U.S. patent application number 08/824418 was filed with the patent office on 2002-04-11 for method for coating substrate with metal oxide coating.
Invention is credited to BUDARAGIN, LEONID V..
Application Number | 20020041928 08/824418 |
Document ID | / |
Family ID | 33476599 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020041928 |
Kind Code |
A1 |
BUDARAGIN, LEONID V. |
April 11, 2002 |
METHOD FOR COATING SUBSTRATE WITH METAL OXIDE COATING
Abstract
The method is disclosed for coating or impregnating a substrate
with a metal oxide. The method includes the steps of applying a
liquid metal carboxylate composition, or a solution thereof, to a
substrate material, and exposing the substrate material to an
environment that will cause vaporization or dissipation of any
excess carboxylic acids in the liquid metal carboxylate composition
and conversion of the metal carboxylates to metal oxides.
Inventors: |
BUDARAGIN, LEONID V.;
(MOSCOW, RU) |
Correspondence
Address: |
JOHN S PRATT
KILPATRICK STOCKTON
1100 PEACHTREE STREET SUITE 2800
ATLANTA
GA
30309
|
Family ID: |
33476599 |
Appl. No.: |
08/824418 |
Filed: |
March 26, 1997 |
Current U.S.
Class: |
427/229 ;
427/226; 427/376.2; 427/376.3; 427/376.4; 427/380 |
Current CPC
Class: |
Y10T 428/265 20150115;
C23C 18/1216 20130101; C23C 18/1291 20130101; C23C 26/00 20130101;
Y02T 50/60 20130101; Y10T 428/12007 20150115 |
Class at
Publication: |
427/229 ;
427/376.2; 427/376.3; 427/376.4; 427/380; 427/226 |
International
Class: |
B05D 003/02 |
Claims
What is claimed is:
1. A method for forming a metal oxide coating on a substrate,
comprising the steps of: (a) applying metal carboxylate
composition, or a solution thereof, to a substrate material, and
(b) exposing the substrate material to an environment that will
cause vaporization or dissipation of any excess carboxylic acids in
the liquid metal carboxylate composition and conversion of the
metal carboxylates to metal oxides.
2. The method or claim 1, wherein the liquid metal carboxylate
composition comprises a solution of the metal salt of a carboxylic
acid.
3. The method of claim 2, wherein the carboxylic acid is an
alpha-branched carboxylic acid having having the
formulaR--C(R")(R')--COOHwherein: R is selected from H and C.sub.1
to C.sub.24 alkyl groups; and R' and R" are each independently
selected from C.sub.1 to C.sub.24 alkyl groups.
4. The method of claim 2, wherein the carboxylic acid is a mixture
of carboxylic acids having the formula
CH.sub.3(CH.sub.2).sub.nC(CH.sub.3)(C- .sub.2H.sub.5)--COOH,
wherein n is 7 to 10.
5. The method of claim 4, wherein the average molecular weight of
the acids contained in this mixture is from about 220 to 270.
6. The method of claim 5, wherein the mixture of carboxylic acids
contains the acid CH.sub.3CH.sub.2CH.sub.2CH(CH.sub.3)--COOH as its
lowest boiling acid constituent.
7. The method of claim 2, wherein the liquid metal carboxylate
composition comprises a mixture of metals.
8. The method of claim 2, wherein the liquid metal carboxylate
composition comprises one or more metals selected from the group
consisting of Lithium, Beryllium, Sodium, Magnesium, Potassium,
Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel,
Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium,
Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Lanthanum,
Hafnium, Tantalum, Gold, Thallium, Lead, Bismuth, Cerium,
Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium,
Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Thorium
and Uranium.
9. The method of claim 3, wherein the liquid metal carboxylate
composition comprises one or more metals selected from the group
consisting of Lithium, Beryllium, Sodium, Magnesium, Potassium,
Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel,
Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium,
Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Lanthanum,
Hafnium, Tantalum, Gold, Thallium, Lead, Bismuth, Cerium,
Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium,
Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Thorium
and Uranium.
10. The method of claim 4, wherein the liquid metal carboxylate
composition comprises one or more metals selected from the group
consisting of Lithium, Beryllium, Sodium, Magnesium, Potassium,
Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel,
Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium,
Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Lanthanum,
Hafnium, Tantalum, Gold, Thallium, Lead, Bismuth, Cerium,
Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium,
Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Thorium
and Uranium.
11. The method of claim 2, wherein the metal is a mixture
comprising: up to 15% by weight of cobalt; up to 20% by weight of
nickel; and the balance iron; wherein the minimum total amount of
cobalt and nickel is at least 3%.
