Thermal insulating materials

1350661 Thermal storage heaters MICROPORE INTERNATIONAL Ltd 10 June 1971 [10 June 1970] 28052/70 Addition to 1247674 Heading F4U [Also in Division F2] A thermal insulating panel, e.g. in a thermal storage heater comprises a porous envelope containing a block of consolidated dry particulate insulating material, the material of the envelope being in a state of tension and the block being bonded to the envelope by penetration of particles of insulating material on the surface of the block into the pores of the envelope having taken place under pressure. In an example, a microporous thermal insulating material is prepared by admixing microporous silica aerogel with titanium oxide as an opacifier. A fibrous material can also be included in the mix, e.g. ceramic fibres if the insulating panel is to be used at high temperatures. Alternative microporous particulate materials include finely divided microporous metal oxides such as alumina, zirconia and titania of similar particle size and structure as silica aerogel. The insulating material is placed in a porous envelope in the form of a bag of fibre-glass cloth of low permeability, and the bag is placed on the bottom die of a press, the upper die of which is then lowered whereby the bag of insulating material is formed into a semi-rigid panel. The two dies of the press are so formed as to permit the escape of air through the pores of the bag. On application of pressure to the bag causing air to escape, the particles of microporous silica aerogel become bonded to each other and to the fibre-glass bag, at least part of the bonding between the bag and the particles resulting from penetration of the pores of the fibre-glass by the particles. There is a build-up of pressure within the bag which creates a tension strain in the fibre-glass, which strain remains after release of the applied pressure and this induced tension strain provides additional rigidity for the insulating panel. If the fibre-glass cloth is composed of a smooth yarn, this is preferably pretreated by the deposition on it of a ceramic oxide or chemical "starch" to increase the degree of bonding between the yarn and the insulating material. The porous envelope can alternatively be formed of paper, a fibrous synthetic plastics material, perforated or porous metal foil, or perforated sheet such as polyethylene sheet. It can also be formed of cotton, the use of a cotton envelope resulting in a flexible structure which can be shaped to fit contoured surfaces.