Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
.,
Field of the Invention
The present invention relates generally to the art of
pyrolytic deposition of metal oxide films and more particularly to
- 5 the pyrolytic deposition of metal oxide films from aqueous solutions
of coating reactants.
The Prior Art
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The pyrolytic deposltion of metal oxides onto a glass sur-
face is described in U.S. Patent No. 3,660,061 to Donley et al.
Organometallic saltsj preferably acetylacetonates, are dissolved in
an organic vehicle such as methylene chloride. Other suitable solvents
include aliphatic and olefinic halocarbons, halogenated hydrocarbons,
alcohols and nonpolar aromatic compounds such as benzene and toluene.
The organic solution is sprayed onto a hot glass surface where it
~, 15 thermally decomposes to fonn a metal oxide film which changes the
reflectance and transmittance of solar energy by the glass.
In U.S. Pa~ent No. 3,411,934, Englehart et al disclose that
cobalt oxide is particularly suited for use as a coatin~ on glass be-
cause of its good solar heat shieldin~ properties. However, cobalt
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oxide coatings are not as uniform and adherent as desired. Englenart
et al teach that the adherence, durability and optical quality of
cobalt oxide films are improved by providing the glass surface with
a thin tin oxide undercoating and then overcoating with cobalt oxide
by thermal pyrolysis of a cobalt compound such as cobalt acetylacetonate.
Preferably, the cobalt oxide coating also contains the oxides of iron
and chromium since these oxides improve the scratch resistance of the
coating without detracting from the solar heat shielding properties
of the cobalt oxide~ A preferred solvent system for the metal coating
reactants comprises a polar organic compound and a nonpolar aromatic
compound, particularly methanol combined with either benzene or toluene.
Current interest in eliminating the health and environmental
hazards of using large volumes of organic solvents has encouraged the
development of aqueous coating compositions. It is known from U.S.
Patent ~o. 2,688,565 to Raymond that light reflecting coatings of cobalt
oxide may be deposited by contacting a hot glass surface with an aqueous
solution of cobalt acetate. ~owever, such films have a grainy, irregular
texture and are highly porous resulting in poor acid resistance evidenced
by debonding of the f ilm.
Summar~ of the Invention -
The present invention involves the pyrolytic deposition of a
spinel-type film containing cobalt and tin oxides by thermal decomposition
of an aqueous solution of a water soluble cobalt salt and a water soluble
tin compound. The re~ultant film is more uniform in appearance and less
porous than a cobalt oxide film which does not contain tin oxide. The
cobalt/tin oxide film is also more durable as evidenced by the fact that
it-withstands immersion in 0.5 percent hydrofluoric acid solution for S
minutes with no film debonding while a cobalt oxide film fails this
durability test.
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The cobalt and tin coating reactants are dissolved ln water
The aqueous solution is then applied to a glass surface at a sufficiently
high temperature to pyrolyze the coating reactants to form a metal oxide
film.
More particularly the invention provides a method for depositing
an electrically nonconductlve spinel-type film comprising the oxides of
cobalt and tin on a glass substrate comprising the steps of:
a. maintaining a substrate in an oxidi~ing atmosphere at a
temperature sufficient to pyroly~e metal compounds to
metal oxides;
b. contacting the surface of the substrate at said temperature
with an aqueous solution consisting essentially of water,
water soluble cobalt salt and a water soluble tin compound
capable of thermal decomposition to cobalt oxide and tin
oxide; and
c. thermally reacting said cobalt salt and said tin compound
in said oxidizing atmosphere to form a~ electrically noncon-
ductlve film compri~ing a cobalt/tin oxide spinel wherein
cobalt is the predominant metal in the film.
Description of the Preferred Embodiments
Aqueous solutions of a water soluble cobalt salt, preferably
cobalt acetate, and a water soluble tln compound, preferably dimethyltin
dichloride, are prepared wlth wide variation in the ratio of cobalt to tin.
The ratio of cobalt to tin i8 preferably about 2:1 to 2~:1 by weight and
more preferably about 5:1 to 12:1. The total metal concentratlon in the
solution preferably ranges from about 1 to 12 percent by weight and more
preferably from about 5 to 6 percent.
