Method for improving sphericity of glass microbeads in microgravity

Abstract

The application relates to a method for improving the sphericity of glass microbeads in a microgravity state, and belongs to the technical field of glass microbead preparation. The method uses a falling tower device, so that a microgravity sintering furnace located in the falling tower device can be in free fall, and the microgravity environment of the microgravity sintering furnace is realized through the falling tower method. The method comprises a pretreatment stage, an air extraction stage, a heating stage, a feeding stage, a sintering stage and a collection stage. The method can effectively reduce the influence of gravity on the sphericity in the glass microbead spheroidization process, greatly improve the sphericity of the glass microbeads, and is relatively simple.

Description

TECHNICAL FIELD

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

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

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

[0004] Glass microspheres 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 microspheres 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 microspheres also has a significant impact on their mechanical properties. Spherical microspheres can better withstand pressure when under stress because their shape allows for more even stress distribution. This means that at the same volume, microspheres with high sphericity can provide higher compressive strength and bending strength.

[0007] (3) Influence on thermal conductivity

[0008] The sphericity of glass microspheres also affects their thermal conductivity. The surface area of spherical microspheres is relatively small, which helps to reduce the transfer of heat, so in applications where thermal insulation materials are needed, microspheres 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 microspheres are also affected by the sphericity. Microspheres 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, the sphericity has a wide range of effects on the application of glass microbeads, including improving the uniformity and stability of the material, improving the mechanical properties, affecting the thermal conductivity, and changing the 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 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. Figure 1 、 Figure 2 Figure 1 The solid glass microbeads produced by the conventional method have a sphericity of 85%-88%, as shown by the sphericity instrument. Figure 1 Figure 2 The polarized light microscope photo of the solid glass microbeads in Figure 1 Figure 2 can more directly see the sphericity of the solid glass microbeads shown in Figure 1 . SUMMARY

[0013] The present application provides a method for preparing glass microbeads, which can achieve a higher sphericity under the same particle size by strictly controlling the melting environment. The preparation method of the ultra-high sphericity glass microbeads is also relatively simple.

[0014] It adopts the following technical solutions:

[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 includes the following steps:

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

[0019] S2, vacuum stage: vacuum the falling tower device to 30%-60% vacuum degree and maintain stable, and vacuum the microgravity sintering furnace and discharge the internal waste gas, so that the internal gas pressure range of the microgravity sintering furnace is consistent with the internal gas pressure range of the falling tower device;

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

[0021] S4, feeding stage: the micro-gravity sintering furnace is freely fallen to form a micro-gravity environment, in which the glass micro-bead powder is sprayed into the micro-gravity sintering furnace by compressing the air to pressurize the air;

[0022] S5, sintering forming stage: the glass micro-bead powder is sintered by keeping the constant sintering temperature of the micro-gravity sintering furnace in the micro-gravity environment; after the sintering of the glass micro-bead powder is completed, the temperature in the micro-gravity sintering furnace is reduced to below the sintering temperature, so that the ultra-high sphericity glass micro-bead is formed;

[0023] S6, collecting stage: the micro-gravity sintering furnace is freely fallen to form a micro-gravity environment, in which the glass micro-bead powder is sprayed into the micro-gravity sintering furnace by compressing the air to pressurize the air;

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

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

[0026] Further, the glass micro-bead powder is solid or hollow.

[0027] Further, the tower falling device further comprises a tower body, a vacuum system for air extraction of the tower body, a deceleration recovery system for recovering and decelerating the micro-gravity sintering furnace to stop when the free falling of the micro-gravity 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 releasing system is used for freely releasing the micro-gravity 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 present application can effectively reduce the influence of gravity on the sphericity of the glass micro-bead in the glass micro-bead spheroidization process, and greatly improve the sphericity of the glass micro-bead.

[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 in 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, Grashof number Gr = (Δρ / ρ)gL3 / ν2, which represents the ratio of buoyancy to viscous force, and 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; and the third method has no defects. The combustion under the microgravity condition has the following characteristics: the natural convection is almost eliminated, the combustion of static 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 effect, can be shown; the gravity sedimentation is almost eliminated, 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 by using microgravity in a vacuum environment can practically reduce the influence of gravity on the sphericity in the glass microsphere forming process, and greatly improve the sphericity of the glass microspheres. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0036] Figure 3 is the structure schematic diagram of the falling tower device in the embodiment of the present application;

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

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

[0039] The reference signs are explained as follows: 100, falling tower device; 110, tower body; 120, release system; 130, vacuum pumping system; 140, deceleration recovery system; 150, control system; 160, recording and measuring system; 200, microgravity sintering furnace. DETAILED DESCRIPTION

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

[0041] The method for improving the sphericity of glass microbeads in microgravity state uses a drop tower device 100, so that the microgravity sintering furnace 200 in the drop tower device 100 can be in free fall, and the microgravity environment of the microgravity sintering furnace 200 is realized by the drop tower method. The drop 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 forces. 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 drop tower method requires the use of a drop tower device 100, as shown in detail in Figure 3 The drop 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 be in 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 of delivering gas, powder and energy to the microgravity sintering furnace 200 without affecting the free fall motion can also be used.

