Volume 1 Paper 15
Scientific Engineering of Anti-Corrosion Coating Systems based on Organic Metals (Polyaniline)
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JCSE Volume 1 Paper 15
Submitted 22 April 1999, revised version published for public review 25 October 1999
There are comments on this paper
Scientific Engineering of Anti-Corrosion Coating Systems based on Organic
Dr. Bernhard Wessling, Ormecon Chemie GmbH & Co. KG, Ammersbek (a
subsidiary of Zipperling Kessler & Co.)
The new corrosion protection technology with polyaniline, an Organic Metal
(conductive polymer), is presented. It is based on an immense surface
ennobling and the formation of a passivating metal oxide. The requirements for
efficiently working coating systems, comprising the dispersed Organic Metal
containing primer, eventually an intercoat, and a top coat, are characterized.
An integrated 4-step-method ("scientific engineering") has been
developed and is successfully used for the systematic development of such
coating systems. The combination of the measurement of the open circuit
potential, a new scratch test, EIS and SKP together are a powerful tool for
predicting the results of accelerated corrosion tests and real-time corrosion
prevention performance. Organic Metal coating systems are out-performing even
the best conventional anti-corrosion coating systems.
§2 Keywords Polyaniline, Organic Metal, Conductive Polymer, Corrosion Protection,
Ennobling, Passivation, Metal Oxide, Coatings, Electrochemical Impedance
Spectroscopy (EIS), Scanning Kelvin Probe (SKP), Volta Potential, Open Circuit
Potential, Potential Shift, Scratch Test, Accelerated Corrosion Tests.
§3 1. Early work
We began our research in this area 1986 and prepared the first dispersed
polyaniline (PAni) containing coating in 1987 .
Our goal was to find out, if corrosion protection was possible on just normal
steel, without any pretreatment, especially without previous passivation in
acid or under electrochemical conditions. We wanted to know, if corrosion
protection was feasible using a PAni dispersion in a coating, hence without
any electrochemical deposition of PAni. Our research was motivated by the
publication of deBerry in 1985 
according to which polyaniline, electrochemically deposited on pre-passivated
stainless steel in strong acid environment, was enhancing the corrosion
protection of this metal. Similar observations, however with a composition not
identical with polyaniline, had previously been made by Mengoli et al .
Both authors favoured the conclusion, that PAni, if electrodeposited on pre-passivated
steel, was capable of maintaining the passive state.
§4 This was the only public knowledge available, when we first began our work
with the goal to find out about anti-corrosion effects based on PAni. Our
proprietary knowledge at that time was how to disperse polyaniline, although
still at a relatively low performance level, as we had succeeded with first
dispersions of polyaniline only some 2, 3 years before (mainly in
thermoplastic polymers). It was completely unknown, if a PAni dispersion
coating (with the PAni-free insulating matrix around) would have any effect,
and if, what the effect would be based on, and if not, how to make it to be an
anti-corrosion coating. Nothing at all was known about any anti-corrosion
effect of PAni, if applied non-electrochemically and on a non pre-passivated
steel (or iron or any other metal) surface, and nothing at all was to be
expected in this direction at that time.
§5 In 1987, we surprisingly found some corrosion protection ,
and we also found that an oxide was formed, but this could have been any oxide
or hydroxide, or even a first sign of rust, as we had not yet been able to see
any improvement over state-of-the-art coatings. We followed these first
findings in the next years, partially together with other groups, and also
published another patent application 
with some improvements in corrosion protection, but still not at all
convincing for corrosion experts, still not performing reproducibly, and not
performing any better than conventional coatings, but worse.
§6 At that time, we had no idea, what mechanism was active if there was any
beneficial and remarkable anti-corrosion effect of polyaniline deposited by
other than electrochemical means on other than pre-passivated metal surfaces
(stainless steel) under other than passivating conditions. The conductive
polymer research community, and moreover the corrosion experts outside it, did
not believe in the possibility to realize an anti-corrosion technique using
polyaniline, especially not with a PAni dispersion. Also Allied and Americhem,
with which together we had made the study leading to the second patent ,
stopped their work on this question and left the cooperation, as a success of
the research was not at hand.
§7 2. Breakthrough
It was in 1993 that we found out how to reproducibly realize superior
corrosion protection with Organic Metals. We discovered the phenomena
responsible for the new corrosion protection principle: it was a surface
ennobling (i.e., a shift of the corrosion potential of the metal surface by
about 800 mV to the more noble range) and a new type of passivation (i.e., the
formation of a stoichiometric iron (II) oxide) .
For the basic studies, we used as well pure polyaniline dispersions as
polyaniline dispersion coatings which were deposited on untreated metals like
normal iron, stainless steel, copper and aluminum.
§8 The corrosion current was significantly reduced or even completely
eliminated at comparable potentials (Fig. 1). Investigations with SEM revealed
that an oxide layer was formed between the PAni coating and the metal surface.
