A radar stealth method

Abstract

The present invention relates to a radar stealth method. It is mainly invented to solve the problem that currently, using a glass fiber-reinforced polyester resin composite material to coat the surface of a low-speed moving weapon platform for radar stealth, this material cannot withstand high temperatures and is not suitable for high-speed moving weapons. Boron carbide nanoparticles are produced using boron trifluoride, methane, and hydrogen as raw materials and helium as the carrier gas. Boron nitride nanoparticles are produced using boron trifluoride, ammonia, and hydrogen as raw materials and helium as the carrier gas. Silicon carbide nanoparticles are produced using high-purity silicon carbide as the raw material and helium as the carrier gas. Silicon nitride nanoparticles are produced using high-purity silicon powder and high-purity nitrogen as raw materials and high-purity nitrogen as the carrier gas. Using the plasma spraying method, the above-mentioned boron carbide, silicon carbide, boron nitride, and silicon nitride nanoparticles are sprayed on the surface of the target object in various combinations, one to several layers. The advantages are excellent stealth performance and suitability for the radar stealth of high-speed moving weapon platforms.

Description

Technical Field

[0001] The present invention relates to a radar stealth method, especially suitable for the radar stealth of high-speed flying weapon platforms. Background Art

[0002] In modern warfare, stealth weapons such as stealth aircraft, stealth missiles, stealth warships, and stealth shells play an increasingly important role. The so-called stealth technology, also known as "invisibility technology", is a technology that weakens the characteristic information of target radiation and reflection, making it difficult to be detected by detection systems. It includes technologies such as radar stealth, infrared stealth, video stealth, acoustic stealth, laser stealth, and magnetic stealth. In military applications, various measures such as reasonable design of structures and shapes, ingenious selection of stealth materials, surface coatings, and camouflage painting are often adopted to reduce the target characteristics of weapon equipment and improve the survival ability.

[0003] The stealth involved in this application refers to radar stealth. The specific method is to coat the surface with a stealth material, which is a material that can effectively absorb radar electromagnetic waves and hardly reflect them. There has also been an attempt to coat the surfaces of low-speed moving weapon platforms such as tanks with glass fiber-reinforced polyester resin composites to achieve radar stealth. However, this material cannot withstand high temperatures and is completely inappropriate for high-speed moving weapons such as aircraft, missiles, and shells.

[0004] A certain type of stealth aircraft achieves radar stealth by covering the body surface with a stealth film. Its defect is that once the film is damaged, the repair and maintenance time is long and the cost is high, resulting in a low aircraft attendance rate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a radar stealth method that sprays nano-solid inorganic particles on the surface of a weapon platform by plasma spraying method, thereby effectively absorbing radar electromagnetic waves, hardly reflecting electromagnetic waves, being convenient for maintenance and repair, having low cost, and excellent performance.

[0006] The object of the present invention is achieved as follows:

[0007] Using boron trifluoride (BF3), methane (CH4), and hydrogen as raw materials, and helium as a carrier gas, produce boron carbide (B4C) nanoparticles.

[0008] Using boron trifluoride (BF3), ammonia, and hydrogen as raw materials, and helium as a carrier gas, produce boron nitride (BN) nanoparticles.

[0009] Using purchased high-purity silicon carbide as a raw material (the high-purity silicon carbide is obtained by reducing alkylchlorosilane with hydrogen at 1000 - 1400 °C), and helium as a carrier gas, produce silicon carbide nanoparticles.

[0010] Using high-purity silicon powder and high-purity nitrogen gas as raw materials, and high-purity nitrogen gas as a carrier gas, produce silicon nitride nanoparticles (Si3N4).

[0011] By using the plasma spraying method, spraying one to several layers of the above four kinds of nanoparticles of boron carbide, silicon carbide, boron nitride, and silicon nitride on the surface of the target object in various combinations can achieve the purpose of radar stealth.

