U.S. patent application number 10/530541 was filed with the patent office on 2006-07-27 for formation of corrosion-resistant coating.
Invention is credited to Brian Klotz, Kevin Klotz.
Application Number | 20060166014 10/530541 |
Document ID | / |
Family ID | 32093870 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060166014 |
Kind Code |
A1 |
Klotz; Brian ; et
al. |
July 27, 2006 |
Formation of corrosion-resistant coating
Abstract
A coating process comprising: (A) applying to a surface, for
example, a metallic surface, a coating compositions consisting
essentially of an alkali metal silicate and an aqueous liquid phase
having dispersed therein solid aluminum particles to form on the
surface a wet coating; and (B) drying said wet coating : (I) under
conditions which convert said wet coating to an electrically
conductive, corrosion-resistant, solid coating; or (ii) under
conditions which form a solid coating which is not electrically
conductive (non-conductive) and thereafter treating said
non-conductive coating under conditions which convert said
non-conductive coating to an electrically conductive,
corrosion-resistant coating compositions for use in the process,
and the provision of highly corrosion-resistant coated
articles.
Inventors: |
Klotz; Brian; (PERKASIE,
PA) ; Klotz; Kevin; (Spring City, PA) |
Correspondence
Address: |
Alexis Barron;Synnestvedt & Lechner
2600 Aramark Tower
1101 Market Street
Philadelphia
PA
19107-2950
US
|
Family ID: |
32093870 |
Appl. No.: |
10/530541 |
Filed: |
October 7, 2003 |
PCT Filed: |
October 7, 2003 |
PCT NO: |
PCT/US03/31785 |
371 Date: |
April 6, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60416575 |
Oct 7, 2002 |
|
|
|
Current U.S.
Class: |
428/469 ;
427/180; 427/372.2; 428/701; 428/702 |
Current CPC
Class: |
C04B 2111/34 20130101;
C04B 2111/90 20130101; C23C 18/1241 20130101; C09D 5/103 20130101;
F05D 2300/611 20130101; C23C 24/08 20130101; C23C 18/1283 20130101;
C04B 41/85 20130101; C23C 24/087 20130101; C23C 24/082 20130101;
C23C 18/1225 20130101; C04B 2111/28 20130101; C09D 1/02 20130101;
F05D 2230/90 20130101; C04B 41/5089 20130101; C23C 26/00 20130101;
Y02T 50/671 20130101; C23C 18/00 20130101; F02C 7/30 20130101; C04B
41/009 20130101; F01D 25/007 20130101; Y02T 50/60 20130101; C04B
28/26 20130101; C04B 2111/00525 20130101; C23C 18/1212 20130101;
Y10T 428/263 20150115; C09D 5/24 20130101; C23C 18/127 20130101;
C04B 28/26 20130101; C04B 12/04 20130101; C04B 14/34 20130101; C04B
24/42 20130101; C04B 41/5089 20130101; C04B 41/4505 20130101; C04B
41/455 20130101; C04B 28/26 20130101; C04B 12/04 20130101; C04B
38/02 20130101; C04B 41/009 20130101; C04B 35/00 20130101; C04B
41/009 20130101; C04B 28/26 20130101 |
Class at
Publication: |
428/469 ;
427/372.2; 427/180; 428/701; 428/702 |
International
Class: |
B32B 15/04 20060101
B32B015/04; B32B 9/00 20060101 B32B009/00; B32B 19/00 20060101
B32B019/00; B05D 1/12 20060101 B05D001/12; B05D 3/02 20060101
B05D003/02 |
Claims
1. A coating process comprising: (A) applying to a surface a
coating composition consisting essentially of an alkali metal
silicate and an aqueous liquid phase having dispersed therein solid
aluminum particles to form on the surface a wet coating; and (B)
drying said wet coating: (i) under conditions which convert said
wet coating to an electrically conductive, corrosion-resistant,
solid coating; or (ii) under conditions which form a solid coating
which is not electrically conductive (non-conductive) and
thereafter treating said non-conductive coating under conditions
which convert said non-conductive coating to an electrically
conductive, corrosion-resistant coating.
2. A process according to claim 1 wherein the surface is
metallic.
3. A process according to claim 2 wherein said wet coating is dried
under said conditions of (i).
4. A process according to claim 2 wherein said wet coating is dried
under said conditions of (ii).
5. A process according to claim 4 including burnishing the
non-conductive coating for a sufficient period of time to convert
it to a conductive coating.
6. A process according to claim 2 wherein the coating composition
is applied to the metallic surface of a part of a turbine
engine.
7. A metallic or ceramic surface coated with an electrically
conductive, aluminum-containing silicate coating.
8. A metallic surface according to claim 7 wherein the coating has
a thickness of about 0.8 mil to about 3.5 mils and
corrosion-resistant properties characterized by no greater than
about 1.6 mm loss of adhesion at scribe when subjected to 5%
neutral salt spray at 95.degree. F. for about 1000 hours according
to ASTM B-117.
9. A metallic surface according to claim 7 wherein said coating has
heat-resistant properties characterized by its being substantially
free of cracks, checks, and blisters when the surface is subjected
to the following conditions: heat treatment for 23 hours at a
temperature of about 700.degree. F., followed by heat treatment for
4 hours at a temperature of about 1075.degree. F.
10. A metallic surface according to claim 7 wherein said coating
has flexibility properties characterized by its being substantially
free of flaking or loosening when subjected to the following
conditions: bending a panel coated with the coating through an
angle of 90.degree. around a 1/4 inch diameter mandrel.
11. A metallic surface according to claim 7 wherein said coating
has hydraulic oil-resistant properties characterized by its being
free of peeling, blistering, or softening when the part is
subjected to the following conditions: immersion in Mil-L-7808 oil
for 8 hours at a temperature of about 400.degree. F.
12. A process for converting a solid silicate coating which
contains aluminum particles, which is adhered to a surface, and
which is not electrically conductive (non-conductive) to a
conductive coating by: (A) subjecting the non-conductive coating to
conditions which effect expansion of the aluminum particles to
place them into intimate contact with one another to the extent
that the coating is rendered electrically conductive; or (B)
subjecting the non-conductive coating to a force which is
sufficient to compress the particles into more intimate contact
with one another to the extent that the coating is rendered
electrically conductive.
