CA1090834A - Composition and process for forming cellular inorganic resin cements and resulting product - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Composition and process for forming cellular inorganic plastic cements of magnesium oxychlorides and magnesium oxysulfates.
A water slurry containing a magnesium salt, magnesium oxide and a water-soluble phosphate is formed and to it are added an anionic water-repellent surfactant and a liquid fluorinated hydrocarbon blowing agent. Inorganic filler materials are added to impart strength to the cellular product which is nonflammable and exhibits essentially zero flame spread, zero smoke density and zero fuel contribution. The cellular product is formed of substantially uniformly sized cells, a major portion of which are closed and contain residual blowing agent, a fact which makes the cellular product a good thermal insulator.

Description

~901~34 This invention relates to a foamed inorganic plastic cement and more particularly to a foamed magnesium oxychloride or magnes.ium oxysulfate of controlled, predetermined density and strength which is water-resistant, nonhygroscopic and nonflammable.
The magnesium oxide cements, generally referred to as inorganic plastic cements, are known in the art. An improved pro-cess for the ~reparation of these inorganic plastic cements (mag-nesium oxychloride and magnesium oxysulfate) is described in United States Patent 3,320,077. These inorganic plastic cements have .
found wide use in the manufacture of such articles as building .` bric]~s, and molded structures such as plumbing fixtures, construc-tion panels, flooring and the like.
Because of the strength, water-resistance, and nonflam-mability of these materials they offer the possibility of being used for a wide range of other applications, particularly in a less dense (~oamed) formO The prior art disclosed various processes for foaming magnesium oxychloride and magnesium oxysulfate (See for example United States Patents 2,598,980, 2,702,753, 3,119,704, 3,147,128, 3,522,069, 3,573,941 and 3,778,304). The foaming of refractory materials has also been disclosed (See for example United States Patent 2,662,825). These prior art processes for foaming the inorganic cements have resulted in structures with nonuniform open and closed cells and densities ranging between about 10 and 30 pounds per cubic foot. Although some of these foamed products have found use as acoustical insulation, they do not possess the full range of properties which are attainable from a foamed inorganic plastic cement which has a substantially uniform cell structure, the majority of the cells of which are closed, and a controlled predetermined density ranging from about 6 to about 80 pounds per cubic foot. Such foams with at least partially closed cell struc-

-2-109(~834 ture have excellent thermal insulating properties, and can be designed to possess a desired degree of strength.
It is therefore a primary object of this invention to provide a process for forming a foamed magnesium oxychloride or magnesium oxysulfate having an essentially uniform cell structure - consisting of a continuous solid phase having at least a majority of the cells_closed, thereby defining a gas phase within ~he struc-ture. Another object is to provide a process of the character described which, in its various embodiments, makes possible the formation of inorganic plastic cements of controlled, predetermined densities, strength and other physical characteristics.
Another primary object of this invention is to provide inorganic plastic cement compositions which contain an emulsified blowing agent uniformly distributed therethrough, which release the blowing agent at a uniform and rapid rate before the plastic cement gels, which has a high solids concentration but a relative low viscosity and which give rise to an inorganic plastic foam exhibiting improved properties.
Yet another primary object of this invention is to pro-vide improved foamed inorganic plastic cements having an essential-ly uniform cell size struckure with a gas entrapped within the closed cells and controllable, predetermined densities and strengths.
A further object is provide foamed inorganic pLastic cements of the character described which are water-resistant, nonhygroscopic and nonflammable and which exhibit essentially zero flame spread, zero smoke density and zero fuel contribution. It is an addition-al object of this invention to provide foamed inorganic plastic cements which incorporate an inorganic filter. Still a further object is to provide a new and improved thermal insulation.

