Polycrystalline silicon reduction furnace composite coating, preparation method thereof and polycrystalline silicon reduction furnace

Abstract

The invention discloses a composite coating of a polycrystalline silicon reduction furnace, a preparation method of the composite coating and the polycrystalline silicon reduction furnace. The method comprises the following steps: preparing a first material into hollow sphere powder, and preparing a second material into first solid sphere powder; the hollow sphere powder and the first solid sphere powder are prepared into porous layer spraying powder according to the volume ratio of 0.25-1.50; carrying out polishing and sand blasting treatment on the surface of the inner wall of the polycrystalline silicon reduction furnace; the porous layer spraying powder is deposited on the surface of a substrate on the inner wall of the polycrystalline silicon reduction furnace, and a porous heat insulation coating is obtained; polishing the surface of the porous heat-insulating coating; depositing a surface reflecting layer on the surface of the polished porous heat-insulating coating; and the surface reflecting layer is polished and ground, and preparation is completed. The composite coating for the polycrystalline silicon reduction furnace has the properties of high infrared reflectivity, low heat conductivity, high-temperature chlorine corrosion resistance and the like, meanwhile, the bonding strength with the inner wall of the polycrystalline silicon reduction furnace is high, and the unit consumption of polycrystalline silicon reduction electricity can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of polysilicon, and particularly relates to a composite coating for a polysilicon reduction furnace, a preparation method thereof, and a polysilicon reduction furnace. Background Art

[0002] The polysilicon reduction furnace is the core production equipment for producing polysilicon by the improved Siemens method, and the inner wall state thereof significantly affects production energy consumption. Aiming at the problem that the infrared reflectivity of the inner wall of the polysilicon reduction furnace continuously decays due to factors such as high-temperature chlorine corrosion, wall scaling, and rod-falling and sliding marks, and a large amount of heat is dissipated by the infrared radiation emitted by the silicon rods, resulting in a reduction in energy utilization efficiency, a large amount of research work on the inner wall repair and coating technology of the polysilicon reduction furnace has been carried out in the industry.

[0003] At present, research mostly uses chemical vapor deposition, thermal spraying or cold spraying to prepare the reduction furnace coating. The coating materials include gold, silver, titanium nitride ceramics, etc. with high infrared reflectivity. Among them, the coatings prepared with high-reflectivity metals such as gold and silver have good performance, and have the characteristics of corrosion resistance, high bonding strength, and high infrared reflectivity. However, the material and process costs are relatively high; while the coatings using ceramic materials such as titanium nitride have relatively low compatibility with the inner wall of the reduction furnace, and under the harsh conditions of high temperature and high chlorine in the reduction furnace, problems such as coating peeling and falling off are likely to occur. In addition, during the operation of the reduction furnace, a large amount of silicon micro-powder will be generated in the furnace, and the silicon micro-powder will gradually adsorb on the inner wall of the reduction furnace, resulting in a reduction in the infrared reflection effect of the reduction furnace coating in the later stage of silicon rod growth, and causing radiant heat to be dissipated through the furnace barrel water.

[0004] From the perspective of heat transfer, in addition to using a high-infrared-reflection coating for the reduction furnace coating, an insulating coating with low thermal conductivity can also be used to reduce the proportion of the internal heat of the reduction furnace taken away by the cooling water in the reduction furnace jacket, thereby improving the energy utilization efficiency. At present, the materials of the insulating coatings commonly used in industry are generally ceramic materials with low thermal conductivity, such as metal oxides ceramics such as silicon dioxide and alumina. However, the thermal expansion coefficients of ceramic materials are quite different from those of metal coatings and 316L stainless steel substrates, resulting in problems such as poor bonding strength and easy peeling of the reduction furnace coating made of pure ceramic materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a composite coating for a polysilicon reduction furnace, a preparation method thereof, and a polysilicon reduction furnace in view of the above deficiencies existing in the prior art. The coating has the properties of high infrared reflectivity, low thermal conductivity, high temperature chlorine corrosion resistance, etc., and at the same time has a high bonding strength with the inner wall of the polysilicon reduction furnace, and can reduce the unit power consumption of polysilicon reduction.

[0006] The technical solution for the present invention to solve the above technical problems is as follows:

[0007] According to the first aspect of the present invention, a method for preparing a composite coating for a polysilicon reduction furnace is provided, including:

[0008] Making the first material into hollow sphere powder and making the second material into first solid sphere powder, where the first material is a metal or ceramic material with a melting point higher than the subsequent spraying temperature, the melting point of the second material is lower than that of the first material, and the difference in their melting points is 250 - 650 °C;

[0009] Formulating the hollow sphere powder and the first solid sphere powder into porous layer spraying powder according to a volume ratio of 0.25 - 1.50;

[0010] Grinding and sandblasting the inner wall surface of the polysilicon reduction furnace;

[0011] Depositing the porous layer spraying powder on the inner wall substrate surface of the polysilicon reduction furnace to obtain a porous thermal insulation coating;

[0012] Grinding the surface of the porous thermal insulation coating;

[0013] Depositing a surface reflection layer on the surface of the ground porous thermal insulation coating;

[0014] Polishing and grinding the surface reflection layer to complete the preparation.

[0015] Optionally, the first material is one of tungsten-based alloys, alumina, silica, and cobalt-based alloys.

[0016] Optionally, the sphericity of the hollow sphere powder ≥ 85%, and the sphericity of the first solid sphere powder ≥ 50%.

[0017] Optionally, the particle size of the hollow sphere powder is 15 - 58 μm, and the particle size of the first solid sphere powder is 10 - 58 μm.

[0018] Optionally, the second material is one of stainless steel, nickel-based alloys, and cobalt-based alloys, or is the same as the substrate material of the polysilicon reduction furnace.

[0019] Optionally, the porosity of the porous thermal insulation layer is 20 - 60%.

[0020] Optionally, when depositing the porous thermal insulation layer, the flying speed of the porous layer spraying powder is controlled at 300 - 400 m / s, and the spraying temperature is controlled at 150 - 250 °C higher than the melting point of the first solid sphere powder.

[0021] Optionally, depositing the surface reflection layer on the surface of the ground porous thermal insulation coating includes:

[0022] The third material is made into second solid sphere powder, the sphericity of the second solid sphere powder ≥ 50%, the infrared reflectivity of the third material > 80%, and the melting point of the third material is less than that of the second material or the melting point of the third material is greater than that of the second material but the difference between the two melting points is 0 - 300 °C. Then, the second solid sphere powder is evenly deposited on the surface of the polished porous heat-insulating coating by means of thermal spraying to deposit a surface reflective layer.

[0023] Optionally, when depositing the surface reflective layer, the delivery rate of the second solid sphere powder is controlled at 50 - 150 g / min.

[0024] Optionally, when depositing the surface reflective layer, the spraying speed is controlled at 380 - 500 m / s.

[0025] Optionally, when depositing the surface reflective layer, the spraying temperature is controlled at 150 - 250 °C higher than the melting point of the second solid sphere powder.

[0026] Optionally, when depositing the surface reflective layer, the spraying distance is controlled at 100 - 250 mm, the displacement speed of the gun head is controlled at 0.03 - 0.13 m / s, and the step size is controlled at 0.0015 - 0.002 m.

[0027] Optionally, the thermal spraying method is a supersonic thermal spraying method. Among them, the single-pass spraying thickness of the porous heat-insulating layer and the surface reflective layer is 20 - 50 μm, the total thickness of the porous heat-insulating layer is 800 - 2000 μm, and the total thickness of the surface reflective layer is 200 - 600 μm.

