Note: Descriptions are shown in the official language in which they were submitted.
A CORROSION INHIBITING PASTE FOR AIRCRAFT USE
FIELD OF THE INVENTION
[0001] Corrosion inhibiting compounds for aircraft use, including pastes
with or
without particles for use on, or with, a variety of aircraft assemblies.
BACKGROUND
[0002] Corrosion in aircraft is a multibillion-dollar problem and corrosion
inhibiting
compounds (CICs) or corrosion prevention compounds are a huge industry. There
are
many possible corrosion sites in an aircraft, including joints having
dissimilar materials
close to one another or in contact. These joints are often subject to
vibrational stress.
Often, the joints are also subject to both thermal and pressure cycling as the
aircraft
takes off, climbs, and descends. Also, conditions, especially on an aircraft
exterior, can
vary from dry to wet, acidic to basic.
[0003] CICs are widely used in the aircraft industry to protect aircraft
structures,
materials, spare parts and assemblies from physical and chemical attack. They
come in
a variety of forms with a number of different properties and uses.
[0004] A complication in the development of CICs is the desire for them to
be
environmentally friendly and not hazardous. Unfortunately, some of the best
corrosion
inhibitors have contained chromates (Cr +6) which present health and
environmental
concerns. It is no surprise that the development of effective, safe, chromate
free CICs
has been a difficult task.
[0005] Direct or close contact between two or more different metal alloys
or a metal
alloy and a carbon fiber composite material may occur in aircraft. These
assemblies are
typically subject to environmental and/or mechanical stresses. Joints may
include
fasteners and/or adhesives for bonding or maintaining two or more discreet
panels or
members as an integrated assembly. Joint compounds are often required to
inhibit
corrosion.
[0006] Corrosion may also affect fasteners used in aircraft, such as bolts,
screws,
and rivets. The fasteners may be made from a number of materials, typically
metallic
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Date Regue/Date Received 2022-08-05
materials such as aluminum alloys, steel, and titanium. Fasteners may also be
installed
with a corrosion inhibiting wet coating, typically applied just prior to
installation. Zinc
chromate, wet, and unthinned is a wet install sealant that has been used with
fasteners.
Single component polysulfides have also been used.
[0007] Adhesives, which typically create a bond, are also sometimes used in
the
installation of aircraft fasteners, to impart strength to a joint. They may
also help make a
moisture-proof seal, thus helping inhibit corrosion. Sometimes epoxy is used
to coat a
fastener just prior to installation, to help prevent corrosion and add bonding
strength to
the joint. Some of these prior art CICs may contain potentially harmful
aromatic solvents
or petroleum distillates.
[0008] Corrosion inhibiting compounds may be classified as multi-component,
which
will mix and dry (cure), or single component that may stay moist over time
(non-drying)
and over a wide variation in temperature.
SUMMARY OF INVENTION
[0009] The invention includes a number of Corrosion Inhibiting Pastes
(CIPs) and
methods of applying and using such CIPs, in some embodiments on aircraft
assemblies.
[0010] The CIPs include a base (note: this term is not referencing pH)
having a
number of properties and including and excluding certain components. The CIPs
include, in some embodiments, the base combined with particles, including
metallic
particles, inert particles and corrosion inhibitors, these typically having
certain structure,
dimensions and chemical components, resulting in unique and improved
properties.
[0011] Some bases include an organic, 100% solids, carbon-based polymer,
which
may include oily or fatty polymers, lipids, esters, and may be of plant,
mineral or animal
origin. The organic polymer base may, in some embodiments, have a molecular
weight
between 1,000 and 100,000, or more preferably, 5,000 and 75,000. The base may
be
non-aqueous, non-toxic, and bio-friendly, and in some embodiments is a plant-
derived
base.
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Date Regue/Date Received 2022-08-05
[0012] The CIP includes at least a base. In some embodiments, the CIP
includes
the base and one or more additional compositions from one or more of the
following
three groups: coated or uncoated metal particles, inert particles, and
corrosion
inhibitors.
[0013] Coated or uncoated metal or metal alloy particles may inhibit
corrosion of a
metallic substrate as, in some embodiments, they may act as sacrificial anodes
when
the CIP is applied to a metal or metals, thus providing, primarily, a
corrosion inhibiting
function.