[0012] First, the preparation method of the boron carbide nanoparticles: Replace the process system with high-purity nitrogen until the oxygen content is less than 1 ppm, and then replace the system with Ar gas until the nitrogen content is less than 0.01%. Pressurize the system with Ar gas to 50 Kpa (G) - 100 Kpa (G), and automatically adjust it through the pressure regulating valve to maintain the system pressure. Import the auxiliary gases Ar and H2 into the plasma generator in sequence, turn on the plasma generating power supply to form a plasma jet, and then enter the plasma reactor together with boron trifluoride and methane gases. In the plasma reactor, a plasma-state enriched boron-10 boron carbide and gaseous hydrogen fluoride (HF) are formed. The plasma-state enriched boron-10 boron carbide ( 10 B4C) condenses on the wall of the plasma reactor to generate enriched boron-10 boron carbide ( 10 B4C) nanoparticles. The particle size of the nanoparticles is 20 nanometers - 70 nanometers. The scraping plate scrapes the enriched boron-10 boron carbide powder from the wall and is transported into the cyclone separation product tank by a screw conveyor. The hydrogen fluoride gas generated in the plasma reactor and the unreacted methane, hydrogen, and helium are separated from the product boron carbide particles in the cyclone separation product tank and then come out from the top of the cyclone separation product tank and enter the absorption tower. The hydrogen fluoride in the above gases is absorbed by the water in the absorption tower and goes to the water treatment device with the kettle liquid. Methane, hydrogen, and helium come out from the top of the absorption tower, are dried and dehydrated by a dryer (filled with 3A or 4A or 5A molecular sieve), and are compressed by a compressor and returned to the plasma generator for recycling.

[0013] In the raw material mixed gas, the molar ratio of the raw material components is:

[0014] 10 BF3:CH4 = 3.5 - 4.5:1;

[0015] Ar: ( 10 BF3 + CH4) = 1 - 3:100;

[0016] H2:CH4 = 2 - 3:1; The frequency of the plasma generating power supply is 600 MHZ - 1.45 GHZ. Use the high-frequency power supply to energize the induction coil.

[0017] The coolant in the plasma reactor cooling jacket can be a cooling medium such as cooling brine, circulating water, etc. The inner wall temperature of the plasma reactor is not higher than 60°C. The ultrasonic power is 200 - 450 kw. The pressure of the plasma reactor is -0.095 MPa (G) - 0.15 MPa (G); the reaction temperature inside the plasma reactor is 1600 - 1750°C.

[0018] The enriched boron-10 boron carbide ( 10 B4C) particles prepared continuously by the above method have a particle size of 20 - 70 nanometers, the product purity is above 99.9%, and the yield is greater than 99%.

[0019] The boron trifluoride mentioned above is a commercially available industrial product with a purity ≥ 99.9% (Vol), and boron (B) is in natural abundance; methane is a commercially available industrial product with a purity ≥ 99.99% (Vol); hydrogen is a commercially available industrial product with a purity ≥ 99.95% (Vol); helium is a commercially available industrial product with a purity ≥ 99.99% (Vol).

[0020] Second, the production method of the boron nitride (BN) nanoparticles described:

[0021] Using commercially available industrial boron trifluoride with a purity ≥ 99.99% (Vol), boron in natural abundance, commercially available industrial ammonia (NH3) with a purity ≥ 99.5% (Vol), and commercially available industrial hydrogen with a purity ≥ 99.95% (Vol) as raw materials, and commercially available industrial helium (He) with a purity ≥ 99.99% (Vol) as the carrier gas, hydrogen and helium are introduced into the plasma generator successively, the plasma generation power supply is turned on to form a plasma jet, and then it enters the plasma reactor together with boron trifluoride and ammonia. In the plasma reactor, plasma state boron nitride (BN) and gaseous hydrogen fluoride are generated. The plasma state boron nitride is quenched on the cooling wall of the plasma transformer and deposited to form boron nitride (BN) nanoparticles. The particle size of the nanoparticles is 20 nanometers - 70 nanometers. The boron nitride nanoparticles are collected and transported into the cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas comes out from the top of the cyclone separation product tank and enters the absorption tower. The hydrogen fluoride and ammonia in the above gas are absorbed by the water in the absorption tower and go to the water treatment device with the kettle liquid. Hydrogen and helium come out from the top of the absorption tower, are dried and dehydrated by a dryer (filled with 3A or 4A or 5A molecular sieve), and are compressed by a compressor and returned to the static mixer for recycling.

[0022] The pressure of the plasma reactor is -0.095 MPa (G) - 0.15 MPa (G); the frequency of the plasma generation power supply is 600 MHZ - 1.45 GHZ, and the reaction temperature inside the plasma reactor is 1600 - 1800°C. The volume (mole) ratio of the raw materials is:

[0023] Boron trifluoride: ammonia = 1:1.2 - 1:1.4;

[0024] Boron trifluoride: hydrogen = 1:0.2 - 1:0.4;

[0025] Boron trifluoride: helium = 100:3 - 100:5.

