Method for improving sphericity of glass microsphere under microgravity condition

Abstract

The present invention relates to the technical field of the preparation of glass microspheres, and to a method for improving sphericity of a glass microsphere under microgravity condition. A drop tower device is used in the method, so that a microgravity sintering furnace located in the drop tower device can freely fall, and a microgravity environment of the microgravity sintering furnace is realized by means of a drop tower method. The present method comprises a pretreatment stage, a gas extraction stage, a heating stage, a feeding stage, a sintering stage, and a collection stage. The present invention relates to a method for forming a glass microsphere into a spherical shape by means of microgravity in a vacuum environment, which can effectively reduce the influence of gravity on the sphericity of the glass microsphere during spheroidization and greatly improve the sphericity of the glass microsphere. In addition, the method is also relatively simple.

Description

Method for improving sphericity of glass microbeads in microgravity state TECHNICAL FIELD

[0001] The present application relates to the technical field of glass microbead preparation, and particularly relates to a method for improving sphericity of glass microbeads in microgravity state. BACKGROUND

[0002] Glass microbeads are a widely used inorganic filler material. Glass microbeads are processed from borosilicate and have a particle size of 1-250 μm. Glass microbeads have the same chemical composition as glass fibers, also have low thermal conductivity, good chemical stability and other advantages, and due to their spherical appearance, glass microbeads have very good flowability and dispersibility. In practical applications, glass microbeads with high sphericity are more popular with the combined material, mainly for the following reasons:

[0003] (1) Improve uniformity and stability of materials

[0004] Glass microbeads with high sphericity are arranged more closely and orderly in the material, which helps to improve the uniformity and stability of the material. In coatings, spherical microbeads can provide a smoother surface effect, reduce the generation of bubbles and cracks, and thus improve the durability and aesthetics of the coating.

[0005] (2) Influence on mechanical properties

[0006] The sphericity of glass microbeads also has a significant impact on their mechanical properties. Spherical microbeads can better withstand pressure when under stress because their shape allows for more even stress distribution. This means that at the same volume, microbeads with high sphericity can provide higher compressive strength and bending strength.

[0007] (3) Influence on thermal conductivity

[0008] The sphericity of glass microbeads also affects their thermal conductivity. The surface area of spherical microbeads is relatively small, which helps to reduce the transfer of heat, so in applications where thermal insulation materials are needed, microbeads with high sphericity can provide better thermal insulation effect.

[0009] (4) Influence on rheological properties

[0010] In liquid or semi-solid materials, the rheological properties of spherical microbeads are also affected by sphericity. Microbeads with high sphericity move more smoothly in the fluid, which helps to improve the flowability and processability of the material, and also improves the surface levitation problem of the material, improves the warping problem of the material, and has a good effect on improving the wear resistance of the workpiece

[0011] In summary, sphericity has a wide range of effects on the application of glass microbeads, including improving the uniformity and stability of materials, improving mechanical properties, affecting thermal conductivity, and changing rheological properties. When designing and using glass microbeads, these factors must be considered to ensure that the material meets the requirements of a specific application.

[0012] In the actual production process of glass microbeads, the production equipment and process directly determine the level of sphericity of the microbeads. For example, if the melting environment and atmosphere do not match, or the cooling speed is uneven, it may cause the shape of the microbeads to distort, reducing the sphericity. For example, as shown in Figures 1 and 2, Figure 1 is a solid glass microbead produced by a conventional method, and the sphericity shown in Figure 1 is 85%-88% as measured by a sphericity instrument. Figure 2 is a polarized light microscope photograph of the solid glass microbead in Figure 1, which can more intuitively show the sphericity of the solid glass microbead shown in Figure 1. SUMMARY

[0013] The present application is directed to the problem of low sphericity of existing glass microbeads, which cannot be solved by subsequent screening. The present application provides a method for preparing glass microbeads. The idea of the present application is to strictly control the melting environment to prepare glass microbeads, which can achieve higher sphericity under the same particle size. At the same time, the preparation method of the ultra-high sphericity glass microbead is relatively simple.

[0014] It adopts the following technical scheme:

[0015] A method for improving the sphericity of glass microbeads in a microgravity state:

[0016] It uses a falling tower device, and the release system in the falling tower device releases the microgravity sintering furnace in the tower to do free fall, realizing the microgravity environment of the microgravity sintering furnace.

