LaB6-tib2 eutectic composite and method for preparing the same

Abstract

The application provides a high-performance LaB6[100]-TiB2 eutectic composite material and a preparation method thereof, and a cathode device comprising the material. In the LaB6[100]-TiB2 eutectic composite material, the molar ratio of LaB6[100] to TiB2 is 11:4, LaB6 is a matrix and the crystal orientation is [100]; and TiB2 is a reinforcing phase in the form of fibers. The crystals in the LaB6[100]-TiB2 eutectic composite material are uniform and have very good thermal emission performance.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, specifically relating to a high-performance LaB6

[100] -TiB2 eutectic composite material and its preparation method, as well as a cathode device including the LaB6

[100] -TiB2 eutectic composite material. Background Technology

[0002] Lanthanum hexaboride (LaB6) has traditionally been widely used as a thermionic emitter due to its low electron work function, good electrical conductivity, and good high-temperature chemical stability. However, the presence of BB covalent bonds leads to its room-temperature brittleness and low resistance to thermal cracking at high temperatures, severely limiting its further engineering applications. By adding MeB2 (Me is a transition element such as Zr, Ti, Hf, or V) with a high elastic modulus to the LaB6 matrix, a LaB6-MeB2 eutectic composite material can be formed. This not only improves the mechanical properties of the material but also enhances the diffusion rate of La atoms. Among these methods, the addition of ZrB2 and TiB2 to form a eutectic alloy has the most significant strengthening and toughening effect. Moreover, the required TiB2 content is the lowest in the eutectic system, and its thermionic emission performance is potentially the best.

[0003] Currently, the commonly used methods for preparing LaB6-TiB2 eutectic composite materials are arc melting and high-frequency induction melting. In arc melting, the arc force generated during crystal growth, including arc contraction force and plasma flow pressure, can disturb the stability of the molten zone. This is especially true when growing volatile substances, as the volatiles interfere with the arc force, accelerating the instability of the molten zone and affecting the quality of the composite material, ultimately leading to unsatisfactory thermal emission performance. Similarly, the magnetic field force and eddy currents generated in high-frequency induction melting also affect the stability of the molten zone, thus impacting the quality of the composite material. Therefore, it is necessary to explore new preparation techniques to obtain high-performance LaB6-TiB2 eutectic composite materials. Summary of the Invention

[0004] Technical issues To address the aforementioned problems in the prior art, this invention aims to provide a high-performance LaB6

[100] -TiB2 eutectic composite material and its preparation method, as well as a cathode device comprising this material. In this method, the crystals grow uniformly and steadily, and the high-quality LaB6

[100] -TiB2 eutectic composite material prepared therefrom exhibits excellent thermal emission properties.

[0005] Technical solution According to a first aspect of the present invention, a LaB6

[100] -TiB2 eutectic composite material is provided, wherein the molar ratio of LaB6

[100] to TiB2 is 11:4, LaB6 is the matrix and the crystal orientation is

[100] ; TiB2 is a reinforcing phase existing in the form of fibers.

[0006] Preferably, the diameter of the TiB2 fiber is between 0.20 micrometers and 1.00 micrometers, and the eutectic spacing is between 0.56 micrometers and 1.53 micrometers.

[0007] Preferably, the LaB6

[100] -TiB2 eutectic composite material is manufactured at a temperature of 1873 K and a vacuum degree of 2.0 × 10⁻⁶. -5 The highest thermal emission current density measured under closed-environment conditions of Pa and voltages of 2000–4000 V was 18 A / cm². 2 The above is preferred, 20A / cm. 2 The above is preferred, 23A / cm 2 The optimal value is 35A / cm. 2 above.

