US3055831A

US3055831A - Handleable heat insulation shapes

Info

Publication number: US3055831A
Application number: US143000A
Authority: US
Inventors: Barnett Irvin; Speil Sidney
Original assignee: Johns Manville
Current assignee: Johns Manville Corp; Johns Manville
Priority date: 1961-09-25
Filing date: 1961-09-25
Publication date: 1962-09-25
Anticipated expiration: 1979-09-25

Description

Unitcd States Patent Ofitiee 3,055,831 HANDLEABLE HEAT INSULATION SHAPES Irvin Barnett, Martinsville, and Sidney Speil, Somerville, N.J., assignors to Johns-Manvilie Corporation, New York, N.Y., a corporation of New York Filed Sept. 25, 1961, Ser. No. 143,000 22 Claims. (Cl. 252-62) This invention relates primarily to handleable heat insulation shapes which may be rigid or flexible and which have low thermal conductives comparable to, or below that of free still air.

This application is a continuation-in-part of our co pending US. patent application, Serial No. 792,872, filed February 12, 1959, and now abandoned, which in turn is a continuation-in-part of our then copending but subsequently abandoned US. patent application, Serial No. 270,748, filed February 8, 1952, which in turn is also a continuation-in-part of our earlier copending and subsequently abandoned US. patent application Serial No. 226,548, filed May 15, 1951.

A primary object of the invention is to provide heat insulation shapes which are handleable and which contain a maximum number of minute pore spacings between the finest structural units, such spacings averaging effectively below the approximate mean free path of the molecules comprising air.

Another object is to provide handleable heat insulation shapes which have heat insulating factors K within the range of 0.10.3, and preferably below 0.25, b.t.u./square foot/hour/inch/ F., at 350 F. mean, and which have sufficient strength to render them adaptable for use as structural insulation.

An additional object is to provide bonded handleable heat insulation shapes having such low heat insulating factors, which shapes may be rigid or which may be flexible or deformable, depending upon their composition and/or density.

A further specific object is to provide handleable shapes of improved thermal insulating efiiciency having a chiefly inorganic composition adapted for insulating service at temperatures ranging as high as 2000 F.

A further object is to provide structurally strong, temperature resistant insulations which are adaptable for use as transient insulaticns.

A still further object of this invention is to provide handleable heat insulations' having adequate strength characteristics and rigidity to render them adaptable for use as structural insulations, or having flexible and deformable properties if desired, which effectively control and/ or minimize the principal mechanism of heat transfer in insulating materialsmolecular air conduction-in addition to the other more readily restrainable mechanisms of heat transfer, viz. radiation, solid conduction and convection.

Another object is to provide loose fill type insulations of improved thermal and physical characteristics which are suitable for application by either blowing, pouring, tamping, etc. techniques.

With the above and other objects and features in view, the invention consists of improved thermal insulation materials which are hereinafter described and more particularly defined by the accompanying claims.

The drawing comprises a graph showing a comparison of the thermal conductivities of typical products of this invention with that of air.

An important novel feature of the herein disclosed handleable rigid or deformable heat insulation shapes is that, in general, shapes having densities in the range between 6 and 50 pounds per cubic foot have thermal conductivity factors K below 0.3, and preferably below 0.25, at 350 F. mean, and shapes having densities in the range of from approximately 10-25 pounds per cubic foot have a K of the order of 0.3 at 1000 F. mean. In other words, the preferred bonded handleable shapes of approximately 20 pounds per cubic foot density provide more efiicient heat insulation than a correspondingly dimensioned volume of free still air, which has a thermal conductivity of 0.26 at 350 F. and 0.40 at 1000" F.

The bonded handleable shapes, in the density range indicated, may have thermal conductivity factors below the corresponding thermal conductivity factors of unbonded loose mass mixtures of essentially the same composition as the bonded shapes, even after such mixtures have been consolidated by vibration to densities equaling the density of the bonded handleable shapes. Such a phenomenon is entirely unexpected since in normal instances of bonding together loose insulating particles, the finally formed body has a higher K than a correspondingly dense mass of loose particles. This is usually due, of course, to an increase in the solids conductivity of the mass, due to the binder. The handleable insulating shapes made according to our invention, however, may be prepared to exhibit the converse of this general consideration. For example, a bonded handleable rigid block of 10 pounds per cubic foot density comprising 5% by Weight of phenolaldehyde resin, 5% amosite asbestos fibers, and by weight of a mixture of 9 parts by weight of silica aerogel of approximately Voids by volume, and 1 part carbon black of finer than millimicrons particle size, was tested to have a K factor of 0.14 at F. mean. A bulk mixture of the same pro portions of silica aerogel and carbon black of the type and in the proportion used in molding the bonded shape, was vibrated to a density of 10 pounds per cubic foot and tested to have a K factor of 0.18 at 150 F. mean. The asbestos fiber of the block would also increase the solids conductivity, and would thus be expected to increase the K of the consolidated loose mass. It will be appreciated that a loose mass including fiber could probably not be vibrated to such density and retain homogeneity.

The preferred, bonded, self-sustaining insulating shapes of approximately 20 pounds per cubic foot density made in accordance with the present invention have low thermal conductivities approximating 75% of that of free air. The low thermal conductivities of the bonded self-sustaining shapes of this invention result primarily from uni form compositions containing fine ultimate structural units providing a maximum of average effective spacings between said structural units of the same order of magnitude as the mean free path of the molecules comprising air, said structure possessing high porosity and opacity ofliering maximum interference to continuous heat flow by either molecular gas conduction, solid conduction, convection, or radiation. This fine porous structure of the specified compositions restrains and/or controls movement of the air or the like gaseous mediums, eliminating heat transfer by convection. Heat transfer by radiation is minimized both by the small size of the pores and by the use of an opacifier.

