Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SILICONE INFILTRATED CERAMIC NANOCOMPOSITE COATINGS
The present invention relates to ceramic nano-
composite coatings which comprise porous ceramic coatings
infiltrated with silicone polymers. In a preferred
embodiment of the invention, the nanocomposites are used as
protective coatings to inhibit degradative corrosion.
Ceramic composites and methods for their production
are known in the art. Such composites generally comprise a
continuous matrix phase which surrounds a reinforcing phase.
Typically, the matrix phase comprises materials such a3
ceramics, metals and glasses and the reinforcing phase
comprises fillers (eg., whiskers, powders, etc.) or fibers
which improve the strength of the matrix. By contra~t, the
nanocomposites of the present invention comprise porous
ceramic pha~es which ~urround silicone polymer~.
Compo~ite structures comprising porous ceramics
impregnated with various material~ are also known in the art.
For instance, U.S. Patent No. 4,93Z,438 describes valve
bodie~ made of porous ceramic materials impregnated with
lubricants, including silicone resins. This reference,
however, does not describe impregnated ceramic coatings.
Ceramic coating~ are also known in the art. For
instance, Haluska et al. in U.S. Patent No. 4,756,977
describes a process for forming a ceramic coating on a
substrate comprising diluting hydrogen silsesquioxane resin
in a solvent, applying the solution to a substrate,
evaporating the solvent and heating the coated substrate to a
temperature of about lSO to about 1000C. Depending on the
processing technique used, however, such coatings can be
quite porous and, thus, allow the permeation of undesirable
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materials. For instance, when the silica coatings of Haluska
et al. are applied to an electronic device, they can allow
water, oxygen and chloride ions to reach the surface of the
device and thereby cause corrosion.
The use of silicone as an encapsulant and a coating
agent is also known in the art. For instance, silicone gels
and resins are used in the electronics industry to protect
electronic devices from the environment. Such silicones,
however, often allow contaminants such as water and various
ions to reach the surface of the substrate. These
contaminants, in turn, cause the coating to blister and
thereby lose its effectiveness.
What was not described in the prior art are
nanocomposites which comprise porous ceramic coatings
infiltrated with silicone polymers. The inventors herein
have discovered that such nanocomposites have many desirable
properties.
The present invention relates to a ceramic nano-
composite. The nanocomposite comprises a porous ceramic
coating having a silicone polymer within the pores. In a
preferred embodiment of the invention the ceramic coating i8
a protective ceramic coating on a substrate such as an
electronic device which is prone to corrosion. The present
invention also relates to a method of making such nano-
composites.
The present invention is based on the unexpected
discovery that the infiltration of porous ceramic coatings
with silicone polymers yields novel nanocomposites with
desirable properties. The inventors herein postulate that
the ceramic coating provides a more permanent bond for the
silicone polymer (i.e., the polymer cannot blister) and the
silicone polymer plugs the pores of the ceramic coating to
prevent transport of impurities (i.e., the coating becomes
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less permeable). The present nanocomposite system,
there~fore, takes advantage of the benefits of both the
ceramic and the silicone phase and eliminates some of their
disadvantages. The resultant nanocomposites are particularly
useful as protective coatings on substrates such as metals or
electronic devices which are prone to corrosion.
In the present invention, a 'porous ceramic' is one
which contains voids of a sufficient size to allow
infiltration of the silicone polymer. Such voids can include
pores, pinholes, cracks, etc; a 'preceramic compound' is any
compound which can be converted to a porous ceramic coating
by pyrolysis; a 'preceramic coating' is a coating of a
preceramic compound on a substrate; and an 'electronic
device' or 'electronic circuit' includes, but is not limited
to, silicon based devices, gallium arsenide based devices,
focal plane arrays, opto-electronic devices, photovoltaic
cells and optical devices.
The novel nanocomposite coatings of the present
invention are generally formed by a process which comprises
~pplying a coating comprising a preceramic compound to the
surface of a substrate; converting the preceramic coating to
a porous ceramic coating by heating it to a temperature
sufficient to converts it into the porous ceramic coating;
and infiltrating the porous ceramic coating with a silicone
polymer.