[0026] III. Production method of silicon carbide nanoparticles;

[0027] Using externally purchased high-purity silicon carbide (SiC) (silicon carbide is prepared by reducing alkylchlorosilane with hydrogen at 1000 - 1400 °C, with a purity > 99.99%, and mechanically crushed into micron-sized particles) as the raw material and helium (purity ≥ 99.99%) as the carrier gas. The micron-sized silicon carbide particles are first pre-treated by heating and gasification, and the pre-treatment is carried out in a plasma pre-heater. Using pneumatic conveying (helium as the carrier gas), the silicon carbide particles are fed into the above-mentioned plasma pre-heater. The silicon carbide particles are heated to a gaseous state in the plasma pre-heater. The silicon carbide gas and helium enter the plasma reactor together. The silicon carbide gas is ionized and recombined into plasma-state silicon carbide again. The plasma-state silicon carbide is quenched on the cooling wall of the plasma reactor to form silicon carbide nanoparticles with a particle size of 20 nanometers - 70 nanometers. The silicon carbide nanoparticles are collected and transported into a cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is helium, and the helium comes out from the top of the cyclone separation product tank and returns to the plasma pre-heater as the carrier gas for pneumatic conveying through an absorption tower, a dryer, and a compressor.

[0028] The frequency of the plasma pre-heater is 600 MHz - 1.45 GHz. The inner walls of the plasma pre-heater and the plasma reactor are lined with zirconium boride sintered metal. The outlet temperature of the plasma pre-heater is 2700 °C - 2900 °C. The frequency of the plasma generation power supply of the plasma reactor is 600 MHz - 1.45 GHz, and the reaction temperature is 3250 - 3500 °C. The raw material volume (mole) ratio is silicon carbide: helium = 1:2 - 1:5.

[0029] IV. Production method of silicon nitride (Si3N4) nanoparticles;

[0030] Using purchased high-purity silicon powder (purity ≥ 99.999%, micron-sized particle diameter) and high-purity nitrogen gas (purity ≥ 99.999%) as raw materials, with the high-purity nitrogen gas also serving as the carrier gas, using nitrogen as the gas flow transportation carrier and heating carrier gas, the silicon powder is sent into the plasma pre-heater. The silicon powder is heated and vaporized in the plasma pre-heater, and the silicon gas enters the plasma reactor together with nitrogen. The gaseous silicon and nitrogen are ionized and combined into silicon nitride in a plasma state. The silicon nitride in the plasma state is quenched on the cooling wall of the plasma reactor to form silicon nitride nanoparticles with a particle diameter of 20 nanometers to 70 nanometers. The silicon nitride nanoparticles are collected and transported into the cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is nitrogen, and the nitrogen comes out from the top of the cyclone separation product tank and returns to the plasma pre-heater as the carrier gas for gas flow transportation through an absorption tower, a dryer, and a compressor.

[0031] The frequency of the plasma pre-heater described above is 600 MHz - 1.45 GHz, and the inner wall of the plasma pre-heater is lined with zirconium boride sintered metal. The outlet temperature of the plasma pre-heater is 2500 °C - 2800 °C. The frequency of the plasma generation power supply of the plasma reactor is 600 MHz - 1.45 GHz, and the reaction temperature is 3000 - 3300 °C. The raw material volume (mole) ratio is silicon: nitrogen = 3:8 - 3:10.

[0032] Using the existing mature plasma spraying technology, nanoparticles of boron carbide, boron nitride, silicon carbide, and silicon nitride are respectively sent into the plasma jet machine to be softened, and then these particles are sprayed at high speed onto the workpiece substrate (i.e., the surface of the target object) that has been polished, forming a coating of nano-inorganic particles, so that the target object has radar stealth capabilities.

[0033] The above four kinds of inorganic nanoparticle can be arbitrarily combined to form a composite coating on the surface of the target object. The number of spraying layers can be 1 layer or multiple layers. Typical combined applications include but are not limited to the following forms.

[0034] One, nanoparticles of silicon carbide, boron nitride, silicon nitride, and boron carbide are respectively sprayed onto the workpiece substrate, and then the spraying is repeated in this order once to form a composite coating of four kinds of inorganic nanoparticles.

[0035] Two, any three combinations of the above four kinds of inorganic nanoparticles are selected, first sprayed onto the workpiece substrate respectively, and then repeated once, for a total of six spraying layers.

[0036] Combination methods: silicon carbide, boron nitride, boron carbide; silicon nitride, boron nitride, boron carbide; silicon nitride, boron nitride, silicon carbide; silicon carbide, silicon nitride, boron carbide.

[0037] Three, any two combinations of the above four kinds of inorganic nanoparticles are sprayed onto the workpiece substrate, for a total of eight spraying layers.