Heat transfer or the thermal conductivity of a particu- 'lar material or medium typically comprises a total of the contribution of each of the four mechanisms of heat transfer-solid conduction, convection, radiation, and air or other gaseous molecular conduction. Of these four known mechanisms of heat transfer, molecular air con duotion or transfer of heat energy by molecular motion and collisions of the molecules comprising air or a similar gaseous medium comprises the preponderate and major source of heat transfer through conventional types of low density, bulky and porous insulations such as fibrous materials of various compositions at moderate temperature. Furthermore, at moderate temperatures in conventional types of insulations, the proportion of heat Patented $ept. 25, 1962- transfer or conductivity due to gaseous molecular conduction is typically substantially greater than the sum of all heat transfer due to the balance of the heat transfer mechanisms, i.e., solid conduction, convection and radiation. Moreover, although many conventional types of practical insulations are hi hly effective and efficient in controlling and minimizing heat transfer due to the mechanisms of solid conduction, convection and radiation, they are wholly wanting in diminishing heat transfer through the mechanism of molecular conduction.

To effectively and substantially control and minimize molecular conduction, in addition to the other mechanisms of heat transfer, the structure of the insulation shapes of this invention is such that the average effective pore space between the smallest structural units is of the same order of magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure. The standard mean free path of the molecules comprising air is, of course, the average distance traveled by one of its constituent molecules before suffering a collision with another molecule. Thus, the effective mean free path of the molecules comprising air confined in the pores of insulations of this invention is lower than the standard mean free path of free air because of collisions between the molecules comprising air and the structural elements composing the insulation. Accordingly, since the molecular thermal conductivity of air varies directly with the mean free path of its constituent molecules, this restriction of the mean free path of the heat conveying molecules within the insulations of this invention, that is, the reduction of collisions between the molecules, reduces the amount of heat transferred through such molecular inter-action. Air conduction, the principal mechanism of heat transfer at moderate temperatures in insulations of this type is thereby effectively controlled and reduced. The foregoing is mathematically represented by the formula:

KCFKKET.

where Hence, the lower the value of Lf, the lower the molecular conductivity of the air in the insulation. By determining the curve of the total conductivity vs. air pressure for typical insulations of the type claimed, it is possible to establish conclusively that the effective spacing between structural elements is approximately equal to that of the mean free path of free That is K (molecular conduction of air in a given insulation) approximately equals /zK (molecular conduction of free air).

Moreover, it will be appreciated that the mean free path of free air increases with an increase in absolute temperature or a decrease in atmosphere pressure, i.e., the value of L increases appreciably. Further, the value of L is relatively unaffected because of the low coefficient of thermal expansion of the insulation, and because of the absence of expansion of the structure with decreased gas pressure, thus the ratio of decreases. Hence, at higher temperatures or at elevated altitudes, the insulations of this invention are still more effective in reducing molecular air conduction. Thermal insulating efficiency increases of up to 50% are thus provided by the insulation shapes of this invention when exposed to the low pressure conditions of high altitudes rendering these insulations particularly adaptable for high altitude applications such as in aircraft, missiles, and the like. This improved insulating effect at high alti- 4. tude conditions is demonstrated by the comparative data illustrated in the graph of the drawing.

Current supersonic and high altitude air craft and missile flights frequently impose severe transient thermal conditions upon aircraft and thermal insulations for such aviation applications must be effective upon encountering transient as well as the more familiar steady state thermal conditions. In the case of steady state thermal conditions, the effectiveness of a thermal insulating composition or product is characterized by the product of its conductivity times its density (K X where:

K :conductivity =density The smaller this factor is, the less weight is required for equivalent insulating efficiency. However, in the case of transient thermal applications, although the weight of the insulating composition or product is still an important factor, the fundamental criterion or property for an insulation is its ability to prevent passage of heat during the transient period of exposure to the heat pulse. The effectiveness of the heat barrier is characterized by the conductivity of the insulation and its ability to store heat during exposure to increased temperature, that is, its heat capacity. The mathematical function which demonstrates the effectiveness of an insulating material or a thermal barrier is its diffusivity which is the ratio of the materials conductivity to the product of its density times its specific heat C X p K conductivity C=specific heat p density where:

of these insulations may be reduced by increasing the density of the product to values which would normally be considered incongruous to steady state applications. To this end, the characteristics of the insulations of this invention permit it to be made in relatively high densities while maintaining conductivities lower or comparable to that of free still air and in turn exhibiting desirably low diffusivity values.

The most preferred insulating shapes are composed essentially of a reinforcing skeleton or network of fine staple reinforcing fibers which may be either organic or inorganic; a binder, preferably distributed as a discontinuous coating over the fiber surfaces; and a substantial amount, preferably a major proportion, and usually at least 60% by weight of a particulate material which provides an average effective pore space between the smallest structural units of the same order of magnitude as the mean free path of the molecules comprising air. For most kinds of insulation service, particularly high temperature service, it is desirable to include in the composition finely divided opacifier materials, and also in some instances a small amount of well-distributed water repellent.