Other objects of the invention will in part be obvious 109083~

and will in part be apparent herelnafter.
According to one aspect of this inventi.on there is provided a process for forming an inorganic plastic cement in a foamed cellular form which comprises the steps of forming a water sl-urry of a magnesium salt, a water-soluble phosphate and magnesium oxide having a viscosity ranging between about 700 and 15,000 centipoises, blending an anionic water-repellent surfactant into the slurry, uniformly dispersing a fluorinated hydrocarbon liquid blowing agent throughout the slurry, the temperature of the slurry being a few degrees below the boi1ing point of the blowing agent, whereby -the dispersing of the blowing agent in the slurry increas2s :its temperature to above the boiling point of the blowing agent and effects a desi~ed increase in volume to form a cellular product. It may be desirahle to add a small amount of a nucleating agent; and in-organic reinforcing filler materials may be blended into the foamed slurry to impart a predetermined tensile strength to the foamed product.
According to another aspect of this invention, there is provided a process for forming an inorganic plastic cement in a foamed cellular form, comprising the steps of (a) forming a slurry by first forming a solution of a magnesium salt in water containing a water-soluble phosphate and then slowly adding reactive magnesium oxide to said solution with high-shear blending, the concentration of said magnesium salt in said solution ranging between about 60% and 75% by wei3ht of said salt, said slurry having a viscosity ranging between a~out 700 and 15,000 centipoises, (b) blending .into said slurry an anionic water-repellent surfactant in an amount equal to at least 0.5% by weight of said slurry; (c) uniformly dispersing a fluorinated hydrocarbon liquid blowing agent throughout said . .
~ 4-10~0&~3~

slurry in an amount up to about 8% by weight of said slurry, the temperature of said slurry being at least a few degrees below the boiling point of said blowing agent, thereby to form a foaming composition which when heated to a temperature above the boiling point of said blowing agent experiences a predetermined increase in volume to form an inorganic plastic cement with a cellular structure of predetermined density.
According to another aspect of this invention there is provided a composition for forming a cellular inorganic plastic cement comprising in combination a water slurry of a magnesium salt, magnesium oxide and a water-soluble phosphate having a viscosity ranging between about 700 and 15,000 centipoises, and an anionic water-repellent surfactant and a fluorinated hydrocarbon blowing agent uniformly disparsed throughout the water slurry. The blowing agent is chosen to have a boiling point a few degrees below the temperature of the slurry at the time of its addition to the slurry. The composition may also contain a nucleating agent, and if any appreciable strength is required in the final cellular product, it must also contain an inorganic filler material. By proper adjustment in the amount of each of the components making up the composition, it is possible to form a cellular product having essentially uniformly sized cells up to about 6 mm in diameter, a density ranging from about 5 to 100 pounds per cubic foot and a tensile strength up to 100 pounds per square inch or greater.
According to another aspect of the invention, there is provided a composition for forming a cellular inorganic plastic cement, comprising in combination (a) a slurry having a viscosity ranging between about 700 and 15,000 centipoises and comprising a water solution of a magnesium salt present 1~19(~3~

in an amount ranging between about 60% and 75% by weight of said solution, a water-soluble phosphate and reactive magne-sium oxide; (b) an anionic, water-repellent surfactant present in said slurry in an amount between about 0.5% and 3% by weight of said slurry, and (c) a liquid fluorinated hydrocarbon blowing agent present in an amount up to about 8% by the weight of said slurry uniformly dispersed throughout said slurry thereby to form a foaming composition which when heated to a temperature above the boiling point of said blowing agent experiences a predetermined increase in volume to form an inorganic plastic cement with a ceIlular structure having a predetermined density Formation of the inorganic plastic cement composition of this invention is, up to a certain point, preferably carried out in the accordance with the teaching of U.S. Patént

