Method for preparing a silicification bath

Abstract

Process for preparing a silicifying bath. The invention relates to a process for preparing a silicifying bath comprising boron and silicon in known proportions, comprising at least the following steps: - the removal (E11) of boron from a used bath comprising boron and silicon in unknown proportions, until a treated used bath is obtained in which the boron content is less than or equal to 500 ppm; - the determination (E12) of the quantity of silicon present in the treated used bath after removal of the boron; - the addition (E13) of boron to the treated used bath to obtain a silicifying bath comprising boron and silicon in known proportions. Figure for the abstract: Fig. 2.

Description

Title of the invention: Process for preparing a siliciding bath Technical field

[0001] The present disclosure relates to a method for preparing a siliciding bath. Prior art

[0002] Ceramic matrix composite (CMC) materials withstand temperatures ranging from 600°C to 1400°C.

[0003] Due to their better resistance to high temperatures, CMCs require less cooling. This cooling traditionally comes from a sample in the compressor which impacts the efficiency of the turbomachine, CMC materials therefore make it possible to improve engine efficiency which reduces fuel consumption.

[0004] Furthermore, their use contributes to optimizing the performance of turbo-machines, in particular by reducing the overall mass of the turbo-machine, which further contributes to a reduction in fuel consumption and therefore to a significant reduction in polluting emissions.

[0005] Among the CMC materials, there are in particular materials comprising a silicon carbide fiber reinforcement and a silicon carbide matrix.

[0006] Such materials are called SiC / SiC and are generally obtained by infiltration of molten silicon into a fibrous reinforcement formed by silicon carbide fibers.

[0007] During such infiltration, a silicon bath comprising boron, in known proportions, is generally used, the boron making it possible to protect the fibers from corrosion that could be caused by molten silicon in the absence of boron.

[0008] Nevertheless, it is generally observed that after infiltration of the preform produced, the remaining siliciding bath no longer has the same proportions between boron and silicon.

[0009] The remaining bath cannot be reused for a subsequent infiltration process and the rest of the bath is then completely replaced by a new siliciding bath.

[0010] This results in both significant preparation times and material losses with economic and environmental repercussions that it is desirable to avoid. Description of the invention

[0011] The invention aims precisely to meet the need set out above for improving the methods for preparing a siliciding bath.

[0012] The invention therefore proposes a method for preparing a siliciding bath. comprising boron and silicon in known proportions comprising at least the following steps: - removing boron from a used bath comprising boron and silicon in unknown proportions, until a treated used bath is obtained in which the boron content is less than or equal to 500 ppm; - determination of the quantity of silicon present in the used bath treated after removal of boron; - the addition of boron to the treated used bath to obtain a siliciding bath comprising boron and silicon in known proportions.

[0013] Such a process allows the recycling of a used silicon bath, for example one used for the infiltration of a fiber preform with molten silicon.

[0014] Indeed, rather than replacing the entire bath with a completely new bath, the method of the invention makes it possible to reuse the silicon from the used bath, while ensuring that it is possible to use it to form a siliciding bath.

[0015] In one embodiment, the used bath does not comprise any element other than silicon and boron in a mass content greater than 100 ppm, or even comprises a total content of elements other than silicon and boron less than or equal to 100 ppm.

[0016] This embodiment corresponds to the particular case where the used bath corresponds to a bath previously used for a process of siliciding a fibrous reinforcement by infiltration of molten silicon.

[0017] Furthermore, this embodiment makes it possible to ensure that the treated recycled bath comprises almost exclusively silicon, which simplifies the determination of the quantity of silicon, which can then be a simple weighing or a determination of the volume of the bath.

[0018] In one embodiment, determining the amount of silicon remaining in the treated waste bath after boron removal may be accomplished by weighing the treated waste bath.

[0019] This embodiment makes it possible to know precisely the quantity of silicon remaining in the bath, so that the subsequent addition of boron makes it possible to arrive at known proportions of boron and silicon, all in a very simple manner.

[0020] In one embodiment, the mass content of boron in the siliciding bath may be between 1% and 15% and the mass content of silicon in the siliciding bath may be between 85% and 99%.

[0021] The inventors have determined that this proportion allows excellent infiltration by the molten silicon, while ensuring excellent protection of the matrix against oxidation.

[0022] In one embodiment, the removal of boron occurs by exposing the bath to a treatment atmosphere comprising argon and / or dihydrogen.

[0023] Without wishing to be bound by theory, the inventors have found that exposing a bath comprising boron and silicon to a treatment atmosphere allows a volatile boron monohydride HBO compound to be formed in the bath, which is evacuated, and which carries with it the boron initially present.

