U.S. patent application number 10/412737 was filed with the patent office on 2005-08-11 for releasable corrosion inhibitor compositions.
Invention is credited to Cook, Ronald Lee.
Application Number | 20050176851 10/412737 |
Document ID | / |
Family ID | 37996743 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050176851 |
Kind Code |
A1 |
Cook, Ronald Lee |
August 11, 2005 |
RELEASABLE CORROSION INHIBITOR COMPOSITIONS
Abstract
A new class of releasable corrosion inhibiting materials for
protective coatings, methods of making the same, methods of using
the same, and coatings containing the same are provided. The
materials comprise one or more corrosion inhibitors that are
chemically anchored to the surface of a particle having an aluminum
oxyhydroxide surface through a carboxylate bond. The
carboxylate/aluminum-oxyhydroxide-surface bond breaks under
corrosion-causing conditions (for example the presence of high
levels of hydroxide ions generated by the cathodic oxygen reduction
reaction on metals such as iron and aluminum) thereby allowing the
corrosion inhibitors to detach from the particle surface when
corrosion is present.
Inventors: |
Cook, Ronald Lee; (Lakewood,
CO) |
Correspondence
Address: |
GREENLEE WINNER AND SULLIVAN P C
4875 PEARL EAST CIRCLE
SUITE 200
BOULDER
CO
80301
US
|
Family ID: |
37996743 |
Appl. No.: |
10/412737 |
Filed: |
April 11, 2003 |
Related U.S. Patent Documents
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Application
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Filing Date |
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10412737 |
Apr 11, 2003 |
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10171402 |
Jun 12, 2002 |
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10412737 |
Apr 11, 2003 |
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10171422 |
Jun 12, 2002 |
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6887517 |
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Current U.S.
Class: |
523/210 ;
252/387; 428/402; 428/403; 428/404; 428/405; 428/407; 428/457;
556/173 |
Current CPC
Class: |
Y10T 428/31678 20150401;
Y10T 428/2982 20150115; C08K 3/346 20130101; C01P 2004/64 20130101;
B82Y 30/00 20130101; C09D 163/00 20130101; C08K 9/04 20130101; Y10T
428/2998 20150115; C08K 3/22 20130101; Y10T 428/2993 20150115; Y10T
428/2991 20150115; C09C 1/407 20130101; C09D 163/00 20130101; B01J
2/30 20130101; Y10T 428/2995 20150115; C09D 5/082 20130101; C09C
1/24 20130101; C08L 2666/54 20130101 |
Class at
Publication: |
523/210 ;
428/403; 428/457; 428/402; 428/404; 428/405; 428/407; 556/173;
252/387 |
International
Class: |
B32B 015/04; B32B
005/16; C09K 003/00; C08K 009/10 |
Goverment Interests
[0002] This invention was made, at least in part, with funding from
Navy Contract No. N00014-96-0147, and Air Force Contract No.
F33615-99-C-5013. The United States government may have certain
rights in the invention.
Claims
1. A corrosion inhibiting material comprising: a particle having an
aluminum oxyhydroxide surface; a carboxylate group chemically
anchored to the aluminum oxyhydroxide surface; and one or more
corrosion inhibitors chemically anchored to the aluminum
oxyhydroxide surface through the carboxylate group.
2. The material of claim 1 wherein the particle having an aluminum
oxyhydroxide surface is a boehmite or pseudoboehmite particle.
3. The material of claim 1 wherein the particle having an aluminum
oxyhydroxide surface is a particle having an aluminum oxyhydroxide
surface and a core of a different substance.
4. The material of claim 1, further comprising one or more
non-corrosion inhibiting groups chemically anchored to the
particle.
5. The material of claim 1, wherein the corrosion inhibitors that
are chemically anchored to the aluminum oxyhydroxide surface
through the carboxylate group are selected from the group
consisting of: phenols, organic amines, organic sulfides,
heterocylic rings, substituted aromatic rings, organic phosphates
and phosphonic acids.
6. The material of claim 1, wherein each corrosion inhibitor
chemically anchored to the aluminum oxyhydroxide surface has the
same chemical formula.
7. The material-of claim 1, wherein the material contains at least
two corrosion inhibitors with different chemical formulas.
8. The material of claim 1 wherein the corrosion inhibitor contains
one or more members of the group consisting of: a monovalent,
divalent or trivalent salt of an organic amine, an organic sulfide,
a heterocylic ring, a substituted aromatic ring, an organic
phosphate and a phosphonic acid.
9. A corrosion inhibiting material comprising: a particle having an
aluminum oxyhydroxide surface; and one or more members of the group
consisting of: a non-corrosion inhibiting group directly chemically
anchored to the aluminum oxyhydroxide surface through a carboxylate
group; a corrosion inhibiting group directly chemically anchored to
the aluminum oxyhydroxide surface through a carboxylate group; a
non-corrosion inhibiting group indirectly chemically anchored to
the aluminum oxyhydroxide surface by grafting the non-corrosion
inhibiting group to a surface anchored carboxylate that has a
reactive functional group; and a corrosion inhibiting group
indirectly chemically anchored to the aluminum oxyhydroxide surface
by grafting the corrosion inhibiting group to a surface anchored
carboxylate that has a reactive functional group wherein at least
one corrosion inhibiting group and at least one non-corrosion
inhibiting group are anchored to the aluminum oxyhydroxide surface
of the particle.
10. The material of claim 9 wherein the corrosion inhibiting group
directly chemically anchored to the aluminum oxyhydroxide surface
through a carboxylate group is selected from the group consisting
of: an aromatic acid, an aliphatic acid, a cycloaliphatic acid, an
alkene containing aliphatic acid, an alkene containing
cycloaliphatic acid, an amino acid, a heterocylic aromatic and
aliphatic acid.
11. The material of claim 9 wherein the corrosion inhibiting group
is selected from the group consisting of: organic amines, organic
sulfides, heterocylic rings, substituted aromatic rings, organic
phosphates and phosphonic acids.
12. The material of claim 9 wherein the particle is boehmite,
pseudoboehmite or has a surface of boehmite or pseudoboehmite.
13. The material of claim 1, made by the method comprising:
chemically anchoring a functionalized carboxylic acid molecule to a
particle having an aluminum oxyhydroxide surface, forming an
anchored functionalized carboxylic acid; then grafting one or more
corrosion inhibitors to the anchored functionalized carboxylic
acids.
14. The material of claim 1, made by the method comprising:
chemically anchoring two or more different functionalized
carboxylic acid molecules to a particle having an aluminum
oxyhydroxide surface, forming anchored functionalized carboxylic
acids; then grafting one or more corrosion inhibitors to the
anchored functionalized carboxylic acids.
15. The material of claim 13, wherein the grafting step comprises:
reacting a functionalized corrosion inhibitor with the anchored
functionalized carboxylic acid.
16. The material of claim 13, wherein the grafting step comprises:
reacting the anchored functionalized carboxylic acid with one or
more intermediate reactive compounds, forming an intermediate
particle and reacting the intermediate particle with one or more
corrosion inhibitors.
17. The material of claim 14, wherein the grafting step comprises:
reacting a functionalized corrosion inhibitor with the anchored
functionalized carboxylic acid.
18. The material of claim 14, wherein the grafting step comprises:
reacting the anchored functionalized carboxylic acid with one or
more intermediate reactive compounds, forming an intermediate
particle and reacting the intermediate particle with one or more
corrosion inhibitors.
19. An organic polymer protective coating comprising: a polymer;
and at least one type of corrosion inhibiting material comprising:
a particle having an aluminum oxyhydroxide surface; a carboxylate
group chemically anchored to the aluminum oxyhydroxide surface; and
one or more corrosion inhibitors chemically anchored to the
aluminum oxyhydroxide surface through the carboxylate group,
forming a corrosion-inhibiting particle.
20. The coating of claim 19, wherein each corrosion-inhibiting
particle has one corrosion inhibitor functionality, and the polymer
includes more than one different corrosion-inhibiting particle.
21. The coating of claim 19, wherein at least one
corrosion-inhibiting particle contains more than one different
corrosion inhibitor chemical functionality.
22. (canceled)
23. (canceled)
24. A method for inhibiting corrosion of a metal or alloy surface
comprising: applying an organic polymer protective coating of claim
19 to the metal or alloy surface.
25. The method of claim 24 further comprising: mixing the organic
polymer protective coating with an adhesive composition; prior to
applying the adhesive mixture to the metal or alloy surface.
26. The material of claim 1 wherein the carboxylate is chemically
anchored to the aluminum oxyhydroxide surface such that under
corrosion-causing conditions the chemical bond between the
carboxylate and the aluminum-oxyhydroxide surface breaks thereby
releasing one or more corrosion inhibitors from the particle
surface.
27. The material of claim 26 wherein the corrosion-causing
conditions are basic conditions.
28. The material of claim 26 wherein the one or more corrosion
inhibitors are selected from the group consisting of imidazoles,
azoles, and oximes.
29. The material of claim 26 wherein the one or more corrosion
inhibitors are organic sulfides.
30. The material of claim 26 wherein the one or more corrosion
inhibitors are phosphonic acids.
31. The material of claim 1 wherein the ratio of surface Al atoms
on the aluminum oxyhydroxide surface to the corrosion inhibitors
ranges from 2:1 to 100:1.
32. The material of claim 1 wherein there are between 0.5 and 0.05
corrosion inhibitors per number of surface Al on the aluminum
oxyhydroxide surface.
33. The organic polymer protective coating of claim 19 wherein the
one or more corrosion inhibitors are selected from the group
consisting of: organic amines, organic sulfides, heterocylic rings,
substituted aromatic rings, organic phosphates and phosphonic
acids.