[0017] The method for improving the sphericity of glass microbeads in a microgravity state comprises the following steps:

[0018] S1, pretreatment stage: cleaning the surface of glass microbead powder and removing impurities that may affect the sintering quality;

[0019] S2, air extraction stage: vacuumizing the falling tower device to 30%-60% vacuum degree and maintaining stable, and extracting air from the microgravity sintering furnace and discharging the waste gas in the microgravity sintering furnace, so that the internal air pressure range of the microgravity sintering furnace is consistent with the internal air pressure range of the falling tower device;

[0020] S3, heating stage: gradually heating the microgravity sintering furnace to the sintering temperature of the glass microbead powder;

[0021] S4, feeding stage: the microgravity sintering furnace forms a microgravity environment by free fall, and in the microgravity environment, the glass microbead powder is sprayed into the microgravity sintering furnace by compressing the air pressure with a compression pump.

[0022] S5, sintering forming stage: keeping constant sintering temperature of the microgravity sintering furnace in the microgravity environment to sinter the glass microsphere powder; after the sintering of the glass microsphere powder is completed, the temperature in the microgravity sintering furnace is reduced to below the sintering temperature, so that the ultra-high sphericity glass microspheres are formed;

[0023] S6, collecting stage: after the free fall of the microgravity sintering furnace is completed, the microgravity sintering furnace is naturally cooled, and the cooled ultra-high sphericity glass microspheres are collected.

[0024] Further, the sintering temperature is 1300-1500 DEG C.

[0025] Further, in the step S4, the delivery amount of the glass microsphere powder is 0.2-0.4 kg per kg of gas.

[0026] Further, the glass microsphere powder is solid or hollow.

[0027] Further, the tower falling device further comprises a tower body, a vacuum pumping system for pumping the tower body, a deceleration recovery system for recovering and decelerating the microgravity sintering furnace to stop when the free fall of the microgravity sintering furnace is completed, a control system for accurately controlling and monitoring the whole process, and a measurement system for measuring and recording various physical parameters in the whole process; the release system is used for freely releasing the microgravity sintering furnace from the high tower body.

[0028] Further, the tower falling device further comprises auxiliary facilities for controlling the experimental environment, data processing and analysis.

[0029] The present application has the following beneficial effects compared with the prior art:

[0030] The method for preparing glass microspheres by microgravity can effectively reduce the influence of gravity on the sphericity in the process of forming glass microspheres, and greatly improve the sphericity of glass microspheres.

[0031] Specifically: the reason that glass microspheres can form approximately circular shape in combustion is mainly related to the physical properties of the material and the thermodynamic conditions in the heating process. The surface tension of glass in the molten state is a kind of intermolecular attraction, which makes the liquid glass tend to form the shape with the smallest area, that is, spherical shape. In the combustion process, the temperature inside the glass microspheres rises, causing the material to expand. Because the radius of curvature of the sphere is the same in all directions, this uniform expansion helps to maintain its spherical shape. At the same time, in the heating process, the gas around the glass microspheres will be affected by heat and expand, forming a dynamic fluid environment. This environment can promote the microspheres to maintain spherical shape, because the fluid resistance will resist irregular changes in shape. In the conventional combustion heating process, the shape of the flame is related to the air convection under the influence of gravity. The hot gas in the flame will rise due to its small density, while the surrounding cold air will sink due to its large density, forming convection. This convection will cause the flame to change in shape, and the flame will rise upward, forming a conical or funnel shape. This conical or funnel-shaped flame combined with the condition of gravity will cause the thermal stress of the glass microspheres to concentrate in one direction during the ball forming process, resulting in deformation and reducing the sphericity of the overall glass solid microspheres.

[0032] Although the effect of gravity on many conventional combustion heating processes is not obvious, for some high-requirement glass microsphere ball forming processes, the theory of ignoring the effect of gravity often cannot give a satisfactory explanation of the sphericity. The size of the buoyancy effect in the glass microsphere combustion forming process can be estimated by two dimensionless parameters, namely the Grashof number Gr = (Δρ / ρ)gL3 / ν2, which represents the ratio of buoyancy to viscous force, and the Richardson number Ri = (Δρ / ρ)gL / U2, which represents the ratio of buoyancy to inertial force, where Δρ and ρ are the density difference and density, g is the acceleration of gravity, L is the characteristic size, ν is the kinematic viscosity coefficient, and U is the characteristic velocity. It can be seen that in order to reduce the effect of buoyancy, three methods can be taken: reducing the characteristic size L; reducing the density difference, increasing the kinematic viscosity coefficient; reducing the acceleration of gravity g.

