Method of antioxidant protection of carbon-containing composite parts

Abstract

The invention relates to a method for protecting a carbon-containing composite part against oxidation, comprising: impregnating the internal porosity of the part with an impregnation composition comprising, in percentage by weight: (i) from 1 to 60% of colloidal silica, (ii) from 0.5 to 20% of a fluxing agent precursor comprising at least one nitrate of an alkali metal M1, (iii) from 0.5 to 20% of a lattice-modifying precursor comprising at least one nitrate or oxonitrate of an element M2 chosen from a metal or a lanthanide, and (iv) from 20 to 88% of water; subjecting the part impregnated with the impregnation composition to a glass transition treatment in order to obtain an oxidation-resistant glass comprising at least silica, an oxide of M1 and an oxide of M2.

Description

Technical Field

[0001] This invention relates to oxidation protection for carbon-containing composite material components, specifically a material comprising a fiber-reinforced material densified from a matrix, wherein the interfacial coating between the fiber-reinforced material and / or the matrix and / or the reinforcing fibers and the matrix is ​​made of carbon. A particular application area of ​​this invention is oxidation protection for carbon / carbon (C / C) composite material components, particularly brake discs made of C / C composite materials, especially aircraft brake discs. Background Technology

[0002] The materials used in aircraft braking are C / C composites. These materials are chosen for this application due to their light weight, high heat absorption capacity, and good tribological properties. However, they are susceptible to oxidation, especially by oxygen in the air, at operating temperatures typically above 450°C. This oxidation can also be catalyzed by de-icing products used at airports. Several solutions have been developed to extend the lifespan of carbonaceous materials exposed to high temperatures in oxidizing atmospheres. In particular, a two-layer protection solution can be used, comprising an anti-catalytic inner layer based on aluminum metaphosphate (Al(PO3)3) and an outer layer preventing oxygen diffusion into the material. This solution provides satisfactory protection, but new protection schemes are still needed that are simpler to implement and provide at least equivalent protection against thermal oxidation and, possibly, catalytic oxidation. Summary of the Invention

[0003] This invention relates to a method for protecting components made of carbon-containing composite materials from oxidation, comprising:

[0004] • Impregnate the internal pores of a component with an impregnation composition comprising, by weight percentage: (i) 1% to 60% colloidal silica, (ii) 0.5% to 20% a flux precursor comprising at least one nitrate of an alkali metal M1, (iii) 0.5% to 20% a lattice-modifying precursor comprising at least one nitrate or oxynitrate of an element M2 selected from metals or lanthanides, and (iv) 20% to 88% water; and

[0005] • Perform vitrification heat treatment on the parts impregnated with the impregnation composition to obtain an anti-oxidation glass containing at least silicon dioxide, oxide of M1 and oxide of M2.

[0006] This invention proposes an impregnation composition with a specific formulation that provides excellent antioxidant protection at high temperatures, while allowing for the use of a single protective layer and a single heat treatment, thus simplifying the protection setup compared to the aforementioned two-layer solutions. In particular, this invention eliminates the need for pre-impregnation with aluminum phosphate to form an inner protective layer and the associated heat treatment steps for forming the antioxidant protection; the protective compound is provided in a single impregnation step, and only one glass transition heat treatment is required.

[0007] In one exemplary embodiment, the flux precursor includes at least sodium nitrate, potassium nitrate, or a mixture of these compounds.

[0008] This choice of flux precursor is particularly suitable for the treatment of friction components.

[0009] In one exemplary embodiment, the lattice-modifying precursor comprises at least one alkaline earth metal nitrate, particularly calcium nitrate and / or magnesium nitrate. The phase diagrams of these compounds are known and readily available, which allows for optimization of the heat treatment temperature by significantly reducing it from approximately 1400 °C to approximately 1000 °C.

[0010] Alternatively or in combination, the lattice-modifying precursor comprises at least a nitrate of a transition metal or a metal-poor metal. Choosing such a compound allows for optimization of the heat treatment temperature by significantly reducing it from approximately 1400 °C to approximately 1000 °C.

[0011] In one exemplary embodiment, the impregnation composition further comprises an acid stabilizer in a weight content between 0.05% and 10%.

[0012] Acid stabilizers help prevent gelling of the impregnation composition, thereby promoting impregnation of the internal pores of the component.

