ALD (Atomic Layer Deposition) fluidized reactor of double-cone rotating fluidized bed and method for coating powder particles by using ALD fluidized reactor

Abstract

The ALD fluidized reactor comprises a fluidization chamber, a deposition tank, a rotating mechanism, gas guide pipes and a vacuum pump, the upper end and the lower end of the fluidization chamber are closed, the outer side face of the fluidization chamber is symmetrically communicated with the two gas guide pipes, one gas guide pipe is communicated with a fluidization gas supply system, and the other gas guide pipe is communicated with a vacuum pump. One gas-guide tube is used for conveying fluidizing gas containing precursor reaction gas into the fluidizing chamber, the other gas-guide tube is sequentially communicated with a tail gas detection system and a vacuum pump, the two gas-guide tubes are controlled by a rotating mechanism and used for enabling the reaction kettle to be periodically overturned according to an overturning period, and after the reaction kettle is overturned every time, the reaction kettle is overturned. According to the method, powder with the large particle diameter is made to settle into the deposition tank faster than powder with the small particle diameter, the powder particles settling into the deposition tank stop or are sharply reduced to generate the atomic layer deposition reaction opportunity, and the powder particles which are not settled into the deposition tank suspend in the fluidizing gas and continue to react with the precursor reaction gas to form the single-layer coating.

Description

Technical Field

[0001] The invention belongs to the field of vacuum atomic deposition coating, and in particular relates to a double-cone rotating fluidized bed ALD fluidized reactor and a method for coating powder particles thereof. Background Art

[0002] Atomic layer deposition (ALD) technology was first proposed by Soviet and Finnish scientists in the 1960s and 1970s. The modern concept of "atomic layer deposition" originated from the "atomic layer epitaxy (ALE)" method invented by Dr. Suntola, which is used to prepare high-quality ZnS films on electroluminescent thin-film flat-panel displays. As a special chemical vapor deposition technology, atomic layer deposition has the following reaction principle: two gas-phase precursor pulses are alternately introduced into the reaction chamber, and the film deposition is completed by gas-solidification chemical adsorption reaction on the substrate surface. From the perspective of its deposition principle, it has the characteristics of self-saturated surface adsorption and self-limiting growth. It can self-limitingly modify all surface active sites exposed to the gas phase environment, and can achieve the coating of single micro-nanoparticles. Since micro-nano powder particles themselves have the characteristics of large specific surface area and high specific surface energy, they are easy to agglomerate during the coating process and it is difficult for the precursor to be completely saturated and adsorbed on the surface of the micro-nano powder particles, resulting in uneven coated nano-films and even the appearance of agglomerate coating. This is a key issue that needs to be considered in the development and innovation of atomic layer deposition equipment for micro-nano powder particles.

[0003] In practical applications, as a typical two-dimensional film-forming vacuum technology, traditional ALD coating methods are mainly based on static coating methods, that is, the particles are accumulated in the sample fixing network, relying on the diffusion of precursor molecules to achieve saturated adsorption of the entire surface. This method has no external force field to overcome the force of agglomeration and is only suitable for a small amount of particles with good monodispersity. It is not suitable for systems that are prone to secondary particle agglomeration. At the same time, the gaps between particles are small, and the diffusion in the gaps is limited, which can easily lead to problems such as uneven adsorption and long reaction cycles.

[0004] Using a fluidized bed to evenly distribute powder particles in the fluidized bed can overcome the force of agglomeration, but it requires a sufficient flow of fluidizing gas, which consumes a lot of energy. In addition, after the size of the fluidized bed is enlarged, the mass of powder particles allowed to be loaded in the fluidized bed cannot be enlarged proportionally. Increasing the loading amount of powder particles will increase the volume and height of the equipment exponentially, resulting in forced expansion and height increase of the factory building. Therefore, a new fluidized bed design is urgently needed so that the precursor reaction products can better coat the powder and obtain a better coverage rate. At the same time, it is easy to enlarge the equipment and increase the loading amount of powder particles to meet the needs of industrial-scale production. Summary of the invention

