GB2041908A

GB2041908A - Insulating Material

Info

Publication number: GB2041908A
Application number: GB8003018A
Authority: GB
Original assignee: Tarmac Building Products Ltd
Current assignee: Tarmac Building Products Ltd
Priority date: 1979-02-01
Filing date: 1980-01-29
Publication date: 1980-09-17

Abstract

A foamed insulating material is produced from a soluble silicate binder such as sodium or potassium silicate, in which one or more finely divided fillers is incorporated. The fillers and the proportions in which they are used are selected so that, when thoroughly mixed with an aqueous solution of the silicate binder, each portion of the resulting foam insulator contains the ingredients for glass or ceramic formation which will take place if the insulating material is strongly heated, with consequent absorption of heat by the glass forming reaction. The fillers e.g. hydrated lime or hydrated alumina may also be provided in a form which undergoes endothermic reactions due to removal of water of crystallisation or to structural dissociation of the fillers. In order to reduce the solubility of the silicate, ion exchange is encouraged by the inclusion of calcium or magnesium salt in the fillers. Foam formation may be achieved by rapid, for example microwave, heating or by the use of air entraining agents. Low density or hollow fillers such as pfa cenospheres may also be included.

Description

SPECIFICATION Insulating Material and Method of Making it Description of Invention This invention relates to insulating materials of a substantially incombustible type.

There is a requirement for insulating materials capable of resisting high temperatures without combustion, for example for use in fire resistant panelling and fire doors. In addition to having good heat insulation properties at high temperatures, and to being incombustible it is advantageous if such materials are structurally stable so as to be capable of being made for example into readily handled panels or blocks.

Organic insulating materials such as conventional foamed plastics are unsuitable for such uses because, although they offer a very low thermal conductivity, they are vulnerable to combustion at high temperatures.

Various inorganic materials have been proposed for use as high temperature insulators.

For example, it is known that foams of sodium or potassium silicate can be produced by frothing and rapid drying of aqueous solutions. Although such foams are incombustible and possess low thermal conductivity on account of the voids content, sodium and potassium silicate foams are very fragile, being composed of thin walled cells.

The low thermal conductivity and low thermal mass of a thin cell wall also reduces fire resistance due to localised melting of the walls.

They also tend to be water soluble which limits their usefulness.

It has been proposed to produce foamed glass which avoids this disadvantage of solubility but which is expensive and difficult to produce owing principally to the considerable amount of heat energy required for making the glass.

It is an object of the present invention to provide a new or improved insulating material of a substantially incombustible type.

According to the invention there is provided an insulating material comprising an inorganic foam formed from a binder and a blend of fillers, the binder initially comprising an aqueous silicate solution and the fillers comprising materials capable of being fused together with the binder, on subsequent heating of the final insulating material in use, to form a glass or ceramic composition, the fillers being provided in finely divided form and being blended with the binder in suitable proportions for such glass or ceramic formation to take place.

Preferably, some or all of the individual fillers are such as to have endothermic reactions on heating. For example, the fillers may include hydrated materials such as hydrated lime or alumina, water of hydration being endothermically driven off by heating. As a further example, calcium carbonate in the form of limestone powder may be incorporated as a filler and will dissociate at about 9000C to form calcium oxide with the endothermic evolution of carbon dioxide. Dolomite powder, the double carbonate of calcium and magnesium, can similarly be used and will dissociate at about 7250C. The water soluble silicate is preferably sodium or potassium silicate. Sodium and potassium ions tend to have a fluxing effect on glass formation, causing it to take place at lower temperatures than would otherwise be the case.

It is preferred that some salts are incorporated as fillers which are such as to encourage ion exchange with the electro-positive ions of the silicate binder and hence reduce the water solubility thereof, for example calcium or magnesium salts.

The invention also provides a method of making a thermal insulating material as set out above, comprising the steps of mixing the blend of finely divided fillers with an aqueous solution of the silicate binder, causing or allowing the mixture to form a foam, and drying the foam.

The foam formation may be assisted by incorporating an air entraining agent in the mixture, for example an amine air entraining agent.

