CA1332955C - Method of forming cellular ceramic material and related products - Google Patents

Abstract

Methods of forming by polymerization reaction a silicate gel which exhibits intumescence upon application of heat and various products formed from the resulting ceramic foam materials. Specific formulations and processing steps best suited to particular applications are set forth, together with examples of various types and configurations of the resulting products. These include structural materials, such as sheets of wall board, very low density insulation materials, articles useful as a protective barrier from heat or flame, vitreous materials useful as heat resistant tiles or as abrasive wheels or blocks for grinding or polishing, and ceramic foam materials incorporating silica gel and processed solely with microwave heat.

Description

Application Of: David J. Legare For: Method Of Forming Cellular Ceramic Material and Related Product~
Background Of The Inven'tion The present invention reLates to methods of forming silicate gels by polymerization reaction which exhibit intumescense upon application of heat, and to the fabrication of products and other materials incorporating such gels.
A number of al~ali metal silicate-based insulation materials have been de~cribed in the prior art.
Characteristi'c example~ of such materials are evident from U.S. Patents 4,297,252 (Ca'esar et al); 4,521,333 (Craham et al); 4,118,325 (Becker et al); and Great ~ritain 1,227,482. The~e patents describe well-known methods of hardening an aqueous alkali metal silicate composition to form a gel' or solid product. The basic hardening techniques include chemical methods such as adding sodium or potassium fluorosilicate and/or organic gelling agents ~uch as haloalcohols,,amines, ke,tones, etc., or by heating the gel at low temperature (approx. 100 C) to reduce water content.
Though apparently well-suited to a number of appllcations, these techniques have a number Or serious '- draw-~ack~. ,First of all, methods which involve heating to form the gel are expen~ive in terms of time and energy consumption. 'F,urthermore, this gel ~annot: be easlly molded or extruded. Intumesced ceramics produced 1 _ .

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from these gels have very little structural strength because of their extremely low density, unless large amounts of filler materials have been incorporated into the starting silicate solution. Gels produced using organic hardening agents are easier to machine because of their plastic-like consistency. However, gels containing organic materials such as haloalcohols and amines present fire and toxicity hazards when heated to produce solidification or intumescence.
Fluorosilicates are usually used in combination with organic hardening agents. When used alone, in sufficient quantity to cause solidification of the silicate solution, the resulting material does not exhibit intumescence (expansion and cell formation) when subjected to temperatures which normally cause this reaction to occur (around 1000F) in gels produced by other means. Furthermore, when heated to high temperatures, the fluorosilicate may decompose to produce extremely toxic gasses such as silicon tetrafluoride and fluorine.
It is a principal object of this invention to provide a simple, inexpensive technique for producing alkali metal silicate gels which offer a number of benefits over prior methods.
A further object is to provide a method of producing alkali metal silicate gels which are non-toxic and can be easily molded and machined.

1332~5 Another object is to provide a method of producing silicate gels which can be heated (to cause intumescence) to produce a variety of low and high density insulation materials.
Still another object is to provide useful articles and materials comprising silicate gels formed by polymerization reaction, and novel methods for the production of such articles.
More specific objects within the scope of the foregoing are to provide:
1. structural materials, e.g., sheets suitable for use as wall board, having mechanical properties similar to conventional gypsum board, but of lower density, higher strength and higher degree of fire protection;

2. very low density ceramic foam materials for use in sheets or blocks as bulk insulation in construction applications;

3. a fireproof article including an encapsulated gel material between a pair of liners or substrates useful as a protective barrier layer in packaging and building systems;

4. a vitreous material produced by heating the intumesced ceramic foam to a temperature at which it begins to soften or melt; and f~

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5. ceramic foam materials using silicic acid (silica gel) as a principal additive ingredient and intumesced with microwave heat.
Other objects will in part be obvious and will S in part appear hereinafter.
~ummary Of The Invention In accordance with the foregoing objects, the invention contemplates a process for the formation of a silicate gel material which, in its basic form, is produced by the combination of one or more simple alkali metal halides or nitrates (of the form M1 X1 where M is the alkali metal, and X is the halide or nitrate; e.g.
NaC1) with a solution of sodium or potassium silicate.
Preferably, certain additives such as silicates, carbonates, oxides, and other materials which do not cause precipitation of the soluble silicate are mixed into the solution prior to mixing in the alkali metal halide or nitrate in order to vary the properties of the final product. Also, fibers or other filler substances may be added either prior to, simultaneously with, or after the mixing in of the alkali metal halide or nitrate. The solution may thereby assume the consistency of a slurry or paste, depending upon the quantity of the material added.
After formation of the gel, the material may be molded to essentially any desired form and allowed to harden completely at room temperature. The material may ~'~