The preceramic compounds which can be used in the
process of this invention include those which can be
converted to a porous ceramic with the application of heat.
These ceramics generally form the "continuous" phase of the
ceramic nanocomposite. These compounds can be precursors to
a variety of ceramics including, for example, oxides such as
SiO2, Al203, TiO2 or ZrO2, nitrides such as silicon nitride
or titanium nitride, oxynitrides such as SiOXNy or AlOXNy,
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oxycarbides such as SiOC, carbonitrides such as SiCN,
sulfides such as TiS2 or GeS2, carbides such as SiC,
diamond-like coatings, amorphous silica or any combination of
the above. Particularly preferred in the present invention
is the use preceramic silicon-containing compounds or
polymers.
The preferred preceramic compounds to be used in
the process of this invention are ceramic oxide precursors
and, of these, precursors to SiO2 or combinations of SiO2
precur~ors with other oxide precursors are especially
preferred. The silica precursors which may be used in the
invention include, but are not limited to, hydrogen silses-
quioxane resin (H-resin), hydrolyzed or partially hydrolyzed
RXSi(Z)4 x or combinations of the above, in which R is an
aliphatic, alicyclic or aromatic substituent of 1-20 carbon
atoms such as an alkyl (e.g., methyl, ethyl, propyl), alkenyl
(e.g., vinyl or allyl), alkynyl (e.g., ethynyl), cyclopentyl,
cyclohexyl, phenyl etc., Z is a hydrolyzable 8ubstituent such
as a halogen (Cl, F, Br, I) or (OR) (e.g., methoxy, ethoxy,
phenoxy, acetoxy, etc.) and x is 0-2.
H-resin is used in this invention to describe a
variety of hydridosilane resins which may be either fully
condensed or those which may be only partially hydrolyzed
and/or condensed. Exemplary of fully condensed H-resins are
those formed by the process of Frye et al. in U.S. Patent
No. 3,615,272. This polymeric material has units of the
formula (HSiO3/2)n in which n is generally 10-1000. The
resin has a number average molecular weight of from about
800-2900 and a weight average molecular weight of between
about 8000-Z8,000 (obtained by GPC analysis using
polydimethylsiloxane as a calibration standard). When heated
sufficiently, this material yields a ceramic coating
essentially free of SiH bonds.
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Exemplary H-resin which may not be fully condensed
(polymers containing units of the formula HSi~OH)X0(3 x)/2)
include those of Bank et al. in ~.S. Patent No. 5,010,159 or
those of Weiss et al. in U.S. Patent No. 4,999,397. Bank et
al. de8cribes a process which comprises hydrolyzing hydrido-
silanes in an arylsulfonic acid hydrate hydrolysis medium to
form a resin which i8 then contacted with a neutralizing
agent. Recent experimentation has shown that an especially
preferred H-resin which forms substantially crack-free
coatings may be prepared by this method in which the
acid/silane ratio is greater than about 2.67:1, preferably
about 6/1. Weiss et al. describe a process which comprises
hydrolyzing trichlorosil~ne in a non-sulfur containing polar
organic solvent by the addition of water or HCl and a metal
oxide. The metal oxide therein acts as a HCl scavenger and,
thereby, serves as a continuous source of water.
Exemplary of H-resin which is not fully hydrolyzed
or condenset is that having units of the formula
HSi(OH)x(OR)yOz/2, in which each R i8 independently an
organic group which, when bonded to silicon through the
oxygen atom, forms a hydrolyzable sub8tituent, x = 0-2, y =
0-2, z = 1-3, x ~ y + z = 3 and the average value of y over
all of the units of the polymer is greater than 0. Examples
of R groups in the above equation include alkyls of 1-6
carbon atoms such as methyl, ethyl and propyl, aryls such as
phenyl and alkenyls such as vinyl. These resins may be
formed by a process which comprises hydrolyzing a hydrocar-
bonoxy hydridosilane with water in an acidified oxygen-
containing polar organic solvent.
