Volume 6 Preprint 16
Corrosion Science in the 21st Century
G. S. Frankel
Keywords: corrosion science, nuclear waste storage, aging aircraft, chromate replacement, corrosion prediction
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Volume 6 Paper C028
Corrosion Science in the 21st Century
G. S. Frankel
Fontana Corrosion Center, The Ohio State University, Columbus, OH 43210 USA,
The discipline of corrosion science arguably has been in existence since the WagnerTraud paper appeared 75 years ago. During the last part of the 20th century, most
corrosion science projects were focused on the development and use of new
techniques (e.g. electrochemical methods, surface analysis, and synchrotron radiation
techniques), fundamental studies of corrosion phenomena (e.g. passivity and localized
corrosion), or the properties of advanced materials (e.g. amorphous metals and
“stainless” Al alloys). The understanding that resulted ultimately helped corrosion
practitioners solve real problems, but problem-solving was not at the root of much of
the research. In today's environment, research for the sake of fundamental knowledge
is much less common because of funding constraints. This paper summarizes and
contrasts the approaches taken by three large activities that are either recently
concluded or ongoing in the US: corrosion and prediction of nuclear waste storage
canister materials, predictive models for airplane corrosion and the effects on
structural integrity, and the mechanism of chromate inhibition and chromate
replacement. The future of corrosion science is in the areas of reliability and lifetime
prediction, surface engineering and smart coatings, and infrastructure improvement
Keywords: corrosion science, nuclear waste storage, aging aircraft, chromate
replacement, corrosion prediction
Corrosion science in the 21st century has a history of 3 years and a future of 97 years.
Whereas science is the practice of developing an understanding of the world around
us to make it more predictable, the prediction of the future of science is a
contradiction of terms if not exactly an oxymoron. Science is no doubt inherently
unpredictable; we cannot know with any certainty what discoveries will be made.
Interestingly, prediction of corrosion damage is in fact a hot topic of current and likely
future research. Predictive models of corrosion, both probabilistic and deterministic
models, must be based on a detailed understanding of past and current behavior.
Similarly, any prediction of the future of corrosion science must be based on the past
and current status of the field. In what follows, I will make some observations of the
status of corrosion science and hazard some guesses (the best we can do!) of the
future. It should be noted that the discussion will focus on the United States, which is
admittedly somewhat of a myopic view to present at an international symposium.
There are certainly some differences in the experiences and situation in the rest of the
world, but there are more similarities.
Before launching into this exercise, I will relate a personal experience that is of some
relevance. A decade ago, Norman Hackerman visited the IBM Watson Research
Center in Yorktown Heights, NY, when I was a researcher there. For a long time, Dr.
Hackerman has had positions (such as the presidencies of Rice University, the Univ.
of Texas at Austin, and The Electrochemical Society) that have provided him with a
unique perspective on research and on the field of corrosion. In a seminar during that
visit, Hackerman made a statement that made me, a struggling young corrosion
scientist, squirm: “Corrosion science will not solve corrosion problems.” First, it
should be clear that he used corrosion science as an example of any scientific pursuit,
not intending to cite it as a particularly failed branch of science. Further discussions
led to an elaboration of the meaning behind this statement. In Hackerman's view,
scientists pursue the underlying mechanisms of a problem. They seek the activating
and inhibiting factors. In contrast, engineers solve real problems by combining the
fundamental understanding provided by scientists with practical know-how and
economic considerations. I do not believe that it was the intent of this statement to
provide ammunition to those seeking to save money by cutting research funds,
although at the time I feared it would. He meant only that there should be a clear
understanding of the expectations and capabilities of scientists.
I agree with some aspects of Hackerman's view, but take issue with others. Times
have changed. The distinction between scientific and engineering approaches has
blurred. Scientists now play a much greater role in solving of real world problems.
Engineering solutions are based less on intuition and more on scientific principles,
and scientists are critical participants in large teams formulated to solve the pressing
problems of the world. This is particularly true in the realm of corrosion science.
In order to understand how corrosion science has changed and how it will change
further, it is necessary to look back over the past decades. It is possible to divide the
focus of most corrosion science projects of the last part of the 20th century into three
broad categories: the development and use of new techniques, fundamental studies of
corrosion phenomena, and the properties of advanced materials. Table 1 presents
some examples in each of these general areas.
