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CN-116397329-B - Ternary rare earth hexaboride-zirconium diboride eutectic composite material and preparation method thereof

CN116397329BCN 116397329 BCN116397329 BCN 116397329BCN-116397329-B

Abstract

The invention provides a (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite material, a preparation method thereof and a cathode device comprising the same, wherein in the eutectic composite material, the mol ratio of La 0.5 B 0.5 B 6 to ZrB 2 is 2.1:1, (La 0.5 Ba 0.5 )B 6 is a matrix and the crystal orientation is [100]; zrB 2 is a reinforcing phase in a fiber form).

Inventors

  • YANG XINYU
  • ZHAO WEI
  • DONG CUNCHAO
  • WANG YAN
  • LUO SHIFENG
  • ZHANG JIUXING

Assignees

  • 合肥工业大学

Dates

Publication Date
20260505
Application Date
20230327

Claims (14)

  1. 1. A eutectic composite of La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 , wherein the molar ratio of La 0.5 B 0.5 B 6 to ZrB 2 is 2.1:1, (La 0.5 Ba 0.5 )B 6 is the matrix and the crystal orientation is [100]; zrB 2 is the reinforcing phase in the form of fibers.
  2. 2. The (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 1, wherein the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite has a thermal emission current density of 15A/cm 2 or more measured at a voltage of 2000 to 4000v under a closed environmental condition of a temperature of 1873K and a vacuum of 2.0 x 10 -5 Pa.
  3. 3. The (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 2, wherein the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite has a thermal emission current density of 20A/cm 2 or more measured under a voltage of 2000 to 4000v under a closed environmental condition of a temperature of 1873K and a vacuum of 2.0 x 10 -5 Pa.
  4. 4. The (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 2, wherein the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite has a thermal emission current density of 35A/cm 2 or more measured under a voltage of 2000 to 4000v under a closed environmental condition of a temperature of 1873K and a vacuum of 2.0 x 10 -5 Pa.
  5. 5. The (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite) according to any one of claims 1 to 4, wherein the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite) has a vickers hardness of 18GPa or more and a fracture toughness of 3 MPa-m 1/2 or more.
  6. 6. The method of claim 5 (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite), wherein, The Vickers hardness of the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite material is more than 20 GPa; And/or (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite material) with fracture toughness of 5MPa m 1/2 or more.
  7. 7. A method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to any one of claims 1 to 6, comprising the steps of: 1) Preparing (La 0.5 Ba 0.5 )B 6 -ZrB 2 polycrystalline sample; 2) Cutting the polycrystalline sample with a wire electric discharge machine (La 0.5 Ba 0.5 )B 6 -ZrB 2 polycrystalline sample, smoothing with sandpaper, cleaning and drying; 3) Placing the cleaned (La 0.5 Ba 0.5 )B 6 -ZrB 2 polycrystal rod on an upper drawing rod as a feeding rod, fixing seed crystal LaB 6 [100] on a lower drawing rod as a discharging rod, performing a crystal growth experiment in a sealed high-purity quartz tube, firstly introducing high-purity argon into the tube to clean the tube, then gradually raising the power to 12-15 kW, simultaneously melting the lower end of the discharging rod and the upper end of the feeding rod, welding, after a melting zone is stable, then operating a drawing system, and completing the crystal growth to obtain (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite material; The crystal growth conditions are that the pressure of flowing argon in a quartz tube is 2-3 MPa, the flow speed is 6-8L/min, the feeding rod and the discharging rod reversely rotate at the speed of 10-30 rpm, and the growth speeds of the feeding rod and the discharging rod are 15-100 mm/h.
  8. 8. The method for preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 ) eutectic composite according to claim 7, wherein the growth rate of the feeding rod is 20-40 mm/h and the growth rate of the discharging rod is 10-30 mm/h.
  9. 9. The method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite) according to claim 7 or 8, wherein the feed rod growth rate is 30 mm/h and the feed rod growth rate is 20 mm/h.
  10. 10. The method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 7 or 8, wherein, The (La 0.5 Ba 0.5 )B 6 -ZrB 2 polycrystalline sample described in step 1) was prepared by the following steps: 1-1) mixing lanthanum oxide, barium carbonate, boron carbide and boron powder in a molar ratio of 1:2:4:9, and calcining in a vacuum resistance furnace at 1400-1800 ℃ and a vacuum degree of 10 -2 Pa to obtain La 0.5 Ba 0.5 )B 6 powder with a particle size of 10-50 mu m; 1-2) ball milling ZrB 2 powder until the particle size is 10-50 mu m, then mixing the powder (La 0.5 Ba 0.5 )B 6 powder and ZrB 2 powder according to the mol ratio of 2.1:1 and the ball powder ratio of 10:1, and then carrying out vacuum drying to obtain mixed powder (La 0.5 Ba 0.5 )B 6 -ZrB 2 ; 1-3) filling the mixed powder (La 0.5 Ba 0.5 )B 6 -ZrB 2 ) obtained in the step 1-2) into a graphite mold, prepressing and forming, wherein the prepressing force is 2-10 MPa, then placing the graphite mold filled with the powder into a furnace chamber of a discharge plasma sintering furnace, vacuumizing to a vacuum degree of below 20Pa, applying an axial pressure of 40-60 MPa, heating at a heating rate of not more than 80 ℃ per minute, heating to 1700-1900 ℃, preserving heat for 5-10 min, and taking out a sample after cooling to a furnace temperature of below 50 ℃ along with furnace cooling to obtain a (La 0.5 Ba 0.5 )B 6 -ZrB 2 ) polycrystalline sample.
  11. 11. The method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 7 or 8, wherein, The cleaning condition in the step 2) is that ultrasonic cleaning is carried out in alcohol.
  12. 12. The method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 11, wherein, The drying condition in the step 2) is that the drying temperature is 50-150 ℃ and the drying time is 8-24 h.
  13. 13. The method of preparing the (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite according to claim 10, wherein, The purity of lanthanum oxide, barium carbonate, boron carbide and boron powder is not lower than 99.9%, and the purity of ZrB 2 powder is not lower than 99.9%.
  14. 14. A cathode device comprising (La 0.5 Ba 0.5 )B 6 [100]-ZrB 2 eutectic composite) according to any one of claims 1 to 6.