The second type of silica precursor material useful
herein includes hydrolyzed or partially hydrolyzed compounds
of the formula RxSi(Z)4 x in which R, Z and x are as defined
above. Specific compounds of this type include
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methyltriethoxysilane, phenyltriethoxysilane,
diethyldiethoxysilane, phenyltrichlorosilane,
methyltrichlorosilane, methyltrimethoxysilane,
dimethyldimethoxysilane, phenyltrimethoxy~ilane,
vinyltrimethoxysilane, tetramethoxysilane, tetraethoxysilane,
tetrapropoxysilane and tetrabutoxysilane. Compounds in which
x = 2 are generally not used alone as volatile cyclic
structures are generated during pyrolysis, but small amounts
of said compounds may be cohydrolyzed with other silanes to
prepare useful preceramic materials.
The addition of water to a solution of these
compounds in an organic solvent results in hydrolysi~ or
partial hydrolysis. Generally, a small amount of an acid or
base is used to facilitate the hydrolysis reaction. The
resultant hydrolyzates or partial hydrolyzates may comprise
silicon atoms bonded to C, halogen, OH or OR groups, but a
substantial portion of the material is believed to be
condensed in the form of soluble Si-O-Si resins.
Additional 8ilica precursor materials which may
function equivalently in thi8 invention include condensed
e8ter8 of the formula (RO)3SiOSitOR)3, disilanes of the
formula (RO)xRySiSiRy(OR)x, compounds containing structural
units such as SiOC in which the carbon containing group is
hydrolyzable under the thermal conditions or any other source
of SiOR.
In addition to the above SiO2 precursors, other
ceramic oxide precursors may also be advantageously used
herein either as the sole compound or in combination with the
above SiO2 prec~rsors. The ceramic oxide precursors
specifically contemplated herein include compounds of various
metals such as aluminum, titanium, zirconium, tantalum,
niobium and/or vanadium as well as various non-metallic
compounds such as those of boron or phosphorous which may be
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dissolved in solution, hydrolyzed and subsequently pyrolyzed
at relatively low temperatures and relatively rapid reaction
rates to form ceramic oxides.
The above ceramic oxide precursor compounds
generally have one or more hydrolyzable groups bonded to the
above metal or non-metal, depending on the valence of the
metal. The number of hydrolyzable groups to be included in
these compounds is not critical as long as the compound is
soluble in the solvent. Likewise, selection of the exact
hydrolyzable substituent is not critical since the
sub~tituents are either hydrolyzed or pyrolyzed out of the
system. Typical hytrolyzable groups include, but are not
limited to, alkoxy, such as methoxy, propoxy, butoxy and
hexoxy, acyloxy, such as acetoxy, other organic groups bonded
to said metal or non-metal through an oxygen such as
acetylacetonate or ar amino group~. Specific compounds,
therefore, include zirconium tetracetylacetonate, titanium
dibutoxy diacetylacetonate, aluminum triacetylacetonate ant
tetraisobutoxy titanium.
When SiO2 i9 to be combined with one of the above
ceramic oxide precur90rs, generally it is used in an amount
such that the final ceramic contains 70 to 99.9 percent by
weight SiO2.
The above preceramic compound is then formed into
the desired coating. The preferred method of forming the
coating comprises coating a substrate with a solution
comprising a solvent and the preceramic compound or compounds
followed by evaporating the solvent and heating.
If such a solution approach is used to form the
coating, the preceramic solution is generally formed by
simply dissolving the preceramic compound in a sol~ent or
mixture of solvents. Various facilitating measures such as
stirring and/or heat may be used to assist in the
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dissolution. The solvents which may be used in this method
include, for example, alcohols such as ethyl or isopropyl,
aromatic hydrocarbo~s such as benzene or toluene, alkanes
such as n-heptane or dodecane, ketones, cyclic dimethylpoly-
siloxanes, esters or glycol ethers, in an amount sufficient
to dissolve the above materials to low solids. For instance,
enough of the above solvent can be included to form a 0.1-85
weight percent solution.
