Paintable compositions for protecting metal and ceramic substrates

Paintable compositions for the formation of coatings on, for example, iron-based metals that, when dry, inhibit deleterious reactions and emissions when the metal is heated to, or thermally cycled at, temperatures of about 600-900 degrees C. The preferred binder portion of the composition, which in itself provides reasonable protection when dry, consists essentially of an aqueous silica containing solution containing an aqueous alkali, together with oxides selected from the transition metals cobalt, chromium, iron, manganese, nickel, titanium, zinc and zirconium. The preferred ranges of composition are described as well as certain additives to enhance performance under various conditions. These include the use of filler materials, such as high expansion additives. The coating is useful for other metal and ceramic substrates to prevent or reduce deleterious damage to or emission from the surface at high temperatures.

TECHNICAL FIELD 
This invention relates to a paintable composition for applying to metal and 
ceramic substrates for primarily high temperature applications and, more 
particularly, to compositions to give protection to those substrates. 
Included are the applications for preventing or reducing deleterious 
damage to the surface of objects during high temperature treatment 
operations, for encasing certain ceramic materials (such as 
asbestos-containing substrates) to reduce environmental problems, for 
producing a protective coating for ladles used for molten metals and the 
like, etc. 
BACKGROUND ART 
It is commonplace in the metal-working industry to subject metals to 
various heating operations, e.g., for annealing and/or stress relieving or 
in conjunction with hot working operations. For example, a steel billet or 
slab, prior to rolling into rod or sheet, is commonly placed in a 
heat-treating furnace in which it is uniformly heated. During such 
heating, the surfaces of the metal are especially liable to suffer the 
effects of oxidation phenomena, e.g., the formation of a layer of the 
metal oxide on the surface of the metal object and/or the selective 
oxidation of an alloying constituent of the metal. The latter phenomenon 
is particularly exemplified by the surface decarburization of steel or 
other ferrous alloys. The effects may be exhibited by the formation of an 
oxide scale or, in the case of decarburization, by the creation of a 
surface layer which has changed chemical and physical characteristics. If 
this layer is extensive, it subsequently must be removed. Metal losses 
incurred in these ways can be severe and, therefore, very costly. The high 
temperature treatment of ceramic substrates also often leads to 
deleterious degradation of the surface. This is evidenced by corrosion, 
erosion and the like. It is, therefore, of prime importance that some 
means should be found of shielding the surfaces from reactive atmospheres 
during any heat-treating operation. 
It is well known that, in order to reduce these losses, small items may be 
subjected to their necessary heat treatment in a controlled inert or 
non-oxidizing atmosphere. Although this expedient has been fairly 
successful in many instances, expensive equipment is necessary, e.g., gas 
flow control apparatus and specially-constructed furnaces in which air may 
be prevented from entering. Furnaces in which the atmosphere can be 
controlled are suitable for heating small objects such as tools but it is 
costly to make use of such apparatus to heat large objects such as billets 
and slabs which may weigh several tons. Moreover, if the metal object is 
required to be removed from the furnace while still in a heated condition, 
fairly severe oxidation, decarburization or the like can still take place 
upon exposure to the atmosphere. 
Alternative means of protecting the surfaces of metal articles to be heated 
have therefore been developed. Thus, it is known to apply a paint to the 
surfaces of the metal before subjecting it to heat treatment. Such paints 
may include materials which are preferentially oxidized (e.g., powdered 
aluminum, ferrosilicon or silicon) and are thus intended to function in a 
sacrificial manner. Other types of paint depend upon the physical 
exclusion of the atmosphere from the surface by the ability of their 
constituents to form a glaze when heated. Materials used in such paints 
are mixtures of various refractory oxides, slags, silica and ground glass. 
The preferentially oxidized materials mentioned above have also been 
included in the glaze-forming preparations. Varying degrees of success 
have been achieved by the use of these known paints which are generally 
applied to the metal surface as a layer of the order of 1/8 inch thick. 
However, none of them has been found to be capable of consistently 
reducing oxidation losses to a satisfactory degree although, in some 
instances, the amount of metal lost as oxide scale has been reduced by as 
much as 70%. A reduction in losses even of this magnitude is, however, 
considered unsatisfactory in that the degree of oxidation still suffered 
is inevitably accompanied, in the case of steels, by surface 
decarburization. Thus, a machining operation is necessary to remove the 
decarburized layer. 
It may be observed in this connection that where a mechanical protection is 
to be achieved, as by a glaze, it is important that there should be no 
cracks or pinholes in the protective layer. Otherwise, the oxidation 
and/or decarburization effects tend to spread beneath the glaze far beyond 
the crack or pinhole itself. 