[0038] Combinations: boron nitride, silicon carbide; silicon carbide, boron carbide; silicon nitride, boron nitride; boron nitride, boron carbide; silicon nitride, boron carbide; silicon nitride, silicon carbide.

[0039] Fourthly, these four kinds of inorganic nanoparticle can also be separately sprayed 8 times to form a single-variety coating.

[0040] Fifthly, spray silicon nitride once on the workpiece substrate, then cover it with boron carbide once, or only spray boron carbide twice.

[0041] After using this method, the radar electromagnetic wave is effectively absorbed by the nano-inorganic composite or single coating on the surface of the target object, and the radar cross-section will be reduced to 1 / 10 - 1 / 20 of the original amount.

[0042] The advantages of the present invention are as follows: The nano-solid inorganic particles are coated on the surface of the weapon platform by the plasma spraying method, which can effectively absorb the electromagnetic wave of the radar with almost no reflection, has excellent stealth performance, is convenient for maintenance and repair, and has low cost. The above-mentioned stealth material coating has high strength, hardness second only to diamond, can withstand high temperatures above 2500 °C, is especially suitable for the radar stealth of high-speed moving weapon platforms, and can be widely used in the production of new stealth weapon platforms and the stealth transformation of old weapon platforms. Brief Description of the Drawings

[0043] Figure 1 It is a schematic diagram of the equipment for producing four kinds of nanoparticles of boron carbide, silicon carbide, boron nitride, and silicon nitride in the present invention; in the figure, 3 is a plasma reactor, 1 is a plasma generator, 5 is a cyclone separation product tank, 2 is a plasma generation power supply, 6 is an absorption tower, 4 is a dryer, and 7 is a compressor. Detailed Embodiment

[0044] Using boron trifluoride (BF3), methane (CH4), and hydrogen as raw materials, and helium as a carrier gas to produce boron carbide (B4C) nanoparticles.

[0045] Using boron trifluoride (BF3), ammonia, and hydrogen as raw materials, and helium as a carrier gas to produce boron nitride (BN) nanoparticles.

[0046] Using purchased high-purity silicon carbide as raw material (the high-purity silicon carbide is obtained by reducing alkyl chlorosilane with hydrogen at 1000 - 1400 °C), and helium as a carrier gas to produce silicon carbide nanoparticles.

[0047] Using high-purity silicon powder and high-purity nitrogen as raw materials, and high-purity nitrogen as a carrier gas to produce silicon nitride nanoparticles (Si3N4).

[0048] By using the plasma spraying method, the above four kinds of nanoparticles of boron carbide, silicon carbide, boron nitride, and silicon nitride are sprayed on the surface of the target object in various combination ways for one to several layers, and the radar stealth purpose can be achieved.

[0049] 1. The preparation method of the boron carbide nanoparticles described above: Replace the process system with high-purity nitrogen until the oxygen content is less than 1 ppm, and then replace the system with Ar gas until the nitrogen content is less than 0.01%. Pressurize the system with Ar gas to 50 Kpa (G) - 100 Kpa (G), and automatically adjust through the pressure regulating valve to maintain the pressure of the system. Introduce the auxiliary gases Ar and H2 into the plasma generator successively, turn on the plasma generating power supply to form a plasma jet, and then enter the plasma reactor together with boron trifluoride and methane gases. In the plasma reactor, a plasma-state enriched boron-10 carbide and gaseous hydrogen fluoride (HF) are formed. The plasma-state enriched boron-10 carbide ( 10 B4C) condenses on the wall of the plasma reactor to generate boron-10 enriched boron carbide ( 10 B4C) nanoparticles. The particle size of the nanoparticles is 20 nanometers - 70 nanometers. The scraping plate scrapes the boron-10 enriched boron carbide powder from the wall and is conveyed into the cyclone separation product tank by a screw conveyor. The hydrogen fluoride gas generated in the plasma reactor and the unreacted methane, hydrogen, and helium are separated from the product boron carbide particles in the cyclone separation product tank and then enter the absorption tower from the top of the cyclone separation product tank. The hydrogen fluoride in the above gases is absorbed by the water in the absorption tower and goes to the water treatment device with the kettle liquid. Methane, hydrogen, and helium come out from the top of the absorption tower, are dried and dehydrated by a dryer (filled with 3A or 4A or 5A molecular sieve), and are compressed by a compressor and returned to the plasma generator for recycling.

