A double-cone rotary fluidized bed ALD fluidized reactor and a method for coating powder particles thereof

Abstract

The application discloses a double-cone rotary fluidized bed ALD fluidized reactor and a powder particle coating method thereof. The reactor comprises a fluidized chamber, a deposition tank, a rotating mechanism, gas guide pipes and a vacuum pump. The upper and lower ends of the fluidized chamber are closed. The outer side of the fluidized chamber is symmetrically connected with two gas guide pipes. One of the two gas guide pipes is connected with a fluidizing gas supply system and is used for conveying fluidizing gas containing precursor reaction gas into the fluidized chamber. The other gas guide pipe is sequentially connected with a tail gas detection system and the vacuum pump. The two gas guide pipes are controlled by the rotating mechanism and are used for periodically overturning the reactor according to a overturning period. After each overturning of the reactor, the powder with a large particle diameter is more quickly settled into the deposition tank than the powder with a small particle diameter. The powder particles settled into the deposition tank stop or sharply reduce the opportunity of atomic layer deposition reaction, and the powder particles not settled into the deposition tank are suspended in the fluidizing gas and continue to react with the precursor reaction gas to form a single-layer coating.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of vacuum atomic deposition coating, and particularly relates to a double-cone rotating fluidized bed ALD fluidized reactor and a method for coating powder particles. BACKGROUND

[0002] Atomic Layer Deposition (ALD) technology was first proposed by scientists from the Soviet Union and Finland in the 1960s and 1970s. The modern concept of "atomic layer deposition" originated from the "atomic layer epitaxy (ALE)" method invented by Dr. Suntola to prepare high-quality ZnS thin films on electroluminescent thin-film flat panel displays. As a special chemical vapor deposition technology, the reaction principle of atomic layer deposition is that two gas precursors are alternately introduced into the reaction chamber, and the deposition of the thin film is completed by the gas-solid chemical adsorption reaction on the surface of the substrate. From the deposition principle, it has the characteristics of self-saturation surface adsorption and self-limiting growth, can modify all surface active sites exposed to the gas phase environment in a self-limiting manner, and can realize the coating of single micro-nano particles. Due to the characteristics of large specific surface area and high specific surface energy of micro-nano powder particles, it is easy for them to agglomerate during coating, and it is difficult for the precursors to completely saturate on the surface of the micro-nano powder particles, so that the coated nano thin film is not uniform and even agglomerates, which is a key problem 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, the traditional ALD coating method mainly uses static coating method, that is, the particles are accumulated in the sample fixing net, and the saturation adsorption of the entire surface is achieved by relying on the diffusion of the precursor molecules. This method does not have an external field to overcome the agglomeration force, and is only suitable for a small amount of well-dispersed particles, and is not suitable for systems that are easy to form secondary particle agglomeration. At the same time, the gap between the particles is small, and the diffusion in the gap is limited, which easily leads to uneven adsorption, long reaction period and other problems.

[0004] Using a fluidized bed to uniformly distribute powder particles in the fluidized bed can overcome the agglomeration force, but requires a sufficient flow of fluidizing gas, which consumes a lot of energy. In addition, the allowable loading mass of powder particles in the fluidized bed cannot be proportionally enlarged when the size of the fluidized bed is enlarged. Increasing the loading amount of powder particles will cause the volume and height of the equipment to increase exponentially, which forces the expansion and heightening of the factory building. Therefore, a new type of fluidized bed design is urgently needed to make the precursors react to better coat the powder and obtain better coating rate, and the equipment can be easily enlarged to increase the loading amount of powder particles and meet the needs of industrial-scale production. SUMMARY