[0033] The first method is limited by the minimum size limit and the observation means, and it is difficult to obtain ideal results. The second method affects the chemical reaction. The third method has no defects. The combustion under microgravity has the following characteristics: the natural convection is almost eliminated, and the combustion of stationary and low-speed flow can be studied; the secondary forces and phenomena such as electrostatic force, thermophoretic force, thermal capillary force and diffusion, which are covered by the buoyancy and its induced effects, can be shown; the gravity sedimentation is almost eliminated, and the combustion of stable, free-suspended droplets, particles and dust can be studied; the elimination of the buoyancy can increase the time and length scale of the combustion. Therefore, according to the above basic theory, the method for preparing glass microspheres under vacuum environment by using microgravity can effectively reduce the influence of gravity on the sphericity of glass microspheres in the process of forming glass microspheres, and greatly improve the sphericity of glass microspheres. BRIEF DESCRIPTION OF DRAWINGS

[0034] Fig. 1 is an electron micrograph of glass microspheres with low sphericity under the conventional method of the prior art;

[0035] Fig. 2 is a polarizing micrograph of glass microspheres with low sphericity under the conventional method of the prior art;

[0036] Fig. 3 is a schematic view of the structure of a falling tower device in an embodiment of the present application;

[0037] Fig. 4 is an electron micrograph of glass microspheres with high sphericity under the method of the present application;

[0038] Fig. 5 is a polarizing micrograph of glass microspheres with high sphericity under the method of the present application.

[0039] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0040] In order to make the present application clearer, a method for improving the sphericity of glass microspheres under microgravity is further described below in conjunction with the drawings. The specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0041] The method for improving the sphericity of glass microbeads in microgravity state uses a falling tower device 100, so that the microgravity sintering furnace 200 in the falling tower device 100 can do free fall, and the microgravity environment of the microgravity sintering furnace 200 is realized by the falling tower method. The falling tower method is a technology for simulating a microgravity environment through free fall motion. In this method, the experimental equipment or sample is placed in a closed experimental equipment, which is then released from a tall tower with a certain degree of vacuum, and free fall is performed. When the experimental equipment falls freely in the tower, all objects inside the equipment will experience the same acceleration, i.e. the acceleration of gravity, due to the lack of external force. During the falling process, these objects are stationary relative to each other, and the objects inside the experimental equipment do not feel gravity relative to each other, thereby simulating a microgravity or vacuum state.

[0042] In connection with the present application, the falling tower method requires the use of a falling tower device 100, as shown in Figure 3. The falling tower device 100 includes a tall tower body 110, a release system 120 at the top of the tower body 110, a vacuum pumping system 130 in the tower body 110, a deceleration recovery system 140 at the lower part of the tower body 110, a control system 150 for precise control and monitoring of the entire process, a measurement system 160 for measuring and recording various physical parameters during the process, and auxiliary facilities for experimental environment control, data processing and analysis.

[0043] The microgravity sintering furnace 200 has the same structure as a conventional sintering furnace, and also has a heating unit, a vacuum pumping unit, a gas inlet and outlet unit, a feeding unit, etc. It has the traditional functions of air pumping, heating, heat supply, sintering, etc. The difference is that the microgravity sintering furnace 200 can do free fall in the tower body 110. In the free fall motion of the microgravity sintering furnace 200, the delivery path of the gas, powder and energy supply can be realized by a long enough flexible delivery pipe, which does not affect the free fall of the microgravity sintering furnace 200. Related data transmission can be realized by wired or wireless means. Of course, other ways can also be used to deliver the gas, powder and energy of the microgravity sintering furnace 200 without affecting the free fall motion.

[0044] The method for improving the sphericity of glass microbeads in microgravity state includes the following steps:

[0045] S1, pretreatment stage: clean the surface of the glass microbead powder and remove impurities that may affect the sintering quality.

[0046] S2, the air extraction stage: the inside of the tower body 110 of the tower falling device is extracted to 30%-60% vacuum degree by the vacuum extraction system 130 and maintained stable; the micro-gravity sintering furnace 200 is extracted and the internal waste gas is discharged, so that the internal air pressure range of the micro-gravity sintering furnace is consistent with the internal air pressure range of the tower falling device; this step is crucial for excluding other gases in the furnace and realizing micro-gravity heating.

[0047] S3, the heating stage: the micro-gravity sintering furnace 200 is gradually heated until the sintering temperature of the glass microsphere powder. In this embodiment, the sintering temperature is 1300-1500°C.