Preferred cobalt salts include cobalt nitrate and cobalt per-
chlorate as ~ell as cobalt acetate. Preferred water soluble tin compounds
7(~2
lnclude tin chlorides such as SnC12 and SnC14 and other alkyltin chlorides
such as methyltin trichloride, trimethyltin chloride, diethyltin dichloride,
diisopropyltin dichloride, stannic bisacetylacetone dichloride and stannic
acetate.
The aqueous solution of cobalt and tin coating reactants is ap-
plied to a surface of a glass substrate which is maintained at a temperature
sufficient to pyrolyze the coating reac~ants to form an oxide film, prefer-
ably at least about 500F. (about 260C.) and more preferably about 1000-
1200 F. (about 538 to 650 C.).
In a particularly preferred embodiment of the present invention,
a stock solution ~f cobalt acetate containing 5.0 percent by weight cobalt
is prepar2d by dissolving the cobalt acetate in water, preferably including
about 5 percent by weight glacial acetic acid to provide long shelf life.
The selected hydrolyzable tin compound is separately dissolved in water.
Coating solutions having a variety of cobaltltin ratios are prepared by
mixing the two solutions in various proportions.
A particularly preferred method for applying the above solution
to a hot glass surface is to spray the aqueous solution onto the surface of
a continuous glass ribbon formed on a bath of molten metal in a refractory
tank after the ribbon has been lifted from the bath and conveyed beyond the
reduci~g atmosphere which protects the bath. A detalled descriptlon of a
preferred method for the pyrolytic deposition of metal oxide films on glass
ln found $n U.S. Patent ~o. 3,660,061, commonly assigned.
The present invention will be further understood from the de-
scrlptions of specific examples whlch follow. Spectral properties of the
glass coated according to these examples are shown in Table I.
EXAMPLE I
A stock cobalt acetate solution is prepared by combining 21.13
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702
percent by weight cobalt acetate tetrahydrate, Co(C2H302)2 4 H20, 5 25
percent by weight glacial acetic acid, and 73.62 percent by weight water.
This stock cobalt solution contains 5 0 percent by weight cobalt. A stock
tin solution is prepared by dissolving 23.13 percent by weight dimethyltin
dichloride, (CH3)2 SnC12, in 76.87 percent by weight water. This stock tin
solution contains 12.5 percent by weight tln.
A coating solution for depositing a cobalt/tin oxide spinel-type
film is prepared by combining 100 parts by volume of the stock cobalt solu-
9 tion with 11.08 parts by volume of the stock tin solution. The ratio
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of cobalt to tin is 3.5 to 1.0 and the total metal concentration
- is 5.85 percent by weight. The coating solution is sprayed onto
a glass surface at a temperature of 1050 to 1070F. (about 566 to
577C.). The coating reactants pyrolyze to form a durable, uniform
cobalt/tin oxide spinel-type film on the glass surface.
EX~LES II THROUG~ VIII
Cobalt Tin Metal
Solution Solution Concentration Cobalt/Tin
(parts by (parts by (percent by (weight
Example volume) volume) weight~ ratio)
II 100 7.75 5-59 5.0/1.0
III 100 5.96 5.44 6.5/1.0
IV 100 5.17 5.38 7.5/1.0
V 100 4.56 5.34 8.5/1.0
VI 100 4.08 5.31 9.5/1.0
VII 100 3.88 5.29 10.0/1.0
VIII 100 3.52 5.26 11.0/1.0
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The above examples are offered to illustrate the present
invention. Various modifications apparent to ones skilled in the
art are included within the scope of the present invention. Other
water soluble metal compounds may be employed as well as ratios and
concentrations of metals outside the range of the specific examples.
Cobalt/tin oxide spinel-type coatings may be deposited in conjunction
with other films and on a variety of substrates other than glass,
particularly nonmetallic substrates such as ceramics and other re-
fractory materials. The scope of the present invention is defined by
the following claims.
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