34. The organic polymer protective coating of claim 19 wherein the
one or more corrosion inhibitors are selected from the groups
consisting of quaternary ammonium compounds, imidazolines,
aldehydes, sulfoxides, carboxylic acids, mercaptocarboxylic acids,
imidazoles, oximes, azoles, tannins, substituted phenols,
substituted quinolines and quinalizarin.
35. The organic polymer protective coating of claim 19 wherein the
one or more corrosion inhibitors are selected from the group
consisting of imidazoles, azoles, oximes, organic sulfides, and
phosphonic acids.
36. The organic polymer protective coating of claim 19 wherein the
one or more corrosion inhibitors are chelating agents.
37. The organic polymer protective coating of claim 19 wherein the
polymer is selected from the group consisting of latexes, amino
resins, polyurethanes, epoxies, phenolic resins, acrylic resins,
polyester resins, alkyd resins, polysulfide resins and halogenated
polymer resins.
38. The organic polymer protective coating of claim 19 wherein the
polymer is a polyurethane or an epoxy.
39. The method of claim 24 wherein the metal or alloy surface is
iron, aluminum, copper, magnesium, nickel, brass or bronze.
40. The method of claim 24 wherein the metal or alloy surface is
iron or aluminum.
41. The method of claim 24 wherein the organic protective coating
is applied to the metal or alloy surface by painting, baking powder
coatings, flame spraying or electrostatic spraying.
42. The method of claim 24 wherein each corrosion-inhibiting
particle of the organic polymer coating has one corrosion inhibitor
functionality, and the polymer includes more than one different
corrosion-inhibiting particle.
43. The method of claim 24 wherein at least one
corrosion-inhibiting particle of the organic polymer coating
contains more than one different corrosion inhibitor chemical
functionality.
44. The method of claim 24 wherein the corrosion is under-coat
corrosion, or corrosion that occurs when the protective coating is
damaged or defective.
45. The method of claim 24 wherein in at least one corrosion
inhibiting material in the organic polymer coating, a corrosion
inhibitor is chemically anchored to the aluminum oxyhydroxide
particle surface such that under corrosion-causing conditions the
corrosion inhibitor is released from the particle surface.
46. The method of claim 46 wherein the corrosion inhibitor that is
released can be transported to the site of corrosion to inhibit the
corrosion reaction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application takes priority to U.S. patent application
Ser. No. 10/171,402 and U.S. patent application Ser. No.
10/171,422, both filed on Jun. 12, 2002, both of which are
incorporated by reference to the extent not inconsistent with the
disclosure herewith.
FIELD OF THE INVENTION
[0003] This invention relates generally to compositions of matter
and methods of preparation of surface modified aluminum
oxyhydroxide particles that release one or more types of corrosion
inhibitors when triggered by corrosion products. Corrosion
inhibitors are anchored to the particles through a carboxylic acid.
Hydroxide ions generated from the corrosion of metals triggers
release of the corrosion inhibitors from the particles. The
particles carrying the corrosion inhibitors are incorporated into
protective coatings to inhibit corrosion on metals and alloys such
as iron, aluminum, copper, magnesium, nickel, brass and bronze.
BACKGROUND OF THE INVENTION
[0004] The corrosion of metals has widespread economic and
environmental effects and also has a significant impact on public
safety and health. The annual cost of corrosion to the US is
estimated to be approximately 3% of GDP. A substantial part of that
cost is due to atmospheric corrosion, and protection against
atmospheric corrosion constitutes about 50% of all corrosion
protection measures. Corrosion has led to bridge collapses, fatal
airplane and train crashes, and the leakage and subsequent
explosion of natural gas pipelines. The environmental health
effects attributed to corrosion are also widespread. Structures
such as storage tanks, pipelines, ships, railcars, and tanker
trucks, which store and/or transport hazardous materials can be
weakened and made unsafe by corrosion, and corrosion is also the
leading cause of leaking chemical storage tanks.
[0005] Protective organic coatings (also known as paints) are one
of the most cost-effective methods of preventing the corrosion of
metals. These protective organic coatings are typically polymeric.
In typical practice, the protective organic coating is applied over
an inorganic conversion coating. The protective organic coating may
comprise one or more layers of different organic coatings. The
first layer is typically an epoxy that adheres well to the
conversion coating and has excellent chemical and barrier
properties. The epoxy coating is typically overlaid with a second
coating, such as polyurethane, that is more resistant to weathering
than the epoxy.
[0006] Conversion coatings are produced directly on the metal
surfaces by treatment with a chemical agent [such as a soluble
chromate or zinc phosphonate] to passivate or seal the surface.
Conversion coatings are thin, new phases produced by the reaction
of the metal and the chemical agent and are typically either metal
phosphates or metal chromates. The conversion layers can enhance
adhesion of the protective organic coating to the metal, provide an
enhanced barrier to corrosion and can contain corrosion
inhibitors.
[0007] The primary function of the protective organic coating is to
prevent corrosion by physically blocking agents that cause
corrosion (water, solubilizing organic or inorganic anions, certain
oxidizing agents, etc.) from reaching the metal surface. However,
this approach is defeated if the coating has a defect, if the
coating becomes damaged or simply if water or other corrosive
agents slowly penetrate through the intact coating. In order to
deal with under-coat corrosion, or corrosion that occurs when the
coating is damaged or defective, soluble or dispersible corrosion
inhibitors are often added to the protective organic coatings.
[0008] A corrosion inhibitor for use in coatings is generally a
soluble or dispersible material that is incorporated into the
coating and can be transported by convection or diffusion to the
site of corrosion where it slows down the corrosion reaction. The
corrosion inhibitor must therefore be mobile and be able to migrate
to the corrosion site, because the site is often a scratch or a gap
in the coating that is not directly in contact with the coating
itself.
[0009] Corrosion inhibitors can be divided into two broad
categories, those that enhance the formation of a native protective
oxide film through an oxidizing effect and those that inhibit
corrosion by selectively adsorbing on the metal surface and
creating a barrier that prevents access of the corrosive agent to
the surface. In the former group are materials such as inorganic
chromates, inorganic nitrates, molybdates and organic nitrates. The
latter group includes materials such as carbonates, silicates and
phosphates and organic molecules containing heteroatoms such as
nitrogen, sulfur, phosphorus and oxygen (e.g. materials such as
anthranilic acid, thiols, organic phosphonates and organic
carboxylates). Some of these materials also act as poisons for the
cathodic oxygen reduction reaction that is linked to the anodic
dissolution of the metal. Slowing down the cathodic reaction slows
down the overall corrosion reaction.
[0010] Soluble chromates are widely used corrosion inhibitors due
to their high effectiveness in arresting corrosion. Chromates are
highly effective corrosion inhibitors because they simultaneously
provide several mechanisms to retard corrosion. (Frankel, G. S. and
R. L. McCreery, "Inhibition of Al Alloy Corrosion by Chromates," J.
Electrochem. Soc., Interface, Winter, 34-38, 2001). Soluble
chromates are oxidizing compounds that can also react with the
corroding surfaces of aluminum and steel to provide an insoluble
and a somewhat hydrophobic barrier. Chromates are also thought to
inhibit corrosion by poisoning of the oxygen reduction reaction and
inhibiting the initiation of corrosion. In current practice, high
concentrations of chromates (sometimes up to 50% by weight) are
added to the protective coating to provide a reservoir of the
corrosion inhibitor so that a high level of corrosion protection
can be maintained over several years, even in severe
environments.
[0011] Unfortunately, soluble chromate corrosion inhibiting
additives have adverse environmental effects, and there is a widely
recognized need for non-chromate corrosion inhibitors. The toxic
properties of chromates are well documented. The Public Health
Service (ACGIH 1986/Ex. 1-3, p. 140) reports nasal irritation,
evidence of liver enlargement and kidney dysfunction among chromate
workers exposed to 0.06 to 0.07 mg Cr(VI)/m.sup.3. This report also
cites excess lung cancer among chromate workers exposed to 0.01 to
0.15 mg/m.sup.3 soluble chromate and 0.1 to 0.58 mg/m.sup.3
insoluble chromate. The use of chromate-inhibited spray-on coatings
creates inhalable chromate tainted dusts. Removing
chromate-inhibited coatings by chemical or mechanical means also
generates a hazardous chromated waste that requires expensive
disposal.
[0012] A number of chromate-like inorganics (e.g. molybdates,
vanadates, and manganates) have been proposed as replacements for
chromate conversion coatings and as additives for protective
coatings (Cohen, S. M. "Replacements for Chromium Pretreatments on
Aluminum", Corrosion, 51(1), 71-78, 1995). Rare earth materials
such cerium have also been evaluated as corrosion inhibitors
(Mansfeld, F., V Wang and H. Shih "Development of "Stainless
Aluminum", J. Electrochem. Soc., 138(12), L74-L75, 1991). However,
heavy metal chromate replacements may also be strictly regulated in
the future.
[0013] Organic corrosion inhibitors are an alternative to the toxic
heavy metal corrosion inhibitors currently used in coatings. The
inhibition of corrosion of a metal or an alloy by organic corrosion
inhibitors can be achieved by many mechanisms, the effectiveness of
which depends on many factors; including the nature of the metal,
the oxidation-reduction potential of the environment, the
temperature, and the concentration and strength of adsorption of
the organic molecule to the metal surface. Organic corrosion
inhibitors are generally low to moderate molecular weight molecules
that primarily prevent corrosion by either reacting with the
surface of the metal, its oxide, or its corrosion products to form
a thin film. (Kuznetsov, Y. I., J. G. N. Thomas and A. D. Mercer.
