Oxide-doped LaB6 polycrystalline material as well as preparation method and application thereof

Abstract

The invention discloses an oxide-doped LaB6 polycrystalline material and a preparation method and application thereof.The preparation method comprises the steps that lanthanum hexaboride and metal oxide are mixed, ball-milled to be uniform and dried to obtain first powder, the metal oxide is an oxide of M, and M is Al, Zr and Ti; the first powder is placed in a mold, the first powder is located in the center of the mold and has the same apparent density, in the inert gas atmosphere, the pressure is increased from the pressure P1 to the pressure P2, heat preservation is carried out for 0.5-3 h at the pressure P2 and the temperature of 1400-2000 DEG C, hot pressing sintering is carried out, cooling is carried out, meanwhile, pressure preservation is carried out for 0-3 h at the pressure P2, the LaB6 polycrystalline material doped with the oxide is obtained, the P1 ranges from 5 MPa to 9 MPa, and the P2 ranges from 20 MPa to 60 MPa. By adding the oxide phase, the sintering temperature of the pure LaB6 ceramic is reduced from 1975 DEG C to 1800 DEG C or below, the conductivity of the LaB6 ceramic is not deteriorated after doping, and the bending strength is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rare earth hexaboride electron emission materials, and particularly relates to a doped oxide LaB6 polycrystalline material, a preparation method and application thereof. BACKGROUND

[0002] Lanthanum hexaboride (LaB6) has the characteristics of low electron work function (or work function), good ion bombardment resistance, and good high-temperature chemical stability, and is an excellent electron emission cathode material. However, due to the strong covalent bond of B-B in LaB6, atomic diffusion is difficult, which makes it difficult to realize sintering densification below 1975 DEG C. LaB6 single crystal material is complex to prepare, has high cost and small size, and LaB6 polycrystalline material has been widely concerned.

[0003] Currently, there are mainly two kinds of preparation processes for LaB6 polycrystalline material: hot-pressing sintering (HP) and spark plasma sintering (SPS). SPS can produce local high temperature of several thousand degrees Celsius instantaneously under the action of an electric field when discharging between the gaps of the grains, thereby strengthening diffusion and accelerating sintering densification. However, the SPS equipment is complex and expensive, thereby limiting the application range of the product, and the method has high cost and is commonly used for academic research, and it is difficult to realize industrial application. HP is a sintering method in which the sample is sintered in a vacuum or atmosphere sintering furnace while an external pressure is applied, and the obtained sample has high density and high hardness, and the size is not limited. However, due to the difficulty of diffusion during sintering of LaB6, the sintering temperature of LaB6 polycrystalline material is high (>1900 DEG C), the energy consumption is large, and the sintering furnace has high requirements. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a preparation method of a doped oxide LaB6 polycrystalline material.

[0005] Another object of the present application is to provide a doped oxide LaB6 polycrystalline material obtained by the above preparation method, which is a ceramic material with large size, high density and high breaking strength.

[0006] The object of the present application is achieved by the following technical scheme.

[0007] A preparation method of a doped oxide LaB6 polycrystalline material, comprising the following steps:

[0008] Step 1, mixing lanthanum hexaboride (LaB6) and metal oxide, ball milling to be uniform, drying to obtain a first powder, wherein the ratio of lanthanum hexaboride (LaB6) and metal oxide is (91-99) : (1-9) by mass fraction, the metal oxide is oxide of M, M is Al, Zr and Ti, the oxide of M is Al2O3, ZrO2 and TiO2, the ratio of Al2O3, ZrO2 and TiO2 is (10-45) : (15-55) : (0-35) by mass fraction;

[0009] In step 1, the lanthanum hexaboride (LaB6) is in powder form, and the particle size of the lanthanum hexaboride (LaB6) is 0.5-10 μm.

[0010] In step 1, the metal oxide is in powder form, and the particle size of the metal oxide is 0.5-5 μm.

[0011] In step 1, the ball milling time is 2-8 h, preferably 6-8 h.

[0012] In step 1, the ball milling speed is 250-350 r / min, and the ball milling ratio is 1 : (2-6).