12. The method of claim 2, wherein the metal is a mixture
comprising: up to 20% by weight of cobalt; up to 10% by weight of
chromium; and the balance cerium; wherein the minimum total amount
of cobalt and chromium is at least 3%.
13. The method of claim 2, wherein the metal is a mixture
comprising: 3 through 5% by weight of cobalt, 0 through 20% by
weight of chromium, and the balance cerium.
14. The method of claim 1 wherein the vaporization or dissipation
of any excess carboxylic acids in the liquid metal carboxylate
composition and conversion of the metal carboxylates to metal
oxides is carried out by heating the coated substrate.
15. The method of claim 14, wherein the substrate is heated to a
temperature greater than about 400.degree. C.
16. The method of claim 2, wherein the amount of metal in the
liquid metal carboxylate composition is preferably in the range of
30-50 grams of metal per kilogram of liquid metal carboxylate
composition.
17. The method of claim 2, wherein the amount of metal in the
liquid metal carboxylate composition is 30 to 40 grams of metal per
kilogram of liquid metal carboxylate composition.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
surface coatings. In particular, the invention is a method for
coating a wide variety of different substrates with a wide variety
of metal oxide coatings.
BACKGROUND OF THE INVENTION
[0002] It is desirable in many situations to coat or impregnate the
outer surface of a substrate with a coating, including a metal
oxide coating.
[0003] One method of coating substrates, such as a the ceramic
insulator of a sparkplug, using active noble metals, such as
silver, palladium or platinum, is disclosed in German Patent
3918272. The primary disadvantage of this method is its high cost.
The use of platinum and other noble metals adds significantly to
the cost of materials used to form the coating.
[0004] One known method for the formation of metal oxide coatings
on substrates is via the electrochemical sedimentation of metal
oxides from solution. However, this method can only used to coat
electrically conductive substrates, a significant limitation where
the substrate is non-conductive.
[0005] Another method of forming metal oxide coatings on substrates
is a sputtering process. In this process, a metal oxide powder is
vaporized, using, for example, laser, plasma, flame or detonation
methods. The vapors are carried in a gas carrier until they reach
the surface to be coated. This surface is generally relatively
cool, so that the vaporized metal oxide powder condenses on the
surface.
[0006] The sputtering process is impractical and expensive to use
for coating most substrates, making it commercially unreasonable.
It requires the use of specialized manufacturing equipment to
maintain the necessary vacuum conditions. These requirements
increase the cost and difficulty of manufacturing the coated
substrate product. Further, the materials used in the sputtering
process, solid solutions of oxides, are expensive.
[0007] Detonation spraying is another possible method that could be
used to produce coatings on various substrates. However, this
method requires a large amount of catalyst material and specialized
manufacturing equipment.
[0008] Another potential method for coating substrates is by
deposition of metal oxides from aqueous solutions, followed by heat
treatment. However, this method requires the use of a binder, such
as phosphoric acid, in the metal oxide solution. The presence of
phosphorus containing compounds in the catalytic layer reduces its
catalytic activity.
[0009] A further potential method is chemical vapor deposition
(CVD) However, CVD requires the use of a carefully developed system
of safety equipment, as toxic components are used in this process.
These materials include .beta.-diketones and metal-carbonyl
complexes.
[0010] Another known method for the deposition of a metal oxide
coating on a substrate is described in U.S.S.R. Inventors
Certificate No. 923232. This process uses a single trivalent metal
salt formed by adding the metal to a solution of carboxylic acids.
The salt is applied to a substrate and subjected to a temperature
of 500 to 600.degree. C. for 20 to 30 seconds in a nonoxidizing
atmosphere.
[0011] This process suffers from several drawbacks. First, it
requires the use of a special furnace that contains a nonoxidizing
atmosphere. In addition, the short heat treatment time produces a
coating that has internal strains, leading to the lack of a well
defined crystalline structure and creating a highly absorptive
coating that can absorb water, gases or hydrocarbons. This
absorption can make the coating conductive. Furthermore, the use of
a single metal in the coating is undesirable because a number of
metals, for example zirconium, do not form resistant coatings
without additional additives. This would create weak coatings.
Finally, this process only uses trivalent and tetravalent metals.
As a result, desirable materials, such as nickel, copper and gold,
can not be used therein.
[0012] As noted above, the above-referenced conventional coating
processes suffer from a variety of disadvantages that would make
them undesirable for the commercial-scale production of most
substrates. In addition, the coatings produced by these methods are
relatively thick, which can reduce their adhesion to the substrate
and cause scaling or flaking off of the coating. Further, the above
methods require additional procedures to remove the coating from
areas of the surface where no coating is desired. Finally, all of
the above methods have high material consumption, increasing their
cost.