In cooperation with R. Elsenbaumer, we found that it is mainly composed by Fe2O3
(with an underlayer of Fe3O4) .
We repeated the study with a cleaner steel surface to begin with by XPS in
cooperation with a group at Kiel 
(Fig. 2) showing that there was no Fe3O4, but only a
clean a-Fe2O3. (This does not
exclude, that Fe3O4 might also occur in real situations,
but it shows that a-Fe2O3 is
the passivating layer composition formed by PAni, which has also independently
been confirmed by R. Elsenbaumer  and
T. Schauer et al. , although there is
some dispute if it is the a- or the g-
form which is formed).
§9 It is of basic interest that an oxide like that has - to our knowledge -
never been observed or analysed for the "passive" state of stainless
steel (or simple steel), which is not a stable property (after removing the
steel from the passivating medium, its passivity is completely lost). In
contrast, A.-M. LeGoff et al. have published, that the nature of the passive
layer is FeOOH . This means, that
our new technology is also the first one which allows to produce Fe2O3
as a passivating oxide layer. 
§10 In the meantime, in research together with G. Nimtz 
et al. using microwave, and in work together with A. Kaiser et al. 
using thermopower measurements, we had discovered that polyaniline not only is
a conductive polymer, but a true, though "mesoscopic" metal, and
hence can be considered as an "Organic Metal". Now we understood
that the ennobling was possible due to its metallic property, as it is
situated slightly less noble than silver in the galvanic serie .
§11 Our group later succeeded in improving the dispersed PAni containing paints
and coating systems (primer + top coat) 
which are capable of inducing the same passivation effect, but are moreover
industrially applicable and effective as corrosion prevention coating systems.
They perform significantly better than anti-corrosion coating systems composed
by zinc rich epoxy primers and epoxy top coats .
§12 We also discovered the reaction sequence which is responsible for the
passivation (oxide layer formation) and the corrosion protection induced by
the PAni layer. Fig. 3 shows an improved version of the reaction scheme
elaborated by us . It involves
Fe-oxidation by PAni (the more noble metal, Emeraldine salt ES), which is
thereby reduced to Leucoemeraldine base (LE) ;
further oxidation of Fe (II) to Fe (III) and reoxidation of LE to PAni (ES)
via the Emeraldine base EB occur both by oxygen; and Fe2O3
deposition by resulting OH-. This scheme shows furthermore, that
our Organic Metal acts as a catalyst, and that the full catalytic cycle (ES �
LE � EB and back to ES) will only take place, if
the necessary H+ will not be removed by the surrounding medium,
i.e. only, if the acidic pH will be maintained within the primer, e.g. due to
the barrier property of the top coat.
§13 It should be noted, that this new ennobling and passivation technology is
only feasible with well advanced Organic Metal (PAni) dispersions in specially
composed coatings. The particle size of PAni in our dispersions is about 70
nm. At such small particle size level, the dispersed Organic Metal phase will
form the necessary network flocculation structures at very low concentrations 
(we are using only about 2% PAni in our liquid coatings).
§14 Other PAni formulations like "soluble polyaniline" 
do not offer any corrosion prevention effect. It is important to know, that
the sample (3) mentioned in Section 4 and Table 4 in  is our Pani
dispersion (in other publications P. Kinlen referred to it as "PAni/thermoplastic"),
was transferred by us to Monsanto for their comparison tests. It performed
comparably well as a zinc-rich primer with an epoxy topcoat .
The samples "PAni/Phenoxy" and "PAni/Acrylic" are PANDA
products, which do not show any interesting anti-corrosion effect .
We hypothesize, that this is due to the special structure of PANDA, which is
called a "solution", but is in fact a fine dispersion with a (mainly
insulating) dispersion stabilization layer adsorbed on the particle surface .
§15 Other approaches like neutral PAni dispersions in NMP (wrongly been
assigned as "solutions") to be doped after application on the metal 
are not only not effective, but also not practical .
§16 N-PAni (the Emeraldine base, "undoped") is also contributing some
anti-corrosion effect, but by a factor of 100 to 1000 smaller ; this effect
is probably due to its amine groups and could therefore be attributed to a
pure inhibition mechanism.
§17 It seems that the new effects of ennobling and passivation found by us are
linked with well structured ultrafine dispersions (50 - 100 nm) of the Organic
Metal in suitable matrices, forming a conductive and catalytically reactive
continuous (and conductive!) network of flocculated PAni particles.
§18 3. The need for a systematic, scientific development tool
When we started our primer and coating system development, we were aware of
the fact, that we had no practical experience in corrosion phenomena, and even
less in coatings. On the other hand, corrosion and coatings experts did not
believe in our findings, and we were unable to convince them to combine their
experience in coatings with ours in the Organic Metal polyaniline, its
synthesis and dispersion, and in "ennobling and passivation" by it.
