CN115504814A - A kind of electronic escape cooling thermal protection material and preparation method thereof - Google Patents

Abstract

The invention relates to an electron escape cooling thermal protection material and a preparation method thereof. The material takes a high-temperature resistant material with the conductive characteristic at high temperature as a matrix, and takes high-temperature resistant, oxidation resistant and low-work-function ceramic as a surface electron escape material. The preparation method comprises the following steps: mixing ceramic powder, a solvent and a binder, and preparing spraying ceramic slurry by a vacuum auxiliary oscillation speed planetary ball milling method; and preparing a compact ceramic coating on the surface of the substrate by a pressure oscillation spraying-temperature oscillation drying-solid phase reaction method to obtain the thermal protection material with the electron escape cooling characteristic. Compared with the prior art, the thermal protection material prepared by the invention has an electron escape cooling effect, can play an active thermal protection role without an auxiliary system, and does not change the aerodynamic shape of an aircraft in a service process.

Description

A kind of electronic escape cooling thermal protection material and preparation method thereof

technical field

The invention relates to the field of heat protection materials, in particular to an electron escape cooling heat protection material and a preparation method thereof.

Background technique

The tip, leading edge, wing edge, and windward side of a hypersonic vehicle are the areas with the most severe aerodynamic heating. The thermal environment faced by the sharp leading edge is often higher than 2000 ° C, and there is a high aerodynamic pressure. Under ultra-high temperature conditions, the aircraft shell generally uses low-ablation or zero-ablation materials for passive thermal protection, mainly including refractory metals, ceramic matrix composites, and carbon/carbon composites.

However, with the development of a new generation of hypersonic vehicles toward the goal of long-distance, wide-speed range, and super-maneuverability, the requirements for thermal protection systems are becoming more and more stringent. Traditional passive heat protection materials are difficult to meet the long-term heat protection requirements at higher temperatures due to the limitation of low energy dissipation efficiency of their own materials. However, the existing active cooling thermal protection systems based on the sweat cooling effect all need to use cooling fluid (solid, liquid, gaseous) to stop or take away the aerodynamic heat flow, and an additional auxiliary system is required to ensure the supply and circulation of the cooling fluid. The structure of the thermal protection system is too complicated, and it will cause structural changes in the thermal protection system, which seriously limits its engineering application.

Contents of the invention

The object of the present invention is to provide an electron escape cooling thermal protection material and a preparation method thereof in order to overcome at least one of the above-mentioned defects in the prior art. It is used to solve the shortcomings of traditional active cooling and thermal protection systems, which are complex in structure and easy to cause structural changes during service.

The purpose of the present invention can be achieved through the following technical solutions:

The invention relates to an electron escape cooling thermal protection material, which uses a high-temperature-resistant material with electrical conductivity at high temperature as a matrix, and uses high-temperature-resistant, oxidation-resistant, and low-work function ceramics as a surface electron escape material. Electron escape materials should have high temperature resistance and oxidation resistance to ensure the stability of structure and performance during service, and should have a lower work function to ensure that the material has a lower electron escape threshold temperature. A high-temperature-resistant material with conductive properties at high temperatures is selected as the matrix material to ensure that electrons can form an effective return channel, avoiding enrichment on the surface of the structure and affecting the efficiency of electron escape.

Further, the electrical conductivity of the high temperature resistant material above 1000°C is higher than 1×10 ^-8 S/m.

Further, the matrix includes dense C/C composite material, C _f /SiC ceramic matrix composite material, SiC _f /SiC ceramic matrix composite material, SiC _f /ZrB ₂ ceramic matrix composite material or C _f /ZrB ₂ ceramic matrix composite material composite material.

Further, the ceramics include CaO·Al ₂ O ₃ ceramics.

Further, the molar ratio of CaO to Al ₂ O ₃ in the CaO·Al ₂ O ₃ ceramic is (1-2):1.

A method for preparing the above-mentioned electron escape cooling thermal protection material, the method comprises the following steps:

Mix ceramic powder, solvent and binder, and prepare spray ceramic slurry by vacuum-assisted oscillation speed planetary ball milling method;

A dense ceramic coating is prepared on the surface of the substrate by pressure oscillation spraying-temperature oscillation drying-solid-state reaction method, and a thermal protection material with electron escape cooling characteristics is obtained.