SUMMARY OF THE INVENTION
[0013] The present method overcomes the drawbacks described above
in known techniques for coating substrates with metal oxides. The
method generally comprises the steps of (a) applying a liquid metal
carboxylate composition, or a solution thereof, to a substrate
material, and (b) exposing the substrate material to an environment
that will cause vaporization or dissipation of any excess
carboxylic acids in the liquid metal carboxylate composition and
conversion of the metal carboxylates to metal oxides.
[0014] Usually, step (b) above is carried out by heating the
substrate in a furnace, in normal air, at a temperature of at least
about 300.degree. C., and preferably of at least about 400.degree.
C., for at least about two minutes. However, for some items, such
as large cast steel structures, the step can be accomplished by
merely exposing the substrate to normal ambient conditions for a
sufficiently long time to allow the metal oxide coating to form on
the substrate.
[0015] The invention also includes devices or structures coated
with metal oxide coatings in accordance with the method described
above.
[0016] Suitable substrates for this process include metals,
including steel alloys and aluminum, silica based materials
(including optic and fiber optic materials), and various ceramic
materials, that need to be protected from a range of environmental
conditions, including atmospheres rich in corrosive fluids,
combusted or partially combusted hydrocarbons (such as the
combustion chambers of internal combustion engines, jet engines,
and turbines, and in emission or pollution control systems attached
thereto), saline conditions (such as in saline or brine
conditioners), lead oxides, abrasive particles or degradative
contaminants.
[0017] For example, sensors used in catalytic converters, part of
the required emission control systems for automobiles manufactured
or sold in the United States, are commonly coated with platinum. To
reduce the cost of these sensors, the present coating could be used
to replace the platinum coating, thereby offering a low-cost
alternative. There are numerous other examples of materials that
could be coated in accordance with the present invention.
[0018] For instance, one embodiment of the present invention is to
deposit a metal oxide coating onto various heating elements in
heating or air conditioning elements, including condenser or heat
exchanger tubes.
[0019] Another embodiment of the present invention is to deposit a
metal oxide coating onto a casting mold or press mold. For
instance, in some countries, press molds for rubber goods, such as
tires, gaskets, cups, and seals, are made of hydrocarbon and low
alloy steels. The lifetime of these machines can be significantly
shortened by corrosion. To increase the life of such products, a
thin (up to 5 mcm) metal oxide coating can be applied onto the
working surfaces of the press, in accordance with the present
method, by heat decomposition of a liquid metal carboxylate
composition at, for example, 370-390.degree. C.
[0020] Another embodiment of the present invention is to deposit a
metal oxide coating onto a metal tool. For instance, formation of a
metal oxide coating on the surface of hard-faced (carbide tip)
cutting tools will increase the lifetime of cutting tips.
[0021] Another embodiment of the present invention is to deposit a
metal oxide coating onto salt water marine propellers.
[0022] Another embodiment of the present invention is to deposit a
metal oxide coating onto turbine blades.
[0023] Another embodiment of the present invention is to deposit a
metal oxide coating onto metallic moving parts in machinery, such
as aluminum parts.
[0024] Another embodiment of the present invention is to deposit a
metal oxide coating onto steel castings used in air
conditioners.
[0025] Another embodiment of the present invention is to deposit a
metal oxide coating onto silicon or silica based materials,
including optic or fiber optic materials.
[0026] Another embodiment of the present invention is to deposit a
metal oxide coating onto various metal parts exposed to abrasion or
continuous high temperatures or high impact conditions (such as
tools, dies, stamping materials).
[0027] Another embodiment of the present invention is to deposit a
metal oxide coating onto boat hulls, for instance, to prevent
corrosion and to prevent barnacle formation.
[0028] Another embodiment of the present invention is to deposit a
metal oxide coating onto molds used for molding nonferrous metals.
In the manufacture of such products, a basic mold is first made
with a size that is larger than the product to be made, by
approximately 50-100 microns. The surface of the mold is then
powder coated by a protective coating in such a way that the size
of the mold corresponds to the size of the desired article. A
primary drawback of this method is the necessity for double
treatment of the metal mold, and the restricted resistance of the
metal mold. The present invention can be used to form a protective
film in the mold when the mold is manufactured, corresponding to
the size of the corresponding articles. This involves (1)
manufacturing the mold with a size corresponding to the size of the
article to be made, and (2) forming a protective surface of
approximately 2 microns thickness on the surface of the mold. This
provides a significant decrease in labor, and an increase in metal
mold resistance at casting of at least 50%.