[0014] The inert particles are termed "inert" as they do not, primarily, or
typically
have a significant corrosion inhibiting function. Rather, they may be added
primarily for
other purposes such as flow characteristics, color, UV inhibitors (blockers),
flame and
fire retardant purposes, and thickening and sag characteristics.
[0015] The corrosion inhibitors are chemicals, usually added, in some
embodiments,
as powders, non-metallic (but may include organometallic) compositions that
function as
corrosion-inhibitors when the paste is applied to a substrate, including a
metallic
substrate.
[0016] The CIP may be free of one, more, or preferably all of the
following:
chromates, chromium, sulfides, polysulfides, silicone, petroleum distillates,
and
solvents. Chromates and chromium have been said to raise environmental
concerns, as
have polysulfides. Sulfides may promote drying out. Silicone may affect paint
adhesion.
Solvents and petroleum distillates may cause environmental and/or adhesion
issues.
The applicant has observed that some of the foregoing may also affect the
ability of a
composition to be an effective sealant for corrosion inhibiting purposes.
[0017] The inventions also include methods of applying the CIPs and
aircraft
assemblies to which they may be applied.
[0018] According to one aspect of the invention there is provided a
corrosion
inhibiting paste for aircraft use including use with: a joint, as anti-seize
or the wet
installation of fasteners for aircraft use or use on an aircraft part, the
corrosion inhibiting
paste comprising:
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Date Regue/Date Received 2022-08-05
a. a non-hardening, one-part, solvent-free, hydrophobic, non-shrinking
organic polymer base having uniform consistency, having a viscosity
of between 300 to 10,000 centipoises at 20 C, and having a
molecular weight between 1,000 and 100,000, the base being free of
chromium, including chromates, sulfides, silicone and petroleum
distillates, and solvents; and,
b. particles, loaded into the base sufficiently to result in a viscosity of
between 9,000 and 10,000,000 centipoise.
[0019] The particles may be inert particles and/or coated or uncoated metal
particles.
[0020] The paste may further include non-metal corrosion inhibitors.
[0021] The particles may be metal particles in the range of 1 to 300
microns in their
longest dimensions.
[0022] The metal particles may be aluminum including aluminum alloy.
[0023] The metal particles may be coated with an electrically conductive or
semi-
conductive coating.
[0024] The coating may be a TCP (Trivalent Chromium Passivation).
[0025] The coating may be a molybdate coating.
[0026] The inert particles may be polymers.
[0027] The particles may be loaded at a range of 10 to 85 percent of the
total paste
weight.
[0028] The paste may include particles which are inert particles and/or
coated or
uncoated metal particles and may further include non-metal corrosion
inhibitors.
wherein;
a. the particles include metal particles may be in the range of 1 to 200
microns in their longest dimensions;
b. the metal particles may be aluminum or an aluminum alloy; and
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Date Regue/Date Received 2022-08-05
c. wherein the metal particles may be coated with an electrically
conductive or semi-conductive coating.
[0029] The paste may be non-hygroscopic.
[0030] The paste may be resistant to drying.
[0031] Preferably, the paste passes the 3000-hour salt fog test on an
aluminum
alloy substrate.
[0032] The paste may be used to coat at least a part of an aircraft
assembly.
[0033] The corrosion inhibiting compounds may include one or more of a:
lithium
salt, a mixed complex of zinc and magnesium oxalate, a metal polycarboxylate,
a
magnesium salt, a salt phosphate, or is a chromium-free corrosion inhibitor.
[0034] The corrosion inhibitor may be ionic, a covalent organometallic, or
organic.
[0035] The paste may include at least one corrosion inhibitor selected from
the
group comprising: a lithium salt, an organic or inorganic lithium salt,
lithium phosphate,
a cation phosphate, lithium carbonate, at least one metal polycarboxylate, non-
metallic
magnesium-containing materials, a cation polycarboxylate, magnesium oxide,
oxyaminophosphate salts of magnesium, magnesium carbonate and magnesium
hydroxide, magnesium citrate, magnesium oxalate, zinc citrate, zinc oxalate,
organometallic compounds and combinations thereof.
[0036] The corrosion inhibitor may be lithium free.
[0037] The base may be non-adhesive to a substrate.
[0038] The metal particles may be one or more of the following: Aluminum,
Magnesium, Zinc, or alloys thereof.