[0028] Optionally, the third material is one of silver, nickel-based alloy, and cobalt-based alloy.

[0029] According to the second aspect of the present invention, a polysilicon reduction furnace composite coating is provided, which is prepared by using the above-mentioned preparation method.

[0030] According to the third aspect of the present invention, a polysilicon reduction furnace is provided, which includes the above-mentioned polysilicon reduction furnace composite coating.

[0031] Advantages of the present invention:

[0032] (1) By first using the porous layer spraying powder composed of high-melting-point hollow sphere powder and low-melting-point first solid sphere powder to prepare a porous heat-insulating layer, and then using the second solid sphere powder with high infrared reflectivity and high temperature chlorine corrosion resistance to prepare a surface reflective layer, the finally obtained coating has properties such as high infrared reflectivity, low thermal conductivity, and high temperature chlorine corrosion resistance, which can reduce the unit power consumption of polysilicon reduction, thereby reducing the production cost of polysilicon; and, by regulating the hollow sphere powder /

[0033] By controlling conditions such as the volume ratio of the first solid sphere powder, the powder particle size, and the spraying parameters, the thermal conductivity of the composite coating can be controlled.

[0034] (2) Since ceramic materials have poor ductility, a porous heat-insulating layer is prepared by using a porous layer spraying powder. By taking advantage of the excellent ductility of the metal to make up for the brittleness of the ceramic hollow spheres, the bonding strength between the coating and the inner wall of the reduction furnace can be improved. At the same time, the peeling of the coating caused by uneven heating and the interfacial stress between the ceramic and the metal can be avoided. The ceramic hollow sphere powder in the porous heat-insulating layer can play a role as a mold, and after the ceramic peels and cracks due to stress changes in the coating, it will not affect the porosity and bonding strength of the porous heat-insulating layer.

[0035] (3) The process is simple and easy to operate. There is no need to switch spraying equipment for different materials such as ceramic and metal powders during the equipment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the preparation method of the composite coating for the polysilicon reduction furnace in the embodiment of the present invention;

[0037] Figure 2 It is the preparation process conditions and preparation results of the porous heat-insulating layer in Comparative Example 4 of the present invention;

[0038] Figure 3 It is the preparation process conditions and preparation results of the surface reflection layer in Comparative Example 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0040] Aiming at the deficiencies of the existing coatings for polysilicon reduction furnaces, such as high cost, low bonding strength, and easy peeling, which make the energy-saving coatings on the inner walls of reduction furnaces unable to be widely applied, resulting in high electricity consumption per unit, etc. In order to improve the energy-saving performance of the coatings on the inner walls of polysilicon reduction furnaces, the present invention discloses a preparation method for a composite coating for a polysilicon reduction furnace, including:

[0041] Making the first material into hollow sphere powder and making the second material into the first solid sphere powder. The first material is a metal or ceramic material with a melting point higher than the subsequent spraying temperature, and the melting point of the second material is lower than that of the first material, and the difference in melting points between the two is 250 - 650 °C;

[0042] The hollow sphere powder and the first solid sphere powder are formulated into a porous layer spraying powder according to a volume ratio of 0.25 to 1.50;

[0043] The inner wall surface of the polysilicon reduction furnace is polished and sandblasted;

[0044] The porous layer spraying powder is deposited on the inner wall substrate surface of the polysilicon reduction furnace to obtain a porous thermal insulation coating;

[0045] The surface of the porous thermal insulation coating is polished;

[0046] A surface reflective layer is deposited on the polished surface of the porous thermal insulation coating;

[0047] The surface reflective layer is polished to produce a mirror effect on the surface, and the preparation is completed to obtain a polysilicon reduction furnace composite coating.

[0048] Correspondingly, the present invention also provides a polysilicon reduction furnace composite coating, which is prepared by the above-mentioned preparation method and includes a porous thermal insulation layer and a dense surface reflective layer. The involved working principle includes:

[0049] During the production process, the high-temperature silicon core continuously emits near-infrared light with a peak wavelength of 2 to 2.3 μm. This part of the infrared radiation transfers 60 - 70% of the heat generated by electricity in the furnace to the inner wall of the reduction furnace cylinder with a water-cooled jacket, so that valuable high-grade thermal energy is taken out of the reduction furnace system by the water in the furnace cylinder. However, when the inner wall of the polysilicon reduction furnace is sprayed with the polysilicon reduction furnace composite coating of the present invention, after the energy of the near-infrared radiation irradiates from the silicon rod to the inner wall of the furnace cylinder, since the infrared reflectivity of the surface reflective layer exceeds 80%, most of the near-infrared radiation energy can be effectively reflected, and the surface temperature of the silicon rod can be maintained under low electric power conditions; at the same time, since the infrared reflectivity of the surface reflective layer is 80%, according to Kirchhoff's law, its absorptivity is 20%, that is, only 20% of the radiation energy is absorbed by the furnace cylinder wall surface. Therefore, compared with the original furnace cylinder, the inner wall temperature of the reduction furnace can be decreased. From the perspective of the energy transfer path, part of the near-infrared radiation reflected by the surface reflective layer returns to the surface of the silicon rod, and part is absorbed by the wall surface and transferred to the porous thermal insulation layer by heat conduction. The heat conduction formula is as follows:

[0050]

[0051] λ eff =(1 - ∈)·λ s +∈·λ g

[0052] Among them, Q is the heat transfer rate, A is the heat transfer area, T1 and T2 are the temperatures on both sides of the heat conduction wall surface respectively, d is the wall thickness; λ effis the effective thermal conductivity of the porous material (i.e., the porous thermal insulation layer), ∈ is the porosity, and λ s is the thermal conductivity of the solid part (for example, the thermal conductivity of 316L stainless steel is 16.3 W / (m·K)), and λ g is the thermal conductivity of the gas (for example, nitrogen is about 0.025 W / (m·K)).

[0053] For the composite coating of the polysilicon reduction furnace of the present invention, due to its porous structure (i.e., the porous thermal insulation layer), the thermal conductivity of the gas in the porous structure is much smaller than that of the metal, so the effective thermal conductivity of the porous structure is greatly reduced, thereby effectively weakening the heat transfer by thermal conduction, reducing the wall temperature on the side of the jacket water, lowering the heat dissipation rate in the polysilicon reduction furnace, and thus enabling the polysilicon reduction furnace to maintain a relatively high surface temperature of the silicon rod during operation under low-power conditions, thereby ensuring the silicon deposition rate and achieving the purpose of energy conservation.

[0054] Furthermore, the present invention also provides a polysilicon reduction furnace, which includes the above-mentioned composite coating of the polysilicon reduction furnace.

[0055] Example 1

[0056] As Figure 1 shown, the present embodiment discloses a preparation method of a composite coating for a polysilicon reduction furnace, including:[[]]

[0057] Step 1: Use the template method to make the first material into hollow sphere powder, and use the gas atomization method to make the second material into the first solid sphere powder. Among them, the first material is a metal or ceramic material with a melting point higher than the spraying temperature in the subsequent steps; the melting point of the second material is lower than that of the first material, and the difference between their melting points is 250-650 °C, so as to ensure that the first solid sphere powder melts uniformly during the coating preparation process while the structure of the hollow sphere powder is not damaged by heat, playing a bonding role, firmly embedding the hollow sphere powder inside the porous thermal insulation layer, and improving the bonding strength. Otherwise, if the difference in melting points is too small (i.e., less than 250 °C), the hollow sphere powder is prone to heat deformation such as softening during the spraying process, resulting in uncontrollable porosity, while if the difference in melting points is too large (i.e., greater than 650 °C), the first solid sphere powder will melt too fast, forming large droplets, which is likely to cause particle splashing during the spraying process, resulting in uncontrollable porosity and deposition rate of the coating; at the same time, the second material also has high-temperature chlorine corrosion resistance and has no requirement for infrared reflection performance. Specifically, the corresponding material can be selected according to the spraying process of the porous thermal insulation layer in Step 4 and the surface reflection layer in Step 6.