13329~5 also be applied to a substrate with a sprayer before the gelling (polymerization) reaction is completed. Since this reaction may occur very quickly, (within a few seconds) for some mixtures, it may be necessary to mix in the alkali metal halide or nitrate as the material is being sprayed, e.g., within the sprayer nozzle.
The material may be left in the gel state to serve as a heat and flame resistant layer in packaging and construction materials, specific examples of which are disclosed. As such, the gel reacts to heat and flame by expanding through intumescence to form a highly insulative and reflective barrier. The dehydration of the gel during this process also serves to carry away damaging heat.
The gel may also be heated, preferably at around 1000F, to cause intumescence and the consequent formation of a cellular ceramic foam. The surface of this foam may be quickly heated to its melting point to create a glazed surface.
The invention also encompasses a number of embodiments providing optimum material compositions for use in particular applications. For example, wall board materials having relatively high melting points for fire protection, and very low density ceramic foams useful as bulk or block insulation are disclosed, in addition to specific examples of the aforementioned heat and flame ~.j ~
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protective packaging and construction materials, and vitreous products.
Brief DescriPtion of the Drawin~s Figure 1 is a graphical representation of the relationship between the time required for gel formation and the amount of a particular gelling salt which is added to an alkali metal silicate solution;
Figure 2 is a diagrammatic illustration of the steps in the gel production process;
Figure 3 is a graph illustrating a number of physical properties of a material formed by the process of the invention in relation to the molar ratio between additive substances and alkali metal silicate;
Figure 4 is a graph illustrating some of the thermal insulating properties of a 1 cm thick sheet of ceramic foam wherein the molar ratio between the additive substances and the alkali metal silicate was approximately .4;
Figure 5 is a diagrammatic, perspective view of a product exemplifying one aspect of the invention;
Figure 6 is a diagrammatic, perspective view of another form of the product of Figure 5; and Figure 7 is an enlarged, fragmentary, elevational view of a portion of Figure 6.
Detailed Description The present invention is directed to a process for the formation of silicate gels which can be made to `'~' ~ ' 13329~5 exhibit a wide range of properties to suit a number of different applications.
The process primarily involves the combination of alkali metal silicates in aqueous solution with alkali metal halide and/or nitrate salts to produce a pliable, plastic-like gel. The use of these alkali metal halide and nitrate salts allows the production of materials which are not possible by any other known method, particularly with fluorosilicates commonly used in the prior art. For example, using equivalent quantities of potassium or sodium fluorosilicate (silicofluoride) in place of the alkali metal nitrate or halide in any of the compositions described by this invention results in a gel which will not intumesce to any noticeable degree. The heated gel merely hardens into a stone-like composition.
By contrast, with the methods of the present invention, tough ceramic foams can be produced which are several times the volume of the starting gel. Furthermore, denser ceramics can be produced by the inclusion of additive substances as described later herein.
The alkali metal silicate used in this invention should be sodium or potassium silicate with a silicon to metal oxide ratio e.g., (SiO2:Na20) between 2:1 and 5:1 (preferably, between 2:1 and 4:1). The solution may also contain colloidal SiO2. However, the molar ratio of colloidal sio2 to soluble silicate should preferably be no more than about 3:1. A commercially available sodium silicate solution (water glass) wllt~ a SiO2 Na20 ratio of around 3.4:1 and colloidal sio2 to soluble silicate ratio of around 2:1 appears to work well for most currently comtemplated implementations of this invention. Gel formation optimally takes place when the alkali metal silicate solution concentration is between about 10 to 40% by weight. The rate of the polymerization reaction is most affected by the amount of gelling material used.
Figure 1 is an illustrative example of this relationship.
It should be noted that the gel formation process using equal quantities of sodium or potassium fluorosilicate can take up to 20 times as long (10 to 20 minutes as opposed to 30 seconds to 1 minute) as with the alkali metal halide and nitrate salts.
The materials used to polymerize the alkali metal silicate solution are simple, monovalent, alkali metal salts, specifically one or more of sodium, potassium, or lithium fluoride, chloride, bromide, iodide, or nitrate.
The word "simple" implies that the molecular structure is of the form M1:X1 where M represents the alkali metal ion and X represents the halide or nitrate ion.
Experimentation has shown that potassium and sodium salts are generally preferred over lithium in terms of reactivity and the quality of the gel formed.
Experimental data further indicates that potassium and sodium chloride and nitrate can be used to satisfy most applications currently contemplated for this invention.

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Therefore, toxic substances such as fluorides and bromides can be avoided in producing materials for home insulation products and similar applications.
The amount of alkali metal nitrate or halide required to polymerize the silicate solution can vary considerably depending upon solution concentration, additive materials, and the particular alkali metal halide or nitrate (gelling salt) used. In general, it appears that a minimum of about 1 part (by weight) of gelling salt to about 20 parts of low concentration (around 10%) silicate solution is required for gelling to occur within a reasonable time (on the order of several minutes or less). However, the optimum ratio appears to be about 1 to 4 parts gelling salt to about ~, .~,~, . . .
,- ~".

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10 parts silicate ~olution (prior to the incorporation of additives). Larger quantities o~ gelling salt may be u~ed, but do not appear to be nece~ary. The gelling ~alt i~ u~ually added to the solution as a coarse or fine powder, but can be added a~ a ~trong ~olution or pa~te a~ long as its water content doe~ not reduce the soluble silicate Qolution concentration to a level below which gelling cannot occur.
Additive ~ub~tance~ may be incorporated into the gel to create a variety of de~ired propertie~ in the final product. These ~ub~tance~ are preferably added to the ~ilicate solution prior to the addition of the gelling ~alt. Although they could be added in a ~ingle ~tép with gelling salt, thi~ may prevent a good di~per~ion of the~e ~ub~tance~ throughout the gel.
The~e additive ~ub~tance~ are basically ~ilicate~, oxide~, carbonate~, and other ceramic ~ub~tance~ obvious to anyone ~killed in the art, cho~en to create certain propertie~ in the final product. The only re~triction on the~e ~ub~tance~ i~ that they do not react with the ~ilicate in ~olution to any extent which would seriou~ly inhibit or prevent the polymerization reaction cau~ed by the addition of the gelling ~alt. ~lence, the~e material~ are for the mo~t part non-aqueou~-soluble and non-reactive in the alkali metal ~ilicate ~olution at room temperature. Sepcific example~ of such materials are ~ilica gel (~ilicic acid), ~ilicateq ~uch a~