Alternatively, or in addition, an ingredient containing trapped air may be introduced. Such an ingredient may be for example pfa cenospheres which are effectively air bubbles trapped by a thin spherical skin derived from pulverised fuel ash.

Alternatively, or additionally, foaming may be produced by rapid heating of the aqueous solution, for example by microwave irradiation so as to drive off water from the solution in the form of steam bubbles. Where some other method of foaming is used, for example involving the use of air entraining agents, drying of the foam may be achieved by warm air.

The invention will now be described in more detail, two particular compositions embodying the invention being described by way of example only.

In the following examples all percentages are by weight.

Example 1 The composition was as follows:- 100 grams aqueous solution of sodium silicate (38% solids).

20 grams powdered limestone filler (calcium carbonate).

20 grams hydrated alumina.

70 grams pfa cenospheres.

The fillers were mixed with the aqueous solution of sodium silicate and were heated in a microwave oven which had the effect of causing the material to foam by evolution of steam bubbles caused by evaporation of the water medium. The microwave heating then caused the foams to dry out and the final composition had a density of 450 kilograms per cubic metre (specific gravity 0.45). The thermal conductivity was 0.147 watts per metre degree centrigrade.

Example 2 The composition was as follows:- 1000 grams aqueous solution of sodium silicate (38% solids).

10 grams amine air-entraining agent (hexadecyltrimethyl ammonium chloride commercially supplied by Akzo Chemie U.K.

Ltd.).

200 grams limestone filler.

200 grams hydrated alumina.

700 grams pfa cenospheres.

The materials were mixed in aqueous solution with sufficient agitation to enable air to be entrained in the mixture. The amine is an air entraining agent which modifies the properties of the solution to permit air to be entrained. The mixture was then air dried in an oven at approximately 800 C. The resulting material was a rigid foam having a smaller void size than that produced in Example 1 and having a density of 500 kilograms per cubic metre (specific gravity 0.50). The thermal conductivity was approximately 0.120 watts per metre degree centigrade.

In both the foregoing examples, the material produced was a rigid foam capable of being made in panels or blocks which could be used for insulations of walls, fire doors or the like. Samples were tested by application of flame and could be heated to incandescence for prolonged periods of time without any evidence of flame penetration or substantial reduction in the thermal insulating properties.

It is envisaged that various blends of fillers can be used to produce insulating materials embodying the invention. The chemistry of glass and ceramic formation is fairly well understood and it is possible to select blends of different fillers incorporating quantities of calcia, silica and alumina for example which are such as to lead to formation of glass or ceramic materials on heating. Other compounds used in the manufacture of glass and ceramics can be incorporated, such as oxides of boron, zinc, iron, lead and antimony, provided that their use in this application is compatible with the properties required of the material and with health and safety considerations.

The particular composition chosen will of course depend on factors such as cost and availability of materials, particular requirements as to density, setting time and so on. For example, Portland cement which consists of a complex calcium silicates and aluminates, can be used as one of the fillers. Due to its weli known setting properties, the structural strength of a material incorporating Portland cement may be substantial.

It is desirable to ensure that the initially water soluble silicate binder (which may be sodium or potassium silicate for example) is rendered less soluble by ion exchange with a calcium or a magnesium salt in one or more of the fillers.

Sodium and potassium act as fluxes for glass formation, causing it to take place at a lower temperature than otherwise.

The basic insulating material according to the invention can be regarded as a foam having a silicate binder and a blend of fillers. The fillers are specifically selected and blended together in finely divided form so that, throughout the foamed insulator, there are to be found the ingredients for the formation of a glass or ceramic material, if strong heating is applied. It is to be appreciated that heating to bring about glass or ceramic formation is not part of the manufacturing process envisaged for the insulating material but may occur in use if, for example, a partition or fire door is subjected to a high temperature due to a fire occurring.

In this case the materials which are to be found in the insulating foam will be heated to a temperature sufficient to cause fusion to form a glass or ceramic layer adjacent the high temperature region. This reaction is of course endothermic. The resulting glass tends to act as a thermal barrier.

