Device and method for preparing spherical metal single crystals by electron beam heating

Abstract

The present invention discloses a device and method for preparing spherical metal single crystals by electron beam heating. The device comprises a vacuum chamber; a heating element in a circular ring structure disposed within the vacuum chamber for emitting an electron beam; a driving structure disposed within the vacuum chamber for driving a metal wire to move along the central axis of the circular ring structure within the heating element; and a high-voltage source for applying a negative high voltage to the heating element to accelerate the electron beam toward the metal wire. The present invention provides a heating element in a circular ring structure and uses a method in which the driving structure moves the single crystal sphere upward to control the solidification and cooling rates of the single crystal. In this method, it is only necessary to first adjust the parameters to maintain the solid-liquid interface at the top of the droplet. Subsequently, it is only necessary to observe the liquid-solid interface to uniformly move the solid-liquid interface to achieve more precise control of the single crystal solidification rate, avoid defects such as vacancies, dislocations, and polycrystalline grain boundaries, and thereby obtain a single crystal of superior quality.

Description

Technical Field

[0001] The present invention relates to the field of single crystal preparation, and in particular to a device and method for preparing spherical metal single crystals by electron beam heating. Background Art

[0002] Single crystals have excellent physical, chemical and mechanical properties. Among them, small spherical single crystals can be used as single crystal substrates that are easy to clean and heat, and are used in research in the fields of surface science, thin film growth, electrochemistry, and sensing applications.

[0003] It has been reported that small spherical single crystals of precious metals can be produced by melting the end of a metal wire using a gas flame such as hydrogen or propane. This method includes flame melting and flame floating zone methods. The end of the wire is heated by a gas flame moving along the wire axis until a liquid metal droplet or sphere forms. As the liquid metal sphere slowly cools, one or several grains within the solidified wire serve as nuclei for the solidified sphere. After a period of melting and recrystallization, the metal sphere solidifies from a single nucleus, forming a spherical single crystal.

[0004] However, these methods are limited to the preparation of spherical single crystals of precious metals such as platinum and gold. For other non-precious metals and metal alloys, gases diffuse from the flame into the spherical single crystals under natural environmental conditions. Using flame melting processes, nearly all wires made from non-precious metals will oxidize. Therefore, it is impossible to prepare spherical single crystals of non-precious metals using existing flame melting or flame floating zone processes.

[0005] In the prior art, there is a method for preparing non-precious metal spherical single crystals by electron beam heating. However, in this method, the electron beam is directly generated by heating the bottom of the metal wire with an electric heating wire, and the heating wire is usually arranged under the metal wire in a coil-like structure, such as Figure 3 As shown, the generated electron beam is emitted through the top opening of the metal shell, and the emitted electron beam hits the bottom end of the metal wire to be heated, thereby causing it to heat and melt, thereby achieving the purpose of preparing non-precious metal spherical single crystals.

[0006] While existing methods can produce spherical single crystals of various metals, they suffer from low heating efficiency and relatively long preparation times. Furthermore, research has found that spherical single crystals produced using these methods often contain numerous defects, such as vacancies and dislocations, which severely impact their performance. This is particularly true when producing larger diameter spherical single crystals, which can result in the formation of multiple grains. Summary of the Invention

[0007] Therefore, the first technical problem to be solved by the present invention is to overcome the defects of low heating efficiency and relatively long preparation time when the equipment in the prior art uses electron beams to prepare spherical single crystals.

[0008] The second technical problem to be solved by the present invention is to overcome the defects of spherical single crystals prepared by the electron beam preparation method in the prior art, such as vacancies, dislocations, and polycrystalline grain boundaries.

[0009] In order to solve the first technical problem, the present invention provides a device for preparing spherical metal single crystals by electron beam heating, comprising:

[0010] vacuum chamber;

[0011] The heating element has a circular ring structure and is arranged in the vacuum chamber to form an electron beam;

[0012] A driving structure, disposed in the vacuum chamber and used to drive the metal wire to move along the central axis of the annular structure in the heating element;

[0013] The high voltage source is used to apply negative high voltage to the heating element to accelerate the electron beam toward the metal wire.

[0014] The vacuum chamber also has a focusing plate arranged parallel to the annular structure; the focusing plates are two pieces, respectively arranged on opposite sides of the heating element;

[0015] The focusing plate is also provided with a through hole for facilitating the movement of the metal wire;

[0016] The distance between the focusing plate and the heating element is 2-50 mm;

[0017] The focusing plate and the heating element are both connected to a high voltage source, and negative high voltage is applied to both the focusing plate and the heating element through the high voltage source. A grounding terminal for grounding the metal wire is provided on the driving structure at a position fixed to the metal wire.

