Preparation method of a beryllium foam material

Abstract

The present invention discloses a preparation method of a beryllium foam material, belonging to the technical field of metal beryllium functional materials. In the present invention, PAMS is used as a pore-forming material. First, it is ball-milled to a certain particle size or directly uses PAMS hollow microspheres as the mandrel, and then a beryllium coating with a certain thickness is sputter-deposited on its surface. Then, the composite is placed in a heating furnace and heated to cause the thermal decomposition of PAMS. Under a certain pressure, small PAMS gas molecules escape from the microcracks of the beryllium coating, and at the same time, the beryllium coating undergoes diffusion bonding at high temperature, thereby obtaining a beryllium foam with a certain density and skeleton structure. The beryllium foam prepared by this method has the advantages of adjustable density and pore size, single composition, high purity, and easy availability of raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of beryllium functional materials, and particularly to a preparation method of beryllium foam material. Background Art

[0002] Beryllium metal has excellent properties such as low density, high strength, large specific heat, large neutron scattering cross-section, and almost no absorption of X-rays, and is widely used in the fields of nuclear energy, national defense, optics, and X-rays. Foam metal is a porous metal material with countless three-dimensional spatial network structures formed in a metal matrix. Due to its combination of metal properties and some special physical properties of non-metals, it has received widespread attention at home and abroad. There are many preparation methods for it, such as powder metallurgy method, infiltration method, spray deposition method, melt foaming method, eutectic directional solidification method, pressure casting method, etc.

[0003] With the development of modern society and the shortage of energy, the demand for new fusion clean energy is becoming increasingly urgent, and laser inertial confinement fusion (ICF) and Z-Pinch are two possible ways to achieve it. In ICF experiments, researchers have proposed many new types of structural functional materials, such as foam bulk materials, as low-energy X-ray scattering and radiation transport cavity target filling materials. In Z-Pinch experiments, beryllium foam bulk materials can prevent wire array fragments or particles from mixing into the hot spot and affecting thermonuclear fusion. In addition, X-rays have extremely strong penetration ability through beryllium foam with almost no loss, but it can filter out extreme ultraviolet light. The soft X-ray energy and density distribution are more uniform after passing through beryllium foam, which is beneficial to eliminating the interference of stray light and obtaining better experimental results. Therefore, beryllium foam has attracted much attention as a barrier layer and homogenization layer material in Z-Pinch experimental research. In the field of X-ray applications, beryllium metal sheets are usually used as the tube wall and window materials of synchrotron beam pipes, and the window materials of industrial and medical X-ray imaging equipment. In order to improve the quality of X-ray imaging, a layer of beryllium foam material is usually inserted in the middle of the beryllium metal sheet as an X-ray scattering element to improve the X-ray field in time and space, which can effectively eliminate the spot structure on the film and hardly attenuate the intensity of the X-ray beam.

[0004] Currently, the preparation of beryllium foam materials usually adopts the powder metallurgy physical method, that is, uniformly mixing beryllium metal powder with pore-forming agent powders such as sodium chloride and sodium carbonate, then pressing and molding and high-temperature sintering, and finally dissolving the pore-forming agent powders with water to obtain beryllium foam materials. This method has a small adjustable range of the relative density of beryllium foam, and it is easy to cause the oxidation of beryllium powder. The pore-forming agent is also difficult to remove, and the purity of beryllium foam is not high, generally not higher than 90%.

[0005] In addition, Chinese Patent Application CN107824791A discloses a method for preparing beryllium foam material: respectively using beryllium hydride powder and beryllium metal powder for ball milling and refinement, then mixing them in proportion and heating in a sealed container. After the decomposition of beryllium hydride and the consolidation reaction are completed, a beryllium foam product can be obtained. This method requires beryllium hydride as one of the raw materials, but the preparation of beryllium hydride is difficult and it is still in the laboratory research and development stage, which restricts the large-scale application of this process. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing beryllium foam material to solve the above problems.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing beryllium foam material successively includes the following steps:

[0009] (a) Grinding and refining PAMS raw materials to obtain PAMS particles with a particle size range of 5 - 100 μm, or directly using PAMS hollow microspheres as degradation mandrels;