3,320,077 That is, up to the point of adding the surfactant and blowing agent, ~along with any nucleating agent and filler if used), it is preferable to use high shear blending in mixing the magnesium oxide into the gaging solution of magnesium salt and water-soluble phosphate additive. Therefore the process for the forming of the foaming composition comprises the steps described below. The components, alony with the ranges in which they may be used, will be identified in this process description.
The magnesium salt used may be either magnesium chloride used as the hexahydrate, MgC12.6HzO, or magnesium sulfate used as the heptahydrate, MgS04.7H20. The first step of the process is the formation of a solution of the magnesium salt in water. This solution, known as the gaging solution, may be supersaturated with the magnesium salt and is formed to contain a small amount of a water-soluble phosphate which -5a-1~9083~L

may be added prior to the addition of the magnesium salt to the water as is preferable in the case of the use of sodium hexametaphosphate, or subsequently to the addition of the salt as may be done in the use of phosphoric acid. The role of the water-soluble phosphate is probably a dual one, to improve the wet strength of the foam formed and to control the viscosity of the foaming composition. Among the water-soluble phosphates which may be used are phosphoric acids, polyphosphates and particularly so-called sodium hexameta-phosphate, various alkali -5b-i -`~'~

~ 0~;~4 metal mono- and dibasic phosphates, ammonium phosphates and the like. The term "sodium hexametaphosphate" is used hereinafter, as is customary, to include a large number of glassy chain phos-phates wherein the molar ratio of Na20/P205 may range from about one to about 1.5. The amount of the water-soluble phosphate used ranges between about 1% and about 6% by weight of the ~agnesium oxide added while a preferable range is between about 1~ and 4~.
As will be shown, each of the components in the composition has some influence on the final physical properties of the foamed product and in choosing an optimum composition for any one set ` of properties it is necessary to take the effects of each into account.
The data in Table 1 illustrates the effect on cell struc-ture and foam density of the presence of a water-soluble phosphate in the foam composition. In forming the compositions of Table 1, concentration of MgC12-6H20 in the water was about 70% by weight, the molar ratio of MgC12 6H20 to MgO was 1 to 5, 2~ by slurry weight of ammonium stearate was used as the surfactant and 4~ by slurry weight of CC13F was used as the blowing agent.

Table 1 Effect of Water-Soluble Phosphate on Foam Density and Cell Structure Phosphate ¦ ¦ Denslty Weight Structure ¦ lbs/ft3 _ ~ __ .. ~__ __ 0.0 nonfoaming 80 - 85 :L.O ultrafine6.0 2.0 ultrafine8.0 - 9.5 ....

~09(~33~

These data in Table 1 show how the phosphate enables the composition to be foamed and then to possess sufficient wet strength to set up in a permanent foam form.
In preparing the gaging solution, the weight concentra-tion of the magnesium salt in the water solution formed should range between about 60% ~nd 75% based on the weight of the hydrated salts. It will be seen from Table 2 that concentrations of the magnesium salt of less than about 60% give rise to the formation of excessively large, open, nonuniform cells in the foamed product.
In formulating the compositions to obtain the data of Table 1, ` the gaging solution contained 70% by weight MgC12-6H20; the slurry had a molar ratio of MgC12 6H2O to MgO of 1 to 5; and it contained

4% by weight CC13F as a blowing agent and 2% ammonium stearate as the surfactant.