[0039] At least some of the particles may be coated with an electrically
semi-
conductive or conductive coating.
[0040] The paste may comprise by non-volatile weight of the corrosion
inhibiting
paste composition:
i. 30 - 95% base;
Date Regue/Date Received 2022-08-05
ii. 0.0 - 40% inert particles;
iii. 10 - 70% metal particles; and
iv. 0.0 - 65% corrosion inhibitors.
[0041] The metal particles may be coated with a conversion coating.
[0042] The paste may further include an ultraviolet light blocker or a
colorant.
BRIEF DESCRIPTION OF DRAWINGS
[0043] Fig. 1 illustrates components of applicants' CIPs on an aircraft
substrate.
[0044] Fig. 2A and 2B illustrate the use of the applicant's CIPs on an
aircraft part
namely, a static joint.
[0045] Figs. 3A and 3B illustrate the use of the applicant's CIPs on the
wet
installation of a fastener.
DETAILED DESCRIPTION
[0046] Fig. 1 illustrates a corrosion inhibiting paste 10 which includes a
base 16,
further including a mix, the mix may add to the base 16 one or more of the
following
additional components: metallic particles 12 (coated or uncoated, in some
embodiments
1-300 microns longest dimension) or non-metallic corrosion inhibitors 14, such
as
corrosion inhibiting powders (typically less than a micron in longest
dimension), and
inert particles 17, for example, polymer spheres or fibers (which may be 10
nano to 100
microns in their longest dimension). The corrosion inhibiting paste 10 and,
may be
spread on or applied to a substrate 18 which may be a metallic aircraft part
or
assembly.
[0047] Applicant's corrosion inhibiting pastes typically have a paste
consistency, a
viscosity in some embodiments between 9,000 and 10,000,000 cP. A paste is, at
room
temperature, a non-curing, thick, soft, spreadable, moist substance, that may
be
dispensed from a container, such as by a spatula or a brush, by squeezing from
a tube,
cartridge, or applicator (for example, syringe type) but will hold its shape
on and stick
(adhere, but not bond) to a substrate including a metal such as aluminum alloy
or a
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Date Regue/Date Received 2022-08-05
carbon fiber reinforced plastic substrate. It may in some embodiments flow
under
pressure but sets up (thickens) and holds its shape when the pressure is
released. This
property may be referred to as thixotropic. In preferred embodiments, a curing
agent is
not used with the paste.
[0048] Applicants' corrosion inhibiting pastes, including the base 16, are
able to
stand a wide variety of time-temperature conditions without drying out or
excessively
hardening, cracking, or flowing. They, in some embodiments, may be able to
withstand
attack from aircraft fuels (such as Jet A) or other aircraft fluids (hydraulic
fluids,
including Skydrol). They may be hydrophobic and non-hygroscopic. The paste may
substantially maintain its properties over a wide temperature range. In some
embodiments, the pastes are resistant to flow at elevated temperatures when
applied
on an aluminum alloy (2024) substrate mounted perpendicular (20 mils thick, 7
days,
95 C).
[0049] The corrosion inhibiting pastes may include inert particles 17,
which may
include spheres or fibers, such as polymer fibers, including polyethylene,
PTFE,
polypropylene, HDPE, or polyolefin fibers or a mix thereof. These inert
particles may be
hydrophilic or hydrophobic. These inert particles may be non-reactive polymer
particles
with different shapes. These, in some embodiments, may be 0.1mm long (.01-
1.0mm
range), and 5 microns in diameter (1-10 micron range), having a surface area
of
12m2/gr. It is believed they help hold the paste together (coherence),
especially when
the metallic particles are added. They are typically non-reactive to both the
base (or any
other component of the paste) and the substrate to which it is applied. The
addition of
inert particles 17 such as mica and silicates, to the base, may also add to
the toughness
of the corrosion inhibiting paste or change its flow characteristics. Titanium
dioxide is
another inert particle that may be added as a colorant.
[0050] The non-hygroscopic nature of the paste may be shown by 7 days of
immersion in tap water at 70 F, with no material change in weight (less than
1%). The
paste may be used on aircraft surfaces, and such ability to resist corrosion
may be
demonstrated by no significant visible corrosion (less than about 5% surface
area) nor
loss of cohesion or adhesion after the following test: 3000-hour salt fog
(ASTM B117).