[0029] Another embodiment of the present invention is to deposit an
oxide coating of yttrium or cerium on the surface of nichrome
heating elements, such as that used in many irons, stoves and
resistance furnaces. This will increase the maximum working
temperature of a typical nichrome element from approximately
1100.degree. C. to approximately 1220-1250.degree. C. or higher,
while increasing the life of the heating element.
[0030] While these are examples of various specific applications
for the present invention, this list is by no means exhaustive, as
the invention can be used to treat a wide variety of different
components with a wide variety of different types and combinations
of metal oxides.
[0031] The term alkyl, as used herein, refer to a saturated
straight, branched, or cyclic hydrocarbon, or a combination
thereof, typically of C.sub.1 to C.sub.24, and specifically
includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl,
isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl,
2,3-dimethylbutyl, heptyl, octyl, nonyl, and decyl.
[0032] The terms alkenyl and alkynyl, as used herein, refers to a
C.sub.2 to C.sub.24 straight or branched hydrocarbon with at least
one double or triple bond, respectively.
[0033] The term aryl or aromatic, as used herein, refers to phenyl,
naphthyl, or substituted phenyl or naphthyl, wherein the
substituent is alkyl, alkenyl, alkynyl or alkoxy.
[0034] The liquid metal carboxylate composition is a solution of
the carboxylic acid salts of one or more metals ("metal
carboxylate"). Metal carboxylates are well known and can be
produced by a variety of methods known to one skilled in the art.
Non-limiting examples of methods for producing the metal
carboxylate are shown in the following reaction schemes:
[0035] RCOOH+Me.fwdarw.(RCOO).sub.nMe.sup.n+ 0.5nH.sub.2 (for
alkaline earth metals, alkali earth metals and thallium);
[0036] RCOOH+Me.sup.n+(OH).sub.n.fwdarw.(RCOO).sub.nMe.sup.n+
H.sub.2O (for practically all metals having a solid hydroxide);
[0037]
RCOOH+Me.sup.n+(CO.sub.3).sub.0.5n.fwdarw.(RCOO).sub.nMe.sup.n+
H.sub.2O CO.sub.2 (for alkaline earth metals, alkali earth metals
and thalluim); and
[0038] RCOOH+Me.sup.n+(X).sub.n.fwdarw.(RCOO).sub.nMe.sup.n+
H.sub.mX (liquid extraction, usable for practically all metals
having solid salts).
[0039] The liquid metal carboxylate composition can contain a
single metal, to form a single metal carboxylate, or a mixture of
metals, to form a corresponding mixture of metal carboxylates.
Preferably, the liquid metal carboxylate composition contains a
mixture of metals, as these compositions form mixed oxides having
superior properties.
[0040] Preferably, the solvent used in the liquid metal carboxylate
composition is an excess of a liquid carboxylic acid which was used
to form the metal carboxylate. Alternatively, the solvent can be
the solution of a carboxylic acid in another solvent, including,
but not limited to, organic solvents such as acetone, ethanol,
methanol, propanol, benzene, toluene, chloroform and
dichloromethane.
[0041] Carboxylic acids that are suitable for use to form the
liquid metal carboxylate composition are those which: (1) can form
a metal carboxylate, where the metal carboxylate is soluble in
excess acid or another solvent; and (2) can be vaporized at a
temperature which overlaps the oxide conversion temperature.
[0042] The carboxylic acid should have a formula R-COOH, where R is
alkyl, alkenyl, alkynyl or aryl.
[0043] Preferably, the liquid monocarboxylic acid comprises one or
more carboxylic acids having the formula I below:
R--C(R")(R')--COOH (I)
[0044] wherein:
[0045] R is selected from H and C.sub.1 to C.sub.24 alkyl groups;
and
[0046] R' and R" are each independently selected from C.sub.1 to
C.sub.24 alkyl groups.
[0047] Preferably, these alpha branched carboxylic acids have a
molecular weight in the range 130 to 420. More preferably, the
carboxylic acids have a molecular weight in the range 220 to
270.
[0048] Either a single carboxylic acid or a mixture of carboxylic
acids can be used to form the liquid metal carboxylate. Preferably,
a mixture of carboxylic acids is used. The use of a mixture
provides several advantages. First, the mixture has a broader
evaporation temperature range, making it more likely that the
evaporation temperature of the acid mixture will overlap the metal
carboxylate decomposition temperature, allowing the formation of an
optimum oxide coating. Second, the production of purified
individual acids is expensive. Thus, the use of an individual acid
could unnecessarily raise the cost of this method.