Further, the solvent includes one or more of n-butanol, isopropanol, ethanol or ethylene glycol, and the mass ratio of the solvent to the ceramic powder is (1-3):1; the viscosity The binder includes one or more of ethyl cellulose, cyanoacrylate, and cyanoacrylate-polyethylene glycol, and the mass ratio of the binder to the ceramic powder is (0.02-0.1):1; the ceramic The particle size of the powder is 50-300nm, and the purity is ≥99.5%. Nano-sized ceramic powder has high sintering activity, which is beneficial to sintering densification. The material produced by the reaction of ceramic powder with higher purity has a lower defect concentration, which is conducive to the excitation and escape of electrons at high temperatures.

Further, in the vacuum-assisted oscillation speed planetary ball mill, the set vacuum degree is higher than -0.08MPa, the rotational speed is 100-250rpm, the speed oscillation amplitude is 5-10% of the set rotational speed value, and the oscillation frequency is 0.1-0.5Hz. The ratio is (50-100):1, and the ball milling time is 60-180min. By vacuum-assisted planetary ball milling, the air in the ceramic slurry can be excluded. By oscillating the planetary ball grinding speed at a certain frequency and amplitude, the mixture can be made more uniform.

Further, the preparation of the ceramic coating specifically includes steps including:

Place the prepared ceramic slurry in a pressure spray gun for pressure oscillation spraying;

Put the sprayed green body into the oven, and carry out temperature oscillation drying;

The dried green body is placed in a pressure furnace for solid phase sintering reaction.

Further, in the pressure oscillation spraying, set the precompression pressure to 0.2-1.0MPa, the pressure oscillation amplitude to 2-10% of the set pressure value, the oscillation frequency to 0.2-1.0Hz, and the spraying time to 1-10min; by making the spraying The pressure oscillates at a certain frequency and amplitude, which can make the ceramic slurry spray more evenly, which is beneficial to the uniformity of the thickness of the coating. In temperature oscillation drying, the temperature is 50-75°C, the temperature oscillation amplitude is 2-5% of the set temperature value, the oscillation frequency is 0.5-1.5Hz, and the drying time is 3-10h; by making the drying temperature at a certain frequency and amplitude Oscillation is conducive to the removal of solvents and can avoid cracking of the coating. The sintering atmosphere is nitrogen or argon, the sintering temperature is 1650-2000° C., the pressure is 10-50 MPa, the time is 60-120 minutes, and the furnace is cooled.

Compared with the prior art, for materials with thermoelectric effect in the present invention, thermally excited electrons will absorb thermal energy from the material body in the form of kinetic energy and potential barrier energy while overcoming the binding effect of atomic nuclei on the surface of the material, thereby Decrease the surface temperature of the material, known as the electron escape cooling effect. Compared with the traditional sweating cooling technology, the material body structure will not change significantly by using the electron escape cooling effect, which can well ensure the aerodynamic shape of the sharp leading edge structure of the hypersonic vehicle.

Description of drawings

Fig. 1 is the oxyacetylene ablation surface temperature curve of the composite material prepared in embodiment 1;

Fig. 2 is the oxyacetylene ablation surface temperature curve of the composite material prepared in embodiment 2;

Fig. 3 is the oxyacetylene ablation surface temperature curve of the composite material prepared in Example 3.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

An electron escape cooling thermal protection material and a preparation method thereof, the preparation method comprising the following steps:

S1: Choose CaO·Al ₂ O ₃ ceramics with high temperature resistance, oxidation resistance and low work function as the surface electron escape material. The molar ratio of CaO and Al ₂ O ₃ in the CaO·Al ₂ O ₃ material is 1-2:1.

S2: Select a high temperature resistant material with electrical conductivity at high temperature as the base material. The conductivity of high temperature resistant materials above 1000°C is higher than 1×10 ^-8 S/m, including but not limited to dense C/C composites, C _f /SiC ceramic matrix composites, SiC _f /SiC ceramic matrix composites, SiC _f /ZrB ₂ ceramic matrix composites, C _f /ZrB ₂ ceramic matrix composites.

S3: Select CaO and Al ₂ O ₃ nano powders as raw materials, select solvent and binder, and prepare spray ceramic slurry by vacuum-assisted oscillation speed planetary ball milling method. The CaO and Al ₂ O ₃ powders have a particle size of 50-300nm and a purity of ≥99.5%. The selected solvent is one or more of n-butanol, isopropanol, ethanol or ethylene glycol, and the mass ratio to the ceramic powder is 1-3:1. The selected binder is one or more of ethyl cellulose, cyanoacrylate, and cyanoacrylate-polyethylene glycol, and the mass ratio to the ceramic powder is 0.02-0.1:1. Vacuum-assisted oscillation speed planetary ball mill, the set vacuum degree is higher than -0.08MPa, the speed is 100-250r/min, the speed oscillation amplitude is 5-10% of the set speed value, the oscillation frequency is 0.1-0.5Hz, the ball-to-material ratio 50-100:1, ball milling time 60-180min.