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Date Regue/Date Received 2022-08-05
[0051] The particles of corrosion inhibiting paste 10 seen in Fig.1 may, in
some
embodiments, be metallic particles 12 and/or inert particles 17. The addition
of metallic
particles to the base will, primarily, enhance corrosion resistance (including
resistance
to galvanic corrosion) of the corrosion inhibiting paste as well as help
determine flow
characteristics. The particles 12/17 may be flake-like, oblong, rod-shaped,
irregular in
shape, or spherical. They may be 1 micron to 300 microns in their longest
dimension
(preferred range 1-200 microns for metallic particles). They may be mixed into
the base
at a weight loading (compared to the total weight of the corrosion inhibiting
paste)
between 20-85%, more preferred 40-65%, mixed in uniformly so the corrosion
inhibiting
paste is smooth (homogenous and without lumps).
[0052] Metallic particles 12 (as distinguished from inert particles 17) may
be coated
or uncoated metal in some embodiments aluminum or aluminum alloy including an
alloy
of the 2000, 3000, 4000, 5000, 6000, and 7000 series. The particles, prior to
mixing with
the base 17, may be coated with a coating that will inhibit the natural
oxidation of the
aluminum (or other metal) so as to aid in electrical conductivity when added
to the base.
Metallic particles, especially coated aluminum alloy, will function to help
the aircraft joint
or wet installed fastener to resist galvanic corrosion that may occur when
dissimilar
metals are close to one another in the presence of an electrolyte. The
metallic particles,
especially coated aluminum, may act as a sacrificial anode. The metallic
particles
include the particles set forth in US 8,277,688 and US 8,262,938, (the "Navy
patents").
These patents disclose coated aluminum alloy particles in a paint binder,
acting to
inhibit corrosion when the paint is applied to a metal substrate. These
patents also
disclose the use of magnesium or zinc particles (or alloys thereof) In their
use as
disclosed herein, the coated particles are used mixed with a base.
[0053] The referenced Navy patents disclose a number of conductive or semi-
conductive coatings for metal particles including aluminum alloy particles.
Applicant has
found these coated particles remain electrically active when mixed into
applicant's base
and help prevent corrosion of metals more cathodic than the particles and/or
the metal
particle is more anodic than the substrate. These particle coatings may be
free of
chromates, that can be harmful to the environment. Some of the metal particle
coatings
are derived from an aqueous trivalent chromium solution. Other metal coatings
are free
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Date Regue/Date Received 2022-08-05
of any chromium, see US 17/655,298, filed 3/17/2022 (for coatings derived from
a
molybdate solution).
[0054] A chromium-free, molybdate-based aluminum alloy reactive liquid
aqueous
solution is disclosed in US 17/655,298 leaving oxidation reaction products on
aluminum
particles which in turn are combined with binders such as binders used for
paint or other
material. Optionally, organic or ionic-based or other corrosion inhibitors may
also be
added to the base. The result is a paste that is used to help prevent
corrosion of
metallic substrates, in part due to the coated alloy particles acting as
sacrificial anodes.
[0055] The molybdate-based coating that may be used for coating the metal
particles 12 including aluminum alloy particles, in some embodiments is
prepared from
an aqueous solution comprising a molybdate, a permanganate, and a hexafluoro
zirconate, adjusted to a pH range of 0-14 (but preferably acidic), and applied
to the
particles to form an electrically conductive or semi-conductive corrosion
preventative
coating (typically about 1 nanometer-5 micron thick). The coated particles, in
some
embodiments, are mixed into the base to form a corrosion inhibiting paste.
[0056] In some embodiments the molybdate of the aqueous solution is a
potassium
molybdate (K2Mo04), the permanganate is potassium permanganate (KMn04), and
the
hexafluoro zirconate is potassium hexafluoro zirconate (K2ZF6). These
components'
molar range is in some embodiments from 0.001-0.50 moles per liter for each.