[0010] (b) Loading the PAMS particles or PAMS hollow microspheres described in step (a) into a vibrating disk, and then fixing them on the sample holder of a magnetron sputtering device equipped with a beryllium target;

[0011] (c) Sputtering and coating the PAMS mandrels in the vibrating disk described in step (b) to deposit a beryllium coating on the surface of the PAMS mandrels, and the coating thickness range is 0.1 - 50 μm;

[0012] (d) According to the density and pore size requirements of the desired beryllium foam material, selecting the composite deposited with a beryllium coating on the PAMS mandrel described in step (c) and loading it into a quartz tube;

[0013] (e) Vertically placing the quartz tube described in step (d) into a heating device filled with inert gas for heating, causing the PAMS to thermally decompose to form small molecule gases, and the small molecule gases escape from the microcracks formed after heating the beryllium coating. Then continue to heat up to cause the beryllium coating to undergo diffusion bonding, and then naturally cool down to room temperature to obtain the beryllium foam material.

[0014] The present invention uses PAMS (poly alpha methylstyrene) as a pore-forming material, firstly ball-mills it to a certain particle size or directly uses PAMS hollow microspheres as a core shaft, sputters and deposits a certain thickness of beryllium coating on its surface, and then places it in a heating furnace to heat up so that PAMS undergoes thermal decomposition. Under the action of heating and gas pressure, the grains in the beryllium coating grow and the microstructure coarsens. Some growth defects in the preparation process will form microcracks, and the small gas molecules after the thermal decomposition of PAMS escape from these microcracks, and the pore structure of the beryllium coating remains basically intact. Subsequently, the temperature is continued to rise so that the beryllium coating undergoes diffusion bonding at high temperature, thereby obtaining foamed beryllium with a certain density and skeleton structure. The foamed beryllium prepared by this process has the advantages of adjustable density and pore size, single composition, high purity, and easy availability of raw materials.

[0015] As a preferred technical solution, in step (a), the PAMS raw material is a white irregular block solid with a loose structure, brittleness and a purity of more than 99%; a planetary ball mill is used for ball milling, and ceramic spheres are used for grinding balls; the PAMS hollow microspheres are prepared by emulsion microencapsulation method, and its preparation process is a public technology. The maximum particle size can be close to the millimeter level, about 800μm, and the wall thickness is between tens of μm.

[0016] Schematic diagram of ball milling Figure 1 As shown, the irregularly shaped PAMS block is placed in a ball mill, and ceramic balls are used. The ball-to-material ratio, ball milling time, and ball mill speed are determined according to the required particle size. According to the ball milling process, the final PAMS particle size can be controlled between tens of μm.

[0017] As a preferred technical solution, in step (b), the vibration disk is a quartz vibration disk made of high-purity quartz, in an arc shape, with an outer diameter of φ25-30 mm, a wall thickness of 1.5-2 mm, a disk height of 8-10 mm, and a 4.5-5 mm rounded corner at the bottom of the disk; a 3-inch beryllium target is installed on the target gun of the magnetron sputtering device, and the purity of the beryllium target is 99wt.%.

[0018] As a preferred technical solution, in step (c), the sputtering process parameters are: the background vacuum is less than 1×10 -5 Pa, the sputtering medium uses Ar gas with a purity of 99.99%, the sputtering pressure is 0.2-0.4Pa, the sputtering power is 100-120W, and the target-base spacing is 110-120mm; the vibration plate rotates at a speed of 6-10r / min and is assisted by knocking to make the PAMS mandrel roll in the stone vibration plate; according to the deposition process conditions, the beryllium coating thickness is controlled at 0.1-50μm, and the deposition time is determined according to the thickness value; the sputtering schematic diagram is shown in Figure 2 As shown;

[0019] As a preferred technical solution, in step (d), the quartz tube has a structure with one end arc-sealed and the other end open, with a total length of 50 - 60 mm, an outer diameter of φ12 - 15 mm, and a wall thickness of about 1 - 2 mm.