Table 2 Effect of MgC12 6H2O Concentration on Cell Size and Uniformity . I .. _ % Conc.
MgCl26H2O Average in Gaging Cell Size Uniformity Density Solution* mm2** Structure-~ lbs/ft _ oversize N, W, O9.00 oversize N, W, O6.50 2.05 N, W, o6.50 1.24 U, S, C6.10 0.53 U, S, C5.74 0.64 U, S, C5.90 0 46 U, S, C6.40 *Gaging solution formed of MgC12 6H2O and water **Measured area of cut cell ~N nonuniform; W - weak; O ~ open;
U - uniform; S - strong; C - closed The magnesium oxide used may be either natural or syn-thetic, the synthetic being preferred due to its plate-like structure, uniform consistency and absence of trace amounts of impurities which may discolor the foam. A preferred form of magnesium oxide is one which has an iodine n~mber between 15 and 60, a particle size distribution such that 50% is less than 0.2 to 0.3 micron and substantially all is less than 20 microns, a hexagonal plate crystal system and a crystal size between about 0.02 and 0.035 micron. Magnesium oxide with these characteristics is generally considered to be active and it will react with the magnesium salt ` used.
The amount of magnesium oxide depends upon the magnesium salt used to form the inorganic plastic cement. If magnesium chlo-ride is used, then the molar ratio of MgC12 6H2O to MgO is between about 1 to 3 and about 1 to 8; while if MgSO4-7H2O is used the molar ratio is between about 1 to 3 and about 1 to 14.
The magnesium oxide is added to the magnesium salt solution containing the phosphate. It is preferable that the magnesium oxide be added slowly and that the slurry during formation be pro-cessed in a high~shear blender (e.g., a Daymax or Meyers in com-mercial production) to deflocculate and thoroughly disperse the magnesium oxide particles. The use of very fine magnesium oxide and its thorough dispersion for reaction with the magnesium salt result in a low viscosity slurry and hence in a less dense foam.
Thus the quality of the magnesium oxide is a important contributing factor to foam density.
In forming a foam of the character described, it is n necessary to use what may be termed an "emulsified" surfactant.
This surfactant exercises some control over the cell structure of the foamed product. It is thought that the particular type ~'~1190~34 of surfactant used is at least partially responsible for the fact that a major portion of the cells are closed, makiny it possible to entrap the blowing agent in them.
The surfactant is added to the water slurry of phosphate, magnesium salt and magnesium oxide. The addition of the surfac-tant should be done in such a manner as to ensure its uniform dis-persion throughout the slurry. This is preferably accomplished in a high-shear mixing device. The surfactant shouId be one which is water repellant and anionic in character. Such suitable sur-factants include, but are not limited to, stearic acid, the saltsof stearic acid such as ammonium, sodium, magnesium, zinc and calcium stearate, dimethylpolysiloxane, anionic silicone resin emulsions, mixtures thereof, and the like.
A number of compositions were made up, each one using a different one of the above-listed surfactants in an amount equal to 2% or 3% by slurry weight. The compositions contained MgC12 6H2O
and MgO in a molar ratio of 1 to 5, 1~ by slurry weight of sodium hexametaphosphate and 4~ by slurry weight of CC13F as a blowing agent. The foaming efficiency was rated good and the resulting foamed inorganic plastic cements had densities ranging between

5.9 and 8.6 pounds per cubic foot.
When similar compositions were made up using nonionic surfactants such as a sorbitan monostearate, a cationic surfactant such as a quaternary organosilicone or a nonwater repellant anionic such as an alkyl sulfonate, the foaming efficiency was not acceptable and the foam collapsed.
There does not appear to be a direct correlation between the amount of surfactant added and the density of the foamed pro-duct. However, a minimum amount of surfactant is required to obtain a desirable cell structure. It will generally be desirable to use 1[)90&~34 between about 0.5% and 3~ of the anionic, water-repellent surfactant based upon the total weight of the slurry weight.
In some cases it may be desirable to add a small amount, e.g., up to about 0.5% by slurry weight of a nucleating agent, e.g., a silicone oil, to assist the transportation of the blowing agent molecule from solution in the slurry into the gas phase.
When the anionic surfactant itself is a silicone resin emulsion (e.g., a surfactant sold under the tradename of U.C.R.-230 Silicone Emulsion by Union Carbide Company) it will not be necessary to add a separate nucleating agent. If used, the nucleating agent ` is added along with or subsequent to the addition of the surfactant to the slurry in an amount up to about 0.5% by slurry weight.
The aqueous slurry thus formed and containing the water-soluble phosphate, magnesium salt, magnesium oxide, surfactant and nucleating agent, if used, should have a viscosity ranging between about 700 and 15,000 centipoises with a preferred range being between about 700 and 2500 centipoises. It is preferable that the slurry at this stage prior to the addition of the blowing agent be nonthixotropic, particularly if it is desired to obtain minimum densities in the final product.
Once the slurry with the desired viscosity has been formed and thoroughly mixed, it may be necessary to adjust its temperature prior to adding the blowing agent. The slurry tem-perature should be at least a few degrees (e.g., about 4 to 5F) below the boiling point of the blowing agent. This permits the thorough dispersion of the blowing agent as a liquid throughout the slurry before any appreciable volume increase takes place.
The blowing agent is a fluorinated hydrocarbon liquid having a boiling point below the curing temperature of the foam.
The blowing agent is preferably one which has a boiling point ~09'~