[0005] In view of the above problems, the present application provides a double-cone rotary fluidized bed ALD fluidized reactor, comprising a fluidized chamber, a deposition tank, a rotating mechanism, a gas guide pipe, and a vacuum pump, wherein the fluidized chamber is a columnar box with open upper and lower ends, a sedimentation channel penetrates through the upper and lower end faces of the columnar box, two gas guide pipes are connected to the outer side of the fluidized chamber, the two gas guide pipes are coaxial and symmetrically arranged relative to the fluidized chamber, one of the two gas guide pipes is connected to a fluidizing gas supply system for conveying fluidizing gas containing precursor reaction gas into the fluidized chamber, the other gas guide pipe is connected to a tail gas detection system and a vacuum pump in sequence for discharging reaction tail gas, the two gas guide pipes are centrally arranged on the outer side of the fluidized chamber and are controlled by the rotating mechanism for periodically turning the fluidized chamber by a turning period, two bowl-shaped deposition tanks have their bowl openings facing the sedimentation channel and symmetrically closing the two ends of the sedimentation channel to form a fluidized reactor, and the conical surface of one of the deposition tanks is provided with a discharge valve.

[0006] The part where the fluidized chamber is connected to the two gas guide pipes is uniformly provided with uniform flow holes connecting the sedimentation channel and the gas guide pipes.

[0007] The double-cone rotary fluidized bed ALD fluidized reactor further comprises a stirrer arranged in the fluidized reactor, and the end of the other deposition tank away from the bowl opening is provided with a driving mechanism, and the driving mechanism is pivotally connected to the stirrer.

[0008] The deposition tank is designed in a conical or spherical cap shape, the stirrer comprises a stirring rod and stirring blades uniformly 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 one of the deposition tanks away from the bowl opening, the stirring blades are arranged in a spiral around the stirring rod, and the stirrer is used for lifting the powder particles with a larger particle size, which are first deposited at the bottom of the deposition tank at the bottom of the fluidized reactor, to the upper part of the deposition tank, and simultaneously making the powder particles with a smaller particle size, which are later deposited at the upper part of the deposition tank, flow to the bottom of the deposition tank.

[0009] The discharge valve is arranged at least twice at different heights of the conical surface of the sedimentation tank.

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

[0011]

[0012] d x is the particle size of the powder particles when the ALD atomic layer deposition thickness is reached, g is the acceleration of gravity, and p xs is the particle size d xthe density of the powder particles, p is the density of the fluidization gas under the atomic layer deposition reaction condition, m is the viscosity of the fluidization gas under the atomic layer deposition reaction condition, V s is the flow rate of the fluidization gas, T is the average value of the cumulative time of the precursor reaction gas introduced into the fluidization chamber after each time the fluidization chamber is turned over, u x is the settling velocity of the powder particles with a particle size of d x after coating.

[0013] The method for coating powder particles by using the double-cone rotary fluidized bed ALD fluidization reactor comprises the following steps:

[0014] S1. Filling the powder particles before coating from the deposition slot at the bottom of the fluidization reactor, then inputting the inert gas and exhaust gas through the gas guide pipe to replace the air in the fluidization reactor, and then heating and pressurizing the fluidization reactor to reach the reaction condition;

[0015] S2. Turning over the fluidization chamber by the rotating mechanism to turn the settling tank at the bottom of the fluidization chamber to the upper part of the fluidization chamber, so that the powder particles can settle downward, and at the same time, the fluidization gas carrying the precursor reaction gas is input through the fluidization pipe, under the action of the fluidization gas, the powder particles are fluidized and stay in the fluidization chamber, the surface of the powder particles reacts with the precursor reaction gas to complete the deposition of the thin film, and then the residual gas in the fluidization reactor is replaced by pure fluidization gas when the tail gas detection system monitors that the atomic layer deposition reaction is completed;

[0016] S3. Repeating step S2, and changing the type of the precursor reaction gas carried by the fluidization gas;

[0017] S4. Repeating steps S2-S3 until the number of times of repeating steps S2-S3 reaches the set cycle number, 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 application has the following advantages and beneficial effects:

[0019] Through the double-cone rotary fluidized bed ALD fluidization reactor, the powder particles can achieve uniform particle size after completing the atomic layer deposition coating.

