DEVICE FOR CHEMICAL VAPOUR DEPOSITION

Abstract

A device for fluidised bed chemical vapour deposition, includes a reactor including a treatment zone in which the fluidised bed chemical vapour deposition is intended to be carried out using at least a first and a second reactive gas and a diffuser under the treatment zone delimiting the reactor, and a heating system configured to heat at least the treatment zone. The device includes a first channel for introducing the first reactive gas and a second channel for introducing the second reactive gas, which second channel is separate from the first channel and opens out under the diffuser, and wherein the first introduction channel is capable of being moved with respect to the heating system.

Claims

1. A device for fluidised bed chemical vapour deposition, comprising: a reactor comprising a treatment zone in which the fluidised bed chemical vapour deposition is intended to be carried out using at least a first and a second reactive gas and a diffuser under the treatment zone delimiting the reactor, a heating system configured to heat at least the treatment zone, a first channel for introducing the first reactive gas and a second channel for introducing the second reactive gas, which second channel is separate from the first channel and opens out under the diffuser, wherein the first introduction channel is capable of being moved with respect to the heating system.

2. The device according to claim 1, wherein the first channel for introducing gas is capable of passing through the diffuser and of opening out into the treatment zone.

3. The device according to claim 1, wherein the first channel for introducing gas is capable of opening out under the diffuser or even in the diffuser.

4. The device according to claim 1, wherein the diffuser is capable of being moved with respect to the heating system.

5. The device according to claim 1, wherein the reactor further comprises a thermal insulator, between the diffuser and the treatment zone.

6. The device according to claim 1, further comprising an additional heating system configured to heat a zone downstream of the treatment zone to a temperature greater than or equal to the temperature of the treatment zone.

7. A method for coating particles by fluidised bed chemical vapour deposition, comprising: introducing particles into the treatment zone of a reactor, the particles being made of ceramic material or of carbon; introducing a first reactive gas into a first channel for introducing gas; introducing a second reactive gas into a second channel for introducing gas, which second channel is separate from the first channel for introducing gas; and heating the treatment zone to a temperature enabling the reaction of the first and second reactive gases in the treatment zone so as to coat the particles, the first introduction channel opening out into a zone where the temperature is greater than that of the zone where the second channel opens out.

8. The coating method according to claim 7, wherein the method is carried out in a device according to claim 1.

9. The coating method according to claim 7, wherein the particles are short fibres having an average length less than or equal to 5 mm.

10. The coating method according to claim 7, wherein the first and second reactive gases are BCl.sub.3 and NH.sub.3, so as to coat the particles with boron nitride.

11. The coating method according to claim 7, further comprising an additional heating step, carried out in a zone downstream of the treatment zone where the temperature is higher than in the treatment zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 schematically shows a device according to a first configuration capable of implementing the invention.

[0074] FIG. 2 schematically shows a device according to a second configuration capable of implementing the invention.

[0075] FIG. 3 schematically shows a device according to a third configuration capable of implementing the invention.

DESCRIPTION OF THE EMBODIMENTS

[0076] The invention will now be described by means of particular embodiments which are detailed for the purpose of understanding the invention, but which should not be interpreted in a limiting manner.

[0077] As described above, the invention relates to a device 100 for chemical vapour deposition.

[0078] FIG. 1 illustrate such a device 100.

[0079] The device 100 comprises a first channel 20 for introducing a first reactive gas 22, which opens out, in the illustrated embodiment, in a thermal insulator 30.

[0080] In the embodiment shown, the thermal insulator rests on a diffuser 31 formed by a porous sinter. Such a sinter participates in the homogenisation of the reactive gases which pass through it. In the embodiment proposed in FIG. 1, the first channel 20 can pass through the porous sinter.

[0081] For example, the porous sinter 31 can be a platinum-rhodium plate.

[0082] The device also comprises a second channel 10 for introducing a second reactive gas 14.

[0083] In the embodiment shown, the flow of first 22 and second 14 reactive gases, represented by arrows, takes place respectively in the first 20 and second 10 channels for introducing gases.

[0084] For example, the first and second channels for introducing gases 10, 20 can be directly connected to the sources (not shown) of the reactive gases chosen to carry out the reaction. In the illustrated example, the distinct channels for introducing gases 10, 20 enable the mixing of the first and second reactive gases 14, 22 to take place in the insulator 30.

[0085] In an embodiment, the thermal insulator 30 can be a porous thermal insulator having a thermal conductivity at 20 C. less than or equal to 4.0 W.Math.m.sup.1.Math.K.sup.1, for example less than or equal to 3.0 W.Math.m.sup.1.Math.K.sup.1. In an embodiment, the thermal insulator can have a thermal conductivity at 20 C. greater than or equal to 0.1 W.Math.m.sup.1.Math.K.sup.1.

[0086] In an embodiment, the degree of porosity by volume of the thermal insulator 30 is greater than 26%, for example greater than or equal to 32%.

[0087] The thermal insulator 30 can obtain a temperature difference between the treatment zone 40, provided with a heating system 50 and the zone under the thermal insulator.