[0008] According to a second aspect of the present invention, a method for preparing the LaB6

[100] -TiB2 eutectic composite material according to the present invention is provided, comprising the following steps: (1) After mixing lanthanum hexaboride and titanium diboride powders, place them in a ball mill and ball mill them under an inert gas atmosphere, preferably for 5-15 hours, and then dry them to obtain mixed powder; (2) The mixed powder is loaded into a graphite mold and manually pre-pressed into a blank, and then placed into a spark plasma sintering furnace. The DC pulse of the sintering furnace is 40:7. Under vacuum atmosphere and pressure of 25-50MPa, the temperature is raised to 1350-1550℃ at a rate of 30-80℃ / min, and held for 3-10min. After cooling with the furnace, the composite material sintered body is obtained. (3) The composite material sintered body is processed into a cylinder with a diameter of 5-10 mm and a length of 35-55 mm by electrical discharge wire cutting. After the surface of the cylinder is polished with sandpaper, it is cleaned in acetone and alcohol in turn. After drying, the composite material blank rod is obtained. (4) The blank rod is suspended on the upper pull rod of the optical levitation zone furnace as a test rod. The

[100] LaB6 single crystal rod of the same size is used as a seed crystal and fixed on the ceramic joint of the lower pull rod of the optical levitation zone furnace. The test rod and the seed crystal are rotated in opposite directions on the same axis and the lower end of the test rod and the upper end of the seed crystal are located in the heating zone. The power of the optical levitation zone furnace is increased in an inert gas atmosphere to melt the test rod and keep the melting zone stable. The pull rate and stroke of the pull rod are set to pull the test rod, so that the seed crystal and the test rod are directionally driven away from the heating zone, thereby obtaining the LaB6

[100] -TiB2 eutectic composite material.

[0009] As a further aspect of the present invention: in step (1), the purity of both LaB6 and TiB2 powders is not less than 99.9%, the particle size is 200-400 mesh, and the molar ratio of LaB6 to TiB2 is 11:4.

[0010] As a further aspect of the present invention: in step (2), the pressure of manual pre-compression is 1-10 MPa, and the holding time is 1-5 min.

[0011] As a further aspect of the present invention: in step (2), the density of the composite sintered body is above 70%.

[0012] As a further aspect of the present invention: in step (3), the equipment for cleaning and polishing the sintered body is an ultrasonic cleaner, wherein the ultrasonic frequency is 40-60kHz and the cleaning time of acetone and alcohol is 5-10min.

[0013] As a further embodiment of the present invention: in step (4), the pulling speed of the pull rod of the optical suspension zone furnace is set to 2-300 mm / h, preferably 50-100 mm / h, the rotation speed is 10-20 r / min, the stroke is 20-40 mm, and the power is 11-13 kW; the Ar gas pressure of the inert atmosphere is 0-1 MPa.

[0014] According to a third aspect of the invention, a cathode device is provided, comprising the LaB6

[100] -TiB2 eutectic composite material according to the invention.

[0015] Compared with existing single-crystal preparation techniques, the present invention has the following advantages: The LaB6

[100] -TiB2 eutectic composite material prepared by the present invention using spark plasma sintering technology and optical levitation zone melting method has the following advantages: The optical levitation zone melting method used in the experiment inside the high-temperature and high-pressure quartz tube can effectively suppress the volatilization of each component. The heating source is four high-energy beam power density xenon lamps evenly distributed around the test rod. During the heating process, no interference force is generated that affects the crystal growth process or disturbs the stability of the melting zone. This provides technical support for the preparation of large-size samples and ensures uniform and steady-state crystal growth. The prepared high-quality composite material has very good thermal emission performance. Attached Figure Description

[0016] Figure 1 A photograph of the LaB6

[100] -TiB2 eutectic composite material prepared according to Example 1; Figure 2 SEM images of the LaB6

[100] -TiB2 eutectic composite material prepared according to Example 1; Figure 3 The XRD pattern of the LaB6

[100] -TiB2 eutectic composite material prepared according to Example 1; Figure 4 The current-voltage characteristic curves of the LaB6

[100] -TiB2 eutectic composite material prepared according to Example 1 are shown. Detailed Implementation

[0017] The present invention will now be described with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. Any modifications and improvements made without altering the inventive concept are within the scope of protection of the present invention.

[0018] The hot pressing equipment used in the following embodiments is a LABOX-350 spark plasma sintering furnace; The zone furnace used in the following embodiments is an FZ-T-2000-XI-VPO-PC optical levitation zone furnace, which is heated by four xenon lamps, each with a power of 5Kw, and the maximum temperature can reach 3000℃.