There are other applications where a high-temperature paintable composition 
would be useful. For example, it would be desirable to have a coating that 
can be applied to devices from which asbestos-containing materials have 
been removed. It is very difficult to remove all residue of the asbestos; 
therefore, a paintable sealant could be utilized to encase the device to 
prevent the escape of this residual asbestos. Some applications will 
involve subsequent operation at elevated temperatures. Since large surface 
areas may be involved in this application, the coating material should 
have low cost. 
Still another application for paintable coatings involves providing a 
protective surface for the base material (usually a ferrous metal) of 
ladles used for molten aluminum, magnesium, zinc, etc. This coating, to be 
effective, must be abrasion resistant, be relatively thick (0.005 to 0.125 
inch), and be adequately adherent even during thermal cycling. 
A very similar application is the forming of a coating on the interior 
surfaces of a "permanent" mold in, for example, the aluminum industry. 
This coating typically is up to 0.125 inch thick and must provide thermal 
insulation, quick release, etc. 
Typical of prior art coatings is that described in U.S. Pat. No. 3,440,112 
issued to F. E. G. Ravault on Apr. 22, 1969. This composition included 
silicon carbide, ferrosilicon, silica flour, bentonite, powdered glass and 
sodium or potassium cryolite to form a fusible glaze. Another of the prior 
art protective coatings is described in U.S. Pat. No. 3,861,938, issued to 
R. P. Jackson on January 21, 1975. The coating of this reference involves 
the use of an alkali-stabilized sol form of silica together with chromic 
oxide formed by the in situ oxidation of chromium metal. 
U.S. Pat. No. 3,037,878, issued to R. J. Cowles, et al., on June 5, 1092, 
describes another coating composition for use in protecting metals against 
oxidation and/or decarburization during heat treatment. The composition 
involves oxides of aluminum, silicon and an alkali metal which fuse to 
form various crystalline phases. This coating is used at thicknesses of 
1/64 to 1/32 inch (15.6 to 31.2 mils). 
Another protective coating is described in U.S. Pat. No. 3,301,702, issued 
to S. L. Ames, et al., on Jan. 31, 1967. This coating, for which the 
surface must first be cleaned, consists of an alkali metal silicate and 
aluminum oxide. 
A coating based upon sodium metaborate is described in U.S. Pat. No. 
2,785,091, issued to C. A. M. Rex on Mar. 12, 1957; a coating based upon 
mica is described in U.S. Pat. No. 2,774,681, issued to P. Huppert, et 
al., on Dec. 18, 1956; and coatings based upon self-spalling ceramics are 
described in U.S. Pat. Nos. 3,459,601 and 3,459,602, issued to E. E. 
Muller on Aug. 5, 1969. Other patents generally related to protective 
coatings are: U.S. Pat. Nos. 3,399,078, issued to C. A. M. Bang on Aug. 
27, 1968; 3,454,433, issued to E. E. Muller on July 8, 1969; 3,178,321, 
issued to W. R. Satterfield on Apr. 13, 1965; and 3,677,796, issued to R. 
T. Girard, et al., on July 18, 1972. 
In general, the compositions of the above-cited prior art have certain 
drawbacks. Those compositions that form glass-like coatings at the 
temperatures of heat treatments often transfer a portion of the glaze to 
rolls of a rolling mill or to other handling apparatus. This type of glaze 
also can cause coated pieces to bond together when placed in contact with 
each other at a high temperature. This, of course, is detrimental to the 
equipment. Some coatings can only be removed using some form of 
substantial abrasion after the heat treatment step. For other 
compositions, numerous layers must be applied (and dried) before a 
thickness is achieved that will give satisfactory protection against 
oxidation and/or decarburization, etc. Furthermore, as discussed above, 
the surface of the item to be protected must be first cleaned before use 
of certain of the protective coatings. 
The paintable composition described in our above-referenced U.S. Pat. No. 
4,898,618, the content of which is included herein by reference, provides 
a suitable composition for most of the applications described above. 
However, several of the specific compositions disclosed therein are 
relatively expensive and therefore are precluded from applications where 
large quantities are required. Of the compositions in that patent 
application, the composition disclosed in Example 8 is a dilute 
composition of reduced cost; however, this composition is too expensive 
for some of the applications such as the asbestos sealant coating. 
Accordingly, it is an object of the present invention to provide a 
paintable composition for use in the protection of a substrate, such as a 
metal object, against corrosion, oxidation and/or decarburization, etc., 
during heat treating steps at elevated temperatures to about 2400 degrees 
F. 
It is another object to provide a coating composition for this protection 
that can be applied to the surface in thin coats (a few mils) and result 
in satisfactory protection. 
Another object is to provide a protective coating composition that can be 
applied without previous treatment of the surface. 
A further object of the present invention is to provide a protective 
coating composition which will not adversely affect apparatus used to 
process the item after the heat treating step or cause similarly coated 
pieces to bond together during heating. 