[0048] S4, the feeding stage: the micro-gravity sintering furnace 200 is released to do free fall by the releasing system 120, so that the micro-gravity sintering furnace 200 is in a micro-gravity environment. In this environment, the glass microsphere powder is sprayed into the micro-gravity sintering furnace 200 by compressing the air, that is, the feeding is carried out in the process of free fall of the micro-gravity sintering furnace 200. Among them, about 0.2-0.4 kg of glass microsphere powder is contained in every kg of gas.

[0049] S5, the sintering forming stage: the glass microsphere powder is sintered by keeping the constant sintering temperature of the micro-gravity sintering furnace in the micro-gravity environment. When the sintering of the glass microsphere powder is completed, the temperature in the micro-gravity sintering furnace 200 is reduced to below the sintering temperature, for example, the heat source switch of the micro-gravity sintering furnace 200 can be turned off. When the temperature in the micro-gravity sintering furnace is lower than the sintering temperature, the ultra-high sphericity glass microsphere is formed, and the sphericity no longer changes. The duration of this stage is about 2-3 s, which can ensure that the glass microsphere is fully melted and re-crystallized to form. This stage is the most critical part of the whole preparation process, which determines the microstructure and final performance of the microsphere.

[0050] When the heat source in the micro-gravity sintering furnace is turned off at the end of the sintering of the glass microsphere powder before the end of the free fall of the tower, the temperature in the micro-gravity sintering furnace is lower than the sintering temperature,

[0051] S6, the collection stage: when the free fall of the micro-gravity sintering furnace 200 is completed, it can be recovered and decelerated to stop by the deceleration recovery system 140, and at the same time, the sintering of the glass microsphere powder is completed. Then the micro-gravity sintering furnace 200 is naturally cooled, usually to 30-60°C, so as to facilitate collection, and then the ultra-high sphericity glass microsphere after cooling is collected by the collecting device.

[0052] The following experimental tests are carried out by using this method:

[0053] Hollow glass microsphere series:

[0054] Group 1

[0055] Select M series hollow glass microsphere raw powder, the hollow glass microsphere obtained under normal sintering environment has a sphericity of 85%-87%, and the compressive strength is 6,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0056] By using the method, the vacuum degree of the falling tower device is maintained at 30%, and the free-fall time of the microgravity sintering furnace 200 is about 5-6 s. In a limited time, 0.5-1 kg of hollow glass microsphere raw powder can be sintered. The sintered hollow glass microsphere powder is collected, gravity elutriated and dried, the sphericity is increased to 90%, and the compressive strength can be increased from the initial 6,000 Psi (20% broken rate) to 8,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0057] Implementation group 2

[0058] Select M series hollow glass microsphere raw powder, the hollow glass microsphere obtained under normal sintering environment has a sphericity of 85%-87%, and the compressive strength is 6,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0059] By using the method, the vacuum degree of the falling tower device is maintained at 50%, and the free-fall time of the microgravity sintering furnace 200 is about 5-6 s. In a limited time, 0.5-1 kg of hollow glass microsphere raw powder can be sintered. The sintered hollow glass microsphere powder is collected, gravity elutriated and dried, the sphericity is increased to 92%, and the compressive strength can be increased from the initial 6,000 Psi (20% broken rate) to 9,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0060] Implementation group 3

[0061] Select M series hollow glass microsphere raw powder, the hollow glass microsphere obtained under normal sintering environment has a sphericity of 85%-87%, and the compressive strength is 6,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0062] By using the method, the vacuum degree of the falling tower device is maintained at 60%, and the free-fall time of the microgravity sintering furnace 200 is about 5-6 s. In a limited time, 0.5-1 kg of hollow glass microsphere raw powder can be sintered. The sintered hollow glass microsphere powder is collected, gravity elutriated and dried, the sphericity is increased to 95%, and the compressive strength can be increased from the initial 6,000 Psi (20% broken rate) to 11,000 Psi (20% broken rate) detected by a hollow glass microsphere (gas) pressure tester.

[0063] Solid glass microsphere series:

[0064] Group 4

[0065] The solid glass microsphere powder is selected, and the spheroidization degree of the solid glass microsphere formed by sintering in a traditional sintering furnace is 85%-88%, as shown in FIG. 1 and FIG. 2.

[0066] According to the method, the vacuum degree of the falling tower device is kept at 30%, and the free falling time of the microgravity sintering furnace 200 is about 5-6s. In a limited time, 1-2kg of the solid glass microsphere powder can be sintered. The spheroidization degree can be increased to 92% through detection, as shown in FIG. 4 and FIG. 5.