[0020] During the coating process, after each time the fluidization chamber is turned over, the powder particles are subjected to resistance during the settling process, so that the powder particles with large particle diameters settle faster than the powder particles with small particle diameters, and the particle size of the powder particles in the settling tank is arranged in ascending order from top to bottom, the spacing between the powder particles settled in the settling tank is reduced, the dispersibility is poor, and the contact area with the precursor reaction gas is reduced, so that the atomic layer deposition reaction opportunity is stopped or sharply reduced, and the powder particles that have not settled in the settling tank are suspended in the fluidization gas and continue to react with the precursor reaction gas until a 0.1-0.2 nm single-layer coating is formed on the surface.

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

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

[0023] In order to make the invention purpose, technical scheme and invention advantage of the present application more clearly, the present application will be further explained in detail below in combination with the drawings of the specification.

[0024] As shown in the drawings, Figure 1 A double-cone rotary fluidized bed ALD fluidized reactor includes a fluidized chamber 1, a deposition tank 2, a stirrer, a rotating mechanism, a gas guide pipe 5, and a vacuum pump. The fluidized chamber 1 is a cylindrical box body with open upper and lower ends. The settling channel penetrates the upper and lower end faces of the cylindrical box body. Two gas guide pipes 5 are connected to the outer side of the fluidized chamber 1. The two gas guide pipes 5 are coaxial and symmetrically arranged relative to the fluidized chamber 1. One gas guide pipe 5 is connected to a fluidizing gas supply system for delivering fluidizing gas containing precursor reaction gas into the fluidized chamber 1. The other gas guide pipe 5 is connected to a tail gas detection system and a vacuum pump in sequence for discharging reaction tail gas. The two gas guide pipes 5 are centrally arranged on the outer side of the fluidized chamber 1 and are controlled by the rotating mechanism for periodically turning the fluidized chamber 1 by a turning period. The parts of the fluidized chamber 1 connecting the two gas guide pipes 5 are uniformly provided with uniform flow holes 6 connecting the settling channel and the gas guide pipe 5.

[0025] The bowl openings of the two bowl-shaped settling tanks 2 face the settling channel and symmetrically close the two ends of the settling channel to form a fluidized reactor. The stirrer is arranged in the fluidized reactor. A driving mechanism 4 is installed at the end of one settling tank 2 away from the bowl opening. The driving mechanism 4 is pivotally connected to the stirrer. A discharge valve 7 is installed on the conical surface of the other settling tank 2. Multiple discharge valves 7 can be provided and installed at different heights on the conical surface of the settling tank 2 for discharging powder particles at different depths in the settling tank 2. When the settling tank 2 is rotated to the upper position with the fluidized chamber 1, the discharge valve 7 is also used to load the powder particles.

[0026] The deposition tank 2 can be designed as a cone or a spherical cap, the stirrer comprises a stirring rod and stirring blades uniformly arranged on the circumferential surface of both ends of the stirring rod, one end of the stirring rod is pivotally connected with the driving mechanism 4, and the other end of the stirring rod is close to one end of the deposition tank 2 away from the bowl opening. The stirring blades are spirally arranged around the stirring rod. When the stirring rod is operated to rotate, the stirrer is used to lift the powder particles with a larger particle size, which are firstly deposited on the bottom of the deposition tank 2 at the bottom of the fluidized reactor, to the upper part of the deposition tank 2, and at the same time, the powder particles with a smaller particle size, which are secondly deposited on the upper part of the deposition tank 2, are flowed to the bottom of the deposition tank 2, so as to shorten the time of the powder particles with a larger particle size to settle into the lower deposition tank 2 and prolong the time of the powder particles with a smaller particle size to settle into the lower deposition tank 2 after the fluidized chamber 1 is operated to be turned over.

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

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

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

[0030]

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

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

[0033] V s is the flow rate of the fluidizing gas, A0 is the transverse cross-sectional area of the fluidized chamber 1, g is the acceleration of gravity, ρ s is the density of the powder particles before coating, ρ xs is the density of the powder particles with a particle size of d x after coating, ρ is the density of the fluidizing gas under the atomic layer deposition reaction condition, μ is the viscosity of the fluidizing gas under the atomic layer deposition reaction condition, 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 before coating, and the transverse cross section is a plane perpendicular to the central axes of the two deposition tanks 2.