§19 We realized very soon [5c, 15],
that a polyaniline containing primer alone was not sufficient as a practically
convincing coating system, but that it needed a top coat. This top coat (or
eventually an intercoat between primer and final top coat) had to fulfill
certain requirements in order to be compatible with the primer. The primer
itself had to meet the following demands:
good adherence to the metal substrate (in dry stage, as well during the
corrosion attack / dry and wet adhesion)
good overcoating ability
practical application demands (viscosity, drying time, ...)
and most important: the full metallic (ennobling) and catalytic
§20 The top coat (or the intercoat, resp.) had to offer
a good (chemical and physical) compatiblity with the primer 
sufficient "sealing" properties (which we first decided not to
offer with the primer itself, but only by the top coat, or by primer + top
coat system together) 
all necessary weatherability and other surface properties needed (colour,
gloss, mechanical or chemical and UV resistance, ...).
§21 Having no practical experience and not enough time for the development of
such coating systems, which should not only to be competitive, but moreover
out-performing generally used state-of-the-art products, we had no other
chance than to follow a scientific systematic route, in contrast to a
§22 We started with the open circuit potential (and corrosion current density)
measurement as described in [5b] in combination with a
wheel-driven alternating immersion test according to DIN 50905 T4 as a 2-step
screening tool. Systems which passed our test 
were subjected to other laboratory tests, salt spray and outside weathering
corrosion tests (cf. ). We found an acceptable correlation in performance
and decided to let one of our systems be tested by a neutral paint research
institute, the "Forschungsinstitut f�r Pigmente und Lacke" in
§23 Two studies were performed by them on our behalf. The first study was a
comparison between a system composed of our primer 900 226/32 plus our
selected epoxy top coat ("2-C EP") and 2 comparative systems having
the same primer, but different top coats ("2-C AY" and "1-C
AY", resp.). The study comprised measurement of dry and wet adhesion, and
salt spray test performance. The system /32 + "2-C EP" performed by
far at best , and the performance
was in accordance with our previous internal results and .
This system is a first model system for our first commercial product (CORRPASSIVTM
4900), introduced in late 1996 .
§24 The second study involved a system we had developed for aluminum, which
requires a different primer used with the same "2-C EP" top coat.
Here, the filiform corrosion was tested, both in laboratory as in an outside
weathering site at Netherlands. Also this system performed very well, as
documented by FPL . This system has
been further developed by us to a commercial product.
§25 In parallel, the FPL investigated some other properties 
of some systems comparable to those evaluated in the first study. They
confirmed the immense potential shift found by us earlier 
and found comparable potential values. The formation of the iron oxide Fe2O3
was confirmed, too. They also confirmed a link between barrier properties,
stability of potential shift and corrosion protection performance.
§26 However, for further development of more and different systems for
different corrosion environments, we needed a tool which was not only capable
of screening between "good" and "bad", but was moreover
capable of delivering quantitative data enabling us to predict corrosion test
results, both of accelerated and real-time tests and practical behaviour.
§27 4. "Scientific Engineering": a new research and development tool
for anti-corrosion coatings
This was the reason why we continued to study and develop other techniques 
for evaluating those properties which we consider being the key requirements
for good corrosion protection performance with Organic Metal coatings,
the ennobling (i.e., the potential shift)
the passivation (i.e., the oxide layer formation)
adhesion of primer (+ top coat) also under corrosive conditions, and
resistance against underfilm corrosion (i.e., minimum underfilm corrosion
optimal barrier properties to be maintained as long as possible under
§28 These 4 properties are now measured by us with the following methods:
open circuit potential measurement
a scratch test developed by us
Scanning Kelvin potential measurement (SKP)
electrochemical impedance spectroscopy (EIS), using a new routine FFT
§29 Test 1 and 2 are used as a first screening. Test 3 and 4 are used for
advanced screening, before they are combined with an immersion cycling,
cycling climate test or salt spray test for those systems which pass the
advanced screening successfully.
§30 Industrially useful coating systems have been developed by us following
this "Scientific Engineering Method". The results reported below
were found on test panels coated with PAni containing primer 
applied with a thickness of 20 �m and coated with various top coats.
§31 4.1 Open Circuit Potential Measurement
This routine measurement can be performed under various well-known
conditions [5b, 6, 8,
32] and does not need to be described further. Schauer
et al.  have confirmed the range of the high
potential shift found by us earlier . Our internal
specification is a potential shift to at least +100mV and a long term
stability of it.
§32 4.2 Scratch Test
This test can be performed in two ways, (a) by coating half of a panel with
Pani containing primer, the other half with a conventional epoxy primer, then
applying a top coat (e.g. 2-C EP) on both primers, or (b) by coating a panel
completely with the coating system to be tested.
