Anti-oxidation protection method for carbon-containing composite material part

Abstract

The present invention relates to a method of protecting a carbon-containing composite component from oxidation, comprising: impregnating the internal pores of the component with an impregnating composition comprising, in weight percent: (i) from 1% to 60% colloidal silica, (ii) from 0.5% to 20% flux precursor comprising at least one alkali metal M1 nitrate, (iii) from 0.5% to 20% lattice-modified precursor, and (iv) from 20% to 88% of water, comprising at least one nitrate or oxygen-containing nitrate of an element M2 selected from a metal or lanthanide, and (iv) from 20% to 88% of water; the component impregnated with the impregnation composition is subjected to a vitrification heat treatment to obtain an antioxidant glass comprising at least silica, an oxide of M1 and an oxide of M2.

Description

Field of the Invention

[0001] The present invention relates to the antioxidant protection of carbon-containing composite parts, i.e. a material comprising a fiber-reinforced material densified by a matrix, wherein the fiber-reinforced material and / or the matrix and / or the interfacial coating between the reinforcing fibers and the matrix are made of carbon. A particular field of application of the present invention is the antioxidant protection of carbon / carbon (C / C) composite parts, in particular brake discs made of C / C composites, especially aircraft brake discs. Background Art

[0002] The materials used for aircraft braking are C / C composites. These materials are selected for this application because of their low weight, high heat absorption capacity and good tribological properties. However, at operating temperatures usually above 450 °C, they are prone to oxidation, especially by oxygen in the air. This oxidation can also be catalyzed by de-icing products used at airports. Several solutions have been developed to extend the life of carbon-containing materials exposed to high temperatures in an oxidizing atmosphere. In particular, a double-layer protection solution can be used, comprising an anti-catalytic inner layer based on aluminum metaphosphate Al(PO3)3 and an outer layer that prevents oxygen from diffusing into the material. This solution provides satisfactory protection, but there is still a need to provide new protection solutions that are simpler to implement and provide at least equivalent protection against thermal oxidation and possibly catalytic oxidation. Summary of the Invention

[0003] The present invention relates to a method for protecting a part made of a carbon-containing composite material from oxidation, comprising:

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

[0005] · subjecting the part impregnated with the impregnating composition to a vitrification heat treatment to obtain an antioxidant glass comprising at least silica, an oxide of M1 and an oxide of M2.

[0006] The present invention proposes the use of an impregnating composition with a specific formulation, which can obtain good antioxidant protection at high temperatures while allowing the use of a single protective layer and a single heat treatment, thus simplifying the protection setup compared to the above-mentioned double-layer solution. In particular, the present invention can eliminate the steps of pre-impregnating with aluminum phosphate to form an internal protective layer and the heat treatment step for forming the relevant antioxidant protection. The protective compound is provided in a single impregnation step, and only one vitrification heat treatment is carried out.

[0007] In an exemplary embodiment, the flux precursor at least includes 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 an exemplary embodiment, the lattice modifier precursor at least includes a nitrate of an alkaline earth metal, particularly calcium nitrate and / or magnesium nitrate. The phase diagrams of these compounds are known and easily accessible, which enables the optimization of the heat treatment temperature by significantly reducing the heat treatment temperature from approximately 1400 °C to approximately 1000 °C.

[0010] Alternatively or in combination, the lattice modifier precursor at least includes a nitrate of a transition metal or a poor metal. Selecting such compounds allows the optimization of the heat treatment temperature by significantly reducing the heat treatment temperature from approximately 1400 °C to approximately 1000 °C.

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

[0012] The acid stabilizer helps prevent the gelling of the impregnating composition, thus facilitating the impregnation of the internal pores of the component.

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

[0014] Selecting boric acid H3BO3 or phosphoric acid H3PO4 can further enhance the protection provided by the glass by forming a protective phosphorus oxide or boron oxide after the vitrification heat treatment.