"Organic Inhibitors of Corrosion of Metals", Plenum Pub Corp.
1996). Highly effective organic corrosion inhibitors generally
interact with the metal via chemical adsorption. Chemical
adsorption involves the formation of a coordinate bond between the
metal surfaces and the organic corrosion inhibitor. The nature of
the metal and the structure of the organic have a decisive effect
on the strength of the bond and therefore the efficiency of the
organic corrosion inhibitor. Organic corrosion inhibitors generally
have donor atoms such as S, O and N that can donate electrons to
the metal, thereby forming the coordinate bond. All other things
being equal, higher electron density and larger polarizabilities
usually lead to better corrosion protection, as known in the art.
Because film formation is a chemical adsorption process, the
temperature and the concentration of the inhibitors are also
important factors in determining the effectiveness of the organic
corrosion inhibitors.
[0014] Corrosion inhibitors can be added directly to the protective
organic coating, and using several different corrosion inhibitors
can produce a synergistic effect. For example, combinations of
oleic acid and phenyl anthranilate have been reported to be
significantly more effective than either of the inhibitors alone
(Kuznetsov, Y. I., J. G. N. Thomas and A. D. Mercer. "Organic
Inhibitors of Corrosion of Metals", Plenum Pub Corp. (1996)).
[0015] Although there are numerous organic compounds that are
excellent corrosion inhibitors in solution (V. S. Sastri, Corrosion
Inhibitors: Principles and Applications, John Wiley and Sons,
Chichseter, England 1998), these materials have yet to find
widespread use in protective organic coatings. The primary
technical reason for their lack of use is that the best organic
corrosion inhibitors work because they contain functional groups
(e.g. amines, amides, thiophenes, carboxylic acids, etc.) that form
strong bonds to the metal surfaces. These same functional groups,
can unfortunately, also react with the polymer resins used to
produce the coating. The corrosion inhibitor is then locked into
the polymer chain, thereby immobilizing it and preventing it from
diffusing to the paint/metal interface where it is needed to block
corrosion.
[0016] Even if the organic corrosion inhibitors are designed so
that they would not be locked into the polymer structure (e.g.
using latent reactive groups), when the corrosion-inhibited
coatings are exposed to water (e.g. rain or aqueous detergent
solutions used to clean the coatings), the inhibitors can be lost
from the film by leaching, migration or extraction. The loss of
inhibitor reduces the effectiveness and useful service lifetime of
the coating. However, to work, the corrosion inhibitor must be able
to diffuse through the coating to reach the corrosion site;
especially if a hole or a scratch in the coating produced the
corrosion site. Unfortunately, it is this mobility that allows the
corrosion inhibitor to escape from the coating. Furthermore, if the
coatings contain toxics (as do the currently used chromated
epoxies), the toxics can be leached into the environment. In
addition, adding a high concentration of a corrosion inhibitor to a
coating can change the physical properties and chemical properties
of a coating, often for the worse.
[0017] One way of solving these problems (e.g. immobilization of
the inhibitor by reaction with the coating resins, loss to the
environment and degradation of film properties) is by encapsulating
the inhibitor molecule and using the encapsulant as an
anti-corrosion pigment in a paint (J. D. Scantlebury and Dezhu Xiu,
Journal of Corrosion Science and Engineering Abstract 22: A Sol-gel
derived anti-corrosion pigment,
http://www.umist.ac.uk/corrosion/JCSE/). Another approach is to
ion-exchange the corrosion inhibitors onto a particle surface.
Compositions that release corrosion inhibiting agents from
particles include ion-exchange resins, ion-exchanged zeolites and
carbon molecular sieves, ion-exchanged solid particles and water
soluble glasses.
[0018] U.S. Pat. No. 3,899,624 discloses the use of organic
ion-exchange resins incorporating corrosion inhibiting anions or
cations and the release of said ions into a paint to arrest
corrosion by ion exchange. The corrosion inhibiting ions include
zinc and chromates. U.S. Pat. No. 4,738,720 discloses the use of a
calcium ion-exchange zeolite composition and its use in a paint.
H856, a statutory invention registration, discloses the use of
calcium and barium exchanged Y-zeolites and their incorporation
into a paint as corrosion inhibitors for steel panels.
[0019] U.S. Pat. 6,383,271B1 discloses the use of fillers with
hollow cellular structures such as diatomaceous earth, zeolite or
carbon, wherein the hollow cells or pores are loaded with
inhibitors or antioxidants as corrosion inhibitors for paints.
Inhibitors disclosed include carbonic acids, amines, ketones,
aldehydes, heterocyclic compounds, phosphates, benzoates,
silicates, vanadates, tungstates, zirconates, borates, or
molybdates.
[0020] U.S. Pat. Nos. 4,405,493, 4,419,137, 4,459,155, 4,474,607,
4,594,369, 4,643,769, 4,687,595, 4,749,550, 4,795,492, and
5,041,241 disclose compositions of alumina and silica inorganic
particles whose surfaces are ion exchanged with corrosion
inhibiting cations and anions including calcium, zinc, cobalt,
lead, strontium, lithium, barium, magnesium, yttrium or cations of
one or more metals of the lanthanide group, phosphates, chromates,
benzoates or molybdates. The ion exchanged particle surfaces
release their cations and ions via a subsequent ion-exchange
thereby providing corrosion to metal substrates. U.S. Pat. Nos.
4,405,493, 4,419,137, 4,459,155, 4,474,607, 4,594,369, 4,687,595,
4,749,550, 4,795,492, 5,041,241 also provide for the incorporation
of the ion-exchanged particles as corrosion inhibitors in
paints.
[0021] In the above patents the corrosion inhibitors are
ion-exchanged onto particle surfaces having ion-exchangeable
groups. The corrosion inhibitors are released from the particle
surfaces by a subsequent ion exchange with ions (e.g. chlorides,
sulfates, sodium ions) transported into the coating via water
penetrating through the coating. The present invention provides for
chemically anchoring carboxylic acids to the surface of aluminum
oxyhydroxide surfaces, as evidenced by quantum mechanical
calculations based on Density Functional Theory and solid-state NMR
studies. The chemically anchored corrosion inhibitors of the
present invention are not released by ion-exchange, but they are
released by chemical disruption of the carboxylate bond between the
corrosion inhibitor and the aluminum oxyhydroxide surface.
[0022] U.S. Pat. Nos. 4,210,575, 4,428,774, 4,346,184, 4,518,429,
and 4,561,896 disclose water soluble glass compositions, including
as its major constituents phosphorous pentoxide and either zinc
oxide or calcium oxide, which together form the glass forming oxide
and glass modifying oxide respectively of the glass, together with
a minor proportions of one or more oxides of an element or elements
of Group IIA or Group IIIB of the periodic table, the compositions
of the glass being such that, when the glass is contacted with
water, phosphate ions and either zinc or calcium cations are
leached into solution. The leached ions are disclosed as effective
in the corrosion protection of iron or steel surfaces. These
patents disclose that the glass material can be dispersed in a
resin carrier, and thereby release corrosion inhibiting ions into
the coating when the glass composition is contacted with water. In
U.S. Pat. Nos. 4,210,575, 4,428,774, 4,346,184, 4,518,429, and
4,561,896, the corrosion inhibitors that comprise the water soluble
glass are released when the glass dissolves upon contact with
water.
[0023] U.S. Pat. No. 5,489,447 discloses the use of carrier bound
ketocarboxylic acids as corrosion inhibitors. The ketocarboxylic
acids are preferably bound to the surfaces of oxides, hydroxides,
silicates or carbonates, where examples of these materials are
alumina, magnesium oxide, aluminum hydroxide, magnesium hydroxide,
kieselguhr, talc, aluminium silicate, calcium carbonate or iron
oxide. These materials are incorporated into paints where they are
disclosed to arrest corrosion.
[0024] In the present invention the material to which the corrosion
inhibitors are chemically anchored are aluminum oxyhydroxides or
inorganic particles that are fully or partially covered with
aluminum oxyhydroxides, a class of materials not disclosed in U.S.
Pat. No. 5,489,447. Furthermore, in the present invention the
materials are designed to release the corrosion inhibitors under
certain conditions, e.g. alkaline environments with pH greater than
9. The present invention provides for an improvement over the above
disclosures. In all of the inventions described above (excepting
U.S. Pat. No. 5,489,447), the materials are designed to release the
corrosion inhibitors over time whether or not there is any
corrosion occurring at the metal surface. The concentration of the
organic inhibitor may therefore be reduced by leaching of the
corrosion inhibitor from the coating before corrosion occurs. This
reduces the effectiveness of the inhibitor and the effective
service life of the coating.
[0025] The present invention describes methods and materials for
providing the triggered release of organic corrosion inhibitors
from particle carriers. The invention also provides for
incorporating these corrosion inhibiting particles into protective
organic coatings. In this invention, corrosion inhibitors are
chemically anchored to a particle surface through a labile chemical
bond that can be broken by interaction with hydroxide ions
generated by corrosion of the metal surface. In the presence of
oxygen most metals of practical interest corrode by anodic
dissolution of the metal and cathodic reduction of oxygen, e.g.
M.fwdarw.M.sup.n++ne.sup.-
O.sub.2+2H.sub.2O+4e.sup.-.fwdarw.4OH.sup.-
[0026] The basic hydroxide ions generated by the corrosion process
break the chemical bond between the corrosion inhibitor and the
particle, and thereby release the previously anchored and
immobilized corrosion inhibitor into the protective organic
coating. In the present invention the corrosion inhibiting
particles comprise one or more organic corrosion inhibitors that
are covalently anchored to an aluminum oxyhydroxide surface through
a carboxylic acid.