S4: Prepare a dense CaO Al ₂ O ₃ coating on the surface of a high-temperature-resistant substrate material by pressure oscillation spraying-temperature oscillation drying-solid-state reaction method, so as to obtain a thermal protection material with electron escape cooling characteristics. The specific steps are as follows:

(1) Place the configured ceramic slurry in a pressure spray gun for pressure oscillation spraying; during pressure oscillation spraying, set the pre-compression pressure to 0.2-1.0MPa, and the pressure oscillation amplitude to 2-10% of the set pressure value, and oscillate The frequency is 0.2-1.0Hz, and the spraying time is 1-10min.

(2) Put the sprayed green body into an oven for temperature oscillation drying; during temperature oscillation drying, the temperature is 50-75°C, the temperature oscillation amplitude is 2-5% of the set temperature value, and the oscillation frequency is 0.5-1.5 Hz, the drying time is 3-10 hours.

(3) The dried green body is placed in a pressure furnace for solid phase reaction. The sintering atmosphere is nitrogen or argon, the sintering temperature is 1650-2000° C., the pressure is 10-50 MPa, the time is 60-120 minutes, and the furnace is cooled.

Example 1

Step 1. Select CaO powder with a particle size of 50nm and a purity ≥ 99.5% and an Al ₂ O ₃ powder with a particle size of 100 nm and a purity ≥ 99.8% as raw materials, wherein the molar ratio of CaO and Al ₂ O ₃ is 12 :7.

Step 2. Select a dense C/C composite material as the matrix material; the preparation process of the selected C/C composite material is the same as that in Example 1 in patent ZL201811327116.0.

Step 3. Select ethanol as the solvent, and the mass ratio to the ceramic powder is 1:1. Ethyl cellulose is selected as the binder, and the mass ratio of ethyl cellulose to ceramic powder is 0.02:1.

Step 4. Mix the materials through the vacuum-assisted oscillation speed planetary ball milling method, set the vacuum degree to -0.08MPa, the rotation speed to 100r/min, the speed oscillation amplitude to 10%, set the rotation speed value, the oscillation frequency to 0.2Hz, and the ball-to-material ratio The ratio is 100:1, and the ball milling time is 120min.

Step 5. Put the configured ceramic slurry in the pressure spray gun, set the pre-compression pressure to 0.2MPa, the pressure oscillation amplitude to 2%, set the pressure value, and the oscillation frequency to 1.0Hz, and spray the ceramic slurry on the dense C/ C Composite material surface, spraying time is 5min.

Step 6. Put the sprayed body into an oven for temperature oscillation drying treatment, the temperature is 50°C, the temperature oscillation range is 5% of the set temperature value, the oscillation frequency is 1.0Hz, and the drying time is 5 hours to obtain a dry body body.

Step 7. Put the dried green body into an atmosphere sintering furnace for pressure sintering. The sintering atmosphere is nitrogen, the sintering temperature is 1800°C, the pressure is 30MPa, and the time is 60 minutes. After cooling in the furnace, 12CaO·7Al ₂ O ₃ -C is obtained. /C Composite.

Figure 1 is the oxyacetylene ablation surface temperature curve of the 12CaO·7Al ₂ O ₃ -C/C composite material prepared in Example ¹ at a heat flux of 4.18MW/m2, and the matrix C/C composite material at 4.18MW/m ² The surface temperature curve of oxyacetylene ablation under heat flux. The ablation surface temperature of the 12CaO·7Al ₂ O ₃ -C/C composite material with electron escape cooling effect prepared by the invention is obviously lower than that of the C/C composite material.

Example 2

Step 1. Select CaO powder with a particle size of 100nm and a purity of ≥99.8% and an _Al2O3 powder with a particle size of 300nm and a purity of _≥99.7 % as raw materials, wherein the molar ratio of CaO and _Al2O3 is ₁₀ :7.