[0049] The carboxylic acid may be a mixture of tertiary and
quaternary carboxylic acids of formula I. One preferred carboxylic
acid mixture is a mixture manufactured by the Sterlitamakski
Production Complex "KAUSTIK," Bashkortostan, Sterlitamak City,
Russia and other petrochemical enterprises, such as the
Dneprodzerzhinski Complex in Dneprodzerzhinsk city, Ukraine. These
materials are sold under the name "VIK acids." The VIK acids are a
material consisting of a mixture of carboxylic acids having the
general formula CH.sub.3(CH.sub.2).sub.nC(CH.sub.3)(C.sub.2H.s-
ub.5)--COOH, wherein n is 7 to 10. The average molecular weight of
the acids contained in this mixture is from about 220 to 270. This
mixture also contains the acid
CH.sub.3CH.sub.2CH.sub.2CH(CH.sub.3)--COOH as its lowest boiling
acid constituent.
[0050] The VIK acids should have the properties set forth in Table
1.
1 TABLE 1 CHARACTERISTIC NORM appearance transparent homogeneous
liquid color less or low-yellow. Color, maximum 7.0 Density at 20
C. 0.90-0.93 g/cm.sup.3 Acid Fraction composition: content of
C.sub.3 acids-maximum 1.0 b) content of C.sub.5-C.sub.11, acids and
90.0% higher-maximum Acid number, mg 300-350 KOH/gr Ether number,
mg 20.0 KOH/gr-maximum Water content-maximum 0.5% Refraction
coefficient, 1.42-1.43 .eta. 20 C. 189779.1
[0051] The critical properties of the VIK acid are the acid number,
which should not be above 380 mg/g KOH and the appearance; the
liquid should be clear. The liquid alpha-branched carboxylic acids
can be used as received from the manufacturer and do not require
any additional purification, such as the removal of alcohol, ethers
or other organic impurities.
[0052] Metals that are particularly suitable for use to form the
liquid metal carboxylates include those selected from the group
consisting of: Lithium, Beryllium, Sodium, Magnesium, Potassium,
Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel,
Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium,
Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Platinum,
Lanthanum, Hafnium, Vanadium, Niobium, Molybdenum, Indium,
Promethium, Plutonium, Curium, Californium, Tantalum, Gold,
Thallium, Lead, Bismuth, Cerium, Praseodymium, Neodymium, Samarium,
Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium,
Thulium, Ytterbium, Lutetium, Thorium and Plutonium and
Uranium.
[0053] Any of the above metals or combinations thereof can be used
to form coatings according to the present process. Depending on the
particular use of the coating, those skilled in the art can select
appropriate metal mixtures to form the desired metal or metal oxide
coating. For example, the metals can be selected taking into
consideration the nature of the substrate to be coated, the purpose
of the substrate, and the environment to which the substrate is
exposed.
[0054] For example, the above-named inventor is filing
contemporaneously herewith an application directed to a method for
coating the ceramic insulators of sparkplugs, just one of the many
applications of the present invention. By way of example, for the
formation of a coating on the ceramic insulator of a sparkplug, the
oxide coating should not be electrically conductive. In addition,
if the engine is operating with a highly enriched fuel mixture, the
partial reduction of iron, nickel and cobalt oxides is possible due
to the interaction of these oxides with partially combusted fuel
products. Thus, in these conditions, the amounts of these materials
should be limited to that necessary to provide a stable coating.
Preferably in these circumstances, thermodynamically stable oxides,
such as chromium and cerium oxides should be the major components
of the coating. Similarly, chromium oxide should not be the sole
component of the coating for a sparkplug, as it may form
agglomerates or a crystalline structure with reduced resistance.
Thus, if chromium is used, it is preferably used in combination
with other oxides, such as cerium. In addition, the use of divalent
nickel with trivalent metals, such as cobalt, iron or chromium, may
cause the formation of electrically conductive spinels. The
electrically conductive spinels are, of course, undesirable for use
on sparkplug insulators, although they may have other applications.
Accordingly, if sparkplugs are being coated, the use of nickel with
trivalent metals should be carefully monitored.
[0055] In general, the liquid metal carboxylate composition
preferably contains a mixture of metal carboxylates. This mixture
preferably contains one metal carboxylate as its major component
and one or more additional metal carboxylates as stabilizing
additives. The stabilizing additives are preferably trivalent metal
carboxylates. Preferred trivalent stabilizing additives include
chromium, iron, manganese and nickel carboxylates. Preferably, the
liquid metal carboxylate composition contains both cerium and
chromium carboxylates.