As heretofore mentioned, insulating shapes according to this invention may be either rigid, as for example, in the form of a rigid block or slab, and they may be flexible or deformable. Such characteristics of the shape are dependent upon various factors such as fiber content, binder, density, compresion in forming, etc. 'These characteristics, among others, also determine whether or not a fibrous material or binder is required in the body. Rigid insulating shapes according to this invention do not require the use of fiber, and may consist essentially of the particulate material together with an opacifier and a binder distributed throughout. In those shapes which are flexible or deformable, however, a fibrous material is an essential ingredient of the composition in that the fiber serves as a reinforcing network to allow the deformation of the shape as desired. It is of note, however, that the shapes of this invention are handleable, regardless of their flexibility or rigidity. Further, in certain applications conventional types of binder components, though typically desirable, are not essential and may even be detrimental for transient high temperature applications.

The staple reinforcing fibers may comprise such materials as various types of asbestos fibers of reinforcing grade synthetic mineral fibers, organic fibers, fine diameter glass fibers preferably pre-treated, as with acid, to roughen the surface, or otherwise to improve the surface adhesion characteristics, or mixtures thereof. The preferred inorganic fiber is a well-opened fine staple amosite asbestos classifying as to length at least 25% longer than /4". Suitable organic fibers may be natural fibers such as cotton, or synthetic fibers such as viscose or acetate rayon, polyamideor polyacrylic which in the case of the latter may, in some instances, be heat treated. All of such fibers should preferably classify finer than 20 microns diameter, and further, finer than microns. When utilized, the amount of fiber present in the bonded insulation shape may vary over a considerable range, depending on the strength requirements for the particular insulation service. In most cases where fiber is utilized in the formation of a rigid shape, the fiber content will comprise up to and most preferably approximately 5%, by weight of the insulating shape but optimum fiber content typically depends to a great degree upon the dimensions and/or strength requirements of the shapes. In the formation of deformable or flexible handleable shapes, however, the amount of fiber will also depend upon the extent of deformability or flexibility desired. It will be appreciated that the more flexible shapes will usually contain the greater amounts of fiber. We have found that preferred deformable or flexible shapes are attained when at least 35% by Weight fiber content is used, and up to 75% fiber may be utilized. For example, a deformable insulating shape according to this invention whichcontains 50% asbestos fiber by weight has a K of less than 0.25 at 350 F. mean.

Incorporation of a conventional binder material in the insulating bodies of this invention in amounts suficient to lend and/or enhance their handleable characteristic and structural strength is typically desirable and often necessary. As a practical matter the binder content should be suflicient to give the body ample strength to prevent breakage and maintain its integrity throughout manufacture, transportation, installation and the like, but it should be appreciated that in the deformable shapes a suflicient amount of fiber can serve alone to hold the particulate material of the body with sufficient tenacity to maintain its integrity. In general, binders may be utilized in any amount up to about 15% by weight of the insulating body and for most applications the binder may comprise approximately 5% by Weight but relatively smaller quantities of say 0.5% by weight up to as high as 35% by weight may be satisfactory in special applications. Suitable inorganic binders include, for example, among other conventional inorganic bonding materials, low temperature fusing glasses or enamels, phosphates, sodium silicate, etc. Organic binders, however, are often preferred over those of inorganic composition. A desirable organic binder, principally due to its ease of application and relatively high strength is a thermosetting resin of phenolic type, although urea-formaldehyde type or substantially any of the typical thermosetting as well as certain thermoplastic resin binders or heat-or catalyst-- activated binders such as, for example, vinyl chloride, vinyl chloride-acetate copolymers or silicones may be utilized.

Organic binders, however, being combustible comprise a fugitive bond when heat cured or incorporated in installations exposing the insulating body to temperatures above about 500 F. for extended periods. Accordingly, although a specific amount or an organic binder component is incorporated into the initially prepared product, exposure to elevated temperatures during curing or upon installation may remove a substantial portion or even all of the binder. The curing of a phenolic resin bond is an exothermic reaction which generates heat within the insulation and the thermal insulating etficiency of the bodies of this invention is such that internally produced heat is not readily dissipated or released from the interior of said bodies. Thus, the temperature of the interior of the block may rise materially above that of the curing oven, especially if the binder content is in excess of about 5% or the sample is in excess of approximately 1 inch in thickness. The resulting internal temperatures frequently rise sufficiently to initiate exothermic combustion of the binder with a further increase in the rate of heat evolution. This binder burn-out accelerates and propagates from the interior outwards toward the surface until the rate of heat dissipation from the block exceeds the rate of heat evolution and eventually stops leaving a thin shell of insulation containing binder on all exposed surfaces but with no appreciable binder remaining in the core or central portion of the body.

In applications subjected to temperatures exceeding approximately 500 F. the same situation may occuriwith binder combustion starting from the hot side and propagating towards the cold side, but in any case the organic binder such as phenolic resin will be eventually destroyed Wherever the temperature exceeds 450 F. for any prolonged period of time. It should be noted, however, that binder removal through burnt-out or the like is not necessarily objectionable and/ or detrimental in that conductivity is substantially unaffected and in many installations, insulating bodies totally void of binder throughout or in portions of the shape are entirely satisfactory, binders being primarily present in many applications to simplify fabrication, improve ability to maintain dimensional tolerances and diminish the degree of care in handling, etc. sible and practical means of controlling and regulating the extent and degree of potential binder burn-out is by governing the amounts of binder component included in the initial insulating body and the curing temperature.

Very thin insulation bodies in the range of about 0.1 inch may require higher binder contents, e.g., up to 35%, to insure adequate handling characteristics and such pieces can be cured without binder burn-out because of their thinness. When this material is subjected to high temperature in use, the binder may be destroyed, but without impairing the thermal effectiveness for continuous use.