aluminum, calcium, and zinc silicate, oxides such as aluminum and magnesium oxide, and carbonates such as magnesium, calcium, zinc, and lithium carbonate.
Examples of some aqueous-soluble materials which do not adversely react with the silicate solution, and which appear to enhance the uniformity and strength of some intumesced compositions are alkali metal sulfates and phosphates. Figure 2 illustrates the preferred method for mixing the raw materials to form the gel.
The most noted general effect of using additive materials is the increase in hardness and density of the gel, and the increa~e in density and toughness of the intumesced gel (ceramic foam). Gels containing little or no additives may exhibit a great deal of expansion (up to ~everal hundred percent) during heating to cause intumescence, while those with large quantities of additives may form dense materials exhibiting very little expansion. Ceramic foams with densltie~ ranging from as little as a few hundredths of a gram per cubic centimeter to as high as a few grams per cubic centimeter can be produced by varying the types and amounts of these additive substances. Additive sub3tance~ may also be included to create other effect~
such as coloring the final product. For example, copper and iron silicates may be added to produce blue and yellow ceramic foams or glazed sùrfaces (by heating the surface of the foam to induce self-glazing).

s -\

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For most applications envisioned at the present time, and for ea~e of manufacturing the gel, it appearq that the ratio of additive substance~ to silicate solution should be between about 0:1 to 1:1. It should be noted that the insoluble (colloidal) SiO2 present in most commercial sodium silicate formulations is included in the above ratio. It is assumed that mo~t implementations of this invention will utilize commercially available sodium or potassium silicate solution~ which contain a molar ratio of colloidal silica to soluble silicate of around 2:1. The amounts of additive sub~tances required to produce similar results u~ing other sodium or potassium silicate solution formulations can therefore be ea~ily calculated by con~idering the concentration~ of in~oluble SiO2 they contain.
Figure 3 illustrates ~ome of the physical properties of a particular ceramic foam compo~ition in term~ of the ratio between additive sub~tances and sodium silicate (including colloidal SiO2) in the ~olution. Figure 4 illustrates the results of an experiment to measure ~ome of the in~ulative properties of these material~. In this experiment, a 1 centimeter thick sheet of ceramic foam containing approximately 2 parts additive substances to 10 part~ commercial sodium silicate ~olution wa~ used as one wall of an electric furnace. The furnace wa~ quickly heated to 900F and .. .... . .
f i3329 ~5 allowed to cool to room temperature over a period of 8 hours. Other experiments indicate that even very low den~ity foam~ remain rigid at temperature~ up to around 1100 F. However, higher den~ity ceramic~ made from gels containing additives such as magnesium oxide can remain rigid at temperature~ exceeding 2000F. Such materials may have a variety of industrial applications.
A further step in the proces~ of this invention may include the addition of filler and reinforcing material~ ~uch as fibers, particulate~ (~and, crushed gla~s, etc.), screen or mesh to the gel to enhance the strength of the final product. These could be added to the silicate solution, or mixed, pressed, layered, or folded into the gel during or after its formation. The total quantity of the~e substance~ that may be added is only limlted by the saturation limits of the gel mixture.
The ~ilicate gel materials described above can be formed into sheets, cast around pipes, etc., or molded into any de~ired configuration. The gel can be u~ed as is to form a reactive barrier again~t heat and fire, or heated to cause intumescence and the formation of a ceramic foam. To form the ceramic foam, the gel is heated u~ing a thermal ~ource, preferably between about 900F and 1300F, or mlcrowave energy may be used.
Either thermal or microwave heating (or ~ome combination of the two) may be more appropriate for different gel ... . .......... . ... .. .. . ..

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composition~. The duration of the heating proce~s should be sufficient to cause partial or complete intumeqcence of the gel (a~ de~ired), and will vary for different gel compo~ition~ and thicknes~e~. Complete intume~cence of an average gel ~ample of 1 centimeter thicknesq takes approximately 5 to 8 minute~ at 1000F.
The method~ described above can be used to manufacture a number of u~eful materials. Among the po~sible application~ for these materials are ~heets of wall board, or ~imilar construction material~ which are light in weight, provide excellent thermal in~ulating qualitie~, are eaqily machined (sawed, drilled, ground, etc.), and which are non-toxlc and fireproof. The material may al~o be used a~ bulk insulation or molded in variou~ ~hapes to serve aq an in~ulating layer or jacket on variou~ items, including being ca~t in place directly around plpe~, and the like. The properties of the material are controlled to quit the particular application by ~election of the type~ and amount~ of addltive ~ub~tance~ and fillers, proce~3 temperatureq, and other variable~. Finally, it ~hould be noted that the material may be prepared in a plurality of layer~, providing ~ub~trate~ having different propertie~, and diverse materialq ~uch aq rod3, wire me~h, etc. may be embedded or otherwise incorporated into the material for added ~trength or for other prupo~e~. Likewi~e, the material of the invention may be depoqited upon and/or bonded to layers of other materials, such a~ wood, paper, etc.
A number of ~pecific examples illustrating the general principles and scope of thi~ invention are provided below. It will be understood that the examples are in no way intended to be limiting.

A ~trong, low-density ceramic foam with good heat inqulating properties is formed by mixing or blending 1 -to 3 part~ sodium or pota~iurn chloride into 10 parts of commercial sodium silicate solution. The resùlting gel hardens quickly and can be used a~ is or heated at about 1000~ to intumescence.