[0058] In some embodiments, the first material is one of high-melting-point materials such as tungsten-based alloys, alumina, silica, and cobalt-based alloys.

[0059] In some embodiments, the material of the second material may be the same as the base material of the polysilicon reduction furnace, but is not limited thereto, and may also be different from the base material of the polysilicon reduction furnace. For example, it may be a stainless steel material such as 316L, or a low-melting-point nickel-based alloy and cobalt-based alloy, etc.

[0060] In some embodiments, the sphericity of the hollow sphere powder ≥ 85%; the sphericity of the first solid sphere powder ≥ 50%. A higher requirement for the sphericity of the hollow sphere powder is beneficial to the uniform heating of the hollow sphere powder in the flame, avoiding local softening and breakage of the hollow sphere caused by uneven heating; a certain sphericity is required for the first solid sphere powder to reduce the flight resistance during spraying, promote uniform heating and melting of the particles.

[0061] In some embodiments, the particle size of the hollow sphere powder is 15 - 58 μm. Experiments have found that this particle size range is beneficial to improving the controllability of the coating porosity; when the particle size is less than 15 μm, the proportion of the internal volume of the hollow sphere powder decreases, and in a coating with the same porosity, the volume proportion of the hollow sphere powder increases, resulting in problems such as poor coating bonding and coating peeling during the spraying process; while when the particle size is greater than 58 μm, problems such as the rupture and collapse of the hollow sphere structure may occur during the spraying process due to thermal stress, impact force, etc., resulting in uncontrollable porosity.

[0062] In some embodiments, the particle size of the first solid sphere powder is 10 - 58 μm, preferably 10 - 30 μm. Experiments have found that this particle size range is beneficial to improving the controllability of the coating porosity, enabling the first solid sphere powder to melt uniformly and firmly embed the hollow sphere powder inside the porous thermal insulation layer to form a concrete-like structure, further improving the bonding strength and porosity controllability of the coating; when the particle size is less than 10 μm, the first solid sphere powder melts too fast in the supersonic flame, forming large droplets, which easily cause particle splashing during the spraying process, resulting in uncontrollable coating porosity and deposition rate; while when the particle size is greater than 58 μm, it will cause uneven melting of the particles and unable to form a stable concrete-like porous thermal insulation coating, resulting in easy peeling of the coating.

[0063] Step 2: Prepare a porous layer spraying powder for regulating the porosity of the porous thermal insulation layer by mixing the hollow sphere powder and the first solid sphere powder at a volume ratio of 0.25 - 1.50. Experiments have found that this volume ratio is beneficial to balancing the high bonding strength, appropriate porosity, and low thermal conductivity of the coating, enabling the coating performance to meet the performance requirements as much as possible. Otherwise, if the volume ratio is too small (i.e., the volume ratio of the hollow sphere powder to the first solid sphere powder is lower than 0.25), the porosity of the porous thermal insulation layer will be lower than 20%, the porosity is relatively low, and the thermal conductivity is relatively high, unable to meet the insulation requirements of the coating; while if the volume ratio is too large (i.e., the volume ratio of the hollow sphere powder to the first solid sphere powder is higher than 1.50), the proportion of the particles of the hollow sphere powder will be too high, resulting in a decrease in the bonding force of the coating, and it is easy to have the phenomenon of coating peeling when it is lower than 15 MPa.

[0064] Step 3: Substrate pretreatment. Grind and sandblast the inner wall surface of the polysilicon reduction furnace to remove the silicon scale accumulated during long-term production and the scars caused by furnace tipping, and change the wall surface roughness to improve the coating bonding strength.

[0065] Step 4: Deposit the porous layer spraying powder on the surface of the inner wall substrate of the polysilicon reduction furnace to obtain a porous thermal insulation coating with low thermal conductivity (also known as a porous layer).

[0066] In some embodiments, when depositing the porous thermal insulation layer, according to the material of the hollow sphere powder, control the spraying parameters: control the flying speed of the porous layer spraying powder at 300 - 400 m / s, and control the spraying temperature at 150 - 250 °C higher than the melting point of the first solid sphere powder to regulate the deformation of the hollow sphere powder, avoid the crushing or collapse of the hollow sphere structure, and prevent a large change in its internal volume. Also, combined with the volume ratio of the hollow sphere / first solid sphere powder of the porous layer spraying powder in Step 2 at a ratio of 0.25 - 1.50, the porosity of the porous thermal insulation layer can be controlled, that is, the thermal conductivity can be controlled, so that the first solid sphere powder melts uniformly and firmly embeds the hollow sphere powder inside the porous thermal insulation layer.

[0067] Experiments have found that if the flying speed of the porous layer spraying powder is too small (i.e., lower than 300 m / s), not only the spraying temperature and powder delivery volume may not be guaranteed, but also the bonding strength between the coating and the substrate will decrease, and it is easy to have the phenomenon of coating peeling when it is lower than the lower limit of 15 MPa. While if the flying speed is too large (i.e., higher than 400 m / s), the spraying temperature and powder delivery volume may not match, resulting in phenomena such as over-melting of the powder and particle splashing, reducing the coating deposition rate; if the spraying temperature of the porous layer spraying powder is controlled at 0 - 150 °C higher than the melting point of the first solid sphere powder (i.e., the melting point of the second material), the first solid sphere powder cannot be melted uniformly, and if it is higher than 250 °C above the melting point of the first solid sphere powder (i.e., the melting point of the second material), it is easy to have droplet splashing and reduce the deposition rate.

[0068] In some embodiments, when depositing the porous thermal insulation layer, controlling the spraying parameters further includes controlling the delivery rate of the porous layer spraying powder at 100 - 200 g / min to maintain a high coating deposition rate and a high coating bonding strength. Otherwise, if the delivery rate of the porous layer spraying powder is too small (i.e., less than 100 g / min), the coating deposition rate will be too slow, while if the delivery rate of the porous layer spraying powder is too large (i.e., more than 200 g / min), the coating will be deposited too fast, and problems such as uneven melting of metal powder, low coating bonding strength, uncontrollable porosity, and gun clogging are likely to occur.

[0069] In some embodiments, when depositing the porous thermal insulation layer, controlling the spraying parameters further includes controlling the spraying distance at 100 - 250 mm to improve the controllability of the coating porosity, enabling the first solid sphere powder to melt uniformly and firmly embedding the hollow sphere powder inside the porous thermal insulation layer. Otherwise, if it is less than 100 mm, the particles will not be cooled sufficiently, and droplet splashing is likely to occur, reducing the deposition rate. If it is more than 250 mm, the particles will be cooled too fast, and the coating bonding strength and deposition rate are likely to decrease.