It is also an object of the present invention to provide a coating 
composition that can be used on essentially all iron-based materials and, 
thus, is compatible with the various expansion behaviors of these 
materials. 
An additional object of the present invention is to provide a paintable 
coating composition that provides a sealant to prevent the escape of 
environmental substances from a substrate. 
Also, it is an object of the present invention to provide a paintable 
composition which can be applied to produce coatings of sufficient 
thickness to protect ladles used for molten metals and the like, such as 
molten aluminum, magnesium and zinc. 
It is another object of the present invention to provide a paintable 
composition for various high temperature applications having a 
sufficiently low cost such that the composition can be used for coating 
extensive surfaces economically. 
Additionally, it is an object of the present invention to provide a 
paintable composition that can be used to produce a coating of up to about 
0.125 inch in molds used in casting of molten metals. 
These and other objects of the present invention will become apparent upon 
a consideration of the full description of the invention which follows. 
DISCLOSURE OF THE INVENTION 
In accordance with the present invention, there is provided a composition 
which can be painted upon various substrates. These include metal surfaces 
to be protected against oxidation and/or decarburization, etc., during 
heat treating steps to about 2400 degrees F. (1300 degrees C.). Other 
applications include use as a sealant or as a ladle coating, for example. 
This is a water-based composition that, when dry, is adherent and highly 
water insoluble. This composition is particularly applicable for 
iron-based materials, although it has use with other metals and ceramics. 
The preferred composition includes colloidal silica (SiO.sub.2), potassium 
hydroxide (KOH) and transition metal oxides (TMO). Other alkali ions can 
be used, such as Li, or Na, and various powder additives can be used when 
those powder additives are compatible with alkaline systems having a pH of 
about 11. Specifically, the TMO of value is the oxide of any transition 
metal selected from cobalt, chromium, iron, manganese, nickel, titanium, 
zinc and zirconium. Of these, the oxides of cobalt, iron and manganese are 
preferred. The preferred levels of these main ingredients are: 23-47 wt % 
colloidal silica solution (30% colloidal SiO.sub.2, 0.45% Na.sub.2 O); 
28-56 wt % potassium hydroxide solution (45% KOH in water); and 19-25 wt % 
TMO (oxide of selected transition metals). For some applications, a 
pre-reacted silicate solution is useful as at least a partial substitution 
for the KOH solution. Certain pigments, fillers and expansion modifying 
agents, such as nepheline syenite, calcium carbonate, and mixtures 
thereof, can be added for specific applications. Also, additives can be 
included to improve paintability/suspension; these include sodium 
carbomethylcellulose (CMC), hectorite clay and/or acrylics. 
BEST MODE FOR CARRYING OUT THE INVENTION 
To be suitable for protecting metal against oxidation, decarburization 
and/or other deleterious chemical actions occurring at elevated 
temperatures, the coating material must be easily applied to provide a 
complete coat, readily dried, and preferably should be water insoluble 
when dry. Protection should be afforded by relatively thin coatings. Any 
diluent for these compositions must be removable by vaporization to 
provide a dry coating. 
In order to evaluate compositions for use of the present invention for 
protecting metal surfaces, sample compositions were applied to the surface 
of a stainless steel spatula. The coatings were dried and then subjected 
to various performance tests such as adherence, paintability, hardness and 
water insolubility. Protection of the substrate metals was demonstrated by 
heating in air at temperatures up to about 2400 degrees F. (1300 degrees 
C.). Evaluation tests were generally conducted on type 4330 steel rods 1/2 
inch in diameter and 11/2 inches long. One to three thin coatings were 
applied. Complete drying was achieved between each coating when multiple 
coats were applied. The final protective coatings were less than 10 mils 
thick. Generally the coated test sample was heated to 1050-1080 degrees C. 
in one hour and held at that temperature for one hour. As in many other 
coating applications, the composition includes a basic binder portion 
together with additives to achieve selected properties for selected 
applications. These applications include, for example, substantially 
permanent coatings (e.g., for cyclic applications) versus coatings that 
are substantially self-separating ("pop-off"). 
Initial studies were performed to evaluate the essential constituents of 
the binder portion, referred hereinafter as the "Triplex Binder System" 
because of the three components: colloidal silica solution, alkali oxides 
(in the form of aqueous hydroxide solutions) and certain transition metal 
oxides. The hydroxide solutions typically are standard concentrations: 45% 
KOH in water; 50% NaOH in water and 18% LiOH.H.sub.2 O in water. These can 
be represented as SiO.sub.2, R.sub.2 O (where R is Na, K and/or Li), and 
TMO (transition metal oxide), respectively. These initial tests 
demonstrated that when the colloidal silica (a commercial suspension of 8 
millimicron SiO.sub.2, 30 wt %, having 0.45 wt % Na.sub.2 O and pH of 
10.7) was used alone, poor adherence and poor high temperature protection 
occurs. Improved adherence was obtained, as well as protection, using a 
hydroxide solution (especially KOH) alone as the binder; however, problems 
associated with drying were experienced as well as the problem of handling 
a very caustic solution. 