[0018] The focusing plate is made of molybdenum, niobium or tantalum.

[0019] The heating element is composed of an electric heating wire bent into a circular ring structure and a power source for providing energy to the electric heating wire.

[0020] The material of the heating wire is tungsten, molybdenum or tantalum.

[0021] The diameter of the heating wire is 0.1-2 mm, and the diameter of the circular ring structure formed by the heating wire is 5-50 mm.

[0022] A method for preparing spherical metal single crystals by electron beam heating is obtained by using the above-mentioned device for preparing spherical metal single crystals by electron beam heating.

[0023] In order to solve the second technical problem, the present invention provides a method for preparing spherical metal single crystals by electron beam heating, comprising:

[0024] the acquisition of wire;

[0025] Fixing of the metal wire: The top of the metal wire is fixed above the heating element through the driving structure and grounded, and the central axis of the metal wire is controlled to coincide with the central axis of the circular structure in the heating element;

[0026] Vacuuming;

[0027] Melting and solidification: Start the heating element and high-voltage source to melt the bottom end of the metal wire to form a large liquid metal ball, and maintain the liquid-solid interface for 2-5 minutes; then move it vertically upward at a speed of 0.5-5mm / min, so that the liquid large metal ball cools and solidifies from top to bottom to form a spherical metal single crystal.

[0028] The material of the metal wire is W, Ta, Mo, Nb, Ni, Cr, Cu, Al, Pd, Ir, Rh, Ru, Au, Pt, Ag, Re or a metal alloy. For example, the metal alloy is Ag / Au, Pt / Pd, Pt / Rh or Pt / Re.

[0029] The diameter of the metal wire is 0.1-10 mm;

[0030] After the vacuuming step, the pressure in the vacuum chamber is less than 1 Pa;

[0031] Before the melting and solidification steps, the linear distance between the bottom end of the metal wire and the plane where the heating element is located is adjusted to less than 10 mm;

[0032] The melting process in the melting and solidification steps is as follows: starting the heating element and the high voltage source so that the annular structure emits an accelerated electron beam toward the metal wire, the electron beam heats and melts the bottom end of the metal wire to form a small liquid metal ball; then, the driving structure drives the metal wire to move vertically downward at a speed of 0.5-5 mm / min, and after a large liquid metal ball is formed at the bottom end of the metal wire, the liquid-solid interface is maintained for 2-5 minutes;

[0033] Preferably, the melting and solidifying steps are repeated at least once;

[0034] The diameter of the spherical metal single crystal ranges from 0.2 to 15 mm.

[0035] The technical solution of the present invention has the following advantages:

[0036] 1. The present invention provides an apparatus for preparing spherical metal single crystals by electron beam heating, which includes a heating element in a circular ring structure disposed within a vacuum chamber. The heating element can uniformly heat the metal wire 360°, thereby achieving higher heating efficiency and shorter heating time.

[0037] Moreover, the heating element with a circular ring structure has a simpler structure and is easier to process and prepare.

[0038] 2. The present invention provides a method for preparing spherical metal single crystals by electron beam heating, which further optimizes the single crystal solidification method and controls the single crystal solidification and cooling rate by moving the single crystal ball upward through a driving structure. In this method, it is only necessary to adjust the parameters first to maintain the solid-liquid interface at the top of the droplet. Subsequently, it is only necessary to observe the liquid-solid interface and adjust the movement parameters of the driving structure to make the solid-liquid interface move at a uniform speed. This can achieve the purpose of more precise control of the solidification rate of the single crystal, avoid defects such as vacancies, dislocations, and polycrystalline grain boundaries, and thus obtain single crystals with better quality.

[0039] 3. When the apparatus and process of the present invention are used to prepare spherical metal single crystals, the purpose of preparing spherical single crystals from non-precious metal wires can be achieved. The method is no longer limited to preparing spherical single crystals from precious metal materials. Specifically, the raw materials of the wires during preparation include but are not limited to W, Ta, Mo, Nb, Ni, Cr, Cu, Al, Pd, Ir, Rh, Ru, Au, Pt, Ag, Re or metal alloys. For example, the metal alloy is Ag / Au, Pt / Pd, Pt / Rh or Pt / Re. The above materials can be easily formed into spherical single crystals, and the prepared spherical single crystals are free of gas inclusions, vacancies, dislocations, polycrystalline grain boundaries and other defects, and have a wider range of applications.

