Fluidized bed chemical vapor deposition equipment

Abstract

The invention discloses fluidized bed chemical vapor deposition equipment which comprises a furnace tube, the upper end of the furnace tube is sealed through an upper sealing cover, the lower end of the furnace tube is sealed through a lower sealing cover, one side of the upper portion of the furnace tube is provided with a feeding hole, and one side of the lower end of the furnace tube is connected with a process gas inlet pipe; the feeding bin is connected to the feeding hole; the air filtering screen plate is positioned at the lower part of the inner cavity of the furnace pipe and is positioned above the process gas inlet pipe, and an air supply cavity is formed below the air filtering screen plate; an impeller of the fan assembly is located in the air supply cavity; the inner cylinder covers the impeller downwards, and an outlet of the process gas inlet pipe is exposed inwards on the side where the process gas inlet pipe is located; a backflow space is reserved between the upper end of the inner cylinder and the upper sealing cover, and a backflow gap is reserved between the outer wall of the inner cylinder and the inner wall of the furnace tube. According to the fluidized bed chemical vapor deposition equipment, the fluidized gas utilization rate is high, and powder accumulation is not prone to being caused.

Description

Technical Field

[0001] The invention relates to a fluidized bed chemical vapor deposition device. Background Art

[0002] Fluidized bed chemical vapor deposition (FBCVD) technology is a chemical process for preparing coated composite powders. Its basic principle is that under the action of airflow, the particles are in a fluidized state in a given relatively closed reactor. This technology mainly uses one or several gas phase compounds or single substances containing film elements to chemically react on the substrate surface to form a film.

[0003] During the FBCVD process, the powder is in a suspended rolling state in the fluidized bed under the action of the airflow, so that the gas and solid are fully in contact, so that the reaction products can be evenly deposited on the surface of the powder. So far, FBCVD technology has been widely used in the coating of high-temperature gas-cooled reactor fuel particles, the mass production of carbon nanotubes, and the preparation of polycrystalline silicon. At the same time, the fluidized bed chemical vapor deposition technology has achieved the effective coating of various metals (Ni, Al, Cu), non-metals (Si) or metal and non-metal compounds (A1203, TiN, TiC, Si3N4, etc.) on various substrates, and the prepared powder has good uniformity.

[0004] Based on the aforementioned principle of fluidized bed, fluidization requires the fluidizing gas to reach a given flow rate so that the raw material powder is in a suspended state with the help of the fluidizing gas's impact force, and this state needs to be maintained throughout the vapor deposition. The fluidizing gas is usually directly discharged and cannot be recycled. The FBCVD reaction time is as long as more than 10 hours, resulting in a large consumption of fluidizing gas.

[0005] In addition, in order to suspend the powder, the gas velocity must reach the speed that allows the process powder to suspend. It should be known that fluidization has three stages, the middle stage is the fluidized bed stage, and the last stage is the fluid transport stage, that is, the gas flow rate is sufficient to transport the process powder away. It is recorded that after FBCVD is completed, the gas flow can be increased to transport the coated process powder away.

[0006] Figure 1The figure shows a schematic diagram of a known fluidized bed chemical vapor deposition device. In the figure, process gas is introduced from the process gas inlet pipe 1, but the amount of process gas usually cannot meet the fluidization requirements. Therefore, it is generally necessary to mix fluidizing gas into the process gas. In other words, the gas introduced from the process gas inlet pipe 1 is a mixed gas of process gas and fluidizing gas, in which the fluidizing gas has a relatively large specific gravity. After the flow rate of the fluidizing gas reaches a predetermined flow rate, the feeding device feeds the reaction zone 4, and the falling process powder is in a suspended state under the support of the fluidizing gas and the process gas, and presents Figure 1 The suspended powder area 7 shown in the figure, the gas-solid mixture in the suspended powder area 7 is in a tumbling state, i.e., a fluidized bed. The process powder will tumble violently in the suspended powder area 7, similar to boiling liquid, so the fluidized bed is also called a boiling bed. In the fluidized bed stage, the suspended powder area 7 has a relatively obvious upper interface, and the bed porosity and bed height both increase with the increase of the apparent flow velocity.