[0056] For most components in general, the metal forming the metal
carboxylate which is the major component of the liquid metal
carboxylate composition is preferably present in an amount from
about 65 to 97% by weight, relative to the total weight of the
metal in the composition. Preferably, the metal forming the metal
carboxylate which is the major component is present in an amount
from about 80-87% by weight. Another preferred amount for the metal
forming the major component of the metal carboxylate composition is
in the range from about 90-97% by weight.
[0057] The stabilizing additives should be present, such that the
total amount of the metal in metal carboxylates which are the
stabilizing additives is at least 3% by weight, relative to the
total weight of the metal in the liquid metal carboxylate
composition. This can be achieved by using 3% of a single
stabilizing additive, or less than 3% of more than one stabilizing
additive, provided that the total weight of the metal in the
stabilizing additives is greater than 3%. Preferably, the total
weight of the metal in the stabilizing additives is in a range from
about 3% to about 35% by weight. Another preferred total weight
range for the metal in the stabilizing additives is from about 3 to
30% by weight. One preferred total weight range for the metal in
the stabilizing additives is from about 3 to 10 percent by
weight.
[0058] Non-limiting examples of liquid metal carboxylate
compositions suitable for use in the present process are set forth
below. In these compositions, weight range percentages for the
metals are based on 100 percent total by weight of the metal in the
liquid metal carboxylate composition. As noted above, the minimum
amount of the stabilizing additives, those defined below as being
present in "up to" a certain amount, is a total stabilizing
additive weight of at least 3 percent. For example, the liquid
metal carboxylate composition can have 3% of a single stabilizing
additive or 1.5% of one stabilizing additives and 1.5% of another,
or 2% of one stabilizing additive and 1% of the other. Non-limiting
examples of suitable compositions are, particularly preferred in
coating sparkplugs, are: up to 15% cobalt, up to 20% nickel, and
the balance iron; up to 10% chromium, up to 20% cobalt, and the
balance cerium; 3 through 5% cobalt, up to 20% chromium, and the
balance cerium.
[0059] The amount of metal in the liquid metal carboxylate
composition should be enough to provide an adequate metal oxide
coating. Preferably, this amount is in the range from about 20 to
150 grams of metal per kilogram of liquid metal carboxylate
composition. A preferred amount of metal in the liquid metal
carboxylate composition is 30 to 100 grams of metal per kilogram of
liquid metal carboxylate composition. More preferably, the liquid
metal carboxylate composition contains about 40-60 grams of metal
per kg of composition.
[0060] Amounts of metal less than 20 grams per kg of composition
can be used. However, this low concentration requires that the
process be repeated several times to provide an adequate
coating.
[0061] Similarly, amounts of metal greater than 150 grams per kg of
composition can be used, however, the use of more metal raises the
cost of the present Method.
[0062] One preferred liquid metal carboxylate composition comprises
VIK acids and the following metals (metal weight percentages are
given relative to the total weight of metal in the liquid metal
carboxylate composition):
2 cerium - 94 to 96% chromium - 2 to 3% Iron - 2 to 3%
[0063] The above metals are preferably present in the liquid metal
carboxylate composition in an amount from about 30 to 40 grams of
metal per kilogram of liquid metal carboxylate composition.
[0064] Another preferred liquid metal carboxylate composition
comprises VIK acids and the following metals (metal weight
percentages are given relative to the total weight of metal in the
liquid metal carboxylate composition):
3 Cerium - 90% Chromium - 7% Cobalt - 3%
[0065] The above metals are preferably present in the liquid metal
carboxylate composition in an amount of 50 g of metal per kilogram
of liquid metal carboxylate composition.
[0066] These liquid metal carboxylate compositions are commercially
available from the state enterprise Vserossiiski Scientific
Research Institute of Chemical Technologies, Moscow, Russia.
[0067] As discussed above, the primary purpose of the disclosed
method is the production of a metal oxide coating on the surface of
a substrate. The method can be carried out on a variety of
different structural products or components, whenever it is
desirable to provide a metal oxide coating on the product or
component. The coating can be applied to individual components
prior to assembly into a multicomponent product, or can be applied
to a finished multicomponent product.
[0068] The liquid metal carboxylate composition can be applied to
the substrate neat (without the use of an additional solvent) or in
solution. Preferably, the liquid metal carboxylate composition is
applied without a solvent.
[0069] Any known method of application of the liquid metal
carboxylate composition is suitable for use in the present process,
so long as it provides an adequate coating of the liquid metal
carboxylate composition on the substrate. For example, the
substrate component can be dipped into a container of the liquid
metal carboxylate composition. Alternatively, a swab, sponge,
dropper, pipet or other applicator can be used to apply the liquid
metal carboxylate composition to the substrate.