[0040] 4. The present invention provides a method for preparing spherical metal single crystals by electron beam heating, which can effectively prepare spherical single crystals with a diameter of about 0.2 to 15 mm, and the single crystals have a smooth surface and a more regular shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 It is a structural schematic diagram of the present invention;

[0043] Figure 2 for Figure 1 Schematic diagram of the structure of the heating element;

[0044] Figure 3 This is a schematic diagram of the structure of the equipment for preparing single crystals by conventional electron beam heating as described in the background technology of the present invention;

[0045] Figure 4 This is a macroscopic photograph of a spherical W single crystal prepared by electron beam heating in Example 2 of the present invention;

[0046] Figure 5 This is a metallographic photograph of the spherical W single crystal after grinding, polishing, and electrochemical etching in Example 2 of the present invention;

[0047] Figure 6 is the XRD pattern of the spherical W single crystal in Example 2 of the present invention;

[0048] Figure 7 This is a metallographic photograph of the spherical W single crystal after grinding, polishing, and electrochemical etching in Comparative Example 3 of the present invention;

[0049] Figure 8 This is a metallographic photograph of a spherical W crystal with a larger diameter after polishing and electrochemical etching in Comparative Example 3 of the present invention;

[0050] Figure 9 This is the XRD pattern of the spherical W crystals with a larger diameter in Comparative Example 3 of the present invention.

[0051] Description of reference numerals:

[0052] 1-vacuum chamber, 2-heating element, 3-driving structure, 4-focusing plate, 5-through hole, 6-high voltage source;

[0053] 21- electric heating wire, 22- power supply. DETAILED DESCRIPTION

[0054] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0055] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

[0056] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0057] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] Example 1

[0059] A device for preparing spherical metal single crystals by electron beam heating, such as Figure 1 As shown, it includes a vacuum chamber 1, a heating element 2, a driving structure 3 and a high-voltage source 6, wherein the heating element 2 is in a circular ring structure and is arranged in the vacuum chamber 1 for forming an electron beam; the driving structure 3 is arranged in the vacuum chamber 1 for driving the metal wire to move along the central axis of the circular ring structure in the heating element 2; the high-voltage source 6 is used to apply negative high voltage to the heating element 2 to accelerate the electron beam toward the metal wire.

[0060] The principle of preparing spherical metal single crystals by electron beam heating using the above device is as follows:

[0061] The heating element 2 and the driving structure 3 are both located in the vacuum chamber 1, and the vacuum degree of the vacuum chamber 1 is reduced to 3×10 -3 Pa below, the heating element 2 is arranged in a circular ring structure in the vacuum chamber. The heating element 2 can emit an electron beam 360 degrees to the metal wire. The metal wire is grounded. A negative high voltage is applied to the heating element 2 emitting the electron beam through the high-voltage source 6, and the electron beam accelerates toward the metal wire. When the electron beam hits the metal wire, heat is generated, causing the lower end of the metal wire to melt, and then a small liquid metal ball is formed at the lower end of the metal wire. After heating for 1-2 minutes, the metal wire is then moved vertically downward at a speed of 0.5-5mm / min relative to the electric heating wire 21. The metal wire further melts. Due to the effect of surface tension, the droplets will slowly climb up to form a large liquid metal ball with a diameter of 1-4mm. The liquid-solid interface is maintained for 2-5 minutes, and then the liquid ball is steadily and slowly removed from the circular ring structure of the heating element 2 at a moving rate of 0.5-5mm / min. The liquid ball is allowed to slowly cool from top to bottom, and the crystal surface grows from top to bottom to form a spherical metal single crystal. Alternatively, cooling can be performed by gradually decreasing the current of heater 2 or by controlling the electron beam heating power until the upper portion of the metal sphere solidifies, gradually forming a spherical metal single crystal. The phase boundary movement between the solid and liquid phases of the spherical single crystal is observed through the vacuum chamber, and the melting and solidification steps may or may not be repeated depending on the situation.

[0062] Using the principles and forming process described in this invention, after a period of melting and recrystallization, the metal sphere solidifies from a core, then extends throughout the sphere to form a single crystal. The resulting bead single crystal can have a diameter of approximately 1 to 4 mm, with the resulting spherical metal single crystal having a larger diameter. Furthermore, the repeated melting and solidification process can improve the purity of the crystal.

[0063] The advantage of electron beam heating in the present invention is that the high voltage of the high-voltage source 6 or the current of the heater 2 can be used to simply and precisely control the phase boundary, producing a spherical metal single crystal by slowly solidifying the liquid metal sphere. The circular ring structure of the heater 2 enables uniform 360-degree heating of the metal wire. The resulting spherical single crystal is heated uniformly horizontally, without significant temperature gradients or thermal stresses, resulting in a more regularly shaped spherical metal single crystal. This also results in higher heating efficiency and shorter heating time. Furthermore, the circular ring-shaped heater has a simpler structure and is easier to process and prepare.