[0027] The triggered release of the anchored corrosion inhibitors
from the aluminum oxyhydroxide surfaces of the present invention is
observed when an aqueous dispersion of the carboxylate-anchored
surface modified pseudoboehmite/boehmite particles is titrated.
Above pH 6 to about pH 9 the solution viscosity increases, but no
precipitation is observed. FTIR of the particles recovered from
solution in this pH range shows that the organics are still
anchored to the surfaces of the particles. However, above .about.pH
9, the particles precipitate out of solution. FTIR of the particles
recovered from the latter experiment show no organic anchored to
the surface and the quantitative recovery of the organics from the
solution was achieved. Thus, the bond between the carboxylic acid
and the pseudoboehmite/boehmite surfaces is unstable in basic
conditions (i.e. above .about.pH 9).
[0028] There are several advantages to the present invention. The
release of corrosion inhibitors is linked to and triggered by the
corrosion process. Since the release of the organic corrosion
inhibitors occurs only when triggered by the corrosion processes,
this minimizes the amount of corrosion inhibitor that can be
leached out of the coating. Secondly, the invention allows multiple
organic corrosion inhibitors to be incorporated simultaneously into
a protective polymer coating at concentrations sufficient to
inhibit corrosion without degrading the physical properties and
performance of the coating (either by anchoring different types of
inhibitors to a single particle or by using two or more types of
particles each with a single type of inhibitor attached). This
means organic corrosion inhibitors that are active over a wide
range of pH conditions (corrosion can also be occurring at
additional sites where the electrolyte conditions are neutral or
acidic) are available in the coating for arresting corrosion. The
ability to chemically anchor multiple types of releasable corrosion
inhibitors to the particle carriers is also important since
numerous studies have shown that mixed organic corrosion inhibiting
agents can have a synergistic effect.
[0029] The materials described in the present invention are of
class of materials known as alumoxanes. U.S. Pat. No. 5,593,781
discloses preparation of alumoxanes by surface modification of
pseudoboehmite powders of nanometer size particles with small
molecular weight organic compounds in a one-step process by
dispersing the ceramic powder in water or an organic solvent and
adding the low molecular weight organic compound. Apblett et al.
[Mat. Res. Symp. Proc. Vol. 249 1992] also disclose the formation
of carboxy substituted particles from the reaction of
pseudoboehmite and carboxylic acids in a one-step process. Landry
et al. [J. Mater. Chem. 1995, 5(2), 331-341] describe the reaction
of [Al(O)(OH)]n with carboxylic acids to form [Al(O)x(OH)y(O2CR)z]n
where R=C1-C13 and 2x+y+z=3 using a one-step reaction. U.S. Pat.
No. 6,369,183 discloses thermoset polymer networks formed from
surface modified carboxylate-anchored amine, hydroxyl, acrylic and
vinyl modified aluminum oxyhydroxide particles. However, the above
patents do not disclose the use of carboxylate surface-modified
aluminum oxyhydroxide particles or inorganic (non-aluminum
oxyhydroxide) particles whose surfaces are coated with an aluminum
oxyhydroxide and then carboxylate surface modified that provide for
the triggered release of corrosion inhibitors
SUMMARY OF THE INVENTION
[0030] The present invention relates to a new class of corrosion
inhibiting materials for protective coatings that provide for the
triggered release of corrosion inhibitors, methods of making the
corrosion inhibiting materials, methods of using the corrosion
inhibiting materials, and coatings containing the corrosion
inhibiting materials The materials comprise one or more corrosion
inhibitors that are chemically anchored to a particle having an
aluminum oxyhydroxide surface through the carboxylate end of an
organic carboxylic acid. The said corrosion inhibitors may
themselves contain the carboxylic acid and be directly chemically
anchored to the aluminum oxyhydroxide surface or the corrosion
inhibitors may be grafted to the particle having an aluminum
oxyhydroxide surface by chemical reaction with functional groups
that are present in a carboxylic acid that is chemically anchored
to the aluminum oxyhydroxide surface through the carboxylate
functionality. The release of the corrosion inhibitor from the
aluminum oxyhydroxide surface is triggered by disruption of the
particle-carboxylate bond under corrosion-causing conditions (e.g.
the strongly basic conditions generated by the cathodic oxygen
reduction reaction that is part of the corrosion process, or other
conditions that cause the particle-carboxylate bond to break).
[0031] The present invention also allows multiple types of
corrosion inhibitors to be incorporated into a protective coating,
preferably at concentrations sufficient to inhibit corrosion
without degrading the physical properties and performance of the
coating, either by adding particles having several different types
of corrosion inhibitors chemically anchored to the particle surface
or by adding several types of particles, each with a different type
of corrosion inhibitor chemically anchored to the particle surface
to the coating. This approach allows corrosion inhibitors that act
via different mechanisms and at different pHs to be incorporated
into the coating via the particles so that different types of
corrosion inhibitors can be released to the corrosion site.
[0032] Furthermore, additional compounds (for example, low
molecular weight compounds or oligomers or polymers that may or may
not be corrosion inhibitors (including polyethers, polyesters,
alkanes, polyaromatics, polysilicones), and other desired
substances, as known in the art), can be chemically grafted to the
carboxylate-derivatized particles. These additional compounds
include substances that improve the dispersibility of the particles
(including polyethylene oxides, polyacrylates, stearic acid, and
other desired substances, as known in the art), substances that
improve the compatibility of the particles with the coating, such
as epoxy diluents (including Heloxy 65 adducted to an anchored
amine, Tomah PA14 adducted to an anchored acrylate, and other
desired substances, as known in the art), or substances that
improve the adhesion of the coating with the metal surface
(including polyacrylates, polyesters, and other desired substances,
as known in the art). The corrosion inhibitors and additional
compounds may be chemically anchored directly to the surface of the
particle through a carboxylate bond or can be chemically grafted to
the particle surface though functionalized carboxylic acid(s) that
were previously anchored to the particle.
[0033] More specifically, provided is a corrosion inhibiting
material for use as an additive for a protective organic coating
comprising: a particle having an aluminum oxyhydroxide surface; and
one or more organic structures having corrosion inhibiting
properties that are anchored to the aluminum oxyhydroxide surface
via carboxylate groups.
[0034] Methods of making the materials and their uses are also
described herein. The particles may be used in a variety of
different ways in a variety of applications, as will be apparent to
one of ordinary skill in the art. For example, the materials may be
incorporated into coatings (such as polymers) or paints applied to
a metal surface. The materials can also be incorporated into powder
coatings and baked onto a surface. Also the materials can be
incorporated into a polymer by a solvent process and then flame
sprayed onto a surface. These uses are known to one of ordinary
skill in the art.
[0035] The preferred particles of the present invention are
materials having the crystal structure related to boehmite and
having surface areas of at least 10 m.sup.2/g or higher.
Preferably, the surface areas should be 100 m.sup.2/g to 300
m.sup.2/g or higher. High surface areas are preferred since they
allow a higher quantity of corrosion inhibitor to be delivered into
the coating. Preferred particles are also a form of boehmite known
as pseudoboehmite. The particles can also be inorganic materials
having a boehmite surface. The particles serve as the carriers for
the anchored corrosion inhibitors. The particles are described
further below. In the most preferred embodiment the core and
surface of the particles are both made of the same material,
pseudoboehmite [AlOOH.cndot.x(H.sub.2O)]. The particles are
composed of either aluminum oxyhydroxide, or have or can form an
aluminum oxyhydroxide surface covering at least 5% of the particle.
Surface modification procedures have been developed to chemically
graft a range of surface modifiers to the carboxylate-derivatized
inorganic particles.
[0036] As used herein, an "anchor" is a carboxylate group that
chemically bonds to the surface of the particle. As used herein
"particle" or a "particle having an aluminum oxyhydroxide surface"
includes particles of aluminum oxyhydroxide (for example, boehmite
or pseudoboemite), particles that have a surface of aluminum
oxyhydroxide and a core of a different substance, and particles
that can form a surface of aluminum oxyhydroxide. "Surface" does
not necessarily indicate a uniform layer of material is present.
For example, there may be portions with no material, or the surface
may be unevenly thick. When a corrosion inhibitor is "grafted" or
"attached" or "anchored" or "chemically anchored" to a carboxylate
group anchored to the aluminum oxyhydroxide surface, there may be
one or more intermediate groups between the corrosion inhibitor and
the carboxylate group, or the corrosion inhibitor may be directly
chemically grafted (i.e., one bond) to the anchored carboxylate
group. The intermediate groups may be bifunctional, i.e., contain a
different reactive group on each end, or may be difunctional, i.e.,
contain the same reactive group on each end. "Corrosion inhibitor"
is a structure that includes at least one portion that reduces at
least one effect of corrosion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 shows the release of a carboxylate anchored corrosion
inhibitor from an aluminum oxyhydroxide surface.
[0038] FIG. 2 shows the release of a corrosion inhibitor that has
been grafted to an acrylate group that is anchored to the aluminum
oxyhydroxide surface.
[0039] FIG. 3 shows a two-step procedure for bonding corrosion
inhibitors (or other compounds) to an aluminum oxyhydroxide
surface.
[0040] FIG. 4 shows a general multi step procedure for grafting a
corrosion-inhibitors (or other organic structures) to a reactive
organic that is anchored via a carboxylate group to an aluminum
oxyhydroxide surface.
[0041] FIG. 5 shows photographs of an unfilled epoxy coated Al-7075
panel after 500 hrs salt testing (left) and an otherwise identical
epoxy coating that contains 10-wt % of 4-hydroxybenzoic acid
surface modified pseudoboehmite particles after 2000 hrs salt fog
testing (right).