It is a fair generalization that many of the research activities in the recent decades
were focused on topics such as those in Table 1, with no intent of solving real
problems. There are of course examples of large coordinated projects involving teams
of corrosion scientists to solve important real problems. One example is the
considerable effort that was put into solving a variety of corrosion and cracking
problems in the nuclear power industry in the last several decades of the last century.
Research at universities, government labs, and corporate labs led to many solutions,
such as the reduction of impurities in the water and the development of the all volatile
water treatment (AVT) to mitigate SCC of alloy 600 . However, it can be argued
that the involvement of large numbers of corrosion researchers in teams to solve real
problems is currently much more common than in the past, when it was typically the
primary intent of researchers to develop a new technique, understand a mechanism
better, or explore the properties of a new material. Proof of this is the fact that many
of the topics developed into “fads” or “bandwagons.” Examples of fads in corrosion
science include metallic glasses and surface science in the 70's and 80's, and
metastable pitting and “stainless aluminum” in the 80's and 90's. Research projects on
these topics addressed no dire, real problems. Nonetheless, many different researchers
from a variety of labs and countries got involved, partly to make a contribution to
something new and interesting, but also to provide basic understanding and
approaches that can and have been used to solve real problems.
Table 1. Past research topics in corrosion science. This table is not intended to be an
Env. Assisted Cracking:
Vapor deposited films
Another interesting aspect of the past and present of corrosion science is the
involvement of industrial research labs. In the twentieth century, major developments
in corrosion science were made by researchers at a number of corporate research
centers. With time and the vagaries of financial good fortune, the active industrial labs
have ebbed and flowed. A partial list of companies who have been active in corrosion
research is given in Table 2.
The involvement of corporate research centers in scientific endeavors was important
for bringing a connection to the real world to the scientific community. Many of the
activities in these labs were truly research and were divorced from practical
applications. These companies saw benefit in allowing their employees to use at least
a part of their time to pursue science. Scientific activities and the connections to other
scientists around the world provided the researchers with an understanding that
enabled them to contribute better to solutions of real problems.
Table 2. US corporate and government research labs that were active in corrosion
research in the twentieth century (not an exhaustive list).
Naval Research Lab
Oil and Gas
The present status of corrosion research is quite different than it was even a decade
ago, at the time of the last UMIST anniversary celebration. The NSF approach to
funding research purely for the sake of research is extremely rare in the field of
corrosion. Even prior to the recent economic downturn, many companies divested
themselves of expensive research centers as a cost-savings measure. IBM is a good
example. The IBM Corporation was extremely profitable through the mid-80's
because of a cash-cow product: mainframe computers. The company could afford a
world-leading research division employing thousands of scientists, many of whom
never needed to provide a justification for the relevance of their work. The area of
corrosion was considered to be of interest to IBM because of the dimensions of
devices and the reactivity of some critical materials, in particular magnetic materials.
Researchers could easily justify the pursuit of fundamental studies in atmospheric
corrosion, thin film corrosion, localized corrosion, inhibition and passivity. Funding
and support staff were available. However, the situation changed in the early 90's as
computing switched to smaller machines, such as PCs, and the company's financial
situation plummeted. By the mid 90's, most researchers at IBM had to find projects
supported financially by the operating divisions. The practical applications of
corrosion science at IBM were primarily performed in a fire-fighting mode, as little
thought went into corrosion in the design phase of new projects. Corrosion is not a
topic that leads to new products in the electronics industry. It is only a
manufacturability and reliability concern. At present, no corrosion research is carried
out at IBM. The situation is similar at most of the companies listed in Table 2. If one
defines activity in corrosion research as necessarily involving publications in the top
journals and participation at research conferences, then it can be argued that GE is the
only large corporation from that list that has an active corrosion research group.
(Rockwell might be included, but the Rockwell Science Center is now essentially a
contract research lab.) The companies performing contract research are still active,
though much of their activity is proprietary and not published. The military and
government labs also still have research activities in the area of corrosion. However,
in general those activities are currently at a lower level than they once were. The
corrosion community suffers from the lack of involvement of industrial researchers.
As mentioned, in the past industrial researchers brought to the scientific discussion
table their practical experience of interacting with engineers in the pursuit of solutions
to real problems in their respective companies. The absence of industrial researchers
is now partially balanced by the change in the type of work now done by corrosion
scientists in academia and government labs.