[0064] In the present invention, the annular structure of the heating element 2 has a diameter of approximately 1 cm and can provide a power of approximately 90-200 W. The high-voltage source 6 can provide the heating element 2 with a negative high voltage of approximately 1-2 kV. The metal wire can be 5-6 cm long and have a diameter of approximately 0.2-4 mm. The values ​​for voltage, power, size, distance, movement speed, and heating and holding time given above are merely examples. Those skilled in the art can freely set other values ​​based on the material of the metal wire used to produce spherical single crystals.

[0065] The spherical single crystal prepared as described above can be used as a single crystal substrate in the fields of surface research, thin film technology, etc.; it can also be used to construct sensors and be used in electrochemistry.

[0066] In order to obtain a smaller melting zone and more significantly improve the formation efficiency of spherical metal single crystals, the vacuum chamber 1 is further provided with a focusing plate 4 arranged parallel to the annular structure. Figure 1 As shown; the focusing plate 4 consists of two pieces, which are respectively arranged on opposite sides of the heating element 2; the focusing plate 4 is also provided with a through hole 5 for facilitating the movement of the metal wire; the size of the through hole 5 should be slightly larger than the diameter of the spherical metal single crystal to be formed, preferably 0-4mm larger, and the maximum diameter of the through hole 5 is 10mm; the distance between the focusing plate 4 and the heating element 2 should be less than 10mm, preferably 5mm.

[0067] In the present invention, either a positive high voltage can be applied to the metal wire to thereby place the heating element 2 in a negative high voltage state, or a negative high voltage can be applied directly to the heating element 2; both of the above methods can achieve the purpose of accelerating the electron beam. In the present invention, when a focusing plate 4 is provided, in order to place the focusing plate 4 in a negative high voltage state and improve the focusing effect, the focusing plate 4 and the heating element 2 are both connected to a high voltage source 6, and a negative high voltage is applied to both the focusing plate 4 and the heating element 2 by the high voltage source 6. At this time, a grounding terminal for grounding the metal wire is provided at a position fixed to the metal wire on the driving structure 3, such as Figure 1 and Figure 2 shown.

[0068] The heating element 2 described in the present invention is composed of an electric heating wire 21 bent into a circular ring structure and a power supply 22 that provides energy for the electric heating wire 21. The material of the electric heating wire 21 in the present invention is tungsten, molybdenum or tantalum. In actual use, the material of the electric heating wire 21 includes but is not limited to the above-mentioned tungsten, molybdenum or tantalum, as long as it can achieve the purpose of emitting an electron beam. Similarly, the material of the focusing plate 4 can also be any material that can achieve the purpose of focusing the electron beam, including but not limited to molybdenum, niobium or tantalum. The driving structure 3 in the present invention can be any structure that can cause the metal wire to move in a straight line, such as a motor, a cylinder, etc.

[0069] In this embodiment, a specific device for preparing spherical metal single crystals by electron beam heating is provided, which includes a vacuum chamber 1, a heating element 2, a driving structure 3, a high-voltage source 6 and a focusing plate 4; wherein the vacuum chamber 1 is made of quartz; the heating wire 21 in the heating element 2 is a W wire with a diameter of 0.4 mm, which is bent into a circular ring structure with a diameter of 1 cm; the driving structure 3 is a linear stepping motor, and a chuck is provided at the end of the screw of the linear stepping motor to facilitate clamping the metal wire, and a grounding terminal is provided on the chuck to facilitate grounding of the metal wire; the high-voltage source 6 is simultaneously connected to the heating wire 21 and the focusing plate 4 to provide negative high voltage to the heating wire 21 and the focusing plate 4; the focusing plate 4 is made of molybdenum, the diameter of the through hole in the focusing plate 4 is 0.5 mm, and the focusing plate 4 consists of two pieces, which are respectively arranged on the upper and lower sides of the heating wire 21, and the distance between it and the heating wire 21 is 5 mm.

[0070] Example 2

[0071] This embodiment adopts the method for preparing spherical W single crystals using the apparatus for preparing spherical metal single crystals by electron beam heating provided in Example 1. The specific preparation process is as follows:

[0072] A W wire with a diameter of 0.5 mm was ultrasonically cleaned twice with ultrapure water and alcohol, each time for about 3 minutes. The W wire was mounted on the chuck, with the linear distance between the bottom end of the W wire and the electric heating wire 21 being 1 mm. Vacuum the vacuum to a degree of less than 2×10 -3 A 15A current and 12V voltage are applied to the heating wire 21 to generate thermal electrons. The W filament is grounded, and the high-voltage source 6 is activated, exposing the heating wire 21 and the Mo sheet focusing plate 4 to a negative high voltage of 2kV, accelerating the electron beam toward the W filament. The negative high voltage of the Mo sheet focusing plate 4 further focuses the electron beam, resulting in a narrow melt zone.