[0013] Step 2, the first powder is loaded into a mold, the first powder is in the center of the mold and has the same loose bulk density, under an inert gas atmosphere, the pressure P1 is increased to the pressure P2, and the pressure P2 is kept at 1400-2000 ℃ for 0.5-3 h to perform hot-pressing sintering, and then cooled while keeping the pressure P2 for 0-3 h to obtain a doped oxide LaB6 polycrystalline material, wherein P1 is 5-9 MPa, and P2 is 20-60 MPa.

[0014] In step 2, the rate of increasing the pressure P1 to the pressure P2 is 0.2-10 MPa / min.

[0015] In step 2, the 1400-2000 ℃ for 0.5-3 h is preferably 1600-1800 ℃ for 1-2 h.

[0016] In step 2, the 1400-2000 ℃ for 0.5-3 h is more preferably 1700-1800 ℃ for 1-2 h.

[0017] In step 2, the heating rate is 6-30 ℃ / min, and when the temperature reaches above 600 ℃, the heating rate is preferably 15-20 ℃ / min.

[0018] In step 2, P2 is preferably 40-50 MPa.

[0019] In step 2, the first powder is in the center of the mold and has the same loose bulk density by vibration.

[0020] The doped oxide LaB6 polycrystalline material obtained by the preparation method.

[0021] In the technical scheme, the doped oxide LaB6 polycrystalline material has a bending strength of ≥200 MPa.

[0022] In the technical scheme, the doped oxide LaB6 polycrystalline material has a relative density of ≥95%.

[0023] In the technical scheme, the doped oxide LaB6 polycrystalline material has an electrical conductivity of 3-11 MS / m.

[0024] The application of the doped oxide LaB6 polycrystalline material in an electron emission cathode device.

[0025] In the technical scheme, the doped oxide LaB6 polycrystalline material is used as an electron emission cathode material of an electron emission cathode device.

[0026] Compared with the prior art, the application has the following beneficial effects:

[0027] 1. By adding the oxide phase, the sintering temperature of pure LaB6 ceramic is reduced from 1975℃ to below 1800℃, which is directly reduced by 275℃ compared with Example 3 (1700℃), and a doped oxide LaB6 polycrystalline material with a density (relative density) of ≥95% and stable composition is obtained, the bending strength is effectively improved from 137 MPa to more than 200 MPa, and the electrical conductivity of LaB6 ceramic is not deteriorated after doping, and the electrical conductivity of the doped oxide LaB6 polycrystalline material is still ≥6 MS / m.

[0028] 2. By reducing the temperature of hot-pressing sintering, the reaction degree of LaB6 with the graphite mold is reduced, the demolding is simpler, and the yield is higher. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 SEM of the doped oxide LaB6 polycrystalline material prepared in Examples 1-4;

[0030] Figure 2 Photo of the doped oxide LaB6 polycrystalline material prepared in Example 3;

[0031] Figure 3 XRD of the doped oxide LaB6 polycrystalline material prepared in Example 4;

[0032] Figure 4 Elemental distribution map of the doped oxide LaB6 polycrystalline material prepared in Example 3. DETAILED DESCRIPTION

[0033] The technical solutions of the present application are further illustrated below in combination with specific examples.

[0034] The raw material information involved in the following examples is as follows:

[0035] Raw materials Molecular formula Purity Origin Lanthanum hexaboride LaB6 ≥99.9％ China Aluminum trioxide Al2O3 ≥99.9％ China Zirconium dioxide ZrO2 ≥99.9％ China Titanium dioxide TiO2 ≥99.9％ China

[0036] The instrument information involved in the following examples is as follows:

[0037]

[0038] Examples 1-4

[0039] A preparation method of a doped oxide LaB6 polycrystalline material, comprising the following steps:

[0040] Step 1, mix lanthanum hexaboride (LaB6) and metal oxide, ball mill in a high-energy ball mill at a speed of 250 r / min for 6 h to be uniform (the ball mill material ball ratio is 1:4), place in a drying box, and dry at 120℃ for 12 h to obtain a first powder, wherein the ratio of lanthanum hexaboride (LaB6) and metal oxide is 98:3 by mass fraction, the metal oxide is Al2O3, ZrO2 and TiO2, the ratio of Al2O3, ZrO2 and TiO2 is 36:39:25 by mass fraction, the lanthanum hexaboride (LaB6) is in powder form, the average particle size of the lanthanum hexaboride (LaB6) is 5.35 μm, the metal oxide is in powder form, the average particle size of the metal oxide is 1.65 μm, and the metal oxide needs to be ball milled in a high-energy ball mill at a speed of 250 r / min to be uniform before being mixed with the lanthanum hexaboride (LaB6);