[0015] In one embodiment, the impregnating composition contains by weight percentage:

[0016] · 10% to 60% of colloidal silica;

[0017] · 0.5% to 20% of the flux precursor;

[0018] · 0.5% to 20% of the lattice modifier precursor;

[0019] · 0.05% to 10% of the acid stabilizer; and

[0020] · 20% to 88% water.

[0021] According to this example, the impregnation composition may be free of metal phosphates, in particular aluminium phosphate.

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

[0023] · 1% to 10% colloidal silica;

[0024] · 20% to 35% aluminium phosphate;

[0025] · 1% to 7% flux precursor;

[0026] · 1% to 5% lattice modification precursor;

[0027] · 50% to 77% water;

[0028] And after heat treatment, an antioxidant glass and an anti-catalytic aluminium phosphate phase are obtained. The anti-catalytic aluminium phosphate phase may be the Al(PO3)3 phase.

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

[0030] In an 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. Description of the Drawings

[0031] Figure 1 is a flowchart showing a series of steps that can be implemented in the context of an example of the method of the present invention.

[0032] Description of Embodiments

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

[0034] First, a flowchart will be combined Figure 1 with the flowchart to describe an example of the method according to the present invention.

[0035] Components made of carbon-containing composite materials can be obtained in a manner known per se, for example by densifying a fiber-reinforced material 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 gas manner, i.e., by chemical vapor infiltration. The obtained components have surface pores and internal pores that communicate with the surface pores and are 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 per se. For this purpose, an aqueous solution of a wetting agent can generally be used, such as a product called "Marlophen NP9" sold by Sasol GmbH, Germany. The presence of the wetting agent helps the impregnating composition to penetrate into the accessible pores of the composite material.

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

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

[0039] The impregnating composition in the form of a suspension contains an aqueous phase and a solid phase, with a flux precursor and a lattice modification precursor dissolved in the aqueous phase and colloidal silica suspended in the aqueous phase.

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

[0041] The flux is obtained from a flux precursor during heat treatment and is capable of reducing the melting temperature of the glass, causing it to soften during the formation heat treatment so as to form glass inside the component at a temperature 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 a mixture, the sum of the weight contents of the compounds present is within the content range of the above-mentioned flux precursors. In particular, the flux precursor can be selected from: sodium nitrate, potassium nitrate, and mixtures of these compounds.

[0042] The flux precursor nitrate can be used in hydrated or anhydrous form.

[0043] The lattice modifier precursor is converted into a lattice modifier during heat treatment, and the lattice modifier is a compound capable of regulating glass properties, such as hydrolysis resistance, acid or alkali erosion resistance, melting temperature, or viscosity. According to one example, the lattice modifier precursor is selected from: magnesium nitrate Mg(NO3)2, calcium nitrate Ca(NO3)2, strontium nitrate Sr(NO3)2, barium nitrate Ba(NO3)2, vanadyl nitrate 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 the flux precursor, in the case of a mixture, the sum of the weight contents of the compounds present is within the content range of the above-mentioned lattice modifier precursors. In particular, the lattice modifier precursor can be selected from: magnesium nitrate, calcium nitrate, and mixtures of these compounds. It is advantageous to use these compounds because they are readily available. According to one variant, the lattice modifier precursor can be a metal-deficient nitrate, such as zinc nitrate.

[0044] The lattice modifier precursor nitrate can be used in hydrated or anhydrous form.

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

[0046] · The flux precursor is sodium nitrate and the lattice modifier precursor is calcium nitrate;

[0047] · The flux precursor is sodium nitrate and the lattice modifier precursor is zinc nitrate;

[0048] · The flux precursor is a mixture of sodium nitrate and potassium nitrate and the lattice modifier precursor is calcium nitrate; or

[0049] · The flux precursor is sodium nitrate and the lattice modifier 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 respectively, which enables a finer adjustment of the M1 / Si ratio, thereby improving the effectiveness of the antioxidant protective glass compared to using a sodium silicate solution. Omitting sodium silicate also helps to improve the stability of the impregnation composition over time (lower risk of gelling). Generally, the impregnation composition mainly consists of colloidal silica, flux precursor, lattice modification precursor, and water, optionally with aluminum phosphate and / or acid stabilizer, each component being present in the above-mentioned amounts.