[0073] After the W wire is heated for 2 minutes, it will gradually melt to form a small droplet. Then the metal wire moves vertically downward relative to the electric heating wire 21 at a speed of 0.5mm / min. Due to the effect of surface tension, the droplet will slowly climb up. After moving for 1 minute, a liquid ball with a diameter of about 1.2mm will be formed. Maintain the liquid-solid interface for 2 minutes, and then slowly and steadily move the liquid ball out of the circular structure of the electric heating wire 21 at a moving rate of 0.5mm / min. Let the liquid ball slowly cool from top to bottom, and the crystal surface grows from top to bottom. The resulting spherical W single crystal is as follows: Figure 4 shown.

[0074] Finally, the W single crystal cross section was ground and polished, and electrochemically corroded in a 5% NaOH solution with a corrosion current of about 1A. The metallographic photographs obtained are as follows: Figure 5 As shown. It can be seen that spherical W single crystals are obtained, and the unmelted part is still polycrystalline. X-ray diffraction shows a single crystal diffraction pattern as shown Figure 6 As shown, the diffraction surface of the single crystal is 200 of W.

[0075] Example 3

[0076] The difference between this embodiment and embodiment 2 is that the material and size of the metal wire in this embodiment are different. In this embodiment, a spherical Ta single crystal with a diameter of 2.5 mm is prepared. The specific process is as follows:

[0077] The Ta wire with a diameter of 1 mm was ultrasonically cleaned twice with ultrapure water and alcohol, each time for about 3 minutes. The Ta wire was mounted on the chuck, and the linear distance between the bottom end of the Ta wire and the electric heating wire 21 was 50 mm. Vacuum the wire to a vacuum degree of less than 8×10 -4 The heating wire 21 is passed through with a current of 12A and a voltage of 11V to generate thermal electrons. The Ta wire is grounded, and the high voltage source 6 is activated to make the heating wire 21 and the Mo sheet focusing plate 4 at a negative high voltage of 1.5kV, and the electron beam is accelerated toward the Ta wire.

[0078] After heating the Ta wire for 2 minutes, it gradually melts and forms a small droplet. The metal wire is then moved vertically downward relative to the heating wire 21 at a speed of 5 mm / min. After 2 minutes of movement, a liquid ball with a diameter of 2.5 mm is formed. The liquid-solid interface is maintained for 2 minutes. The liquid ball is then slowly and steadily removed from the circular structure of the heating wire 21 at a speed of 5 mm / min. The liquid ball is allowed to slowly cool from top to bottom, and the crystal plane grows from top to bottom.

[0079] Example 4

[0080] The difference between this embodiment and embodiment 2 is that the material and size of the metal wire in this embodiment are different. In this embodiment, a spherical Mo single crystal with a diameter of 4 mm is prepared. The specific process is as follows:

[0081] The Mo wire with a diameter of 2 mm was ultrasonically cleaned twice with ultrapure water and alcohol, each time for about 3 minutes; the Mo wire was mounted on the chuck, and the linear distance between the bottom end of the Mo wire and the electric heating wire 21 was 2 mm. Vacuum to a vacuum degree of less than 8×10 -4 The heating wire 21 is passed through with a current of 10A and a voltage of 10V to generate thermal electron emission. The Mo wire is grounded, and the high voltage source 6 is activated to make the heating wire 21 and the Mo sheet focusing plate 4 at a negative high voltage of 1kV, and the electron beam is accelerated toward the Mo wire.

[0082] After heating the Mo wire for 1 minute, it gradually melts and forms a small droplet. The metal wire then moves vertically downward relative to the heating wire 21 at a speed of 1 mm / min. Due to surface tension, the droplet slowly climbs upward. After 5 minutes of movement, a liquid ball with a diameter of 4 mm is formed. The liquid-solid interface is maintained for 2 minutes. Then, the liquid ball is slowly and steadily removed from the circular structure of the heating wire 21 at a speed of 1 mm / min. The liquid ball is allowed to slowly cool from top to bottom, and the crystal surface grows from top to bottom.

[0083] Example 5

[0084] The difference between this embodiment and embodiment 2 is that the material and size of the metal wire in this embodiment are different. In this embodiment, a spherical Re single crystal with a diameter of 2.5 mm is prepared. The specific process is as follows:

[0085] The Re wire with a diameter of 1 mm was ultrasonically cleaned twice with ultrapure water and alcohol, each time for about 3 minutes. The Re wire was mounted on the chuck, and the linear distance between the bottom end of the Re wire and the electric heating wire 21 was 5 mm. Vacuum the vacuum to a vacuum degree of less than 8×10 -4 The heating wire 21 is passed through with a current of 13A and a voltage of 12V to generate thermal electron emission. The wire is grounded, and the high voltage source 6 is started to make the heating wire 21 and the Mo sheet focusing plate 4 at a negative high voltage of 2kV, and the electron beam is accelerated toward the wire.