a few degrees within ambient temperature to permi-t adding it to the slurry without requiring any great amount of slurry cooling while at the same time making it possible, if desired, to achieve curing of the foam at a temperature only slightly above ambient.
Under normal conditions, the slurry, after mixing is completed, will be a few degrees above 70F. If it is then cooled to 70~, a fluorinated hydrocarbon such as CC13F (b.p. 74.9F) may be added. It is important that the blowing agent be thoroughly and uniformly blended into the slurry to ensure the formation of uniformly-sized cells. As the mixture is thoroughly blended to ` disperse the blowing agent, the temperature will rise to a point where the blowing agent reaches its boiling point with resultant bubble formation and subsequent bubble growth resulting in a marked increase in volume. When the foaming composition is formed in the manner described, the foamed slurry does not gel before it reaches its maximum volume increase. Moreover, the foam possesses sufficient green strength stability so that it does not collapse before the plastic cement sets and can be cured. These perfor-mance characteristics of the foam are, of course, essential and they are inherent in the process and composition of this invention.
Final foam density is primarily controlled by the amount of blowing agent added. However, the surfactant used, the vis-cosity of the slurry and the ratio of magnesium salt to magnesium oxide as well as the solids concentration of the gaging solution in conjunction with the amount of blowing agent also exert some influence on the density of the foamed inorganic plastic cement formed. Table 3 presents data which are illustrative of the effect of the amount of blowing agent used. In obtaining the data of Table 3 a slurry was formed in which the molar ratio of ~IgC12~6EE2O
to MgO was 1 to 5, the concentration of the gaging solution was ~ V~

70~, 1% by MgO weight of sodium hexametaphosphate was added as the water-soluble phosphate, 2~ by slurry weight of ammonium stearate was used .as the surfactant and 0.5% by slurry weight of a silicone oil was added as a nucleating agent. The blowing agent was CC13F.
The slurry had a viscosity of about 700 to 2500 centipoises.

_ Table 3 Effect of slowing Agent on Foam Density % Blow ng ~ Density Slurry Weightlbs/ft 0.75 40.0 1.0 30.0 1.5 25.0 2.5 15~0 4.0 . 6.0 From the data of Table 3, it will be seen that for the particular slurry composition chosen, the amount of blowing agent ranged between about 0.75% and about 4% by slurry weight to ob-tain a density range of 6 to 40 pounds per cubic foot. However,for other compositions and other slurry viscosities, the amount - of blowing agent may vary between about 0.5% and about 8% by slurry weight.
For many of the applications of the foamed organic plastic cements of this invention it will be desirable to incorporate inorganic reinforcing filler materials such as milled or chopped glass fibers, mica, mineral fibers such as those of marble and asbestos and the like in-to the slurry during the foaming. These reinforcing material may be added just prior to, with or just after ~0~0~33~

the addition of the blowing agent. The viscosity of the final foaming composition, with or without reinforcing material, may be up to about lO0,000 centipoises with a range between 2,000 and 25,000 centipoises being preferable. It is not necessary that the final foamed composition be thixotropic.
These filler materials impart strength to the foamed product and are desirable in those foams which are to be used in applications where any appreciable degree of tensile strength is required. However, there are applications where strength is `not important, e.g., as thermal insulation within a supporting structure, and where reinforcing filler material is not required.
The amount of reinforcing filler material which can be added depends upon the nature of the material. Thus, if it is in very finely dlvided form and if it is readily wettable for easy dispersion throughout the foam structure, a greater amount may be added than if it is of larger size and less easily dispersed.
This is illustrated in the data of Table 4. The basic slurry composition used was that used to obtain the data of Table 3 having 4~ by slurry weight of CC13F as the blowing agent. The tensile strengths of the foamed inorganic plastic cements were determined by the procedure of ASTM Test No. D638.