[0070] In some embodiments, when depositing the porous thermal insulation layer, controlling the spraying parameters further includes controlling the gun head displacement speed at 0.08 - 0.2 m / s to maintain a high coating deposition rate and a high bonding strength. Otherwise, if it is less than 0.08 m / s, the deposition rate will be too low, and if it is more than 0.2 m / s, the coating bonding strength will decrease, and wire breakage is likely to occur.

[0071] In some embodiments, when depositing the porous thermal insulation layer, controlling the spraying parameters further includes controlling the step size at 0.0015 - 0.002 m to make each spraying path connect up and down, ensuring the integrity and uniformity of single - pass spraying. Otherwise, if it is less than 0.0015 m, the spraying will be too slow, and in severe cases, the surface will be uneven. If it is more than 0.002 m, the integrity of single - pass spraying will be reduced, and there will be unsprayed areas in the middle of each path.

[0072] In some embodiments, the porosity of the porous thermal insulation layer is 20 - 60%.

[0073] Step Five, post - treatment of the surface of the porous thermal insulation layer, performing a grinding treatment on the surface of the porous thermal insulation coating to improve the surface flatness and roughness, and enhancing the coating bonding strength and uniformity of subsequent processes.

[0074] Step Six, depositing a surface reflection layer (referred to as the reflection layer) on the surface of the polished porous thermal insulation coating.

[0075] In some embodiments, depositing the surface reflection layer on the surface of the polished porous thermal insulation coating includes:

[0076] First, the third material is made into the second solid sphere powder. Among them, the third material has a high infrared reflectivity. Specifically, the infrared reflectivity after good polishing is > 80%. And the melting point should not be too high. The melting point of the third material is less than the melting point of the second material, or the melting point of the third material is greater than the melting point of the second material, but the difference between the two melting points is 0 - 300 °C, so as to avoid causing great damage to the porous thermal insulation layer during the subsequent spraying process. At the same time, it has high-temperature chlorine corrosion resistance and can be used for a long time without affecting the coating performance, and can also avoid polluting high-purity silicon products;

[0077] Then, the second solid sphere powder is evenly deposited on the surface of the polished porous thermal insulation coating by thermal spraying to deposit a surface reflection layer.

[0078] In this embodiment, it is preferred that the melting point of the third material is less than the melting point of the second material. That is to say, the melting point of the first solid sphere powder is greater than the melting point of the second solid sphere powder; if the above conditions are not met, then select that the melting point of the third material is greater than the melting point of the second material, but the difference between the two melting points is 0 - 300 °C, that is, the melting point of the first solid sphere powder is less than the melting point of the second solid sphere powder in the range of 0 - 300 °C. It is found through experiments that when the melting point of the first solid sphere powder is less than the melting point of the second solid sphere powder by more than 300 °C, it is easy to damage the porous thermal insulation layer, resulting in problems such as a decrease in its porosity, an increase in thermal conductivity, and a decrease in the coating bonding strength.

[0079] In some embodiments, the particle size of the second solid sphere powder is 15 - 58 μm to maintain a high coating deposition rate and high bonding strength. Otherwise, if the particle size is less than 15 μm, the powder will melt too fast, forming large droplets, which is likely to cause particle splashing during the spraying process and a low deposition rate. If the particle size is higher than 58 μm, the particles will melt unevenly, resulting in a decrease in bonding strength. When the bonding strength is less than 15 MPa, the coating is prone to peeling and other phenomena.

[0080] In some embodiments, the third material is one of precious metals such as silver, or can also be one of alloy materials with high-temperature chlorine corrosion resistance and high infrared emissivity, such as nickel-based alloys and cobalt-based alloys, so as to ensure that the surface reflection layer will not have problems such as a decrease in surface roughness and a change in physical properties due to corrosion in a high-temperature and high-chlorine environment. After long-term use, the surface infrared reflectivity can still be maintained at a high level.

[0081] It should be noted that if the third material is a high-melting-point alloy, when depositing the surface reflection layer, the spraying distance and the supersonic thermal spraying process parameters should be adjusted to make the surface of the second solid sphere powder present a slightly melted state, so as to improve the deposition efficiency and bonding strength and avoid damage to the porous thermal insulation layer due to its too high melting point.

[0082] In some embodiments, the thermal spraying method is a supersonic thermal spraying method. Among them, the single-pass spraying thickness of the porous heat-insulating layer and the surface reflective layer is 20-50 μm, which is specifically related to powder delivery rate, gun head displacement speed, spraying distance, etc., and will not be elaborated here one by one to ensure the coating bonding strength while avoiding increasing unnecessary process costs. The total thickness of the porous heat-insulating layer is 800-2000 μm to enhance the heat-insulating effect of the porous heat-insulating layer. At the same time, to balance the high bonding strength, appropriate porosity, and low thermal conductivity of the coating, so that the coating performance can meet the actual application requirements as much as possible. Otherwise, if it is less than 800 μm, the heat transfer speed will be very fast, and the heat-insulating effect of the coating cannot be highlighted. If it is higher than 2000 μm, the coating bonding strength will decrease, affecting the preparation of the subsequent surface reflective layer. The total thickness of the surface reflective layer is 200-600 μm to ensure that the composite coating has a high infrared reflectivity, and can exert the infrared reflectivity and high-temperature chlorine corrosion resistance of the second solid sphere powder. Otherwise, if it is less than 200 μm, it is easy to cause problems such as the coating being worn through during the grinding and polishing process and subsequent service use, exposing the porous heat-insulating layer, and the composite coating cannot guarantee the infrared reflectivity and high-temperature chlorine corrosion resistance. If it is higher than 600 μm, the cost will increase.

[0083] In some embodiments, when depositing the surface reflective layer, the spraying parameters are controlled as follows:

[0084] The delivery rate of the second solid sphere powder is controlled at 50-150 g / min to maintain a high coating deposition rate and high bonding strength. Otherwise, if it is less than 50 g / min, the coating deposition rate will be too slow. If it is higher than 150 g / min, the coating deposition will be too fast, and problems such as uneven melting of metal powder, low coating bonding strength, and uncontrollable porosity are likely to occur.

[0085] The spraying speed is controlled at 380-500 m / s to maintain a high coating deposition rate and high bonding strength. Otherwise, if it is less than 380 m / s, the spraying temperature and powder delivery rate may not be guaranteed, resulting in a decrease in the bonding strength between the coating and the substrate, falling below the lower limit of 15 MPa, and causing problems such as coating peeling off. If it is higher than 500 m / s, the spraying temperature and powder delivery rate may not match, resulting in over-melting of the powder or too high a speed causing particle splashing and reducing the coating deposition rate.

[0086] The spraying temperature is controlled at 150-250 °C higher than the melting point of the second solid sphere powder to maintain a high coating deposition rate and high bonding strength. Otherwise, if it is less than 150 °C, the first solid sphere powder cannot be uniformly melted. If it is higher than 250 °C, droplet splashing is likely to occur and the deposition rate decreases.

[0087] Control the spraying distance within 100 - 250 mm, control the displacement speed of the gun head within 0.03 - 0.13 m / s, and control the step size within 0.0015 - 0.002 m, so that each spraying path is connected up and down, ensuring the integrity and uniformity of single-pass spraying. Otherwise, if it is lower than 0.0015 m, the spraying will be too slow, and in severe cases, the surface is likely to be uneven. If it is higher than 0.002 m, the integrity of a single pass will be reduced, resulting in an unsprayed area in the middle of each path.