[0020] As a preferred technical solution, in step (e), the heating device is a tube furnace. Before pyrolysis, vacuum is pumped first, then Ar gas is filled and maintained in a flowing state. The purity of the Ar gas introduced is 99.99%; the heating rate is 10 °C / min, the pyrolysis temperature is 320 - 350 °C, and the heat preservation time is 48 hours; after the PAMS pyrolysis is completed, the temperature is raised to 600 - 700 °C and kept warm for 24 hours to cause diffusion bonding of the beryllium coating; the schematic diagram of thermal degradation is as Figure 3 shown;

[0021] As a preferred technical solution, in step (e), the pore size of the beryllium foam material is 5 - 800 μm.

[0022] Compared with the prior art, the advantages of the present invention are as follows: In the method of the present invention, the PAMS particles or PAMS hollow microspheres obtained by ball milling act mainly as pore-forming cores, and they can basically reach 100% thermal decomposition at 320 - 350 °C without residue. Therefore, the purity of the obtained beryllium foam can reach more than 99 wt.%; in the method of the present invention, the relative density of the beryllium foam material mainly depends on the particle size of the PAMS core and the thickness of the beryllium coating, and it has the advantages of adjustable density and pore size, single composition, high purity, and easy availability of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of ball milling of PAMS raw materials of the present invention;

[0024] Figure 2 is a schematic diagram of magnetron sputtering deposition of beryllium coating on PAMS particles or PAMS hollow microspheres of the present invention;

[0025] Figure 3 is a schematic diagram of thermal degradation of "PAMS particles + Be coating" or "PAMS hollow microspheres + Be coating" composite. EMBODIMENTS

[0026] The present invention will be further described below with reference to the accompanying drawings. Example 1:

[0027] A method for preparing a beryllium foam material successively includes the following steps:

[0028] (a) Put the PAMS raw materials into a planetary ball mill for grinding and refinement to obtain PAMS particles with a particle size of 10 μm;

[0029] The PAMS raw material used in this embodiment is a white irregular block solid with a loose structure, brittleness, and a purity of more than 99%. The ball mill uses ceramic balls, and the large and small balls are proportionally proportioned. The ball milling time is 12 hours. The particle size of the PAMS particles used in this embodiment is finally controlled to be about 10 μm.

[0030] (b) loading the PAMS particles described in step (a) into a quartz vibrating plate, and then fixing it on a sample holder of a magnetron sputtering device equipped with a beryllium target;

[0031] The quartz vibration disk is made of high-purity quartz, has an arc shape, an outer diameter of about φ30mm, a wall thickness of about 1.5mm, a disk height of about 8mm, and a bottom corner of about 5mm; the surface quality of the high-purity quartz disk is high, the surface roughness is very low, and the Ra value can reach below 2nm, and the spherical PAMS particles or PAMS hollow microspheres can roll unimpeded in the quartz disk; the quartz disk is cleaned with anhydrous ethanol and placed in the PAMS mandrel, and then the quartz disk is fixed on the sample holder of the magnetron sputtering device, and a 3-inch beryllium target is installed on the target gun, and the purity of the beryllium target is 99wt.%;

[0032] (c) performing sputtering coating on the PAMS core shaft in the quartz vibration disk described in step (b), so that a beryllium coating with a thickness of 500 nm is deposited on its surface;

[0033] When magnetron sputtering is used, the mechanical pump is turned on first, followed by the molecular pump, so that the background vacuum in the sputtering chamber is less than 1×10 -5 Pa, then close the gate valve, and introduce Ar gas with a purity of 99.99% to stabilize the sputtering pressure in the vacuum chamber at 0.2Pa; then turn on the sputtering power of the beryllium target gun, maintain the sputtering power at 120W, and the target-base spacing at 110mm; finally adjust the sample holder equipped with a vibrating quartz disk to rotate at 6r / min, and tap it to keep the PAMS particles in the quartz disk in a rolling state, so that the beryllium coating can be evenly deposited on its surface during the coating process; in this embodiment, due to the small particle size of the PAMS particles, the thickness of the beryllium coating deposited on its surface should not be too thick, and is finally controlled at about 500nm, and finally a "10μmPAMS solid particle + 0.5μmBe" composite is formed;

[0034] (d) placing the “10 μm PAMS solid particles + 0.5 μm Be” composite deposited on the PAMS mandrel in step (c) into a small quartz tube;

[0035] Small quartz tube for SiO 2 The material can withstand a certain high temperature and has high chemical stability. It is a commonly used experimental equipment used in heating furnaces. Its structure is a circular arc bottom seal at one end and an open end. The total length is about 60mm, the outer diameter is about φ15mm, and the wall thickness is about 1.5mm.