§33 The coating is then injured with scratches 1 mm wide and 50 mm long, down
to the metal. The panels are immersed in 10% salt containing water. After 1
night and after 100 and 300 hours, the panels are checked with respect to rust
formation in the scratch: only those systems will be accepted to become
commercial products, where no rust will be formed within the open scratch
during this time (see Fig. 4). Conventional systems, also the very good
ones, will develop rust in the open scratch, because the area there is not
protected. They also develop rust under the coating, propagating at various
velocities (cf. 4.3).
§34 The protection provided by the polyaniline dispersion coating, the
ennobling, however is a far-reaching effect because of its metallic nature. We
are assuming furthermore, that it is not only the ennobling which provides
protection for open scratches of this size, but also the passivation by Fe2O3
formation: this oxide can be found up to about 400 �m away from the coating
edge as seen by XPS .
§35 This protection can be effective more than 1 mm away from a coating edge,
which makes anti-corrosion systems based on our Organic Metal a powerful edge
corrosion protection technology. We even have sometimes found much bigger
areas being protected even after removal of the coatings .
§36 4.3 Scanning Volta Potential Measurements (Kelvin Probe)
The Volta potential measured with a Kelvin sensor is suitable for
non-contact measurements of surface potentials even under undamaged surface
coatings , .
The function principle and experimental set-up is shown in Fig. 5. The
measurement object, the working electrode, and the reference electrode of the
Kelvin probe form, due to the small gap between them, a capacitor. Between
them a potential is developed, the amplitude of which gives a measure of the
chemical nature of the material on the surface of the metal. A periodic
variation in separation by means of an actuator built into the sensor changes
the capacitance of the set-up. The resulting signal is converted to a
measurement signal by means of a lock-in amplifier .
§37 The resulting data is a scan of the surface Volta potential of the metal
under the coating, which can - under certain conditions - be related with the
corrosion potential. But for the purpose we are looking for, this is not a
necessary relation . In this part
of our method, we only need to know the differences of potentials (a) between
various sites, i.e. between the open scratch and the not injured areas of the
coating (b) with the change in immersion time.
§38 With this technique, we monitor and predict adhesion (or delamination) of
the coating under corrosive attack. The underfilm corrosion propagation
velocity (more precise: the corrosion potential propagation velocity, due to
the first delamination of the coating before even first corrosion occurs) can
be quantitatively measured.
§39 In contrast to the sample design by Stratmann ,
we are measuring on samples like those used in our scratch test (4.2.). This
leads to the phenomenon, that in the best of our systems, no potential
negative enough for even to start any corrosion develops, so that no
delamination or even rust formation or underrusting can occur.
§40 Fig. 6 is showing a development of the Volta potentials in the open scratch
and in the neighbourhood under the coating with time (polyaniline dispersion
primer plus top coat). We are interested to follow the potential change
especially in the first 24 hours of immersion in salt water (after usual
conditioning in humid atmosphere). Typically, in the best system, a
"W" form of the potential distribution forms, with no potential
approaching strong enough negative values (Fig. 7), to allow corrosion. Only,
when the bottom of the "W" form reaches values of -200mV or lower, a
delamination (the prerequisite for corrosion) can be observed and corrosion
may start. The delamination velocity is estimated with widening of the
negative corrosion potential "W" valley, if it occurs at all (Fig.
§41 In contrast, scratches in coatings without Organic Metal primer have a big
potential difference, a broad and deep valley, resulting in a high
underrusting propagation velocity (Table 1). Very quickly, in the middle of
the scratch the potential is strongly increasing now as the sign of rust
§42 We differentiate various polyaniline dispersion coating systems under
development by comparison with the actually best performing benchmark, where
no corrosion potential is reached in the scratch, hence no delamination
§43 Three systems, each built up on the same primer, but top coated with
different paints (Table 1), have all passed the scratch test but were
different in their OCP. The question to be evaluated was: Do we see a
difference in the delamination velocity? Table 1 contains the answer
"Yes": after 24 hours, significant differences can be noticed. Note,
that the performance order is in parallel with all other results. Primer
formulations (same basis) without polyaniline under even the best top coats
have 5-10 times quicker delamination. The best top coat on polyaniline
dispersion primer alone (on epoxy primer or even on Zn-rich epoxy primer) does
not perform comparably well at all. It is the most important conclusion, that
underrusting or persistent passivation, resp., is also strongly influenced by
the top coat, a conclusion which is not at all self-explanatory, but can be
understood in view of [17, 7] and
§44 We set our internal specification as an underfilm corrosion propagation
velocity of between 3 and 5 �m/h or less. Epoxy coating systems (primer plus
top coat) are generally showing a velocity of around 20 to 60 �m/h, a factor
of 10 or more faster than polyaniline dispersion coating systems.