[0052] The impregnation composition is obtained by mixing different components; it should be noted that in the case where 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 no reaction occurs between silica and other cations.

[0053] As an example of an impregnation composition that can be used in the context of the present invention, the following formulation can be mentioned, where 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 can be present inside the component at a depth greater than or equal to 1 mm, 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] Then, the component impregnated with the impregnation composition is subjected to a vitrification heat treatment (step 40). The vitrification heat treatment is carried out by raising the temperature to a temperature between 700 °C and 1200 °C to obtain an antioxidant glass. This temperature can be maintained for one hour or longer, for example 10 hours to 15 hours. The vitrification heat treatment can be carried out in a neutral atmosphere, for example under nitrogen (N2). As a result of this heat treatment, an antioxidant glass is present in the internal pores of the component. The antioxidant glass can be present inside the component 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 component. This depth can be between 2 mm and 10 mm.

[0056] According to one example, the antioxidant glass may have the following molar percentage composition: between 68% and 73% SiO2, between 15% and 23% Na2O, and between 5% and 11% CaO. Examples of other glass compositions (molar percentages) 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 expression "between... and..." should be understood to include the boundary values.

Claims

1. A method for protecting a carbon-containing composite component from oxidation, comprising: ·Impregnate the internal pores of the component (30) with an impregnation composition, the impregnation composition comprising by weight percentage: (i) 1% to 60% of colloidal silica, (ii) 0.5% to 20% of a flux precursor, the flux precursor comprising at least one alkali metal nitrate M1, (iii) 0.5% to 20% of a lattice modification precursor, the lattice modification precursor comprising a nitrate of at least one element M2 selected from alkaline earth metals, transition metals, poor metals or lanthanide elements or an oxynitrate of an element M2 selected from metals or lanthanide elements, and (iv) 20% to 88% of water; ·Subject the component impregnated with the impregnation composition to a vitrification heat treatment (40) to obtain an antioxidant glass containing at least silica, the oxide of M1 and the oxide of M2.

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

3. The method according to claim 1 or 2, wherein, The lattice modification precursor comprises a nitrate of at least one alkaline earth metal.

4. The method according to claim 3, wherein, The lattice modification precursor comprises at least calcium nitrate and / or magnesium nitrate.

5. The method according to any one of claims 1 to 4, wherein, The lattice modification precursor comprises a nitrate of at least one transition metal or poor metal.

6. The method according to any one of claims 1 to 5, wherein, The impregnation composition further comprises an acid stabilizer in a weight content between 0.05% and 10%.

7. The method according to claim 6, wherein, The acid stabilizer is selected from boric acid H3BO3, phosphoric acid H3PO4, nitric acid HNO3 or a mixture of these compounds.

8. The method according to any one of claims 6 to 7, wherein, The impregnation composition comprises by weight percentage: ·10% to 60% of colloidal silica; ·0.5% to 20% of a flux precursor; ·0.5% to 20% of a lattice modification precursor; ·0.05% to 10% of an acid stabilizer; and ·20% to 88% of water.

9. The method according to any one of claims 1 to 7, wherein, The impregnation composition comprises by weight percentage: ·1% to 10% of colloidal silica; ·20% to 35% of aluminum phosphate; ·1% to 7% of a flux precursor; ·1% to 5% of a lattice modification precursor; and ·50% to 77% of water; And wherein, after the heat treatment, an antioxidant glass and an anti-catalytic aluminum phosphate phase are obtained.

10. The protection method according to any one of claims 1 to 9, wherein, The component is a friction component.

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