[0036] (e) Vertically place the quartz tube described in the fourth step into a tube furnace filled with Ar gas for heating. Maintain the degradation temperature and diffusion temperature for a period of time, and then naturally cool down to room temperature to obtain the foamed beryllium material. The specific method is as follows:

[0037] Vertically place the quartz tube containing the "PAMS particles + Be coating" composite into the tube furnace. Close the valves on both sides of the heating furnace, turn on the mechanical pump to pump to a low vacuum. Wait until the pressure drops below 1 Pa, then turn on the Ar gas switch with a purity of 99.99% and maintain the Ar gas in a flowing state to discharge the small PAMS molecules after thermal decomposition. The heating rate is 10 °C / min, and finally reach 350 °C and hold for 48 hours. After the thermal decomposition of PAMS is completed, raise the temperature to 650 °C and hold for 24 h to cause the Be coating to undergo diffusion bonding at a high temperature to form foamed beryllium.

[0038] The initial pyrolysis temperature of PAMS is generally between 240 and 260 °C. After reaching the pyrolysis temperature, raise the temperature to the complete degradation temperature of 320 - 350 °C to completely pyrolyze the PAMS inside the Be coating into small gas molecules. Under the action of heating and gas pressure, the grains in the Be coating grow, the microstructure coarsens, and some growth defects during the preparation process will form microcracks. The small gas molecules after the thermal decomposition of PAMS escape from these microcracks, and the pore structure of the Be coating remains basically intact. Since the Be coating is a nanocrystalline structure, its thermal diffusion temperature is lower than that of coarse-grained beryllium and it has strong diffusivity. The Be coating undergoes diffusion migration of the microscopic crystal structure at a high temperature of 650 °C, and the surface diffusion and volume diffusion are enhanced, and finally bond together to form foamed beryllium. After PAMS is completely degraded to form foamed beryllium, the heating furnace slowly cools down to room temperature naturally. The entire degradation process is carried out in an Ar gas atmosphere to prevent the high-temperature oxidation of the Be coating and ensure its single composition. Since PAMS can be 100% degraded, the purity of the finally prepared foamed beryllium is equivalent to that of the used beryllium target, which is 99%.

[0039] After the heating furnace cools down to room temperature, close the Ar gas valve, open the heating furnace, and carefully take out the prepared foamed beryllium. In this example, after the degradation of the "10 μm PAMS solid particles + 0.5 μm Be" composite obtained, the finally obtained foamed beryllium has a relative theoretical density of about 24.9%, and the pore size in the foamed beryllium is similar to the outer diameter of the PAMS mandrel used, about 10 μm. Example 2:

[0040] Compared with Example 1, in step (a), the directly used PAMS hollow microspheres are prepared by the emulsion microencapsulation method, and their maximum particle size can be close to the millimeter level, about 800 μm, and the wall thickness is between dozens of μm. The outer diameter of the PAMS hollow microspheres used in this example is about 500 μm, and the PAMS thickness is about 20 μm.

[0041] In step (c), due to the large diameter of the PAMS hollow microsphere mandrel, the beryllium coating thickness is controlled at 8 μm, and the sputtering process is the same as that in Example 1. Finally, a "500 μm outer diameter / 20 μm wall thickness PAMS hollow microsphere + 8 μm Be" composite is formed;

[0042] After degradation, the relative theoretical density of the finally obtained beryllium foam is 9.0%. The pore size in the beryllium foam is similar to the outer diameter of the PAMS mandrel used, about 500 μm, and the purity is 99%.

[0043] Example 3 and Example 4:

[0044] Compared with Example 1 and Example 2, Example 3 and Example 4 only have changes in steps (a) and (c), and the rest are the same as steps (b), (d), and (e). The corresponding parameters are shown in Table 1 below.