[0019] The ultrasonic cleaner used in the following examples is the SB25-12DTD ultrasonic cleaner manufactured by Ningbo Xinzhi Biotechnology Co., Ltd. The wire EDM machine used in the following embodiments is a DK77 type CNC wire EDM machine tool, which uses molybdenum wire for cutting; The purity of the LaB6 and TiB2 powders used in the following examples is 99.9%, and the particle size is 200-400 mesh.

[0020] Example 1 In this embodiment, the LaB6

[100] -TiB2 eutectic composite material was prepared according to the following steps: (1) Weigh 88.70g of lanthanum hexaboride and 11.00g of titanium diboride powder, combine them, put them into a ball mill, and ball mill them for 10 hours in an inert gas atmosphere. After taking them out, put them into a vacuum drying oven and dry them at 80°C. After drying, take them out to obtain the mixed powder. (2) The prepared powder was loaded into a graphite mold and manually pre-pressed into a preform. Then it was placed in a spark plasma sintering furnace (pressure 5 MPa, holding time 2 min). The DC pulse of the sintering furnace was 40:7. Under vacuum atmosphere and 40 MPa pressure, the temperature was raised to 1500℃ at 60℃ / min and held for 5 min. After cooling in the furnace, the composite sintered body was obtained. The density of the sintered body was measured to be 81.3%. (3) The composite sintered body is processed into a cylinder with a diameter of 6 mm and a length of 50 mm by wire electrical discharge machining. After the surface of the cylinder is polished with sandpaper, it is placed in an ultrasonic cleaner and cleaned in acetone and alcohol in sequence (ultrasonic frequency of 40 kHz, cleaning time of each reagent is 5 min). After drying, the composite blank rod is obtained. (4) The blank rod is suspended on the upper pull rod of the optical levitation zone furnace as a test rod. The same size

[100] LaB6 is fixed on the ceramic joint connected to the lower pull rod of the optical levitation zone furnace as a seed crystal. The test rod and the seed crystal are rotated in opposite directions on the same axis, and the lower end of the test rod and the upper end of the seed crystal are located in the heating zone. The power of the optical levitation zone furnace is increased (power is 11.88kW) under an argon atmosphere with a pressure of 0.5MPa to melt the test rod. The pulling speed and stroke of the pull rod are set for pulling (pulling speed 65mm / h, rotation speed 15r / min, stroke 30mm). The ceramic joint moves unidirectionally from the heating zone to the outside of the heating zone to achieve directional solidification. When the specified stroke is reached, the heating is stopped and cooled to room temperature to obtain the LaB6

[100] -TiB2 eutectic composite material.

[0021] The macroscopic morphology of the LaB6

[100] -TiB2 eutectic composite material is as follows: Figure 1 As shown, the diameter of the eutectic composite material is 7 mm and the length is 43 mm.

[0022] Figure 2 The image shows a SEM image of the LaB6

[100] -TiB2 eutectic composite material. It can be seen that the eutectic structure is a typical rod-shaped eutectic with a fiber diameter of 0.592µm and a eutectic spacing of 1.05µm. There are no other impurities or cracks in the microstructure.

[0023] Figure 3 The image shows the XRD pattern of the LaB6

[100] -TiB2 eutectic composite material. It can be seen that the matrix has only the

[100] orientation and no impurity phase peaks.

[0024] Figure 4 The thermal emission properties of the LaB6

[100] -TiB2 eutectic composite material are shown. It can be seen that the temperature is 1873K and the vacuum degree is 2.0×10⁻⁶. -5 The highest current density measured under closed-circuit conditions at voltages of 2000–4000 V was 39.48 A / cm². 2 The highest thermal emission current density of the LaB6-TiB2 eutectic composite material reported in the literature is only 12 A / cm². 2 .

[0025] Example 2 In this embodiment, LaB6

[100] -TiB2 eutectic composite material was prepared in the same manner as in Example 1, with the only difference being that the pulling speed of the optical levitation zone furnace in step (4) was 5 mm / h and the power of the zone furnace was 11 kW.