[0005] In view of the above problems, this invention provides a double-cone rotating fluidized bed ALD fluidized reactor, including a fluidizing chamber, a sedimentation tank, a rotating mechanism, an air duct, and a vacuum pump. The fluidizing chamber is a cylindrical box with unsealed upper and lower ends, and the sedimentation channel runs through the upper and lower end surfaces of the cylindrical box. Two air ducts are connected to the outer side of the fluidizing chamber, and the two air ducts are coaxial and symmetrically arranged relative to the fluidizing chamber. One air duct is connected to the fluidizing gas supply system for conveying fluidizing gas containing precursor reaction gas into the fluidizing chamber, and the other air duct is connected to the exhaust gas detection system and the vacuum pump in sequence for discharging the reaction exhaust gas. The two air ducts are centrally arranged on the outer side of the fluidizing chamber and are controlled by the rotating mechanism to make the fluidizing chamber periodically flipped according to the flipping cycle. The bowl mouths of the two bowl-shaped sedimentation tanks face the sedimentation channel, and the two ends of the sedimentation channel are symmetrically closed to form a fluidized reactor. A discharge valve is installed on the conical surface of a sedimentation tank.

[0006] The portion of the fluidizing chamber connected to the two air guide pipes is evenly arranged with equal flow holes communicating with the sedimentation channel and the air guide pipes.

[0007] The double-cone rotating fluidized bed ALD fluidized reactor also includes a stirrer, which is arranged in the fluidized reactor. A driving mechanism is installed at one end of the other sedimentation tank away from the bowl mouth, and the driving mechanism is pivotally connected to the stirrer.

[0008] The sedimentation trough is designed to be conical or spherical, and the agitator includes a stirring rod and stirring blades evenly arranged on the circumferential surfaces of both ends of the stirring rod. One end of the stirring rod is pivotally connected to the driving mechanism, and the other end of the stirring rod is close to the end of a sedimentation trough away from the bowl mouth. The stirring blades are spirally arranged around the stirring rod. The agitator is used to lift the larger powder particles first deposited at the bottom of the sedimentation trough at the bottom of the fluidized reactor to the upper part of the sedimentation trough, and at the same time make the smaller powder particles deposited later at the upper part of the sedimentation trough flow to the bottom of the sedimentation trough.

[0009] At least two discharge valves are provided and are respectively installed at different heights of the conical surface of the sedimentation tank.

[0010] The distance between the sedimentation tanks at both ends of the fluidized reactor is H, H = T*u x ;

[0011]

[0012] d x is the particle size of the powder particles when they reach the ALD atomic layer deposition thickness, g is the gravitational acceleration, ρ xs The particle size after coating is d xis the density of the powder particles, ρ is the density of the fluidizing gas under the conditions of atomic layer deposition reaction, μ is the viscosity of the fluidizing gas under the conditions of atomic layer deposition reaction, V s is the flow rate of fluidizing gas, T is the average cumulative time of the precursor reaction gas entering the fluidizing chamber after each turnover of the fluidizing chamber, and u x The particle size after coating is d x The sedimentation velocity of powder particles.

[0013] The method for coating powder particles in a double-cone rotating fluidized bed ALD fluidized reactor comprises the following steps:

[0014] S1. The powder particles before coating are loaded into the deposition slot at the bottom of the fluidized reactor, and then the inert gas and exhaust gas are input through the air duct to replace the air in the fluidized reactor, and then the temperature and pressure in the fluidized reactor are increased to reach the reaction conditions;

[0015] S2. The fluidizing chamber is flipped by a rotating mechanism, so that the sedimentation tank at the bottom of the fluidizing chamber is flipped to the upper part of the fluidizing chamber, so that the powder particles can fall downward, and at the same time, the fluidizing gas carrying the precursor reaction gas is input through the fluidizing pipe. Under the action of the fluidizing gas, the powder particles are fluidized and stay in the fluidizing chamber, and the surface of the powder particles and the precursor reaction gas undergo a gas-solidification chemical adsorption reaction to complete the deposition of the thin film. When the tail gas detection system monitors that the atomic layer deposition reaction is fully completed, the residual gas in the fluidized reactor is replaced with pure fluidizing gas;

[0016] S3 repeats step S2, and replaces the type of precursor reaction gas carried by the fluidizing gas;

[0017] S4. Repeat steps S2 to S3 until the number of repetitions of steps S2 to S3 reaches a set number of cycles, that is, the particle size of the powder particles reaches or exceeds the ALD atomic layer deposition thickness.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] The double-cone rotating fluidized bed ALD fluidized reactor of the present invention can achieve uniform particle size of powder particles after atomic layer deposition coating.