[0050] In the raw material mixed gas, the molar ratio of the raw material components is:

[0051] 10 BF3:CH4 = 3.5 - 4.5:1;

[0052] Ar: ( 10 BF3 + CH4) = 1 - 3:100;

[0053] H2:CH4 = 2 - 3:1; The frequency of the plasma generating power supply is 600 MHZ - 1.45 GHZ. Use the high-frequency power supply to energize the induction coil.

[0054] The coolant in the cooling jacket of the plasma reactor can be cooling brine, circulating water and other cooling media. The inner wall temperature of the plasma reactor is not higher than 60 °C. The ultrasonic power is 200 - 450 kw. The pressure of the plasma reactor is -0.095 MPa (G) - 0.15 MPa (G); the reaction temperature in the plasma reactor is 1600 - 1750 °C.

[0055] The boron-10 enriched boron carbide prepared continuously by the above method ( 10B4C) particles, with a particle size of 20 - 70 nanometers, product purity above 99.9%, and a yield greater than 99%.

[0056] The boron trifluoride mentioned is a commercially available industrial product with a purity ≥ 99.9% (Vol), and boron (B) is in natural abundance; methane is a commercially available industrial product with a purity ≥ 99.99% (Vol); hydrogen is a commercially available industrial product with a purity ≥ 99.95% (Vol); helium is a commercially available industrial product with a purity ≥ 99.99% (Vol).

[0057] Second, the production method of the boron nitride (BN) nanoparticles:

[0058] Using commercially available industrial boron trifluoride with a purity ≥ 99.99% (Vol), boron in natural abundance, commercially available industrial ammonia gas (NH3) with a purity ≥ 99.5% (Vol), and commercially available industrial hydrogen with a purity ≥ 99.95% (Vol) as raw materials, and commercially available industrial helium (He) with a purity ≥ 99.99% (Vol) as the carrier gas. Hydrogen and helium are successively introduced into the plasma generator, the plasma generation power supply is turned on to form a plasma jet, and then it enters the plasma reactor together with boron trifluoride and ammonia. In the plasma reactor, plasma-state boron nitride (BN) and gaseous hydrogen fluoride are generated. The plasma-state boron nitride is quenched on the cooling wall of the plasma transformer and deposited to form boron nitride (BN) nanoparticles. The particle size of the nanoparticles is 20 nanometers - 70 nanometers. The boron nitride nanoparticles are collected and transported into the cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas comes out from the top of the cyclone separation product tank and enters the absorption tower. The hydrogen fluoride and ammonia in the above gas are absorbed by the water in the absorption tower and sent to the water treatment device with the kettle liquid. Hydrogen and helium come out from the top of the absorption tower, are dried and dehydrated by a dryer (filled with 3A or 4A or 5A molecular sieve), and are compressed by a compressor and returned to the static mixer for recycling.

[0059] The pressure of the plasma reactor is -0.095 MPa (G) - 0.15 MPa (G); the frequency of the plasma generation power supply is 600 MHz - 1.45 GHz, and the reaction temperature in the plasma reactor is 1600 - 1800 °C. The volume (mole) ratio of the raw materials is:

[0060] Boron trifluoride: ammonia = 1:1.2 - 1:1.4;

[0061] Boron trifluoride: hydrogen = 1:0.2 - 1:0.4;

[0062] Boron trifluoride: helium = 100:3 - 100:5.

[0063] Third, the production method of silicon carbide nanoparticles;

[0064] Using externally purchased high-purity silicon carbide (SiC) (the silicon carbide is obtained by reducing alkyl chlorosilane with hydrogen at 1000 - 1400 °C, with a purity > 99.99%, and is mechanically crushed into micron-sized particles) as the raw material and helium (purity ≥ 99.99%) as the carrier gas. The micron-sized silicon carbide particles are first subjected to pre-treatment of heating and gasification, and the pre-treatment is carried out in a plasma pre-heater. Using pneumatic conveying (helium as the carrier gas), the silicon carbide particles are sent into the above-mentioned plasma pre-heater. The silicon carbide particles are heated to the gaseous state in the plasma pre-heater, and the silicon carbide gas enters the plasma reactor together with helium. The silicon carbide gas is ionized and recombined into silicon carbide in a plasma state. The silicon carbide in the plasma state is quenched on the cooling wall of the plasma reactor to form silicon carbide nanoparticles with a particle size of 20 nanometers - 70 nanometers. The silicon carbide nanoparticles are collected and conveyed into a cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is helium, and the helium comes out from the top of the cyclone separation product tank, passes through an absorption tower, a dryer, and a compressor, and then returns to the plasma pre-heater as the carrier gas for pneumatic conveying.