Step 2. Select C _f /SiC ceramic matrix composite material as the matrix material; the preparation process of the selected C _f /SiC ceramic matrix composite material is the same as that in Example 1 in patent ZL201610471632.5.

Step 3. Select n-butanol as the solvent, and the mass ratio to the ceramic powder is 3:1. Cyanoacrylate was selected as the binder, and the mass ratio of cyanoacrylate to ceramic powder was 0.1:1.

Step 4. Mix materials by vacuum-assisted oscillation speed planetary ball milling method, set the vacuum degree to -0.09MPa, the rotation speed to 200r/min, the speed oscillation amplitude to 5%, set the rotation speed value, the oscillation frequency to 0.3Hz, and the ball-to-material ratio 70:1, ball milling time is 70min.

Step 5. Put the configured ceramic slurry in the pressure spray gun, set the pre-compression pressure to 1.0MPa, the pressure oscillation amplitude to 10%, set the pressure value, and the oscillation frequency to 0.5Hz, and spray the ceramic slurry at C _f / On the surface of SiC composite material, the spraying time is 5 minutes;

Step 6. Put the sprayed green body into an oven for temperature oscillation drying treatment, the temperature is 60°C, the temperature oscillation amplitude is 4% of the set temperature value, the oscillation frequency is 1.5Hz, and the drying time is 10 hours to obtain a dried green body body.

Step 7. Put the dry green body into the atmosphere sintering furnace for pressure sintering. The sintering atmosphere is nitrogen, the sintering temperature is 2000°C, the pressure is 10MPa, and the time is 80 minutes. After cooling in the furnace, 10CaO·7Al ₂ O ₃ -C is obtained. _f /SiC composites.

Figure 2 is the oxyacetylene ablation surface temperature curve of the 10CaO·7Al ₂ O ₃ -C _f /SiC composite material prepared in Example 2 at a heat flux of 4.18MW/m ² , and the matrix C _f /SiC composite material at 4.18MW Surface temperature curve of oxyacetylene ablation under heat flux/m ² . The ablation surface temperature of the 10CaO·7Al ₂ O ₃ -C _f /SiC composite material with electron escape cooling effect prepared by the present invention is obviously lower than that of the C _f /SiC composite material.

Example 3

Step 1. Select CaO powder with a particle size of 100nm and a purity of ≥99.8% and an _Al2O3 powder with a particle size of 300nm and a purity of _≥99.7 % as raw materials, wherein the molar ratio of CaO and _Al2O3 is ₁₀ :7.

Step 2. Select BN-Si ₂ N ₂ O composite ceramics with insulating properties as the matrix material; the preparation process of the selected BN-Si ₂ N ₂ O composite ceramics is the same as that in Example 1 in patent ZL201310106226.5.

Step 3. Select n-butanol as the solvent, and the mass ratio to the ceramic powder is 3:1. Cyanoacrylate was selected as the binder, and the mass ratio of cyanoacrylate to ceramic powder was 0.1:1.

Step 4. Mix materials by vacuum-assisted oscillation speed planetary ball milling method, set the vacuum degree to -0.09MPa, the rotation speed to 200r/min, the speed oscillation amplitude to 5%, set the rotation speed value, the oscillation frequency to 0.3Hz, and the ball-to-material ratio 70:1, ball milling time is 70min.

Step 5. Put the configured ceramic slurry in the pressure spray gun, set the pre-compression pressure to 1.0MPa, the pressure oscillation amplitude to 10%, set the pressure value, and the oscillation frequency to 0.5Hz, and spray the ceramic slurry on the BN-Si ₂ N ₂ O composite ceramic surface, spraying time is 5min;

Step 6. Put the sprayed green body into an oven for temperature oscillation drying treatment, the temperature is 60°C, the temperature oscillation amplitude is 4% of the set temperature value, the oscillation frequency is 1.5Hz, and the drying time is 10 hours to obtain a dried green body body.

Step 7. Put the dry green body into an atmosphere sintering furnace for pressure sintering. The sintering atmosphere is nitrogen, the sintering temperature is 2000°C, the pressure is 10MPa, and the time is 80 minutes. After cooling in the furnace, 10CaO·7Al ₂ O ₃ -BN is obtained. -Si ₂ N ₂ O composite material.