§45 Zn-rich epoxy primers (with epoxy top coat) do even show much quicker
underfilm propagation, at least in the first 1-2 days. Such systems are not
scratch-tolerant, they perform very well only with intact coatings. In
comparison to that, our systems based on Organic Metals are performing
extremely well both with and without scratches.
§46 Only the best cataphoretic coatings on Zn-Phospate electrochemically
pretreated steel in car manufacturing are showing figures (3-5 �m/h)
comparable with polyaniline dispersion coating (0 - 5 �m/h). We are convinced
to be able to achieve these numbers also with future product developments (as
we actually see with some developmental products).
§47 4.4 Electrochemical Impedance Spectroscopy
The technique is used by us to predict the performance of the complete
primer / top coat (or eventually including an intercoat) system. We developed
this technique as a routine method together with G. Popkirov based on his new
FFT-EIS technique . Measurements
are carried out with a three-electrode system using a cell as described in .
The experimental set-up for this Fast Fourier Transformation Electrochemical
Impedance Spectrometer is given in Fig. 9. A frequency-rich perturbation
signal with a small amplitude is applied to the electrochemical cell
controlled by an EG&G Princeton Research potentiostat Model 263A. In the
present investigation a computer programmed sum of 42 sine waves distributed
over 4 decades was used to synthesize the perturbation signal of a home-built
signal generator The peak-to-peak amplitude of the perturbation voltage was
usually 150 mV. The perturbation and the response signal are amplified and
filtered by a Stanford Research Systems Inc. Model SR 640 Dual Channel
Low-Pass filter. A/D and D/A conversion, timing and controlling were carried
out by a 16-bit, 100 kHz transient recorder PC-card from United Electronic
Industries, Inc. Model Win- 30/3016. Impedance spectra were evaluated by fast
Fourier transformation of the perturbation and the response signal (Fig. 10).
§48 For the experiments describing our procedure and representative examples,
the following lacquer systems were used on polyaniline dispersion primer:
two-component epoxy top coat - amine hardened = 2-C EP
two-component acrylic top coat = 2-C AY
one-component acrylic top coat = 1-C AY
§49 The tests were made on sand blasted panels from Mercedes Benz and are from
the same serie with those evaluated in 4.5 (cf. ).
§50 Fig. 11a-c show experimental EIS data for the three different top coated
steel panels as a function of immersion time. The measurements were carried
out in 10% NaCl. Changes in the impedance spectra were observed over a six day
period except for the 1-C acrylic top coat with a one day period.
§51 The recording of the spectra takes about 5 - 20 seconds, the Nyquist and
Bode plots are available for interpretation after another 15 seconds. The
bottleneck for measuring more samples is only the number of available
immersion cells, as they are placed and immersed in the same cell as they are
measured. But as we are not measuring all of the systems under development,
but only those which have passed the first screening, this is not a
practically important limitation.
§52 The performance of the complete system under evaluation can be assessed
after 1 or 2 weeks at most. If their impedance spectra do not change
significantly during this time (as shown by sample 1, which is a commercial
polyaniline dispersion coating), we can expect a very good long-term corrosion
§53 Systems, which will fail, are loosing their capacitance during 1 week or
even quicker. It can be seen, that the stability of the EIS spectra or loss of
the pure capacitance behaviour is parallel to the results found in 4.5, a good
or bad performance in VDA cycling test.
§54 It should again be noted, that systems (samples #5 and #6) composed by a
pure epoxy primer or a Zn-rich epoxy primer top coated with the same EP top
coat as in the polyaniline dispersion coating /2-C EP (sample #1) again perfom
worse (i.e., they loose impedance very quickly, Fig. 12).
§55 Intermediate conclusion
Scratch test, OCP, RKS and EIS are probing each different aspects of the
integral named "corrosion protection performance". Ennobling and
passivation, primer adhesion (delamination/underrusting) or coating barrier
properties, being tested somewhat in a separated manner, belong and work
together. Both underrusting (delamination) and barrier property (impedance)
are not only dependant on the primer or the topcoat, but the
combination of both.
§56 4.5 Climate cycling test (VDA) / Salt Spray Test
This test is used by us only after successful basic and advanced screening
(4.1 to 4.4).
§57 The systems described above (scratched panels) have been subjected to these
accelerated corrosion tests for comparison of these test results with our
4-step method (cf. ). Underfilm corrosion,
blistering and degree of rusting are summarised in Table 1. In this test, as
in real life, both the performance of the intact coating on the metal itself,
as also the injured (scratch) coating behaviour plays a role. These effects
have been tested in the 4 tests shown above, and they are working together in
accelerated corrosion tests and in outside weathering or other real corrosion
§58 The tests showed that all three coating systems provide highly efficient
corrosion protection and complete suppression of underfilm corrosion over a
period of more than 1000 h; especially with top coat 2-C EP no change at all
was found even after 1000 h. The other top coats allow some blistering. None
of the systems are really failing, but they are slightly different in their
overall acceptable performance.