[0065] The frequency of the plasma pre-heater is 600 MHz - 1.45 GHz, and the inner walls of the plasma pre-heater and the plasma reactor are lined with zirconium boride sintered metal. The outlet temperature of the plasma pre-heater is 2700 °C - 2900 °C. The frequency of the plasma generation power supply of the plasma reactor is 600 MHz - 1.45 GHz, and the reaction temperature is 3250 - 3500 °C. The volume (mole) ratio of the raw materials is silicon carbide:helium = 1:2 - 1:5.

[0066] IV. Production method of silicon nitride (Si3N4) nanoparticles;

[0067] Using externally purchased high-purity silicon powder (purity ≥ 99.999%, particle size in microns) and high-purity nitrogen gas (purity ≥ 99.999%) as the raw materials, and the high-purity nitrogen gas also serves as the carrier gas at the same time. Using nitrogen gas as the carrier for pneumatic conveying and the heating carrier gas, the silicon powder is sent into the plasma pre-heater. The silicon powder is heated and gasified in the plasma pre-heater, and the silicon gas enters the plasma reactor together with nitrogen gas. The gaseous silicon and nitrogen gas are ionized and combined into silicon nitride in a plasma state. The silicon nitride in the plasma state is quenched on the cooling wall of the plasma reactor to form silicon nitride nanoparticles with a particle size of 20 nanometers - 70 nanometers. The silicon nitride nanoparticles are collected and conveyed into a cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is nitrogen gas, and the nitrogen gas comes out from the top of the cyclone separation product tank, passes through an absorption tower, a dryer, and a compressor, and then returns to the plasma pre-heater as the carrier gas for pneumatic conveying.

[0068] The frequency of the described plasma pre-heater is 600 MHz - 1.45 GHz, and the inner wall of the plasma pre-heater is lined with sintered zirconium boride metal. The outlet temperature of the plasma pre-heater is 2500 °C - 2800 °C. The frequency of the plasma generation power supply of the plasma reactor is 600 MHz - 1.45 GHz, and the reaction temperature is 3000 - 3300 °C. The raw material volume (mole) ratio is silicon: nitrogen = 3:8 - 3:10.

[0069] Using the existing mature plasma spraying technology, the nanoparticles of boron carbide, boron nitride, silicon carbide, and silicon nitride are respectively fed into a plasma jet machine to be softened, and then these particles are sprayed at high speed onto the workpiece substrate (i.e., the surface of the target) that has been polished to form a coating of nano-inorganic particles, so that the target has radar stealth capabilities.

[0070] Refer to Figure 1 , the equipment used to prepare the four kinds of nanoparticles includes: a plasma reactor, a plasma generator, a cyclone separation product tank, a plasma generation power supply, an absorption tower, a dryer, and a compressor; a material feed pipeline is provided on the plasma generator, the outlet of the plasma generator is connected to the inlet of the plasma reactor, the plasma generator and the plasma generation power supply are connected by a wire, and an induction coil is wound around the outer wall of the plasma reactor; the plasma reactor is a reactor made of 316L alloy steel with a sintered zirconium boride lining, which includes an inner wall and an outer wall, and there is a jacket between the inner wall and the outer wall. The inner surface of the inner wall is plated with a gold or silver coating, and a coolant inlet and outlet connected to the jacket are provided on the outer wall; a screw conveyor is installed inside the plasma reactor, and a scraper is fixed on the screw of the screw conveyor. The screw conveyor works by driving the scraper to rotate through the screw, and the outer edge of the scraper contacts the inner surface of the inner wall. The materials of the scraper and the screw conveyor are both carbon fiber composite materials and are plated with a gold or silver coating on the surface. The outlet of the plasma reactor is connected to the inlet of the cyclone separation product tank, the cyclone separation product tank is connected to the bottom of the absorption tower by a pipeline, there is a water inlet pipeline at the upper part of the absorption tower, the top of the absorption tower is connected to the dryer by a pipeline, the dryer is connected to the compressor by a pipeline, and the outlet pipeline of the compressor is connected to the carrier gas feed pipeline. When producing silicon carbide and silicon nitride, a plasma pre-heater is added, and the outlet of the plasma pre-heater is connected to the inlet of the plasma generator.

[0071] The above four kinds of inorganic nanoparticles can be arbitrarily combined to form a composite coating on the surface of the target. The number of spraying layers can be 1 layer or multiple layers. Typical combined applications include but are not limited to the following forms.