Although NaOH and LiOH can be used in the formulation, results using KOH 
(with all other constituents constant) were far superior. Accordingly, 
most further tests were limited to the use of the standard concentration 
KOH solution. Some tests were conducted with a 2:1 ratio of the standard 
KOH solution and the standard NaOH solution. These were commercial 
solutions as available from suppliers. 
A mixture including colloidal silica suspension and KOH solution gave good 
adherence to the metal, good drying characteristics, and a hard coating. 
Some spalling occurred, however, during heating with the result that some 
oxidation/decarburization was noted. However, the addition of certain 
TMO's overcame this spalling tendency. 
Tests using just the colloidal silica suspension and TMO constituents 
likewise exhibited inadequate protection even though initially the coating 
appeared to cover the surface. Further, a combination of just KOH and the 
TMO constituents gave results similar to KOH alone. 
On the basis of these initial tests, a preferred range of the constituents 
of the Triplex Binder System was determined to be: 
Silica-containing Solution 23-56.5 wt % 
Potassium Hydroxide Solution14-57 wt % 
TMO Addition 8.5-53.5 wt % 
Various of the transition metal oxides were investigated for use in this 
binder composition. With all other constituents optimized, very good 
results were obtained using Co.sub.3 O.sub.4 and MnO.sub.2. Slightly 
poorer results were obtained using Fe.sub.2 O.sub.3, Cr.sub.2 O.sub.3 and 
NiO, with marginal results being obtained using TiO.sub.2, ZnO and 
ZrO.sub.2. Scandium oxide (Sc.sub.2 O.sub.3) was not tested due to its 
cost, and oxides of copper and vanadium were not useful for various 
reasons. It will be understood that precursors of the TMO's can be used 
that will dissociate into, or form, the oxides at high temperatures. This 
includes, for example, nitrates, sulfates, carbonates, hydroxides, etc., 
as well as the TMO metals that will oxidize upon heating (firing). 
The results were generally the same for various sources of the 
silica-containing solution. Tested in this connection were KASIL No. 6, 
NYACOL-830, and silicate Type D, as available from Nyacol Products, Inc., 
an affiliate of the PQ Corporation, P.O. Box 349 Ashland, Mass., and 
LITHSIL No. 4 available from Lithium Corp. of America, 449 N. Cox Road, 
Gastonia, N.C. All of these contained 27.+-.9 wt % finely divided 
SiO.sub.2 as colloidal suspensions or solutions in water, and all 
performed substantially equally. NYACOL-830 is a colloidal silica 
suspension. The other sources of silica-containing solution are 
pre-reacted R.sub.2 O-SiO.sub.2, thus providing a portion of the needed 
R.sub.2 O of the binder. 
In order that the composition is easily "paintable", a diluent is needed. 
The diluent must, however, be completely removed during drying of the 
coating. The most typical diluent for these compositions is water. Aqueous 
acrylic diluents are also known for this use. Such a diluent is, for 
example, a combination of about 3 parts by weight of an aqueous acrylic 
polymer solution (e.g., Acrysol A-1 polyacrylic acid) with one part by 
weight of an aqueous acrylic emulsion (e.g., Rhoplex AC-64 Emulsion). The 
Acrysol A-1 and the Rhoplex AC-64 are available from Rohm and Haas of 
Philadelphia, Pa. The Rhoplex is 40 wt % water and 60 wt % acrylic 
polymer. The Acrysol is 75 wt % water and 25 wt % polyacrylic acid. 
As stated above, various additions can be made to the Triplex Binder System 
for specific applications. One such addition is a color pigment such as a 
yellow pigment (e.g., No. 51498, available from Drakenfeld-Ciba-Geigy 
Corp., P.O. Box 519, Washington, Pa.). This pigment is a pre-reacted 
material consisting essentially of 40 wt % TiO.sub.2, and 20 wt % of each 
of the oxides Cr.sub.2 O.sub.3, Na.sub.2 O and Sb.sub.2 O.sub.3. This 
particular additive, in addition to providing a color to the coating, was 
found to improve the performance of the resultant coating. A principal 
constituent of this particular pigment, other than the TMO and R.sub.2 O, 
is antimony oxide (Sb.sub.2 O.sub.3). A study of this constituent, when 
added to the binder system, resulted in a range of optimum effectiveness 
of about 2.2 wt % to about 5.2 wt % in the binder although useful coatings 
can be obtained without the use of Sb.sub.2 O.sub.3. 