[0024] Furthermore, the inventors have found that this process makes it possible to achieve extremely low residual boron concentrations in the treated used bath.

[0025] It should be understood from the formulation “comprising argon and / or dihydrogen” that the treatment atmosphere may comprise argon, dihydrogen or even both argon and dihydrogen.

[0026] In one embodiment, the exposure of the bath to the treatment atmosphere is done by bubbling said atmosphere into the bath or by exposing the surface of the bath to said treatment atmosphere.

[0027] The inventors have in fact found that these methods are particularly suitable for a process of the invention.

[0028] In one embodiment, the exposure of the bath to the treatment atmosphere takes place for a period of 1 hour to 10 hours.

[0029] The inventors have in fact found that this duration was sufficient to allow effective elimination of boron.

[0030] In one embodiment, the exposure of the bath to the treatment atmosphere takes place at a temperature between 1400°C and 1600°C.

[0031] The inventors have in fact found that this temperature was sufficient to allow effective elimination of boron.

[0032] In one embodiment, the treatment atmosphere comprises argon at a partial pressure of between 1.0 bar and 5.0 bar and a partial pressure of dihydrogen of between 0 and 1.0 bar.

[0033] In this embodiment, the atmosphere may or may not comprise dihydrogen.

[0034] In the present application the partial pressure of a gas takes its usual meaning in the field of ideal gas thermodynamics, and intends to represent the pressure which would be exerted by the molecules of this gas if it alone occupied the volume offered to the mixture, at the temperature of said mixture.

[0035] In one embodiment, the treatment atmosphere comprises dihydrogen at a partial pressure of between 1.0 bar and 5.0 bar and does not comprise argon.

[0036] This embodiment makes it possible to use a single source of gas for the creation of the treatment atmosphere.

[0037] In one embodiment, the treatment atmosphere further comprises water vapor at a partial pressure of between 0 and 1.0 bar, excluding 0.

[0038] It is not essential to the described method that the treatment atmosphere comprises water. However, the inventors found that the latter allowed the oxidation of dissolved boron into boron monohydride HBO.

[0039] According to another of its aspects, the invention also relates to a method for siliciding a fibrous reinforcement comprising a step of infiltrating the porosity of said fibrous reinforcement with an infiltration composition by soaking at least a portion of said fibrous reinforcement in a siliciding bath, the method being characterized in that the infiltration step is preceded by a step of preparing a siliciding bath as just described.

[0040] This embodiment makes it possible to have a method for siliciding a fibrous reinforcement with performances identical to that of the prior art, but whose infiltration bath has, at least in part, been able to be obtained at lower costs.

[0041] This results in a process for siliciding a fiber preform that is more economical than the processes of the prior art.

[0042] According to another of its aspects, the invention relates to an installation for carrying out a method as described above.

[0043] Such an installation may, for example, comprise a reaction chamber in which the used bath may be placed, the reaction chamber being placed between a gas source and a gas outlet.

[0044] In one embodiment, the gas source may comprise a water vapor source, a dihydrogen source, an argon source, or a mixture of two or more of these sources.

[0045] These sources are chosen and allow the installation to have the advantages already described in connection with the process. In particular, these sources make it possible to have the treatment atmospheres described above in connection with the process prevail in the installation.

[0046] In one embodiment, the installation comprises means for evaluating the quantity of silicon in the treated used bath.

[0047] In one embodiment, such means may be a scale for determining the weight of the treated used bath.

[0048] Alternatively or in a complementary manner, such means may be optical devices making it possible to quantify the volume of the used bath treated. Brief description of the drawings

[0049] [Fig. 1] [Fig. 1] represents a flowchart representing an embodiment of the method for preparing a siliciding bath according to the invention.

[0050] [Fig.2] [Fig.2] represents a flowchart representing an embodiment of a siliciding process according to the invention.

[0051] [Fig.3] [Fig.3] represents an installation allowing the realization of a process in one embodiment. Description of the embodiments

[0052] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0053] [Fig.l] schematically represents a flowchart showing the steps of a method according to the invention

[0054] [Fig.l] represents a first step El 1 in which boron is removed from a used bath comprising boron and silicon in unknown proportions.

[0055] For example, such a used bath may come from a siliciding bath used in a process for manufacturing a part made of SiC / SiC composite material by infiltration of an infiltration composition into a fibrous reinforcement.

[0056] In one embodiment, the used bath may comprise a mixture of several baths each having been used in a method of manufacturing a part made of SiC / SiC composite material by infiltration of molten silicon into a fibrous reinforcement.