In transient insulation applications of this invention it is imperative to minimize the amount of heat generated due to binder destruction during actual use.. This may be accomplished by forming pieces containing less than 1% organic hinder or even no binder. In other cases it may be desirable to use an inorganic binder with lower but still significant strengthening effect.

As heretofore indicated, the low conductivity insulating shapes of this invention must contain a substantial amount of a particulate material. Three general types of particulate material are specifically contemplated in the present compositions. Each type in the form used comprises Moreover, as indicated hereinbefore, a pos-.

agglomerates of ultimate structural units which have average effective pore spaces between said ultimate structural units of the same order of magnitude as the average mean free path of the molecules comprising air. One type consists of agglomerates of finely divided solid particles of average ultimate dimension finer than 100 millimicrons, such as the finer grades of channel type carbon blacks. Another general type of particulate filler material has a porous or fabrillate structure, and is exemplified by aerogels such as those of silica, chromic oxide, thoria, magnesium hydrate, alumina, and mixtures thereof. Such aerogels in particle form are understood to have a straw stack agglomerate fibril structure, with the fibrils composing the ultimate or finest structural unit of diameter finer than 100 millimicrons, and may have been treated to render them hydrophobic in nature. The average aerogel particles should embrace a total void or dead air space of 7599% by volume. A third general type of particulate filler material having an average effective pore space of the same order of magnitude as the average mean free path of the molecules comprising air is a pyrogenic silica comprising a colloidal silica material formed by a vapor-phase hydrolysis of a silica compound such as silicon tetrachloride. Being of high chemical purity or of very low alkali content, pyrogenic silica materials exhibit high sintering temperatures and, in turn, high temperature limits in addition to improved resistance to water vapor and water soaking. Such colloidal silica products are commercially available under the trade name of Cab-O-Sil, a product of Godfrey L. Cabot, Inc.

The aerogel and/ or pyrogenic silica particles are most preferred as the particulate filler of the insulating shapes of this invention. Further unexpected novel results are obtained with the use of aerogel and/or pyrogenic silica which are not attained by the use of other fillers such as the fine carbon black particles. For example, if insulating shapes of the same general composition are formed, differing only in the use of aerogel or pyrogenic silica as filler in one and all carbon black as filler in the other, the shapes will all have the heretofore-described fine insulating characteristics, but the aerogel or pyrogenic silica containing shape will be harder and yet more resilient than that formed from carbon black. The aerogel or pyrogenic silica containing shape will also exhibit a corklike resiliency and hence is, of course, a more handleable product, since it may be, for example, dropped by a workman-applicator and not destroyed. Additionally, as compared to a block of all carbon black filler, the aerogel or pyrogenic silica blocks are stronger, that is, have a higher modulus of rupture, are, of course, far cleaner, and the composition may be molded to more complicated shapes due to excellent molding flow characteristics. It is also Worthy of note that the aerogel and pyrogenic silica insulating shapes may be relatively fireproof and can be used at high temperatures, while the all carbon black shapes are not as suitable due to the fact that carbon black, as an organic material, cannot be used satisfactorily for continuous operation in oxidizing conditions at temperatures above 500 F., and will be destroyed by combustion once it is ignited.

The amount of particulate material of the above-entitled nature which must be utilized is dependent upon the nature of the insulating shape formed and its desired-use. It has been found that rigid insulating bodies should be chiefly filler particles, and from 6090% by weight is preferred for most such applications. If the shapes are to be utilized for high temperature insulation, the preferred proportion is 35-80% by weight, and a greater amount of an opacifying material is used. For deformable insulating shapes, a lesser amount of filler particles may be utilized. A proportion of from 20-65% by weight of filler particles is preferred for such deformable shapes.

In such products as incorporate aerogels as a principal constituent, the high insulating efficiency primarily results from the fact that the effective pore spacing between adjacent fibrils in the particulate material averages less than the mean free path of the molecules comprising air. In cases where pyrogenic silica or solid carbon blacks of channel grade are used as the particulate material, the insulating value primarily results from the fact that the effective spacing between ultimate fine pyrogenic silica or carbon black particles averages below the mean free path of the molecules comprising air.

Below 150 F., the opacity of an aerogel such as silica aerogel or the like, is adequate for insulating against heat transfer by radiation. However, above this temperature, the insulation shape should be composed in part of finely divided thermal radiation opacifying materials of either organic or inorganic composition, usually dependent upon the insulating service temperature. These opacifiers may be of the metallic type which combines radiation reflection and absorption, such as metallic aluminum, tungsten or silicon powder; of the radiation absorbing type, such as finely divided carbon black or finely divided pigments, as for example, ilmenite, manganese oxide, or chromium oxide; or of the radiation scattering type, such as zircon, titanium dioxide, lead monoxide (litharge), or other mate rials with a high index of refraction in the infra red. Various of these opacifiers, including carbon black of finer than millimicrons particle size, may advantageously be used as an opacifier for the aerogel and/ or pyrogenic silica fillers in amounts up to approximately 60% by weight of the total weight. It will be appreciated that the amount of opacifier required is usually determined by the severity of the radiation problem, which increases with an increase in temperature.

