A La 1-x Ce x B6 nanocrystalline bulk material and method of making the same

Abstract

This invention relates to a La 1‑x Ce x This paper describes the preparation method of B6 nanocrystalline bulk materials and its application in the field of rare earth hexaboride bulk material preparation technology. Nano-LaH2, CeH2, amorphous B powder, and liquid Ga are ball-milled and mixed according to a set stoichiometric ratio. The mixed powder is then loaded into a graphite mold in a glove box, compacted using a static press, and then sintered in a vacuum resistance furnace at a temperature of 700-1000 ℃ with a heating rate of 5-20 ℃. After reaching the sintering temperature, the holding time is 0.5-2 h to obtain La6 nanocrystalline bulk materials. 1‑x Ce x B6 nanocrystalline bulk material. La prepared by the method described above. 1‑ x Ce x B6 nanocrystalline bulk material has a controllable grain size of 50-100 nm. The preparation method of this nanocrystalline bulk material is simple to operate and low in cost, which is conducive to its widespread application.

Description

Technical Field

[0001] This invention belongs to the field of rare earth hexaboride nanocrystalline bulk material preparation technology, and particularly relates to a La 1-x Ce x B6 nanocrystalline bulk material and its preparation method. Background Technology

[0002] Rare-earth hexaborides, especially lanthanum hexaboride (LaB6), are considered the most promising hot cathode electron emission materials for next-generation space electric propulsion systems (such as Hall thrusters and ion thrusters) due to their extremely low work function (approximately 2.7 eV), high melting point (approximately 2210 °C), and excellent chemical stability. Compared to traditional binary single-crystal LaB6, theoretically, nanocrystalline multi-component rare-earth hexaborides (such as LaB6) offer greater potential. 1-x Ce x B6) possesses superior electron emission performance and lower raw material costs, which is of great significance for meeting the stringent requirements of high specific impulse, long life, and high reliability for propulsion systems in missions such as deep space exploration and satellite constellation. Although La 1-x Ce x B6 bulk materials are of great theoretical and practical value, but current technologies face significant challenges in preparing high-performance nanocrystalline bulk materials. Traditional preparation processes (such as high-temperature solid-state reaction sintering or liquid-state reaction sintering) typically require holding the raw materials at high temperatures (1500~2200℃) and high pressures (50MPa~1GPa) for several hours. While such high temperatures and pressures can ensure material densification, they lead to severe abnormal grain growth (grain sizes typically exceeding micrometers), failing to yield a nanocrystalline structure. This not only significantly reduces the material's mechanical properties (such as fracture toughness) but also degrades its resistance to ion bombardment and thermal stability required for use as a hot cathode, severely limiting its application in long-lifespan space devices. To suppress grain growth, some studies have attempted to employ techniques such as spark plasma sintering (SPS) or hot isostatic pressing (HIP). Although these methods can achieve rapid densification at lower temperatures (>1200℃), the equipment is extremely expensive, the processes are complex, and they are mostly used for small-batch production, making it difficult to meet the demands of engineering applications for low-cost, large-scale preparation. Therefore, it is necessary to develop a novel process that can achieve rapid densification at lower temperatures and pressures, effectively suppress grain growth, and significantly reduce preparation costs, in order to prepare La with both high density and nanocrystalline structure. 1-x Ce x The B6 bulk material has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] In view of this, the present invention aims to provide a novel La 1-x Ce xA method for preparing B6 nanocrystalline bulk materials was developed to address the aforementioned technical challenges. By introducing a small amount of liquid metal Ga as an activator into traditional raw materials, La was successfully and rapidly prepared in a conventional vacuum sintering furnace at temperatures below 1000°C. 1-x Ce x B6 nanocrystalline bulk material. The introduction of liquid Ga activates the synthesis process, lowers the reaction temperature, and hinders grain growth during the synthesis reaction. In a conventional vacuum resistance furnace, the low-pressure compacted raw materials can be sintered into a dense structure, and when held at temperature for more than 0.5 hours, Ga elements are almost entirely precipitated on the surface of the sintered bulk, without introducing impurities. This preparation method is simple to operate and low in cost, and the prepared La... 1-x Ce x B6 nanocrystalline bulk material has high purity and high density, and the grain size is controllable between 50-100 nm.

[0004] This invention provides a La 1-x Ce x B6 nanocrystalline bulk material and its preparation method, characterized by comprising the following steps: 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce x B6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1. The mixture is then ball-milled for half an hour under an argon protective atmosphere. The value of x ranges from 0 to 1, and the mass ratio of liquid Ga ranges from 1% to 3%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) Place the high-strength graphite abrasive containing the mixed powder into the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 700-1000 ℃, the heating rate is 5-20℃ / min, and the holding time after reaching the sintering temperature is 0.5-2 h. 4) After sintering, La 1-x Ce x The surface of B6 nanocrystalline bulk material is polished and then placed in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities and precipitated Ga, yielding single-phase, high-purity, high-density La with a grain size controllable in the range of 50-100 nm. 1-x Ce x B6 nanocrystals.