13. A coating composition which is effective in forming on a
metallic or ceramic surface a corrosion-resistant coating and which
consists essentially of (a) an alkali metal silicate, (b) an
aqueous liquid phase having dispersed therein solid aluminum
particles, and (c) an additive which is effective in improving the
corrosion-resistance of the coating and which is selected from the
group consisting of (i) an organic solvent which is partially
miscible or immiscible in water; (ii) an organofunctional silane,
and (iii) a mixture of said additives.
14. A composition according to claim 13 wherein the additive is an
organic solvent which has a miscibility in water of about 1 ml to
about 20 ml of solvent per 100 ml of water at about 20.degree.
C.
15. A composition according to claim 14 wherein the solvent has a
miscibility in water of up to about 10 ml.
16. A composition according to claim 15 wherein the solvent has a
miscibility in water of up to about 5 ml.
17. An aqueous coating composition which is effective in forming a
corrosion-resistant coating on a metallic or ceramic surface and
which consists essentially of aluminum particles dispersed in the
composition and a mixture of sodium silicate and lithium silicate,
the total silicate content of the composition being about 2.5 wt. %
to about 30 wt. % and the weight ratio of sodium silicate to
lithium silicate being about 0.25 to 1 to about 4 to 1.
18. A composition according to claim 17 wherein the total silicate
content of the composition is about 7 wt. % to about 13 wt. %.
19. A process for forming a multi-ply coating on a metallic or
ceramic surface by applying thereto an aqueous coating composition
consisting essentially of an alkali metal silicate and having
dispersed therein solid aluminum particles in which (A) the
composition is applied to the surface to form thereon a layer of
wet coating; and (B) the layer of wet coating is air-dried; (C) the
composition is applied to the surface of the air-dried coating to
form thereon an overlying layer of wet coating; and (D) said
overlying layer of wet coating is (i) dried under conditions which
convert said wet coating to an electrically conductive, solid
corrosion-resistant multi-ply coating or (ii) said wet coating is
dried under conditions which form a solid multi-ply coating which
is not electrically conductive (non-conductive) and said
non-conductive multi-ply coating is thereafter treated under
conditions which convert said non-conductive coating to an
electrically conductive, corrosion-resistant, multi-ply coating.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. application Ser.
No. 60/416,575, filed Oct. 7, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to the formation of a
corrosion-resistant coating on a metallic surface. More
particularly, the present invention relates to a silicate coating
composition, to its use to form on a metallic surface a coating
which is highly corrosion-resistant, and to a coated article having
thereon a silicate coating which is highly corrosion-resistant.
[0003] The present invention will be described initially in
connection with its use to form highly corrosion-resistant coatings
on the surfaces of turbine engines, for example, airplane turbine
engines and gas- or steam-powered ground turbine engines. It should
be understood, however, that the present invention can be used also
in other applications, as will be evident from the detailed
description of the invention which appears below.
[0004] The operation of a turbine engine generates very high
temperatures to which various parts of the engine are exposed. For
example, the temperature in the combustion chamber of the engine
can reach 2200.degree. F. or higher. Other parts of turbine engines
which are subjected to such high temperatures include, for example:
stators; blades; discs; turbine shafts; and exhaust ducts.
[0005] The housing of a turbine engine and parts comprising the
engine are made typically from specialty steels, for example,
stainless steel and from high-strength, light-weight,
titanium-based alloys. As is well known, iron-based metals tend to
corrode (rust) in the presence of water and are weakened
structurally as the rusting process progresses. Turbine engines and
the parts thereof typically come into contact with water, for
example, as moisture condenses on the various surfaces of the
engine when the engine is not in use. Also, airplane turbine
engines can come into contact with salt water which has a highly
corrosive effect on iron-based parts. If the various surfaces of
the turbine engine are not protected from contact with water, there
can be engine failure as one or more of the parts lose strength due
to the corrosive effect of the water.
[0006] Accordingly, it is well known to apply to the various
surfaces of turbine engines coatings which protect the underlying
metallic surfaces from contact with water and which function as
corrosion-resistant coatings. Such coatings must withstand, of
course, the high operating temperatures of the engine.
[0007] At the high operating temperatures of the engine, the
various metallic surfaces of the engine, including those comprising
iron-based and titanium-based alloys, are subject also to being
oxidized, a reaction known as "heat oxidation". Parts of the engine
which are vulnerable to heat oxidation include the combustion
chamber, the power turbine and the exhaust chamber. Heat oxidation
can result also in engine failure as parts of the engine are
weakened structurally. Accordingly, the corrosion- and
heat-resistant coating should function also to protect critical
underlying metallic surfaces from being oxidized in the presence of
the large amounts of heat generated by the operation of the
engine.
[0008] For industrial acceptance, the coatings for use in such
turbine engine applications must have also a combination of other
properties, including, for example, flexibility properties,
crack-resistant properties, hydraulic oil-resistant properties, and
abrasion-resistant properties.
[0009] The present invention relates to the provision of a coating
composition which is capable of forming on a metallic surface a
highly corrosion-resistant coating that has a combination of
properties of the type required for successful use in industrial
turbine engine applications as well as other industrial coating
applications.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, there is provided
a coating process comprising: (A) applying to a surface an aqueous
coating composition consisting essentially of an alkali metal
silicate and having dispersed therein solid aluminum particles to
form on the surface a wet coating; and (B) drying said wet coating
under conditions which convert said wet coating to an electrically
conductive, solid corrosion-resistant coating or drying said wet
coating under conditions which form a solid coating which is not
electrically conductive (non-conductive) and thereafter treating
said non-conductive coating under conditions which convert said
non-conductive coating to an electrically conductive,
corrosion-resistant coating.
[0011] In preferred form, the coating composition is substantially
free of chromium. Also, in preferred form, the aluminum particles
are dispersed in an aqueous solution of the alkali metal silicate.
In addition, the preferred form of the coating composition includes
one or more additives which are effective in improving the
corrosion-resistant properties of the coating. An organic solvent
and a silane are examples of such additives.
[0012] Another aspect of the present invention is the provision of
a surface coated with an electrically conductive silicate coating
comprising aluminum. In preferred form, a metallic surface is
provided with a coating that has a thickness of about 0.8 mil to
about 3.5 mils and corrosion-resistant properties characterized by
no greater than about 1.6 mm loss of adhesion at scribe when
subjected to 5% neutral salt spray at 95.degree. F. for at least
about 1000 hours (ASTM B-117).