In some
embodiments, the pH of the aqueous solution may be adjusted with potassium
hydroxide or sulfuric acid to be basic or acidic with a pH in the range of 0-
14. To
increase surface growth and reaction efficiency, an ionic barium or boron salt
may be
added, to act as a pH buffer. The solution deposits a semi-conducting
corrosion
inhibiting molybdate oxide-based coating onto the aluminum alloy particles and
reduces
or eliminates particle self-corrosion when the coated particles are added to
base 16
which may be applied to a metal substrate such as aluminum alloy. For galvanic
corrosion protection, metal particles may be those that are more non-noble
relative to
the metallic substrate. The coatings, in some embodiments, may passivate the
metal
particles to form a conversion coating on the surface thereof.
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Date Regue/Date Received 2022-08-05
[0057] A chromium containing sem iconductive corrosion-inhibiting coating
to an
aluminum alloy or other metal particle may be derived by soaking a particle in
an acidic
aqueous solution of from about:
a. 0.01 to 22 parts trivalent chromium compound;
b. 0.01 to 12 parts hexafluoro zirconate;
c. 0.01 to 12 parts of at least one fluorocarbon, which may be
selected from the group comprising tetra fluoroborates, hexafluoro
silicates, and hexafluoro titanates; and may include at least one
divalent zinc compound and 0.00 to 5 parts by weight of a water-
soluble organic corrosion inhibitor. The divalent zinc may be zinc
sulfate. A stabilizing compound such as polyhydroxy or carboxylic
compounds may be used. The metal particles may be aluminum
which may be alloyed with zinc, cadmium, magnesium, barium,
manganese, indium, gallium, tin, and bismuth.
[0058] A process to apply a trichromium-based semi-conductive corrosion-
inhibiting
coating to active aluminum alloy pigments follows. To one liter of distilled
water, add 3.0
grams of basic chromium sulfate, 4.0 grams of potassium hexafluoro zirconate,
and
0.12 grams potassium tetrafluoroborate. Stir solution until all chemicals are
dissolved.
Let stand for seven days before use to allow for the inorganic polymer of
chromium
sulfate to complex with the fluoride salts and equilibrate. Dilute this
solution to 40% by
volume with distilled water.
[0059] Approximately 100 grams of Al-5%Zn-0.015%In particles were added to
a
one-liter flask. Particles processed were 40 to 100 microns in diameter and
spherical.
To the flask, add approximately 500 milliliters of inorganic polymer solution
at ambient
conditions and agitate or stir for approximately five minutes. The powder
tends to settle
quickly in the solution so constant agitation is necessary. After 5 minutes,
decant off the
inorganic polymer solution.
[0060] The wet powder was added slowly to a large Buchner funnel with
filter paper.
After wet slurry was added, a vacuum was applied. The powder was rinsed
Date Regue/Date Received 2022-08-05
approximately three times with distilled water to remove unreacted inorganic
polymer
solution. After rinsing, the powder cake and filter paper were removed and
placed on a
large watch glass and allowed to dry at ambient conditions overnight. In the
morning,
the coated powder was dry to handle and placed in a glass container, and
sealed.
[0061] Corrosion inhibitors 14 may be the lithium salt-based inhibitors
found in
US 2012/0025142 and/or US 10,889,723. Corrosion inhibitors may be one or more
polycarboxylates and may also include synergistic polycarboxylate blends as
found in
US 2018/0282555. Other corrosion inhibitors may be found in the following Navy
publications: US 8,262,938; 8,277,688; 9,243,333; 9,243,150; PCT/U52015/065301
(WO 2017091239) and PCT/U52016/016509 (WO 2017105528). The corrosion
inhibitors may be loaded into base 16 at 0.0-70% by weight of the final
corrosion
inhibiting paste. In some embodiments, the corrosion inhibitors are relatively
insoluble
and have a solubility of less than 100 milligrams per liter. In some
embodiments, any
semisolid phosphate salt may be used in the paste as a corrosion inhibitor.
[0062] Corrosion inhibiting pastes for aircraft use include applications to
a joint, as
anti-seize or the wet installation of fasteners for aircraft use or use on an
aircraft part. It
may also be used as a topcoat on a metal substrate. The corrosion inhibiting
paste
comprises a non-hardening, one-part, solvent-free, hydrophobic, non-shrinking
organic
polymer base having uniform consistency, and in some embodiments, a viscosity
of
between 300 to 10,000 centipoises at 20 C, the base typically free of
chromium,
including chromates, sulfides, silicone, and petroleum distillates, solvents,
and particles,
loaded sufficiently to result in a viscosity of between, in some embodiments,
about
9,000 and 10,000,000 centipoise. Further, the paste may include non-metal
powder-
sized corrosion inhibitors and particles that are inert particles and/or metal
particles.