[0072] First, the nanoparticles of silicon carbide, boron nitride, silicon nitride, and boron carbide are respectively sprayed onto the workpiece substrate, and then the spraying is repeated once in this order to form a composite coating of the four kinds of inorganic nanoparticles.

[0073] Second, select any three combinations of the above four inorganic nanoparticles, spray coat them onto the workpiece substrate separately first, and then repeat once, for a total of six layers.

[0074] Combination methods: silicon carbide, boron nitride, boron carbide; silicon nitride, boron nitride, boron carbide; silicon nitride, boron nitride, silicon carbide; silicon carbide, silicon nitride, boron carbide.

[0075] Third, select any two combinations of the above four inorganic nanoparticles and spray coat them onto the workpiece substrate, for a total of eight layers.

[0076] Combinations: boron nitride, silicon carbide; silicon carbide, boron carbide; silicon nitride, boron nitride; boron nitride, boron carbide; silicon nitride, boron carbide; silicon nitride, silicon carbide.

[0077] Fourth, these four inorganic nanoparticles can also be spray coated separately 8 times to form a single-variety coating.

[0078] Fifth, spray coat silicon nitride once on the workpiece substrate, then cover it with boron carbide once, or only spray coat boron carbide twice.

[0079] After using this method, the radar electromagnetic wave is effectively absorbed by the nano-inorganic composite or single coating on the surface of the target object, and the radar cross-section will be reduced to 1 / 10 - 1 / 20 of the original amount.