As mentioned, one defining characteristic of corrosion research in 2003 that
distinguishes it from the past is the involvement of researchers and scientists (as
opposed to engineers and practitioners) from academia and government labs in large
coordinated team efforts to solve real problems. A few of these efforts will be
summarized below. Again, it should be noted that this is not an exhaustive list, and is
limited to activities in the US.
Nuclear Waste Storage - The Yucca Mountain Project
Long term storage of high level radioactive waste is the ultimate problem for
corrosion research. For many reasons, it is clear that the canisters designed to hold the
waste material must be fabricated from metal. The complete storage system, including
natural and man-made barriers must maintain integrity and prevent leakage for a
period of about 10,000 years to allow the radioactivity to decay to natural background
levels. Therefore, nuclear waste storage presents the ultimate corrosion prediction
problem. We corrosion scientists must make a prediction for a time period that is 200
times longer than the history of the field!
The US Department of Energy is responsible for designing and constructing a longterm nuclear waste repository, and the President and US Congress approved a Site
Recommendation designating Yucca Mountain, Nevada as the site for a permanent
waste repository. Details of the corrosion aspects of the Yucca Mountain repository
can be found in an excellent review by Gerry Gordon  and in the final report of a
Peer Review Panel headed by Joe Payer .
From a corrosion perspective, there are several critical issues that only can be
addressed by scientists doing fundamental research. These issues include the
evolution of the local environment on the surfaces of interest, the long term stability
of passive films on corrosion resistant alloys (CRAs), and the conditions under which
localized corrosion and stress corrosion cracking will never occur.
The repository will be in the unsaturated zone, 300 m above the level of the
groundwater. The environment inside Yucca Mountain is well characterized. The
rock, a volcanic tuff, contains faults and fine porosity that is filled with pore water. A
fraction of the very small amount of annual precipitation seeps into the mountain,
eventually permeating down to groundwater below the repository. The various waters
in the mountain are very dilute, containing low amounts of chloride, nitrate, sulfate,
and bicarbonate anions as well as sodium, calcium, potassium, and magnesium
cations. A relatively high level of nitrate compared to most ground waters, a result of
the low level of biological activity on and in the mountain, is fortuitous because of its
corrosion inhibition properties. A primary issue is what exactly the environment on
the waste packages will be, which is a strong function of the repository temperature
profile with time and the integrity of the planned Ti grade 7 drip shields. Will water
drip directly onto the waste packages or will they be exposed only to humidity? How
will the composition of these waters change upon contact with a hot surface? Is it
possible for trace elements such as Hg and Pb to enrich over long periods?
CRAs such as stainless steel and Alloy 22, which is the material from which the outer
canister is to be made, were invented less than 100 years ago. Our experience with
them is 9900 years less than the design life of the repository, so we must determine if
there are processes that can occur over a period of millennia by which passivity would
be spoiled and the reactive metals under the passive films would destabilize. For
instance, will passive films thicken over long periods of time to the point where they
spall, like high temperature oxides, and create crevices that would not repassivate? Or,
is it possible that a very low S content in the alloy will with time, as the passive film
slowly sweeps through the material, concentrate at the surface and spoil passivity
It is well known that CRAs, which rely on the presence of a thin passive surface film,
are susceptible to localized corrosion as a result of breakdown of the film. Under the
simultaneous action of a tensile stress, CRAs are also susceptible to stress corrosion
cracking (SCC). The alloys of interest, Alloy 22 and Ti-Gr 7, are extraordinarily
resistant to localized corrosion and SCC. Nonetheless, they are susceptible under
extreme conditions. The kinetics of these processes are so fast relative to the time
scale of interest that they should never occur if the package is to maintain integrity,
unless the stifling processes are well understood. What then are the conditions under
which one can be absolutely certain that localized corrosion and SCC will not occur?
The pitting potential is certainly not a sufficiently conservative design criterion. It has
been suggested that localized corrosion (both pitting and crevice corrosion) will not
occur if the corrosion potential remains below the repassivation potential for a
creviced sample that has undergone considerable attack [4,5]. In that case, it is
important to have a good prediction of the corrosion potential as a function of time
and environmental conditions. In the case of SCC, is there a true threshold stress
intensity? The limitations in measurement of crack growth rate are such that a crack
growing at the slowest measurable rate will penetrate the Alloy 22 canister in a
fraction of the design life. In other words, even if the most sensitive measurements
predict that SCC will not occur under non-accelerated conditions, it is possible that
the crack growth rate is too high. Finally, the processes by which localized corrosion
is stifled are not well understood.