~0~ 334~

Table 4 Effect of Inorganic Fillers on Foam Properties ... ___ . __ .... _ .
Filler Foam Tensile Blowing by Slurry ns y Strength Agent Filler Weight lbs/ft psi Weight _ _ _-- __ _ _ . 1/4" 0.0 9.0 1 4 bon~ed 8.0 11.2 6 4 milled glass 10.0 17.9 40 4*
0.0 15.6 12 2.5 8.0 23.0 98 2.5 . . . .: _ - --1/4" 16.0 16~5 56 4 water-bonded 20.0 17.4 60 4 milled glass ... . .. _ milled 16.0 16.0 42 4 glass with20.0 17.8 53 4 cationic ; surfactant .... __ _ .
: 1/4" 2.0 16.3 44 2.5 chopped .
fibers 4.0 25.4 52 2.5 8.0 2.5*
*These compositions were extremely thick and not acceptable for processing.

~0~083~

It will be seen from the data of Table 4 that in those instances where milled glass fibers are used as the reinforcing filler material, a greater amount of the filler may be used because of the presence of very fine materials. ~oreover, when the milled glass is water-bonded or treated with a cationic surfactantt even more may be added than in the case where the glass is untreated because these surface treatments give rise to easy dispersibility.
Thus the amount of inorganic reinforcing filler material added will depend upon the nature of the filler material and the tensile strength desired. The maximum ~uantity of filler material used will be that ` which is no greater than the amount which will raise the viscosity of the foaming composition up to about 100,000 cen-tipoises and less than that which will cause the collapse of the foam. The optimum amount of filler material within these ranges will be that required ; to obtain a predetermined desired tensile strength. Table 4 shows that about 20~ filler by slurry weight is the maximum amount for any filler.
In choosing the filler material it is desirable that a major portion (over 50%) of it is not greater than 1/4 inch in length if it is a fiber or not greater than 325-mesh if it is par-ticulate material. Fibers ranging in length between about 1/32 and 1/4 inch are preferred. In general, the finer the size of the filler the more of it may be added and still have a foaming composition capable of setting up into a desirable structure.
Once the foamed composition is formed it may be poured into any suitable mold for final gelling, setting and curing.
The mold surface may be coated with a suitable release coating such as a silicone oil or a wax.
Although the foam may be cured at room temperature over an extended period of time, e.g., several days, it is preferable 10~ 3~

in commerical practice to accelerate curing by using heat. The heat may be supplied in the form of infrared radiation, hot gases, e.g r air, and the like. The temperature at which this curin~
is carried out should be that which :raises the temperature o~ the foamed structure to no greater than about 350F.
The foamed product of this invention may be distinguished and characterized by its physical properties. Tlle cell structure is one in which the uniformity of the size of the cells throughout any one foam depends at least in part on the cell size, the degree of uniformity increasing with decreasing size. In those structures ` wherein the cells may be classed as large sized (e.g., having diam-eters greater than 3 mm) the nonuniformity of the cell sizes is sufficiently marked to make such structures generally unacceptable.
In the case of structures wherein the cell diameters range from about 1.25 to 3 mm (cross sectional area from about 1 to 7 mm2) the cells are substantially uniform in size; and in structures having the cells classed as fine (less than 1.25 mm in diameter and no greater than about l mm2 in diameter and no greater than about 1 mm in cross section) the cells are essentially all of uniform size. It is preferable that essentially all of the cel~s have cross sectional areas no greater than about 2 mm2.
In the preferred embodiment of the foamed product of this invention a major portion, i.e., more than 50%, of the cells are closed and contain the blowing agent entrapped therein. Since the blowing agent used has a very low coefficient of thermal con-ductivity, those foamed structures having a large percentage of closed cells make excellent thermal insulation.
The density of the foamed product may range between about 5 and about 100 pounds per cubic foot, while a perferred density range is between about 5 and 50 pounds per cubic foot. As noted i~19~33~