[0020] During the coating process, after each flipping of the fluidizing chamber, the powder particles encounter resistance during the sedimentation process, causing powders with larger particle diameters to settle into the sedimentation tank faster than powders with smaller particle diameters. The particle sizes of the powder particles in the sedimentation tank are therefore arranged in ascending order from top to bottom. The distance between the powder particles that settle into the sedimentation tank decreases, the dispersion becomes worse, and the contact area with the precursor reaction gas decreases, thereby stopping or drastically reducing the chance of atomic layer deposition reaction. The powder particles that have not settled into the sedimentation tank are suspended in the fluidizing gas and continue to react with the precursor reaction gas until a single layer coating of 0.1 to 0.2 nm is formed on the surface.

[0021] The double-cone rotating fluidized bed ALD fluidized reactor of the present invention can increase the diameter of the fluidized chamber to expand the loading amount of powder particles. The fluidized reactor with a larger diameter can also meet the requirements of controlling the thickness of the coating layer in the fluidized coating process when the powder particle loading amount is small, without the need to replace equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a cross-sectional view of a double-cone rotating fluidized bed ALD fluidized reactor. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly explained, the present invention will be further explained in detail below in conjunction with the accompanying drawings.

[0024] like Figure 1 As shown, a double-cone rotating fluidized bed ALD fluidized reactor includes a fluidizing chamber 1, a sedimentation tank 2, an agitator, a rotating mechanism, an air guide pipe 5, and a vacuum pump. The fluidizing chamber 1 is a cylindrical box body with unsealed upper and lower ends, and the sedimentation channel runs through the upper and lower end surfaces of the cylindrical box body. Two air guide pipes 5 are connected to the outer side of the fluidizing chamber 1. The two air guide pipes 5 are coaxial and symmetrically arranged relative to the fluidizing chamber 1. One air guide pipe 5 is connected to the fluidizing gas supply system for conveying fluidizing gas containing precursor reaction gas into the fluidizing chamber 1. The other air guide pipe 5 is connected to the tail gas detection system and the vacuum pump in sequence for discharging the reaction tail gas. The two air guide pipes 5 are both centrally arranged on the outer side of the fluidizing chamber 1 and are controlled by the rotating mechanism to cause the fluidizing chamber 1 to be periodically flipped according to the flipping cycle. The portion of the fluidizing chamber 1 where the two air guide pipes 5 are connected is evenly arranged with equal flow holes 6 connecting the sedimentation channel and the air guide pipe 5.

[0025] The bowl mouths of the two bowl-shaped sedimentation tanks 2 face the sedimentation channel, and the two ends of the sedimentation channel are symmetrically closed to form a fluidized reactor. The agitator is arranged in the fluidized reactor, and a driving mechanism 4 is installed at one end of the sedimentation tank 2 away from the bowl mouth, and the driving mechanism 4 is pivotally connected to the agitator. A discharge valve 7 is installed on the conical surface of the other sedimentation tank 2. Multiple discharge valves 7 can be provided, which are respectively installed at different heights of the conical surface of the sedimentation tank 2, and are used to discharge powder particles at different depths in the sedimentation tank 2. When the sedimentation tank 2 rotates to the top with the fluidizing chamber 1, the discharge valve 7 is also used to load powder particles.

[0026] The sedimentation tank 2 can be designed to be conical or spherical, and the agitator includes a stirring rod and stirring blades evenly arranged on the circumferential surfaces of both ends of the stirring rod, one end of the stirring rod is pivotally connected to the driving mechanism 4, and the other end of the stirring rod is close to the end of a sedimentation tank 2 away from the bowl. The stirring blade is arranged in a spiral shape around the stirring rod. When the stirring rod is operated to rotate, the agitator is used to lift the powder particles with larger particle size that are first deposited at the bottom of the sedimentation tank 2 at the bottom of the fluidized reactor to the upper part of the sedimentation tank 2, and at the same time, the powder particles with smaller particle size that are later deposited at the upper part of the sedimentation tank 2 are transferred to the bottom of the sedimentation tank 2, so that after the fluidization chamber 1 is flipped, the time for the powder particles with larger particle size to settle in the sedimentation tank 2 below is shortened, and the time for the powder particles with smaller particle size to settle in the sedimentation tank 2 below is prolonged.