It should be noted that other countries are taking a very different approach to long
term nuclear waste storage. It is possible to use thermodynamics rather than kinetics
to ensure long-term stability by using a noble metal, such as Cu, as the barrier and
placing the repository in an anoxic saturated zone, i.e. in a region saturated with
ground water that is non-complexing and has a very low dissolved oxygen content.
Once the oxygen introduced into the environment during emplacement is consumed, a
Cu canister should be perfectly stable in such an environment. The concern in this
case is long term prediction of the composition of the groundwater over the 10,000
year period. If the underground currents were to bring aerated waters to the repository,
Cu canisters would be quickly breached.
The scientific questions raised above and others related to Alloy 22 and Yucca
Mountain have been the focus of a considerable amount of research over the past few
years that has involved an increasing number of corrosion scientists from around the
world. The design and construction of the Yucca Mountain repository is a huge
engineering undertaking. However, scientists have a major role in justifying the
design and addressing the considerable attention and concerns raised by opponents
and the public in general. Scientists also have a role in assisting those who oppose the
project. Political considerations will likely dominate the decision-making process.
Nonetheless, there must be a vigorous and honest debate about the underlying science.
Corrosion Prediction in Aging Aircraft
It is generally considered that the US Air Force (USAF) spends about $1B/yr fighting
corrosion in its fleet of aircraft. Many planes such as KC135 tankers have been in
service for about 40 years, but still have a considerable remaining life based on
fatigue considerations because of the service profile . Military planes fly less
frequently than commercial planes, and spend more time on the ground corroding.
Airplanes in the USAF fleet currently undergo regularly scheduled periodic
maintenance. During maintenance, any corrosion that is found must be fixed by a
repair process or the part must be replaced, regardless of whether it is critical to the
structural integrity of the plane. This "find and fix" approach is partly responsible for
the high maintenance cost. It would be even more expensive to purchase new planes,
so it is imperative to decrease maintenance costs. Furthermore, the extensive time
each plane spends in depots for maintenance affects mission readiness.
In the past, corrosion has been considered to be a small modification of the fatiguebased structural integrity programs that have successfully managed the USAF and
commercial fleets with few corrosion-related disasters. However, the issues of cost
and mission readiness of aging aircraft have been receiving attention at high levels in
the military . A new approach toward maintenance, which could be called
"anticipate and manage" is being developed by a large team managed by S&K
Technologies in Dayton, OH . In this approach, aircraft are inspected upon entering
a maintenance depot and the state of corrosion is assessed, as is the effect of that
corrosion on the structural integrity. Furthermore, using assumptions about the future
deployment of the plane and the Air Force bases at which it will spend time, a
prediction of the change in the corrosion state of the plane with time and an
assessment of the effects of those changes on the structural integrity are made. Based
on that analysis, the corrosion found is either repaired, replaced, suppressed, or
ignored. In essence, the analysis should be able to predict the "to be" condition from
the "as is" state. This approach involves effective and thorough non-destructive
inspection (NDI), knowledge of the environmental severity of the Air Force bases at
which the plane will be deployed, an understanding of the growth kinetics of the
existing corrosion sites and the influence of the environmental factors and suppression
technologies on those kinetics, and, finally, the influence of the "as is" and "to be"
states of corrosion on structural integrity. Ultimately, the prediction will be aided by a
suite of on-board sensors that will report in real time or near real time on the status of
the local environment and damage state.
This project is primarily an engineering task, but there are a number of scientific
issues, and corrosion scientists are fully integrated into the team. The complexity of
the problem necessitates the involvement of empirical considerations if any progress
is to be made. However, a scientific underpinning for the framework is required if the
predictive model is to be robust. For example, the growth kinetics of localized
corrosion is considered to be the best understood aspect of localized corrosion, and it
is possible to guess a reasonable kinetic expression based on past studies. However, a
detailed understanding of the effects of a variety of factors is needed: microstructure
and temper; environment including composition, time of wetness, relative humidity
cycles and temperature; and stress. The concepts of stifling of growing sites and
initiation of new sites must also be considered, and these are very complex issues.
Initiation involves coating degradation and breakdown. The reactions inside crevices
and the development of crevice chemistry and profiles over time require scientific
approaches, as does the development of effective suppression technologies.