[0013] There are numerous advantages that are associated with the
present invention. Chromium-based coating compositions have been
considered for many years as the standard in industry for forming
coatings which are highly corrosion-resistant. The present
invention enables one to form such highly corrosion-resistant
coatings, but without the need to use environmentally detrimental
constituents like hexavalent chromium. Another advantage of the
composition of the present invention is that it is a "one-part"
composition in that all of the constituents can be mixed together
into a single formulation well prior to use and without one or more
of the constituents affecting adversely other constituents of the
composition. Non-chromium-based compositions of the prior art are
typically "two-part" compositions which need to be mixed together
just prior to use. Other advantages of the present invention are
discussed below.
[0014] It is believed that the present invention will be used
widely to coat and protect various types of surfaces, particularly
the metallic surfaces of a turbine engine, including the housing
and various parts of the engine.
DETAILED DESCRIPTION OF THE INVENTION
[0015] As set forth above, the present invention includes within
its scope the provision of an electrically conductive, silicate
coating which includes aluminum, which is highly
corrosion-resistant, and which has other desirable properties, as
discussed in detail below. As discussed below also, various of the
desired properties of the conductive silicate coating are much
better than those of a silicate coating which is non-conductive.
The term "electrically conductive" means that the coating has an
ohm value of no greater than about 20, preferably no greater than
about 15, and more preferably less than about 10, as determined by
the conductivity test which is described below in the text of
Example 1 hereof.
[0016] The silicate component of the coating functions as a
film-former and binder which binds together the other
constituent(s) of the coating and the coating to the underlying
substrate. The aluminum constituent of the coating imparts thereto
sacrificial corrosion properties, that is, the aluminum reacts
preferentially with materials which would tend to react with the
underlying substrate and cause degradation thereof. This
"sacrificial property" deters corrosion of the underlying
substrate.
[0017] The electrically conductive silicate coating can be formed
on the underlying substrate in any suitable way. In accordance with
the present invention, it is recommended that the coating be formed
initially as a wet coating from a liquid composition that contains
an alkali metal silicate, aluminum particles, and water and that
the wet coating be dried under conditions which convert the wet
coating to an electrically conductive solid form or that the wet
coating be dried under conditions which form a non-conductive solid
coating which is then converted to an electrically conductive form.
It should be appreciated that the conventional use of the
aforementioned type of liquid silicate coating composition results
in the formation of a coating which is non-conductive and which has
properties, including corrosion-resistant properties, which are
substantially poorer than the conductive form of the coating.
[0018] The corrosion-resistant coating of the present invention can
be formed from an aqueous coating composition comprising an alkali
metal silicate and aluminum particles dispersed therein. The
composition can include also optional ingredients, as described
below. As mentioned above, one of the advantages associated with
the use of the composition is that it is not necessary to keep one
or more of the constituents comprising the composition separated
from another of the constituent(s) just prior to the time the
composition is to be used. Other types of prior art compositions
that have been used industrially to coat turbine engine parts
include components which have a short "pot-life", that is, upon
being mixed, the resulting composition has to be used in a
relatively short period of time (for example, within about 1 hour
to about 6 hours) or it becomes unusable for the coating
application. Preferred compositions for use in the present
invention are stable and indeed have a long shelf-life, for
example, about 10 months or longer.
[0019] Alkali metal silicates are well known materials which are
available in liquid form or solid form, for example in, powdered
form. Any suitable alkali metal silicate can be used in the
composition of the present invention. Examples of alkali metal
silicates are sodium silicate, lithium silicate, and potassium
silicate. A mixture of two or more alkali metal silicates may be
used also. Preferred alkali metal silicates are sodium silicate and
lithium silicate. It is preferred particularly to use a mixture of
sodium silicate and lithium silicate.
[0020] Sodium silicate is used preferably in liquid form, for
example, as an aqueous solution of glasses made by fusing varying
proportions of sand and soda ash. The proportions of sand and soda
ash that are used determine the SiO.sub.2:Na.sub.2O weight ratio of
the sodium silicate. For example, there are available commercially
liquid (water-based) sodium silicates that have a
SiO.sub.2:Na.sub.2O weight ratio of about 1.6:1 to about 3.75:1 and
that have viscosities which range from those of a syrupy liquid
(for example, 1.8 poises at 20.degree. C.) to a thick alkaline
liquid (for example, 700 poises at 20.degree. C.). A preferred
liquid silicate has a SiO.sub.2:Na.sub.2O weight ratio about 2.5:1
to about 3.2:1.
[0021] Examples of commercially available liquid sodium silicates
include those sold by The PQ Corporation under the registered
trademarks: "STIXSO RR"; N; E; O; K; M; RU; D; C; and STAR.
Examples of powdered sodium silicates are those sold by The PQ
Corporation under the registered trademarks "SS" 65 pwd; "G"; "GA";
and GD. Commercially available sodium silicates include those which
comprise about 9 to about 27 wt. % Na.sub.2O and about 20 to about
75 wt. % SiO.sub.2.
[0022] Any suitable lithium silicate can be used in the
composition. The lithium silicate can be in solid or liquid form
and have, for example, a SiO.sub.2:Li.sub.2O weight ratio of about
9.4:1 to about 17:1, with the preferred ratio being about 9:1 to
about 10:1. Examples of commercially available lithium silicates
include Ludox.RTM. lithium polysilicate.
[0023] Any suitable potassium silicate can be used in the
composition. The potassium silicate can be in solid or liquid form
and have, for example, a SiO.sub.2:K.sub.2.sub.2O weight ratio of
about 1.6:1 to about 2.5:1. Examples of commercially available
liquid potassium silicates those sold by The PQ Corporation under
the registered trademark KASIL.
[0024] The alkali metal silicate should be used in the composition
in an amount at least sufficient to form a continuous adherent
coating on the surface of the substrate and to bind the aluminum
particles which are included in the coating. The maximum amount of
alkali metal silicate comprising the coating composition is
dictated by the ability to bond the aluminum particles to the
surface without the coating's blistering or mud cracking as it is
cured. It is believed that the most widely used compositions will
comprise about 2.5 to about 30 wt. % of the alkali metal silicate.
Preferably, the composition comprises about 7 to about 13 wt. % of
the alkali metal silicate.
[0025] In the use of a mixture of sodium silicate and lithium
silicate, it is recommended that the sodium silicate:lithium
silicate weight ratio be about 0.25:1 to about 4:1, with the
preferred ratio being about 0.6:1 to about 1.5:1. In the use of a
mixture of sodium and lithium silicates, it is recommended that the
composition comprise a total silicate content of about 2.5 wt. % to
about 30 wt. %, with the preferred amount being about 7 wt. % to
about 13 wt. %.