§59 Our 4-step "Scientific Engineering" test method is able to
differentiate much quicker and much more sensitively than do these generally
accepted accelerated corrosion tests.
§60 5. Conclusions and Outlook
The new Organic Metal polyaniline, almost a noble metal, ennobles steel and
other metal surfaces while shifting their surface potential. It furthermore
passivates the conventional metals by forming a metal oxide layer of up to 1
�m thickness. This exciting new technology is based on extremely fine
dispersions of PAni in coating matrices of special composition.
§61 Many internal and independant tests [4, 8,
20, 24] have shown that the
presence of polyaniline at the metal surface (to be protected) alone in
regardless what chemistry form or matrix is by far not sufficient for a
reproducible and practically convincing high-performance corrosion protection
§62 As shown, the systematic combination of 4 tests, the measurement of the
corrosion potential shift, a new simple scratch test, the Volta potential
measurement with the Scanning Kelvin probe, and electrochemical impedance
spectroscopy, eventually to be combined with salt spray or climate cycling
test according to VDA (Association of German Automobilists) is a productive
tool for testing and improving corrosion protection coating systems. In
contrast to salt spray and climate cycling tests (3-6 months), useful results
from measurements with EIS and the SKP can be obtained within 1-2 weeks (after
complete drying of the coatings to be tested), from where accelerated
corrosion test results and real-world corrosion prevention performance can be
§63 Polyaniline dispersion coating coating systems for various industrial
applications have been developed with this method .
They were specified and are released by several customers; practical
industrial reference objects have been realized, e.g. pipelines, bridges,
boats, container ships, steel constructions in chemical plants, hydraulic
construction in waste water management, hydraulic service center in Airbus
manufacturing etc. . They are
performing much better than any other conventional anti-corrosion coating.
They can be applied at a 25 to 60% reduced coating thickness compared to
conventional systems, without any loss of performance .
§64 Recently, new systems have been developed with the help of these
a system for coil coating (4500), which is now under first technical
tests; this product is designed to replace chromates in coil coating;
a completely new water-born system comprising a water-born primer and a
water-born, or a 100% solids, resp., top-coat; this system will perform at
least as well as generally available well performing solvent-borne
Both systems will soon be presented for independent performance tests.
§65 It might also be of interest, that our polyaniline dispersion coating
systems have shown a well advanced performance on structural light metal
alloys, like Mg alloys for automotive use. We are following this area, too,
whereby we still need to develop our "Scientific Engineering" method
for these metal substrates. Another system for structural Al applications
(aerospace) is under development. Here again, the replacement of chromates is
the environmentally important goal of the project.
§66 Considering the short time we had for the development, our systematic
4-step method has helped us to develop coating systems of the highest
performance at significantly lower coating thickness, because it led to a deep
understanding of the phenomena during corrosion attack, ennobling and
passivation. We were able to show, that
our Organic Metal allows for a powerful anti-corrosion technology, and
the development of corrosion prevention coatings must not necessarily be
based only on long-term practical studies with a
"trial-and-error-"strategy, but can also be based on systematic
scientific tests allowing to gather reliable results within a few weeks
§67 It would certainly be of interest to find out, if this method can also be
applied on general, non-PAni-coating systems, to predict their performance.
§68 Both, the Organic Metal anti-corrosion technology and our Scientific
Engineering of anti-corrosion coating systems, have the potential to
revolutionize corrosion protection. Not only new systems can be quickly
developed with a high correlation between short term measurement and long-term
performance, but also coatings with about 5 times longer lifetime for the
metals to be protected, at 25 - 60% lower coating thickness, replacing
chromates and zinc can be provided.
§69 Considering the fact, that corrosion is responsible for the loss of about
4% of each countries Gross National Product per year, and considering, that
the repair of the lost values not only requires financial, but even more
environmental resources, our new technology could significantly contribute to
reduce costs and to a future ecologically acceptable economy
§70 Fig. 1: Corrosion current density-potential curves of various metals, both
original and coated with polyaniline [4b].
a) untreared with Fe and FeOOH signal
b) in the presence of polyaniline with pure Fe2O3
§71 Fig. 2: XPS analysis of passive iron oxide layers 
§72 Fig. 3: reaction scheme.
Left: heavy rust formation in the damaged site
Right: no corrosion attack - the ennobled and
passivated metal surface is resistant, even without coating.
§73 Fig. 4: St-14 panel after 300 hours in permanent immersion test (DIN
50905 T4) in 3% NaCl solution; (Click on the photograph for an enlarged view)
§74 Fig. 5: Function principle of corrosion potential measurements using a
§75 Fig. 6: 3D plot of the potential development in the scratch and under
the coating; top t=0, bottom t=24 hours of immersion, for sample #2, cf. Fig.