[0086] After heating the wire for 2 minutes, it gradually melts to form a small droplet. The metal wire is then moved vertically downward relative to the heating wire 21 at a speed of 2 mm / min. Due to surface tension, the droplet slowly climbs upward. After 2.5 minutes of movement, a liquid ball with a diameter of 2.5 mm is formed. The liquid-solid interface is maintained for 5 minutes, and then the liquid ball is slowly and steadily removed from the circular structure of the heating wire 21 at a moving speed of 2 mm / min. The liquid ball is allowed to slowly cool from top to bottom, and the crystal surface grows from top to bottom.

[0087] Example 6

[0088] The difference between this embodiment and embodiment 2 is that the material and size of the metal wire in this embodiment are different. In this embodiment, a spherical Ag / Au alloy single crystal with a diameter of 8 mm is prepared. The specific process is as follows:

[0089] The Ag / Au alloy wire with a diameter of 4 mm was ultrasonically cleaned twice with ultrapure water and alcohol for about 3 minutes each time. The Ag / Au alloy wire was mounted on the chuck, and the linear distance between the bottom end of the Ag / Au alloy wire and the electric heating wire 21 was 5 mm. Vacuum the wire to a vacuum degree of less than 8×10 -4 The heating wire 21 is passed through with a current of 9A and a voltage of 10V to generate thermal electron emission. The Ag / Au alloy wire is grounded, and the high-voltage source 6 is activated to apply a negative high voltage of 2kV to the heating wire 21 and the Mo focusing plate 4, accelerating the electron beam toward the Ag / Au alloy wire.

[0090] After heating the Ag / Au alloy wire for 2 minutes, it gradually melts and forms a small droplet. The wire is then moved vertically downward relative to the heating wire 21 at a speed of 3 mm / min. Due to surface tension, the droplet slowly climbs upward. After 2 minutes of movement, a liquid ball with a diameter of 8 mm is formed. The liquid-solid interface is maintained for 3 minutes. The liquid ball is then slowly and steadily removed from the circular structure of the heating wire 21 at a speed of 2 mm / min. The liquid ball is allowed to slowly cool from top to bottom, and the crystal plane grows from top to bottom.

[0091] Example 7

[0092] The difference between this embodiment and embodiment 6 is that the diameter of the circular ring structure of the electric heating wire in this embodiment is different. The diameter of the circular ring structure of the electric heating wire in this embodiment is 50 mm. The specific process is as follows:

[0093] The Ag / Au alloy wire with a diameter of 4 mm was ultrasonically cleaned twice with ultrapure water and alcohol for about 3 minutes each time. The Ag / Au alloy wire was mounted on the chuck, and the linear distance between the bottom end of the Ag / Au alloy wire and the electric heating wire 21 was 5 mm. Vacuum the wire to a vacuum degree of less than 8×10 -4 The heating wire 21 is passed through with a current of 13A and a voltage of 11V to generate thermal electron emission. The Ag / Au alloy wire is grounded, and the high-voltage source 6 is activated to apply a negative high voltage of 2kV to the heating wire 21 and the Mo focusing plate 4, accelerating the electron beam toward the Ag / Au alloy wire.

[0094] After heating the Ag / Au alloy wire for 2 minutes, it gradually melts and forms a small droplet. The wire is then moved vertically downward relative to the heating wire 21 at a rate of 2 mm / min. Due to surface tension, the droplet slowly climbs upward. After 2 minutes of movement, a liquid ball with a diameter of 8 mm is formed. The liquid-solid interface is maintained for 3 minutes. The liquid ball is then slowly and steadily removed from the circular structure of the heating wire 21 at a rate of 2 mm / min. The liquid ball is allowed to cool slowly from top to bottom, and the crystal plane grows from top to bottom.

[0095] Comparative Example 1

[0096] The only difference between this comparative example and Example 2 is that the existing electron beam heating equipment for preparing single crystals is used, and its structure is as follows: Figure 3 Specifically, in this comparative example, the heating element 2 has the same length as the heating wire 21, but a different structure. The focusing plate 4 is omitted, and a housing with an opening is added above the heating element 2. The opening has a diameter of 5 mm, and the straight-line distance between the top of the heating wire 21 and the opening is 2 mm. The diameter and length of the heating wire 21 are the same as those in Example 2, as are all other parameters. During downward movement, the bottom end of the W-wire moves a maximum of 1 mm above the heating wire 21.