If hydrogen silsesquioxane resin is used, a
platinum or rhodium catalysts may also be included in the
above coating solution to increase the rate and extent of its
conversion to silica. Any platinum or rhodium compound or
complex that can be solubilized in this solution will be
operable. For instance, an organoplatinum composition such
as platinum acetylacetonate or rhodium catalyst
RhC13[S(CH2CH2CH2CH3)2]3, obtained from Dow Corning
Corporation, Midland, Michigan, are all within the scope of
this invention. The above cataly~ts are generally added to
the solution in ~n amount of between about 5 and 500 ppm
platinum or rhodium based on the weight of resin.
The solution containing the preceramic compound(s),
solvent and, optionally, a platinum or rhodium catalyst is
then coated onto the substrate. The method of coating can
be, but is not limited to, spin coating, dip coating, spray
coating or flow coating.
The solvent is allowed to evaporate resulting in
the deposition of a preceramic coating. Any suitable means
of evaporation such as simple air drying by exposure to an
ambient environment or the application of a vacuum may be
used. It is to be noted that when spin coating is used, an
additional drying period i~ ~enerally not nece9~ary as the
spinning drives off the solvent.
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Although the above described methods primarily
focus on forming a preceramic coating by a solution method,
one skilled in the art would reco~nize that other equivalent
means of producing the porous ceramic coating would also
function herein and are contemplated to be within the scope
of this invention.
The preceramic coating is then converted to the
porous ceramic coating by heatin8 it to a temperature
sufficient for ceramification without causing complete
densification. Generally, the temperature is in the range of
about 50 to about 800C. depending on the pyrolysis
atmosphere and the preceramic compound. For silica
precursors, temperatures in the range of about 50 to about
600C., preferably 50-400C., are generally used. The
preceramic coatings are usually sub~ected to these
temperatures for a time sufficient to form the porous
ceramic, generally up to about 6 hours, with a range of
between about 5 minutes and about 2 hours being preferred.
The above heating may be conducted at any effective
atmospheric pressure from vacuum to superatmospheric and
under any effective oxidizing or non-oxidizing gaseous
environment such as those comprising air, 2~ an inert gas
(N2, etc.), ammonia, amines, moisture, etc.
Any method of heating such as the use of a
convection oven, rapid thermal processing, hot plate or
radiant or microwave energy is generally functional herein.
The rate of heating, moreover, is also not critical, but it
is most practical and preferred to heat as rapidly as
possible.
The resultant porous ceramic coating is then
infiltrated with a silicone polymer. It should be noted that
the expression "silicone polymer" as used herein is meant to
include homopolymers, copolymers and branched or
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crosslinked polymers. In addition, it is contemplated that
silicon monomers ~eg., dimethyl dimethoxysilane) may be
infiltrated into the pores and hydrolyzed in situ to form the
silicone polymer. Such polymers can be in the form of a
fluid or a resin and generally have the structures:
R - Si - 0 - Si - 0~ - Si - ~ or Si - 0 l
R n R R n
in which each R is independently a hydrogen, a hydroxyl, an
alkyl such as methyl, ethyl, propyl, etc., an alkenyl such as
vinyl, an aryl such as phenyl or a siloxy and n is in the
range of about 0-1000. These polymers are well known in the
art and can be produced by known techniques. Exemplary
compounds include polydimethylsiloxanes having viscosities in
the range of about 0.65 to 600,000 centistokes, hydroxy-
terminated polydimethylsiloxane, polyphenylmethyl~iloxanes,
polyvinylmethylslloxanes, vinyl-terminated polydimethyl-
siloxane, methylhydrogenpoly8iloxanes, dimethyl, methyl-
hydrogen polysiloxane copolymers, methyvinyl cyclosiloxanes
and the like. Of the polydimethylsiloxanes, tho~e with a
viscosity in the range of about 500-10,000 centistokes are
particularly preferred. Polysiloxanes having lower
viscosities (eg., 10-10,000 centistokes) which can be cured
in place are also preferred. For instance, polysiloxanes
containing Si-H and/or Si-Vinyl groups can be cured with
curing catalysts such as peroxides or platinum.
These silicones may be used neat or they may be
dissolved in solvents for infiltration. Similarly, the
polymers may be filled with other materials such as silica to
aid in formation of a desirable nanocomposite. Such filler
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materials, however, should be sufficiently small to allow
entry into the pores.
