CN101575211A - High dense (SmxBa<1-x>)B6 polycrystalline block cathode and rapid preparation method thereof - Google Patents

Abstract

A (Sm _x Ba _1-x )B ₆ polycrystalline block cathode and a preparation method thereof belong to the technical field of rare earth boride materials. The chemical composition of the cathode material provided by the present invention is (Sm _x Ba _1-x ) B ₆ , 0.2≤x≤1. In the present invention, the SmH ₂ and BaH ₂ nanometer powders are prepared respectively by direct current arc evaporation method, and then mixed with raw material B powder according to the ratio, and the discharge plasma reaction liquid phase sintering is adopted, the pressure is 40-70MPa, and the heating rate is 90-150°C/ min, the sintering temperature is 1300-1500°C, and the temperature is kept for 5-15 minutes to obtain single-phase and dense (Sm _x Ba _1-x )B ₆ . The method of the invention has low sintering temperature, short time and simple process.

Description

A highly dense (SmxBa1-x) B6 polycrystalline bulk cathode and its rapid preparation method

technical field

The invention belongs to the technical field of rare earth boride materials, and in particular relates to a high-density (Sm _x Ba _1-x ) B ₆ polycrystalline block cathode material and a preparation method thereof.

Background technique

Rare earth borides have many excellent physical and chemical properties, especially lanthanum hexaboride has excellent electron emission characteristics, and is widely used in various electronic cathode devices. With the rapid development of electron beam and ion beam technology, higher performance requirements are put forward for related cathode materials. Multi-element rare earth boride cathodes have become a research hotspot, and cathode materials such as (LaBa)B ₆ and (LaEu)B ₆ have been developed successively (Liu Shuping, Yang Qingshan, Chen Weiping, Liu Jiaxiang, Li Zhonghua. Rare Metals and Hard Alloys. 2006, 34( 3): 8-11). The traditional preparation method of rare earth borides is generally divided into two steps: the first step is to use boron heating, boron carbide reduction and other methods to prepare multi-element rare earth boride powders, and the powders are purified by chemical methods, washed with water, dried, crushed, and sieved etc.; in the second step, the multi-component rare earth boride bulk material is prepared by sintering for a long time (2-10 hours) at high temperature (1800°C-2100°C) by solid-state sintering. The disadvantages of these methods are that the sintering temperature is too high, the sintering time is long, the product is not dense enough, the product purity is not high, and the process is complicated, which will seriously affect the performance of the product.

Contents of the invention

The purpose of the present invention is to solve the problems of the prior art, and provide a highly dense (Sm _x Ba _1-x ) B ₆ polycrystalline block cathode and a rapid preparation method thereof. The method provided by the invention has the advantages of low sintering temperature, short time, simple process and the like.

The chemical composition of a highly dense (Sm _x Ba _1-x ) B ₆ polycrystalline block cathode provided by the present invention is (Sm _x Ba _1-x ) B ₆ , where 0.2≤x≤1.

The present invention adopts the method of combining direct current arc evaporation condensation and spark plasma sintering reaction liquid phase sintering to prepare (Sm _x Ba _1-x ) B ₆ polycrystalline block, and the specific steps are as follows:

1) Using DC arc evaporation and condensation equipment, after vacuuming to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of (0~3):1, the total pressure is 0.1MPa, and the single metal Sm block is used as Anode, the metal W is the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 40-60A, the reaction voltage is 30-50V, the reaction time is 45min, and the SmH ₂ nanometer powder is prepared;

2) Using DC arc evaporation and condensation equipment, after vacuuming to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of (1~3):1, the total pressure is 0.1MPa, and the elemental metal Ba block is used as Anode, the metal W is the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 40-60A, the reaction voltage is 30-50V, the reaction time is 40min, and the BaH ₂ nanometer powder is prepared;

3) Put the SmH ₂ nano powder, BaH ₂ nano powder and B powder in an argon atmosphere with an oxygen content of less than 50ppm, and mix them according to the atomic ratio x: (1-x): 6, wherein 0.2≤x≤1, grind After mixing, put it into a graphite mold;

4) Put the graphite mold in the SPS sintering cavity, pressurize to 40-70Mpa under the vacuum condition of 5Pa, raise the temperature to 1300-1500℃ at a heating rate of 90-150℃/min and keep it warm for 5-15min, then The furnace was cooled to room temperature to obtain (Sm _x Ba _1-x )B ₆ polycrystalline bulk cathode, where 0.2≤x≤1 (the principle is shown in equations (1), (2) and (3)).