In order to minimize cracking, spalling, etc., when an object is to be 
repetitively heated, the coating is improved through the use of a "high 
expansion" oxide additive. One such substance is nepheline syenite powder. 
Nepheline syenite is a holocrystalline, granular, igneous rock, whose 
principal constituents are SiO.sub.2 (60.4%), Al.sub.2 O.sub.3 (23.6%), 
Na.sub.2 O (9.8%) and K.sub.2 O (4.6%). This, when added at about 35 wt % 
to about 40 wt % to the binder, provides a coating that can be easily 
applied and withstands the effects of expansion and contraction of the 
base metal during any thermal cycling. 
In contrast, there are applications where the coating must only withstand 
one heating cycle and, preferably, "self-destruct" after danger of 
oxidation/decarburization is eliminated. For such application a "low 
expansion" additive, or an additive with a large volumetric change from a 
phase transition, can be mixed with the binder. Typical materials for this 
application are SiO.sub.2 powder (large volumetric change) or low 
expanding kyanite or kaolin clays; however, other clays are known for this 
property. A coating including SiO.sub.2 powder was observed to "pop-off" 
when the coated object was quenched in air from 950 degrees C. A mixture 
of these two types of expansion additives can produce a coating that is 
more easily removed, as by a water spray or quench, following heat 
treating operations. 
Other materials having known property-altering characteristics, or serving 
as fillers, can be added to the binder if they are compatible with the 
basic (about pH11) nature of the solutions. These include, for example, 
SiO.sub.2, Fe.sub.2 O.sub.3, Al.sub.2 O.sub.3 and ZrO.sub.2.

The following examples contain compositions that are illustrative of 
coatings that are effective for the protection of an iron-based metal 
during heating to about 1300 degrees C. against any substantial oxidation 
and/or decarburization. The values of the constituents are in wt %. 
______________________________________ 
EXAMPLE 1 
______________________________________ 
Binder: Colloidal Silica Sol. 
20.18 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
17.86 
(45% KOH in water) 
Yellow Pigment.sup.(a) 
12.00 
Diluent: Water 11.97 
Additive: Nepheline Syenite 
38.00 
______________________________________ 
.sup.(a) Pre-reacted TMO: 2.40% Na.sub.2 O; 4.80% TiO.sub.2 ; 2.40% 
Cr.sub.2 O.sub.3 ; 2.40% Sb.sub.2 O.sub.3 
______________________________________ 
EXAMPLE 2 
______________________________________ 
Binder: Colloidal Silica Sol. 
16.93 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
10.35 
(45% KOH in water) 
Unreacted TMO: Co.sub.3 O.sub.4 
4.33 
Yellow Pigment.sup.(b) 
4.33 
Diluent: Water 5.49 
Acrylic 7.94 
Additives: Alumina Powder 4.31 
Nepheline Syenite 
37.04 
Silica Powder 9.09 
______________________________________ 
.sup.(b) Pre-reacted TMO: 0.90% Na.sub.2 O; 1.81% TiO.sub.2 ; 0.90% 
Cr.sub.2 O.sub.3 ; 0.90% Sb.sub.2 O.sub.3 
______________________________________ 
EXAMPLE 3 
______________________________________ 
Binder: Colloidal Silica Sol. 
18.04 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
11.03 
(45% KOH in water) 
Unreacted TMO: MnO.sub.2 
4.45 
Yellow Pigment.sup.(c) 
4.28 
Diluent: Water 5.85 
Acrylic 8.46 
Additives: Alumina Powder 4.10 
Nepheline Syenite 
35.16 
Silica Powder 8.63 
______________________________________ 
.sup.(c) Pre-reacted TMO: 0.86% Na.sub.2 O; 1.71% TiO.sub.2 ; 0.86% 
Cr.sub.2 O.sub.3 ; 0.86% Sb.sub.2 O.sub.3 
______________________________________ 
EXAMPLE 4 (BINDER ALONE) 
______________________________________ 
Colloidal Silica Sol. 
12-56.5 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
14-57 
(45% KOH in water) 
TMO* 8.5-53.5 
Sb.sub.2 O.sub.3 0-5 
______________________________________ 
*Oxides (prereacted or physically mixed) of at least one of the metals 
cobalt, manganese, chromium, nickel, iron, titanium, zinc, zirconium. 
______________________________________ 
EXAMPLE 5 (BINDER ALONE) 
______________________________________ 
Colloidal Silica Sol. 
47 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
29 
(45% KOH in water) 
TMO* 25 
______________________________________ 
*Oxides (prereacted or physically mixed) of at least one of the metals 
cobalt, manganese, chromium, nickel, iron, titanium, zinc, zirconium. 
______________________________________ 
EXAMPLE 6 
______________________________________ 
Binder: Colloidal Silica Sol. 