The polymers are infiltrated into the porous
ceramic coating by known infiltration techniques. For
instance, the ceram'c may be vacuum infiltrated, high
pres~ure infiltrated or infiltrated by solution or
supercritical fluid techniques. After infiltration, any
excess polymer may then be wiped off or left on the surface
to provide a thicker silicone coating. If curable silicones
are used, they can be cured in place with heat or any
suitable curing agent or technique.
By the above methods, infiltrated ceramic
nanocomposites coatings are produced. These coatings are
useful on various substrates as protective coatings, as
corrosion resistant and abrasion resistant coatings, as
temperature and moisture resistant coatings and as a
diffusion barrier against ionic impurities such as sodium and
chloride.
Additional coatings may be applied over the nano-
composite coating if de9ired. These can include, for
example, SiO2 coatings, SiO2/ceramic oxide layers, silicon
containing coatings, silicon carbon containing coatings,
silicon nitrogen containing coatings, silicon oxygen nitrogen
coatings, silicon nitrogen carbon containing coatings and/or
diamond like carbon coatings.
The silicon containing coating described above can
be applied by methods such as (a) chemical vapor deposition
of a silane, halosilane, halodisilane, halopolysilane or
mixtures thereof, (b) plasma enhanced chemical vapor
deposition of a silane, halosilane, halodisilane, halopoly-
silane or mixtures thereof or (c) metal assisted chemical
vapor deposition of a silane, halosilane, halodisilane,
halopolysilane or mixtures thereof. The silicon carbon
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coating can be applied by a means such as (1) chemical vapor
depo~3ition of a silane, alkylsilane, halosilane, halodi-
silane, halopolysilane or mixtures thereof in the presence of
an a:Lkane of one to six carbon atoms or an alkylsilane, (2)
plasJna enhanced chemical vapor deposition of a silane,
alkylsilane, halosilane, halodisilane, halopolysilane or
mixtures thereof in the presence of an alkane of one to six
carbon atoms or an alkylsilane or (3) plasma enhanced
chemical vapor deposition of a silacyclobutane or disila-
cyclobutane as further described in U.S. Patent
No. 5,011,706. The silicon nitrogen-containing coating can
be deposited by a means such as (A) chemical vapor deposition
of a silane, halosilane, halodisilane, halopolysilane or
mixtures thereof in the presence of ammonia, (B) plasma
enhanced chemical vapor deposition of a silane, halosilane,
halodisilane, halopolysilane or mixtures thereof in the
presence of ammonia, (C) plasma enhanced chemical vapor
deposition of a SiH4 N2 mixture such as that described by
Ionic Systems or that of Katoh et al. in the Japanese Journal
of Applied Physics, vol. 22, #5, ppl321-1323, (D) reactive
sputtering such as that described in Semiconductor
International, p 34, August 1987 or (E) ceramification of a
silicon and nitrogen containing preceramic copolymer. The
silicon oxygen nitrogen containing coatings can be deposited
by methods well known in the art such as the chemical vapor
deposition, plasma enhanced chemical vapor deposition or low
pressure chemical vapor deposition of a silicon compound
(e.g., silane, dichlorosilane, etc.) with a nitrogen source
(e.g., am~onia) and an oxygen source (e.g., oxygen, nitrogen
oxides, etc.) by the pyrolysis of a silicon oxynitride
precurqor or by the pyrolysis of a silicon compound in an
environment which results in the formation of a silicon
oxynitride coating. The silicon carbon nitrogen-containing
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coating can be deposited by a means such as (i) chemical
vapor deposition of hexamethyldisilazane, (ii) plasma
enhanced chemical vapor deposition of hexamethyldisilazane,
(iii) chemical vapor deposition of silane, alkylsilane,
halosilane, halodisilane, halopolysilane or mixture thereof
in the presence of an alkane of one to six carbon atoms or an
alkylsilane and further in the presence of ammonia, (iv)
plasma enhanced chemical vapor deposition of a silane, alkyl-
silane, halosilane, halodisilane, halopolysilane or mixture
thereof in the presence of an alkane of one to six carbon
atoms or an alkylsilane and further in the presence of
ammonia and (v) ceramification of a preceramic polymer
solution comprising a carbon substituted polysilazane,
polysilacyclobutasilazane or polycarbosilane in the presence
of ammonia. The diamond-like carbon coatings can be applied
by exposing the substrate to an argon beam containing a
hydrocarbon in the manner described in NASA Tech Briefs,
November 1989 or by one of the methods described by Spear in
J. Am. Ceram. Soc., 72, 171-191 (1989). The silicon dioxide
coating (which may contain a modifying ceramic oxide) is
applied by the ceramification of a preceramic mixture
comprising a silicon dioxide prec~rsor (and a modifying
ceramic oxide precursor) as in the initial coating.