[0045] Table 1 Parameters of beryllium foam in Example 3 and Example 4

[0046]

[0047] In Example 3, PAMS particles with a diameter of 30 μm after ball milling are used, the Be coating thickness is 1 μm, and the relative density of the obtained beryllium foam after degradation is 17.6%, and the pore size of the beryllium foam is 30 μm; in Example 4, PMAS hollow microspheres with an outer diameter of 800 μm / wall thickness of 20 μm are used, the Be coating thickness is 20 μm, and the relative density of the obtained beryllium foam after degradation is 13.6%, and the pore size of the beryllium foam is 800 μm; the purity of both is 99%.

[0048] The density of the beryllium foam obtained by the present invention can be controlled according to the technical state of the PAMS mandrel and the beryllium coating thickness. The density can be less than 10% of the theoretical density of beryllium. This method has the advantages of adjustable density and pore diameter, single composition, high purity, and easy availability of raw materials. Each step of the present invention is a mature and controllable process method, and the raw materials are relatively easy to obtain. It can be applied to the preparation of a large amount of beryllium foam materials and has a certain market prospect.

[0049] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing foamed beryllium material, It is characterized in that The following steps are included in sequence: (a) grinding the PAMS raw material to obtain PAMS particles with a particle size range of 5 to 100 μm, or directly using PAMS hollow microspheres as the degradation core shaft; (b) loading the PAMS particles or PAMS hollow microspheres described in step (a) into a vibrating plate, and then fixing it on a sample holder of a magnetron sputtering device equipped with a beryllium target; (c) performing sputtering coating on the PAMS mandrel in the vibrating disk described in step (b), so that a beryllium coating is deposited on the surface of the PAMS mandrel, and the coating thickness ranges from 0.1 to 50 μm; (d) selecting the composite material having a beryllium coating deposited on the PAMS mandrel as described in step (c) according to the density and pore size requirements of the desired foam beryllium material, and loading it into a quartz tube; (e) The quartz tube described in step (d) is placed vertically in a heating device with an inert gas and heated to decompose the PAMS to form small molecule gas, which escapes from the micro cracks formed after the beryllium coating is heated. The temperature is then continued to rise to allow the beryllium coating to diffuse and bond, and then the temperature is naturally cooled to room temperature to obtain a foamed beryllium material.

2. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (a), the PAMS raw material is a white irregular block solid with a loose structure, brittleness and a purity of more than 99%; a planetary ball mill is used for ball milling, and ceramic balls are used for grinding; and the PAMS hollow microspheres are prepared by an emulsion microencapsulation method.

3. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (b), the vibration plate adopts a quartz vibration plate, which is made of high-purity quartz, has an arc shape, an outer diameter of φ25-30 mm, a wall thickness of 1.5-2 mm, a plate height of 8-10 mm, and a 4.5-5 mm rounded corner at the bottom of the plate; a 3-inch beryllium target is installed on the target gun of the magnetron sputtering device, and the purity of the beryllium target is 99wt.%.

4. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (c), the sputtering process parameters are as follows: the background vacuum is less than 1×10 -5 Pa, the sputtering medium is Ar gas with a purity of 99.99%, the sputtering gas pressure is 0.2 - 0.4 Pa, the sputtering power is 100 - 120 W, and the target-substrate distance is 110 - 120 mm; the vibrating disk rotates at a speed of 6 - 10 r / min and is supplemented by tapping to make the PAMS mandrel roll in the quartz vibrating disk; according to the deposition process conditions, the beryllium coating thickness is controlled within 0.1 - 50 μm.

5. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (d), the quartz tube is a structure with an arc bottom at one end and an open end, with a total length of 50 to 60 mm, an outer diameter of φ12 to 15 mm, and a wall thickness of 1 to 2 mm.

6. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (e), the heating equipment is a tubular heating furnace, which is first evacuated before pyrolysis, and then filled with Ar gas and kept in a flowing state, and the purity of the introduced Ar gas is 99.99%; the heating rate is 10°C / min, the pyrolysis temperature is 320-350°C, and the insulation time is 48 hours; after the pyrolysis of PAMS is completed, the temperature is increased to 600-700°C and maintained for 24 hours to allow the beryllium coating to diffuse and bond.

7. The method for preparing the foamed beryllium material according to claim 1, It is characterized in that In step (e), the pore size of the foamed beryllium material is 5 to 800 μm.

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