The situation with chromate corrosion inhibitors is rather well known and is related to
the last topic of aging aircraft. Chromates are widely used to protect the very
corrodible high strength Al alloys used in aerospace applications, and also for other
materials in a wide range of applications. However, vis-à-vis aging aircraft, part of the
high cost of maintenance is from handling chromates. Furthermore, regulations are
being passed to severely limit the use of chromates because of their carcinogenic
nature. Chromates can be added as dissolved CrVI ions into an aqueous environment,
applied to a surface as a chromate conversion coating (CCC) or added to paint as a
pigment. A very important aspect of the inhibition provided by all embodiments of
chromates is that they promote self-healing.
Considerable efforts have been undertaken for many years to find a replacement for
chromate that is equally or more effective, but environment friendly. In the mid-90's,
the USAF convened a Blue Ribbon Advisory Panel to study aircraft coatings . The
report of that panel indicated that developing a better understanding of the
mechanisms of aluminum corrosion and chromate inhibition should be a top priority
and a prerequisite for the development of a successful replacement. The Air Force
Office of Scientific Research then funded a large program to study chromates. This
type of block funding is another important aspect of the current landscape in corrosion
science funding. Funding agencies are more willing to support multidisciplinary team
efforts to address a problem, and such an approach works. In this case, the money put
into this topic jump-started activities in the area of Al alloy corrosion and chromate
inhibition, and these topics developed into "fad" as discussed above. Other funding
agencies in the US, such as DOE and SERDP, initiated programs in this area and
investigators from around the world got interested. This interest has been reflected by
a large number of publications and conference presentations in the area of Al alloy
corrosion and inhibition over the past several years.
The connection of the scientific work in this area to industry and real solutions has
been more problematic. Coatings companies are, in general, not open with their
technology, which is largely proprietary. They might be benefiting from the science
described in the open literature, but a large coordinated team effort with industry and
academic participation has not materialized. The funding agencies have not followed
up on the initial investment in understanding of chromate inhibition to put together a
similar effort specifically on the topic of chromate replacement.
A number of the important scientific issues have been addressed by the recent
activities, and the results have in fact provided guidance to those who are seeking to
replace chromates. Since CCCs and chromate pigments primarily act by providing
soluble CrVI species to the local environment, it is critical to understand how
dissolved CrVI ions affect corrosion. Are they anodic or cathodic inhibitors? Do they
form a protective film on the surface? If so, what is the nature of that film and why is
it so protective? Replacing CCCs requires detailed knowledge of the CCC. What is its
structure and composition, and do they vary across the surface of a complex alloy
containing intermetallic particle phases? What is the effect of surface pretreatments?
What controls the thickness and deposition rate? How and why does it vary across the
surface of an alloy? What happens during the aging process? How are CrVI ions
released and at what rate? Regarding chromate pigments, it is critical to know the
proper solubility, which changes with the cation. How does the pigment interact with
the polymer matrix? What is the effect of loading?
The answers to some of these questions can be found in recent reports [10,11]. In
summary, there are several reasons why chromate is an extremely effective corrosion
inhibitor for Al alloys.
Chromate can be stored in conversion coatings and as a pigment in
Chromate is released from these coatings, particularly when they are
scratched to refresh the coating area. The released chromate is in equilibrium
with the chromate in the coatings, and higher pH favors CrVI release.
Chromate is mobile in solution and migrates to exposed areas on the Al
Chromate adsorbs on the active sites of the surface and is reduced to
form a monolayer of a CrIII species.
This layer is effective at reducing the activity of both cathodic sites
(Cu-rich IMC particles) and anodic sites in the matrix or at S phase particles.
The combined properties of storage, release, migration, and irreversible
reduction provided by chromate coatings underlie their outstanding corrosion
Inhibition of the oxygen reduction reaction at cathodic Cu-rich IMC
particles is an important part of the overall corrosion inhibition mechanism.
It is reasonable to expect that replication of these characteristics of chromate using
another inhibitor species is necessary to successfully replace chromate as a critical
component for Al alloy corrosion inhibition.
Having glanced at the past and taken stock of the present, it is appropriate to look to
the future. The model of creating large multidisciplinary teams of both engineers and
scientists to solve complex problems will continue to flourish. This approach works
and benefits everyone. The single investigator working in relative isolation should not
be ignored, because breakthroughs can be accomplished in that mode. However,
corrosion scientists can contribute significantly to large projects that are largely
engineering in nature, even with important scientific contributions. And the scientists
benefit from having a focus and customer for their services.