[0067] Group 5

[0068] The solid glass microsphere powder is selected, and the spheroidization degree of the solid glass microsphere formed by sintering in a traditional sintering furnace is 85%-88%, as shown in FIG. 1 and FIG. 2.

[0069] According to the method, the vacuum degree of the falling tower device is kept at 50%, and the free falling time of the microgravity sintering furnace 200 is about 5-6s. In a limited time, 1-2kg of the solid glass microsphere powder can be sintered. The spheroidization degree can be increased to 95% through detection.

[0070] Group 6

[0071] The solid glass microsphere powder is selected, and the spheroidization degree of the solid glass microsphere formed by sintering in a traditional sintering furnace is 85%-88%, as shown in FIG. 1 and FIG. 2.

[0072] According to the method, the vacuum degree of the falling tower device is kept at 60%, and the free falling time of the microgravity sintering furnace 200 is about 5-6s. In a limited time, 1-2kg of the solid glass microsphere powder can be sintered. The spheroidization degree can be increased to 97% through detection.

[0073] As can be seen from the above test groups, the method can effectively reduce the influence of gravity on the spheroidization degree in the glass microsphere forming process, and greatly improve the spheroidization degree of the glass microsphere. Meanwhile, the method is relatively simple.

[0074] The above embodiments of the present application are merely examples for clearly illustrating the present application, and are not intended to limit the implementation manners of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the implementation manners are not required or can not be exhausted. The changes or variations which are extended from the essential spirit of the present application still belong to the protection scope of the present application.

Claims

1. A method for improving the sphericity of glass microspheres under microgravity conditions, characterized in that: It uses a drop tower device (100), and the release system (120) in the drop tower device (100) releases the microgravity sintering furnace (200) in the tower to make free fall, thereby realizing the microgravity environment of the microgravity sintering furnace (200); The method for improving the sphericity of glass microspheres under microgravity conditions includes the following steps: S1. Pretreatment stage: Clean the surface of the glass microsphere powder to remove impurities that may affect the sintering quality; S2, Vacuuming stage: Vacuum the dropping tower device (100) to 30%-60% and maintain it stable. Vacuum the microgravity sintering furnace (200) and exhaust its internal waste gas so that the internal gas pressure range of the microgravity sintering furnace (200) is consistent with the internal gas pressure range of the dropping tower device (100). S3, Heating stage: Gradually raise the temperature inside the microgravity sintering furnace (200) to the sintering temperature of the glass microsphere powder; S4. Feeding stage: The microgravity sintering furnace (200) forms a microgravity environment by free fall. In the microgravity environment, the glass microsphere powder is sprayed into the microgravity sintering furnace (200) by pressurizing the air through a compression pump. S5, Sintering and forming stage: The glass microsphere powder is sintered in a microgravity sintering furnace (200) at a constant sintering temperature in a microgravity environment; after the glass microsphere powder is sintered, the temperature inside the microgravity sintering furnace is reduced to below the sintering temperature to form ultra-high sphericity glass microspheres. S6. Collection stage: After the free fall motion of the microgravity sintering furnace (200) ends, the microgravity sintering furnace is naturally cooled, and the ultra-high sphericity glass microspheres after cooling are collected.

2. The method for improving the sphericity of glass microspheres under microgravity conditions according to claim 1, characterized in that: The sintering temperature is 1300℃-1500℃.

3. The method for improving the sphericity of glass microspheres under microgravity conditions according to claim 1, characterized in that: In step S4, the amount of glass microsphere powder conveyed is 0.2-0.4 kg of glass microsphere powder per kilogram of gas.

4. The method for improving the sphericity of glass microspheres under microgravity conditions according to claim 1, characterized in that: The glass microsphere powder can be solid or hollow.

5. A method for improving the sphericity of glass microspheres under microgravity conditions according to any one of claims 1-4, characterized in that: The tower dropping device (100) also includes a tower body (110), a vacuum system (130) for evacuating the tower body (110), a deceleration and recovery system (140) for recovering and slowing down the microgravity sintering furnace (200) to a stop at the end of its free fall, a control system (150) for precisely controlling and monitoring the entire process, and a measurement system (160) for measuring and recording various physical parameters during the entire process; the release system (120) is used to release the microgravity sintering furnace (200) freely from the height of the tower body (110).

6. The method for improving the sphericity of glass microspheres under microgravity conditions according to claim 5, characterized in that: The drop tower device (100) also includes auxiliary facilities for controlling the experimental environment, processing and analyzing data.

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