[0027] The time it takes for the powder particles to settle to the bottom of the fluidized reactor is θ f The time for the powder particles to move from one side of the fluidizing chamber 1 to the symmetrical side under the action of the fluidizing gas in the fluidized reactor is θ l .

[0028] That is, let H be the distance between the sedimentation tanks 2 at both ends of the fluidized reactor, and R be the radius of the fluidized chamber 1 in the fluidized reactor.

[0029] u0 is the sedimentation velocity of the powder particles,

[0030]

[0031] u is the flow rate of the fluidizing gas.

[0032] The diameter of the powder particles is not greater than d min When θ l ≥θ f .

[0033] V s is the flow rate of fluidizing gas, A0 is the cross-sectional area of ​​fluidizing chamber 1, g is the gravitational acceleration, ρ s is the density of the powder particles before coating, ρ xs The particle size after coating is d x is the density of the powder particles, ρ is the density of the fluidizing gas under the conditions of atomic layer deposition reaction, μ is the viscosity of the fluidizing gas under the conditions of atomic layer deposition reaction, and d x is the particle size of the powder particles after coating, d q ≤d x ≤d min , d q is the particle size of the powder particles when not coated, and the transverse cross section is a plane perpendicular to the central axes of the two sedimentation tanks 2.

[0034] The coating process of powder particles using the double-cone rotating fluidized bed ALD fluidized reactor of the present invention is as follows:

[0035] S1. The powder particles before coating are first loaded into the fluidized reactor and placed in the sedimentation tank 2 at the bottom. Then, the air in the fluidized reactor is replaced by an inert gas, and the temperature and pressure in the fluidized reactor are raised to the reaction conditions.

[0036] S2. The fluidizing chamber 1 is then turned over by a rotating mechanism, so that the sedimentation tank 2 at the bottom is turned over to the upper part of the fluidizing chamber 1, so that the powder particles can fall downward, and at the same time, the fluidizing gas carrying the precursor reaction gas is input through the air guide pipe 5. Under the action of the fluidizing gas, the powder particles are fluidized and stay in the fluidizing chamber, and the surface of the powder particles and the precursor reaction gas undergo a gas-solidification chemical adsorption reaction to complete the deposition of the thin film. When the tail gas detection system monitors that the atomic layer deposition reaction is fully completed, the residual gas in the fluidized reactor is replaced with pure fluidizing gas;

[0037] S3 repeats step S2, and replaces the type of precursor reaction gas carried by the fluidizing gas;

[0038] S4. Repeat steps S2 to S3 until the number of repetitions of steps S2 to S3 reaches a set number of cycles, that is, the particle size of the powder particles reaches or exceeds the ALD atomic layer deposition thickness.

[0039] Steps S2 to S3 are a complete ALD growth cycle, which can be divided into four steps:

[0040] 1. Pulse the first precursor to expose it to the powder surface, and at the same time form covalent bonds with the first precursor at the group sites on the powder surface, saturating the surface sites into a monolayer. Once the surface is saturated, due to the precursor chemistry and process conditions, the excess precursor will not react further with the powder surface;

[0041] 2. The inert carrier gas blows away the remaining unreacted precursor;

[0042] 3. Pulse the second precursor to chemically react on the monolayer surface formed by the first precursor to obtain the desired thin film material;

[0043] 4. The inert carrier gas blows away the remaining precursor and reaction by-products.

[0044] Atomic layer deposition usually involves a cycle of the above four steps, repeated as many times as needed to achieve the desired coating thickness. Each coating after reaction with the precursor will self-limit to a single layer. One ALD growth cycle can form a single layer coating of 0.1 to 0.2nm, and a coating of 10 to 20nm thick requires 100 to 200 ALD growth cycles.