[0013] In particular, the acid stabilizer may be selected from boric acid (H3BO3), phosphoric acid (H3PO4), nitric acid (HNO3), or a mixture of these compounds.

[0014] Choosing boric acid (H3BO3) or phosphoric acid (H3PO4) can further enhance the protection provided by the glass by forming protective phosphorus oxide or boron oxide after the glass transition heat treatment.

[0015] In one embodiment, the impregnation composition comprises, by weight percentage:

[0016] • 10% to 60% colloidal silica;

[0017] • 0.5% to 20% flux precursor;

[0018] • 0.5% to 20% lattice-modified precursors;

[0019] • 0.05% to 10% acid stabilizer; and

[0020] • 20% to 88% water.

[0021] Based on this example, the impregnation composition may be free of metal phosphates, particularly aluminum phosphate.

[0022] According to one variant, the impregnation composition comprises, by weight percentage:

[0023] • 1% to 10% colloidal silica;

[0024] • 20% to 35% aluminum phosphate;

[0025] • 1% to 7% flux precursor;

[0026] • 1% to 5% lattice-modified precursors;

[0027] • 50% to 77% water;

[0028] Furthermore, after heat treatment, an oxidation-resistant glass and a catalyst-resistant aluminum phosphate phase are obtained. The catalyst-resistant aluminum phosphate phase can be an Al(PO3)3 phase.

[0029] This corresponds to an impregnation composition containing dissolved aluminum phosphate. According to this variant, an acid stabilizer can be omitted because aluminum phosphate itself is acidic and prevents the impregnation composition from gelling. Advantageously, in this variant, the aluminum phosphate phase obtained in addition to glass is able to improve resistance to catalytic oxidation.

[0030] In one exemplary embodiment, the component is a friction component, such as an aircraft brake disc. In particular, the friction component may be made of a carbon / carbon composite material. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating a series of steps that can be implemented within the context of one example of the method of the present invention.

[0032] Description of Implementation

[0033] In the following description, antioxidant protection for components made of C / C composite materials is envisioned, particularly brake discs such as aircraft brake discs. More generally, the invention applies to antioxidant protection for all components made of carbon-containing composite materials.

[0034] First, combine Figure 1 The flowchart describes an example of the method according to the present invention.

[0035] Components made from carbon-containing composite materials can be obtained in ways known per se, for example by densifying fiber-reinforced materials with a carbon matrix phase. This densification can be carried out in a liquid manner, i.e., by impregnation and pyrolysis of a polymer precursor, or in a gaseous manner, i.e., by chemical vapor infiltration. The resulting component has surface pores and internal pores communicating with the surface pores and located below the surface of the component.

[0036] The first step involves impregnating the accessible pores of the composite material with a wetting agent (step 10). This step is known in itself. For this purpose, an aqueous solution of a wetting agent can typically be used, such as "Marlophen NP9" sold by Sasol GmbH in Germany. The presence of the wetting agent facilitates the penetration of the impregnation composition into the accessible pores of the composite material.

[0037] After impregnation and drying with a wetting agent (step 20), the impregnation composition is applied to the outer surface of the part (step 30). The impregnation composition can be applied by brushing or by spraying (i.e., spraying with a spray gun). Typically, 5 mg / cm² can be applied per unit area of ​​the treated part. 2 Up to 200 mg / cm 2 The amount of impregnation composition.

[0038] The impregnation composition contains a specific combination of compounds, as described above, which provides good antioxidant protection at high temperatures while allowing the use of a single protective layer and a single heat treatment, thus simplifying the setup of the protection.

[0039] The impregnation composition in suspension form comprises an aqueous phase and a solid phase, wherein the flux precursor and the lattice-modifying precursor are dissolved in the aqueous phase, and the colloidal silica is suspended in the aqueous phase.

[0040] The average size of colloidal silica particles can be less than or equal to 1000 nm, for example, less than or equal to 100 nm. Using such fine particles facilitates impregnation within the internal pores of the composite component. Thus, after vitrification, a protective glass forms on the outer surface of the composite material and inside the material to be protected, below this outer surface, which protects it from external erosion encountered during operation, thereby improving the protective effect. Unless otherwise stated, "average size" refers to the size given by the statistical particle size distribution at half the total size, referred to as D50.