[0026] The composition of the present invention includes also solid
aluminum particles, for example, in the form of flake, powder, or
granules. It is preferred that the aluminum particles be in the
form of a powder. The aluminum particles should be of a size
sufficiently small to enable the particles to be dispersed in the
liquid composition, perferably uniformity throughout the
composition. For dispersiblity, it is preferred that the average
size of the aluminum particles be no greater than about 15 microns.
Typically, the average size of the aluminum particles should be
about 2 microns to about 10 microns. A particularly preferred
average particle size is about 4 microns to about 7 microns.
Examples of commercially available aluminum particles include Toyal
America 105 and Toyal America 5662.
[0027] The aluminum particles should be used in the composition in
an amount such that the coating can be made conductive. The maximum
amount of aluminum particles comprising the composition is governed
by sprayability considerations and coating defects which tend to be
encountered if too much aluminum is used, loss of adhesion and
surface defects in the coating such as mud cracking. It is believed
that the most widely used compositions will comprise about 20 to
about 50 wt. % of the aluminum particles. Preferably, the
composition comprises about 35 to about 45 wt. % of the aluminum
particles.
[0028] Optional materials can be included in the aqueous
composition in amounts effective to achieve desired effects.
Examples of optional materials are wetting agents, phosphates,
fluorocarbons, polysiloxanes, water repellants, rheology modifiers,
and nanopowders.
[0029] Any suitable wetting agent can be used in the composition.
The wetting agent should function to modify the surface
characteristics of the substrate being coated in a manner such that
the uniform application of the water-based coating composition is
more readily achieved and the tendency of surface defects to form
in the coating is reduced. Examples of suitable wetting agents that
can be used and include anionic, nonionic, cationic, and amphoteric
wetting agents. Preferred classes of wetting agents are silanes,
fluoropolymer type wetting agents, polysiloxanes, and phosphates.
Preferred species of wetting agents are Lodyne S222 fluorocarbon,
Byk 348 polysiloxane, Zonyl FSN fluorocarbon, Coat-O-Sil 1211
silane, Cirrasol G-2200 alkyl phosphate. The wetting agent can
comprise about 0.05 wt. % to about 1 wt. %, preferably about 0.05
wt. % to about 0.2 wt. % of the composition.
[0030] Addition of a phosphate containing compound (either organic
or inorganic) may be used to improve various coating properties,
for example, adhesion to the underlying substrate and flexibility.
It has been observed, however, that the presence of a phosphate may
improve certain properties at the expense of affecting adversely
other properties. For example, flexibility of the coating can be
improved by the use of phosphate in the coating composition, but a
decrease in corrosion-resistance can be experienced. Examples of
sources of phosphate, which include water soluble phosphates, are
trisodium phosphate, sodium tripolyphosphate, ferric pyrophosphite,
sodium pyrophosphate (particularly preferred), ammonium phosphate,
and tributyl phosphate (preferred). Typically, the phosphate can
comprise about 0.1% to about 2.5 wt. % of the total composition,
with the preferred range being about 0.2% to about 1 wt. %.
[0031] Including in the coating composition a compound which is
generally referred to in the art as an "organic solvent" can reduce
or prevent the formation of surface blisters in the coating. The
formation of surface blisters has been observed, for example, as
the corrosion-resistant properties of multi-ply coatings have been
evaluated in salt spray tests. Blisters have an adverse effect on
the corrosion-resistant properties of the coating and their
formation in coatings used in industrial applications would be
undesirable. It has been observed also that the use of the organic
solvent improves the ability of the composition to be applied more
readily and uniformly to the substrate and to form smooth
coatings.
[0032] The organic solvent is a liquid at room temperature and has
surface active properties, but differs from a wetting agent, as
described above, in that the solvent is 100% volatile and is
capable of dissolving another substance and, in some cases, can be
used to help dissolve a wetting agent when used and as needed. The
organic solvent is also typically used at a higher percentage
compared to a wetting agent. The organic solvent can be used, for
example, at a level of 2% by weight or higher for beneficial
effects, whereas the effectiveness of a wetting agent can be
realized at concentrations of 1% or lower. The organic solvent
should be a compound which is compatible with the other
constituents of the aqueous coating composition. For example, the
addition of the solvent to the coating composition should not cause
precipitation of the silicate constituent or other constituents of
the composition. A preferred group of organic solvents for use in
the present composition comprises a solvent which is partially
miscible in water, that is, the solvent has a miscibility in water
of about 1 ml to about 20 ml of solvent per 100 ml of water at
about 20.degree. C. An aqueous composition which includes an
organic solvent that has a lower degree of miscibility with water
is evidenced by the formation of a layer of a solution of the water
and organic solvent (the miscible layer) and a layer of the organic
solvent. More preferably, the partially water-miscible organic
solvent is miscible in water up to about 10 ml and, most
preferably, up to about 5 ml of solvent per 100 ml of water at
about 20.degree. C. The solvent may have a miscibility of about 0.1
ml/100 ml of water (or even lower) at 20.degree. C. Accordingly,
the solvent may be immiscible in water.
[0033] Partially water-miscible organic solvents for use in the
practice of the present invention are liquid aliphatic and aromatic
carbon compounds which have typically a hydrophilic group, for
example, an ether group, most typically a hydroxyl (--OH) group.
Examples of classes of compounds which include such solvents are
glycols, glycol ethers, ketones, esters, and alcohols. A glycol
ether is a preferred class of compounds, for example, propylene
glycol n-butyl ether. A particularly preferred glycol ether is
dipropylene glycol n-butyl ether.
[0034] The organic solvent should be included in the composition in
an amount sufficient to reduce the formation of blisters in the
coating in those applications in which they tend to form. It is
believed that, for most applications, the amount of solvent will
fall within the range of about 0.5 to about 10 wt. % of the
composition. Preferably, the composition comprises about 4 to about
6 wt. % of the solvent.
[0035] It is theorized that mechanisms involved in the functioning
of the solvent to reduce blister formation are as follows. The
presence of the solvent in the composition is believed to change
the rate of evaporation of the water constituent; this causes the
silicate to polymerize and precipitate (solidify) in a different
manner than when the solvent is not present. This, in turn, leads
to the formation of coatings that are more resistant to being
degraded by high moisture conditions. It is believed also that the
solvent functions to wet both the surfaces of the substrate being
coated and the aluminum particles; this aids in the formation of a
cured coating which has improved bonds that tightly adhere to the
underlying surface and retain their integrity, even in the presence
of high moisture conditions.