[0045] In step S2, one gas pipe 5 inputs the fluidizing gas carrying the precursor reaction gas, and the other gas pipe 5 simultaneously extracts the reaction tail gas. The tail gas detection system uses the differential electrochemical mass spectrometry in CN113862641B to monitor the tail gas composition, monitor whether the entire atomic layer deposition reaction ALD is sufficient, and judge whether the ALD coating is successfully completed. For example, when using atomic layer deposition (ALD) to coat aluminum oxide on the surface of the powder, the two precursors used are trimethyl aluminum and water. The specific steps for monitoring whether the atomic layer deposition reaction ALD is sufficient are as follows:

[0046] The differential electrochemical mass spectrometer (DEMS) is connected to the exhaust system of ALD. By testing the methane content change curve, the reaction between trimethylaluminum, water and the powder surface in the reactor is judged. If the methane content in the reaction exhaust gas drops from the peak value to below the threshold and no longer increases, and the content of trimethylaluminum or water in the exhaust gas does not decrease, it is judged that the atomic layer deposition reaction is sufficient.

[0047] During the coating process, after each flipping of the fluidizing chamber 1, the powder particles encounter resistance during the sedimentation process, causing the powder with a larger particle diameter to settle into the sedimentation tank 2 faster than the powder with a smaller particle diameter. Therefore, the particle size of the powder particles in the sedimentation tank 2 is arranged in ascending order from top to bottom, and the distance between the powder particles settled in the sedimentation tank 2 is reduced, the dispersion becomes worse, and the contact area with the precursor reaction gas is reduced, thereby stopping or drastically reducing the chance of atomic layer deposition reaction. The powder particles that have not settled in the sedimentation tank 2 are suspended in the fluidizing gas and continue to react with the precursor reaction gas until a single layer coating of 0.1 to 0.2 nm is formed on the surface.

[0048] The double-cone rotating fluidized bed ALD fluidized reactor of the present invention can achieve uniform particle size of powder particles after atomic layer deposition coating.

[0049] When the precursor carried by the fluidizing gas reacts with the carbon powder particles to form a coated aluminum oxide at a temperature of 250°C and a pressure of 100 torr, the gas viscosity collinear diagram is queried to obtain the viscosity of the fluidizing gas, which is the viscosity of nitrogen at a temperature of 250°C and a pressure of 100 torr, μ = 0.0268 mPa·s. The density of nitrogen at a temperature of 250°C and a pressure of 100 torr is ρ = 0.0858 g / L. The operating flow rate V of the fluidizing gas in the atomic layer deposition reaction s The range is 200sccm. The density of carbon powder particles ρ s is 3.0g / ml, the diameter of carbon powder particles before coating is d q is 500nm, the carbon powder is coated with an alumina layer with a coating thickness of 21nm, and the diameter d after coating x is 542nm, the density of alumina is 4.0g / ml, and the density after coating is ρ xsIt is 3.216g / ml.

[0050] Therefore, the sedimentation velocity of the carbon powder particles before coating is u0 = 0.00458 m / s; the sedimentation velocity of the carbon powder particles when coated to 292 nm is u x =0.00576m / s. According to empirical data, when the powder particles are evenly dispersed, the time from the precursor reaction gas entering the fluidization chamber 1 to the complete reaction is T = 60s. Therefore, 60*u x >60*u0,60*u x =H, which can make all powder particles that do not exceed the ALD atomic layer deposition thickness stay in the fluidizing chamber 1 for a time greater than the time required for the atomic layer deposition reaction to be sufficient after the fluidizing chamber 1 is flipped.

[0051] In addition, the double-cone rotating fluidized bed ALD fluidized reactor of this embodiment can increase the diameter of the fluidizing chamber 1 to expand the loading amount of powder particles. The fluidized reactor with a larger diameter can also meet the requirements of controlling the thickness of the coating layer in the fluidized coating process when the powder particle loading amount is small, without the need to replace equipment.