[0042] FIG. 6 shows photographs of polyurethane coated Al-7075
panels exposed to Salt Fog tests: (a) an unfilled polyurethane
coating after 600 hours, (b) and a polyurethane that contains 30-wt
% of a 4-hydroxybenzoic acid modified pseudoboehmite additive after
2000 hrs.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The invention may be further understood by reference to the
following discussion and examples.
[0044] Aluminum oxyhydroxide is to be broadly construed to include
any material whose surface is or can be processed to form a surface
or layer of boehmite, including specifically aluminum metal,
aluminum nitride, aluminum oxynitride (AlON),
.alpha.-Al.sub.2O.sub.3, .gamma.-Al.sub.2O.sub.3, transitional
aluminas of general formula Al.sub.2O.sub.3, boehmite
(.gamma.-AlO(OH)), pseudoboehmite (.gamma.-AlO(OH).cndot.xH.sub.2O
where 0<x<1), diaspore (.alpha.-AlO(OH)), and the aluminum
hydroxides (Al(OH).sub.3) of bayerite and gibbsite.
[0045] Boehmite and pseudoboehmite are aluminum oxide hydroxides of
the general formula .gamma.-AlO(OH).cndot.xH.sub.2O. When x=0 the
material is called boelmite; when x>0 the materials incorporate
water into their crystalline structure and are known as
pseudoboehmite. Boehmite and pseudoboehmite are also described as
Al.sub.2O.sub.3.cndot.zH.sub.2O where, when z=1 the material is
boehmite and when 1<z<2 the material is pseudoboehmite. The
above materials are differentiated from the aluminum hydroxides
(e.g. Al(OH).sub.3, bayerite and gibbsite) and diaspore
(.alpha.-AlOOH) by their compositions and crystal structures.
Boehmite is usually well crystallized with a structure in
accordance with the x-ray diffraction pattern given in the
JCPDS-ICDD powder diffraction file 21-1307, whereas pseudoboehmite
is less well crystallized and generally presents an XRD pattern
with broadened peaks with lower intensities. For the purposes of
this specification, the term `boehmite` implies boelmite and/or
pseudoboehmite.
[0046] Particles with aluminum oxyhydroxide surfaces can be formed
by a number of methods known in the art. For materials containing
aluminum, including but not limited to aluminum metal, aluminum
nitride, aluminum oxynitride (AlON), .alpha.-Al.sub.2O.sub.3,
.gamma.-Al.sub.2O.sub.3, transitional aluminas of general formula
Al.sub.2O.sub.3, diaspore (.alpha.-AlO(OH)), and the aluminum
hydroxides (Al(OH).sub.3) of bayerite and gibbsite, a boehmite
surface can be formed, for example, by the treating the aluminum
atom-containing material with water at temperatures between
80.degree. C. and 300.degree. C. The water can be either in the
liquid state or the vapor state and other materials (e.g. bases or
acids) can be added to change the rate of formation and thicknesses
of the boehmite surface.
[0047] Aluminum oxyhydroxide surfaces can also be formed by
addition of aluminum alkoxides to aqueous dispersions of inorganic
particles. The particles can also be dispersed in other hydrophilic
solvents such as alcohols that also contain some amount of water.
Additionally the surface can be prepared by a passing a volatile
aluminum-containing compound (e.g. AlCl.sub.3, AlEt.sub.3) in the
presence of oxygen and water through a fixed bed or fluidized bed
of inorganic particles.
[0048] In the simplest embodiment of the invention, a single type
of corrosion inhibitor is chemically anchored to the surface of the
particles using the synthetic procedures described below. The same
procedures can be used to chemically anchor many different types of
corrosion inhibitors to the surface of the particles. Useful
concentrations of particles in the coating depends on the
application and the anchored corrosion inhibitor, as known in the
art, but generally, a preferred concentration range gives between
0.5 and 0.05 corrosion inhibitors per number of surface Al. The
useful concentration range for the chemically anchored corrosion
inhibitors is 2:1 (Al:Corrosion inhibitor, where the Al
concentration is the number of surface Al atoms) to 100:1
(Al:Corrosion inhibitor).
[0049] The corrosion inhibitors are anchored to the surface of the
particle though a carboxylic acid functional group. In one
embodiment of the invention, a corrosion inhibitor-containing
carboxylic acid is bonded to the surface of the particles and the
particles are incorporated into a coating. However, many corrosion
inhibitors do not contain a carboxylic acid in their structure.
Therefore, to afford the widest selection of surface modifications,
a multistep surface modification procedure has been developed to
chemically graft additional types of corrosion inhibitors to the
particles. These modifications are described in detail in U.S.
patent applications Ser. No. 10/171,402 and Ser. No. 10/171,422,
which are hereby incorporated by reference. A brief description of
the surface modification process is described below (and see FIGS.
3 and 4)
[0050] Referring to FIGS. 3 and 4 for illustration, the multi-step
surface modification process involves two or more reactions. The
initial step (Step 1) comprises the chemically anchoring of a
carboxylic acid to the surface of the particle. The carboxylic acid
is anchored to the surface of the particles through the oxygens of
the carboxylate group (the Anchor, FIG. 3). These carboxylic acids
(Compound A, FIG. 3) contain at least two reactive functional
groups comprising at least a carboxylic acid anchoring group
(Anchor, FIG. 3) that reacts with the surface of the particle, and,
when anchored to the particle, another reactive functional group
(Group 1, FIG. 3) that is available for subsequent reactions. The
subsequent (second) step grafts a second compound (Compound B) to
the previously chemically anchored Compound A. Compound B contains
at least one reactive group (Group 2, FIG. 3) that reacts with the
Group 1 of the Compound A forming a linkage (Step 2). Compound B
could be a corrosion inhibitor, or a compound whose composition is
chosen to improve the dispersion and compatibility of the particles
with the coating matrix, or a compound with two reactive groups to
act as a spacer for grafting the corrosion inhibitor in a
subsequent step. The multistep synthetic procedure may be repeated
to provide a longer molecular backbone to which the
corrosion-inhibitor can be bonded. The multistep synthetic
procedure can also be used to bond several different corrosion
inhibitors to the same particle. The selection of appropriate
carboxylic acids, reactive groups, corrosion inhibitors and other
compounds is dependent on the application, and is understood by one
of ordinary skill in the art. By appropriate selection of
carboxylic acids, reactive groups, corrosion inhibitors and other
compounds, the reactivity and functionality of the particle can be
tailored for a particular application.
[0051] In the above embodiment (see FIGS. 3 and 4) the carboxylic
acid is defined as a small organic molecule containing less than 40
carbon atoms and comprising at least one carboxylate group (anchor)
and one additional reactive group (Group 1) that reacts with
Compound B. Compound B may be the active component of the corrosion
inhibitor or may be a linkage group between the carboxylic acid and
the active component of the corrosion inhibitor. The chemical
grafting reaction (Step 2) is the reaction between a functional
group on Compound B and the functional group (Group 1) on the
carboxylate-anchored Compound A. During Step 2, Group 1 of Compound
A reacts with Group 2 of Compound B forming a linkage bond.
[0052] Group 1 is a chemical entity capable of undergoing a
non-polymerization reaction that comprises carbon-carbon double
bonds, electrophilic carbon-carbon double bonds, carbon-carbon
triple bonds, electrophilic carbon-carbon triple bonds, dienes,
diynes, polyenes, aromatic rings, heteroaromatic rings,
polyaromatic rings, cycloaliphatic compounds, hydroxyl groups,
alkoxides, ethers, phenols, phenolate esters, lactones, aldehydes,
ketones, quinines, .alpha.,.beta.-unsaturated carbonyl compounds,
other .alpha.,.beta.-unsaturated compounds, carboxylic acids,
carboxylate salts, anhydrides, hydroperoxides, enols, enones,
epoxides, acetals, peroxycarboxylic acids, carbonates, primary,
secondary and tertiary amines, ammonium salts, iminium salts, amine
oxides, nitro groups, nitroso groups, azo groups, diazo groups,
azides, nitrenes, nitriles, imines, Schiff bases, hydoxylamines,
enamines, hydrazines, hydrazones, azines, semicarbazones, oximes,
nitrates, nitrites, amides, imines, amidines, cyanohydrins,
isocyanates, cyanates, urethanes, urea derivatives, carbamate
esters, lactams, carbammic acids, thiols, disulfides, thiophenols,
thioethers, thioesters, thioketones, thioaldehydes, sulfonic acids,
sulfonates, organic sulfates, sulfoxides, sulfones, sulfinic acids,
sulfines, sulfilimines, sulfones, sulfonamides, sulfonium salts,
thioacetals, sulfur yilides, isothiocyanates, thiocyanates, organic
sulfites, thiocarbammic acids, phosphonic acids, phosphonates,
phosphinic acids, phosphines, phosphonium salt, phosphorous ylides,
phosphoranes, phosphites, alkyl halides, alkenyl halides, alkenyl
halides, and aryl halides, carbonyl halides, sulfonyl halides,
boronic acid groups, boronate salts, silanes, siloxanes, silyl
halides, trialkylboranes alkylsilyl derivatives, enolates, silyl
enols, enamines, malonic esters, cyanoacetic esters, cyano
acetamides, nitroalkanes, and the anions in Scheme 1. These
possibilities are representative and not intended to be an
exhaustive list of suitable reactive functional groups. Other
reactive functional groups are known in the art, and selection of
appropriate reactive functional groups is known in the art. 1
[0053] Group 2 is a reactive functional group on Compound B
selected from the functional groups of Group 1, such that a
reaction between Group 1 on Compound A and Group 2 results in an
attachment between Compound A and Compound B.