16.55 
(10% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
10.12 
45% KOH in water) 
Unreacted TMO ZrO.sub.2 
6.48 
Yellow Pigment.sup.(d) 
4.42 
Diluent: Water 5.37 
Acrylic 7.76 
Additives: Alumina Powder 4.21 
Nepheline Syenite 
36.21 
Silica Powder 8.89 
______________________________________ 
.sup.(d) Pre-reacted TMO: 0.88% Na.sub.2 O; 1.77% TiO.sub.2 ; 0.88% 
Cr.sub.2 O.sub.3 ; 0.88% Sb.sub.2 O.sub.3 
______________________________________ 
EXAMPLE 7 
______________________________________ 
Binder: Colloidal Silica Sol. 
14.70 
(10% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
8.75 
(45% KOH in water) 
Unreacted TMO: MnO.sub.2 
4.07 
Yellow Pigment.sup.(e) 
2.40 
Diluent: Water 11.55 
Additive: Nepheline Syenite 
58.51 
______________________________________ 
.sup.(e) Pre-reacted TMO: 0.48% Na.sub.2 O; 0.96% TiO.sub.2 ; 0.48 
Cr.sub.2 O.sub.3 ; 0.48% Sb.sub.2 O.sub.3 
______________________________________ 
EXAMPLE 8 
______________________________________ 
Binder: Colloidal Silica Sol. 
17.68 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
10.53 
(45% KOH in water) 
Unreacted TMO: 
MnO.sub.2 
3.66 
Fe.sub.2 O.sub.3 
2.14 
Diluent: Water 13.89 
Additives: Nepheline Syenite 
26.00 
Kaolin 26.00 
______________________________________ 
______________________________________ 
EXAMPLE 9 
______________________________________ 
Binder: Colloidal Silica Sol. 
21.26 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
12.99 
(45% KOH in water) 
Unreacted TMO: Co.sub.3 O.sub.4 
4.44 
Yellow Pigment.sup.(f) 
11.11 
Black Pigment.sup.(g) 
33.33 
Diluent: Water 6.89 
Acrylic 9.97 
______________________________________ 
.sup.(f) Pre-reacted TMO: 2.67% Na.sub.2 O; 5.35% TiO.sub.2 ; 2.67% 
Cr.sub.2 O.sub.3 ; 2.67% Sb.sub.2 O.sub.3 
.sup.(g) Pre-reacted TMO: 24.86% Cr.sub.2 O.sub.3 ; 15.24% Fe.sub.2 
O.sub.3 
______________________________________ 
EXAMPLE 10 (BINDER ALONE) 
______________________________________ 
Silicate Solution (K, Na, Li) 
64-83% 
(27 .+-. 9% SiO.sub.2 ; 1.6-14% R.sub.2 O; H.sub.2 O) 
R.sub.2 O Aqueous Solution 
6-28% 
(Hydroxide of K, Na, Li) 
(45% KOH, 50% NaOH, 18% LiOH.H.sub.2 O 
in water) 
TMO* 8-11% 
Sb.sub.2 O.sub.3 0-2% 
______________________________________ 
*Oxides (prereacted or physically mixed) of at least one of the metals 
cobalt, manganese, chromium, nickel, iron, titanium, zinc, zirconium. 
From the foregoing, it will be understood by those versed in the art that a 
type of composition has been provided to use as a coating for iron-based 
metals to inhibit oxidation, decarburization or the like during 
high-temperature treatments. Although directed specifically toward 
coatings for iron-based metals, the compositions have applications for 
other metals, such as copper and titanium, ceramics and/or graphite. The 
general formulation includes a silica-containing liquid, an alkali 
hydroxide solution and selected oxides of the transition metals cobalt, 
manganese, chromium, nickel, iron, titanium, zinc, and zirconium. Of 
particular value is potassium hydroxide, and the oxides of cobalt and 
manganese. Special formulations using, as a "binder", the general 
constituents together with additives provides coatings having selected 
properties. In this connection, nepheline syenite provides additional 
expansion properties and antimony oxide (Sb.sub.2 O.sub.3) provides a 
tighter bond to the base metal and a harder coating. 
The additives to the Triplex Binder System are typically from the R.sub.2 
O-Al.sub.2 O.sub.3 -SiO.sub.2 system. For example, nepheline syenite is a 
mixture of Na.sub.2 O, K.sub.2 O, Al.sub.2 O.sub.3 and SiO.sub.2. Kaolin 
and kyanite are mixtures of Al.sub.2 O.sub.3 and SiO.sub.2. With these 
additives, and diluents selected from water and aqueous-based acrylics, 
paintable coating compositions are produced with the following ranges of 
principal constituents, based upon the total weight of the paintable 
composition: SiO.sub.2, 35-47%; Al.sub.2 O.sub.3, 9-18%; R.sub.2 O, 
7.5-15%; and TMO, 5-10%. Additionally, these useful compositions typically 
contain 0.3-0.9% Sb.sub.2 O.sub.3. The remaining constituent is a diluent 
in the form of water or an aqueous-based acrylic (up to 44%). The types of 
aqueous acrylics for use in these compositions will be known to those 
persons skilled in the art. Calculated on a fired basis, these ranges 
become: SiO.sub.2, 52-64%; Al.sub.2 O.sub.3, 14-27%; R.sub.2 O, 11-21%; 
TMO, 7.5-14%. When Sb.sub.2 O.sub.3 is added on a fired basis, it is 
typically 0.5-1.5%. 