Description

Ternary rare earth hexaboride-zirconium diboride eutectic composite material and preparation method thereof Technical Field The invention relates to the technical field of rare earth boride hot cathode materials, in particular to a preparation method of a (La 0.5Ba0.5)B6-ZrB2 eutectic composite material with good mechanical property and excellent heat emission property, and a cathode device comprising the (La 0.5Ba0.5)B6-ZrB2 eutectic composite material). Background LaB 6 is used as an excellent thermionic emission source, and has been widely used because of its high brightness, high melting point, low work function, low vapor pressure and long service life. According to the theory of electronics, in order to further improve the thermionic emission performance of LaB 6, it is necessary to lower its work function. The research on the composite single crystal formed by doping on the surface is an effective way for lowering the work function of the LaB 6. Japanese scholars Futamoto have examined the thermal emission properties of ternary composite single crystals such as (LaSr) B 6、(LaCe)B6、(LaSm)B6 by using an aluminum solvent method comparison system, and have firstly adopted alkaline earth metals Sr (strontium) with low work functions to regulate and control the properties of LaB 6, although aluminum impurities are introduced into the method, so that the thermal emission properties of all composite single crystals are inferior to those of LaB 6 single crystals. However, among alkaline earth metals (Ca, sr, ba), ba has the lowest work function. Australian scholars found that the work function of the material can be effectively reduced by adding alkaline earth Ba to LaB 6 (LaxBa 1-x)B6 polycrystal is more advantageous in preparing high quality single crystal hexaboride than the aluminum solvent method, and the aklanian Balakrishnan prepared high purity single crystal rare earth hexaboride REB 6 (re=la, ce, pr, nd) by using the induction zone-melting directional solidification technique, however, there is no report about the preparation of the zone-melting directional solidification technique at present (La 0.5Ba0.5)B6 single crystal, in addition, la 0.5Ba0.5B6 is a ceramic material, its hard brittleness makes hollow processing of the cathode very challenging. Disclosure of Invention Technical problem In order to solve the problems in the prior art, the invention provides the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite material with high heat emission performance and high toughness and the preparation method thereof, and the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite material has high heat emission performance and excellent mechanical property. Technical proposal According to a first aspect of the present invention there is provided (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite wherein the molar ratio of La 0.5B0.5B6 to ZrB 2 is 2.1:1, (La 0.5Ba0.5)B6 is the matrix and the crystallographic orientation is [100]; zrB 2 is the reinforcing phase present in the form of fibres). Preferably, the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite) has a maximum thermal emission current density of 15A/cm 2 or more, more preferably 20A/cm 2 or more, most preferably 35A/cm 2 or more, measured under closed ambient conditions of temperature 1873K and vacuum of 2.0X10 -5 Pa. Preferably, the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite has a Vickers hardness of 18GPa or more, preferably 20GPa or more, and a fracture toughness of 3MPa m 1/2 or more, preferably 5MPa m 1/2 or more, more preferably the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite has a Vickers hardness of 18-25 GPa, and a fracture toughness of 3-7 MPa m 1/2). According to a second aspect of the present invention, there is provided a method of preparing the (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite, comprising the steps of: 1) Preparing (La 0.5Ba0.5)B6-ZrB2 polycrystalline sample; 2) Cutting the polycrystalline sample with a wire electric discharge machine (La 0.5Ba0.5)B6-ZrB2 polycrystalline sample, smoothing with sandpaper, cleaning and drying; 3) Placing the cleaned (La 0.5Ba0.5)B6-ZrB2 polycrystal rod on an upper drawing rod as a feeding rod, fixing seed crystal LaB 6 [100] on a lower drawing rod as a discharging rod, performing a crystal growth experiment in a sealed high-purity quartz tube, firstly introducing high-purity argon into the tube to clean the tube, then gradually raising the power to 12-15 kW, simultaneously melting the upper end of the discharging rod and the lower end of the feeding rod, welding, after a melting zone is stable, then operating a drawing system, and completing the crystal growth to obtain (La 0.5Ba0.5)B6[100]-ZrB2 eutectic composite material; the crystal growth conditions are that the flowing argon pressure in a quartz tube is 2-3 MPa, the flow speed is 6-8L/min, the feeding rod and the discharging rod reversely rotate at the speed of 10-30 rpm, the growth rate of the feeding rod and the discharging rod is 15-100 mm/h, preferably