[0097] The structure in this comparative example takes about 15 minutes to generate a spherical W single crystal with a diameter of 1.2 mm at the bottom of a 0.5 mm W wire, which is significantly longer than that in Example 2. This results in low thermal energy utilization and production efficiency.

[0098] Comparative Example 2

[0099] The only difference between this comparative example and Example 7 is that the existing electron beam heating equipment for preparing single crystals is used, and its structure is as follows: Figure 3 Specifically, in this comparative example, the heating element 2 has the same length as the heating wire 21 but a different structure. The focusing plate 4 is omitted, and a housing with an opening is added above the heating element 2. The opening has a diameter of 5 mm, and the distance between the top of the heating wire 21 and the opening is 2 mm. The diameter and length of the heating wire 21 are the same as those in Example 7, and other parameters are also the same as those in Example 7. During downward movement, the bottom end of the W wire moves a maximum of 1 mm above the heating wire 21.

[0100] The structure in this comparative example is used to generate a spherical Ag / Au alloy single crystal with a diameter of 8 mm at the bottom end of a 4 mm Ag / Au alloy wire. The time required is about 13 minutes, which is significantly longer than that in Example 7. The thermal energy utilization rate and production efficiency are low.

[0101] Comparative Example 3

[0102] This comparative example differs from Example 2 in that the solidification process was altered in this comparative example, using a conventional method of varying the electron beam intensity (reducing the high voltage at a rate of 200 V / min) to achieve single crystal solidification. Specifically, a liquid sphere with a diameter of approximately 1.2 mm was formed using the same process as in Example 2. After maintaining the liquid-solid interface for 2 minutes, the electron beam intensity was uniformly reduced to zero after 10 minutes, allowing the sphere to slowly solidify into a spherical single crystal.

[0103] The cross section of the spherical W single crystal prepared in this comparative example was ground and polished, and electrochemically corroded in a 5% NaOH solution with a corrosion current of about 1A. The metallographic photograph obtained is as follows: Figure 7 As shown. Figure 7 The photos are the same as those in Example 2 Figure 5 From the comparison of the single crystal photos shown, it can be seen that the corrosion surface of the single crystal prepared in this comparative example has obvious unevenness and substructures, and the quality of the single crystal is poor, which will affect the performance of the single crystal.

[0104] Comparative Example 4

[0105] This comparative example also adopts the conventional method of changing the electron beam intensity (reducing the high voltage at a rate of 200 V / min) to achieve the solidification of larger-sized crystals. Specifically, a liquid ball with a diameter of 8 mm is formed by the same process as Example 6 and the liquid-solid interface is maintained for 3 minutes. Then, the electron beam intensity is uniformly reduced to 0 at 10 minutes, and it is allowed to slowly solidify to form spherical crystals.

[0106] The cross section of the spherical crystal prepared in this comparative example was ground and polished, and electrochemically corroded in a 5% NaOH solution with a corrosion current of about 1A. The metallographic photograph obtained is as follows: Figure 8 As shown. At the same time, the diffraction pattern of the crystal is provided. X-ray diffraction shows that the diffraction pattern of the crystal is as follows Figure 9 As shown, the spectrum shows that the diffraction planes include (310), (110), (211), etc., proving that it forms a polycrystalline structure.

[0107] Through in-depth research, it was found that the growth rate of single crystals is controlled by the solidification rate. Too fast solidification rate, too large axial temperature gradient, and too fast cooling rate after solidification will lead to the formation of polycrystalline, single crystal cracking, vacancies, dislocations and other defects, which seriously affect the performance of single crystals. Therefore, precise control of the solidification rate is crucial to obtaining high-quality single crystal spheres. Specifically, when conventional electron beam heating is used to prepare metal single crystals, the method of reducing the electron beam intensity is used to control the solidification of the single crystal. As shown in Comparative Examples 3 and 4 of the present invention, during the solidification process, as the droplet diameter changes, especially when the droplet diameter is large, there is no linear relationship between the rate of reduction of the electron beam intensity and the temperature change in the molten zone to achieve single crystal solidification. Because there is a certain temperature difference between the center and the surface of the droplet, the method of reducing the electron beam intensity to control solidification will cause the center temperature to drop more than the surface, making it easy to solidify first in the center and form multiple crystal nuclei, which will generate greater thermal stress during subsequent cooling. When the droplet diameter is large, it is more difficult to accurately control the solidification rate of the molten zone by reducing the electron beam intensity. Therefore, the single crystals prepared by the existing method will form defects such as vacancies, dislocations, and polycrystalline grain boundaries, which will seriously affect the performance of the single crystal.