[0007] At the upper limit of the fluidized bed stage, when the superficial velocity of the fluidizing gas increases to a limit value, the particles move upward with the fluid at different speeds, and all particles begin to be carried out of the reaction zone by the fluid, and the upper interface of the suspended powder zone 7 disappears. The porosity in the bed increases with the increase of the superficial velocity. Finally, when all the particles in the bed are carried out by the fluid, the porosity of the bed reaches 100%, and the fluidized bed no longer exists. This is the fluid transport stage, which is about to complete the powder transport of the current process to facilitate the FBCVD of the next given amount of powder. On the contrary, if the fluidizing gas flow is insufficient, the powder particles cannot be suspended and gradually accumulate at the bottom of the furnace tube 2.

[0008] It can be seen that the flow rate of the fluidizing gas is related to the specific gravity and particle size of the process powder, but no matter what kind of fluidized bed, the amount of fluidizing gas used is extremely large. At present, the regulation of the mixed gas passing through the process gas inlet pipe is mainly pressure regulation, or directly using a valve to control its opening and closing, but it is difficult to achieve precision control. As a result, the powder is unevenly distributed in the chamber and easily forms a siltation layer in a local area. Summary of the invention

[0009] The object of the present invention is to provide a fluidized bed chemical vapor deposition device which has high fluidizing gas utilization rate and is not prone to powder accumulation.

[0010] According to an embodiment of the present invention, a fluidized bed chemical vapor deposition device is provided, the basic structure of which includes: The furnace tube is a vertical furnace tube, and the upper end of the furnace tube is sealed by an upper cover with an exhaust hole, and the lower end is sealed by a lower cover, one side of the upper part of the furnace tube is provided with a feeding hole, and one side of the lower end is connected with a process gas inlet pipe; A feeding bin connected to the feeding hole for feeding materials into the furnace tube; The air filter screen is located at the lower part of the furnace tube cavity and above the process gas inlet pipe, forming a transverse screen, and an air supply cavity is formed below the air filter screen; A fan assembly having an impeller disposed in the air supply chamber to force air upward; and The inner cylinder is located in the furnace tube, covers the impeller downwards, and exposes the outlet of the process gas inlet pipe inwardly on the side where the process gas inlet pipe is located; a reflux space is left between the upper end of the inner cylinder and the upper cover, and a reflux gap is left between the outer wall of the inner cylinder and the inner wall of the furnace tube.

[0011] In the fluidized bed chemical vapor deposition equipment, optionally, the lower end surface of the inner cylinder is an inclined end surface; Correspondingly, the side where the inclined end surface is located on the process gas inlet pipe is the highest side, and the opposite side is the lowest side.

[0012] Optionally, the inner cylinder is offset in the furnace tube toward a side away from the process gas inlet pipe.

[0013] Optionally, the maximum gap of the reflux gap is 2 to 3.5 times the minimum gap.

[0014] Optionally, the maximum gap is one tenth to one eighth of the inner diameter of the furnace tube.

[0015] Optionally, the exhaust hole is offset on the upper cover toward a side away from the process gas inlet pipe.

[0016] Optionally, the outer contour of the lower end of the inner cylinder is inwardly inclined, so that the corresponding reflux gap gradually expands at the lower end.

[0017] Optionally, a guide plate is provided between the air filter screen and the impeller; The guide plate is installed in the furnace tube through a horizontal rotating shaft; A second driving device is correspondingly provided to drive the guide plate to swing around the rotating shaft.

[0018] Optionally, there are two guide plates, and the guide plates are rectangular plates or arc-shaped plates; The two guide plates are symmetrically arranged with respect to a predetermined middle section of the furnace tube.

[0019] Optionally, the furnace tube is provided with a powder receiving outlet on the upper side of the air filter screen.