The following non-limiting example is included so
that one skilled in the art may more readily understand the
invention.
ExamPle
Hydrogen silsesquioxane resin made by the method of
Collins et al. in V.S. Patent No. 3,615,272 was diluted to
1.25 wt.% in heptane. A platinum catalyst comprising
platinum acetylacetonate in toluene was added to the solution
at a concentration of approximately 100 ppm platinum based on
the weight of H-resin.
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Fifty CMOS 14011 devices were cleaned with a W
GZone cleaning system and then 40 microliters of the above
H-re~3in solution was placed in the device cavity. The
solvent was allowed to evaporate. The device wa9 placed in
an oxygen plasma reactor and heated to 250C. while being
treated with oxygen plasma for 3 hours. The resultant silica
coating was about 2000 angstroms thick.
Ten of the above coated devices were retained as
controls and 4 sets of 10 devices were infiltrated
respectively with 40 microliters of 100 centistoke (cs)
polydimethylsiloxane (PDMS) fluid, 1000 cs PDMS, a 40%
toluene solution of 10,000 cs PDMS and a 40% toluene solution
of 600,000 cs silicone gum. The devices were placed under a
vacuum of 25 inches of mercury followed by atmospheric
pressure for 3 cycles and the excess fluid was wiped off. In
addition, 20 CMOS 4011 devices (no ceramic coating) were
coated with 40 microliters of 10,000 cs PDMS.
All o the tevices (including controls) were
sub~ected to salt fog stressing in an Associated
Environmental Systems Salt Fog Chamber according to the test
procedure outlined in MIL-STD 883C. The devices were tested
for functionality in a parametric tester. The percent of
devices passing the parametric testing after 1, 3, 50, 100
and 250 hours salt fog exposure were examined. The results
are summarized in Table 1. All of the controls had failed
after 3 hours of exposure and all of the silicone (no ceramic
coating) coated devices failed within 1 hour while all of the
nanocomposites of the invention remained functional after 3
hours. All of the 1000 cs fluid infiltrated samples remained
functional at the end of the test at 250 hours. This example
clearly demonstrates that while neither the silica nor the
silicone alone provide extended salt protection, a
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nanocomposite of the two provided greater than a 100 fold
increase in salt fog protection.
Table 1 - Percentage of Devices Functional
Ceramic 10,000cs
Time Alone 100Cg lOOOc8 lOOOOCg 600 ~ O00CS Alone
1 hr 73 100 100100 100 0
3 hr 0 100 100100 100 0
50 hr 0 30 10090 100 0
100 hr 0 10 10070 80 0
250 hr 0 0 10020 20 0
Example 2
To demonstrate that the silicone polymer is within
the ceramic structure, two 1 inch wafers were spin coated
with a 10% solution of H-resin in a solvent compri3ing 95%
heptane and 5% dodecane. The solution was catalyzed with
platinum acetylacetonate in toluene at a concentration of
approximately 100 ppm platinum based on the weight of
H-resin. ~oth of the coated wafers were pyrolyzed as in
Example 1. One wafer was infiltrated with 1000 cs PDMS and
the surface washed by swabbing with toluene as the coated
wafer was spun at 2000 RPM on a spin coater. FTIR was
performed on both wafers and the results were compared. FTIR
clearly shows additional Si-C peaks in the infiltrated
sample, thus confirming the presence of the silicone within
the ceramic structure.