Add 1 part potassium sulfate to 10 parts commercial sodium silicate solution. To thi~ mixture, add 2 parts pota~sium nitrate (or ~odium or potassium chloride) to cause polymerization. The gel may be heated at around 1000F to form a light-weight ceramic foam, ~imilar to that of Example 1. Preferably, the gel i~ fir~t heated in a microwave oven to cause partial intume~cence and is the further heated at about 1000F
to es~entially complete intumescence. This re~ult~ in a more homogeneou~ foam structure.

A very tough1~high den~ity ceramic is formed by first mixing 4.5 parts ~ilica gel, 1.8 parts aluminum ~ilicate, and 1.5 parts calcium carbonate with 20 parts \
13~29~5 of commercial sodium silicate solution. 4 part~ of potas~ium nitrate are then added to polymerize the mixture. The gel hardens quickly, and can be molded and pre3sed into ~heets. It i~ then heated between 1000 and 1300F to form a tough, dense ceramic foam.

A high temperature ceramic i~ formed by first mixing 1 part ~ilica gel and 5 part~ magne~ium oxide with 10 partq commercial ~odium silicate ~olution.
part pota~sium nitrate i~ then mixed in to ploymerize the mixture. The gel i~ very den3e, but can be molded and pres~ed into sheets. The gel can be heated at around 1000F to produce a ceramlc which can re~l~t temperatureq above 2000F.

A medium den~ity tough ceramic foam which could be u~ed for board~ or ceiling tile~ iq formed by mixing 1 part 3illca gel and .2 part~ calcium carbonate into 10 part~ of commercial ~odium ~ilicate ~olution. 1 part ~odium or pota~3ium chloride i~ then mixed in to form a hard, polymerized gel. The gel i~ molded or pre3~ed into ~heet~. It i~ then heated in a microwave oven to produce a ceramic foam.

Any of the above exampleq in which filler materialq ~uch a~ fiber~ and/or particulate~ (~and, cru~hed gla~, etc.) have been incorporated into the gel.

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A number of more specific applications of the present invention are described in the balance of the specification. The first of these concerns a potentially very high temperature (high melting point) material which can be manufactured as a wall board product with properties similar to conventional gypsum board (e.g., can be nailed to structural members of walls, floors or ceilings), but of lower density, higher strength and providing a greater degree of fire protection than ordinary gypsum board. The preferred composition and method of production of this "wall board" material is as follows:
1. To 20 parts of a 10% to 40% (by weight) aqueous solution of sodium or potassium silicate containing a soluble sio2 to metal oxide ratio between about 1:1 and 5:1, thoroughly mix in about 1 to 10 parts calcium carbonate powder to form a slurry. The sodium or potassium silicate solution should also preferably contain a certain amount of insoluble sio2 such as is found in various commercial compositions of water glass (sodium silicate solution), e.g., soluble SiO2:Na20 ratio of about 3.4:1 and colloidal sio2 to soluble silicate ratio of around 2:1.
2. Add about 2 to 8 parts sodium or potassium chloride (powder or fine granules) to the above slurry, and quickly and thoroughly mix/blend in to form a gel.

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3. Press, mold or extrude the gel into relatively thin sheets (e.g., % to ~ inch or less, for wall board, etc.). A layer of heat-tolerant material such as aluminum foil may be applied to the gel sheets.
5This layer will normally bond to the sheet as it is transformed into the cellular ceramic state.
4. Heat the gel at around 1000F to 1200F for a time sufficient to cause intumescence and the formation of a rigid, light weight, cellular, ceramic product.
105. Optionally, apply to one or both sides of the cellular ceramic sheet a layer of paper or paperboard of the same length and width. A viscous solution of sodium silicate is one type of adhesive that may be used for this purpose.
15This material composition can be made to have a relatively high melting point (as high as about 2300F) by increasing the amount of calcium carbonate (CaC03) in the mixture. Other components such as magnesium carbonate and magnesium silicate (talc) can be added with 20the calcium carbonate to vary the material properties without degrading its high temperature characteristics.
However, the use of calcium carbonate as the major or only additive component, as specified above, provides a superior wall board product, both in terms of its low 25material cost, and because of the good mechanical properties of the resulting ceramic product. Examples of V' .

some experimental compositions and their melting points are as follows:
Table I

C~ ~;al Sodium Silicate NaCI CaC03 MgCO3 Talc Melting pt.
solution (approx. 32% by weight) (degrees F) 1) 20g 4g 2g - - 1250 2) 20g 4g 4g - - 1650 3) 20g 4g 8g - - 2250 4) 20g 6g 2g - - 1250 1 0 5) 20g 6g 4g - - 1650 6) 20g 6g 8g - - 2250 7) 20g 4g 6g 3g - 2000 8) 20g 4g 6g - 3g 2000 The preferred components and range of proportions thereof in forming the wall board product of the invention are: 20 parts commercial (25% to 40% by weight) sodium silicate solution having a soluble SiO2:Na20 ratio of about 3.4:1 and colloidal sio2 to soluble silicate ratio of about 2:1; 3 to 6 parts (by weight) NaCl and/or KCl; 2 to 8 parts (by weight) CaC03.
A second specific application concerns a very low density ceramic foam, and method of production thereof, which can be used as a bulk insulation in home and building construction applications. As such, this material could substitute for fiberglass, urethane foam, and particle fillers for the insulation of walls and ceilings. This ceramic foam could be formed as sheets up ~" ~,~.
. ~,.

