There is known an electro-conductive composition for electro heaters, which contains homogeneous mixture of connecting polymer with powder-like blend at the least of one metal or semimetal, e. g. graphite. As connecting polymers there can be used polystyrenes, resins of polyvinyl, derivatives of polyacrylic acid, polyamides and their derivatives [1].

Electro-conductive composition for electro heaters is the prototype of suggested invention, containing homogeneous mixture of powder-like graphite with polymer connector, wherein polyacrylamide serves as polymer connector [2].

The shortage of the prototype is relatively low temperature limit (200°C), under which the composition changes its properties, i. e. there take place the separation of graphite and destruction of the structure.

The invention task is to heighten electro-conductive composition's temperature limit.

The invention essence is that that there is suggested electro-conductive composition for electro heaters, containing the homogeneous mixture of powder-like graphite with polyacrylamide, which according to the invention, in addition, contains polysiloxane (silicone).

Polysiloxanes are the product of silanedyol polycondensation, having formula R2Si (OH) 3.

They are known under the name of silicones and are used as sealing structure of silicone rubber.

In the following examples of concrete usage as polysiloxane there has been used serially produced by firm Wacker-Chemic (Germany) silicone rubber under WACKER trade mark.

As initial materials for composition preparing there have been taken powder-like graphite, polysiloxane (silicone) in the shape of paste and gel-like polyacrylamide of formulation, with contents of carbon, hydrogen and nitrogen, having (mass) 50. 7%, 7% and 19,7%.

The method of composition preparing is the following. At first polyacrylamide is blended with powder-like graphite for getting paste-like mixture; further there is added silicone paste and got mixture scrupulous is kneaded by hand or mixer till full homogenizing. Such sequence is explained by that that powder of graphite is not blended with silicone paste; though, being

blended with gel-like polyacrylamide up to the paste-like state, it is easily blended with silicone, the latter is in the paste-like state, too. Weight correlation of graphite powder, gel-like polyacrylamide and silicone paste has been modified within wide limits. Got under the different percentage correlation pastes have been dashed smoothly on thermostable dielectric surface (per examples of concrete usage on the ceramic ones) and their specific resistance and limited temperatures have been measured. The data are taken into the Table, wherein PAA is weight percentage content of polyacrylamide in the shape of emulsion; Si is weight percentage content of polysiloxane (silicone paste); t° is temperature limit; within the latter the composition changes its properties, i. e. there take place graphite's separation and structure's destruction; p is specific resistance of the layer. PAA, weight % Graphite, weight % Si, weight % to (ohm-cm) 50 50 0 200 0, 015 47, 5 47, 5 5 220 0, 02 45 45 10 250 0, 03 42, 5 42, 5 15 270 0, 05 35 35 30 300 0, 1 70 15 15 300 0, 2 Within the example of concrete usage the paste has been dashed smoothly on the surface of ceramic plate in II-like shape, per thickness of 0,2 mm, length 40 cm and width 30 cm. To the bases of the layer, the width of which is equal to 10 cm, there have been applied electrodes, arranged to the net of alternating current per 220 Volt. As the tests showed, the stable specific resistance is fixed after the layer is beforehand heated up to maximum temperature. That is why computation of specific resistance has been done after preliminary heating up to the temperature limit. Computations were made by p= R-S/L formula, where R is the resistance of the layer, S is its cross-sectional area and L is its length.

The main influence on the specific resistance there makes the content of graphite powder in the paste. Moreover, as it is seen from the latest example, given in Table, the basic influence on the value of the specific resistance and temperature limit has the correlation of silicone paste and graphite powder. It is explained by that that within getting the maximum temperatures, given in the Table, there takes place modification of polyacrylamide and the basic part, both for electric and mechanic characteristics begins to play the correlation of silicone/graphite. The investigations results have also demonstrated that within absence of polyacrylamide, the specific resistance becomes too great (higher on sequence), and that makes the structure unacceptable for

usage. This is explained by that that graphite with silicone paste without polyacrylamide does not give homogeneous blend and got structure practically is an insulator.

An optimal structure is chosen issuing from the concrete aim of heating. In any case, the most preferable is the content of the graphite in the initial blend, beginning from 25% up to 60% (weight); for within less quantities of graphite the specific resistance becomes too great and there is demanded to widen the width of conductive layer; and, otherwise, if the graphite content is great, so there will be demanded too small value (less than 0,1 mm), and it is not technological.

For heaters, the base of which are ceramic plates, optimal structure is one, given in Table 3; while for heating of greater areas (floors and walls) the optimal structure is one, given in the example of Table 5.

The suggested composition can find the wide usage both in everyday and industrial electro heaters, due to a number of values: - anti-fireness, because of short circuit risk absence; - An exception of chain breakdown possibility. In the worst case only a small part of current-conductive layer can stop heating function; that is easily dismissed by dashing of the paste on the damaged part; - Homogeneous heating along all the area surface.

The suggested composition can especially be useful within the solving of such specific heating tasks, as heating of pipes against frost damage and/or facilitation of liquids with temperature dependant ductility pumping; containers heating, e. g. ones with fuel oil for full fuel oil pumping out within winter conditions, etc. It must be also marked the production simplicity of both electro heaters on the base of suggested composition and composition itself.

1. US 6392209; 2. Armenian Patent Application No. 20020163, filed of 8. 10.2002-prototype.