[0108] In the present invention, by adopting the method of moving the single crystal ball, the parameters are first adjusted to maintain the solid-liquid interface at the top of the droplet. Subsequently, it is only necessary to observe the liquid-solid interface and adjust the movement parameters of the driving structure to make the solid-liquid interface move at a uniform speed. Therefore, the solidification and cooling rate of the single crystal can be controlled more accurately, and the crystal quality obtained is also better. This effect can be verified by the comparison results of Example 2 and Comparative Example 3, and the comparison results of Example 6 and Comparative Example 4. It can be seen from Comparative Example 3 that the W single crystal cross section is ground, polished and electrochemically corroded, and the metallographic photographs obtained are as follows Figure 7 shown. Figure 7 It can be seen from the figure that different morphologies of tissues appeared in the W crystals. Compared with the single crystals obtained in Example 2, the quality of the crystals obtained in this comparison is poor. In addition, it can be seen from Comparative Example 4 that when the droplet size is larger, the core temperature decreases faster, and the W balls obtained are polycrystalline. Figure 8 and Figure 9 shown.

[0109] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing spherical metal single crystals by electron beam heating, characterized in that: It is prepared by using an electron beam heating device for preparing spherical metal single crystals; Among them, a device for preparing spherical metal single crystals by electron beam heating includes: Vacuum chamber (1); The heating element (2) has a circular ring structure and is arranged in the vacuum chamber (1) for emitting an electron beam; A driving structure (3) is arranged in the vacuum chamber (1) and is used to drive the metal wire to move along the central axis of the annular structure in the heating element (2); A high voltage source (6) is used to apply a negative high voltage to the heating element (2) to accelerate the electron beam toward the metal wire; The preparation process of the spherical metal single crystal includes: the acquisition of wire; Fixing the metal wire: fixing the top end of the metal wire above the heating element (2) through the driving structure (3) and grounding it, and controlling the central axis of the metal wire to coincide with the central axis of the circular ring structure in the heating element (2); Vacuuming; Melting and solidification: Start the heating element (2) and the high-voltage source (6) to melt the bottom end of the metal wire to form a large liquid metal ball, and maintain the liquid-solid interface for 2-5 minutes; then move it vertically upward at a speed of 0.5-5 mm / min, so that the large liquid metal ball cools and solidifies from top to bottom to form a spherical metal single crystal.

2. The method according to claim 1, characterized in that The vacuum chamber (1) further comprises a focusing plate (4) arranged parallel to the annular structure; the focusing plate (4) comprises two plates, which are arranged on opposite sides of the heating element (2); The focusing plate (4) is also provided with a through hole (5) for facilitating the movement of the metal wire; The distance between the focusing plate (4) and the heating element (2) is 2-50 mm; The focusing plate (4) and the heating element (2) are both connected to a high-voltage source (6), and a negative high voltage is applied to both the focusing plate (4) and the heating element (2) via the high-voltage source (6). A grounding terminal for grounding the metal wire is provided at a position fixed to the metal wire on the driving structure (3).

3. The method according to claim 2, characterized in that The focusing plate (4) is made of molybdenum, niobium or tantalum.

4. The method according to any one of claims 1 to 3, characterized in that The heating element (2) is composed of an electric heating wire (21) bent into a circular ring structure and a power source (22) for providing energy to the electric heating wire (21).

5. The method according to claim 4, characterized in that The material of the electric heating wire (21) is tungsten, molybdenum or tantalum.

6. The method according to claim 4, characterized in that The diameter of the electric heating wire (21) is 0.1-2 mm, and the diameter of the circular ring structure formed by it is 5-50 mm.

7. The method according to claim 1, characterized in that The material of the metal wire is W, Ta, Mo, Nb, Ni, Cr, Cu, Al, Pd, Ir, Rh, Ru, Au, Pt, Ag, Re or a metal alloy; The metal alloy is Ag / Au, Pt / Pd, Pt / Rh or Pt / Re.

8. The method according to claim 1 or 7, characterized in that The diameter of the metal wire is 0.1-10 mm; After the vacuuming step, the pressure in the vacuum chamber (1) is less than 1 Pa; Before the melting and solidification steps, the linear distance between the bottom end of the metal wire and the plane where the heating element (2) is located is adjusted to less than 10 mm; The melting process in the melting and solidification steps is as follows: starting the heating element (2) and the high voltage source (6) to cause the annular structure to emit an accelerated electron beam toward the metal wire, and the electron beam heats and melts the bottom end of the metal wire to form a small liquid metal ball; then, the driving structure (3) drives the metal wire to move vertically downward by 5-20 mm at a speed of 0.5-5 mm / min, and after a large liquid metal ball is formed at the bottom end of the metal wire, the liquid-solid interface is maintained for 2-5 minutes; The diameter of the spherical metal single crystal ranges from 0.2 to 15 mm.

9. The method according to claim 8, characterized in that The melting and solidifying steps are repeated at least once.

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