The topics discussed in the last section give a hint as to the focus of the future of
corrosion science, which I believe to be: reliability and lifetime prediction, surface
engineering and smart coatings, and infrastructure improvement and maintenance.
These will be addressed in turn.
Reliability and Lifetime Prediction
Reliability and lifetime prediction certainly will be a major thrust of the field of
corrosion. This is the focus of the projects on long term nuclear waste storage and
aging aircraft described above. We cannot with accuracy predict how much the
lifetime of a component will change if the chloride concentration in the environment
is cut in half even though we know precisely how the pitting potential will change. If
the field of corrosion is to have any impact in design science, as has been promoted by
Roger Staehle in recent years [12,13], then we will need to develop lifetime prediction
tools. The situations of a buried waste canister or a military airplane are relatively
simple. The environments of both are quite limited; the repository is perfectly defined,
and military planes will land at one of a hundred or so bases around the world
(corrosion during flight is typically minimal since the temperature at high altitude is
far below the freezing point.) Nonetheless, definition of the local environment for
both is very tricky and extremely important. The situation is more complicated for an
automobile, and even more so for other applications, such as an Army vehicle, which
might see a very wide range of environments.
There is no doubt that advanced statistical concepts need be adopted in the field of
corrosion to deal with these complexities. Weibull distributions allow predictions of
the earliest failures from a distributed population of data [12,13]. Other approaches
are suggested from medical and epidemiological studies, which have made wide use
of advanced statistical theories. One can correlate "disease" to "corrosion", "patient"
to "component", and "death" to "failure" and see that there is a perfect analogy
between medicine and corrosion. Two approaches to deal with these types of
problems are survival analysis and logistic regression analysis [14,15]. Finally,
artificial neural networks (ANNs) comprise another tool that recently has been applied
to predicting corrosion .
Survival analysis is appropriate for situations when time to an event, such as death or
failure, is monitored. In general, observations are made until death or failure.
However, observation often ends before failure occurs because the study ends or the
subject is lost to continued observation. Making full use of available information from
these "censored" observations underlies the challenge of working with survival data.
Survival analysis also explores, through the use of specialized modeling techniques,
the role that variables play in hastening or extending the time to failure. Survival
analysis has been used extensively in the study of survival of patients following
medical treatment and should be extremely useful in the prediction of corrosion. It
enables the development of models to predict the influence of a variety of parameters
using data from both components that have suffered corrosion and those that are still
Logistic regression analysis is suitable when there is a "go/no-go" assessment, such as
life or death and corrosion or no corrosion. In this method the presence or absence of
corrosion is used as the response variable rather than the time to the event (as in
survival analysis). The multiple logistic regression model estimates the probability of
an outcome of interest (such as corrosion) given a set of suspected “risk factors.”
Through this approach, it is possible to select, from many potential predictors, those
that are most highly related to corrosion.
Successful application of both survival analysis and logistic regression analysis
requires a reasonable foundation in statistics. Artificial neural networks (ANNs) are
much more accessible to statistical laymen but are still extremely useful for
recognizing complex relationships between input and output data. ANNs are
interconnected mathematical processing elements based on biological nervous
systems. The result of the model is similar to what is obtained by logistic regression
analysis. However, in contrast to a logistic regression approach, which often involves
considerable subjectivity in the modeling process, ANNs develop predictive relations
automatically through a training and validation process. Since ANNs operate by
recognizing complex relationships among data, they are very powerful for modeling
complex physical phenomena where a comprehensive deterministic understanding
does not yet exist. For this reason, they are well suited for make predictions of
damage accumulation due to corrosion, stress corrosion cracking and corrosion
fatigue. ANNs have been used to predict corrosion behavior and their use will likely
increase in the future.
Smart Coatings and Surface Engineering
"Smart coatings" is a buzzword phrase for futuristic corrosion protection. A wide
range of coating intelligence has been promised by "smart coaters," even including the
incorporation of nanomachines to somehow enable physically rebuilding of damaged
coatings. The eventual extent of coating intelligence is debatable, but there is no doubt
that coatings will get smarter.
Actually, CCCs are already rather smart. They store an inhibitor, release it into
aggressive solutions in which it migrates to an active site and irreversibly reduce to
quench corrosion attack. Even duplicating the efficacy of CCCs is a considerable
challenge. Self-healing properties have been documented for chromate-free coatings,
although the extent of inhibition was not equivalent .
Smart coatings will be able to do more than release active corrosion inhibitors.