1 332~5t) to several inches thick through heating of a single gel layer or the combination of two or more foamed (intumesced) gel layers to form a sufficiently thick ceramic foam insulation layer. The preferred composition and method of forming the product of this aspect of the invention is as follows:
1. To 20 parts of a 10% to 40% (by weight) solution of sodium and/or potassium silicate (preferably sodium silicate) with soluble sio2 to alkali metal oxide ratio of about 2:1 to 5:1, mix/blend in 2 to 8 parts potassium or sodium nitrate (preferably potassium nitrate) to form a gel.
la. Optionally, add up to 2 parts sodium and/or potassium sulfate or phosphate, and/or up to 5 parts fiber or mesh fillers (e.g., glass fibers).
2. Mold the gel into a desired shape or form into sheets.
3. Heat the gel at a temperature of about 500F
to 1100F to cause intumescence. The heating process should be carefully controlled to prevent large bubbles from forming in the foam. A more uniform foam product may result from first adding small amounts of sodium and/or potassium sulfate and/or phosphate to the solution in Step 1 (above). Some microwave heating may also be used in combination with the thermal heating to provide a more uniform foam structure.

~' 1332~5 4. The resulting ceramic foam may be cut and/or laminated, or combined in multiple layers, to suit specific applications. For example, foam sheets may easily be cut to fit between wall studs, and could be laminated with common materials such as aluminized paper to provide a vapor barrier such as is commonly found in fiberglass wall insulation products. It should be noted that in order to facilitate the production of foam sheets of sufficient thickness to fully fill the entire wall space (4 inches or more), it may be desirable to process two or more individual foam sheets and layer them together to form a single sheet of the required thickness.
The preferred components and range of proportions thereof in forming the ceramic foam insulating product of the invention are: 20 parts commercial (25% to 40% by weight) sodium silicate solution having a soluble SiO2:Na2O ratio of about 3.4:1 and colloidal sio2 to soluble silicate ratio of about 2:1; 4 parts KNO3. Also, as mentioned under step la above, depending upon the desired properties of the end product, the composition may include 0 to 2 parts sodium and/or potassium sulfate or phosphate, and 0 to 5 parts glass fibers, or-other fiber or mesh fillers.
A third specific application involves a variety of fireproof or fire-retardant packaging or building ~, .~

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materials incorporating a gel composition of the type generally disclosed in the parent patent, including specific, preferred variants thereof. Products of this type may be fabricated by placing a layer of the gel between two substrate layers of cardboard, or the like, without first exposing the gel to heat to initiate intumescence. The resulting laminar structure is used to construct containers for flammable articles or other materials requiring protection from fire and/or heat.
Alternatively, the laminar structure may be incorporated in building constructions in protective relation to flammable or heat-sensitive portions thereof.
When the gel layer is exposed to heat or flame, intumescence occurs, as previously described, with consequent absorption and dissipation of heat through the production and release of steam in formation of a ceramic foam layer. The resulting expanded foam layer continues to protect materials on the opposite side from heat and flame by virtue of its intrinsic flame resistance, reflectivity and extremely low thermal conductivity.
Thus, the contents of packaging materials constructed from the laminar structures, or building members covered or enclosed thereby are afforded a great deal of protection from fire and heat damage. Experimentation has shown that useful gel layer thicknesses can range from as little as about 1 millimeter to a centimeter or more.

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In order to provide optimum heat protection the gel composition should be formulated to maximize its water content. This implies that the use of additive and filler materials should generally be minimized, but only to the extent that the structural integrity of the resulting intumesced ceramic foam is not reduced to the point that the foam does not remain intact and continue to provide heat protection by reflecting radiated heat and minimizing heat conduction to the underlying surface or the inside of the package. Foam strength could be enhanced by the addition of glass, ceramic, or other types of fibers either randomly dispersed or incorporated as a uniform mesh into the gel. This would also help to prevent separation or cracking of the gel layer as the substrate layer(s) is flexed.
The water content of the gel, and therefore its ability to dissipate larger quantities of heat, may be increased by adding any of a number of granular filler materials consisting of hydrated salts such as hydrated magnesium sulfate, lithium chloride, calcium sulfate, etc. which contain high percentages of tightly bound water (large hydration energies). The larger the hydration energy, the greater the amount of heat that must be absorbed to liberate the water. It is important that these materials be added as fillers (after the gel is essentially formed) and not as additives to the slurry ;. .f~

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(before gel formation) so that they do not dissolve into and react chemically with the silicate solution.
Since it is also possible for the hydrated salt filler to react gradually with the silicate in the gel, it may be desirable to first provide a thin, essentially moisture-impervious coating such as parafin, plastic, etc., over the hydrated salt particles to prevent the salt from dissolving into and/or chemically reacting with the gel. This may be of particular importance if the reaction between the hydrated salt and silicate solution results in the formation of an insoluble silicate, and/or the packaging or building material into which the gel is incorporated is intended to be in service for a long period of time.
Another consideration in the production of these packaging or building materials is the dehydration of the gel with exposure to the open air. Although gel compositions can be optimized to resist dehydration, it is preferable that the gel layer be protected by an additional thin, essentially moisture-impervious layer between the gel and the substrate. (It should also be noted here that compositions using potassium silicate solution may have a greater resistance to dehydration).
For example, in a fire-resistant packaging material the gel could be sandwiched between two layers of cardboard which have a waterproof coating such as plastic or parafin on the surfaces which contact the gel.