[0005] Compared with existing preparation techniques, the present invention has the following advantages: The preparation method described in this invention is simple to operate and low in cost, and the prepared La 1-x Ce xB6 nanocrystalline bulk material has high purity and high density, and the grain size is controllable in the range of 50-100 nm, making it a promising material for thermionic cathodes. Attached Figure Description

[0006] Figure 1 Preparation of La in Examples 1-4 1-x Ce x X-ray diffraction pattern of B6 nanocrystalline bulk material.

[0007] Figure 2 Nano-La prepared in Example 3 0.5 Ce 0.5 Transmission electron microscope image of B6 nanocrystalline bulk material. Detailed Implementation

[0008] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0009] 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce x B6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1. The mixture is then ball-milled for half an hour under an argon protective atmosphere. The value of x is 0, and the mass ratio of liquid Ga is 3%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) The high-strength graphite abrasive containing the mixed powder is placed in the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 1000 ℃, the heating rate is 5℃ / min, and the holding time after reaching the sintering temperature is 2 h. 4) Polish the surface of the sintered LaB6 nanocrystalline bulk material and then place it in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities and precipitates of Ga, thereby obtaining a single-phase, high-purity, high-density LaB6 nanocrystalline bulk material with a grain size of 100 nm. Example 2

[0010] 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce xB6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1. The mixture is ball-milled for half an hour under an argon protective atmosphere. The value of x is 0.2, and the mass ratio of liquid Ga is 2.5%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) The high-strength graphite abrasive containing the mixed powder is placed in the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 900 ℃, the heating rate is 10℃ / min, and the holding time after reaching the sintering temperature is 1.5 h. 4) After sintering, La 0.8 Ce 0.2 The surface of B6 nanocrystalline bulk material is polished and then placed in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities and Ga precipitates, yielding single-phase, high-purity, high-density La with a grain size of 80 nm. 0.8 Ce 0.2 B6 nanocrystalline material. Example 3

[0011] 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce x B6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1. The mixture is then ball-milled for half an hour under an argon protective atmosphere. The value of x is 0.5, and the mass ratio of liquid Ga is 2%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) The high-strength graphite abrasive containing the mixed powder is placed in the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 800 ℃, the heating rate is 15℃ / min, and the holding time after reaching the sintering temperature is 1 h. 4) After sintering, La 0.5 Ce 0.5 The surface of B6 nanocrystalline bulk material is polished and then placed in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities and precipitated Ga, yielding single-phase, high-purity, high-density La with a grain size controllable at 60 nm. 0.5 Ce 0.5 B6 nanocrystals. Example 4

[0012] 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce xB6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1. The mixture is then ball-milled for half an hour under an argon protective atmosphere. The value of x is 1, and the mass ratio of liquid Ga is 1%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) The high-strength graphite abrasive containing the mixed powder is placed in the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 700 ℃, the heating rate is 20℃ / min, and the holding time after reaching the sintering temperature is 0.5 h. 4) Polish the surface of the sintered CeB6 nanocrystal block and then place it in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities and Ga precipitates, thereby obtaining a single-phase, high-purity, high-density CeB6 nanocrystal block material with a grain size controllable at 50 nm.

[0013] Preparation of La in Examples 1-4 1-x Ce x X-ray diffraction pattern of B6 nanocrystal material, such as Figure 1 As shown, nanocrystalline La was prepared using this method. 0.5 Ce 0.5 B6 is a single-phase, impurity-free phase with good crystallinity. Figure 2 Nano-La prepared in Example 3 0.5 Ce 0.5 Transmission electron microscopy (TEM) image of B6 nanocrystal bulk material, showing uniform grain size distribution and a grain size of approximately 60 nm.

Claims

1. A La 1-x Ce x B6 nanocrystalline bulk material and its preparation method, characterized in that: 1) Nano-LaH2, CeH2, and amorphous B powder with a molar purity of 99.9% were mixed according to La... 1-x Ce x B6 is stoichiometrically mixed with a certain mass ratio of liquid Ga in a ball mill jar at a ball-to-material ratio of 10:1, and the mixture is ball-milled for 0.5 h under an argon protective atmosphere; the value of x ranges from 0 to 1, and the mass ratio of liquid Ga ranges from 1 to 3%. 2) After mixing the powder evenly in step 1), put it into a high-strength graphite mold in an argon-protected glove box, and then compact it by static pressing for 2 hours. 3) Place the high-strength graphite abrasive containing the mixed powder into the cavity of a vacuum resistance furnace for sintering. The sintering temperature is 700-1000 ℃, the heating rate is 5-20℃ / min, and the holding time after reaching the sintering temperature is 0.5-2 h. 4) After sintering, La 1-x Ce x The surface of B6 nanocrystalline bulk material is polished and then placed in dilute hydrochloric acid with a molar purity of 10% for 1 hour to remove surface impurities, yielding single-phase, high-purity, high-density La nanocrystalline material with a grain size controllable in the range of 50-100 nm. 1-x Ce x B6 nanocrystals.

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