As stated above, another application for a hard, adherent and impervious 
coating occurs where, for example, asbestos-containing insulation has been 
removed. Apparently, it is nearly impossible to remove all traces of the 
asbestos. In order to prevent this remaining amount from affecting the 
environment, a sealant is desired. In addition to its other properties, 
this sealant often must withstand subsequent operation at elevated 
temperatures. Since such surfaces are often very extensive, a sealant for 
this purpose must have a relatively low cost. 
The least expensive of the above-cited compositions is that illustrated in 
Example 8. This is referred to as "Econogard" by the applicants. Various 
attempts to reduce the cost by further aqueous dilution and/or the 
substitution of calcium carbonate for at least a portion of the nepheline 
syenite are illustrated by the compositions listed in Table 1, below. 
These are compared to the composition of Example 8. Also, shown in this 
table is the composition, identified as D, for a coating to be used on 
ladles, permanent molds and the like, as discussed in more detail 
hereinafter. The addition of calcium carbonate initially appeared to 
provide a satisfactory sealant on the basis of good paintability, 
hardness, etc.; however, if the as-prepared composition is permitted to 
stand for a day or two, it becomes virtually unusable. 
TABLE 1 
__________________________________________________________________________ 
EXAMPLE 8 
A B C D 
__________________________________________________________________________ 
BINDER: 
Potassium Silicate Sol. 
0.00 0.00 
0.00 
0.00 
25.00 
(26.5% SiO.sub.2, 12.65% K.sub.2 O in water) 
Colloidal Silica Sol. 
17.68 16.86 
12.96 
15.05 
0.00 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
10.53 10.04 
7.44 
8.70 
0.00 
(45% KOH in water) 
Unreacted TMO: 
MnO.sub.2 
3.66 3.48 
3.46 
3.34 
2.90 
Fe.sub.2 O.sub.3 
2.14 2.04 
1.99 
2.01 
1.80 
Black Pigment* 0.00 0.00 
0.00 
0.00 
1.40 
Diluent: 
Water 13.89 18.00 
24.72 
21.40 
13.20 
Additives: 
Nephelene Syenite 
26.00 24.79 
24.72 
24.75 
42.20 
Kaolin 26.00 24.70 
0.00 
0.00 
0.00 
Calcium Carbonate 
0.00 0.00 
24.72 
24.75 
13.60 
% in binder liquid: 
Potassium Silicate Sol. 
0.0 0.0 
0.0 
0.0 
80.0 
Colloidal Silica Sol. 52.0 52.0 
50.0 
52.0 
0.0 
Potassium Hydroxide Sol. 
31.0 31.0 
29.0 
30.0 
0.0 
TMO 17.0 17.0 
21.0 
18.0 
20.0 
Fixed Composition: 
SiO.sub.2 52.73 52.65 
30.84 
31.38 
45.40 
R.sub.2 O 11.59 12.24 
10.41 
11.00 
13.00 
TMO 8.70 9.18 
8.91 
8.59 
8.58 
Al.sub.2 O.sub.3 26.99 25.92 
9.41 
9.27 
13.80 
Cr.sub.2 O.sub.3 0.00 0.00 
40.40 
39.75 
19.20 
__________________________________________________________________________ 
NOTE: 
All % by wt. 
*Black Pigment: Prereacted TMO: 62% Cr.sub.2 O.sub.3,; 38% Fe.sub.2 
O.sub.3 
TABLE 2 
__________________________________________________________________________ 
EXAMPLE 8 
A B C D 
__________________________________________________________________________ 
BINDER: 
Potassium Silicate Sol. 
12.50 37.50 
31.00 
19.00 
6.00 
(26.5% SiO.sub.2, 12.65% K.sub.2 O in water) 
Colloidal Silica Sol. 
0.00 0.00 
0.00 
0.00 
0.00 
(30% SiO.sub.2 in water) 
Potassium Hydroxide Sol. 