It has been found that certain of these opacifiers serve to improve the heat insulating efiiciency in other ways than by merely reducing the transfer of heat by radiation. For example, certain finely divided carbon blacks have such fine particle size as to fill in any large macroscopic pore spaces between the grains of filler particles, and act thereby to also reduce the amount of heat transfer by molecular air conduction. It may thus be seen that such fine carbon blacks may be used in conjunction with the above-described filler particles whereby the opacifying characteristic of the carbon black will be utilized, or, as hereinbefore-mentioned, a carbon black of fine dimensions and in turn very small effective pore spaces may be used as the only particulate filler, in which case it will serve both functions.

In general, insulation shapes of the preferred compositions herein described exhibit sufficient water repellence so as not to require the presence therein of Waterproofing materials. However, in some cases it is desirable to include in the composition a small amount, say /25%, of a waterproofing agent such as finely divided zincor aluminum-stearate.

Any suitable mixing procedure may be utilized in the manufacture of the foregoing insulating bodies, it being only necessary to intimately mix the various components of the insulating shapes of this invention to achieve a thorough dispersion and intermixing of all components. Curing or setting of the various suitable organic and/or inorganic binder materials should be effected in accordance with conventional procedures and/or the manufacturers instructions such, for example, as heat or catalyst curing in the case of organic binder and thermal drying, reacting, sintering, or other chemical reaction for inorganic-type materials.

The very light, bulky particle-filled mass, either with or without a binder and/ or fibrous component, produced by mixing can be felted or molded to a shape of any desiredconformation and density. This molding operation may take place in a conventional hot press mold, developing suitable pressures and temperatures to activate and develop the thermal cure of a heat curable binder if one is utilized, while consolidating the mold charge to a shape of predetermined uniform porosity, rigidity, and density throughout. For molding purposes, a weighed batch of 9 the blended mixture may be molded to final desired dimension and density, and the shaped product then baked to activate the binder such as a resin to development of a shape-retaining bond.

Molded blocks have been produced having densities in the approximate range of 652 pounds per cubic foot with thermal conductivities, or K factors, approximating 0.1- 0.3 at 350 F. mean and typically below 0.25 at 350 F. means. Opacified blocks having the essentially inorganic compositions which are set forth above are adapted for service over the temperature range of 2000 F.

The following are examples of various rigid and deformable insulating shapes of low thermal conductivity and their general method of preparation. It is understood, of course, that the compositions of, and method for producing, these shapes are exemplary and are not to be considered to limit the invention to the particular compositions and operating conditions outlined. All percentages indicated in the examples are by weight.

Example I A typical rigid insulating body of this invention was obtained by molding, with suificient heat and pressure to obtain a density of 13 pounds per cubic foot and cure the resin, an intimately dispersed mixture of:

Percent Silica aerogel 60 Amosite asbestos fibers Phenol-formaldehyde resin 5 Ilmenite 30 This insulating body had a strong handleable shape and a thermal conductivity factor K of 0.19 B.t.u./ sq. ft./hr./ inch/ F. at 350 mean.

This body was handleable and of suitable strength, had a density of 17 pounds per cubic foot and a K of 0.21 at 350 F. mean and of 0.36 at 1000 F. mean.

Example III A rigid insulating body was obtained by molding with heat and pressure an intimately dispersed mixture of:

Percent Channel grade carbon black (average particle diameter of 18 millimicrons) 75 Amosite asbestos fiber 15 Phenol-formaldehyde resin This body Was handleable and of suitable strength, had a density of 16 pounds per cubic foot and a K of 0.25 at 350 F. mean.

Example IV A deformable insulating shape was obtained by molding with heat and pressure an intimately dispersed mixture of:

Percent Amosite asbestos fiber 38 Channel grade carbon black 14 Silica aerogel 43 Phenol-formaldehyde resin 5 This body was handleable and deformable, had a density of 9 pounds per cubic foot and a K of 0.20 at 350 F. mean.

Example V A deformable felted insulating shape was obtained by 10 uniformly distributing and consolidating a flufiy mass of an intimately dispersed mixture of:

This body was handleable and deformable, had a density of 12 pounds per cubic foot and a K of 0.25 at 350 F. mean.

Examples VI through XI, presented in tabular format for reasons of brevity and to facilitate comparisons, fully illustrate the compositions and physical properties of typical suitable silica aerogel containing insulation shapes of various densities and maximum temperature resistance. Each sample was prepared by thoroughly mixing the specified ingredients in the relative proportion indicated, consolidating the same into an integral body or block of the specified density and curing the resin binder by heating to a temperature of 300-325 F. for a period of 45 minutes in a mold followed by a post cure of 350 F. for 16 hours.

Examples VI VII VIII IX X XI Composition:

Silica aerogel. 81 81 81 81 67 55 Asbestos fiber 5 5 5 5 12 12 Carbon blaek 9 9 9 9 Silicon 16 Titanium dioxide (rutile) 28 Phenolic resin 5 5 5 5 5 5 Physical properties:

Density, p.c.f. 10 12 14 16 2O 20 Transverse strength, p.s.i.;

average 4 18 30 45 46 Average compressive strength, p.s.i.:

5% compression 16. 5 34.0 45.0 75.5 94.0 87.9 10% compression 32.5 67. 5 99.0 180.0 200.0 161.0 Thermal conductivity B.t.u.]

inJhr. sq. ft., at mean temperature:

200 F 0.15 300 F--- 0.16 400 0.17 600 F 800 F 1,000 F The thermal insulating efficiency characteristics or conductivities of the insulating shapes of Examples VI and X, at both sea level and at an altitude of 10 miles, have been plotted over a Wide temperature range in the graph of the drawing for comparison with the insulating characteristics or conductivities of air and typical insulations comprising fibrous materials.