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

[0035] S1. The powder particles before coating are first filled into the fluidized reactor and placed in the deposition groove 2 at the bottom, then the air in the fluidized reactor is replaced with inert gas, and the fluidized reactor is heated and pressurized to reach the reaction conditions;

[0036] S2. The deposition groove 2 at the bottom is flipped to the upper part of the fluidized chamber 1 by the rotating mechanism, so that the powder particles can dust down downward, and the fluidizing gas carrying the precursor reaction gas is input through the gas guide pipe 5, under the action of the fluidizing gas, the powder particles are fluidized and stay in the fluidized chamber, the surface of the powder particles reacts with the precursor reaction gas to complete the deposition of the thin film, and when the tail gas detection system detects that the atomic layer deposition reaction is completed, the residual gas in the fluidized reactor is replaced with pure fluidizing gas;

[0037] S3. Repeat step S2, and change the type of precursor reaction gas carried by the fluidizing gas;

[0038] S4. Repeat steps S2-S3 until the number of times of repeating steps S2-S3 reaches the 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-S3 are a complete ALD growth cycle, which can be divided into four steps:

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

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

[0042] 3. Pulse the second precursor to perform a chemical reaction on the monolayer surface formed by the first precursor to obtain the desired thin film material;

[0043] 4. Inert carrier gas blows away the remaining precursor and reaction byproducts.

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

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

[0046] Connect the differential electrochemical mass spectrometer (DEMS) with the tail gas system of ALD. By testing the content change curve of methane, the reaction of trimethylaluminum, water and the surface of the powder in the reactor is determined. If the methane content in the reaction tail gas decreases from the peak to below the threshold value and does not increase, and the content of trimethylaluminum or water in the tail gas does not decrease, it is determined that the atomic layer deposition reaction is sufficient.

[0047] During the coating process, after each rotation of the fluidized chamber 1, the powder particles are subjected to resistance during the settling process, so that the powder with a larger particle diameter settles faster than the powder with a smaller particle diameter. The particle size of the powder particles in the deposition tank 2 is therefore arranged in ascending order from top to bottom. The spacing between the powder particles settled in the deposition tank 2 is reduced, the dispersion is poor, and the contact area with the precursor reaction gas is reduced. Therefore, the opportunity for atomic layer deposition reaction is stopped or sharply reduced. The powder particles that have not settled in the deposition tank 2 are suspended in the fluidized gas and continue to react with the precursor reaction gas until a 0.1-0.2 nm single-layer coating is formed on the surface.

[0048] Through the double-cone rotary fluidized bed ALD fluidized reactor of the present application, the powder particles can achieve uniform particle size after completing atomic layer deposition coating.

[0049] When the precursor carried by the fluidized gas reacts with the carbon powder particles to form an aluminum oxide coating at a temperature of 250℃ and a pressure of 100torr, refer to the gas viscosity collinear diagram to obtain the viscosity of the fluidized gas, which is the viscosity of nitrogen at a temperature of 250℃ and a pressure of 100torr, μ=0.0268mPa·s. The density of nitrogen at a temperature of 250℃ and a pressure of 100torr is ρ=0.0858g / L. The operating flow rate V of the fluidized gas in the atomic layer deposition reaction is in the range of 200sccm. The density of the carbon powder particles is ρ=3.0g / ml, the diameter of the carbon powder particles before coating is d=500nm, the coating thickness of the carbon powder is 21nm, the diameter of the carbon powder after coating is d=542nm, the density of the aluminum oxide is 4.0g / ml, and the density of the coated powder is ρ=3.0g / ml. s s q x xs ​​​​3.216 g / 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 after coating to 292 nm is u x = 0.00576 m / s. According to the empirical data, when the powder particles are uniformly dispersed, the time for the precursor reaction gas to flow from the input fluidized chamber 1 to the reaction chamber is T = 60 s. Therefore, 60*u x > 60*u0, 60*u x = H, the time for all the powder particles that do not exceed the ALD atomic layer deposition thickness to stay in the fluidized chamber 1 after the fluidized chamber 1 is turned over is greater than the time required for the atomic layer deposition reaction to be sufficient.