Wherein, the particle diameter of the SmH ₂ nanometer powder is 20-80nm; the particle diameter of the BaH ₂ nanometer powder is 30-80nm.

xSmH ₂ (s)→xSm(s)+xH ₂ (g) (1)

(1-x)BaH ₂ (s)→(1-x)Ba(s)+(1-x)H ₂ (g) (2)

xSm(1)+(1-x)Ba(1)+6B(s)→(Sm _x Ba _1-x )B ₆ (s) (3)

Compared with the prior art, the present invention has the following beneficial effects:

The method of the present invention has low sintering temperature, short time and simple process, and the prepared multi-element rare earth boride (Sm _x Ba _1-x ) B ₆ polycrystalline bulk material has high density, and the crystal grains are uniform and dense according to scanning electron microscope analysis, and the relative density is obtained by The test is as high as 99.41%, the Vickers hardness reaches 2450Kg/mm ² , and it is a pure phase of hexaboride through X-ray diffraction analysis.

Description of drawings

Fig. 1 , the X-ray spectrum of the (Sm _0.2 Ba _0.8 )B ₆ polycrystalline bulk cathode prepared in Example 1.

Fig. 2. Scanning electron micrographs of the (Sm _0.2 Ba _0.8 ) B ₆ polycrystalline bulk cathode prepared in Example 1

Fig. 3, the X-ray spectrogram of the SmB ₆ polycrystalline bulk cathode prepared in Example 3.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the following examples.

Detailed ways

Example 1

1) Using DC arc evaporation and condensation equipment, after evacuating to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of 1:1, the total pressure is 0.1MPa, the single metal Sm block is used as the anode, and the metal W As the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 60A, the reaction voltage is 30-50V, the reaction time is 45min, and the SmH ₂ nanometer powder is prepared;

2) Using DC arc evaporation and condensation equipment, after evacuating to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of 1:1, the total pressure is 0.1MPa, and the single metal Ba block is used as the anode, and the metal W As the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 60A, the reaction voltage is 30-50V, and the reaction time is 40min, and BaH ₂ nanometer powder is prepared;

3) SmH ₂ nanometer powder, BaH ₂ nanometer powder and B powder are in the argon gas atmosphere that oxygen content is 10ppm, according to atomic ratio 0.2: 0.8: 6 batching, after grinding and mixing, put into graphite mould;

4) Put the graphite mold in the SPS sintering cavity, under the vacuum condition of 5Pa, after pressurizing 40Mpa, raise the temperature to 1300℃ at a heating rate of 90℃/min and keep it for 15min, then cool to room temperature with the furnace to get (Sm _0.2 Ba _0.8 ) B ₆ polycrystalline bulk cathode.

The cathode color of the obtained (Sm _0.2 Ba _0.8 )B ₆ polycrystalline block is off-white. From the XRD spectrum (Fig. 1), it can be seen that the main phase of the sample is BaB ₆ , without impurity phases, and Sm atoms are solid-dissolved in the crystal lattice, disordered Instead of a part of Ba atoms. Scanning electron microscope analysis shows that the grains are fine and uniform, dense and well developed, with an average grain size of about 0.5-3 μm, as shown in Figure 2. The relative density is 98.77% tested by the Archimedes drainage method, and the Vickers hardness is 2116Kg/mm ² .

Example 2

1) Using DC arc evaporation and condensation equipment, after vacuuming to 2.0×10 ^-2 Pa, argon gas is introduced, the total pressure is 0.1MPa, the single metal Sm block is used as the anode, and the metal W is used as the cathode. The distance between the cathode and the anode is 2-4mm, the reaction current is 50A, the reaction voltage is 30-50V, the reaction time is 45min, and the SmH ₂ nanometer powder is prepared;

2) Using DC arc evaporation and condensation equipment, after evacuating to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of 3:1, the total pressure is 0.1MPa, the single metal Ba block is used as the anode, and the metal W As the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 40A, the reaction voltage is 30-50V, and the reaction time is 40min, and BaH ₂ nanometer powder is prepared;

3) SmH ₂ nanometer powder, BaH ₂ nanometer powder and B powder are in the argon gas atmosphere that oxygen content is 20ppm, according to atomic ratio 0.5: 0.5: 6 batching, after grinding and mixing, put into graphite mould;

4) Put the graphite mold in the SPS sintering cavity, under the vacuum condition of 5Pa, after pressurizing 60Mpa, raise the temperature to 1400℃ at a heating rate of 120℃/min and keep it for 10min, then cool to room temperature with the furnace to obtain (Sm _0.5 Ba _0.5 ) B ₆ polycrystalline bulk.