[0054] The chemical grafting reaction (Step 2) is a reaction
between two functional groups (Group 1 and Group 2) as understood
by people skilled in the art. Step 2 is carried out by selecting a
combination of Group 1 and Group 2 functions that react with each
other without causing undesired side-reactions, and by choosing the
proper reaction conditions that allows the desired reaction to be
carried out between the chosen pair of functional groups. This
selection process is apparent to people skilled in the art of
organic chemistry and is well described in Organic Chemistry
Textbooks (for example, March, J. 2001; Furniss, B, 1989). Step 2
can be a substitution reaction (e.g. nucleophilic substitutions,
electrophilic substitutions), a condensation reaction (e.g.
esterifications, amidations), an addition reaction (to
carbon-carbon multiple bonds, to carbon-heteroatom multiple bonds,
cycloadditions), a free-radical reaction, or a concerted reaction,
or other reaction known to one of ordinary skill in the art.
[0055] The reaction sequence(s) can be continued in additional
steps using reactions selected from the above reactions. The active
component of the corrosion inhibitor may be incorporated as the
terminal step in the grafting process or may be incorporated at any
step in the grafting process. The reaction sequence(s) can also be
used to graft non-corrosion inhibitors to the surface of the
aluminum oxyhydroxide particles. These non-corrosion inhibitors can
be used for the purpose of compatibilizing the surface of the
particle corrosion inhibitors with the protective coating, and
other uses, as known in the art.
[0056] The corrosion inhibitors that can be anchored to the
particles are numerous. Corrosion inhibitors that can be anchored
to the surface of the particle (either directly as a carboxylic
acid or through reaction with an anchored reactive carboxylic acid)
are organics or organometallics that inhibit corrosion of metals
and metal alloys, and include but are not limited to materials such
as organophosphates, organothiols, organonitrates,
nitrogen-heterocyclics, sulfur-heterocyclics, oxygen-heterocyclics,
aromatics, ring substituted aromatics, cycloaliphatics,
heterocyclic aromatics and cycloaliphatics, sulfides, organo
phosphates, olefins, phenols, substituted phenols, quinones,
amines, aromatic amines, carboxylates, amine-carboxylates, aromatic
amine carboxylates, and salts and/or combinations of any of the
above. Preferred corrosion inhibitors are organic or metal-organic
complexes or metal-organophosphorous complexes. Particularly
effective classes of anchored corrosion inhibitors are chelating
agents (i.e. compounds having two or more functional groups
positioned so that multiple bonds can be formed with a single
atom). These chelants react with metals to form insoluble metal
chelates. While these materials generally work by forming insoluble
films, these materials can also suppress corrosion in the absence
of the formation of a stabilized oxide layer or an insoluble film.
In this latter case, the materials are classified as adsorption
passivators (Kuznetsov, Y. I., J. G. N. Thomas and A. D. Mercer
"Organic Inhibitors of Corrosion of Metals", Plenum Pub Corp.
1996). These materials passivate corrosion via their
hydrophobicity. There is thought to be a "squeezing out" of
corrosion enabling anions from the metal surface.
[0057] There are no universally preferred organic corrosion
inhibitors. The corrosion inhibitors to be selected for
incorporation onto the nanoparticles depend on the corrosion
environment and the metal to be protected, as known in the art.
Examples of some of the preferred corrosion inhibitors for acid,
neutral and alkaline environments are given as follows. For acid
environments, materials such as quaternary ammonium compounds,
imidazolines, aldehydes, and sulfoxides are capable of inhibiting
general corrosion. For neutral solutions, carboxylic acids,
mercaptocarboxylic acids, imidazoles, oximes and azoles are
effective corrosion inhibitors. For alkaline solutions, materials
such as tannins, substituted phenols, substituted quinolines and
quinalizarin are highly effective.
[0058] The types of corrosion inhibitors described above can be
chemically anchored to the nanoparticle surface through a
carboxylate anchor or they can be grafted to the nanoparticle by
reaction with a functional group that is anchored to the
nanoparticle through a carboxylic acid. For example, phenolic acids
such as p-hydroxybenzoic acid and 4,4-bis(4-hydroxyphenyl)valeric
acid can be chemically anchored directly to the aluminum
oxyhydroxide surface through their carboxylate groups. The phenolic
acid modified aluminum oxyhydroxide particles can then be
incorporated into protective organic coatings and provide corrosion
protection. For example, both 4-hydroxybenzoic acid and
4,4-bis(4-hydroxyphenyl)valeric surface modified pseudoboehmite
nanoparticles have been incorporated into epoxy and polyurethane
coatings, and provided very good corrosion protection to Al-7075
alloys for 2000 hours in a salt fog test.
[0059] Furthermore, even better corrosion inhibition can be
achieved by anchoring multiple types of inhibitors to the particle
surface. For example, chemically anchoring p-hydroxybenzoic acid
and oleic acid to the aluminum oxyhydroxide surfaces for subsequent
triggered release offers better corrosion inhibition than aluminum
oxyhydroxide surfaces modified by either of the individual acids
alone.
[0060] Even though basic conditions trigger the release of the
corrosion inhibitors from the aluminum oxyhydroxide surfaces,
corrosion of metals can occur over a wide pH range. Therefore, it
is desirable to anchor corrosion inhibitors to the aluminum
oxyhydroxide surfaces that can arrest corrosion under neutral or
acidic pH environments. When released from the aluminum
oxyhydroxide surfaces by alkaline conditions these corrosion
inhibitors will diffuse through the coating and arrest corrosion
where the surface conditions are neutral or acidic. Anchoring
corrosion inhibitors that protect in alkaline, neutral, and acidic
environments to aluminum oxyhydroxide particles provides protection
over a wide pH range.
[0061] Not all of the, organic structures that protect against
corrosion are available as carboxylic acids that can be anchored
directly to the surfaces of the aluminum oxyhydroxide particles.
However, the carboxylate-free corrosion inhibitor structures can be
chemically grafted to a previously carboxylate-derivatized
particle. For example, the particle can be first derivatized using
acrylic acid (not normally used as a corrosion inhibitor) and then
a corrosion inhibitor such as 2-(4-imidazolyl)ethylamine can then
be Michael adducted to the surface anchored acrylate. Furthermore,
the surface can be simultaneously modified with two or more
corrosion inhibitors. For example, both acrylic acid and
4-hydroxybenzoic acid can be anchored to the boehmite surface. An
amine containing corrosion inhibitor can then be grafted to the
anchored acrylate via a Michael addition reaction. Other addition
or substitution reactions known to those skilled in the art of
organic synthesis can be carried out with the appropriate reaction
pairs as known in the art to graft a wide range of corrosion
inhibitors to the derivatized aluminum oxyhydroxide surface
particle surface. The corrosion inhibitor-modified particles are
then incorporated into a protective organic coating where the
corrosion inhibitors are released from the particle surface by
reaction with hydroxide ions generated by corrosion of the metal
substrate.
[0062] The protective coating is generally a polymeric material
(organic or inorganic polymer) whose primary function is to provide
a physical barrier between the environment and the metal substrate.
The protective coating also serves as a carrier or matrix to hold
the soluble/dispersible corrosion inhibitor in place. Typical
examples of organic protective coatings (e.g. paints) include
latexes, amino resins, polyurethanes, epoxies, phenolic resins,
acrylic resins, polyester resins, alkyd resins, polysulfide resins
and halogenated polymer resins. Other coatings are known in the
art. Particles containing corrosion inhibitors and optional
additives can be introduced into the coating using the methods of
the present invention and other means known in the art, such as
adding the appropriate amount of particles with other components of
the composition. Corrosion inhibitors that interfere with different
mechanisms of the corrosion process can be chemically anchored to
the same particles, or alternatively, each corrosion inhibitor can
be anchored to a different particle surface. In the latter case,
several different types of surface modified particles are added to
the protective coating. The chemically anchored corrosion
inhibitors can then be released into the coating and thus to the
metal surface by the action of hydroxide ions generated by the
cathodic oxygen reduction reaction on metals such as iron and
aluminum. High concentrations of multiple corrosion inhibitors can
incorporated into the protective coating via the particle carriers
without degradation of the properties of the protective
coating.
[0063] In addition to anchoring corrosion inhibitors to the
particle surface, one or more non-corrosion inhibiting groups may
be anchored to the particle surface. The non-corrosion inhibiting
groups provide other functions than corrosion inhibition to the
particles. The surface modified particles may also improve the
effectiveness of the protective organic coating by acting as
barriers to slow difflusion of water and other corrosive agents to
the metal surface.
[0064] The composition of coatings incorporating corrosion
inhibitors as described herein on metal surfaces change as the
surface and coating are exposed to corrosive conditions. For
example, the permeability of the coating may change, and the amount
of corrosion inhibitors present in the coating changes with time,
as particles release their corrosion inhibitors to the surface.
This is expected and desired.
[0065] In one embodiment a corrosion inhibitor can be chemically
anchored directly to the aluminum oxyhydroxide surface via a
carboxylate group (FIG. 1 and FIG. 2). In this embodiment the
corrosion inhibitor contains at least one carboxylic acid group
that is used to chemically anchor the corrosion inhibitor to the
surface of the particle. The carboxylic acid group may in fact be
the primary functional group of the corrosion inhibitor that
chemically adsorbs to the metal surface to arrest corrosion or the
anchored molecule or carboxylic acid may also contain additional
functional groups that inhibit corrosion.