[0088] Step Seven, post-treatment of the surface of the surface reflection layer. Polish and grind the surface reflection layer to produce a mirror effect on the surface, so as to maximize the performance of the surface reflection layer, and obtain a polysilicon reduction furnace composite coating with high infrared reflectivity, low thermal conductivity, high temperature chlorine corrosion resistance, and high bonding strength with the inner wall of the reduction furnace.

[0089] Furthermore, this embodiment also discloses a polysilicon reduction furnace composite coating prepared by the above-described preparation method.

[0090] In some embodiments, the total thickness of the polysilicon reduction furnace composite coating is 1000 - 2600 μm.

[0091] Furthermore, this embodiment also provides a polysilicon reduction furnace including the above-described polysilicon reduction furnace composite coating.

[0092] The preparation method of the polysilicon reduction furnace composite coating in this embodiment designs a polysilicon reduction furnace composite coating including a porous thermal insulation layer and a surface reflection layer by controlling the raw material powder structure and the ratio of various powder materials, and has at least the following beneficial effects:

[0093] (1) By first using a porous layer spraying powder composed of high-melting-point hollow sphere powder and low-melting-point first solid sphere powder to prepare a porous thermal insulation layer, and then using a second solid sphere powder with high infrared reflectivity and high temperature chlorine corrosion resistance to prepare a surface reflection layer, the finally prepared coating has high infrared reflectivity (reaching 80 - 90%), low thermal conductivity (as low as 5 - 12 W / (m·K)), and high temperature chlorine corrosion resistance, etc., which can reduce the single consumption of polysilicon reduction electricity, thereby reducing the production cost of polysilicon; and by adjusting conditions such as the volume ratio of hollow sphere powder / first solid sphere powder, powder particle size, and spraying parameters in the porous layer spraying powder, the thermal conductivity of the composite coating can be controlled.

[0094] (2) Since ceramic materials have poor ductility, a porous thermal insulation layer is prepared by spraying powder on a porous layer. By using the excellent ductility of metals to compensate for the brittleness of ceramic hollow spheres, the bonding strength between the coating and the inner wall of the reduction furnace can be improved (reaching 30 - 60 MPa). At the same time, it is possible to avoid coating peeling caused by uneven heating and the interfacial stress between ceramics and metals. The ceramic hollow sphere powder in the porous thermal insulation layer can act as a mold. After the ceramic peels and cracks due to stress changes in the coating, it will not affect the porosity and bonding strength of the porous thermal insulation layer.

[0095] (3) The process is simple and easy to operate. There is no need to switch spraying equipment for different materials such as ceramic and metal powders during the equipment process.

[0096] Example 2

[0097] This example discloses a composite coating for a polysilicon reduction furnace and its preparation method. This composite coating requires two layers of coatings to be made. The first layer is a porous thermal insulation layer, and the second layer is a highly reflective surface reflective layer. The specific materials used and process parameters are as follows:

[0098] (1) Preparation of hollow sphere powder: Take the first material, alumina, and use the template method to prepare alumina hollow sphere powder, and then sieve it to obtain hollow sphere powder with a particle size of 20 - 40 μm.

[0099] The above template method process steps are as follows: Using polystyrene microspheres as templates, alumina nanoparticles are coated on the template surface by the sol - gel method; then, the template is removed and solidified by high - temperature calcination to obtain alumina hollow sphere powder.

[0100] Preparation of the first solid sphere powder: Take high - purity Fe, Co, Cr, Si, and C materials according to the mass ratio. Among them, Fe accounts for 10 - 50%, Co accounts for 20 - 50%, Cr accounts for 10 - 50%, Si accounts for 1 - 5%, and C accounts for 0.1 - 1%. Through melting in an inert atmosphere at 1500 - 2300 °C, the second material, FeCoCr high - entropy alloy, with a melting point of about 1600 °C is prepared, and the FeCoCr high - entropy alloy is further prepared into FeCoCr high - entropy alloy solid sphere powder by gas atomization method, and then sieve it to obtain the first solid sphere powder with a particle size of 10 - 30 μm.

[0101] The above gas atomization method process steps are as follows: First, the FeCoCr high - entropy alloy raw material is melted into an alloy liquid in a vacuum induction furnace; then, a high - speed inert gas flow (such as argon) from a spray gun is used to break the liquid metal flow into fine droplets, and spherical powder is formed during the cooling process; finally, through screening and classification treatment, FeCoCr high - entropy alloy solid sphere powder meeting the particle size requirements is obtained.

[0102] (2) Mix hollow sphere powder with a particle size of 20 - 40 μm and first solid sphere powder with a particle size of 10 - 30 μm to form a porous layer spraying powder at a volume ratio of 0.45.

[0103] (3) Use white fused alumina sand to roughen the inner wall surface of the reduction furnace, making the roughness greater than 5, and then use compressed air to blow the inner wall to clean the surface floating ash.

[0104] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the delivery rate of the porous layer spraying powder to be 150 g / min, the flying speed to be 380 m / s, the spraying temperature to be 1750 °C, the spraying distance to be 160 mm, the gun head displacement speed to be 0.10 m / s, the step size to be 0.002 m, control the single - pass spraying thickness to be 40 μm, and control the total thickness to be 1500 μm to obtain a porous thermal insulation coating with a porosity of 30%.

[0105] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous thermal insulation layer to remove large protrusions and slag defects.

[0106] (6) Take the third material, FeCoCr high - entropy alloy, and use gas atomization method to prepare FeCoCr high - entropy alloy solid sphere powder, and screen it to obtain second solid sphere powder with a particle size of 25 - 45 μm;

[0107] Subsequently, continue to use a supersonic flame spraying device to spray the second solid sphere powder with a particle size of 25 - 45 μm on the surface of the porous thermal insulation coating. Among them, control the delivery rate of the second solid sphere powder to be 50 g / min, the flying speed to be 420 m / s, the spraying temperature to be 1800 °C, the spraying distance to be 150 mm, the gun head displacement speed to be 0.03 m / s, the step size to be 0.002 m, control the single - pass spraying thickness to be 20 μm, and control the total thickness to be 500 μm to obtain a surface reflection layer.

[0108] (7) Polish and grind the surface reflection layer to reduce the roughness to 0.05 to produce a mirror effect, and the polysilicon reduction composite coating is prepared.

[0109] After testing, the bonding strength of the composite coating in this embodiment reaches 41 MPa, the surface infrared reflectivity reaches 88%, and the coating thermal conductivity is as low as 6.24 W / (m·K), meeting the performance requirements of both high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0110] Example 3

[0111] This embodiment discloses a composite coating for a polysilicon reduction furnace and a preparation method thereof. This composite coating needs to be made into two layers. The first layer is a porous heat-insulating layer, and the second layer is a highly reflective surface reflective layer. The specific materials used and process parameters are as follows:

[0112] (1) Prepare hollow sphere powder: Take the first material, FeCoCr high-entropy alloy, and use the template method to prepare FeCoCr high-entropy alloy hollow sphere powder. After screening, obtain hollow sphere powder with a particle size of 15 - 45 μm.

[0113] The process steps of the above template method are as follows: Using polystyrene microspheres as templates, and using a rolling device to coat FeCoCr high-entropy alloy micropowder on the surface of the templates with a binder; then calcine at high temperature to remove the templates and solidify, obtaining FeCoCr high-entropy alloy hollow sphere powder.

[0114] Prepare the first solid sphere powder: Take the second material, Hastelloy C276, and use the gas atomization method to prepare Hastelloy C276 solid sphere powder. After screening, obtain the first solid sphere powder with a particle size of 10 - 20 μm.