Claims

1. A double-cone rotating fluidized bed ALD fluidized reactor, characterized in that: It includes a fluidizing chamber, a sedimentation tank, a rotating mechanism, an air duct, and a vacuum pump. The fluidizing chamber is a cylindrical box with unsealed upper and lower ends. The sedimentation channel runs through the upper and lower end surfaces of the cylindrical box. Two air ducts are connected to the outer side of the fluidizing chamber. The two air ducts are coaxial and symmetrically arranged relative to the fluidizing chamber. One air duct is connected to the fluidizing gas supply system and is used to transport fluidizing gas containing precursor reaction gas into the fluidizing chamber. The other air duct is connected to the exhaust gas detection system and the vacuum pump in sequence and is used to discharge the reaction exhaust gas. The two air ducts are centrally arranged on the outer side of the fluidizing chamber and are controlled by the rotating mechanism to make the fluidizing chamber be periodically flipped according to the flipping cycle. The bowl mouths of the two bowl-shaped sedimentation tanks face the sedimentation channel, and the two ends of the sedimentation channel are symmetrically closed to form a fluidized reactor. A discharge valve is installed on the conical surface of a sedimentation tank.

2. The double-cone rotating fluidized bed ALD fluidized reactor according to claim 1, characterized in that: The portion of the fluidizing chamber connected to the two air guide pipes is evenly arranged with equal flow holes communicating with the sedimentation channel and the air guide pipes.

3. The double-cone rotating fluidized bed ALD fluidized reactor according to claim 1, characterized in that: It also includes a stirrer, which is arranged in the fluidized reactor. A driving mechanism is installed at one end of another sedimentation tank away from the bowl mouth, and the driving mechanism is pivotally connected to the stirrer.

4. The double-cone rotating fluidized bed ALD fluidized reactor according to claim 3, characterized in that: The sedimentation trough is designed to be conical or spherical, and the agitator includes a stirring rod and stirring blades evenly arranged on the circumferential surfaces of both ends of the stirring rod. One end of the stirring rod is pivotally connected to the driving mechanism, and the other end of the stirring rod is close to the end of a sedimentation trough away from the bowl mouth. The stirring blades are spirally arranged around the stirring rod. The agitator is used to lift the larger powder particles first deposited at the bottom of the sedimentation trough at the bottom of the fluidized reactor to the upper part of the sedimentation trough, and at the same time make the smaller powder particles deposited later at the upper part of the sedimentation trough flow to the bottom of the sedimentation trough.

5. The double-cone rotating fluidized bed ALD fluidized reactor according to claim 1, characterized in that: At least two discharge valves are provided and are respectively installed at different heights of the conical surface of the sedimentation tank.

6. The double-cone rotating fluidized bed ALD fluidized reactor according to claim 1, characterized in that: The distance between the sedimentation tanks at both ends of the fluidized reactor is H, H = T*u x ; d x is the particle size of the powder particles when they reach the ALD atomic layer deposition thickness, g is the gravitational acceleration, ρ xs The particle size after coating is d x is the density of the powder particles, ρ is the density of the fluidizing gas under the conditions of atomic layer deposition reaction, μ is the viscosity of the fluidizing gas under the conditions of atomic layer deposition reaction, V s is the flow rate of fluidizing gas, T is the average cumulative time of the precursor reaction gas entering the fluidizing chamber after each turnover of the fluidizing chamber, and u x The particle size after coating is d x The sedimentation velocity of powder particles.

7. The method for coating powder particles in a double-cone rotating fluidized bed ALD fluidized reactor according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. The powder particles before coating are loaded into the deposition slot at the bottom of the fluidized reactor, and then the inert gas and exhaust gas are input through the air duct to replace the air in the fluidized reactor, and then the temperature and pressure in the fluidized reactor are increased to reach the reaction conditions; S2. The fluidizing chamber is flipped by a rotating mechanism, so that the sedimentation tank at the bottom of the fluidizing chamber is flipped to the upper part of the fluidizing chamber, so that the powder particles can fall downward, and at the same time, the fluidizing gas carrying the precursor reaction gas is input through the fluidizing pipe. Under the action of the fluidizing gas, the powder particles are fluidized and stay in the fluidizing chamber, and the surface of the powder particles and the precursor reaction gas undergo a gas-solidification chemical adsorption reaction to complete the deposition of the thin film. When the tail gas detection system monitors that the atomic layer deposition reaction is fully completed, the residual gas in the fluidized reactor is replaced with pure fluidizing gas; S3 repeats step S2, and replaces the type of precursor reaction gas carried by the fluidizing gas; S4. Repeat steps S2 to S3 until the number of repetitions of steps S2 to S3 reaches a set number of cycles, that is, the particle size of the powder particles reaches or exceeds the ALD atomic layer deposition thickness.

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