[0036] Another additive that can be included in the coating
composition to reduce or prevent the formation of surface blisters
in the coating is an organofunctional silane. It has been observed
that the use of such a silane improves also surface wetting,
adhesion, and moisture-resistance in the cured coating. The silane
can be used in admixture with the organic solvent.
[0037] Many species of organofunctional silanes are known. For
example, the following publications disclose species of such
silanes and contain also a substantial amount of information on
organofunctional silanes: (A) OrganoSilicon,
Products--Systems--Services, Product Information, Union Carbide
Organofunctional Silanes for Coatings, SC-1603B, Union Carbide
Corporation, Specialty Chemicals, Danbury, Conn. (1993); (B)
Silquest.RTM. Silanes Products and Applications, Witco Corporation,
Greenwich, Conn.; (C) Silquest Organofunctional Silanes for
Waterbome Systems, Adhesion Promoters and Crosslinkers, OSi
Specialites, Inc.;(D) Silquest A-1123 Silane, Low Chloride Adhesion
Promoter and Crosslinker, OSi Specialties, Inc.; and (E)
Organofunctional Silanes, PO-2266, SC-1294, December 1991, OSi
Specialties, Inc.
[0038] Speaking generally, an organofunctional silane comprises a
functional moiety that contains an Si atom and an organic moiety
connected to the Si atom. The functional Si-containing moiety is
capable of hydrolyzing in the presence of water to form a silanol
(--Si(OH).sub.n) which in turn is capable of reacting with, for
example, reactive sites on inorganic surfaces, for example,
metallic surfaces and surfaces of pigment particles. The silanol is
capable also of co-condensing to effect crosslinking of polymers
through a moisture-cure mechanism.
[0039] Organofunctional silanes can be grouped into two classes,
namely, organoreactive organofunctional silanes and
non-organoreactive organofunctional silanes (hereafter, for
convenience "organoreactive silanes" and "non-organoreactive
silanes" respectively). These classes are described hereafter.
[0040] The organoreactive silane contains in its organic moiety a
functional group that is capable of reacting with one or more
functional groups on a polymer or on a monomer for use in
polymerization. Examples of reactive functional groups that are
present in organoreactive silanes are vinyl, methacryl, epoxy,
mercapto, amino, ureido, and isocyanato. The organoreactive silanes
are described for use in a variety of applications, for example, in
polymer synthesis as chain transfer, end-blocking, and crosslinking
agents. In addition, they are known to be used in polymer-based
coating or paint compositions where they combine chemically with
the polymeric binder of the composition to improve a variety of
properties in coatings formed from the compositions. Such
properties include, for example, coating strength, adhesion,
durability, weather-resistance, scrub-resistance, and mar- and
abrasion-resistance.
[0041] The non-organoreactive silane has an organic moiety which is
non-reactive with constituents that are present in the environment
of its use. Non-organoreactive silanes are reported as being useful
in improving the dispersion of pigment and filler and various
properties of coating compositions in which they are used and
coatings formed from the coating composition. Examples of such
properties include ease of mixing and improved gloss, hiding power,
and water-resistance of coatings formed from compositions that
contain the silane.
[0042] A silane for use in the practice of the present invention
can be represented by the formula R.sub.n--Si(X).sub.4-n in which R
represents either an organic moiety that contains a reactive
functional group, as described above, or an organic moiety that is
not reactive, as described above. X represents an alkoxy group, for
example, methoxy, ethoxy, and acetoxy. Examples of reactive
functional groups that can be included in the organic moiety (R)
are identified above in connection with the general description of
the organoreactive silanes. Examples of the organic moiety (R) in
the non-organoreactive silanes are alkyl and phenyl.
[0043] Silanes for use in the practice of the present invention can
be represented also by the following formula:
Y--(CH.sub.2).sub.n--SiX.sub.3 in which: Y is an organic moiety
that is attached to the silicon atom by a stable (CH.sub.2)n carbon
chain and that contains a reactive group, for example, --Cl,
--NH.sub.2, --SH, ##STR1## X is a functional group that is capable
of hydrolyzing and reacting with active sites on inorganic
surfaces, for example, --OCH.sub.3, --OC.sub.2H.sub.5, and
--OC.sub.2H.sub.4OCH.sub.3.
[0044] Examples of species of nonorganoreactive silanes include
hexadecyltrimethoxysilane and methyltriethoxysilane.
[0045] The preferred silane for use in the practice of the present
invention is an organoreactive silane. In particularly preferred
form, the organoreactive silane includes in its organic moiety one
or more of an amino or epoxy group, for example,
gamma-aminopropyltriethoxysilane. Particularly preferred species of
organoreactive silanes are
N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane and
gamma-glycidoxypropyltrimethoxysilane.
[0046] The organofunctional silane should be included in the
composition in an amount sufficient to reduce the formation of
blisters in the coating in those applications in which they tend to
form. It is believed that, for most applications, the amount of
silane will fall within the range of about 0.1 to about 5 wt. % of
the composition. Preferably, the composition comprises about 1 to
about 3 wt. % of the silane.
[0047] It is theorized that mechanisms involved in the functioning
of the silane to reduce blister formation are as follows. It is
believed that the silane functions to make the coating more
insoluble to water in that it causes the silicate to precipitate in
a different manner than when the silane is not present. It is
believed also that the silane aids in the wetting of the substrate
and the aluminum particles. The silane may act also as a coupling
agent, helping to bond the coating to the substrate, as well as
reacting onto the backbone of the silicate structure to form a less
water-soluble, silicate-based polymer.
[0048] The amount of water comprising the aqueous-based silicate
composition is generally dictated by viscosity needs, sprayability,
and the amount necessary to allow the coating to cure without
blistering. For most applications, it is believed that the water
content of the composition will comprise about 35 to about 70 wt. %
of the composition, with an amount of about 45 to about 55 wt. %
being preferred.
[0049] An important advantage of the present invention is that the
pH of the aqueous-based silicate composition is such that it does
not degrade the aluminum particles or the metallic surface, for
example, mild steels, which tend to be attacked or degraded by
other types of coating compositions that are relatively acidic. The
pH of the coating composition is dictated generally by the amount
of silicate in the composition and the SiO.sub.2:M.sub.2O ratio.
