Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Patent
1997-02-25
1999-06-01
Kopec, Mark
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
252503, 252506, 252511, 428688, 428924, 2505151, 2505171, H01B 118, H01B 124, G21F 304
Patent
active
059085843
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns an electrically conductive building material.
PRIOR ART
It is known so far to use building materials as electrically conductive shield against electromagnetic radiations. GB patent 1 424 162 discloses electrically conducting coatings based on cement containing dispersed graphite applied on a reinforcing grid for a shield coating which cuts frequencies between 20 KHz to 50 KHz.
In the FR-A-2 216 244 are described coatings based on cement and two dispersed carbons of different granulometry for electrically conductive materials of structure such as grounding connections, antistatic floors and walls cutting radio frequencies.
In the JP-A-63 196 672, one has proposed a component for fabricating electrical resistors and electrical circuits comprising an organic binder, an amorphous carbon, graphite in the form of whiskers and silica.
In the EP-A-032 375, one has described an electrically conductive elastomer comprising a copolyetherester and a mix of carbon and graphite intended for use in electronic equipment and office machines.
However, the attenuation performances of known electrically conductive shields are not linear in a range of frequencies. Some frequency ranges are more important for certain applications than for other, for example a frequency range which is particularly important for safety shielding are the frequencies between 1 MHz to 10 GHz. Nevertheless, the attenuation performances of most materials are relatively weak around 100 MHz. Since the attenuation performance normally presented is a mean value on a large frequency band, the deficiency of attenuation performances in a given particularly important band frequency, for example in the region of 100 MHz is often not apparent.
Carbon is allotropic and is found widely in its elementary crystalline or amorphous solid forms. It is found in coke in an amorphous form and examples crystalline forms are graphite and diamond. In different applications, one has used either amorphous carbon or graphite.
SUMMARY OF THE INVENTION
The aim of the present invention is: electromagnetic radiations and TEMPEST (designation used by NATO concerning non-intentional radiations phenomena resulting from communication and data treatment systems) et more particularly in the range of frequencies comprised between 1 MHz and 10 GHz. construction of antistatic floors, intrusion sensitive barriers, heating elements, grounding elements, large capacitors, antennas.
The material according to the present invention is characterized by the fact that it comprises a mixture of graphite and amorphous carbon and sand and in that the binder comprises polyamide resins or polycarbonate resins and a cement-based material.
The advantage of the material according to the present invention is the fact that the simultaneous use of amorphous carbon and graphite produces an unexpected synergy effect between them which improves the material efficiency.
The examples of binders for the material according to the invention comprise either ordinary Portland cement or pulverized fuel ashes or quick-taking cement or a combination of these elements. The relative ratio of binder, sand and graphite and amorphous carbon in the material affects as much its shielding properties as its physical properties. High concentrations of carbon in the mixture result in a fragile and brittle material which is difficult to work and which necessitates a support, for example taken in sandwich between two plaster sheets. On the other hand, if the ratio of carbon in the mixture is lower than about 20% of the total weight of the material, then the shielding efficacy decreases. The preferred graphite/amorphous carbon ratio with respect to the total weight of the material is between 25% and 75%, and preferably between 35% and 65%.
The percentage of graphite in the mix graphite/amorphous carbon is between 10% and 95% with respect to the weight of this mixture according to the planned use of the material. For example in a material in which graphite represents 10% of the
REFERENCES:
patent: 3301799 (1967-01-01), Rothberg et al.
patent: 3962142 (1976-06-01), Freeman et al.
patent: 5004561 (1991-04-01), Nomura et al.
patent: 5447564 (1995-09-01), Xie et al.
Pat. Abs. of Japan, vol. 012 No. 482 (Asahi Chem Res Lab Ltd), JP 63-196672 Aug. 15, 1988.
Elfinco S.A.
Kopec Mark
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