[0020] In an embodiment of the present invention, a fluidized bed chemical vapor deposition device is provided, in which an inner tube is nested in the furnace tube, and a reflux gap is formed between the inner wall of the furnace tube and the outer wall of the inner tube. A reflux space is left between the upper end of the inner tube and the upper cover used to seal the upper end of the furnace tube. A forced air blower is also provided, and the impeller of the blower is arranged in the inner tube, so that the air flow passes through the inner tube upward by forced air induction. It can be seen that a fluidized bed will be formed in the inner tube. Since the wind pressure is strengthened by forced air supply, the conditions for the formation of the fluidized bed can still be met under the condition of relatively small air intake, and the amount of gas including fluidizing gas is reduced. In addition, due to the use of forced air supply, the wind pressure is enhanced, and powder is not easy to accumulate on the air filter screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the structure of a known fluidized bed chemical vapor deposition equipment.

[0022] Figure 2 It is a schematic diagram of the main cross-sectional structure of a fluidized bed chemical vapor deposition device in one embodiment.

[0023] Figure 3 for Figure 2 I do not enlarge the picture.

[0024] Figure 4 This is a schematic diagram of the left-side cross-sectional structure of the lower part of a fluidized bed chemical vapor deposition device in one embodiment.

[0025] In the figure: 1. process gas inlet pipe, 2. furnace tube, 3. insulation layer, 4. reaction zone, 5. exhaust pipe, 6. heating area, 7. suspended powder area, 8. valve, 9. feeding bin, 10. upper cover, 11. inner cylinder, 12. reflux gap, 13. powder receiving outlet, 14. air filter screen, 15. guide plate, 16. rotating shaft, 17. axial flow fan, 18. lower cover, 19. first magnetic fluid, 20. first motor, 21. second magnetic fluid, 22. second motor. DETAILED DESCRIPTION

[0026] In the embodiments of the present invention, emphasis is placed on increasing the wind pressure by forced air supply, so that the fluidized bed can still be maintained under the condition of relatively limited air supply. Figure 1 and Figure 2 The gas-solid mixture in the suspended powder zone 7 shown in FIG. 1 is a fluidized bed. As for other parts, they are not described in detail in the embodiments of the present invention.

[0027] Since the fluidized bed needs to rely on the rising airflow to support the solid particles, the fluidized bed is often implemented in the furnace tube 2 shown in the example. Obviously, in the furnace tube 2, the fluidizing gas is a rising airflow.

[0028] In addition, the furnace tube 2 is generally a round tube, so it has a certain axial, radial and circumferential direction, and because it is a vertical structure, the axial direction of the furnace tube 2 is also its up and down direction. Unless otherwise specified in the following text, this reference system is used as the main reference system.

[0029] In addition, the furnace tube 2 and the like also have a definite inside and outside, such as an inner wall, an outer wall, etc., which have definite contents.

[0030] exist Figure 2 The furnace tube 2 provided in the illustrated fluidized bed chemical vapor deposition equipment is obviously an illustrated furnace tube. At least in the reaction zone 4, the furnace tube 2 is surrounded by a thermal insulation layer 3. The pipe section of the furnace tube 2 corresponding to the thermal insulation layer 3 is generally wound with an electric heating element, such as an electric heating wire, to form the heating device 6 shown in the figure, so as to perform heating according to the process requirements.

[0031] Accordingly, a contact temperature measuring device such as a thermocouple or a non-contact temperature measuring device such as an infrared thermometer may be provided in the furnace tube to control the temperature in the reaction zone 4 in a closed loop.

[0032] At the same time, it can be seen that if part of the fluidizing gas can be recycled, energy consumption will be reduced. In the known fluidized bed chemical vapor deposition equipment, the fluidizing gas is directly discharged, and the gas introduced through the process gas inlet pipe 1 needs to be reheated. In the embodiment of the present invention, part of the gas is recycled, and the gas is obviously heated, so that energy consumption can be reduced as a whole.

[0033] In addition, Figure 2 In the illustrated structure, the upper cover 10 is provided with an exhaust hole for assembling, for example, an exhaust pipe 5. The cross section of the exhaust hole is obviously much smaller than the cross section of the furnace tube 2. In other words, although the exhaust pipe 5 has a drainage function, the gas with a relatively low pressure generated by forced air supply has a relatively high flow rate when the conditions for forming a fluidized bed are met. Figure 2 The space between the upper end of the inner cylinder 11 and the upper cover 10 shown in the figure will produce backflow.