[0070] The liquid metal carboxylate composition should be applied
at a temperature less than 500 C. Preferably, the liquid metal
carboxylate composition is applied to the substrate component at
room temperature.
[0071] Following application of the liquid metal carboxylate
composition to the substrate, the component is exposed to an
environment sufficient to vaporize or dissipate excess carboxylic
acid in the liquid metal carboxylate composition and to convert the
metal carboxylates to metal oxides. The temperature for the
treatment should be selected such that the temperature ranges for
the evaporation of the carboxylic acid and the formation of the
metal oxide overlap, and the temperature should not damage the
component onto which the coating is being applied.
[0072] For sparkplugs and similar types of components, this
temperature is preferably greater than about 400.degree. C. The
upper limit for the heat treatment is dependent on the materials
contained in the component being treated. The temperature should be
selected so that it will not damage the component which is being
coated. A preferred temperature range for most ceramic and metal
components is from about 400 to 650.degree. C. Another preferred
temperature range is from about 400 to 550.degree. C.
[0073] During the exposure step of the process, two processes take
place. These processes can occur at different temperature levels.
The first process is the evaporation or decomposition of the excess
carboxylic acid in the liquid metal carboxylate composition. This
forms a metal carboxylate layer on the surface of the component.
The second stage is the decomposition of the metal carboxylate
layer to a metal oxide layer and fixation of that layer on the
backing or substrate surface.
[0074] To create an oxide layer which is fixed to the substrate
surface, it is preferred that there be an interaction between the
substrate and the coating during the coating process. Optimum oxide
layer production occurs when the temperature at which the
carboxylate decomposes and the acid evaporates overlap. That is,
when the carboxylate decomposition stage commences, the removal and
decomposition of the acid is not complete. Complete removal of the
acid, prior to the commencement of carboxylate decomposition can
reduce the adhesion of the oxide coating to the substrate.
[0075] Without wishing to be bound to any particular mechanism, it
is believed that the following process occurs during the So
production of the oxide coating. At high temperatures, it is
believed that the carboxylic acid etches or otherwise interacts
with the substrate, activating it. This allows interaction between
the metal carboxylate and the activated substrate, resulting in the
formation of a strong substrate-oxide link.
[0076] The heating can be conducted either by placing the coated
component onto a rack or support and then into a furnace, which has
been preheated to a desired temperature, or by placing the coated
component into a furnace, followed by heating the furnace to the
desired temperature. Any conventional furnace can be used, as no
special heating equipment is required, provided, of course, that
the furnace will accommodate the size and shape of the component
being treated.
[0077] In general, the component should be heated for a time
adequate to produce a uniform oxide coating. For a furnace which
has been preheated to a temperature above 400.degree. C., a
preferred minimum time is at least about 2 min. If several
different components are being treated simultaneously, uneven
heating might take place. For example, the peripheral components
will probably heat to working temperature faster than the
components located in the center of the group. Accordingly, batches
of components should be heated longer, depending on the type of
furnace used and the nature of the components.
[0078] Preferably, the heat treatment should be carried out for at
least two minutes at the desired temperature. More preferably, the
heat treatment should be carried out for 15 to 20 minutes.
[0079] Following treatment, the component should be allowed to cool
to room temperature. Forced air cooling may be used to accelerate
the cooling process. The component should not be cooled by treating
it with a liquid coolant, as this could damage the coating or the
component.
[0080] As noted above, while active heating to high temperatures is
the preferred method of curing the coating, the exposure step can
also be carried out in some situations by exposing the substrate to
ambient air conditions for sufficient time to fix the metal oxide
coating to the substrate.
[0081] The present process is carried out in a normal, i.e. ambient
atmosphere. Accordingly, there is no need to provide any special
atmosphere in the furnace during the heating process. However,
should it be desired, the present process can also be conducted in
specialized atmospheres. If a specialized atmosphere is used, it is
preferably an oxidizing atmosphere, that is, one which is enriched
with oxygen.
[0082] As noted above, one particular application of the present
invention is for coating sparkplugs. Sparkplugs in internal
combustion engines, and igniters in gas turbines and jet engines,
are used for igniting combustible mixtures of gases and vapors.
[0083] Typically, sparkplugs used in internal combustion engines
include a ceramic insulator, which surrounds a central electrode.