[0041] Step 2, load the first powder into a graphite mold of a block material machine (the inner diameter of the graphite mold is 30 mm, and the outer diameter is 70 mm), separate the first powder from the graphite mold by wrapping with graphite paper, vibrate the graphite mold to make the first powder occupy the center position of the graphite mold and have the same loose bulk density, vacuumize to below 10 Pa, introduce argon into the graphite mold, increase the pressure from P1 (P1 = 7 MPa) to pressure P2 (P2 = 50 MPa) at a rate of 2 MPa / min, increase the temperature from 6℃ / min to 600℃, and then increase the temperature from 20℃ / min to X℃ at the same time of increasing the pressure from P1 to P2, heat-press sinter at P2 (50 MPa) and X℃ for 1 h in a vacuum hot-press sintering furnace, cool after the heat-press sintering is completed and at the same time keep the pressure at 50 MPa for 140 min to obtain a doped oxide LaB6 polycrystalline material. The value of X is shown in Table 1.

[0042] Table 1

[0043] Examples X(℃) Example 1 1500 Example 2 1600 Example 3 1700 Example 4 1800

[0044] The relative density of the LaB6 polycrystalline material of the prepared doped oxide in Example 1 is 78.5%, the electrical conductivity is 4.7 MS / m, and the bending strength is 165 MPa.

[0045] The relative density of the LaB6 polycrystalline material of the prepared doped oxide in Example 2 is 83.5%, the electrical conductivity is 5.5 MS / m, and the bending strength is 186 MPa.

[0046] The relative density of the LaB6 polycrystalline material of the prepared doped oxide in Example 3 is 95%, the electrical conductivity is 7 MS / m, and the bending strength is 200 MPa.

[0047] The relative density of the LaB6 polycrystalline material of the prepared doped oxide in Example 4 is 97%, the electrical conductivity is 6.5 MS / m, and the bending strength is 206 MPa.

[0048] Example 5

[0049] A method for preparing a LaB6 ceramic, comprising:

[0050] Step 1: LaB6 raw material powder with a particle size of 20 μm (purchased from Shanghai Xu Tian New Material Technology Co., Ltd.) is ball milled at a speed of 350 r / min for 8 h using a high-energy ball mill, the ball milling medium is anhydrous ethanol, and the ratio of material to ball is 1:4, to obtain LaB6 powder with a D50 of 5.89 μm;

[0051] Step 2: the LaB6 powder obtained in step 1 is loaded into a graphite mold of a block material machine (the inner diameter of the graphite mold is 30 mm, and the outer diameter is 70 mm), the LaB6 powder is separated from the graphite mold by wrapping with graphite paper, the graphite mold is vibrated to make the LaB6 powder located at the center position of the graphite mold and have the same loose bulk density. Vacuumize to below 10 Pa, introduce argon into the graphite mold, increase the pressure from P1 (P1 = 7 MPa) to pressure P2 (P2 = 40 MPa) at a rate of 6 MPa / min, increase the pressure from P1 to P2 at a rate of 6 MPa / min, and increase the temperature to 600°C at a rate of 6°C / min, and then increase the temperature to 1975°C at a rate of 20°C / min, heat-press sinter at 40 MPa and 1975°C for 1 h in a vacuum heat-press sintering furnace, cool and simultaneously keep the pressure at 40 MPa for 140 min after the heat-press sintering is completed, to obtain a LaB6 ceramic.

[0052] The relative density of the LaB6 ceramic prepared in Example 5 is 95.4%, the electrical conductivity is 10.18 MS / m, and the bending strength is 137 MPa.

[0053] Example 6

[0054] A method for preparing LaB6ceramics is basically the same as that of Example 5 "A method for preparing LaB6ceramics", except that "1975°C" is replaced by "1700°C".

[0055] Sintering of LaB6ceramics cannot be achieved at 1700°C, and the relative density of the LaB6ceramics obtained in Example 6 is 85%.

