1
86.1
Average CF*
(s/Sl-cm2) (mg-fl-s -~i)
9.94 x 70-3
7.38 x 70-'
87.5 ± 8.5
*CF = conversion factor.
F. Mansfeld, S. L Jeanjaquet, andM. W. Kendig are with Rockwell International
Science Center, Thousand Oaks, CA 91360; D. K. Roe is with Portland State
University. Portland, OR 97207.
Fred H. Haynie is the EPA Project Officer (see below).
The complete report, entitled "Development and Evaluation of an Instantaneous
Atmospheric Corrosion Rate Monitor," (Order No. PB 85-214 336/AS; Cost:
$11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
•&U. S. GOVERNMENT PRINTING OFFICE: 1985/559-111/20619
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