[0026] The prepared LaB6

[100] -TiB2 eutectic composite material has a fiber diameter of 0.84µm and a eutectic spacing of 1.35µm. The composite material was prepared at a temperature of 1873K and a vacuum degree of 2.0×10⁻⁶. -5 The highest emission current density measured under closed-circuit conditions at voltages of 2000–4000 V can reach 21.21 A / cm². 2 .

[0027] Example 3 In this embodiment, the LaB6

[100] -TiB2 eutectic composite material was prepared in the same manner as in Example 1, with the only difference being that the pulling speed of the optical levitation zone furnace in step (4) was 300 mm / h and the furnace power was 13 kW.

[0028] The fiber diameter in the prepared LaB6

[100] -TiB2 eutectic composite material is 0.22µm, and the eutectic spacing is 0.92µm. At a temperature of 1873 K and a vacuum degree of 2.0 × 10⁻⁶ -5 The highest emission current density measured under closed-circuit conditions at voltages of 2000–4000 V can reach 23.1 A / cm². 2 .

[0029] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A LaB6[100]-TiB2 eutectic composite material, wherein the molar ratio of LaB6[100] to TiB2 is 11:4, LaB6 is the matrix with a crystal orientation of [100]; TiB2 is a reinforcing phase existing in the form of fibers, wherein the LaB6[100]-TiB2 eutectic composite material is subjected to a temperature of 1873K and a vacuum degree of 2.0×10⁻⁶. -5 The highest thermal emission current density measured under closed-environment conditions of Pa and voltages of 2000–4000 V was 18 A / cm². 2 The above; and The LaB6[100]-TiB2 eutectic composite material was prepared by a method including the following steps: (1) Lanthanum hexaboride and titanium diboride powders were mixed and placed in a ball mill, ball milled and mixed under an inert gas atmosphere, and then dried to obtain mixed powder; (2) The mixed powder is loaded into a graphite mold and manually pre-pressed into a blank, and then placed into a spark plasma sintering furnace with a DC pulse ratio of 40:

7. Under a vacuum atmosphere and a pressure of 25-50MPa, the temperature is raised to 1350-1550℃ at a rate of 30-80℃ / min, and held for 3-10 minutes. After cooling in the furnace, the composite material sintered body is obtained. (3) The composite material sintered body is processed into a cylinder with a diameter of 5-10 mm and a length of 35-55 mm by electrical discharge wire cutting. After the surface of the cylinder is polished with sandpaper, it is cleaned in acetone and alcohol in turn. After drying, the composite material blank rod is obtained. (4) The blank rod is suspended on the upper pull rod of the optical levitation zone furnace as a test rod. The [100]LaB6 single crystal rod of the same size is used as a seed crystal and fixed on the ceramic joint of the lower pull rod of the optical levitation zone furnace. The test rod and the seed crystal are rotated in opposite directions on the same axis and the lower end of the test rod and the upper end of the seed crystal are located in the heating zone. The power of the optical levitation zone furnace is increased in an inert gas atmosphere to melt the test rod and keep the melting zone stable. The pull rate and stroke of the pull rod are set to pull the test rod, so that the seed crystal and the test rod are directionally driven away from the heating zone, thereby obtaining the LaB6[100]-TiB2 eutectic composite material.

2. The LaB6[100]-TiB2 eutectic composite material according to claim 1, wherein, The diameter of TiB2 fibers ranges from 0.20 μm to 1.00 μm, and the eutectic spacing ranges from 0.56 μm to 1.53 μm.

3. The LaB6[100]-TiB2 eutectic composite material according to claim 1, wherein, The LaB6[100]-TiB2 eutectic composite material was tested at a temperature of 1873 K and a vacuum degree of 2.0 × 10⁻⁶. -5 The highest thermal emission current density measured under closed-environment conditions of Pa and voltages of 2000–4000 V was 20 A / cm². 2 above.