,~ X

1332~55 Alternatively, the gel layer could be segmented into individually encapsulated, waterproof segments.
Referring again to the drawings, in Figure 5 is shown a laminar structure 10 including gel layer 12 sandwiched between upper and lower substrate layers 14 and 16, respectively, which may be of cardboard, corrugated paperboard, or other conventional materials suited for the intended application of laminar structure 10. Assuming the materials of layers 14 and 16 do not inherently provide moisture protection for gel layer 12, the inner surfaces of both layers 14 and 16 (i.e., the surfaces facing gel layer 12) are covered, coated or otherwise treated with an essentially moisture-impervious material 18 and 20, respectively. In order to protect gel layer 12 from moisture in the surrounding atmosphere, the outer edges of structure 10 may be covered with a further layer of moisture-impervious material 22, a portion of which is shown broken away in Figure 5.
Figures 6 and 7 illustrate diagrammatically a laminar structure including upper and lower substrate layers 24 and 26, corresponding to layers 14 and 16 of Figure 5, with gel layer 28 therebetween. The gel layer in this embodiment is segregated into individually encapsulated segments by flexible, moisture-impervious material 30, which may comprise a thin plastic sheet, or other suitable material. Material 30 is positioned over gel layer 28 on substrate layer 26 and contacted with a X

1332~5 suitable die to be pressed against and bonded to layer 32, of the same or other moisture-impervious material as that of material 30, to form the individual cells or capsules of gel layer 28 which is thus isolated from both layers 24 and 26 as well as the surrounding atmosphere.
Upon exposure to heat and flame the outer cardboard layer disintegrates exposing the underlying intumescent gel layer. The plastic membrane covering the gel quickly melts away and the adjacent gel capsules fuse together as they expand during intumescence, therefore providing a continuous protective coating over the inner cardboard layer and package contents.
Although a large number of gel compositions producible under the present invention could be useful for a number of different heat and/or flame protective applications, the following gel compositions (in parts by weight) would provide a good overall product, particularly for use in packaging materials.

Sodium and/or ~ iulll KNO3, NaCI Filler (Hydrated Filler Silicate Solution (10% to 40% KCI, (or any Salt Granules) (Fibers orby weight) collL ' on) e.g., MgSO4.7H2O Mesh) e.g.
glass fibers 2~ 0-5 0-3 Turning now to a further embodiment of the invention, a number of the ceramic foam (intumesced gel) compositions produced by the method of this invention can be further processed to form a class of vitreous ceramic ~.

~O. . . ~ ., 1332~5S

foam materials. Not all of the ceramic foam composite within the scope of the invention provide useful results with the further heat processing described herein;
however, those that do provide new materials having a number of useful application including low density, heat resistant tiles for structural and/or decorative building materials, and as abrasive wheels or blocks for grinding or polishing. In the latter application, various granular, abrasive materials such as sand, garnet, silicon carbide, etc. are preferably added to the basic gel as filler materials with the fused ceramic foam serving as a matrix for the abrasive particles.
The products of this embodiment are produced by mixing potassium chloride and/or sodium chloride with an aqueous solution of sodium silicate and/or potassium silicate to provide a gel by polymerization reaction; one or more other substances, specified hereinafter, are also mixed into the solution before or together with the alkali metal chloride. The gel is heated until intumescence is substantially complete, forming a cellular ceramic foam material. The intumesced foam is then further heated to a temperature at which it begins to soften or melt. This results in a partial collapse and shrinkage of the foam structure as the foam cells begin to fuse together. It is important to note, however, that the material is not heated to the point X.`

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that it completely melts, but only to the so-called vitrification temperature.
After cooling, the resultant vitreous material is denser and much harder than the intumesced ceramic foam, but still retains a porous, foam-like structure.
Several specific examples of preferred compositions which yield good results in this embodiment of the invention, with approximate vitrification heat processing temperatures for each, are set forth in Table II. The quantities specified are in parts by weight. The sodium silicate solution used was a commercially available product having a soluble SiO2:Na20 ratio of about 3.4:1 and a colloidal sio2 to soluble sio2 ratio of about 2:1.

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13329~

In still another embodiment, the invention concerns a ceramic foam product which can be completely processed using only microwave heating. The materials of this embodiment are characterized by having silicic acid (H2Sio3), (also known as silica gel) as the major or only additive ingredient. The silicic acid is thoroughly mixed or blended into a sodium and/or potassium silicate solution (10-40% by weight) which has a soluble sio2 to alkali metal oxide (i.e., Na2O) ratio of about 2:1 to 5:1.
This silicate solution is preferably sodium silicate and also preferably contains a colloidal sio2 to soluble sio2 ratio of about 1:1 to 3:1 (prior to the addition of the silicic acid). It should be noted that it is desirable to use a hydrated, or at least partially hydrated, form of the silicic acid instead of silicic acid that is in the completely dehydrated state. Furthermore, other additive components such as calcium carbonate and aluminum silicate can be mixed into the slurry to alter the properties of the final ceramic foam product.
Formation of the polymerized gel can be accomplished via the addition of any of the gelling salt agents discussed earlier herein. However, sodium chloride or potassium chloride should preferably be used.
A key feature of this group of materials is that the gel thus formed can be completely processed into a very useful ceramic foam using only microwave heating.