[0034] Furthermore, the inlet air flow generated by the process gas inlet pipe 1 itself will form a negative pressure in the gap between the inner tube 11 and the furnace tube 2, and the axial flow fan 17 used for forced air supply will also generate a negative pressure in the gap, so that the backflow is at least partially converted into a reflux, and flows back to the lower end of the inner tube 11 through the gap.

[0035] Furthermore, the furnace tube 2 is a typical cylindrical tube, and the reaction needs to be carried out in a relatively closed environment. Therefore, the upper end of the furnace tube 2 is sealed by the aforementioned upper cover 10 with exhaust holes, and the lower end is sealed by the lower cover 18.

[0036] exist Figure 2In the illustrated structure, the lower cover 18 is provided with a first magnetic fluid 19 and a first motor 20 for driving the axial flow fan 17 in the figure, wherein the "magnetic fluid" in the first magnetic fluid 19 is a commonly used name, and its full name is a magnetic fluid sealing device, which is a common sealing form and will not be described in detail here.

[0037] However, it can also be seen that the lower cover 18 is provided with a hole for the motor shaft of the first motor 20 or the axial flow fan 17 in the figure to enter or pass through.

[0038] In addition, to avoid interference, Figure 2 In the embodiment, the process gas inlet pipe 1 is arranged at the lower end side of the furnace tube 2. Figure 1 A fluidized bed chemical vapor deposition device is known in the art, in which a process gas inlet pipe 1 is mounted on a lower cover 18. Figure 2 In the illustrated structure, the gas introduced by the process gas inlet pipe 1 is a transverse flow, so that in the circumferential direction of the inner tube 11, the impact on the reflux gap 12 at different positions in the figure is different. Therefore, with respect to the reflux gap 12, the side where the process gas inlet pipe 1 is located is relatively larger, that is, the left side shown in the figure.

[0039] It can be seen from the above that the inner tube 11 is located inside the furnace tube 2 , and the inner tube 11 can be directly fixed on the inner wall of the furnace tube 2 , and can be connected by, for example, a horizontal rod.

[0040] In addition, in the structure shown in the figure, the inner tube 11 can be directly fixed on the lower cover 18 in a supporting connection manner, and the supporting member only needs to leave the process gas inlet pipe 1 aside, so that the gas introduced by the process gas inlet pipe 1 can directly pass into the inner tube 11.

[0041] At the same time, the position of the lower end of the inner tube 11 should ensure that the impeller of the fan assembly is covered, so that the impeller and the inner tube 11 can roughly form an axial flow duct fan, which has obvious characteristics of an axial flow fan 17, and Figure 2 In the illustrated structure, this is represented as an axial flow fan 17 .

[0042] At the same time, if Figure 2 As shown, the height of the lower end of the inner cylinder 11 on the side where the process gas inlet pipe 1 is located is higher than the inlet pipe opening of the process gas inlet pipe 1, so that the cylinder wall of the inner cylinder 11 on this side will not block the inlet gas flow.

[0043] And in Figure 2 On the right side of the illustrated structure, the wall of the inner cylinder 11 extends downward to block the gas introduced by the process gas inlet pipe 1, so that the gas flows upward under the upward forced air supply condition of the axial flow fan 17.

[0044] From the perspective of position, the side of the inner tube 11 facing the process gas inlet pipe 1 should be open. Figure 2 The structure of the inner cylinder 11 shown in the figure is only an option. In some embodiments, the lower end of the inner cylinder 11 may be a flat end surface, and the flat end surface is lower than the process gas inlet pipe 1. Under this condition, a side hole may be provided on the side of the inner cylinder 11 facing the process gas inlet pipe 1 to introduce the process gas.

[0045] In addition, a certain distance should be left between the upper end of the inner cylinder 11 and the upper cover 10 so as to form a reflux space, which is reflected in the size of the reflux space, i.e., its height, which is one-fourth to one-third of the diameter of the inner cylinder 11. The height of the reflux space should not be too large to avoid a significant negative impact on the formation of the suspended powder zone 7. It should also not be too small, otherwise the reflux amount of the process gas will be relatively small.

[0046] In addition, the reflux gap 12 mentioned above can also be expressed as a reflux channel. Based on the above description, it can be known that the reflux channel is formed between the inner tube 11 and the furnace tube 2.