[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℃.

[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. 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, the ultra-high sphericity glass microsphere is formed, and the sphericity no longer changes,

[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℃, 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] The M series hollow glass microsphere raw powder is selected. 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 separated 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] Group 2

[0058] The M series hollow glass microsphere raw powder is selected. 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 separated 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] Group 3

[0061] The M series hollow glass microsphere raw powder is selected. 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 separated 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 solid glass microsphere spheroidization degree is 85%-88% when sintered in a traditional sintering furnace, as shown in Figure 1 , Figure 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. The solid glass microsphere raw powder of 1-2kg can be sintered in a limited time. The spheroidization degree can be improved to 92%, as shown in Figure 4 , Figure 5 .

[0067] Group 5

[0068] The solid glass microsphere powder is selected, and the solid glass microsphere spheroidization degree is 85%-88% when sintered in a traditional sintering furnace, as shown in Figure 1 , Figure 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. The solid glass microsphere raw powder of 1-2kg can be sintered in a limited time. The spheroidization degree can be improved to 95%.

[0070] Group 6

[0071] The solid glass microsphere powder is selected, and the solid glass microsphere spheroidization degree is 85%-88% when sintered in a traditional sintering furnace, as shown in Figure 1 , Figure 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. The solid glass microsphere raw powder of 1-2kg can be sintered in a limited time. The spheroidization degree can be improved to 97%.

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

[0074] The above embodiments of the present application are merely used for clearly explaining the present application, and are not intended to limit the embodiments 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 embodiments are not required to be enumerated. The changes or variations which are extended from the essential spirit of the present application are still within the protection scope of the present application.

Claims

1. A method for improving the sphericity of glass microbeads in a microgravity environment, characterized by: It uses a falling tower device (100), a release system (120) in the falling tower device (100) releases the microgravity sintering furnace (200) in the tower to do free fall, realizes the microgravity environment of the microgravity sintering furnace (200); The falling tower device (100) also includes a tower body (110), a vacuum pumping system (130) for pumping the tower body (110), and a deceleration recovery system (140) for recovering and decelerating the microgravity sintering furnace (200) to stop at the end of free fall, and a control system (150) for precise control and monitoring of the whole process and a measurement system (160) for measuring and recording various physical parameters in the whole process; The release system (120) is used for releasing the microgravity sintering furnace (200) from the tower body (110) at a high place; The method for improving the sphericity of glass microspheres in a microgravity state comprises the following steps: S1, pretreatment stage: cleaning the surface of glass microsphere powder and removing impurities affecting sintering quality; S2, pumping stage: pumping the falling tower device (100) to 30%-60% vacuum degree and maintaining stable, pumping the microgravity sintering furnace (200) and discharging the 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 falling tower device (100); S3, heating stage: gradually heating 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, and in the microgravity environment, the glass microsphere powder is sprayed into the microgravity sintering furnace (200) by compressing the air to pressurize the air; S5, sintering forming stage: the glass microsphere powder is sintered by maintaining the constant sintering temperature of the microgravity sintering furnace (200) in the microgravity environment; 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; S6, collection stage: the microgravity sintering furnace (200) stops free fall, and the ultra-high sphericity glass microspheres are collected after natural furnace cooling.

2. The method of claim 1, wherein the glass microspheres have a sphericity of at least 0.

95. The sintering temperature is 1300-1500℃.

3. The method of claim 1, wherein the glass microspheres have a sphericity of at least 0.

95. In step S4, the delivery amount of the glass microsphere powder is 0.2-0.4 kg per kg of gas.

4. The method of claim 1, wherein the glass microspheres have a sphericity of at least 0.

95. The glass microsphere powder is solid or hollow.

5. The method of claim 1, wherein the glass microspheres have a sphericity of at least 0.

95. The falling tower device (100) also includes auxiliary facilities for controlling the experimental environment, data processing and analysis. The falling tower device (100) also includes auxiliary facilities for controlling the experimental environment, data processing and analysis.

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