[0057] In one embodiment, before removal of boron, the bath of step E1 1 may comprise boron, silicon and other elements, but none of the elements other than boron and silicon are present in a content greater than or equal to 100 ppm.

[0058] Step E1 1 makes it possible to obtain a purified treated bath in which the boron content is less than or equal to 500 ppm.

[0059] Step E1 1 may comprise exposing the used bath to a treatment atmosphere comprising argon, dihydrogen, steam or a mixture of two or more of these compounds.

[0060] Step E1 1 may comprise a step of heating the used bath to a temperature of between 1400°C and 1600°C. In particular, the used bath may be brought to a temperature of between 1400°C and 1600°C throughout the step of exposing the used bath to the treatment atmosphere.

[0061] In one embodiment, step E1 1 jointly comprises maintaining the used bath at a temperature between 1400°C and 166°C and exposing said used bath to a treatment atmosphere.

[0062] For example, the duration of step El 1 can be between 1h and 10h.

[0063] Step E1 1 can be carried out by bubbling the treatment atmosphere into the bath used or by exposure of the surface of the used bath to the treatment atmosphere.

[0064] Step Eli is followed by a step of determining the quantity of silicon E12 remaining in the used bath treated after step Eli.

[0065] Step E12 makes it possible to precisely determine the quantity of remaining silicon and therefore the quantity of boron that would need to be added to achieve the desired siliciding bath, i.e. with the desired proportions of boron and silicon.

[0066] Step E12 is preferably carried out by weighing the treated used bath.

[0067] The method further comprises a step E13 of adding a boron powder to the treated used bath to achieve the desired siliciding bath.

[0068] In one embodiment, the bath obtained at the end of step E13 may comprise a mass content of boron of between 1 and 15% and a mass content of silicon of between 85% and 99% as well as other elements, but none of the elements other than boron and silicon is present in a content greater than or equal to 100 ppm.

[0069] Preferably, the total mass content in the bath obtained at the end of step E13 of elements other than boron and silicon is less than or equal to 100 ppm.

[0070] Such a bath is particularly useful for the siliciding of a fibrous reinforcement in order to form ceramic matrix composite materials and more precisely SiC / SiC ceramic matrix composite materials.

[0071] [Fig.2] represents a method for siliciding a fibrous reinforcement comprising a step E22 of infiltrating the porosity of said fibrous reinforcement with an infiltration composition by soaking at least a portion of the fibrous reinforcement in a bath of said infiltration composition, which comprises silicon and boron.

[0072] In one embodiment, step E22 is carried out with a fibrous reinforcement comprising silicon carbide fibers.

[0073] In one embodiment, such a step E22 can be carried out after a step of loading the porosity of said reinforcement with a slip comprising particles reactive with silicon.

[0074] Such slips are known to those skilled in the art and make it possible to obtain, at the end of step E22, a composite material with a ceramic matrix called SiC / SiC, i.e. one in which the fibrous reinforcement and the matrix are made of silicon carbide.

[0075] In one embodiment, the fiber reinforcements are preforms of parts for turbomachines.

[0076] In a method described here, the infiltration composition bath of step E22 has previously been obtained by a method described above, and visible in [Fig.l].

[0077] Thus, step E22 of [Fig.2] is preceded by steps Eli, E12 and E13.

[0078] In one embodiment, step E22 may itself be followed by a step E11, which makes it possible to recover a portion of the silicon from a used infiltration composition.

[0079] Optionally, an optional step E23 of adding silicon not comprising any other element in a content greater than or equal to 100 ppm can be carried out after step E11 and before step E12, so that the final bath of the infiltration composition comprises a sufficient quantity of silicon for the impregnation of another preform.

[0080] In one embodiment, the method may comprise an optional step E24 at the end of said step E13 and before step E22.

[0081] Step E24 represents the addition to the bath obtained of a mixture comprising boron and silicon in the same proportions as the bath obtained at the end of step E13.

[0082] Such a step E24 makes it possible to have a bath of infiltration composition in sufficient quantity to carry out siliciding similar to step E22, without modifying the proportion of silicon and boron in the treated used bath obtained in step E13.

[0083] The optional steps are represented by dotted lines, and the arrow looping between step E22 and step E11 is intended to signify that at the end of a step E22, the used siliciding bath can again be recycled to make it suitable for a new step E22, with different preforms.

[0084] [Fig.3] represents an installation allowing the carrying out of a process for preparing a siliciding bath described above and represented in [Fig.l].

[0085] The installation 10 shown comprises a container 11 capable of containing the used bath 21, arranged on a support 12.