[0115] The process steps of the above gas atomization method are as follows: First, melt the Hastelloy C276 raw material into an alloy liquid in a vacuum induction furnace; then use a spray gun to break the liquid metal stream into fine droplets with a high-speed inert gas stream (such as argon), and form spherical powder during the cooling process; finally, through screening and grading treatment, obtain Hastelloy C276 solid sphere powder that meets the particle size requirements.

[0116] (2) Mix the hollow sphere powder with a particle size of 15 - 45 μm and the first solid sphere powder with a particle size of 10 - 20 μm according to a volume ratio of 0.70 to form a porous layer spraying powder.

[0117] (3) Use white corundum sand to roughen the inner wall surface of the reduction furnace to make the roughness greater than 5, and then use compressed air to blow the inner wall to clean the surface floating ash.

[0118] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the delivery rate of the porous layer spraying powder to be 180 g / min, the flying speed to be 400 m / s, the spraying temperature to be 1550 °C, the spraying distance to be 155 mm, the gun head displacement speed to be 0.15 m / s, the step size to be 0.002 m, control the single-pass spraying thickness to be 45 μm, and control the total thickness to be 1600 μm, obtaining a porous heat-insulating coating with a porosity of 40%.

[0119] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous heat-insulating layer to remove larger protrusions and slag defects.

[0120] (6) Take the third material, Hastelloy C276, and use the gas atomization method to prepare Hastelloy C276 solid sphere powder. Screen it to obtain the second solid sphere powder with a particle size of 25 - 53 μm.

[0121] Subsequently, continue to use the high - velocity oxy - fuel spraying equipment to spray the second solid sphere powder with a particle size of 25 - 53 μm on the surface of the porous thermal insulation coating. Among them, control the delivery rate of the second solid sphere powder to be 80 g / min, the flying speed to be 450 m / s, the spraying temperature to be 1600 °C, the spraying distance to be 150 mm, the gun head displacement speed to be 0.06 m / s, the step size to be 0.002 m, control the single - pass spraying thickness to be 35 μm, and control the total thickness to be 500 μm to obtain the surface reflection layer.

[0122] (7) Carry out polishing and grinding treatment on the surface reflection layer to reduce the roughness to 0.05, producing a mirror effect, and the polysilicon reduction composite coating is prepared.

[0123] After testing, the bonding strength of the composite coating in this embodiment reaches 40 MPa, the surface infrared reflectivity reaches 83%, and the thermal conductivity of the coating is as low as 7.15 W / (m·K), meeting the performance requirements of high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0124] Example 4

[0125] This embodiment discloses a polysilicon reduction furnace composite coating and its preparation method. This composite coating needs to make two layers of coatings. The first layer is a porous thermal insulation layer, and the second layer is a highly reflective surface reflection layer. The specific materials used and process parameters are as follows:

[0126] (1) Prepare hollow sphere powder: Take the first material, tungsten - based alloy W18Cr4V, and use the template method to prepare W18Cr4V hollow sphere powder. Screen it to obtain the hollow sphere powder with a particle size of 20 - 45 μm.

[0127] The above - mentioned template method process steps are: Using polystyrene microspheres as templates, use a rolling device to coat tungsten - based alloy W18Cr4V micropowder on the surface of the template with a binder; then calcine at high temperature to remove the template and solidify to obtain tungsten - based alloy W18Cr4V hollow sphere powder.

[0128] Prepare the first solid sphere powder: Take the second material, 316L stainless steel, and use the gas atomization method to prepare 316L solid sphere powder. Screen it to obtain the first solid sphere powder with a particle size of 15 - 35 μm.

[0129] The process steps of the above gas atomization method are as follows: First, melt the 316L stainless steel raw material into an alloy liquid in a vacuum induction furnace; then use a spray gun to break the liquid metal stream into fine droplets with a high-speed inert gas flow (such as argon), and form spherical powder during the cooling process; finally, through screening and grading treatment, obtain 316L stainless steel solid sphere powder that meets the particle size requirements.

[0130] (2) Mix hollow sphere powder with a particle size of 20 - 45 μm and the first solid sphere powder with a particle size of 15 - 35 μm according to a volume ratio of 0.90 to form a porous layer spraying powder.

[0131] (3) Use white fused alumina sand to roughen the inner wall surface of the reduction furnace, making the roughness greater than 5, and then use compressed air to blow the inner wall to clean the surface floating ash.

[0132] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the conveying amount of the porous layer spraying powder to be 160 g / min, the flight speed to be 350 m / s, the spraying temperature to be 1580 °C, the spraying distance to be 100 mm, the gun head displacement speed to be 0.10 m / s, the step length to be 0.0015 m, control the single-pass spraying thickness to be 50 μm, and control the total thickness to be 1300 μm to obtain a porous thermal insulation coating with a porosity of 45%.

[0133] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous thermal insulation layer to remove larger protrusions and slag defects.

[0134] (6) Take the third material, nickel-based alloy Inconel 625, and use the gas atomization method to prepare Inconel 625 solid sphere powder, and screen it to obtain the second solid sphere powder with a particle size of 30 - 55 μm;

[0135] The process steps of the above gas atomization method are as follows: First, melt the nickel-based alloy Inconel 625 raw material into an alloy liquid in a vacuum induction furnace; then use a spray gun to break the liquid metal stream into fine droplets with a high-speed inert gas flow (such as argon), and form spherical powder during the cooling process; finally, through screening and grading treatment, obtain nickel-based alloy Inconel 625 solid sphere powder that meets the particle size requirements.

[0136] Subsequently, continue to use a supersonic flame spraying device to spray the second solid sphere powder with a particle size of 30 - 55 μm on the surface of the porous thermal insulation coating. Among them, control the conveying amount of the second solid sphere powder to be 65 g / min, the flight speed to be 420 m / s, the spraying temperature to be 1600 °C, the spraying distance to be 130 mm, the gun head displacement speed to be 0.07 m / s, the step length to be 0.002 m, control the single-pass spraying thickness to be 30 μm, and control the total thickness to be 600 μm to obtain a surface reflective layer.

[0137] (7) The surface reflective layer is polished to reduce the roughness to 0.05, creating a mirror effect, and the preparation of the polysilicon reduction composite coating is completed.

[0138] After testing, the bonding strength of the composite coating in this embodiment reaches 39 MPa, the surface infrared reflectivity reaches 81%, and the thermal conductivity of the coating is as low as 9.51 W / (m·K), meeting the performance requirements of high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0139] Example 5

[0140] This embodiment discloses a polysilicon reduction furnace composite coating and its preparation method. This composite coating needs to be made into two layers. The first layer is a porous heat insulation layer, and the second layer is a highly reflective surface reflective layer. The specific materials used and process parameters are as follows:

[0141] (1) Prepare hollow sphere powder: Take the first material, silica, and use the template method to prepare silica hollow sphere powder, and then screen it to obtain hollow sphere powder with a particle size of 24 - 48 μm.

[0142] The process steps of the above template method are as follows: Using polystyrene microspheres as templates, silica nanoparticles are coated on the surface of the templates through the sol - gel method; then, the templates are removed and solidified by high - temperature calcination to obtain silica hollow sphere powder.

[0143] Prepare the first solid sphere powder: Take the second material, nickel - based alloy Invar 42, and use the gas atomization method to prepare Invar 42 solid sphere powder, and then screen it to obtain the first solid sphere powder with a particle size of 10 - 35 μm.