The cathode color of the obtained (Sm _0.5 Ba _0.5 )B ₆ polycrystalline block is off-white. According to the X-ray diffraction spectrum, the main phase of the sample is BaB ₆ without impurity phases. A part of Ba atoms. Scanning electron microscope analysis shows that the crystal grains are uniform, dense and well developed. The relative density is as high as 99.37% tested by the Archimedes drainage method, and the Vickers hardness is 2434Kg/mm ² .

Example 3

1) Using DC arc evaporation and condensation equipment, after evacuating to 2.0×10 ^-2 Pa, introduce hydrogen and argon with a volume ratio of 3:1, the total pressure is 0.1MPa, the single metal Sm block is used as the anode, and the metal W As the cathode, the distance between the cathode and the anode is 2-4mm, the reaction current is 40A, the reaction voltage is 30-50V, the reaction time is 45min, and the SmH ₂ nanometer powder is prepared;

2) SmH _Nano powder and B powder are mixed in an argon atmosphere with an oxygen content of 50ppm in an atomic ratio of 1:6, ground and mixed, and then packed into a graphite mold;

3) Put the graphite mold in the SPS sintering cavity, under the vacuum condition of 5Pa, after pressurizing 70Mpa, heat up to 1500°C at a heating rate of 150°C/min and keep it for 5min, and cool to room temperature with the furnace to obtain SmB ₆ poly crystal block.

The cathode color of the obtained SmB ₆ polycrystalline block is blue, and the X-ray diffraction spectrum (Figure 3) shows that the main phase of the sample is the SmB ₆ single phase. Scanning electron microscope analysis shows that the crystal grains are uniform, dense and well developed. The relative density is as high as 99.41% tested by the Archimedes drainage method, and the Vickers hardness is 2450Kg/mm ² .

Claims (4)

1, a kind of (Sm _xBa _1-x) B ₆The polycrystalline bulk negative electrode is characterized in that, the chemical constitution of described negative electrode is (Sm _xBa _1-x) B ₆, wherein, 0.2≤x≤1.

2, the described a kind of (Sm of claim 1 _xBa _1-x) B ₆The preparation method of polycrystalline bulk is characterized in that, may further comprise the steps:

1) adopts the direct current arc evaporation condensing plant, be evacuated to 2.0 * 10 ^-2Behind the Pa, feeding volume ratio is (0～3): 1 hydrogen and argon gas, total gas pressure are 0.1MPa, are anode with elemental metals Sm piece, metal W is a negative electrode, and negative electrode and anodic distance are 2～4mm, and reaction current is 40～60A, response voltage is 30～50V, and the reaction times is 45min, prepares SmH ₂Nanometer powder;

2) adopt the direct current arc evaporation condensing plant, be evacuated to 2.0 * 10 ^-2Behind the Pa, feeding volume ratio is (1～3): 1 hydrogen and argon gas, total gas pressure are 0.1MPa, are anode with elemental metals Ba piece, metal W is a negative electrode, and negative electrode and anodic distance are 2～4mm, and reaction current is 40～60A, response voltage is 30～50V, and the reaction times is 40min, prepares BaH ₂Nanometer powder;

3) with SmH ₂Nanometer powder, BaH ₂In nanometer powder and the argon gas atmosphere of B powder below oxygen level is lower than 50ppm, press atomic ratio x: (1-x): 6 batchings, 0.2≤x≤1 wherein, grind mixing after, in the graphite jig of packing into;

4) graphite jig is placed the SPS sintering cavity, under the vacuum condition of 5Pa, be forced into 40～70Mpa after, be warming up to 1300～1500 ℃ of insulation 5～15min with the temperature rise rate of 90～150 ℃/min, cool to room temperature with the furnace, obtain (Sm _xBa _1-x) B ₆The polycrystalline bulk negative electrode, wherein, 0.2≤x≤1.

3, method according to claim 2 is characterized in that, described SmH ₂The particle diameter of nanometer powder is 20～80nm.

4, method according to claim 2 is characterized in that, described BaH ₂The particle diameter of nanometer powder is 30～80nm.

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