ExamPle 3
Hydrogen silsesquioxane resin made by the method of
Collins et al. in U.S. Patent No. 3,615,272 was diluted to 10
wt. % in toluene. A platinum catalyst comprising platinum
acetylacetonate in toluene was added to the solution at a
concentration of approximately 100 ppm platinum based on the
weight of H-resin.
Three 1 ~ 3 inch aluminum panels were cleaned with
toluene, isopropyl alcohol and a UV ozone cleaning system.
The panels were coated with the above H-resin solution and
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~pun at 2100 rpm. The coated panels were placed in a
Lindberg Furnace and heated to 400C. for 1.5 hours.
One of the above coated panels (#3) was retained as
a control, 1 panel (#1) was coated with a mixture comprising
essentially 60% dimethyl, methylhydrogen siloxane copolymer,
270 methyvinyl cyclosiloxane, 23% dimethylsiloxane dimethyl-
vinyl-terminated, 12% dimethylvinylated and trimethylated
silica and a platinum catalyst and the other panel (#2) was
coated with a mixture comprising essentially 59% dimethyl,
methylhydrogen siloxane copolymer, 2% methyvinylcyclo-
siloxane, 24% dimethylsiloxane dimethylvinyl-terminated, 13%
dimethylvinylated and trimethylated silica and a platinum
catalyst. The panels were placed under a vacuum of 25 inches
of mercury followed by atmospheric pressure for 3 cycles. In
addition, 2 panels (no ceramic coating) were coated with the
above polymer mixtures (# 4 and 5)(one mixture on each panel)
and one panel was left uncoated (#6).
Panels #1 and 4 were heated to 160C. for 20
minutes to cure the silicone polymer. Panels 2 and 5 were
heated at 100C. for 30 minutes to cure the ~ilicone polymer.
All of the panels were sub~ected to salt fog
stressing in an Associated Environmental Systems Salt Fog
Chamber with a lZ NaCl solution. The panels were placed in a
horizontal position in the chamber (coated surface up). The
panels were examined for corrosion by visual inspection and
by optical microscopy. The panels were examined after 5, 15,
90, 160, 230, 300, 470, 640 and 1000 hours salt fog exposure
were examined. The results are summarized in Table 2.
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Table 2 - Appearance of Panel After Exposure to Salt Spray
Panel Hour Result
1 5 No corrosion
Z 5 No corro~ion
3 5 Some possible signs of corrosion at
corners and edges
4 5 No corrosion
No corrosion
6 5 Some signs of corrosion at top edge
1 15 No corro~ion
2 15 No Corrosion
3 15 Some Al pitting/corrosion - not extensive
4 15 Some Al pitting/corrosion - possible blistering
No corrosion
6 15 Al pitting/corrosion - not exten~ive but greater
than other panels
1 90 No corrosion
2 90 No Corrosion
3 90 Corrosion
4 90 Extensive coating around edges - blistering
~xtensive corrosion - not as extensive as 4
6 90 Extensive corrosion all over
1 160 No corrosion
2 160 No corrosion
3 160 Corrosion around edges
4 160 Extensive corrosion stemming from edges
160 Corrosion mostly at edges
6 160 Extensive corrosion over entire panel
1 230 No corro~ion
2 230 No corrosion
3 230 Corrosion mostly at edges
4 230 Corrosion quite extensi~e stemming from edges
covering 40-50% of area
230 Corrosion mostly at edges
6 230 Covered completely with corrosion
The panels were again examined at 300 hours. The
corrosion looked similar to that at 230 hours except that the
corrosion on panels 3, 4 and 5 is more pronounced.
The panels were again examined at 470 hours. The
corrosion looked similar to that at 300 hours except for more
pronounced differentiation.
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.
. . . :
-18- ~ 7
The panels were again examined at 640 hours. No
corrosion on the nanocomposites of the invention. The
corrosion on all the other looked worse.
The panels were again examined at 1000 hours. The
results were similar to those obtained at 640 hours. The
nanocompo~ite~ of the invention survived the entire test.
.
~' ~