§76 Fig. 7:
Development of a deep "W" corrosion potential valley in a coating
system (#2) not meeting the specifications: at (top) t=0 (middle) t=12,
(bottom) t=24 hours immersion time, reaching the corrosion potential around
-200mV and showing underrusting (12-30 �m/h)
§77 Fig. 8: Development of a shallow "w" potential distribution at
elevated (passivation) level in the best performing coating system #1 at (top)
t=0 (middle) t=12 (bottom) t=24 hours of immersion: no corrosion, no
§78 Fig. 9: Set-up for FFT electrochemical impedance spectroscopy.
Fig. 10: Time domain and power spectra for perturbation and response
a) 2-C Epoxy top coat
b) 2-C Acrylic top coat
c) 1-C Acrylic top coat.
§79 Fig. 11: Nyquist and Bode plots of selected top coats with PAni
§80 Fig. 12: Bode plot of EIS spectra for sample #5 (EP/2-C EP) and #6
(Zn-EP/2-C EP) at a) t=0 b) t=70 c) t=140 hours of immersion
§81 Table 1: Summary of RKS results for various coating systems.
Potential E, (mV)
0 to 150
100 to 150 (no rust)
150 to 300
-100 to -300
150 to 300
-50 to -300
Primer matrix without polyaniline 2-C EP
-200 to -100
-200 to 100 (rust)
EP primer / 2-C EP
-200 to -100
50 to 250 (rust)
Zn-EP primer/2-C EP
-150 to 0
-700 to -800
§82 Table 2: Results
of salt spray test in accordance with DIN SS 50 021.
Epoxy top coat
Polyaniline/2-C Acrylic top coat
Polyaniline/1-C Acrylic top coat
1) U - underfilm corrosion (DIN 53 167)
2) B - blistering (DIN 53 209)
3) R - degree of rusting (DIN 53 210)
4) n - none
 B. Wessling, German Patent P 37 29
566.7, Zipperling Kessler & Co. (1987).
 D. W. DeBerry, J. Electrochem.
Soc. 132, 1022 (1985).
 G. Mengoli, M. Munari, P. Bianco,
M. Musiani, J. Appl. Polym. Sci. 26, 4247-4257, (1981).
 Joint Patent Application with
Allied Signal, (Morristown/USA), PCT/US 93/00543
 a) B. Wessling, DE 43 34 628 A1,
Zipperling Kessler & Co. (1993).
b) B. Wessling, Adv. Mater. 6, No 3, 226 (1994).
c) B. Wessling, PCT WO 95/00678, Zipperling Kessler & Co. (1993).
 Wei-Kang Lu, R. L. Elsenbaumer, B.
Wessling, Syth. Met. 71, 2163-2166 (1995).
 B. Wessling, Synth. Met. 85,
 Wei-Kang Lu, S. Basak, R.L.
Elsenbaumer, "Corrosion Inhibition of Metals by Conductive
Polymers", in: Handbook of Conducting polymers, T.A. Skotheim, R.
Elsenbaumer, J.R. Reynolds (eds), 881-920 (M. Dekker 1998).
 T. Schauer, A. Joos, L. Dulog,
C.D. Eisenbach, "Protection of iron with polyaniline primers against
corrosion", to be published in Progress in Organic Coatings (in
 A.-M. Hugot-Le Goff, C. Palotta,
J. Electrochem. Soc. 132 (11), 2805-2806 (1985); N. Boucherit,
P. Delichere, S. Joiret, A.-M. Hugot-Le Goff, Mat. Sci. Forum 44&45,
 in case of copper, the oxide is
Cu2O (B. Wessling, J. Posdorfer, W. Strunskus, to be published)
 a) G. Nimtz, A. Enders, P.
Marquardt, R. Pelster, B. Wessling, Synth. Met. 45, 197-201
b) G.Nimtz, R. Pelster, B. Wessling, Physical Review B, 49
(18), 12718-12723 (1994).
 a) C.K. Subramaniam, A.B.
Kaiser, P.W. Gilberd, B. Wessling, Journal of Polym. Sci. Part B: Polym.
Phys. 31, 1425-1430, (1993)
b) C.K. Subramaniam, A.B. Kaiser, P.W. Gilberd, B. Wessling, Synth.
Met. 69, 197-200 (1995)
c) C.K. Subramaniam, A.B. Kaiser, P.W. Gilberd, C.-J. Liu, B.
Wessling, Solid State Commun. 97 (3), 235-238 (1996).
 our own unpublished
 Ormecon Chemie, Ammersbek
(Germany) technical information (previously published by Zipperling Kessler
& Co., Ormecon’s holding)
 Test Report of DECHEMA
(D-Frankfurt), Title: Tests on "passivated" steel specimens; Scope
of order: Corrosion test programme for crevice and pitting corrosion and
galvanic corrosion of various pre-treated steel specimens (6/1994).