Thus, a surface layer of the material will tend to undergo conversion to a glass or ceramic but will itself provide an insulating layer against penetration of heat from the fire into deeper layers of the material. In this way, in spite of the conversion to a glass or ceramic, the insulating properties of the material will not seriously deteriorate until an extremely high temperature, causing complete melting of the material, is reached.

Prior to the formation of a glass or ceramic material, endothermic reactions may be undergone by the individual filler materials themselves. For example, if hydrated alumina or hydrated lime are used as fillers, the initial application of a flame will generate a high temperature and drive off water of hydration, this being an endothermic reaction. Similarly, if powdered limestone is used as a filler, the calcium carbonate will dissociate to calcium oxide, with the endothermic evolution of carbon dioxide gas.

This means that, on initial application of heat to the surface of the material, endothermic reactions tending to absorb and hence dissipate this heat will take place. This time and energy required to complete these reactions will of course tend to increase the resistance to fire penetration of the material somewhat.

It will be appreciated that compositions other than those outlined in the examples given above may be used within the scope of the invention and that the insulating material referred to can be put to other uses than in fire resistant partitioning and fire doors. The material is relatively easy and inexpensive to produce compared with previously proposed fire resistant insulation materials such as glass foam, because of the relatively low process temperatures involved in its manufacture and the use of fairly inexpensive raw materials.

Claims

1. An insulating material comprising an inorganic foam formed from a binder and a blend of fillers, the binder initially comprising an aqueous silicate solution and the fillers comprising materials capable of being fused together with the binder, on subsequent heating of the final insulating material in use, to form a glass or ceramic composition, the fillers being provided in finely divided form and being blended with the binder in suitable proportions for such glass or ceramic formation to take place.

2. An insulating material according to claim 1 wherein some or all of the individual fillers are such as to have endothermic reactions on heating.

3. An insulating material according to claim 2 wherein the fillers include hydrated materials, from which water of hydration is endothermically driven off by heating.

4. An insulating material according to claim 3 wherein the hydrated material is hydrated lime.

5. An insulating material according to claim 3 wherein the hydrated material is hydrated alumina.

6. An insulating material according to claim 2 wherein at least one of the fillers undergoes endothermic dissociation on heating.

7. An insulating material according to claim 6 wherein the material which undergoes endothermic dissociation comprises limestone powder.

8. An insulating material according to claim 6 wherein the material which undergoes endothermic dissociation is powdered dolomite.

9. An insulating material according to any preceding claim wherein the water soluble silicate comprises sodium silicate.

10. An insulating material according to any preceding claim wherein the water soluble silicate comprises potassium silicate.

11. An insulating material according to any preceding claims wherein at least one filler is such as to encourage ion exchange with the electropositive ions of the silicate binder to reduce the water solubility thereof.

12. An insulating material according to claim 11 wherein the ion exchange salt includes a calcium salt.

1 3. An insulating material according to claim 11 wherein the ion exchange salt includes a magnesium salt.

14. An insulating material substantially as hereinbefore described with reference to Example 1 of the foregoing examples.

1 5. An insulating material substantially as hereinbefore described with reference to Example 2 of the foregoing examples.

1 6. A method of making a thermal insulating material according to any one of the preceding claims and comprising the steps of mixing the blend of finely divided fillers with an aqueous solution of the silicate binder, causing or allowing the material to form a foam, and drying the foam.

1 7. A method according to claim 16 and including the step of incorporating an air entraining agent in the mixture.

18. A method according to claim 17 wherein said air entraining agent is amine air entraining agent.

1 9. A method according to any one of claims 1 6 to 1 8 including the step of introducing an ingredient containing trapped air into the mixture,

20. A method according to claim 19 wherein the ingredient containing trapped air comprises pfa cenospheres.

21. A method according to any one of claims 16 to 20 wherein foaming is produced by rapid heating of the aqueous solution.

22. A method according to claim 21 wherein said rapid heating is carried out by microwave irradiation.

23. A method of making a thermal insulating material substantially as hereinbefore described with reference to Example 1 of the foregoing examples.

24. A method of making an insulating material substantially as hereinbefore described with reference to Example 2 of the foregoing examples.