GB2161799A - Improvements in or relating to microporous, thermally insulative material - Google Patents

Abstract

A microporous, thermally-insulative material consists of pyrogenic silica, an infra-red opacifier, preferably rutile titanium dioxide, ceramic fibres and a binder. The binder is selected from a class of materials known as sorel cements. A preferred sorel cement is magnesium oxychloride, which is formed by a mixture of magnesium oxide powder and magnesium chloride solution and which is present in a proportion of from 2% to 20% by weight of the total material.

Description

SPECIFICATION Improvements in or relating to microporous, thermally insulative material This invention relates to microporous, thermally insulative material of the kind used, for example, in conjunction with heating elements, which may be of the conventional, coiled kind, or may take the form of tungsten filaments incorporated within tubular quartz envelopes, for use as the heating arrangements of the hob units of domestic cooking appliances.

Such material is disclosed, for example, in United States Patent No. 3,055,831, and it is an object of this invention to provide such material in improved form and/or by means of an improved process.

According to the invention there is provided a microporous insulation material comprising a pyrogenic silica, an infra red opacifier, ceramic fibres and a sorel cement binder wherein said sorel cement binder is a magnesium or zinc oxy salt and is present in a proportion of from 2% to 10% by weight of the total material.

In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described by way of example.

The material in this example consists of pyrogenic silica, an infra red opacifier (which may be one of a number of materials but rutile titanium dioxide is preferred), ceramic fibres and a binder.

The present invention is particularly concerned with the use of a specially selected binder.

In the present example, the following steps are taken:- Pyrogenic silica and titanium dioxide are mixed in a ratio of 2:1 by weight. This mixture represents 90% by weight of the final mix of insulation.

A stock solution of magnesium chloride is prepared, of which magnesium chloride represents 28% by weight.

To the silica/rutile mix magnesium oxide is added to the equivalent of 4.1% of the final mix of insulating material.

Sufficient ceramic fibres are taken to represent 5% of the final weight of insulation material. to these fibres is added 2 ml of magnesium chloride solution equivalent for every 100 gms of final mix of insulation material. The fibres and magnesium chloride solution are mixed until the fibres are thoroughly wetted. The wetted fibres are transferred to the silica/rutile/magnesium oxide and mixed until the fibres are evenly distributed through the power mix.

The mix is finally transferred to a mould, compressed, dried off at 200"C for two hours and put in a furnance at 6500C for two hours to sinter the mix.

The principle behind this example of the invention is to use as binders a class of materials known as sorel cements, one of which is magnesium oxychloride. If magnesium oxide powder and magnesium chloride solution are mixed, they will set to magnesium oxychloride. Thus, by mixing the magnesium oxide in this bulk powder and wetting the fibres with magnesium chloride these cross link and set, binding the fibres into the matrix. The magnesium oxide/magnesium chloride cement is preferred because it is relatively slow setting.

Other sorel cements can be made by mixing, for example, zinc oxide and zinc chloride, zinc oxide and phosphoric acid, magnesium oxide and phosphoric acid. Some of these are very fast setting and may set before being evenly mixed, presenting subsequent handling difficulties and heterogeneous mixtures, although their use may be satisfactory in some circumstances.

The binder may generally be described as a sorel cement, e.g. magnesium oxide/magnesium chloride, zinc oxide/phosphoric acid magnesium oxide/ phosphoric acid, zinc oxide/zinc chloride, magnesium oxy sulphate or any other similar oxy cement, or basic salt cement.

It is envisaged that suitable results will be obtained with binder ratios up to 20% by weight of the whole.

1. A microporous insulation material comprising a pyrogenic silica, an infra red opacifier, ceramic fibres and a sorel cement binder wherein said sorel cement binder is a magnesium or zinc oxy salt and is present in a proportion of from 2% to 10% by weight of the total material.