[0056] Figure 1 The SEM of the doped oxide LaB6polycrystalline material prepared in Example 1 is shown in (a) of Figure 1. Figure 1 The SEM of the doped oxide LaB6polycrystalline material prepared in Example 1 is shown in (a) of Figure 1. Figure 1 It can be seen that as the hot-press sintering temperature increases from 1500°C to 1800°C, the microstructure of the doped oxide LaB6polycrystalline material becomes denser and the pores decrease.

[0057] Figure 2 The photo of the doped oxide LaB6polycrystalline material prepared in Example 3 is shown in Figure 3. Figure 2 It can be seen that the doped oxide LaB6polycrystalline material prepared in Example 3 is purple and has a smooth surface and a large size of 30 mm in diameter.

[0058] Figure 3 The XRD of the doped oxide LaB6polycrystalline material prepared in Example 4 is shown in Figure 4. Figure 3 "LaB6+3%ATZ" in Figure 4 represents the doped oxide LaB6polycrystalline material prepared in Example 4. Figure 3 It can be seen that the phase composition of LaB6does not change after the addition of metal oxides.

[0059] Figure 4 The EDS element distribution map of the doped oxide LaB6polycrystalline material prepared in Example 3 is shown in Figure 5. Figure 4 The microstructure of the cross section of the doped oxide LaB6polycrystalline material is shown in Figure 5. Figure 4 "LaB6-ATZ" in Figure 5). Figure 4 It can be seen that the doped metal oxides are distributed at the grain boundary positions.

[0060] The outer size of the doped oxide LaB6polycrystalline material can be achieved according to the requirements and the design of the mold, and doped oxide LaB6polycrystalline materials in the shapes of wafers, cubes and columns can be obtained.

[0061] The above has made the exemplary description to the present application, should indicate that, in not departing from the core of the present application, any simple change, modification or other field technicians can not spend the equivalent replacement of creative labor falls into the protection scope of the present application.

Claims

1. A method for preparing LaB6 polycrystalline material doped with oxides, characterized in that, Includes the following steps: Step 1: Lanthanum hexaboride and metal oxide are mixed, ball-milled until uniform, and dried to obtain a first powder. The ratio of lanthanum hexaboride to metal oxide by mass is (91-99):(1-9). The metal oxide is an oxide of M, where M is Al, Zr, and Ti. The oxide of M is Al2O3, ZrO2, and TiO2. The ratio of Al2O3, ZrO2, and TiO2 by mass is (10-45):(15-55):(0-35). Step 2: The first powder is loaded into the mold, with the first powder located at the center of the mold and having the same loose packing density. Under an inert gas atmosphere, the pressure is increased from P1 to P2 and held at 1400-2000℃ for 0.5-3 hours for hot pressing sintering. After cooling, the pressure is held at P2 for 0-3 hours to obtain LaB6 polycrystalline material doped with oxides, where P1 is 5-9 MPa and P2 is 20-60 MPa.

2. The preparation method according to claim 1, characterized in that, In step 1, lanthanum hexaboride is in powder form, and the particle size of lanthanum hexaboride is 0.5 to 10 μm.

3. The preparation method according to claim 1, characterized in that, In step 1, the metal oxide is in powder form, and the particle size of the metal oxide is 0.5 to 5 μm.

4. The preparation method according to claim 1, characterized in that, In step 2, the rate at which pressure P1 is increased to pressure P2 is 0.2 to 10 MPa / min.

5. The preparation method according to claim 4, characterized in that, In step 2, vibration is used to position the first powder at the center of the mold and to give it the same loose packing density.

6. The LaB6 polycrystalline material with doped oxide obtained by the preparation method according to any one of claims 1 to 5.

7. The LaB6 polycrystalline material doped with oxides according to claim 6, characterized in that, The flexural strength of the doped oxide LaB6 polycrystalline material is ≥200 MPa.

8. The LaB6 polycrystalline material doped with oxides according to claim 6, characterized in that, The relative density of the doped oxide LaB6 polycrystalline material is ≥95%.

9. The LaB6 polycrystalline material doped with oxides according to claim 6, characterized in that, The electrical conductivity of the doped oxide-based LaB6 polycrystalline material is 3–11 MS / m.

10. The application of the LaB6 polycrystalline material doped with oxides as described in claim 6 in an electron emission cathode device.

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