[0063] The paste may include at least one corrosion inhibitor selected from
the
group comprising a lithium salt, an organic or inorganic lithium salt, lithium
phosphate, a
cation phosphate, lithium carbonate, at least one metal polycarboxylate,
magnesium-
containing materials, a cation polycarboxylate, magnesium oxide,
oxyaminophosphate
salts of magnesium, magnesium carbonate and magnesium hydroxide, magnesium
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Date Regue/Date Received 2022-08-05
citrate, magnesium oxalate, zinc citrate, zinc oxalate, organometallic
compounds and a
combination thereof.
[0064] The blend of inhibitors may consist of lithium phosphate and at
least one
inhibitor chosen from the following:
[0065] Anions: polycarboxylates chosen from linear and branched aliphatic
molecules like oxalate, citrate, tartrate, succinate, and adipate, and
aromatic molecules
like phthalate, diphenate, mellitate, and trimellitate. These are examples of
some
possible molecules; there are many other polycarboxylates which can be used in
the
combination. Cations: elements chosen from Group Ila¨Magnesium, calcium,
strontium, and barium Group IIIB¨Scandium, yttrium, lanthanum, and the other
lanthanides like cerium, praseodymium, neodymium, samarium, europium,
gadolinium,
etc. Group IVb¨Titanium and zirconium Group Vb¨Vanadium and niobium Group
Vlb¨Chromium and molybdenum Group VIlb¨Manganese Group VIII¨Iron, cobalt,
and nickel Group lb¨Copper Group Ilb¨Zinc Group IIla¨Aluminum Group Va¨
Bismuth.
[0066] Inhibitors may be blended with different molar ratios to obtain the
maximum
synergistic performance for a particular application. Inhibitors may also be
used at
varying concentrations in the particular vehicle for the application.
Inhibitors may be
combined in bulk after synthesis, or they may be blended during synthesis. For
example, additional or different synergistic effects may be garnered by
reacting oxalic
acid with zinc nitrate and magnesium nitrate to achieve a compound with a
mixed
complex of zinc and magnesium oxalate. The solubility synthesized zinc oxalate
and
magnesium oxalate compounds.
[0067] Corrosion inhibitors 14 may include lithium salts (which may be
added to
base 1-40% by volume), metal polycarboxylate, and chromium-free inhibitors.
The
corrosion inhibitor may be ionic or organic. The corrosion inhibitors may be
lithium free.
The corrosion inhibitors may comprise lithium-free synergistic combinations of
metal
oxalates, metal pirates, metal succinate, metal tartrates, and metal adipate.
[0068] U.S. Patent 10,351,715, discloses metal polycarboxylate corrosion,
one or
more of which may be mixed into the paste disclosed herein.
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Date Regue/Date Received 2022-08-05
[0069] The corrosion-resistant inhibitors consist essentially of
synergistic
combinations of:
A. At least one metal polycarboxylate derived from a stoichiometric
reaction of metal compounds and polycarboxylic acids to obtain
polycarboxylic metal salts and
B. At least one metal polycarboxylate derived from a stoichiometric
reaction of metal compounds and polycarboxylic acids to obtain
polycarboxylic metal salts, wherein either the metal or the
polycarboxylic acid in at least one of the polycarboxylic metal salt
combinations is different from the other combination of polycarboxylic
metal salts.
[0070] For example, where the corrosion-resistant synergistic combination
consists
of from about 0.1 to 20 parts by weight of zinc oxalate and from about 0.1 to
20 parts by
weight of zinc citrate, it is important that either the zinc or the
polycarboxylic acid of the
polycarboxylic metal salt of either paragraph (A) or (B) be different. It is
important that
where the carboxylic metal salts are derived from the stoichiometric reaction
of several
different metal compounds and several different polycarboxylic acids, it is
essential that
at least one of the polycarboxylic metal salts has a different anion or cation
from any of
the other polycarboxylic metal salt.
[0071] In some embodiments, the paste by non-volatile weight of the film
forming
composition may be: 30-95% base, 10-70% metal particles (coated, uncoated or
mixed), inert particles 0-40%, and 0.0 - 70% corrosion inhibitor (alternately
0.0-40%).