[0041] The flux is obtained from flux precursors during heat treatment and can lower the melting temperature of the glass, softening it during the heat treatment process to allow for glass formation within the component at temperatures compatible with industrial applications. According to one example, the flux precursor is selected from: lithium nitrate (LiNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), rubidium nitrate (RbNO3), cesium nitrate (CsNO3), and mixtures of these compounds. In the case of mixtures, the sum of the weight contents of the present compounds is within the range of the aforementioned flux precursor contents. Specifically, the flux precursor may be selected from: sodium nitrate, potassium nitrate, and mixtures of these compounds.

[0042] Flux precursor nitrates can be used in hydrated or non-hydrated forms.

[0043] The lattice-modifying precursor is converted into a lattice modifier during heat treatment. A lattice modifier is a compound capable of adjusting glass properties, such as resistance to hydrolysis, resistance to acid or alkali corrosion, melting temperature, or viscosity. According to one example, the lattice-modifying precursor is selected from: magnesium nitrate Mg(NO3)2, calcium nitrate Ca(NO3)2, strontium nitrate Sr(NO3)2, barium nitrate Ba(NO3)2, vanadium oxynitrate VO(NO3)3, manganese nitrate Mn(NO3)2, iron nitrate Fe(NO3)3, cobalt nitrate Co(NO3)2, copper nitrate Cu(NO3)2, zirconium nitrate Zr(NO3)4, zinc nitrate Zn(NO3)2, cadmium nitrate Cd(NO3)2, lead nitrate Pb(NO3)2, lanthanum nitrate La(NO3)3, cerium nitrate Ce(NO3)3, and mixtures of these compounds. For flux precursors, in the case of mixtures, the sum of the weight contents of the present compounds is within the range of the aforementioned lattice-modifying precursors. In particular, the lattice-modifying precursor can be selected from magnesium nitrate, calcium nitrate, and mixtures of these compounds. The use of these compounds is advantageous because they are readily available. According to one variant, the lattice-modifying precursor can be a metal-poor nitrate, such as zinc nitrate.

[0044] The lattice-modified precursor nitrate can be used in hydrated or non-hydrated form.

[0045] Generally, the following combinations can be used in the impregnation composition:

[0046] • The flux precursor is sodium nitrate, and the lattice modification precursor is calcium nitrate;

[0047] • The flux precursor is sodium nitrate, and the lattice modification precursor is zinc nitrate;

[0048] • The flux precursor is a mixture of sodium nitrate and potassium nitrate, and the lattice modification precursor is calcium nitrate; or

[0049] • The flux precursor is sodium nitrate, and the lattice modification precursor is a mixture of calcium nitrate and magnesium nitrate.

[0050] The impregnation composition may contain other compounds, such as acid stabilizers, which may be selected from boric acid (H3BO3), phosphoric acid (H3PO4), nitric acid (HNO3), or mixtures of these compounds.

[0051] The impregnation composition may be free of sodium silicate (Na₂O) with a strictly positive x. x SiO2. The impregnation composition provides colloidal silica and alkali metal M1, which allows for finer adjustment of the M1 / Si ratio, thereby improving the effectiveness of the antioxidant protective glass compared to using sodium silicate solution. Omitting sodium silicate also contributes to improved stability of the impregnation composition over time (lower risk of gelation). Generally, the impregnation composition consists primarily of colloidal silica, flux precursors, lattice-modifying precursors, and water, optionally containing aluminum phosphate and / or an acid stabilizer, each component present in the amounts described above.

[0052] The impregnation composition is obtained by mixing different components; it should be noted that when the impregnation composition does not contain metal phosphates, it is preferable to add the acid stabilizer to the colloidal silica before adding the flux precursor and the lattice modification precursor in order to obtain a pH value below the isoelectric point of silica, so that silica does not react with other cations.

[0053] As an example of an impregnation composition that can be used in the context of this invention, the following formulation can be mentioned, wherein the percentages are by weight: 4% SiO2, 2% Ca(NO3)2, 24% anhydrous aluminum phosphate Al(H2PO4)3, 67% H2O and 3% NaNO3.

[0054] The applied impregnation composition impregnates the internal pores of the component, and may have a depth greater than or equal to 1 mm inside the component, for example greater than or equal to 2 mm, for example between 2 mm and 10 mm. The depth is measured relative to the outer surface of the component.