previously, the tensile strength may he controlled and may be varied from essentially zero for supported insulation up to as much as 100 pounds per square lnch or greater. The ul-timate use of the foamed product will, of course, dicta-te the desired strength.
Since the reactions by which these inorganic plastic cements are formed are ones in which all of the water of hydration and all of the water added to form the slurry are consumed, the amount of the inorganic filler material may range up to about 16~ of the finished cured product.
Finally, the foamed product is water resistant and non-hygroscopic. It is nonflammable and exhibits essentially zero flame spread, zero smoke density and zero fuel contribution. In flame spread tests its performance was equivalent to that of as-bestos which has a zero rating; it was determined to have a limit-ing oxygen index of greater than 95; and in the N.B.S. smoke cham-ber test it had a maximum uncorrected value of DSM3.
The process of this invention thus provides a novel product which has unique properties and which is particularly suitable for construction purposes. A wide range of densities and tensile strengths may be realized, giving the product a wide range of uses.
It will thus be seen that the objects set forth above, among those made apparent from the preceding descriptio~, are ef-ficiently attained and, since certain changes may be made in car-rying out the above process and in the article set forth without departing from the scope of the invention, it is intended that all matter contained in the above descrip-tion shall be interpreted as illustrative and not in a limiting sense.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A process for forming an inorganic plastic cement in a foamed cellular' form, comprising the steps of (a) forming a slurry by first forming a solution of a magnesium salt in water containing a water-soluble phosphate and then slowly adding reactive magnesium oxide to said solution with high-shear blending, the concentration of said magnesium salt in said solution ranging between about 60% and 75% by weight of said salt, said slurry having a viscosity ranging between about 700 and 15,000 centipoises;
(b) blending into said slurry an anionic water-repellent surfactant in an amount equal to at least 0.5% by weight of said slurry;
(c) uniformly dispersing a fluorinated hydrocarbon liquid blowing agent throughout said slurry in an amount up to about 8% by weight of said slurry, the temperature of said slurry being at least a few degrees below the boiling point of said blowing agent, there-by to form a foaming composition which when heated to a temperature above the boiling point of said blowing agent experiences a pre-determined increase in volume to form an inorganic plastic cement with a cellular structure of predetermined density.

2. A process in accordance with claim 1 wherein said magnesium salt is magnesium chloride hexahydrate.

3. A process in accordance with claim 2 wherein the molar ratio of said magnesium chloride hexahydrate to said magnesium oxide ranges between about 1:3 and about 1:8.

4. A process in accordance with claim 1 wherein said magnesium salt is magnesium sulfate heptahydrate.

5. A process in accordance with claim 4 wherein the molar ratio of said magnesium sulfate heptahydrate to said mag-nesium oxide ranges between about 1:3 and about 1:14.

6. A process in accordance with claim 1 wherein the viscosity of said slurry ranges between about 700 and 2500 centi-poises.

7. A process in accordance with claim 1 wherein said water-soluble phosphate is sodium hexametaphosphate and is present in said slurry in an amount ranging between about 1% and 6% by weight of said magnesium oxide.

8. A process in accordance with claim 1 wherein the amount of said anionic water-repellant surfactant ranges between about 0.5% and 3% of the weight of said slurry.

9. A process in accordance with claim 8 wherein said surfactant is stearic acid or a salt thereof.

10. A process in accordance with claim 8 wherein said surfactant is a silicone resin emulsion.

11. A process in accordance with claim 1 including the step of adding to said slurry a nucleating agent for bubble formation in an amount up to about 0.5% by weight of said slurry.

12. A process in accordance with claim 1 wherein said blowing agent is trichlorofluoromethane in an amount equivalent to between about 0.5% and about 8% by weight of said slurry.

13. A process in accordance with claim 1 wherein the viscosity of said foaming composition is no greater than about 100,000 centipoises.

14. A process in accordance with claim 13 wherein said viscosity of said foaming composition ranges between about 2,000 and 25,000 centipoises.