1~329~

As such, the gel is molded into a desired shape or pressed into sheets, and then heated in a microwave oven until intumescence has been completed. The ceramic foam produced by this invention appears to be particularly useful for the formation of wall-board and ceiling tile products. The preferred chemical composition, in parts by weight, of the gel is as follows:
Sodium Silicate Hydrated CaC03 NaCl and/or Solution (25-40% Silicic Acid and/or KCl by weight) Al2(Si03)3 20 1.6-5.0 0-1.0 1.6-4.0 The presently contemplated optimum formulation is:
2.0-3.0 .4 2.0 A preferred sodium silicate to be used in the above compositions is a commercially available product having a soluble SiO2:Na20 ratio of about 3.4:1 and a colloidal sio2 to soluble sio2 ratio of about 2:1.

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Claims (51)

1. A method of forming a silicate gel which exhibits intumescence upon application of heat, said method comprising adding about .5 to 12 parts by weight of at least one alkali metal chloride, bromide, iodide or nitrate to 10 parts of an approximately 10 to 40% (by weight) aqueous solution of sodium or potassium silicate, wherein the soluable SiO2 to alkali metal oxide ratio is between about

2:1 and 5:1 providing a gel by a polymerization reaction being characterized by the essential absence of precipitation of insoluble silicate from said solution.
2. The method according to claim 1 and including the further step of mixing into said solution at least one insoluble silicate, carbonate or oxide which does not react with the soluble silicate or otherwise inhibit the gelling process, wherein the weight ratio of said insoluble material, including any colloidal SiO2 initially present in said solution, to said solution is between about .05 to 1.

3. The method according to claim 1 wherein said alkali metal chloride, bromide, iodide or nitrate is at least one of sodium chloride, sodium nitrate, potassium chloride and potassium nitrate.

4. The method according to claim 1 and including the further step of incorporating into said gel at least one inert particulate material, organic or inorganic fiber in a quantity between about .5 parts by weight and the maximum amount of said particulate material or fiber which can be dispersed in the gel.

5. The method of claims 1, 2 or 4 and including the further step of heating said gel at a temperature of at least about 1000°F until intumescence thereof is substantially complete.

6. The method of claim 5 wherein said heating step is carried out by first heating said gel in a microwave oven to at least initiate intumescence of said gel, and then heating said gel with a thermal heat source at a temperature of at least 1000°F until intumescence is essentially complete.

7. The method according to claims 1, 2 or 4 and including the further step of pressing said gel into essentially flat sheets.

8. The method according to claim 7 and including the further step of heating said sheets at a temperature of at least about 1000°F until intumescence thereof is substantially complete.

9. The method according to claim 1 and including the further step of molding said gel to a desired shape and incorporating therein at least one diverse reinforcing member.

10. The method according to claim 1 and including the further steps of heating said gel at about 1000°F for a time sufficient to at least initiate intumescence and thereafter heating at least one surface of said gel to its melting temperature, thereby providing a glazed surface.

11. A method of producing sheets of wall board, or similar products, comprising the steps of:
a) thoroughly mixing 1 to 10 parts by weight of calcium carbonate powder into 20 parts by weight of a 10%
to 40% (by weight) aqueous solution of sodium or potassium silicate having a soluble SiO2 to alkali metal oxide ratio of about 1:1 to 5:1 to form a slurry;
b) adding about 2 to 8 parts sodium chloride an/or potassium chloride (powder or fine granules) to said slurry, and quickly and thoroughly mixing or blending to provide a gel by polymerization reaction;
c) forming said gel into sheets of predetermined length, width and thickness; and d) heating said gel at about 1000°F to 1200°F
until intumescence is substantially complete to form a rigid, cellular, ceramic product.

12. A sheet of wall board, or the like, produced according to the method of claim 11.

13. The method of claim 11 including the further step of bonding to said sheets of cellular ceramic on at least one major surface thereof a layer of paper or paperboard having said predetermined length and width and a thickness substantially less than said predetermined thickness.

14. The method of claim 11 wherein a sheet of aluminum foil, or other heat-tolerant material is bonded to said gel sheets prior to said heating step.

15. The method of claim 11 including the further step of thoroughly mixing about 3 parts by weight of magnesium carbonate and/or magnesium silicate to said aqueous solution.

16. A sheet of wall board, or the like, produced according to the method of claim 13.

17. A method of producing sheets of wall board, or similar products, comprising the steps of:
a) thoroughly mixing 2 to 8 parts by weight of calcium carbonate powder into 20 parts by weight of a 10%
to 40% (by weight) aqueous solution of sodium or potassium silicate having a soluble SiO2 to alkali metal oxide ratio of about 3.4 to 1 and colloidal SiO2 to soluble silicate ratio of about 2:1;
b) adding about 3 to 6 parts sodium chloride and/or potassium chloride (powder of fine granules) to said slurry, and quickly and thoroughly mixing or blending to provide a gel by polymerization reaction;
c) forming said gel into sheets of predetermined length, width and thickness; and d) heating said gel at about 1000°F to 1200°F
until intumescence is substantially complete to form a rigid, cellular, ceramic product.

18. A sheet of wall board, or the like, produced according to the method of claim 17.

19. A method of producing a very light weight bulk insulation product, or the like, comprising the steps of:

a) thoroughly mixing 2 to 8 parts by weight of potassium nitrate or sodium nitrate into 20 parts by weight of a 10% to 40% (by weight) aqueous solution of sodium silicate or potassium silicate having a soluble SiO2 to alkali metal oxide ratio between about 2:1 and 5:1 to provide a gel by polymerization reaction;
b) forming said gel in sheets or other predetermined shapes;
c) heating said gel at about 500°F to 1100°F
until intumescence is substantially complete to form said bulk insulation product.