Claims

1. A radar stealth method, characterized in that: Using boron trifluoride (BF3), methane (CH4), and hydrogen as raw materials, and helium as a carrier gas, boron carbide (B4C) nanoparticles are produced; Using boron trifluoride (BF3), ammonia, and hydrogen as raw materials, and helium as a carrier gas, boron nitride (BN) nanoparticles are produced; Using purchased high-purity silicon carbide as a raw material, and helium as a carrier gas, silicon carbide nanoparticles are produced; Using high-purity silicon powder and high-purity nitrogen gas as raw materials, and high-purity nitrogen gas as a carrier gas, silicon nitride (Si3N4) nanoparticles are produced; I. Preparation method of boron carbide nanoparticles: Auxiliary gases He and H2 are successively introduced into a plasma generator. The plasma generation power supply is turned on to form a plasma jet, which then enters a plasma reactor together with boron trifluoride and methane gases. In the plasma reactor, a plasma state enriched boron-10 boron carbide and gaseous hydrogen fluoride (HF) are formed. The plasma state enriched boron-10 boron carbide ( 10 B4C) condenses on the wall of the plasma reactor to generate boron-10 enriched boron carbide ( 10 B4C) nanoparticles. The particle size of the nanoparticles is 20 nanometers to 70 nanometers. A scraper plate scrapes the boron-10 enriched boron carbide powder from the wall and is transported into a cyclone separation product tank by a screw conveyor. The hydrogen fluoride gas generated in the plasma reactor and the unreacted methane, hydrogen, and helium are separated from the product boron carbide particles in the cyclone separation product tank and then come out from the top of the cyclone separation product tank and enter an absorption tower. The hydrogen fluoride in the above gases is absorbed by the water in the absorption tower and goes to a water treatment device with the kettle liquid. Methane, hydrogen, and helium come out from the top of the absorption tower, are dried and dehydrated by a dryer, and are compressed by a compressor and returned to the plasma generator for recycling. The frequency of the plasma generation power supply is 600 MHz - 1.45 GHz. An induction coil is energized by a high-frequency power supply. The pressure in the plasma reactor is -0.095 MPa - 0.15 MPa; the reaction temperature in the plasma reactor is 1600 - 1750 °C; II. Method for producing boron nitride nanoparticles: Using boron trifluoride, ammonia, and hydrogen as raw materials, and helium gas as a carrier gas, hydrogen and helium are successively introduced into a plasma generator. The plasma generation power supply is turned on to form a plasma jet, which then enters a plasma reactor together with boron trifluoride and ammonia. In the plasma reactor, plasma-state boron nitride and gaseous hydrogen fluoride are generated. The plasma-state boron nitride is quenched on the cooling wall of the plasma transformer and deposited to form boron nitride nanoparticles; the particle size of the nanoparticles is 20 nanometers to 70 nanometers. The boron nitride nanoparticles are collected and transported into a cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas exits from the top of the cyclone separation product tank and enters an absorption tower. The hydrogen fluoride and ammonia in the above gas are absorbed by the water in the absorption tower and sent to a water treatment device with the kettle liquid. The hydrogen and helium exit from the top of the absorption tower, are dried and dehydrated by a dryer, and are compressed by a compressor and returned to a static mixer for recycling. The pressure of the plasma reactor is -0.095 MPa to 0.15 MPa; the frequency of the plasma generation power supply is 600 MHz to 1.45 GHz, and the reaction temperature in the plasma reactor is 1600 - 1800 °C; III. Method for producing silicon carbide nanoparticles; Using high-purity silicon carbide as a raw material and helium gas as a carrier gas, micron-sized silicon carbide particles are first subjected to a pretreatment of heating and gasification. The pretreatment is carried out in a plasma pre-heater. Using pneumatic conveying, the silicon carbide particles are sent into the above plasma pre-heater. The silicon carbide particles are heated to a gaseous state in the plasma pre-heater. The silicon carbide gas enters the plasma reactor together with helium. The silicon carbide gas is ionized and recombined into plasma-state silicon carbide again. The plasma-state silicon carbide is quenched on the cooling wall of the plasma reactor to form silicon carbide nanoparticles with a particle size of 20 nanometers to 70 nanometers. The silicon carbide nanoparticles are collected and transported into a cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is helium. The helium exits from the top of the cyclone separation product tank and returns to the plasma pre-heater as the carrier gas for pneumatic conveying through an absorption tower, a dryer, and a compressor. The frequency of the plasma pre-heater is 600 MHz to 1.45 GHz, and the outlet temperature of the plasma pre-heater is 2700 °C to 2900 °C; the frequency of the plasma generation power supply of the plasma reactor is 600 MHz to 1.45 GHz, and the reaction temperature is 3250 - 3500 °C; IV. Method for producing silicon nitride (Si3N4) nanoparticles; Using high-purity silicon powder and high-purity nitrogen as raw materials, with high-purity nitrogen also serving as the carrier gas, nitrogen is used as the gas flow transport carrier and heating carrier gas to feed the silicon powder into the plasma pre-heater. The silicon powder is heated and vaporized in the plasma pre-heater, and the silicon gas enters the plasma reactor together with nitrogen. The gaseous silicon and nitrogen are ionized to form silicon nitride in a plasma state. The silicon nitride in the plasma state is quenched on the cooling wall of the plasma reactor to form silicon nitride nanoparticles with a particle size of 20 nanometers to 70 nanometers. The silicon nitride nanoparticles are collected and transported into the cyclone separation product tank by a screw conveyor scraper. The non-condensable tail gas is nitrogen, and the nitrogen comes out from the top of the cyclone separation product tank and returns to the plasma pre-heater as the carrier gas for gas flow transport through an absorption tower, a dryer, and a compressor. The frequency of the plasma pre-heater is 600 MHz - 1.45 GHz, the outlet temperature of the plasma pre-heater is 2500 °C - 2800 °C, the frequency of the plasma generation power supply of the plasma reactor is 600 MHz - 1.45 GHz, and the reaction temperature is 3000 - 3300 °C; Using the plasma spraying technology, nanoparticles of boron carbide, boron nitride, silicon carbide, and silicon nitride are respectively fed into a plasma jet machine to be softened, and then these particles are sprayed onto the workpiece substrate that has been polished at a high speed to form a coating of nano-inorganic particles; Any combination of the above four inorganic nanoparticles is used to form a composite coating on the surface of the target object.

2. The radar stealth method according to claim 1, characterized in that: Nanoparticles of silicon carbide, boron nitride, silicon nitride, and boron carbide are respectively sprayed onto the workpiece substrate, and then the spraying is repeated once in this order to form a composite coating of the four inorganic nanoparticles.

3. A radar stealth method according to claim 1, characterized in that: Any three combinations of the four nanoparticles are selected, first sprayed onto the workpiece substrate respectively, and then repeated once, for a total of six layers.

4. A radar stealth method according to claim 1, characterized in that: Any two combinations of the four nanoparticles are sprayed onto the workpiece substrate, for a total of eight layers.

5. A radar stealth method according to claim 1, characterized in that: The volume ratio of raw materials for producing boron nitride is: boron trifluoride: ammonia = 1:1.2 - 1:1.4; boron trifluoride: hydrogen = 1:0.2 - 1:0.4; boron trifluoride: helium = 100:3 - 100:5; The volume ratio of raw materials for producing silicon carbide is silicon carbide: helium = 1:2 - 1:5; The volume ratio of raw materials for producing silicon nitride is silicon: nitrogen = 3:8 - 3:10.

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