' 15. A process in accordance with claim 1 including the step of adding to said foaming composition a finely divided, in-organic filler material, the amount of said filler being no greater than that which will raise the viscosity of said foaming composition up to about 100,000 centipoises and less than that which will cause the collapse of said cellular structure.

16. A process in accordance with claim 15 wherein said inorganic filler material is milled, waker-bonded glass fibers in an amount up to about 20% by weight of said slurry.

17. A process in accordance with claim 15 wherein said inorganic filler material is milled, starch-bonded glass fibers in an amount up to about 10% by weight of said slurry.

18. A process in accordance with claim 15 wherein said inorganic filler material is milled, cationic suftactant-treated glass fibers in an amount up to about 20% by weight of said slurry.

19. A process in accordance with claim 15 wherein said inorganic filler material is chopped, glass fibers in an amount up to about 7% by weight of said slurry.

20. A process in accordance with claim 1 including the step of curing said inorganic plastic cement with said cellular structure at an elevated temperature up to about 350°F.

.

21. A composition for forming a cellular inorganic plas-tic cement, comprising in combination (a) a slurry having a viscosity ranging between about 700 and 15,000 centipoises and comprising a water solution of a magne-sium salt present in an amount ranging between about 60% and 75%
by weight of said solution, a water-soluble phosphate and reactive magnesium oxide;
(b) an anionic, water-repellent surfactant present in said slurry in an amount between about 0.5% and 3% by weight of said slurry; and (c) a liquid fluorinated hydrocarbon blowing agent present in an amount up to about 8% by the weight of said slurry uniformly dispersed throughout said slurry thereby to form a foaming composi-tion which when heated to a temperature above the boiling point of said blowing agent experiences a predetermined increase in volume to form an inorganic plastic cement with a cellular structure having a predetermined density.

22. A composition in accordance with claim 21 wherein said magnesium salt is magnesium chloride hexahydrate and the molar ratio of said magnesium chloride hexahydrate to said magnesium oxide ranges between about 1:3 and about 1:8.

23. A composition in accordance with claim 21 wherein said magnesium salt is magnesium sulfate heptahydrate and the molar ratio of said magnesium sulfate heptahydrate to said magnesium oxide ranges between about 1:3 and about 1:14.

24. A composition in accordance with claim 21 wherein the viscosity of said slurry ranges between about 700 and 2500 centipoises.

25. A composition in accordance with claim 21 wherein the viscosity of said foaming composition is not greater than about 100,000 centipoises.

26. A composition in accordance with claim 25 wherein said viscosity of said foaming composition ranges between about 2,000 and 25,000 centipoises.

27. A composition in accordance with claim 21 wherein said water-soluble phosphate is sodium hexametaphosphate and is present in said slurry in an amount ranging between about 1% and 6% by weight of said magnesium oxide.

28. A composition in accordance with claim 21 wherein said surfactant is stearic acid or a salt thereof.

29. A composition in accordance with claim 21 wherein said surfactant is a silicone resin emulsion.

30. A composition in accordance with claim 21 including a nucleating agent for bubble formation in an amount up to about 0.5% by weight of said slurry.

31. A composition in accordance with claim 21 wherein said blowing agent is trichlorofluoromethane in an amount equiv-alent to between about 0.5 and about 8% by weight of said slurry.

32. A composition in accordance with claim 21 including a finely divided, inorganic filler material, the amount of said filler being no greater than that which will raise the viscosity of said foaming composition up to 100,000 centipoises and less than that which will cause the collapse of said cellular structure.

33. A composition in accordance with claim 32 wherein said inorganic filler material is milled, water-bonded glass fibers in an amount up to about 20% by weight of said slurry.

34. A composition in accordance with claim 32 wherein said inorganic filler material is milled, starch-bonded glass fibers in an amount up to about 10% by weight of said slurry.

35. A composition in accordance with claim 32 wherein said inorganic filler material is chopped, glass fibers in an amount 36. A composition in accordance with claim 32 wherein said inorganic filler material is milled, cationic surfactant-treated glass fibers in an amount up to about 20% by weight of said slurry.