2. A material according to Claim 1 wherein said sorel cement binder comprises magnesium oxychloride, zinc oxychloride, magnesium oxyphosphate, zinc oxyphosphate or magnesium oxysulphate.

3. A material according to Claim 1 or Claim 2 wherein said sorel cement binder comprises magnesium oxychloride.

4. A material according to any one of Claims 1 to 3 substantially as herein described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to microporous, thermally insulative material This invention relates to microporous, thermally insulative material of the kind used, for example, in conjunction with heating elements, which may be of the conventional, coiled kind, or may take the form of tungsten filaments incorporated within tubular quartz envelopes, for use as the heating arrangements of the hob units of domestic cooking appliances. Such material is disclosed, for example, in United States Patent No. 3,055,831, and it is an object of this invention to provide such material in improved form and/or by means of an improved process. According to the invention there is provided a microporous insulation material comprising a pyrogenic silica, an infra red opacifier, ceramic fibres and a sorel cement binder wherein said sorel cement binder is a magnesium or zinc oxy salt and is present in a proportion of from 2% to 10% by weight of the total material. In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described by way of example. The material in this example consists of pyrogenic silica, an infra red opacifier (which may be one of a number of materials but rutile titanium dioxide is preferred), ceramic fibres and a binder. The present invention is particularly concerned with the use of a specially selected binder. In the present example, the following steps are taken:- Pyrogenic silica and titanium dioxide are mixed in a ratio of 2:1 by weight. This mixture represents 90% by weight of the final mix of insulation. A stock solution of magnesium chloride is prepared, of which magnesium chloride represents 28% by weight. To the silica/rutile mix magnesium oxide is added to the equivalent of 4.1% of the final mix of insulating material. Sufficient ceramic fibres are taken to represent 5% of the final weight of insulation material. to these fibres is added 2 ml of magnesium chloride solution equivalent for every 100 gms of final mix of insulation material. The fibres and magnesium chloride solution are mixed until the fibres are thoroughly wetted. The wetted fibres are transferred to the silica/rutile/magnesium oxide and mixed until the fibres are evenly distributed through the power mix. The mix is finally transferred to a mould, compressed, dried off at 200"C for two hours and put in a furnance at 6500C for two hours to sinter the mix. The principle behind this example of the invention is to use as binders a class of materials known as sorel cements, one of which is magnesium oxychloride. If magnesium oxide powder and magnesium chloride solution are mixed, they will set to magnesium oxychloride. Thus, by mixing the magnesium oxide in this bulk powder and wetting the fibres with magnesium chloride these cross link and set, binding the fibres into the matrix. The magnesium oxide/magnesium chloride cement is preferred because it is relatively slow setting. Other sorel cements can be made by mixing, for example, zinc oxide and zinc chloride, zinc oxide and phosphoric acid, magnesium oxide and phosphoric acid. Some of these are very fast setting and may set before being evenly mixed, presenting subsequent handling difficulties and heterogeneous mixtures, although their use may be satisfactory in some circumstances. The binder may generally be described as a sorel cement, e.g. magnesium oxide/magnesium chloride, zinc oxide/phosphoric acid magnesium oxide/ phosphoric acid, zinc oxide/zinc chloride, magnesium oxy sulphate or any other similar oxy cement, or basic salt cement. It is envisaged that suitable results will be obtained with binder ratios up to 20% by weight of the whole. CLAIMS

1. A microporous insulation material comprising a pyrogenic silica, an infra red opacifier, ceramic fibres and a sorel cement binder wherein said sorel cement binder is a magnesium or zinc oxy salt and is present in a proportion of from 2% to 10% by weight of the total material.

2. A material according to Claim 1 wherein said sorel cement binder comprises magnesium oxychloride, zinc oxychloride, magnesium oxyphosphate, zinc oxyphosphate or magnesium oxysulphate.

3. A material according to Claim 1 or Claim 2 wherein said sorel cement binder comprises magnesium oxychloride.

4. A material according to any one of Claims 1 to 3 substantially as herein described.