Typically, the pH of the composition will be about 10 to about 14,
with a pH of about 11.5 to about 12.5 being preferred.
[0050] As mentioned above, the silicate coatings of the present
invention can be formed from a coating composition that comprises
environmentally acceptable constituents. Accordingly, the coatings
of the present invention are capable of being formed from coating
compositions which do not contain hexavalent chromium.
[0051] The coating composition can be applied to the surface of the
substrate being coated in any suitable way, for example, dipping,
spraying, brushing, and rolling. The amount of composition applied
to the surface will depend on the thickness of the coating to be
formed on the substrate. An exemplary coating thickness is about 1
to about 3 mils.
[0052] After the liquid coating composition is applied to the
substrate, the resulting liquid coating should be allowed to dry
and solidify (cure). This involves typically the evaporation of the
water constituent of the composition and can include also a
chemical setting mechanism, for example, treating the coating with
ZnO, CaO, or an acidic wash. Curing the wet coating utilizing
conventional curing methods, for example, by drying the wet coating
at room temperature or at a relatively low elevated temperature,
for example, about 250 to about 600.degree. F. results in a
solidified coating that is not electrically conductive.
[0053] In one embodiment of the invention, an electrically
conductive coating can be obtained directly by curing the wet
coating at a relatively high temperature. The particular
temperature used will depend on various factors, including, for
example, the thickness of the coating, the amount of aluminum in
the coating, and type of aluminum, and the particle size of the
aluminum. Also, the lower the temperature, the longer the coating
needs to be subjected to the elevated temperature. From a practical
standpoint, the curing temperature should be at least about
950.degree. F. For guideline purposes, it is noted that
electrically conductive coatings have been achieved by curing the
coating at a temperature of about 1000.degree. F. for about 1 hour.
Higher temperatures can be used. The maximum curing temperature is
dictated typically by the temperature at which the aluminum will
change to aluminum oxide in air. It is believed that at such
elevated temperatures and curing conditions, the aluminum particles
of the coating expand and the expanded particles contact one
another more intimately and to the extent that the electrical
conductivity of the coating is improved and converted to a
conductive coating, as defined herein.
[0054] Preferably, multi-stage curing conditions are used, that is,
curing is effected initially for a time and at a temperature which
accelerates evaporation of the water in the coating, but which does
not result in any loss of the water of hydration of the alkali
metal silicate, for example, for about 15 minutes at 175.degree. F.
After the coating has cured to the extent that all of the free
water has evaporated, the temperature can be raised to accelerate
the cure further, such temperature being, for example, about
1000.degree. F. and for a period of time of, for example, about one
hour. The multi-stage curing deters the formation of coating
defects which tend to be formed as a result of the surface of the
coating's curing before all free water has been released.
[0055] In a preferred embodiment of the invention, an electrically
conductive coating is obtained indirectly. This involves curing the
wet coating at a relatively low temperature, for example, about 400
to about 650.degree. F. for about 1/2 hour to about 1 hour to form
a solid coating that is not electrically conductive. In a
particularly preferred embodiment, multi-stage curing conditions
are used, for example, an initial stage involving drying at a
temperature of about 175.degree. F. for 15 minutes and thereafter
at 600.degree. F. for about 30 minutes. Such non-conductive coating
can be converted to an electrically conductive coating by
subjecting the coating to conditions which are effective in
compressing the coating to decrease the distance between the
aluminum particles and force the particles into more intimate
contact with one another and with the substrate. This can be
accomplished, for example, by peening or burnishing the
non-conductive coating. Burnishing the coating is preferred, for
example, by blasting the coating with a material which is effective
in performing said compression. Examples of such materials are
AL203 grit (240 mesh), glass beads, and any other suitable media
which is used in commercial blasting equipment. Burnishing the
coating may be achieved also by tumbling or vibrating the coated
article in the presence of a material which is effective in
performing said compression and/or peening, for example, ceramic
beads, other forms of ceramic, and steel media. Subjecting the
coating to compressive and/or peening forces should be carried out
for a period of time sufficient to convert the coating to an
electrically conductive form. Exemplary time periods for achieving
this are about 30 seconds to about 30 minutes.
[0056] The coating composition of the present invention can be used
to form corrosion-resistant coatings on any suitable surface
including, for example, metallic surfaces such as stainless steel,
low-grade steel, and other iron alloys, titanium-based alloys, and
aluminum and aluminum alloys. It is believed that the present
invention will be used widely'to form corrosion-resistant coatings
on the surfaces of parts of airplane and ground turbine engines.
Other exemplary applications for the use of the present invention
are the coating of fasteners, exhaust headers, turbochargers, other
engine components that are subjected to high temperatures, heat
exchangers, and burner components. An example of a non-metallic
surface on which the electrically conductive coating can be formed
is a ceramic surface.
[0057] The thickness of the coating that is formed on the surface
of the article should be at least sufficient to form a coating that
has the desired corrosion-resistant properties. It is believed
that, for most applications, the thickness of the coating will be
about 1 mil to about 4 mils. For applications which involve a
higher degree of corrosion protection, it is recommended that the
coating thickness be about 2 to about 3.5 mils.
[0058] Multiple coats of the coating composition can be applied to
the substrate to form a multi-ply coating, typically a two-ply
coating. In forming a multi-ply coating, the underlying ply can be
converted to an electrically conductive form prior to applying the
overlying coating or the underlying coating can be left in its
non-conductive form and coated with the overlying coating. In each
of such embodiments, the overlying coating is treated in accordance
with the present invention to convert it into an electrically
conductive coating.
[0059] There have been circumstances where the formation of surface
blisters has been encountered in the production of a multi-ply
coating. (Blister formation has been observed in a multi-ply
coating which has been dried and/or cured at elevated temperatures,
as described above, and which has been subjected to salt spray
tests for evaluation.) In such a circumstance, the following is a
recommended procedure. After applying an underlying layer of wet
coating composition to the substrate, the wet layer is air-dried
before the application thereto of an overlying layer of coating
composition, that is, the underlying layer of wet coating
composition is not subjected to elevated temperature(s) to
accelerate the drying and/or curing thereof. After applying to the
air-dried underlying coating a layer of the overlying coating, the
resultant multi-ply coating is subjected to elevated temperature(s)
to dry and cure the multi-ply coating in the manner described
above. This appears to cause the underlying layer of air-dried
coating and overlying layer of wet coating to fuse together and
cure at the same time. The formation of blisters in the overlying
cured coating can be prevented by following this procedure.