[0072] Fig. 2A and 2B illustrate the use of corrosion inhibiting paste 10
in an aircraft
assembly 20, the assembly in this embodiment comprising two or more aircraft
parts or
members 18 (which may include aluminum or CFRP members) attached and under
compression by fasteners 22, such as a joint formed by rivets or threaded
fasteners 22
as shown here. Figure 2A illustrates a joint with the corrosion inhibiting
paste between
the faying surfaces prior to compression where the corrosion inhibiting paste
may be, in
some embodiments, 2-500 mil thick. Figure 2B illustrates the joint post
compression
where the thickness of the corrosion inhibiting paste 10 may be 0.25-10 mil or
in some
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Date Regue/Date Received 2022-08-05
embodiments, up to 20 mil in thickness. Applicant's corrosion inhibiting
pastes may be
used to seal cracks, small voids, pinholes, gaps, mating areas, and seams and
applied
to fay surfaces or fasteners.
[0073] Fig. 3A and 3B illustrates the "wet installation" of fastener 22
(rivet, threaded,
screw, etc.) into an aircraft part. Fig. 3A illustrates the fastener coated,
at least partly,
with paste 10, typically 1-10 mil, prior to installation. The fastener or any
other substrate
may be coated with CIP by spraying, dipping, brushing, or any other suitable
manner
including dispensing from a syringe.
[0074] In some embodiments the CIP 10 viscosity is between 10,000 and
10,000,000 cP at room temperature and, in some embodiments, may be easily
spread
at room temperature (no heating required). Viscosity, in some embodiments, may
be
adjusted by varying the loading of particles 12/17. In some embodiments, the
viscosity
is in the range of 20,000 to 400,000 cP at 20 C (15,000-750,000 in other
embodiments). In one measure of flow, squeeze out from a Semco 440 nozzle
(0.125"
diameter) at 90 psi ( 5 psi) was 5315 grams/minute at 70 F and 1542
grams/minute at
40 F. The paste may achieve flow rates of between 1000 g/m in to 10,000 g/m
in at 90
p.s.i., 70 F and is therefore described as "flowable". The paste may achieve
high UV
resistance by adding UV blockers such as titanium oxide or carbon black.
[0075] Fig. 3B illustrates the fastener after securement into the aircraft
part, properly
torqued, with some squeeze-out 24 which may be cleaned off a metal surface
with a
clean, dry cloth. Notably, applicant's paste may be cleaned up with or without
a cleaner
(such as a citrus-based cleaner, isopropyl alcohol, or mineral spirits).
Sometimes, just a
clean, dry cloth may be used to wipe off the paste. It has been noted that the
CIP with
metal particles acts not only to inhibit corrosion but to act as an anti-seize
agent
allowing easy removal of the fastener at a later time. The ease of removal is
found with
using the paste in aircraft joints also and is achieved even through seven
thermal (-40 F
to 120 F) and pressure (1.0 to 0.1 atm) cycles (18 hours on, 6 hours off) over
a range of
50-100% RH (relative humidity).
[0076] The paste is typically smooth and tacky to the touch, like
toothpaste in that
regard. It maintains the non-drying and thixotropic properties in a
temperature range
14
Date Regue/Date Received 2022-08-05
of -67 F (minus 67 F) to 203 F, including non-sag at thicknesses less than
0.020 inches
(aluminum vertical). It does not bake on the substrate or bond to surfaces as
an
adhesive or paint may.
[0077] A base is available from KBS Chemical, Dodd City Texas as part
number
06429. Metal particles are available in a number of sizes and compositions
including
aluminum alloy particles coated with a trivalent chromium passivation coating
as
disclosed in the Navy patents, incorporated herein by reference. Part numbers:
(TCP
treated) ARP-02-04, ARP-02-08, ARP-02-25, (Non-treated) AP-03-04, AP-03-08, AP-
03-25, (Chrome Free treated) ARP-06-04, ARP-06-08, ARP-06-25, ARP-07-04, ARP-
07-08, ARP-07-25. The particles may be those molybdate coated particles found
in US
17/655,298, filed 3/17/2022.