[0066] In another embodiment the corrosion inhibitor can be
chemically grafted to the aluminum oxyhydroxide surface through
reactions that graft the corrosion inhibitor to carboxylates that
have previously been chemically anchored to the surface of the
aluminum oxyhydroxide surface. The nature of these grafting
reactions is elaborated herein. In yet another embodiment the
corrosion inhibitors can be chemically grafted to the aluminum
oxyhydroxide materials by a series of reactions. The series of
reactions may comprise separate sequential reactions with recovery
of intermediates, or a series of reactions in a single pot where
only the final product is recovered.
[0067] The purpose of the described chemical surface anchoring
methods is to allow anchoring of different corrosion inhibitors to
the surface of the aluminum oxyhydroxide particles or to anchor
both corrosion inhibitors and non corrosion inhibitors such as
compatibilizing agents to the particle surfaces. The resulting
surface modified aluminum oxyhydroxide particles are then
incorporated into a protective coating applied to a metal surface.
The anchored corrosion inhibitors are released from the aluminum
oxyhydroxides by the strongly basic conditions that are encountered
following the onset of corrosion of metals such as aluminum and
iron.
[0068] The corrosion inhibitors of the invention may be used in a
variety of applications, including but not limited to polymers
coated on a metal surface, paints painted on the metal surface and
adhesives coated on a metal surface, powder coatings baked onto
metal surfaces, polymers flame sprayed onto metal surfaces, coating
materials electrostatically sprayed onto metal surfaces. The
corrosion inhibitors can be used with a variety of additives, that
may be active or inert, including fillers, anti-oxidants, pigments,
colorants, leveling agents, thixotropic agents, UV absorbers,
wetting agents, dispersion agents, defoamers biocides, fungicides,
etc.
EXAMPLE
[0069] The following examples are non-limiting examples of the
compositions of corrosion inhibiting particle materials. In the
following examples "dried" means spray-dried. Dispersion or
redispersion of the dried materials was achieved by stirring with a
Cowles blade or mixing with mini-media in a ball mill. The initial
syntheses (e.g. chemically anchoring the carboxylic acid to the
particle surface) uses a 15-wt % dispersion of boehmite in water.
In the following examples this refers to using 150 grams of
boehmite or pseudoboehmite in 1000 grams of water. Both boehmite
and pseudoboehmite were used as the aluminum oxyhydroxide materials
from which the corrosion inhibiting particles were prepared. The
aluminum oxyhydroxides that were used were Catapal A
(pseudoboehmite) and Catapal D (boehmite), both produced by Sasol,
North America. The use of these materials is illustrative and is
not to be construed as limiting.
[0070] A typical aqueous preparation of the carboxylate-anchored
aluminum oxyhydroxide materials (15 wt % in water) described in the
examples is presented below. Aluminum oxyhydroxide (Catapal A or
Catapal D, 4550 g) was added to 9100 ml of distilled water. The
water dispersible carboxylic acid (6:1 aluminum oxyhydroxide to
acid or for example 777 g for acrylic acid) is then mixed with 2275
ml of distilled water and added slowly (15 to 30 minutes) with
stirring to the aluminum oxyhydroxide slurry. Additional distilled
water (18300 ml) is then added slowly over 30-60 minutes while
stirring. The resulting mixture is then heated to 80.degree. C.
overnight before being spray dried. The inlet temperature of the
spray-dryer was 170.degree. C. to 190.degree. C. and the outlet
temperature was 60.degree. C. to 70.degree. C.
[0071] Corrosion testing of the metal panels was carried out
according to ASTM B 117-97 (Standard Practice for Operating Salt
Spray (Fog) Apparatus) and the corrosion results evaluated using
D714-87 (Standard Test Method for Evaluating Degree of Blistering
of Paints). In the B117-97 test standards the coated test panels
were scribed with an X through the paint down to the metal and the
test substrates were then placed into the salt fog chamber. The
coating substrates were visually inspected and rated from 0
(complete detachment from the substrate) to 10 (no blisters or
underfilm corrosion) using the criteria specified in D714-87.
[0072] The following are examples of boehmite particles having a
single corrosion inhibitor anchored to the surface of the particle
by a carboxylate group.
[0073] 1. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using p-hydroxybenzoic acid (Al:p-hydroxybenzoic acid=3:1
molar ratio) and heated to 80.degree. C. overnight. The
p-hydroxybenzoic acid corrosion inhibitor was anchored to the
pseudoboehmite particle through the carboxylate group. The
resulting material was dried and then redispersed in a waterborne
epoxy resin at a 10-wt % (dry solids) loading. The waterborne epoxy
resin (EPI-REZ 5522-WY-55) and the water reducible curative
(EPI-CURE 8290-Y-60) (both made by Resolution Performance Products)
were mixed in amounts and under conditions suggested by the
technical documents for these two materials. The corrosion
inhibiting particles were added to the epoxy side. The epoxy resin
was applied to a bare, solvent wiped Al-7075 alloy panel and cured
for two weeks at room temperature. The coating was then scribed and
tested according to ASTM-B117. After 2000 hours the panels were
evaluated by the criteria set forth in ASTM method D714-87. The
panels were rated 10 out of 10 according to the ASTM method
D714-87, indicating that essentially no corrosion had occurred
during the 2000-hour test period. In contrast, an Al-7075 panel
coated with the same epoxy but without the corrosion-inhibiting
additive had extensive corrosion after only 500 hours and was rated
a 4 after 500 hours using the D714-87 standard. FIG. 5 shows a
comparison of the two panels.
[0074] 2. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using p-hydroxybenzoic acid (Al:p-hydroxybenzoic acid=3:1
molar ratio) and heated to 80.degree. C. overnight. The
p-hydroxybenzoic acid corrosion inhibitor was anchored to the
pseudoboehmite particle through the carboxylate group. The
resulting material was dried and then redispersed in a clear two
component polyurethane resin (e.g. Proreco 508 (PRA600+PRA560)) at
a 30-wt % (dry solids) loading and applied to a bare, solvent wiped
Al-7075 alloy panel and cured for two weeks at room temperature.
The coating was then scribed and tested according to ASTM-B 117.
After 2000 hours the panels were evaluated by the criteria set
forth in ASTM method D714-87. The panels were rated 10 out of 10
according to the ASTM method D714-87, indicating that essentially
no corrosion had occurred during the 2000-hour test period. In
contrast, an Al-7075 panel coated with the same polyurethane but
without the corrosion-inhibiting additive had extensive corrosion
after only 600 hours and was rated a 4 using the D714-87 standard.
FIG. 6 shows a comparison of the two panels.
[0075] 3. Boehmite (Catapal D, Sasol, N. A.) was dispersed in water
using 4,4-bis(4-hydroxyphenyl)valeric acid (DPA) (Al:DPA=3:1 molar
ratio) and heated to 80.degree. C. overnight. The
4,4-bis(4-hydroxyphenyl)valeric acid corrosion inhibitor was
anchored to the boehmite particle through the carboxylate group.
The resulting material was dried and then redispersed in an epoxy
resin at a 10-wt % (dry solids) loading. The waterborne epoxy resin
(EPI-REZ 5522-WY-55) and the water reducible curative (EPI-CURE
8290-Y-60) were mixed in amounts and under conditions suggested by
the technical documents for these two materials. The corrosion
inhibiting additives were added to the epoxy side. The resulting
mixture was then applied to a bare, solvent wiped Al-7075 alloy
panel and cured for two weeks at room temperature. The coating was
then scribed and tested according to ASTM-B117. After 2000 hours
the panels were evaluated by the criteria set forth in ASTM method
D714-87. The panels were rated 10 out of 10 according to the ASTM
method D714-87, indicating that essentially no corrosion had
occurred during the 2000-hour test period. In contrast, an Al-7075
panel coated with the same epoxy but without the
corrosion-inhibiting additive had extensive corrosion after only
500 hours and was rated a 4 using the D714-87 standard.
[0076] 4. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using 4,4-bis(4-hydroxyphenyl)valeric acid
(Al:4,4-bis(4-hydroxyphenyl)va- leric acid=3:1 molar ratio) and
heated to 80.degree. C. overnight. The
4,4-bis(4-hydroxyphenyl)valeric acid corrosion inhibitor was
anchored to the pseudoboehmite particle through the carboxylate
group. The resulting material was dried and then redispersed in a
clear two component polyurethane resin (e.g. Proreco 508
(PRA600+PRA560)) at a 30-wt % (dry solids) loading and applied to a
bare, solvent wiped Al-7075 alloy panel and cured for two weeks at
room temperature. The coating was then scribed and tested according
to ASTM-B117. After 2000 hours, the panels were evaluated by the
criteria set forth in ASTM method D714-87. The panels were rated 10
out of 10 according to the ASTM method D714-87, indicating that
essentially no corrosion had occurred during the 2000-hour test
period. In contrast, an Al-7075 panel coated with the same
polyurethane but without the corrosion-inhibiting additive had
extensive corrosion after only 600 hours and was rated a 4 using
the D714-87 standard.
[0077] Other non-limiting corrosion-inhibiting compositions
containing mixed carboxylic acids include but are not limited to
the following. Some of the anchored carboxylic acids (e.g.
propionic acid) are added to improve compatibility with the coating
and may or may not themselves be effective corrosion inhibitors. As
known in the art, various substances are useful to improve
compatibility with coatings, and these substances may be
incorporated into the materials of the invention without undue
experimentation.
[0078] 5. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using propionic acid and p-hydroxybenzoic acid
(Al:propionic-acid=12:1, Al:p-hydroxybenzoic acid 12:1 molar ratio)
and heated to 80.degree. C. overnight. The mixed propionic
acid/p-hydroxybenzoic acid corrosion inhibitors are anchored to the
pseudoboehmite particle through the carboxylate group. The
propionic acid assists in the dispersion of the boehmite particle
and provides a limited amount of corrosion protection, while the
p-hydroxybenzoic acid provides the bulk of the corrosion
protection. The mixed acid material was dried and then redispersed
in an epoxy resin formulation (Epon Resin 828) at a 10-wt % (dry
solids) loading. The resulting mixture was then mixed with an amine
curative (Ancamide.RTM. 2445) and applied to a bare, solvent wiped
Al-7075 alloy panel and cured for two weeks at room temperature.