The end portion of the sparkplug, including the end of the ceramic
insulator, is exposed to the interior of the combustion chamber of
the engine. During normal operation of the engine, there are times
when operating conditions contaminate the ceramic insulator of the
sparkplug. Often, this contamination takes the form of
electroconducting coke. This contamination can occur, for example,
during engine idle when the engine has just been started and the
fuel mixture is enriched, when the weather is cold, and when the
engine is not properly tuned. It has been found that even when an
engine is properly tuned, carbonization of the sparkplug can still
take place, for example, when driving on a cold engine or using an
enriched fuel mixture. The contamination can also take the form of
lead-oxide, due to the presence of lead in leaded gasolines.
[0084] The contamination of the sparkplug's ceramic insulator can
interfere with the operation of the sparkplug. For example,
contamination with electroconductive coke or lead oxide reduces the
sparking ability of the sparkplug, because the electrical current
dissipates through the contaminant layer to the metal casing of the
sparkplug.
[0085] The present invention prevents or inhibits contamination of
the sparkplug's ceramic insulator by carbon-based materials, such
as coke, or by lead-oxide. The method can be used either during the
sparkplug manufacturing process, for example, on an intermediate
assembly, such as the ceramic insulator, or on the completed
sparkplug. The present coating process can be used with any known
process for manufacturing sparkplugs. For example, the present
oxide coating can be applied to the sparkplug's ceramic insulator
prior to its assembly into the completed sparkplug. Alternatively,
the coating can be applied to an assembled sparkplug. In addition,
the present process can be used to form oxide coatings on
sparkplugs which have been used in internal combustion engines,
provided that the used sparkplug has been cleaned of any
contaminants prior to formation of the oxide coating.
EXAMPLES
[0086] The following examples illustrate the application of the
present process to the coating of sparkplugs.
[0087] The metal carboxylate compositions used in Examples 1 to 3
were obtained from VserosBiiski Scientific Research Institute of
Chemical Technologies, in Moscow, Russia.
Example 1 Preparation of Coated Insulator
[0088] The upper electrode to which a sparkplug wire was attached,
was removed from a group of sparkplugs. The sparkplugs were then
placed in a basket in a container over a boiling hydrocarbon
solvent, in order to remove any grease or organic contamination
which was present on the sparkplug. The basket containing the
sparkplugs was removed from the degreasing chamber and was cooled
to a temperature below 50.degree. C.
[0089] The degreased sparkplugs were placed in a holder, with the
threaded portion of the sparkplug facing up, and were placed in a
furnace which had been preheated to a temperature in the range 180
to 220.degree. C. This treatment removed any solvent or moisture
which had been absorbed onto the sparkplug. The sparkplugs were
removed from the furnace and cooled to a temperature below
50.degree. C.
[0090] Two drops of a liquid metal carboxylate mixture were
manually applied to the tip of the central electrode insulator of
each spark plug. The metal carboxylate mixture had the following
proportions of metal: 90% cerium, 7% chromium, and 3% cobalt. The
carboxylic acid was VIK acid. The total metal concentration in the
liquid carboxylate mixture was 50 g metal per kilogram of liquid
carboxylate mixture.
[0091] The sparkplugs were placed in a furnace which had been
heated to a temperature of 420.degree. C. and were kept in the
furnace for 30 minutes, forming the oxide coating. At the
conclusion of the heat treatment, the sparkplugs were cooled to
room temperature, and the upper electrode was reassembled into the
sparkplug to provide the completed article.
Example 2 Preparation of Coated Sparkplug
[0092] A Russian type All/1 sparkplug was prepared (degreased and
dried) as set forth in Example 1, without the removal of the
central electrode. The sparkplugs central insulator was dipped into
the liquid carboxylate composition used in Example 1 to a depth
between 10 to 15 mm. The sparkplug was then introduced into a
furnace which had been preheated to 650.degree. C., kept in the
furnace for 10 minutes, removed and cooled to room temperature.
Example 3 Coating of a Previously used Sparkplug
[0093] The procedure of Example 2 was repeated using a Russian
All/l sparkplug which had been used in an internal combustion
engine which had been run for 20,000 kilometers. A coated sparkplug
was produced.
Example 4 use of Coated Sparkplug
[0094] The sparkplugs manufactured according to the process set
forth in Example 2 were used in a Lada automobile to determine
their effects on the performance of the automobile, compared to
uncoated sparkplugs. The use of the sparkplugs coated according to
the present process significantly reduced the average time
necessary to start the engine of a Lada automobile in cold weather
from 2 min to 15-20 sec. In addition, the fuel consumption economy
of the engine was improved by 5-7%.
[0095] As noted above, the present method can be used to coat
numerous different substrates, with a variety of metal oxides.
While the invention has been described by reference to various
specific examples, it should be understood that the invention is
not limited to those specific examples, and various modifications
may be made to the embodiments described above without departing
from the scope and spirite of the invention as claimed below.
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