[0078] Applicant's CIP is resistant to drying, 75 grams were tested at
about 20 mil
thickness on a vertical aluminum coupon, for 7 days at 95 C, very little
shrinkage or
drying in some embodiments, less than 3% weight loss (that is, non-drying). As
it is
insoluble in water (less than 0.22%), it is ideal for preventing wicking
between faying
surfaces.
[0079] Applicant's CIP passed qualitative (visual) evaluation (less than
10% surface
area affected) in a sandwich corrosion test based on ASTM F1110-09, using 2024
T-3
and 7075 T-6 Al clad coupons. No significant discoloration or pitting was
found. These
tests were performed with Example Al, KBS base, and 50% (by weight to base)
loading
of trivalent chromium coated aluminum particles (2-200 micron). Examples A2,
A3, Bl,
B2, and Cl are set forth below and proved to be satisfactory in inhibiting
corrosion.
[0080] In some embodiments, the corrosion inhibitors 14 are a mix of two or
more
parts. In some embodiments, the corrosion inhibitors 14 are a mix of three
parts with
any one part being at least 10% by weight of the total weight of the corrosion
inhibitor
component.
[0081] Example Al four-part mix (base, metal particles, inert particles,
corrosion
inhibitors) includes a base (KBS), treated aluminum alloy (Zn/In, 2-100
micron, tri-
chromium passivation coating), inhibitor mix (1 part Zn citrate, 0.5 part Zn
oxalate, 0.3
part insoluble lithium phosphate), and inert polymer fibers as a thickener.
Example A2
Date Regue/Date Received 2022-08-05
four-part mix (base, metal particles, inert, corrosion inhibitors) includes a
base (KBS),
treated aluminum alloy (Zn/In, 2-100 micron, tri-chromium passivation
coating), inhibitor
mix (1 part Zn citrate, 0.5 part Zn oxalate), and inert polymer fibers as a
thickener.
Example A3 four-part mix (base, metal particles, inert, corrosion inhibitors)
includes a
base (KBS), untreated magnesium particles, inhibitor mix (1 part Zn citrate,
0.5 part
magnesium oxalate, 0.3 part insoluble lithium phosphate), and inert polymer
fibers as a
thickener.
[0082] Example B1 three-part mix (base, metal particles, inert particles,
no corrosion
inhibitors) includes a 50/50 base/metal, particles 1-20 micron, TCP treated or
untreated
Aluminum alloy (Zn/In/Sn). Example B2 three-part mix (base, metal particles,
inert
particles, no corrosion inhibitors) includes a 50/50 base/metal, particles 21-
200 micron,
TCP treated or untreated Aluminum alloy (Zn/In/Sn).
[0083] Example Cl three-part mix (base, inert particles, corrosion
inhibitors, no
metal particles) includes a base (KBS), inhibitor mix (1 part Zn citrate, 0.5-
part Zn
oxalate, 0.3 part insoluble lithium phosphate), and inert polymer fibers as a
thickener to
a viscosity of between 15,000 cP and 750,000 cP.
[0084] These examples in the viscosity ranges indicated will result in a
CIP with
beneficial corrosion inhibiting properties.
[0085] Any combination of the following are included as embodiments:
particles
(inert, coated, uncoated), inhibitors, mixed to the referenced viscosity
ranges may
comprise the paste.
[0086] In an embodiment disclosed, an aircraft assembly or sub-assembly
disclosed
includes one or more component at least partially coated or at least two or
more
components at least partially coated and joined with fasteners at least
partially coated or
at least one fastener at least partially coated, with the CIP of the present
disclosure. The
component and/or components may comprise one or more of aluminum, aluminum
alloy, carbon fiber composite material (e.g. CFRP), or varieties or
combinations thereof.
[0087] In the preceding description, for purposes of explanation, numerous
details
are set forth in order to provide a thorough understanding of the embodiments.
16
Date Regue/Date Received 2022-08-05
However, it will be apparent to one skilled in the art that these specific
details are not
required. In other instances, well-known structures and components are shown
in block
diagram form in order not to obscure the understanding.
[0088] The above-described embodiments are intended to be examples only.
Alterations, modifications and variations can be affected to the particular
embodiments
by those of skill in the art. The scope of the claims should not be limited by
the particular
embodiments set forth in the examples but should be given the broadest
interpretation
consistent with the specification as a whole.
17
Date Regue/Date Received 2022-08-05