[0047] Another technical problem mentioned in the foregoing is the problem of the deposition of raw material powder, which may be deposited on the air filter screen 14, which may block the air filter screen 14 and cause problems in the recovery of the raw material powder.

[0048] In an embodiment of the present invention, an axial flow fan 17 is used for forced air supply to increase the wind speed. Under the condition of relatively limited air volume, an airflow with a relatively large flow rate can more easily lift the raw material powder in particle form at the air filter screen 14.

[0049] From the positional relationship, at least the functional part of the air filter screen 14 is located in the inner tube 11, and it is located in the lower part of the inner cavity of the furnace tube 2, and is obviously located above the process gas inlet pipe, thereby forming a horizontal partition screen. For the convenience of description, the space below the air filter screen 14 is called an air supply chamber.

[0050] Regarding raw material powder, it is necessary to feed from the upper part of the furnace tube 2. Therefore, a feeding hole is provided on one side of the upper part of the furnace tube 2. Figure 2 In the illustrated structure, the feeding bin 9 filled with raw material powder is connected to the feeding hole through a feeding pipe.

[0051] Figure 2 The position of the feeding hole is schematically shown, and the feeding pipe can be inserted into the inner tube 11 from the side, and can also be set above the upper opening of the inner tube 11.

[0052] The feeding pipeline is provided with a valve 8, which may be a stop valve or an actuator-controlled valve with adjustable opening, so as to adjust the feeding rate according to different process requirements.

[0053] Regarding the power configuration, mainly Figure 2 and Figure 4 The power part of the axial flow fan 17 shown in the figure is located outside the chamber defined by the inner tube furnace tube 2, the upper cover 10 and the lower cover 18, so as to facilitate the heat dissipation of the first motor 20, for example.

[0054] Similarly, in Figure 2 and Figure 4 The illustrated structure is also provided with a guide plate 15, the power part of which is also arranged outside the chamber defined by the inner tube furnace tube 2, the upper cover 10 and the lower cover 18. The corresponding shaft is shown in the figure as being dynamically sealed using a magnetic fluid seal.

[0055] Furthermore, regarding the guide plate 15, its main purpose is to respond to the aforementioned problem that the raw material powder is prone to local accumulation. Affected by the feeding method and the fact that the upward wind from the inner cylinder 11 is different and unstable in the radial direction, the raw material powder is prone to local accumulation, that is, it is easy to accumulate in a certain area on the air filter mesh plate 14. In the foregoing, the main consideration is to use forced air supply to send the raw material powder settled on the air filter mesh plate 14 back to the suspended powder area 7. However, experiments have found that this method has a relatively limited effect.

[0056] Furthermore, regarding the guide plate 15, first of all, its position setting is Figure 2 and Figure 4 In the illustrated structure, the guide plate 15 is arranged between the air filter mesh plate 14 and the impeller. At the same time, the guide plate 15 is installed in the furnace tube through the horizontal rotating shaft 16, and its plate body is located in the inner tube 11. The guide plate 15 makes the air flow blow in the expected direction by adjusting the rotation angle of the horizontal rotating shaft 16, so that the raw material powder accumulated at a certain position can be blown up again. This adjustment can be achieved by detecting the upper surface of the air filter mesh plate 14. When the raw material powder accumulates too much on the air filter mesh plate 14, the rotating shaft 16 is driven to change the air flow guidance of the guide plate 15, so that the air flow is directly blown to the raw material powder accumulation area.

[0057] Furthermore, there are two guide plates 15, and the guide plates 15 are rectangular plates or arc-shaped plates; and the two guide plates 15 are symmetrically arranged with respect to a predetermined middle section of the furnace tube 2, such as the left and right middle sections.

[0058] As for the lower end of the inner tube 11, it is pointed out in the foregoing that the inner tube 11 can have various forms. Figure 2 and Figure 4 In the illustrated structure, the lower end surface of the inner cylinder 11 is an inclined end surface; accordingly, the side of the inclined end surface located on the process gas inlet pipe 1 is the highest side, and the opposite side is the lowest side, thereby forming Figure 2 In the state shown in , the gas flow of the process gas inlet pipe 1 can enter the inner cylinder 11 without being hindered, and will not further enter the reflux gap 12.