20. A bulk insulation product, or the like, produced by the method of claim 19.

21. The method of claim 19 including the further step of adding up to 2 parts by weight sodium and/or potassium sulfate and/or phosphate to said aqueous solution prior to formation of said gel.

22. The method of claim 19 wherein said silicate is sodium silicate.

23. The method of claim 22 wherein said nitrate is about 4 parts by weight of potassium nitrate.

24. The method of claim 23 including the further step of adding up to 5 parts by weight of fiber or mesh fillers to said aqueous solution prior to or during formation of said gel.

25. The method of claim 19 wherein a sheet of aluminum foil or similar materials is applied to the gel layer before heating, or to the finished cellular ceramic product.

26. A bulk insulation product, or the like, produced by the method of claim 25.

27. A laminar structure for use as a fire and heat retardant product comprising a first layer of gel which exhibits intumescence upon application of heat formed by polymerization reaction by mixing at least one alkali metal chloride, bromide, iodide or nitrate in an aqueous solution of sodium silicate or potassium silicate sandwiched between second and third, substrate layers, whereby upon exposure of said product to heat or flame said gel layer intumesces with consequent absorption and dissipation of heat through the production and release of steam in transition of said gel layer to a ceramic foam layer.

28. The product of claim 27 wherein said substrate layers are of flammable material.

29. The product of claim 28 and further including an essentially moisture-impervious barrier between said gel layer and each of said substrate layers.

30. The product of claim 28 and further including an essentially moisture-impervious barrier surrounding said gel layer.

31. The product of claim 30 wherein said gel layer comprises a plurality of separately encapsulated portions each surrounded by said moisture-impervious barrier.

32. The product of claim 31 wherein said moisture-impervious barrier comprises a flexible, plastic membrane.

33. The product of claim 27 wherein said gel layer includes particles of at least one hydrated salt comprising up to 20 percent by weight of the total material and other filler materials such as glass or ceramic fibers or mesh comprising up to 12 percent by weight of the total material.

34. The product of claim 33 wherein said hydrated salt particles are added to and dispersed throughout said gel layer during and/or after the gel is essentially formed.

35. The product of claim 33 and further including a layer of essentially moisture-impervious material individually covering each of said salt particles.

36. The product of claim 27 wherein said silicate is potassium silicate.

37. A method of producing a vitreous ceramic foam product comprising the steps of:
a) thoroughly mixing about 2 to 8 parts by weight sodium chloride and/or potassium chloride, and about 2 to 12 parts by weight of one or more of the class of compositions consisting of Bentonite clay, MgCO3, MgSiO3, Al2O3, Li2SiO3, LiCl, and CaCO3 into 20 parts by weight of a 10% to 40% (by weight) aqueous solution of sodium silicate and/or potassium silicate having a soluble SiO2 to alkali metal oxide ratio of about 1:1 to 5:1, forming a gel by polymerization reaction;
b) heating said gel at about 1000°F to 1200°F
until intumescence is substantially complete, forming a rigid, cellular, ceramic foam product;

38 c) heating said foam product to a temperature at or near its melting point until the foam cells begin to fuse together, resulting in partial collapse and shrinkage but short of complete melting of said foam product; and d) cooling the resulting vitreous, ceramic product.
38. A vitreous ceramic product produced by the method of claim 37.

39. The method of claim 37 wherein about 3 to 5 parts sodium chloride and/or potassium chloride are mixed into said aqueous solution.

40. The method of claim 37, and further including adding filler materials consisting of particles of an abrasive material to said gel in a quantity which is essentially up to the saturation point of the gel.

41. The method of claim 40 wherein said abrasive material is at least one of sand, garnet and silicon carbide.

42. An abrasive wheel or block for grinding or polishing produced by the method of claim 40, wherein said vitreous, ceramic product serves as a matrix for said abrasive particles.

43. A method of producing a cellular, ceramic material comprising the steps of:
a) thoroughly mixing about 1.6 to 5 parts by weight hydrated silicic acid into 20 parts by weight of a 10% to 40% (by weight) aqueous solution of sodium silicate or potassium silicate having a soluble SiO2 to alkali metal oxide ratio of about 2:1 to 5:1 to form a slurry;
b) thoroughly mixing about 1.6 to 4 parts by weight of at least one alkali metal chloride, bromide, iodide or nitrate into said slurry, thereby producing by polymerization reaction a gel which exhibits intumescence upon application of heat;
c) heating said gel via microwave energy (microwave oven) until intumescence is substantially complete.

44. The method of claim 43 and further comprising forming said gel into substantially flat sheets prior to said heating step.

45. A wall board product produced according to the method of claim 44.

46. The method of claim 43 wherein said silicate is sodium silicate.

47. The method of claim 46 wherein said alkali metal chloride, bromide, iodide or nitrate is sodium chloride and/or potassium chloride.

48. The method of claim 47 wherein said aqueous solution has a colloidal SiO2 to soluble SiO2 ratio of about 1:1 to 3:1, prior to the addition of said silicic acid.

49. The method of claim 48 wherein about 2 to 3 parts by weight of said silicic acid and about 2 parts by weight of said sodium chloride and/or potassium chloride are mixed into said aqueous solution to form the gel.

50. The method of claim 49 and further comprising mixing into said slurry up to about 1 part by weight of CaCO3 and/or aluminum silicate.

51. The method of claim 50 wherein about .4 parts of CaCO3 are mixed into said slurry.