[0060] In preferred form, the coating is formed on a grit blasted
clean iron alloy surface and has a thickness of about 0.8 mil to
about 3.5 mils and corrosion-resistant properties characterized by
no greater than about 1.6 mm loss of adhesion at scribe when
subjected to 5% neutral salt spray at 95.degree. F. for about 1000
hours (ASTM B-117).
EXAMPLES
[0061] The following is an example of a coating composition for use
in the present invention. Unless indicated otherwise, "%" means
weight percent based on the total weight of the composition.
Example No. 1
[0062] TABLE-US-00001 Constituents Wt. % sodium silicate, wt. ratio
SiO.sub.2:Na.sub.2O - 3.22 11.6 aluminum powder, average particle
size 4.5 microns 43 sold by Toyal America as No. 105 water 45.4
The source of the sodium silicate was a thick liquid (viscosity of
20.degree. C.-4.0 poises) which is sold by The PQ Corporation under
the trademark "O" and which comprises 9.15% Na.sub.2O, 29.5%
SiO.sub.2, and 61.35% water. Additional water was added to the
liquid sodium silicate to adjust the total water content of the
composition fo 45.4% and the resulting mixture was stirred for
about 5 minutes to mix completely the sodium silicate. Next, the
aluminum powder was added to the mixture and stirred therein for
about 10 minutes to form 19 ml of an aqueous silicate solution
having dispersed uniformly therein the aluminum powder. The
resulting coating composition was applied to 1010 steel panels
(3''.times.5''.times.0.03'') by spray application with conventional
air-spray equipment until a uniform wet coating of the desired
thickness was obtained.
[0063] The wet coating formed from the coating composition was then
air dried until dry to the touch and then further cured at a
temperature of 175.degree. F. for 15 minutes followed by
600.degree. F. for 30 minutes. Curing of the wet coating resulted
in a solid coating which had a thickness of 2 mils and which was
determined to be non-conductive in that it has an ohm reading of
greater than 20 ohms. The conductivity (or lack thereof) of the
cured coating was determined by measuring the resistance of the
coating in ohms using an ohmmeter with 2 blunt probes. The 2 probes
are lightly placed one inch apart on the cured coating so as not to
penetrate the surface of the coating. A reading of no greater than
about 20 ohms is considered conductive.
[0064] The non-conductive coating (greater than about 20 ohms) was
burnished in order to convert it into a coating that was
electrically conductive by burnishing for about 1 minute with 240
mesh aluminum oxide grit at 40 psi in a suction blast cabinet. The
conductivity of the burnished coating was measured and determined
to have an ohm reading of 2.5 ohms. Accordingly, the coating was
conductive. The conductivity of the burnished coating was evaluated
in the same way as that of the aforementioned non-conductive
coating.
[0065] The electrically conductive coating was then evaluated for:
corrosion-resistance; adhesion; flexibility; abrasion-resistance;
and hydrolytic stability. The tests used to evaluate such
properties are described below: [0066] (A) corrosion-resistance:
ASTM B-117 salt spray test involving placing a coated article
having an "x" scribed on the coating into an environmental- and
temperature-controlled chamber and subjecting the coated article to
a 5 wt. % neutral NaCl salt water spray at 95.degree. F. for a
predetermined number of hours; [0067] (B) adhesion and flexibility:
bend test involving bending a coated metal panel at 90.degree.
around a 1/4 inch mandrel, then attempting removal of the coating
by applying 3M #250 tape at the bend and thereafter removing the
tape quickly; [0068] (C) abrasion-resistance: ASTM D968-81 falling
sand test involving dropping sand onto a coated article at a rate
of 2 liters of sand in 21 to 23.5 seconds; and [0069] (D)
hydrolytic stability: boiling water test involving immersing a
coated metal panel in boiling water for a period of 10 minutes,
removing it from the water, allowing it to air dry and cool for at
least 1 hour at room temperature, and then subjecting it to the
above bend test.
[0070] The results of testing various samples of panels coated as
described above are set forth below. TABLE-US-00002 Properties
Evaluated Test Results corrosion-resistance 2000 hours with no
signs of corrosion in scribed "x" or on face of article adhesion
and flexibility pass, with no coating loss or cracking
abrasion-resistance pass, 0.001 inch coating thickness loss for 300
liters of sand hydrolytic stability pass, with no coating loss or
cracking
[0071] The following examples describe coating compositions which
can be used in the practice of the present invention. In all of the
examples herein, the average particle size of the aluminum powder
is about 4.5 microns and the pH of each of the exemplary
compositions is within the range of 10 to 14.
[0072] Example No. 2 below comprises a coating composition which
includes phosphate.
Example No. 2
[0073] 10 g of aqueous solution of sodium silicate, "O" (The PQ
Corporation)
[0074] 9 g of H.sub.2O
[0075] 0.13 g of tributyl phosphate
[0076] 0.06 g of silicone wetting aid (to help emulsify the
tributyl phosphate in water)
[0077] 14.4 g of aluminum powder
[0078] The next example comprises a coating composition which also
includes phosphate (but from a different source than the phosphate
used in the composition of Example No. 2).
Example No. 3
[0079] 10 g of aqueous solution of sodium silicate, "STAR" (The PQ
Corporation)
[0080] 9.65 g of H.sub.2O
[0081] 0.25 g of sodium pyrophosphate
[0082] aluminum powder at a ratio of 9 g to 10 ml of above
ingredients
[0083] The next example comprises a coating composition which
includes a mixture of sodium and lithium silicates and which also
contains phosphate.
Example No. 4
[0084] 5 g of aqueous solution of lithium polysilicate, "48"
(DuPont)
[0085] 5 g of aqueous solution of sodium silicate, "STAR" (The PQ
Corporation)
[0086] 10 g of H.sub.2O
[0087] 0.5 g of sodium pyrophosphate
[0088] aluminum powder at a ratio of 9 g to 10 ml of above
ingredients
[0089] The next example comprises a coating composition which
includes a wetting agent and a mixture of sodium and lithium
silicates.
Example No. 5
[0090] 5 g of aqueous solution of sodium silicate, "STAR" (The PQ
Corporation)
[0091] 10 g of water
[0092] 5 g of aqueous solution of lithium silicate, "48"
(Dupont)
[0093] Aluminum powder in an amount of 16.2 g was added to 18 ml of
the above liquid composition and 0.27 g of Coat-O-Sil 1211 silane
wetting agent was added also and the composition was then mixed.