[0059] In addition, the inner tube 11 is offset in the furnace tube 2, which may cause the reflux gap 12 to be different at different locations in the circumferential direction of the furnace tube 2. Therefore, as a specific limitation, the maximum gap of the reflux gap 12 is 2 to 3.5 times the minimum gap.

[0060] Furthermore, the maximum gap is one tenth to one eighth of the inner diameter of the furnace tube 2.

[0061] As an adaptive configuration, the exhaust hole is offset on the upper cover 10 toward a side away from the process gas inlet pipe 1 , which is beneficial for combing the direction of the airflow when the process gas inlet pipe 1 is placed horizontally, and is more conducive to the formation of the suspended powder zone 7 .

[0062] exist Figure 2 and Figure 3 In the embodiment, the outer contour of the lower end of the inner cylinder 11 is inclined inward, so that the corresponding reflux gap 12 is gradually expanded at the lower end, which is beneficial to the reflux of the process gas.

[0063] In addition, the furnace tube 2 is provided with a powder receiving outlet 13 on the upper side of the air filter mesh plate 14 to collect the material settled on the air filter mesh plate 14 regularly or irregularly.

Claims

1. A fluidized bed chemical vapor deposition device, characterized in that: include: The furnace tube is a vertical furnace tube, and the upper end of the furnace tube is sealed by an upper cover with an exhaust hole, and the lower end is sealed by a lower cover, one side of the upper part of the furnace tube is provided with a feeding hole, and one side of the lower end is connected with a process gas inlet pipe; A feeding bin connected to the feeding hole for feeding materials into the furnace tube; The air filter screen is located at the lower part of the furnace tube cavity and above the process gas inlet pipe, forming a transverse screen, and an air supply cavity is formed below the air filter screen; A fan assembly, wherein the impeller is located in the air supply chamber to force air upward; as well as The inner cylinder is located in the furnace tube, covers the impeller downwards, and exposes the outlet of the process gas inlet pipe inwardly on the side where the process gas inlet pipe is located; a reflux space is left between the upper end of the inner cylinder and the upper cover, and a reflux gap is left between the outer wall of the inner cylinder and the inner wall of the furnace tube.

2. The fluidized bed chemical vapor deposition equipment according to claim 1, characterized in that: The lower end surface of the inner cylinder is an inclined end surface; Correspondingly, the side of the inclined end surface located on the process gas inlet pipe is the highest side, and the opposite side is the lowest side.

3. The fluidized bed chemical vapor deposition equipment according to claim 2, characterized in that: The inner tube is offset in the furnace tube toward a side away from the process gas inlet pipe.

4. The fluidized bed chemical vapor deposition equipment according to claim 3, characterized in that: The maximum gap of the reflux gap is 2 to 3.5 times the minimum gap.

5. The fluidized bed chemical vapor deposition equipment according to claim 4, characterized in that: The maximum gap is one tenth to one eighth of the inner diameter of the furnace tube.

6. The fluidized bed chemical vapor deposition equipment according to any one of claims 2 to 5, characterized in that: The air extraction hole is offset on the upper cover toward a side away from the process gas inlet pipe.

7. The fluidized bed chemical vapor deposition equipment according to claim 2, characterized in that: The outer contour of the lower end of the inner tube is inclined inward, so that the corresponding reflux gap gradually expands at the lower end.

8. The fluidized bed chemical vapor deposition equipment according to claim 1, characterized in that: A guide plate is provided between the air filter screen plate and the impeller; The guide plate is installed in the furnace tube through a horizontal rotating shaft; A second driving device is correspondingly provided to drive the guide plate to swing around the rotating shaft.

9. The fluidized bed chemical vapor deposition equipment according to claim 8, characterized in that: There are two guide plates, and the guide plates are rectangular plates or arc-shaped plates; The two guide plates are symmetrically arranged with respect to a predetermined middle section of the furnace tube.

10. The fluidized bed chemical vapor deposition equipment according to claim 1, characterized in that: The furnace tube is provided with a powder receiving outlet on the upper side of the air filter screen plate.

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