Examples XII and XIII illustrate the use of a pyrogenic silica as the particulate material in the insulating shapes of this invention and fully set forth the pertinent physical properties of such shapes in addition to appropriate and exemplary compositions. These shapes were prepared in accordance with the procedure of Examples VI through 1 1 Examples )HV through XX demonstrate the eifect of varying the initial binder content upon the physical properties of the insulation shapes of this invention. A conventional phenol-formaldehyde resin binder, identical to that of Examples VI through XI, was combined with 12 5 parts by weight of amosite asbestos fiber combined with the particular opacifier and inorganic binder, if any, specified. The opacifying component of Examples XXIX, XXX and XXXI Was included in amount sufiicient to provide zirconium equivalent to 12 parts by weight of a base com osition com arable to the ingredients of zircon. Thus, in most instances, these examples each EX 1 X p t b ht E comprise 78% particulate filler material, 5% reinforcing amp 6 Par y welg 81 aero' fiber, 12% opacifier and of the specified inorganic gel, 12 Parts by Welght of alnoslte asbestos fi and 16 binder. Handleable insulation shapes comprising uni- Pafts by wfilght of 511K301}, m amounts a y from 0 form mixtures of each component of the following comup. through 15%, Insulatmg hapes comprising the fOTepositions were prepared by consolidating the mixtures to golng Components and blndflf 1n the following P P the indicated densities in a mold while heating the same tions were prepared as herelnbefore, 1.e., consohdated to th i t a tgmperature f 400 F fo thi t i t a density 0f p.c.f. and the 13116110116 168111 binder heat cooling the molded shapes while in the mold and subsecured at 300-325 F. for 45 mmutes 1n a mold followed 15 quently curing them for :16 hour t 200 F 2 h ur by apost cure at 350 F. for 16 hours. at 300 F., 2 hours at 400 F., and 2 hours at 600 F.

Thermal, Conduct., Modulus Example Opac1fier Binder Density 350 F. 500 F. rupture,

mean mean p.s.i.

IV 5% sodium perborate 18 0.23 0. 27 42 5% borax 18 0.23 0.27 45 5% borax and sodium silicate 18 0.23 0.27 30 do 18 0.22 0.26 30 o 5% sodium perborate and sodium silicate 18 0.22 0.27 38 Zirconium hydroxide Calcium hydroxide and Glaubers salt 18 0. 24 0. 28 33 Sodium zirconyl sulphate. Calcium hydroxide 1 18 0. 24 0.27 45 Zirconium oxide Calciu hydroxide and Glaubcrs salt L 18 0. 24 0. 27 45 12% zircon N0 blnder 17 0. 21 0. 24 32 (1 do 13 0.21 0.26 40 5% calclum hydroxide and Glaubers salt" 18 0.22 0. 25 46 5% A1203:3PO5 1s 0. 21 0. 2s 39 do. I Wit-A1203 22.2%, P2O 37.8%, S10 10.0%.. 18 0.20 0.25 XXXVII. 12% alummum flakes 5% bo 1s 0. 21 0. 20 51 1 Total of opacifier and binder is 17% by weight.

Examination of Examples XIX and XX revealed that the binder had been burned out to a considerable extent during heat curing and the actual binder content of the resulting products was much lower in both cases. In addition, the sintering observed in Examples XIX and XX indicated that the temperature reached a point wherein part of the silicon opacifier was oxidized to silicon dioxide destroying the effectiveness of the opacifier.

Examples XXI through XXIII illustrate the use of typical thermosetting binders in an insulating shape of a composition otherwise comparable to Example X. The insulation shapes were prepared like those of the foregoing examples.

Examples XXIV through XXXVII of the following table fully illustrate the applicability of several conven-" tional inorganic binder in the insulation shapes of this invention. The following examples each comprise a base mixture of 78 parts by weight of silica aerogel and Examples XXXVIII through XLIII demonstrate relatively high density thermal insulations Within the concept of this invention having diffusivity characteristics rendering them adaptable to transient as well as steady state insulating applications. Rigid insulations comprising uniform mixtures of the hereinafter given compositions were prepared by compressing the particular mix given to the density specified and heating the consolidated mass within a press to a temperature of about 300-325 F. for 45 minutes to set up the phenolic resin component, followed by a post cure of approximately 350 F. for 16 hours.

Example XXXVIII A rigid insulating body comprising:

Percent Pyrogenic silica 81 Asbestos fiber (amosite) 5 Chromium oxide (Cr O 12 Phenol-formaldehyde resin 2 consolidated to a density of 28 pounds per cubic foot and cured, produced a strong handleable block having a thermal conductivity factor K of 0.29 at 350 F. mean and of 0.32 at 850 F. mean.

Ex'amples XXXIX and XL A mixture consisting of:

Percent Pyrogenic silica 52 Asbestos fiber (amosite) 3 Litharge powder (PbO) 43 Phenol-formaldehyde resin 2 when consolidated to a density of 30 pounds per cubic foot and cured had a thermal conductivity K of 0.24 at 350 F. mean and the same mixture when consolidated to a greater density of 33 pounds per cubic foot and cured had a K of 0.25 at 350 F., respectively.

13 Examples XLI, XLII and XLIII Rigid insulations composed of the following composition:

when consolidated to the specified densities and cured exhibited thermal conductivity factors K of:

Density Conducitivity Example pounds per Btu/sq. ft./ cubic foot hr./in./F. at 350 F. mean.