Sensing of corrosion, either the direct product of corrosion such as metal cations 
or indirect products such as hydroxyl associated with the cathodic reaction , has
already been studied, though practical embodiments have not yet been achieved. It is
also possible to use x-rays to sense structural changes of a pigment added to an
organic primer coating as an indicator of the presence of moisture in that layer .
Of course, the presence of moisture is necessary, but not sufficient evidence that
corrosion is occurring. Ion-exchange compounds used as pigments can also provide
added functionality by removing aggressive anions such as chloride from the coating
or from a blister under the coating and replacing them with beneficial inhibiting
anions . Finally, color change on demand for camouflage purposes is a property
that could reasonably be achieved by different technologies. Smart coatings are
definitely in their infancy, and will be a hot topic of research and development in the
Related to smart coatings is surface engineering, which is a term that implies a more
classical surface science approach to surface modification. It is clear that corrosion
happens at surfaces, so it is possible to retard corrosion by controlling surface
properties. For instance, corrosion under organic paint coatings occurs when the
coating disbands or delaminates. Improvement in the metal/coating bonding is a very
practical approach for improving corrosion protection. One needs to understand the
oxide formed on the metal substrate, the nucleation and growth of sacrificial layers
such as galvanizing, the oxides formed on top of these layers, the effects of surface
treatments, the interaction of organic adhesion promoters with the surface and with a
bulk pigmented organic coating, and the functionalization of polymer surfaces. To
understand these interactions requires careful experimentation using surface analytical
tools. A fundamental understanding developed by surface science approaches should
enable the design and development of improved coating systems.
A study on the cost of corrosion in the US published in 2001 was based on analyses of
industrial sectors . A remarkable finding of that study is that the sector with the
highest cost is not defense or motor vehicles. The cost associated with corrosion of
drinking water and sewer systems, $36B/yr, vastly exceeds any other sector. When
other infrastructure sectors are included, such as highway bridges, electric utilities, oil
and gas transmission pipelines and local gas distribution piping, the cost is a
staggering $63B/yr. Certainly, known engineering fixes are all that is required for
most of these corrosion problems. However, the magnitude of the problem
necessitates that new and innovative solutions be sought. Governments should
assemble a large, multidisciplinary team including both engineers and scientists to do
Computation and instrumentation
Advanced computational power and instrumentation will continue to affect and
improve corrosion science. Electrochemical measurements are extremely easy and
inexpensive relative to even 10 years ago, which greatly enhances the productivity of
corrosion scientists and engineers. Commercially-available multichannel potentiostats
allow for up to 100 simultaneous measurements. If used with appropriate samples
containing arrays of electrodes, this equipment allows for incredible parallel
processing and reduction of experimental time. Such advances will continue to
facilitate the activities of corrosion science.
Another aspect of computation that will have a big impact on corrosion science and
engineering in the future is the application of thermodynamic databases to predict
speciation and alloy stability. Commercial products  are already providing
capability that far exceeds what was available 10 years ago, the Pourbaix Atlas. Such
tools are incredibly useful for engineering applications in complex environments, such
as those used in the chemical process industry. For corrosion scientists, this type of
analysis should improved understanding of situations like the environment in pits and
The future of corrosion research will depend to a great extent on available resources,
so a good question to ask about any predictions of the future is "Who's going to pay
for it?" Research in universities will be on subjects for which funding is available.
Another important fact about the present status of corrosion science in the US is that it
is driven largely by funding from the Department of Defense. The Navy has
traditionally been a strong supporter of corrosion science. As mentioned, the Air
Force has taken up the subject with some vigor over the last 8 years. Finally, the US
Army has renewed interests in corrosion. The DOD has sufficient resources to set the
agenda and to fund large activities, as was described above regarding the areas of
aging aircraft and chromate replacement.
There should be concern for the future funding of corrosion research. Corrosion is not
sexy and trendy. Contract monitors in funding agencies, even within DOD, must be
provided with support for the cause. Corrosion problems will not vanish, but the
impetus to fund them will dwindle unless corroders can show success in important
areas, such as lifetime prediction, coatings, and infrastructure.
The future of corrosion science lies in teaming with other scientists and engineers to
address large important problems. In particular, the areas of reliability and lifetime
prediction, surface engineering and smart coatings, and infrastructure improvement
and maintenance will attract attention.
The author gratefully acknowledges input from N. Hackerman, R.G. Buchheit, R.W.
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