[0086] The support here comprises a scale 13. This scale advantageously makes it possible to know precisely the quantity of silicon present in the bath after elimination of the boron, in particular at the end of step E12.

[0087] The installation further comprises a reaction chamber 14 in which the container 11 is arranged.

[0088] The chamber 14 may further comprise heating elements 15. [Fig. 3] shows susceptors, heated by inductors not shown and arranged for example outside the chamber 14.

[0089] However, the heating elements 15 can also be resistive members.

[0090] In the embodiment of [Fig.3], a path for supplying the chamber 14 with gas is shown.

[0091] [Fig. 3] represents a first gas source 31, for example argon, and a second gas source 32, for example dihydrogen, which are arranged upstream of a humidifier 33.

[0092] The gas supply path is connected to a supply pipe 34 making it possible to supply the reaction chamber 14 with gases from the source, possibly humidified.

[0093] The chamber further comprises a gas evacuation, not shown.

[0094] When carrying out a method as described above, and for example illustrated in [Fig.l], step E11 can be carried out by supplying the reaction chamber with a treatment atmosphere from sources 31, 32, possibly humidified by humidifier 33 and via injection pipe 34.

[0095] The treatment atmosphere is, if necessary, heated via the heating elements. 15.

[0096] The treatment atmosphere can, in the reaction chamber 14, come into contact with the used bath 21, which is arranged in the container 11.

[0097] In one embodiment, the injection rod 34 may be disposed in the spent bath 21, such that the treatment atmosphere bubbles into the bath 21.

[0098] The embodiment is not limited to a single injection rod 34.

[0099] Once step E11 has been carried out, step E12 can be carried out directly in the room 14 thanks to scale 13 measuring the mass of bath 21.

[0100] Preferably, the assembly is then removed from the chamber 14 to carry out a step E13, and where appropriate E22.

[0101] [Fig.3] is for illustrative purposes only and is not intended to represent the only embodiment of an installation.

[0102] Throughout the present application, the expression "between ... and..." must be understood inclusively.

Claims

Claims

1. A method for preparing a siliciding bath comprising boron and silicon in known proportions comprising at least the following steps: - removing (El 1) boron from a used bath (21) comprising boron and silicon in unknown proportions, until a treated used bath is obtained in which the boron content is less than or equal to 500 ppm; - determining (El2) the quantity of silicon present in the treated used bath after removing the boron; - adding (E13) boron to the treated used bath to obtain a siliciding bath comprising boron and silicon in known proportions.

2. A method of preparing a siliciding bath according to claim 1, wherein the used bath (21) does not comprise any element other than silicon and boron in a mass content greater than 100 ppm.

3. A method of preparing a siliciding bath according to claim 1 or 2, wherein the mass content of boron in the siliciding bath may be between 1% and 15% and the mass content of silicon in the siliciding bath may be between 85% and 99% in the siliciding bath.

4. A method of preparing a siliciding bath according to any one of claims 1 to 3, wherein the removal of boron takes place by exposing the bath (21) to a treatment atmosphere comprising argon and / or dihydrogen.

5. A method of preparing a siliciding bath according to claim 4, wherein the exposure of the bath (21) to the treatment atmosphere is by bubbling said atmosphere into the bath or by exposing the surface of the bath to said treatment atmosphere.

6. A method of preparing a siliciding bath according to any one of claims 1 to 5, wherein the exposure of the bath (21) to the treatment atmosphere takes place for a period of 1 hour to 10 hours.

7. A method of preparing a siliciding bath according to any one of claims 4 to 6, wherein the treatment atmosphere comprises argon at a partial pressure of between 1.0 bar and 5.0 bar and a partial pressure of dihydrogen of between 0 bar and 1.0 bar.

8. A method of preparing a siliciding bath according to any one of claims 4 to 6, wherein the treatment atmosphere comprises dihydrogen at a partial pressure of between 1.0 bar and 5.0 bar and does not comprise argon.

9. A method of preparing a siliciding bath according to one of claims 7 or 8, wherein the treatment atmosphere further comprises water vapor at a partial pressure of between 0 bar and 1.0 bar, 0 excluded.

10. A method of siliciding a fibrous reinforcement comprising a step of infiltrating the porosity of said fibrous reinforcement with an infiltration composition by soaking at least a portion of said fibrous reinforcement in a siliciding bath, the method being characterized in that the infiltration step is preceded by a step of preparing a siliciding bath according to one of claims 1 to 9.

11. Installation (10) for carrying out a method according to one of claims 1 to 9.

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