[0088] The diffuser 31 delimits the reactor 12 under the treatment zone 40. In the embodiment shown, a thermal insulator 30 is also present. However, the device 100 can further comprise other thermal insulators such as those conventionally usually used outside, around or in the walls of a chemical deposition furnace.

[0089] In an embodiment, the thermal insulator is a granular bed.

[0090] Such a feature advantageously contributes to yet further reducing the effective thermal conductivity of the thermal insulator 30, yet further stabilising the temperature of the fluidised bed during the deposition of the coating. In the particular case of a granular bed, such porosity values correspond to a bulk state, in other words an irregular or non-compact state.

[0091] It is possible, for example, to use a granular bed formed of bulk grains having an average diameter d50 less than or equal to 10 mm, for example between 0.5 m and 10 mm, and a density greater than or equal to 3 g/cm.sup.3, for example between 3.2 g/cm.sup.3 and 9 g/cm.sup.3. For example, a bulk stack of zirconia beads can be used, having an average diameter d50 equal to 1 mm in order to constitute the thermal insulator 30.

[0092] In an embodiment, the wall of the device 100 can be made of mullite or treated alumina.

[0093] In an embodiment, the reactive gases can be BCl.sub.3 and NH.sub.3, the decomposition of which at the temperature of the treatment zone 40 makes it possible to obtain reactive compounds, the reaction of which makes it possible to deposit a coating of BN directly on the carbon or ceramic particles 80 introduced into the treatment zone 40, for example on the diffuser 31.

[0094] For example, the flow of the first 22 and second reactive gas 14 can be obtained by imposing a pressure difference between the ends of the device 100, by means of devices that are known per se, for example pumps, and not shown in FIG. 1.

[0095] In an embodiment, the flow of first 22 and/or second reactive gas 14 can further comprise an inert carrier gas, for example molecular nitrogen. Gaseous precursors can be used under standard conditions, in which case they can be mixed with the carrier gas before their introduction into the device 100.

[0096] For example, the flow rate for introduction of the carrier gas into a reactor 12, as shown schematically in FIG. 1, can be between 500 standard cubic centimetres per minute and 4000 standard cubic centimetres per minute, for example between 1000 standard cubic centimetres per minute and 2000 standard cubic centimetres per minute.

[0097] The first introduction channel 20 is a movable rod, the vertical position of which can be adjusted. The device thus comprises a movement system which enables the first introduction channel 20, and optionally the diffuser 31, to move with respect to the heating system 50.

[0098] In the embodiment shown, the diffuser 31 is porous and delimits the lower part of the reactor 12, into which particles 80 are introduced.

[0099] In the embodiment shown, the particles 80 are short fibres.

[0100] In the device for fluidised bed chemical vapour deposition, the reactive gases introduced, and the decomposition of which makes it possible to obtain the coating on the particles 80 present in the treatment zone 40, also make it possible to obtain a dispersion of particles 80 which contributes to obtaining a homogeneous coating.

[0101] In FIGS. 2 and 3, the elements bear the same numbers representing elements analogous to those of FIG. 1.

[0102] FIG. 2 shows a configuration in which the first channel 20 for introducing a first reactive gas 22 opens out into the treatment zone 40 enabling mixing of the first 22 and second reactive gas 14 directly in the treatment zone.

[0103] FIG. 3 shows a configuration in which the first channel 20 for introducing a first reactive gas 22 opens out under the diffuser 31, for example at a short distance 23 from the diffuser 31, for example less than or equal to 2 mm. It is understood that this distance 23 is measured in the direction of gas flow between the upper end of the first introduction channel 20 and the diffuser 31.

[0104] In any one of the embodiments described above, it is also possible to introduce, into the treatment zone 40, spacer particles, distinct from the particles to be coated, in order to again further improve the homogeneity of the coating obtained.

[0105] Such particles can, for example, be made of ceramic material (oxide or non-oxide), such as alumina, silicon carbide or silicon nitride. Alternatively, the spacer particles can be metallic.

[0106] The average diameter of the spacer particles is between 100 m and 500 m.

[0107] The spacer particles are only present to promote the distribution of gases and particles to be covered in the fluidised bed.

[0108] The content of spacer particles by volume in the mixture with the particles to be coated can be between 70% and 95%.

[0109] When such spacer particles are present, coated particles are obtained in a more unitary and homogeneous manner.

[0110] The treatment zone 40, situated under the diffuser 31, can be heated by means of a heating system 50 that is known per se.

[0111] In the configurations shown in FIGS. 1, 2 and 3, the treatment zone 40 is followed, in the direction of gas flow, by a zone situated downstream 70, the temperature of which can be further increased by means of an additional heating system 60, that is also known per se, and separate from the first heating system 50. As described above, such a zone 70 can ensure, due to a temperature that is still higher than that of the treatment zone 40, decomposition of the reactive gases which have not reacted in the treatment zone 40.

[0112] The device can be used for the deposition of a ceramic material on the particles 80, for example boron nitride, silicon carbide or silicon nitride.