[0055] The part impregnated with the impregnation composition is then subjected to a vitrification heat treatment (step 40). The vitrification heat treatment is performed by raising the temperature to between 700°C and 1200°C to obtain an anti-oxidation glass. This temperature can be maintained for one hour or longer, for example, 10 to 15 hours. The vitrification heat treatment can be performed in a neutral atmosphere, such as nitrogen (N2). As a result of this heat treatment, the anti-oxidation glass is present in the pores within the part. The anti-oxidation glass can exist within the part at a depth greater than or equal to 1 mm, for example, greater than or equal to 2 mm, measured relative to the outer surface of the part. This depth can be between 2 mm and 10 mm.

[0056] As an example, antioxidant glass can have the following molar percentage composition: SiO2 between 68% and 73%, Na2O between 15% and 23%, and CaO between 5% and 11%. Examples of other glass compositions (molar percentage) are listed below:

[0057] ·67%SiO2–22%Na2O–11%ZnO;

[0058] ·70%SiO2–15%Na2O–5%K2O–10%CaO;

[0059] ·70%SiO2–20%Na2O–5%CaO–5%MgO.

[0060] The phrase “between… and…” should be understood to include boundary values.

Claims

1. A method for protecting carbon-containing composite material components from oxidation, comprising: • Impregnate the internal pores of the component with an impregnation composition comprising, by weight percentage: (i) 1% to 60% colloidal silica, (ii) 0.5% to 20% flux precursor comprising at least one alkali metal nitrate M1, (iii) 0.5% to 20% lattice-modifying precursor comprising at least one nitrate of element M2 selected from alkaline earth metals, transition metals, depleted metals or lanthanides or an oxygen-containing nitrate of element M2 selected from metals, and (iv) 20% to 88% water; • The part impregnated with the impregnation composition is subjected to vitrification heat treatment (40) to obtain an anti-oxidation glass containing at least silicon dioxide, oxide of M1 and oxide of M2.

2. A method for protecting carbon-containing composite material components from oxidation, comprising: • Impregnate the internal pores of the component with an impregnation composition comprising, by weight percentage: (i) 1% to 60% colloidal silica, (ii) 0.5% to 20% flux precursor comprising at least one alkali metal nitrate M1, (iii) 0.5% to 20% lattice-modifying precursor comprising at least one nitrate of element M2 selected from alkaline earth metals, transition metals, depleted metals or lanthanides or an oxygen-containing nitrate of element M2 selected from lanthanides, and (iv) 20% to 88% water; The part impregnated with the impregnation composition is subjected to vitrification heat treatment (40) to obtain an anti-oxidation glass containing at least silicon dioxide, oxide of M1 and oxide of M2.

3. The method according to claim 1 or 2, wherein, The flux precursor includes at least sodium nitrate, potassium nitrate, or a mixture of these compounds.

4. The method according to claim 1, wherein, The lattice-modifying precursors include at least one alkaline earth metal nitrate.

5. The method according to claim 4, wherein, The lattice-modifying precursors include at least calcium nitrate and / or magnesium nitrate.

6. The method according to claim 1, wherein, The lattice-modifying precursors include nitrates of at least one transition metal or a metal-poor metal.

7. The method according to claim 1, wherein, The impregnation composition also contains an acid stabilizer in a weight percentage of 0.05% to 10%.

8. The method according to claim 7, wherein, The acid stabilizer is selected from boric acid (H3BO3), phosphoric acid (H3PO4), nitric acid (HNO3), or a mixture of these compounds.

9. The method according to claim 7, wherein, The impregnation composition comprises, by weight percentage: • 10% to 60% colloidal silica; • 0.5% to 20% flux precursor; • 0.5% to 20% lattice-modified precursors; • 0.05% to 10% acid stabilizer; and • 20% to 88% water.

10. The method according to claim 1, wherein, The impregnation composition comprises, by weight percentage: • 1% to 10% colloidal silica; • 20% to 35% aluminum phosphate; • 1% to 7% flux precursor; • 1% to 5% lattice-modified precursors; and • 50% to 77% water; Furthermore, after heat treatment, an antioxidant glass and a catalytically resistant aluminum phosphate phase are obtained.

11. The protection method according to claim 1, wherein, The component is a friction component.

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