The coating was then scribed and tested according to ASTM-B 117.
After 2000 hours the panels were evaluated by the criteria set
forth in ASTM method D714-87. The panels were rated 10 out of 10
according to the ASTM method D714-87.
[0079] 6. Boehmite (Catapal D, Sasol, N. A.) was dispersed in water
using a mixture of propionic acid and
4,4-Bis(4-hydroxyphenyl)valeric acid (Al:propionic-acid=12:1,
Al:4,4-Bis(4-hydroxyphenyl)valeric acid=12:1 molar ratio) and
heated to 80.degree. C. overnight. The mixed propionic
acid/4,4-bis(4-hydroxyphenyl)valeric acid corrosion inhibitors are
anchored to the boehmite particle through the carboxylate group.
The propionic acid assists in the dispersion of the boehmite
particle and provides a limited amount of corrosion protection,
while the 4,4-Bis(4-hydroxyphenyl)valeric acid provides the bulk of
the corrosion protection. The mixed acid material was dried and
then redispersed in an epoxy resin formulation (Epon Resin 828) at
a 10-wt % (dry solids) loading. The resulting mixture was then
mixed with an amine curative (Ancamide.RTM. 2445) and applied to a
bare, solvent wiped Al-7075 alloy panel and cured for two weeks at
room temperature. The coating was then scribed and tested according
to ASTM-B117. After 2000 hours the panels were evaluated by the
criteria set forth in ASTM method D714-87. The panels were rated 10
out of 10 according to the ASTM method D714-87.
[0080] 7. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using a mixture of sorbic acid (previously dispersed in
alcohol) and p-hydroxybenzoic acid (Al:sorbic acid=12:1,
Al:p-hydroxybenzoic acid=12:1 molar ratio) and heated to 80.degree.
C. overnight. The mixed sorbic acid/p-hydroxybenzoic acid corrosion
inhibitors were anchored to the pseudoboehmite particle through the
carboxylate group. The resulting material was dried and can used as
a corrosion inhibitor in epoxy or polyurethane coatings.
[0081] 8. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using a mixture of oleic acid (previously dispersed in
alcohol) and p-hydroxybenzoic acid (Al:oleic acid=12:1,
Al:p-hydroxybenzoic acid=12:1 molar ratio) and heated to 80.degree.
C. overnight. The mixed oleic acid/p-hydroxybenzoic acid corrosion
inhibitors were anchored to the pseudoboehmite particle through the
carboxylate group. The resulting material was dried and can be used
as a corrosion inhibitor in epoxy or polyurethane coatings.
[0082] 9. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed in
water using a mixture of oleic acid and p-nitrobenzoic acid
(Al:propionic-acid=12:1, Al p-nitrobenzoic acid=12:1 molar ratio)
and heated to 80.degree. C. overnight. The mixed oleic
acid/p-nitrobenzoic acid corrosion inhibitors were anchored to the
pseudoboehmite particle through the carboxylate group. One role of
the p-nitrobenzoic acid material is to enhance the formation and
stability of the protective metal oxide film at the metal/coating
interface. The resulting material was dried and can used as a
corrosion inhibitor in epoxy or polyurethane coatings.
[0083] 10. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed
in water using a mixture of oleic acid and histidine (Al:oleic
acid=12:1, Al:histidine=12:1 molar ratio) and heated to 80.degree.
C. overnight. The mixed oleic acid/histidine corrosion inhibitors
are chemically anchored to the pseudoboehmite particle through the
carboxylate group. The resulting material was dried and can used as
a corrosion inhibitor in epoxy or polyurethane coatings.
[0084] Other non-limiting corrosion-inhibiting compositions
containing mixed grafted corrosion inhibiting compositions include
but are not limited to the following examples. Some surface
modifications (e.g. the anchored acrylate subsequently Michael
adducted with Huntsman XTJ-507) are added to improve compatibility
with the coating and may or may not be effective corrosion
inhibitors. These modifications to improve compatibility are known
in the art and are useful in the invention without undue
experimentation.
[0085] 11. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed
in water using acrylic acid (Al:acrylic-acid=6:1 molar ratio) and
heated to 80.degree. C. overnight. The resulting acrylate surface
modified pseudoboehmite materials were then spray-dried. The
resulting material was redispersed in water and anthranilic acid
was Michael adducted to the surface anchored acrylate. The grafted
corrosion inhibitors are chemically anchored to the boehmite
particle through formation of a chemical bond with the acrylate
group on the acrylic acid, which in turn is anchored to the
aluminum oxyhydroxide surface through its carboxylate group. The
resulting material was dried and can used as a corrosion inhibitor
in protective organic coatings.
[0086] 12. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed
in water using acrylic acid (Al:acrylic-acid=6:1 molar ratio) and
heated to 80.degree. C. overnight. The resulting acrylate surface
modified pseudoboehmite materials were then spray-dried. The
resulting material was redispersed in water and both anthranilic
acid and steryl amine (each 12:1 with respect to the Al) were
Michael adducted to the surface anchored acrylates. These compounds
were grafted to the surface-anchored acrylate by heating the
acrylate-modified aluminum oxyhydroxides and the amines in water to
80.degree. C. A small amount of catalyst (Et.sub.3N, 0.1 wt %) was
added to the mixture before heating. The grafted corrosion
inhibitors are chemically anchored to the boehmite particle through
formation of a chemical bond with the acrylate group on the acrylic
acid, which in turn is anchored to the aluminum oxyhydroxide
surface through its carboxylate group. The resulting material was
dried and can used as a corrosion inhibitor in protective organic
coatings.
[0087] 13. Boehmnite (Catapal D, Sasol, N. A.) was dispersed in
water using a mixture of acrylic acid and oleic acid
(Al:acrylic-acid=12:1, molar ratio, Al:oleic acid=12:1, molar
ratio) and heated to 80.degree. C. overnight. The resulting
acrylate and oleic acid surface modified boehmite materials were
then spray-dried. The resulting material was then redispersed in
water and both anthranilic acid and steryl amine (24:1 with respect
to the Al) were Michael adducted to the surface anchored acrylate.
These compounds were grafted to the surface-anchored acrylate by
heating the acrylate-modified aluminum oxyhydroxides and the amines
in water to 80.degree. C. A small amount of catalyst (Et.sub.3N,
0.1 wt %) was added to the mixture before heating. The grafted
corrosion inhibitors are chemically anchored to the boehmite
particle through formation of a chemical bond with the acrylate
group on the acrylic acid, which in turn is anchored to the
aluminum oxyhydroxide surface through its carboxylate group. The
resulting material was dried and can used as a corrosion inhibitor
in protective organic coatings.
[0088] 14. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed
in water using a mixture of acrylic acid and p-nitrobenzoic acid
(Al:acrylic-acid=12:1, molar ratio, Al:p-nitrobenzoic acid=12:1,
molar ratio) and heated to 80.degree. C. overnight. The resulting
acrylate and oleic acid surface modified pseudoboehmite materials
were then spray-dried. The resulting material was redispersed in
water and anthranilic acid (12:1 with respect to the Al) was
Michael adducted to the surface anchored acrylate. These compounds
were grafted to the surface-anchored acrylate by heating the
acrylate-modified aluminum oxyhydroxides and the amines in water to
80.degree. C. A small amount of catalyst (Et.sub.3N, 0.1 wt %) was
added to the mixture before heating. The grafted corrosion
inhibitors are chemically anchored to the boehmite particle through
formation of a chemical bond with the acrylate group on the acrylic
acid, which in turn is anchored to the aluminum oxyhydroxide
surface through its carboxylate group. The resulting material was
dried and can used as a corrosion inhibitor in protective organic
coatings.
[0089] 15. Pseudoboehmite (Catapal A, Sasol, N. A.) was dispersed
in water using acrylic acid (Al:acrylic-acid=12:1 molar ratio) and
heated to 80.degree. C. overnight. The acrylic acid modified
pseudoboehmite materials were then spray-dried. The resulting
material was redispersed in water and Huntsman XTJ-507 was Michael
adducted to the acrylic acid (24:1 with respect to the Al).
Glysine-N,N-(dimethylene phosphonic acid) Al:acid=12:1 molar ratio)
was then chemically anchored to the surface of the pseudoboehmite
particles. The role of the Huntsman XTJ-507 adduct was to provide
steric stabilization to the particles and to compatibilize the
particles with the polymer resin. The resulting material was dried
and can used as a corrosion inhibitor in the protective
coatings.
[0090] Although applicant does not wish to be bound by theory, the
above non-liming examples when added to protective resins such as
polyurethanes and epoxies offer improved corrosion resistance by
serving as reservoirs of corrosion inhibitors that are released to
the corrosion site by reaction of the surface modified particles
with hydroxide ions that are generated following the onset of
corrosion of the metal.
[0091] Although the description above contains many specificities,
these are not meant to limit the invention but as merely to provide
illustrations of some of the preferred embodiments. For example,
the examples are not meant to limit the polymer resins to which the
corrosion inhibiting particles can be added, but serve as
illustrations of some of the compositions of the corrosion
inhibiting particles. In addition, different corrosion inhibitors
other than those exemplified may be used. All references cited
herein are hereby incorporated by reference to the extent not
inconsistent with the disclosure herewith.
* * * * *
References