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

Claims

1. A biconical rotating fluidized bed ALD fluidized reactor, characterized in that, The fluidized chamber, the deposition groove, the rotating mechanism, the air guide pipe and the vacuum pump are provided, the fluidized chamber is a columnar box with open upper and lower ends, the sedimentation channel penetrates the upper and lower end faces of the columnar box, two air guide pipes are connected to the outer side of the fluidized chamber, the two air guide pipes are coaxial and symmetrically arranged relative to the fluidized chamber, one air guide pipe is communicated with the fluidized gas supply system and is used for conveying the fluidized gas containing the precursor reaction gas into the fluidized chamber, the other air guide pipe is communicated with the tail gas detection system and the vacuum pump in sequence and is used for discharging the reaction tail gas, the two air guide pipes are centrally arranged on the outer side of the fluidized chamber and are controlled by the rotating mechanism and are used for periodically overturning the fluidized chamber according to the overturning period, the bowl mouths of the two bowl-shaped deposition grooves face the sedimentation channel and symmetrically seal the two ends of the sedimentation channel to form the fluidized reactor, and the conical surface of one deposition groove is provided with a discharge valve; the overturning makes the deposition groove at the bottom of the fluidized chamber overturn to the upper part of the fluidized chamber; The deposition groove is designed in a conical or spherical cap shape and is provided with a stirrer, the stirrer comprises a stirring rod and stirring blades uniformly arranged on the circumferential surfaces of both ends of the stirring rod, one end of the stirring rod is pivotally connected with a driving mechanism, the other end of the stirring rod is close to one end of the deposition groove away from the bowl mouth, the stirring blades are spirally arranged around the stirring rod, and the stirrer is used for lifting the powder particles with large particle size, which are firstly deposited at the bottom of the deposition groove at the bottom of the fluidized reactor, to the upper part of the deposition groove and simultaneously making the powder particles with small particle size, which are secondly deposited at the upper part of the deposition groove, flow to the bottom of the deposition groove.

2. The dual cone rotating fluidized bed ALD fluidized reactor of claim 1, wherein, The positions, where the fluidized chamber is connected with the two air guide pipes, are uniformly provided with uniform flow holes, which are communicated with the sedimentation channel and the air guide pipe.

3. The dual cone rotating fluidized bed ALD fluidized reactor of claim 1, wherein, The discharge valve is provided at least two and is arranged at different heights of the conical surface of the deposition groove.

4. The method of coating powder particles in a biconical rotating fluidized bed ALD fluidized reactor according to any one of claims 1 to 3, wherein The method comprises the following steps: S1. filling the powder particles before coating into the bowl mouth of the deposition groove at the bottom of the fluidized reactor, then inputting the inert gas and the exhaust gas through the air guide pipe to replace the air in the fluidized reactor, and then increasing the temperature and pressure in the fluidized reactor to reach the reaction condition; S2. overturning the fluidized chamber by the rotating mechanism to make the deposition groove at the bottom of the fluidized chamber overturn to the upper part of the fluidized chamber, so that the powder particles can be downwardly settled, and at the same time, the fluidized gas carrying the precursor reaction gas is inputted through the air guide pipe, the powder particles are fluidized and stayed in the fluidized chamber under the action of the fluidized gas, the surface of the powder particles is subjected to the gas-solid chemical adsorption reaction with the precursor reaction gas to complete the deposition of the thin film, and the residual gas in the fluidized reactor is replaced by the pure fluidized gas when the atomic layer deposition reaction is fully completed by the tail gas detection system; S3. repeating the step S2 and changing the type of the precursor reaction gas carried by the fluidized gas; S4. repeating the steps S2-S3 until the number of times of repeating the steps S2-S3 reaches the set cycle number, that is, the particle size of the powder particles reaches or exceeds the ALD atomic layer deposition thickness.

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