0.00 0.00 
0.00 
0.00 
0.00 
(45% KOH in water) 
Unreacted TMO: 
MnO.sub.2 
2.90 2.90 
2.90 
2.90 
2.90 
Fe.sub.2 O.sub.3 
1.80 1.80 
1.80 
1.80 
1.80 
Black Pigment* 1.40 1.40 
1.40 
1.40 
1.40 
Diluent: 
Water 25.70 0.80 
7.20 
19.20 
32.20 
Additives: 
Nephelene Syenite 
42.00 42.20 
42.20 
42.20 
42.20 
Kaolin 0.00 0.00 
0.00 
0.00 
0.00 
Calcium Carbonate 
13.60 13.60 
13.60 
13.60 
13.60 
% in binder liquid: 
Potassium Silicate Sol. 
67.0 86.0 
84.0 
76.0 
50.0 
Colloidal Silica Sol. 0.00 0.00 
0.00 
0.00 
0.00 
Potassium Hydroxide Sol. 
0.00 0.00 
0.00 
0.00 
0.00 
TMO 33.0 14.0 
16.0 
24.0 
50.0 
Fixed Composition: 
SiO.sub.2 42.75 46.84 
46.12 
44.64 
42.80 
R.sub.2 O 11.58 14.26 
13.63 
12.35 
10.76 
TMO 9.23 8.04 
8.32 
9.88 
9.59 
Al.sub.2 O.sub.3 14.87 12.95 
13.40 
14.32 
15.46 
Cr.sub.2 O.sub.3 20.57 17.92 
18.54 
19.81 
21.39 
__________________________________________________________________________ 
NOTE: 
All % by wt. 
*Black Pigment: Prereacted TMO: 62% Cr.sub.2 O.sub.3,; 38% Fe.sub.2 
O.sub.3 
For example, the compositions identified as B and C in Table 1 appeared 
satisfactory when initially prepared; however, they yielded poor 
paintability, poor hiding power, etc., upon standing. The composition 
identified as A in the table, which contained additional water diluent as 
compared to that of Example 8, did perform well for a sealant for 
asbestos-contaminated surfaces and the like. While the composition of the 
constituents in the binder liquid were identical to the standard 
Econogard, the fired composition was slightly modified. 
A coating for ladles utilized in handling and/or casting molten non-ferrous 
metals, such as aluminum, magnesium, zinc, etc., is desired to protect the 
ladles and molds from attack by these materials. A relatively thick 
coating is desired (0.005 to 0.125 inches), with that coating being hard 
and abrasion resistant. One of the major problems encountered with thick 
coatings is their tendency to spall off upon cooling or thermal cycling. 
The above-cited coatings containing nepheline syenite are generally 
suitable for coatings up to about 0.010 inches, but substantial spalling 
occurs when thicker coatings are utilized. Also, spalling is often 
demonstrated at all thicknesses when the operating temperature is in a 
range of about 600 to 900 degrees C. 
Calcium carbonate has a higher thermal expansion property than the 
nepheline syenite; however, it dissociates above about 825 degrees C. and 
thus is only useful as an additive for coatings to be used below about 800 
degrees C. Since the metals of interest (aluminum, magnesium and zinc) 
melt well below that temperature, compositions containing calcium 
carbonate can be used. Unfortunately, as described above, calcium 
carbonate does not form a suitable coating composition when colloidal 
silica and potassium hydroxide are used (compositions B and C of Table 1). 
In contrast, it has been found that the calcium carbonate addition is 
suitable when a pre-reacted potassium silicate solution is substantially 
substituted for the colloidal silica and potassium hydroxide. Such a 
composition is Composition D of Table 1 which has been given the name 
"Ladlewash Hardcoat" by the applicants. 
Variations of the concentrations of Kasil #6 (a pre-reacted solution of 
potassium silicate in water as obtained from the PQ Corporation) were 
investigated. For all of the tested compositions, calcium carbonate was 
substituted for a portion of the nephelene syenite (see specific ratios). 
The Kasil #6 is 26.5% SiO.sub.2 and 12.65% K.sub.2 O in water. The 
specific compositions are listed in Table 2. It can be seen that the 
potassium silicate solution can range from about 6 wt % (composition I) in 
the liquid binder portion of the composition, this being the thinnest 
composition and providing about the lower limit of satisfactory 
performance, to about 31 wt % (composition F having the thickest 
consistency). The composition identified as D in Table 1 is one of the 
series of tests; however, it was included in that table for comparison 
with the various Econogard compositions. 
Although the compositions illustrated as D through I in Tables 1 and 2 are 
specifically suitable for the coating of ladles and molds in contact with 
molten metals, these compositions can also be utilized for the various 
other coatings discussed herein. Wherein only thin coatings are required, 
the most dilute of these compositions containing Kasil #6 can be used. 
It is to be understood that the examples given herein are only exemplarily 
of the compositions having use in the protection of various substrates. As 
such, these examples are not given as limitations of the invention. 
Rather, the invention is to be limited only by the appended claims and 
their equivalents when read together with the detailed description herein.