Production of ceramic filaments

Details Production of ceramic filaments Production of ceramic filaments

1993-02-17

1995-01-17

Beck, Shrive

Coating processes

Immersion or partial immersion

Running lengths

427399, 4274342, 427598, 118DIG5, 118DIG19, 118402, 118405, 118423, B05D 118

Patent

active

053824563

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to refractory fibers and in particular but not exclusively to the production of silicon carbide and silicon carbide coated carbon fibers.


DISCUSSION OF PRIOR ART

GB Patent No 2,227,483 describes a method of manufacture of refractory fibers of silicon carbide or silicon carbide coated carbon by passing fine carbon fibers through molten silicon. Molten silicon is contained within a crucible provided with one or more holes in its base through which fiber(s) can be drawn. The holes are dimensioned such that surface tension forces in the molten silicon prevent silicon from flowing out of the crucible.
The object of the present invention is to provide apparatus and method for manufacture of refractory filaments, particularly silicon carbide, utilizing molten material such as silicon without problems associated with crucible containment.
The invention provides in one form apparatus for producing refractory material filaments comprising: an enclosure; means for heating the constituents of the refractory material; non-contacting means to support a drop, of molten material, being one of the constituents of the refractory material, within the enclosure; and means to transport a filament made of material, being a second constituent of the refractory material, through the drop of molten material in use.
In one arrangement the apparatus may be used with a carbon filament: and molten silicon.
The means to support or levitate the silicon drop may be a levitation coil and/or a gas jet. A silica glass or other refractory tube may be provided to direct the gas jet and the gas may be selected to provide an inert, protective atmosphere to prevent oxidation.
Advantageously the enclosure includes opposed side arms which are respectively for entry and exit of the filament. Alternatively the filament may be passed vertically through the molten silicon drop. An inclined side tube may be provided through which grains of silicon may be introduced into the enclosure for addition to the molten drop.
In one form, initial heating of the silicon prior to levitation may be achieved by providing a resistively heated silicon nitride platform on which the silicon can be melted, the platform being removable from the field of the levitation coil so as to leave a levitated silicon drop. Alternatively a laser may be provided to melt the silicon.
The invention also provides in a second form a method of making silicon carbide filaments comprising the steps of:
The molten drop may be formed by:
In one form the platform is made of silicon nitride such that it is not wetted by molten silicon. The silicon can then be melted by resistively heating the platform or heating by means of a laser.
Once the silicon is melted the means to levitate the molten silicon may be applied and the platform removed to leave the levitated drop of silicon.
The levitation may be achieved by application of an electromagnetic field from a levitation coil or by forming an upward jet of supporting gas.
Preferably the gas is selected such that oxidation of the molten silicon does not occur.
The carbon filament may conveniently be passed horizontally through the molten drop.
Preferably the molten drop of silicon is replenished by addition of solid silicon to the molten drop to thereby enable continuous manufacture of silicon carbide filaments.


DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described with reference to the accompanying Figure which shows a carbon filament 10 being fed into a reaction enclosure 11. The reaction enclosure 11 is formed by a vertical silica tube 12, open at its lower end 13 and closed at its upper end 14. Two opposed lateral side tubes 15, 16 are provided through which the carbon filament 10 is fed from a take-off spool (not shown) to a take-up spool (not shown). As shown, a spherical drop 17 of molten silicon is levitated by means of an external levitation coil (not shown for clarity) such that the carbon fiber 10 passes through the molten silicon. An inert gas is introd

REFERENCES:
patent: 4122212 (1978-10-01), Walling et al.
patent: 4325930 (1982-04-01), Vallet
patent: 4473105 (1984-09-01), Pryor
patent: 4565571 (1986-01-01), Abbcschian
patent: 4762553 (1988-08-01), Savage et al.
patent: 5171734 (1992-12-01), Sanjurjo et al.
Chemical Abstracts, vol. 77, No. 14, Oct. 2, 1972; Abstract no. 91928N, A. A. Fogel et al; Parameters of a Molten Metal Held In et al.
Chemical Abstracts, vol. 104, No. 20, May 19, 1986; Abstract no. 173252C, H. Izawa `Surface Treatment of Carbon Products` p. 296; column 2.

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