In the specific description as herein presented, most of the examples have given data based on comparative K factor tests taken at a temperature of 350 F. It will be understood that, since the preferred insulation is adapted for use at temperature over the full range up to at least 2000 F., the advantages of improved thermal conductivity as compared to the mean free path of air, are realized at any temperatures within this normal use range.

Loose fill insulations prepared by merely mixing filler ingredients used in making up the present bonded shapes have various disadvantages; notably they frequently are not resistant to moisture, are difiicult and disagreeable to handle, and have extremely undesirable flow characteristics. For example, excessive moisture will convert an aerogel to an aquagel, and upon drying, an xerogel will be formed, which xerogel does not have the fine ultimate structure required in the fillers utilized in this invention. An improved fill type insulation may be obtained by breaking up preformed blocks of the bonded insulation produced as herein described. Such loose fill insulation has the advantages of being more resistant to flow caused by vibration, more resistant to moisture, is susceptible of control with regard to particle size, and is easily handled by conventional pouring or filling techniques. Such material is preferably classified as to size in uniform gradation between 4- mesh and 325 mesh, U.S. standard screen. A preferred composition is a fiber-reinforced lightly bonded mixture of inorganic aerogel particles and opacifier particles of the type heretofore described.

The invention which has thus been described by detailed example is not limited as to such details and it is to be understood that variations, changes and modifications are contemplated within the scope of the invention as defined by the following claims.

What we claim is:

1. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said body having an ultimate structure with average eifective pore spaces between the smallest of' the structural units of approximatelythe same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to 95% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, and a fibrous skeleton of strength imparting interlaced reinforcing fiber in amount of approximately 2 to 75% by weight holding said body in shape retaining form.

2. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. means, said body having an ultimate structure with average effective pore spaces between the smallest structural units of approximately the same magnitude as the free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to by weight of particulate material having an ulti mate structural unit with an average dimension finer than millimicrons and with an everage effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 7 to 60% by weight of thermal radiation opacifying material and binder material in amount of approximately 0.5 to 35% by weight distributed throughout and holding said body in shape retaining form.

3. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said body having an ultimate structure with average elfective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to 95 by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average efiective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 75% by weight of reinforcing fiber, and binder material in amount of approximately 0.5 to 35% by weight distributed throughout and holding said body in shape retaining form.

4. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to 95% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an everage elfective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 75% by weight of reinforcing fiber, thermal radiation opacifying material in amount up to approximately 60% by weight, and binder material in amount of approximately 0.5 to 35% by weight distributed throughout in holding said body in shape retaining form.

5. The insulating body of claim 4 wherein the binder material is an inorganic resin.

6. The insulating body of claim 5 wherein the thermal radiation opacifying material is selected from the group consisting of ilmenite, manganese oxide, chromium oxide, zircon, titanium dioxide, metallic aluminum, silicon powder, zirconium oxide, zirconium hydroxide, sodium zirconyl sulfate, tungsten, and lead monoxide, and mixtures thereof.

7. A handleable, flexible insulating body having a density of from approximately 6 to 25 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of at least 35 up to 75% by weight of a fibrous skeleton of strength imparting interlaced staple reinforcing fiber with at least 20% up to approximately 65% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, said particulate material being distributed substantially uniformly throughout and held in shape retaining form by said fibrous skeleton.

8. A handleable, flexible insulating body having a den sity of from approximately 6 to 25 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of app iimately the same magnitude as the mean free path the molecules comprising air at 150 F. and atmospmgic pressure and consisting essentially of at least 35 up to 75% by weight of a fibrous skeleton of strength imparting interlaced staple reinforcing fiber with at least 20% up to approximately 65% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, and approximately 7 to 45% by weight of thermal radiation opacifying material, said particulate material and opacifying material being distributed substantially uniformly throughout and held in shape retaining form by said fibrous skeleton.

9. Granular loose fill heat insulation sized chiefly in the range between approximately standard 4 mesh and approximately 325 -mesh screen and having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said granules having an ultimate structure with average effective pore spaces between the smallest structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to 95% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 15% by weight of staple reinforcing fibers, and approximately 0.5 to 35% by weight of binder material distributed throughout said particulate material and staple reinforcing fibers.

10. Granular loose 'fill heat insulation sized chiefly in the range between approximately standard 4 mesh and approximately 325-mesh screen and having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K of from 0.1 to 0.3 at 350 F. mean, said granules having an ultimate structure with average effective pore spaces between the smallest structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of 20 to by weight of particulate material having an ultimate structural unit with an average dimension finer than millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 15% by weight of staple reinforcing fibers, approximately 7 to 60% by weight of thermal radiation opacifying material, and approximately 0.5 to 35% by weight of binder material distributed throughout said particulate material, staple reinforcing fibers and opacifying material.

11. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K from 0.1 to 0.3 at 350 F., said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of approximately 45 to 95 by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 15 by weight of reinforcing fiber, and binder material in amount of approximately 0.5 to 35% by weight distributed throughout and holding said body in shape retaining form.

12. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K from 0.1 to 0.3 at 350 F., said body having an ultimate structure with average efiiective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of approximately 35 to 90% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 15% by weight of reinforcing fiber, thermal radiation opacifying material in amount up to approximately 60% by weight, and binder material in amount of approximately 0.5 to 35 by weight distributed throughout and holding said body in shape retaining form.