Figure 3 is the oxyacetylene ablation surface temperature curve of the 10CaO·7Al ₂ O ₃ -BN-Si ₂ N ₂ O composite material prepared in Example 3 at a heat flux of 4.18MW/m ² , and the matrix BN-Si ₂ N ₂ The oxyacetylene ablation surface curves of O composite ceramics at a heat flux of 4.18MW/m ² have little difference between the two. Therefore, it can be seen that using materials with insulating properties as the substrate does not have the effect of reducing the surface temperature of the material. Combined with the results of Example 2, this result also further proves that 10CaO·7Al ₂ O ₃ can reduce the surface temperature of the material through the electron escape cooling effect.

In summary, the thermal protection material prepared by the present invention has electron escape cooling effect, can play the role of active thermal protection without the need for auxiliary systems, and at the same time does not change the aerodynamic shape of the aircraft during service.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention to other forms. Any skilled person who is familiar with this profession may use the technical content disclosed above to change or modify the equivalent of equivalent changes. Example. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims (10)

1. An electron escape cooling thermal protection material, characterized in that the material uses a high temperature resistant material with electrical conductivity under high temperature as a substrate, and uses ceramics with high temperature resistance, oxidation resistance and low work function as a surface electron escape material. 2 . The thermal protection material for electron escape cooling according to claim 1 , wherein the electrical conductivity of the high temperature resistant material above 1000° C. is higher than 1×10 ⁻⁸ S/m. 3 . 3. A kind of electronic escape cooling thermal protection material according to claim 1, characterized in that, the matrix comprises dense C/C composite material, C _f /SiC ceramic matrix composite material, SiC _f /SiC ceramic matrix Composite material, SiC _f /ZrB ₂ ceramic matrix composite or C _f /ZrB ₂ ceramic matrix composite. 4 . The heat protection material for electron escape cooling according to claim 1 , wherein the ceramics include CaO·Al ₂ O ₃ ceramics. 5. A kind of electron escaping cooling thermal protection material according to claim 4, is characterized in that, described CaO·Al ₂ O ₃ In ceramics, the mol ratio of CaO and Al ₂ O ₃ is (1-2): 1. 6. A preparation method for electron escape cooling thermal protection material as claimed in any one of claims 1-5, characterized in that the method comprises the following steps: Mix ceramic powder, solvent and binder, and prepare spray ceramic slurry by vacuum-assisted oscillation speed planetary ball milling method; A dense ceramic coating is prepared on the surface of the substrate by pressure oscillation spraying-temperature oscillation drying-solid-state reaction method, and a thermal protection material with electron escape cooling characteristics is obtained. 7. the preparation method of a kind of electron escape cooling thermal protection material according to claim 6, is characterized in that, described solvent comprises one or more in n-butanol, Virahol, ethanol or ethylene glycol The mass ratio of the solvent to the ceramic powder is (1-3): 1; the binder includes one of ethyl cellulose, cyanoacrylate, cyanoacrylate-polyethylene glycol or Various, the mass ratio of the binder to the ceramic powder is (0.02-0.1):1; the particle size of the ceramic powder is 50-300nm, and the purity is ≥99.5%. 8. The preparation method of a kind of electron escape cooling heat protection material according to claim 6, characterized in that, in the vacuum-assisted oscillating speed planetary ball mill, the vacuum degree is set to be higher than -0.08MPa, and the rotation speed is 100-250rpm, The speed oscillation amplitude is 5-10% of the set speed value, the oscillation frequency is 0.1-0.5Hz, the ball-material ratio is (50-100):1, and the ball milling time is 60-180min. 9. A method for preparing an electron escape cooling thermal protection material according to claim 6, wherein the preparation of a ceramic coating specifically includes steps comprising: Place the prepared ceramic slurry in a pressure spray gun for pressure oscillation spraying; Put the sprayed green body into the oven, and carry out temperature oscillation drying; The dried green body is placed in a pressure furnace for solid phase sintering reaction. 10. The method for preparing an electron escape cooling thermal protection material according to claim 9, characterized in that, in the pressure oscillation spraying, the pre-compression pressure is set to 0.2-1.0MPa, and the pressure oscillation amplitude is 2-10% Set the pressure value, the oscillation frequency is 0.2-1.0Hz, and the spraying time is 1-10min; in the temperature oscillation drying, the temperature is 50-75°C, and the temperature oscillation amplitude is 2-5%. Set the temperature value, and the oscillation frequency is 0.5- 1.5Hz, the drying time is 3-10h; the sintering atmosphere is nitrogen or argon, the sintering temperature is 1650-2000°C, the pressure is 10-50MPa, the time is 60-120 minutes, and the furnace is cooled.

Images