[0144] The process steps of the above gas atomization method are as follows: First, the nickel - based alloy Invar 42 raw material is melted into an alloy liquid in a vacuum induction furnace; then, a high - speed inert gas stream (such as argon) from a spray gun is used to break the liquid metal stream into fine droplets, and spherical powder is formed during the cooling process; finally, through screening and classification, nickel - based alloy Invar 42 solid sphere powder meeting the particle size requirements is obtained.

[0145] (2) Mix the hollow sphere powder with a particle size of 24 - 48 μm and the first solid sphere powder with a particle size of 10 - 35 μm in a volume ratio of 1.2 to form a porous layer spraying powder.

[0146] (3) Use white corundum sand to roughen the inner wall surface of the reduction furnace to make the roughness greater than 5, and then use compressed air to blow and sweep the inner wall to clean the surface floating dust.

[0147] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the conveying amount of the porous layer spraying powder to be 150 g / min, the flying speed to be 300 m / s, the spraying temperature to be 1500 °C, the spraying distance to be 200 mm, the gun head displacement speed to be 0.12 m / s, and the step size to be 0.0018 m. Control the single-pass spraying thickness to be 30 μm and the total thickness to be 1400 μm to obtain a porous thermal insulation coating with a porosity of 53%.

[0148] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous thermal insulation layer to remove large protrusions and slag defects.

[0149] (6) Take the third material silver and use the gas atomization method to prepare silver solid sphere powder, and sieve it to obtain the second solid sphere powder with a particle size of 40 - 58 μm.

[0150] The above gas atomization process steps are as follows: First, melt the silver raw material into an alloy liquid in a vacuum induction furnace; then use a spray gun with a high-speed inert gas flow (such as argon) to break the liquid metal flow into fine droplets, and form spherical powder during the cooling process; finally, through screening and grading treatment, obtain silver solid sphere powder that meets the particle size requirements.

[0151] Subsequently, continue to use a supersonic flame spraying device to spray the second solid sphere powder with a particle size of 40 - 58 μm on the surface of the porous thermal insulation coating. Among them, control the conveying amount of the second solid sphere powder to be 100 g / min, the flying speed to be 420 m / s, the spraying temperature to be 1100 °C, the spraying distance to be 120 mm, the gun head displacement speed to be 0.13 m / s, and the step size to be 0.0018 m. Control the single-pass spraying thickness to be 30 μm and the total thickness to be 500 μm to obtain a surface reflection layer.

[0152] (7) Carry out polishing and grinding treatment on the surface reflection layer to reduce the roughness to 0.05 and produce a mirror effect, and the polysilicon reduction composite coating is prepared.

[0153] After testing, the bonding strength of the composite coating in this embodiment reaches 33 MPa, the surface infrared reflectivity reaches 90%, and the thermal conductivity of the coating is as low as 6.61 W / (m·K), meeting the performance requirements of high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0154] Example 6

[0155] This embodiment discloses a polysilicon reduction furnace composite coating and its preparation method. This composite coating needs to make two layers of coatings. The first layer is a porous thermal insulation layer, and the second layer is a highly reflective surface reflection layer. The specific materials used and process parameters are as follows:

[0156] (1) Preparation of hollow sphere powder: Take the first material, tungsten-based alloy W18Cr4V, and use the template method to prepare W18Cr4V hollow sphere powder. After screening, hollow sphere powder with a particle size of 45 - 58 μm is obtained.

[0157] Preparation of the first solid sphere powder: Take the second material, 316L stainless steel, and use the gas atomization method to prepare 316L solid sphere powder. After screening, the first solid sphere powder with a particle size of 45 - 58 μm is obtained.

[0158] (2) Mix the hollow sphere powder with a particle size of 45 - 58 μm and the first solid sphere powder with a particle size of 45 - 58 μm according to a volume ratio of 1.50 to form a porous layer spraying powder.

[0159] (3) Use white corundum sand to roughen the inner wall surface of the reduction furnace so that the roughness is greater than 5, and then use compressed air to blow the inner wall to clean the surface floating dust.

[0160] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the conveying amount of the porous layer spraying powder to be 100 g / min, the flying speed to be 360 m / s, the spraying temperature to be 1590 °C, the spraying distance to be 120 mm, the gun head displacement speed to be 0.08 m / s, the step size to be 0.0015 m, control the single-pass spraying thickness to be 50 μm, and control the total thickness to be 2000 μm to obtain a porous thermal insulation coating with a porosity of 60%.

[0161] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous thermal insulation layer to remove large protrusions and slag defects.

[0162] (6) Take the third material, Hastelloy C276, and use the gas atomization method to prepare Hastelloy C276 solid sphere powder. After screening, the second solid sphere powder with a particle size of 15 - 30 μm is obtained;

[0163] Subsequently, continue to use a supersonic flame spraying device to spray the second solid sphere powder with a particle size of 15 - 30 μm on the surface of the porous thermal insulation coating. Among them, control the conveying amount of the second solid sphere powder to be 50 g / min, the flying speed to be 380 m / s, the spraying temperature to be 1580 °C, the spraying distance to be 100 mm, the gun head displacement speed to be 0.05 m / s, the step size to be 0.0015 m, control the single-pass spraying thickness to be 30 μm, and control the total thickness to be 200 μm to obtain a surface reflective layer.

[0164] (7) Polish and grind the surface reflective layer to reduce the roughness to 0.05 to produce a mirror effect, and the polysilicon reduction composite coating is prepared.

[0165] After testing, the bonding strength of the composite coating in this embodiment reaches 30 MPa, the surface infrared reflectivity reaches 83%, and the thermal conductivity of the coating is as low as 6.80 W / (m·K), meeting the performance requirements of high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0166] Example 7

[0167] This embodiment discloses a composite coating for a polysilicon reduction furnace and a preparation method thereof. The composite coating needs to be made into two layers. The first layer is a porous heat-insulating layer, and the second layer is a highly reflective surface reflective layer. The specific materials used and process parameters are as follows:

[0168] (1) Prepare hollow sphere powder: Take the first material, tungsten-based alloy W18Cr4V, and use the template method to prepare W18Cr4V hollow sphere powder, and sieve it to obtain hollow sphere powder with a particle size of 30 - 40 μm.

[0169] Prepare the first solid sphere powder: Take the second material, 316L stainless steel, and use the gas atomization method to prepare 316L solid sphere powder, and sieve it to obtain the first solid sphere powder with a particle size of 20 - 45 μm.

[0170] (2) Mix the hollow sphere powder with a particle size of 30 - 40 μm and the first solid sphere powder with a particle size of 20 - 45 μm in a volume ratio of 0.25 to form a porous layer spraying powder.

[0171] (3) Use white corundum sand to roughen the inner wall surface of the reduction furnace to make the roughness greater than 5, and then use compressed air to blow the inner wall to clean the surface floating ash.

[0172] (4) Use a supersonic flame spraying device to spray the porous layer spraying powder on the inner wall surface of the polysilicon reduction furnace. Among them, control the delivery rate of the porous layer spraying powder to be 200 g / min, the flight speed to be 340 m / s, the spraying temperature to be 1580 °C, the spraying distance to be 250 mm, the gun head displacement speed to be 0.20 m / s, the step length to be 0.0018 m, control the single-pass spraying thickness to be 20 μm, and control the total thickness to be 800 μm to obtain a porous heat-insulating coating with a porosity of 20%.