13. The insulating body of claim 12 wherein the aerogel is silica aerogel.

14. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K from 0.1 to 0.3 at 350 F., said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of approximately 35 to 80% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 7 to 60% by weight of thermal radiation opacifying material, and approximately 1 to 15 by weight of binder material distributed throughout and holding said body in shape retaining form.

15. The insulating body of claim 14 wherein the binder material is an organic resin.

16. A handleable insulating body having a density of from approximately 6 to 52 pounds per cubic foot and a thermal conductivity factor K from 0. 1 to 0.3 at 350 F., said body having an ultimate structure with average eftective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of approximately 35 to 80% by weight of particulate material having an ultimate structural unit with an average dimension finer than 100 millirnicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of the molecules comprising air at 150 F. and atmospheric pressure selected from the group consisting of inorganic aero-gel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 2 to 15% by weight of reinforcing fiber, thermal radiation opacifying material in amount up to approximately 60% by weight, and approximately 1 to 15% by weight of binder material distributed throughout and holding said body in shape retaining form.

17. The insulating body of claim 16 wherein the binder material is an organic resin,

18. The insulating body of claim 16 wherein the thermal radiation opacifying material is selected from the group consisting of ilmenite, manganese oxide, chromium oxide, zircon, titanium dioxide, metallic aluminum, silicon powder, zirconium oxide, zirconium hydroxide, sodium zirconyl sulfate, tungsten, and lead monoxide, and mixtures thereof.

19. A handleable insulating body having a density of from approximately 6 to 35 pounds per cubic foot and a thermal conductivity factor K from 0.1 to 0.3 at 350 F., said body having an ultimate structure with average effective pore spaces between the smallest of the structural units of approximately the same magnitude as the mean free path of molecules comprising air at 150 F. and atmospheric pressure and consisting essentially of approximately 35 to by weight of particulate material having an ultimate structural unit with an average dimension finer than millimicrons and with an average effective pore space between the smallest of said structural units of approximately the same magnitude as the mean free path of molecules comprising air at F. and atmospheric pressure selected from the group consisting of inorganic aerogel, pyrogenic silica and channel grade carbon black, and mixtures thereof, approximately 5 to 15 by weight of staple reinforcing fiber, approximately 7 to 55% by weight of thermal radiation opacifying material, and approximately 5 to 15% by weight of a binder material distributed throughout and holding said body in shape retaining form.

20. The insulating body of claim 19 wherein the binder material is an organic resin.

21. The insulating body of claim 20 wherein the thermal radiation opacifying material is selected from the group consisting of ilmenite, manganese oxide, chromium oxide, zircon, titanium dioxide, metallic aluminum, silicon powder, zirconium oxide, zirconium hydroxide, sodium zirconyl sulfate, tungsten, and lead monoxide, and mixtures thereof.

22. The insulating body of claim 21 wherein the aerogel is silica aerogel.

References Cited in the file of this patent UNITED STATES PATENTS 1,307,549 Headson June 24, 1919 1,782,384 Greider Nov. 18, 1930 1,980,119 Wait Nov. 6, 1934 2,005,356 Toohey et al. June 18, 1935 2,049,878 Stresino Aug. 4, 1936 2,062,879 Hammenecker Dec. 1, 1936 2,093,454 Kistler Sept. 21, 1937 2,250,009 Coble July 22, 1941 2,456,643 Napier Dec. 21, 1948 2,469,379 Fraser May 10, 1949 2,579,036 Edelman Dec. 18, 1951 2,586,726 Schuetz Feb. 19, 1952 2,600,321 Pyle June 10, 1952 2,692,844 Hyde Oct. 26, 1954 2,760,941 -Iler Aug. 28, 1956 2,808,338 Bruno et a1. Oct. 1, 1957 2,811,457 Speil et a1. Oct. 29, 1957

Claims

1. A HANDLEABLE INSULATING BODY HAVING A DENAITY OF FROM APPROXIMATELY 6 TO 52 POUNDS PER CUBIC FOOT AND A THERMAL CONDUCTIVITY FACTOR K OF FROM 0.1 TO 0.3 AT 350* F, MEANS, SAID BODY HAVING AN ULTIMATE STRUCTURE WITH AVERAGE EFFECTIVE PORE SPACES BETWEEN THE SMALLEST OF THE STRUCTURAL UNITS OF APPROXIMATELY THE SAME MAGNITUDE AS THE MEANS FREE PATH OF THE MOLECULES COMPRISING AIR AT 150* F, AND ATMOSPHERIC PRESSURE AND CONSISTING ESSENTIALLY OF 20 TO 95% BY WEIGHT OF PARTICULATE MATERIAL HAVING AN ULTIMATE STRUCTURAL UNIT WITH AN AVERAGE DIMENSION FINER THAN 100 MILLICRONS AND WITH AN AVERAGE EFFECTIVE PORE SPACE BETWEEN THE SMALLEST OF SAID STRUCTURAL UNITS OF APPROXIMATELY THE SAME MAGNITUDE AS THE MEAN FREE PATH OF THE MOLECULES COMPRISING AIR AT 150* F, AND ATMOPSPHERIC PRESSURE SELECTED FROM THE GROUP CONSISTING OF INORGANIC AEROGEL, PYROGENIC SILICA AND CHANNEL GRADE CARBON BLACK, AND MIXTURES THEREOF. AND A FIBROUS SKELETON OF STRENGTH IMPARTING INTERLACED REINFORCING FIBER IN AMOUNT OF APPROXIMATELY 2 TO 75% BY WEIGHT HOLDING SAID BODY IN SHAPE RETAINING FORM.