The resulting composition was well suited for application by
spraying.
[0094] In the examples which follow, "%" means weight percent. The
next example shows the use of a coating composition which contains
an organic solvent and the use of the composition to form a
multi-ply coating.
Example No. 6
[0095] 16.9% of sodium silicate, "STAR" (The PQ Corporation)
[0096] 14.2% of lithium silicate, "Ludox Lithium Silicate" (Grace
Davidson Co.)
[0097] 19.5% of H.sub.2O
[0098] 5.4% of dipropylene glycol n-butyl ether--organic
solvent
[0099] 44.0% of aluminum powder, "ATA 105" from Toyal America
[0100] The source (STAR) of the sodium silicate comprised 10.6%
Na.sub.2O, 26.5% SiO.sub.2, and 62.9% water. The source (Ludox,
previously sold as "48 Dupont") of lithium silicate comprised 2.1%
Li.sub.2O, 20% SiO.sub.2, and 77.9% water. A mixture of the sodium
silicate, lithium silicate, and water was stirred for 5 minutes to
completely mix the silicates. Next, the dipropylene glycol n-butyl
ether was added to the mixture with stirring and the resulting
mixture was stirred for another 5 minutes. The aluminum powder was
then added to the mixture and stirred therein for about 10 minutes
to form an aqueous silicate solution having dispersed uniformly
therein aluminum powder. The resulting coating composition was
applied to 1010 steel panels (3''.times.5''.times.0.03'') by spray
application with conventional air-atomizing paint spray equipment
until a uniform layer of wet coating was obtained.
[0101] The coating was allowed to air dry at ambient conditions
(24.degree. C. and 50% R.H.) for a minimum of one hour. A second
coat of the coating composition was then applied to form a uniform
overlying layer of wet coating. The multi-ply coating was allowed
to dry to the touch at ambient conditions and was then placed in an
oven at 175.degree. F. for 20 minutes, followed by heating for 30
minutes at 650.degree. F. Curing of the multi-ply coating resulted
in a solid coating which had a thickness of 2.4 mils and which was
determined to be non-conductive in that it had an ohm reading of
greater than 20 ohms. The cured multi-ply coating was then made
electrically conductive in the same manner as the coating of
Example No. 1. TABLE-US-00003 Property Evaluated Test Results
corrosion-resistance 1000 hours with no signs of corrosion in
scribed "x" or on face of article and no blisters (ASTM B-117)
[0102] The next example shows the use of a coating composition
which contains a silane and the use of the composition to form a
multi-ply coating.
Example No. 7
[0103] 16.2% of sodium silicate, "STAR" (The PQ Corporation)
[0104] 13.6% of lithium silicate, "Ludox Lithium Silicate" (Grace
Davidson Co.)
[0105] 22.6% of H.sub.2O
[0106] 1.5% of
N-beta-(aminoethyl)-ganmma-aminopropyltrimethoxysilane, "Silquest
A-1123" (OSi Specialties, Inc.)
[0107] 46.7% of aluminum powder, "ATA 105" from Toyal America
[0108] The description of the sodium silicate and lithium silicate
is given above in Example No. 6. The mixture of sodium silicate,
lithium silicate, and water was stirred for 5 minutes to completely
mix the silicates. Next, the gamma-aminopropyltriethoxysilane was
added to the mixture with stirring and stirring was continued for
another 5 minutes. The aluminum powder was then added to the
mixture and stirred therein for about 10 minutes to form an aqueous
silicate solution having dispersed uniformly therein aluminum
powder. The resulting coating composition was applied to 1010 steel
panels (3''.times.5''.times.0.03'') by spray application with
conventional air-atomizing paint spray equipment until a uniform
layer of wet coating was obtained.
[0109] The coating was allowed to air dry at ambient conditions
(24.degree. C. and 50% R.H.) for a minimum of one hour. A second
coat of the coating composition was then applied to form a uniform
overlying layer of wet coating. The multi-ply coating was allowed
to dry to the touch at ambient conditions and was then placed in an
oven at 175.degree. F. for 20 minutes, followed by heating for 30
minutes at 650.degree. F. Curing of the multi-ply coating resulted
in a solid coating which had a thickness of 2.4 mils and which was
determined to be non-conductive in that it had an ohm reading of
greater than 20 ohms. The cured coating was then made electrically
conductive in the same manner as the coating of Example No. 1.
TABLE-US-00004 Property Evaluated Test Results corrosion-resistance
1000 hours with no signs of corrosion in scribed "x" or on face of
article and no blisters (ASTM B-117)
[0110] The next example describes a coating composition which
includes a silane different from the silane used in Example No.
7.
Example No. 8
[0111] 16.3% of aqueous solution of sodium silicate, "N" (The PQ
Corporation)
[0112] 13.0% of aqueous solution of lithium silicate, "48" (Dupont,
now Ludox)
[0113] 22.8% of H.sub.2O
[0114] 2.5% of Silquest A187
(gamma-glycidoxypropyltrimethoxysilane)
[0115] 45.4% of aluminum powder
[0116] Particularly preferred coating compositions are described
below in Example Nos. 9 and 10, each of which contains a preferred
wetting agent.
Example No. 9
[0117] 16.9% of aqueous solution of sodium silicate, "N" (The PQ
Corporation)
[0118] 13.5% of aqueous solution of lithium silicate, "48" (Dupont,
now Ludox)
[0119] 23.7% of H.sub.2O
[0120] 0.5% of polyether modified poly-dimethyl-siloxane wetting
agent, "bYK 348" (BYK Chemie)
[0121] 45.4% aluminum powder
Example No. 10
[0122] 17.4% of aqueous solution of sodium silicate, "STAR" (The PQ
Corporation)
[0123] 14.5% of aqueous solution of lithium silicate, "48" of
(Dupont, now Ludox)
[0124] 19.9% of H.sub.2O
[0125] 2.64% of dipropylene glycol n-butyl ether solvent
[0126] 0.36% of polyether modified poly-dimethyl-siloxane wetting
agent, "bYK 348" (BYK Chemie)
[0127] 45.2% of aluminum powder
[0128] It should be appreciated from the above description that the
present invention provides an environmentally compatible
composition that is capable of forming in a convenient fashion a
highly corrosion-resistant coating that protects underlying
substrates from being degraded even under the most severe of
conditions, for example, those encountered in the operation of
turbine engines.
* * * * *