4. The LaB6[100]-TiB2 eutectic composite material according to claim 3, wherein, The LaB6[100]-TiB2 eutectic composite material was tested at a temperature of 1873 K and a vacuum degree of 2.0 × 10⁻⁶. -5 The highest thermal emission current density measured under closed-environment conditions of Pa and voltages of 2000–4000 V was 23 A / cm². 2 above.

5. The LaB6[100]-TiB2 eutectic composite material according to claim 3, wherein, The LaB6[100]-TiB2 eutectic composite material was tested at a temperature of 1873 K and a vacuum degree of 2.0 × 10⁻⁶. -5 The highest thermal emission current density measured under closed-environment conditions of Pa and voltages of 2000–4000 V was 35 A / cm². 2 above.

6. A method for preparing a LaB6[100]-TiB2 eutectic composite material according to any one of claims 1 to 5, comprising the following steps: (1) Lanthanum hexaboride and titanium diboride powders were mixed and placed in a ball mill. The mixture was ball milled and dried under an inert gas atmosphere to obtain a mixed powder. (2) The mixed powder is loaded into a graphite mold and manually pre-pressed into a blank, and then placed into a spark plasma sintering furnace with a DC pulse ratio of 40:

7. Under a vacuum atmosphere and a pressure of 25-50MPa, the temperature is raised to 1350-1550℃ at a rate of 30-80℃ / min, and held for 3-10 minutes. After cooling in the furnace, the composite material sintered body is obtained. (3) The composite material sintered body is processed into a cylinder with a diameter of 5-10 mm and a length of 35-55 mm by electrical discharge wire cutting. After the surface of the cylinder is polished with sandpaper, it is cleaned in acetone and alcohol in turn. After drying, the composite material blank rod is obtained. (4) The blank rod is suspended on the upper pull rod of the optical levitation zone furnace as a test rod. The [100]LaB6 single crystal rod of the same size is used as a seed crystal and fixed on the ceramic joint of the lower pull rod of the optical levitation zone furnace. The test rod and the seed crystal are rotated in opposite directions on the same axis and the lower end of the test rod and the upper end of the seed crystal are located in the heating zone. The power of the optical levitation zone furnace is increased in an inert gas atmosphere to melt the test rod and keep the melting zone stable. The pull rate and stroke of the pull rod are set to pull the test rod, so that the seed crystal and the test rod are directionally driven away from the heating zone, thereby obtaining the LaB6[100]-TiB2 eutectic composite material.

7. The method for preparing LaB6[100]-TiB2 eutectic composite material according to claim 6, wherein, The ball milling mixture in step (1) is carried out for 5-15 hours.

8. The method for preparing LaB6[100]-TiB2 eutectic composite material according to claim 6, wherein, The purity of both LaB6 and TiB2 powders is not less than 99.9%, and the particle size is 200-400 mesh.

9. The method for preparing LaB6[100]-TiB2 eutectic composite material according to claim 6, wherein, In step (2), the manual pre-compression pressure is 1-10 MPa and the holding time is 1-5 min.

10. The method for preparing LaB6[100]-TiB2 eutectic composite material according to any one of claims 6 to 9, wherein, In step (2), the density of the composite sintered body is above 70%.

11. The method for preparing LaB6[100]-TiB2 eutectic composite material according to any one of claims 6 to 9, wherein, In step (3), the equipment for cleaning and polishing the sintered body is an ultrasonic cleaner, wherein the ultrasonic frequency is 40-60kHz and the cleaning time of acetone and alcohol is 5-10min.

12. The method for preparing LaB6[100]-TiB2 eutectic composite material according to any one of claims 6 to 9, wherein, In step (4), the optical suspension zone furnace is set with a pulling speed of 20-300 mm / h, a rotation speed of 10-20 r / min, a stroke of 20-40 mm, and a power of 11-13 kW; the inert gas atmosphere is Ar gas with a pressure of 0.5-1 MPa.

13. The method for preparing LaB6[100]-TiB2 eutectic composite material according to claim 12, wherein, In step (4), the pulling speed of the pull rod set in the optical suspension zone furnace is 50-100 mm / h.

14. A cathode device comprising a LaB6[100]-TiB2 eutectic composite material according to any one of claims 1 to 5.

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