 B. Wessling, together with S.
Schr�der, S. Gleeson, H. Merkle and F. Baron, Materials and Corrosion
47, 439 (1996).
 note: our Organic Metal is the
first metal which can be reduced (2 e- and 2 H+ per
 the structures are comparable
to those described in:
B. Wessling, Polym Eng. & Sci., 31 (16), 1200-1206
The thermodynamic reasons for the structure formation are explained by
non-equilibrium thermodynamics, cf.:
a) B. Wessling, Synth. Met. 45, 119-149 (1991).
b) B. Wessling, Zeitschrift f. Physikalische Chemie 191,
For more recent overviews about flocculation in dispersions, their
thermodynamical basis and relationship with properties see:
a) B. Wessling in: Handbook of Conducting Polymers, Skotheim,
Elsenbaumer, Reynolds (eds), 467-530 (M. Dekker 1998).
b) B. Wessling in: Handbook of Organic Conductive Molecules and Polymers,
Hari Singh Nalwa (ed.), vol. 3, 497-632, (Wiley 1997).
 cf. P. Kinlen, D. Silverman, C.
Jeffreys, Synth. Met. 85, 1327-1332 (1997).
 reference deleted (this has
been done for a number of references that either introduce references to
tradenames that do not benefit the reader, or reference results that are not
available to the reader, and therefore provide no useful information - the
reference numbers will be resequenced prior to publication)
 reference deleted
 cf B. Wessling:
"Conductive Polymer / Solvent Systems: Solutions or Dispersions?"
a) Proceedings of SEAM (Search for Electroactive Materials), workshop at
Brooklyn Polytechnic Institute, N.Y., Dec. 1996,
b) Proceedings of 3rd BPS (Bayreuth Polymer & Materials
Research Symposion), Bayreuth (Germany) April 1997, manuscript available at: http://www.ormecon.de/Research/soludisp.
see especially ch. 2.5 and 3 and Fig. 13.
 D.A. Wroblewski, B.C. Bencewicz,
K.G. Thompson, C.J. Bryan, Polym. Prepr. 35 (1), 265 (1994).
 a) R. Racicot, T. Brown, S.C.
Yang, Synth. Met. 85, 1263 (1997).
b) M. Fahlmann, S. Jasty, A. Epstein, Synth. Met. 85,
 reference deleted
 there are several
incompatibility phenomena which may occur: (a) insufficient wetting or
interlayer adhesion (b) insufficient curing of the top coat due to the
chemical properties of the primer, as the primer contains an acid salt and
provides an acid environment, which cannot be tolerated by all top coat
 later developments might be
offered as single coat systems, comprising all 3 necessary effects (ennobling,
passivation, sealing) together
 internal test requirements: (1)
potential shift comparable as described in [5b] (2) similar or better
corrosion performance - in blistering, corrosion in scratch, underfilm
corrosion and its progression - compared with a zinc-rich epoxy primer + epoxy
top coat (as used in )
 T. Schauer, A. Joos and E.
Praschak, in Investigation of the compatibility of selected top coats with
primer 900226/32, test report on behalf of Zipperling Kessler & Co. (Ormecon
Chemie), Forschungsinstitut f�r Pigmente und Lacke e.V., Stuttgart, (1996).
 Test performed by Research
Institute for Pigments and Paints, Stuttgart (Germany), Title: Filiform
corrosion on aluminum: Polyaniline primer offers superior protection.
 Cf. ,
S.1 and Fig. 5.
 B. Wessling, J. Posdorfer,
"Corrosion prevention with an Organic Metal (Polyaniline): surface
ennobling, passivation, corrosion test results", Procedings Electrochem.
Soc. (Dourdan), Sept. 1997
 reference deleted
 reference deleted
 cf. "Industrial reference
objects" / Reports Ormecon Chemie, here: "Protection of cattle barn
 M. Stratmann, H. Streckel and
R. Feser, Corros. Sci. 32, 467 (1991).
 M. Stratmann, R. Feser and A.
Leng, farbe und lacke 100, 2, 93 (1994).
 Technical Information UBM
 we prefer to measure the
corrosion potential and its shift during ennobling with the open circuit
potential technique as described in 4.1, which is more realistic in relation
to the corrosion process
 G. S. Popkirov, R.N. Schindler,
Electrochim. Acta 39, 2025 (1994); we are now using a
principally comparable, but more modern and commercially useful apparatus
 U. Rammelt and G. Reinhard, farbe
und lacke 98, 4, 261 (1992).
 Technical Information Ormecon
Chemie, printed versions or Internet http://www.ormecon.de/Products
 Ormecon Chemie, Industrial
Reference object reports; printed information or http://www.ormecon.de/corrprax
 reference deleted
Comments on this paper
1. Dr Frank Lux