[0173] (5) Use 100 - 150 mesh sandpaper to polish the surface of the porous heat-insulating layer to remove large protrusions and slag defects.

[0174] (6) Take the third material, nickel-based alloy Inconel 625, and use the gas atomization method to prepare solid sphere powder, and sieve it to obtain the second solid sphere powder with a particle size of 40 - 58 μm;

[0175] Subsequently, continue to use the supersonic flame spraying equipment to spray the second solid sphere powder with a particle size of 40 - 58 μm on the surface of the porous thermal insulation coating. Among them, control the delivery rate of the second solid sphere powder to be 150 g / min, the flight speed to be 500 m / s, the spraying temperature to be 1650 °C, the spraying distance to be 250 mm, the gun head displacement speed to be 0.05 m / s, and the step size to be 0.0018 m. Control the single-pass spraying thickness to be 50 μm and the total thickness to be 600 μm to obtain the surface reflective layer.

[0176] (7) Perform polishing treatment on the surface reflective layer to reduce the roughness to 0.05, producing a mirror effect, and the preparation of the polysilicon reduction composite coating is completed.

[0177] After testing, the bonding strength of the composite coating in this example reaches 45 MPa, the surface infrared reflectivity reaches 81%, and the thermal conductivity of the coating is as low as 11.43 W / (m·K), meeting the performance requirements of having high infrared reflectivity, low thermal conductivity, and high bonding strength with the inner wall of the reduction furnace.

[0178] Comparative Example 1

[0179] Compared with Example 2, in this comparative example, only the inner wall surface of the polysilicon reduction furnace is polished to reduce the roughness to 0.05, and its infrared reflectivity and inner wall thermal conductivity are detected. The infrared reflectivity is 60% and the thermal conductivity is 16.30 W / (m·K).

[0180] Compared with it, the infrared reflectivity of the polysilicon reduction furnace composite coating prepared in Example 2 is significantly improved and the thermal conductivity is significantly reduced.

[0181] Comparative Example 2

[0182] The difference between this comparative example and Example 2 is that: the coating in this comparative example only contains a porous thermal insulation layer.

[0183] After testing, the bonding strength of the coating in this comparative example is 40 MPa. However, since the porous thermal insulation layer cannot be polished, the infrared reflectivity of the coating is only 20% and the effective thermal conductivity is 5.50 W / (m·K).

[0184] Comparative Example 3

[0185] The difference between this comparative example and Example 2 is that: the coating in this comparative example only contains a surface reflective layer made of FeCoCr high-entropy alloy material.

[0186] After testing, the bonding strength of the coating in this comparative example is 50 MPa, the infrared reflectivity of the coating is 88%, and the thermal conductivity is 9.10 W / (m·K).

[0187] Comparative Example 4

[0188] This comparative example is different from Example 2 in that the specific preparation process conditions of the porous thermal insulation layer and the surface reflection layer are different. Specifically, as Figure 2 , Figure 3 shown. For each working condition, except for the controlled variables, other parameters are the same as those in Example 2.

[0189] It can be seen from Figure 2 , Figure 3 that the bonding strengths of D1, D14, and D16 in this comparative example are relatively low, and the coating is likely to fall off during the periodic thermal shock in the production process.

[0190] The porosity of the porous layer of D5 is relatively low. Compared with Example 2, the thermal conductivity of the composite coating increases by 36%, and the thermal insulation performance decreases.

[0191] The bonding strength of D6 is very low, and the coating is likely to fall off.

[0192] Compared with Example 2, for D19, D20, and D25, the porosity of the surface reflection layer increases, resulting in a decrease in the bonding strength of the coating and a decrease in the infrared reflectivity.

[0193] It should be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered within the protection scope of the present invention.

Claims

1. A preparation method of a composite coating for a polysilicon reduction furnace, comprising: Making hollow sphere powder from a first material and making first solid sphere powder from a second material, where the first material is a metal or ceramic material with a melting point higher than the subsequent spraying temperature, the melting point of the second material is lower than that of the first material, and the difference in their melting points is 250 - 650 °C; Formulating a porous layer spraying powder by mixing the hollow sphere powder and the first solid sphere powder at a volume ratio of 0.25 - 1.50; Grinding and sandblasting the inner wall surface of the polysilicon reduction furnace; Depositing the porous layer spraying powder on the inner wall substrate surface of the polysilicon reduction furnace to obtain a porous heat insulation coating; Grinding the surface of the porous heat insulation coating; Depositing a surface reflection layer on the surface of the ground porous heat insulation coating; Polishing and grinding the surface reflection layer to complete the preparation.

2. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, wherein The first material is one of tungsten-based alloys, alumina, silica, and cobalt-based alloys.

3. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, wherein, The sphericity of the hollow sphere powder is ≥85%, and the sphericity of the first solid sphere powder is ≥50%.

4. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, wherein The particle size of the hollow sphere powder is 15 - 58 μm, and the particle size of the first solid sphere powder is 10 - 58 μm.

5. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, wherein The second material is one of stainless steel, nickel-based alloys, and cobalt-based alloys, or is the same as the substrate material of the polysilicon reduction furnace.

6. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, characterized in that, The porosity of the porous heat insulation layer is 20 - 60%.

7. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, characterized in that, When depositing the porous heat insulation layer, controlling the flying speed of the porous layer spraying powder at 300 - 400 m / s and the spraying temperature at 150 - 250 °C higher than the melting point of the first solid sphere powder.

8. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 1, characterized in that, The depositing a surface reflection layer on the surface of the ground porous heat insulation coating includes: Making second solid sphere powder from a third material, where the sphericity of the second solid sphere powder is ≥50%, The infrared reflectivity of the third material is >80%, and the melting point of the third material is less than that of the second material or the melting point of the third material is greater than that of the second material but the difference in their melting points is 0 - 300 °C; Then using a thermal spraying method to uniformly deposit the second solid sphere powder on the surface of the ground porous heat insulation coating to deposit the surface reflection layer.

9. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 8, characterized in that, When depositing the surface reflection layer, controlling the delivery rate of the second solid sphere powder at 50 - 150 g / min.

10. The preparation method of the polysilicon reduction furnace composite coating according to claim 8, characterized in that, When depositing the surface reflection layer, controlling the spraying speed at 380 - 500 m / s.

11. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 8, characterized in that, When depositing the surface reflection layer, controlling the spraying temperature at 150 - 250 °C higher than the melting point of the second solid sphere powder.

12. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 8, characterized in that, When depositing the surface reflection layer, controlling the spraying distance at 100 - 250 mm, the gun head displacement speed at 0.03 - 0.13 m / s, and the step size at 0.0015 - 0.002 m.

13. The preparation method of the polysilicon reduction furnace composite coating according to claim 8, wherein, The thermal spraying method is a supersonic thermal spraying method. Among them, the single-pass spraying thickness of both the porous heat insulation layer and the surface reflection layer is 20 - 50 μm, the total thickness of the porous heat insulation layer is 800 - 2000 μm, and the total thickness of the surface reflection layer is 200 - 600 μm.

14. The preparation method of the composite coating for the polysilicon reduction furnace according to claim 8, characterized in that, The third material is one of silver, nickel-based alloys, and cobalt-based alloys.

15. A composite coating for a polysilicon reduction furnace, characterized in that, Prepared by using the preparation method according to any one of claims 1 to 14.

16. A polysilicon reduction furnace, characterized in that, The polysilicon reduction furnace includes the polysilicon reduction furnace composite coating according to claim 15.

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