CN114920560A - LaB 6 Powder and method for producing sintered body thereof - Google Patents
LaB 6 Powder and method for producing sintered body thereof Download PDFInfo
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- 239000000843 powder Substances 0.000 title claims abstract description 51
- 238000004519 manufacturing process Methods 0.000 title description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims abstract description 25
- 238000002360 preparation method Methods 0.000 claims abstract description 24
- 238000006243 chemical reaction Methods 0.000 claims abstract description 23
- 238000005245 sintering Methods 0.000 claims abstract description 21
- 239000000463 material Substances 0.000 claims abstract description 18
- 239000000203 mixture Substances 0.000 claims abstract description 16
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 15
- 238000005406 washing Methods 0.000 claims abstract description 15
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 12
- 239000010439 graphite Substances 0.000 claims abstract description 12
- 238000011049 filling Methods 0.000 claims abstract description 9
- 230000001681 protective effect Effects 0.000 claims abstract description 9
- 239000012153 distilled water Substances 0.000 claims abstract description 7
- 238000001035 drying Methods 0.000 claims abstract description 7
- 238000000746 purification Methods 0.000 claims abstract description 7
- 238000001291 vacuum drying Methods 0.000 claims abstract description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000002156 mixing Methods 0.000 claims abstract description 6
- 238000003825 pressing Methods 0.000 claims abstract description 6
- 238000010438 heat treatment Methods 0.000 claims abstract description 5
- 239000003701 inert diluent Substances 0.000 claims abstract description 5
- 238000005303 weighing Methods 0.000 claims abstract description 5
- 238000007731 hot pressing Methods 0.000 claims abstract description 4
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 3
- 238000002386 leaching Methods 0.000 claims abstract description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical group [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 12
- 239000007789 gas Substances 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 11
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical group [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 10
- 239000002245 particle Substances 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 7
- 229910052786 argon Inorganic materials 0.000 claims description 6
- 229910021193 La 2 O 3 Inorganic materials 0.000 claims description 5
- 239000002253 acid Substances 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 239000003085 diluting agent Substances 0.000 claims description 5
- 239000011780 sodium chloride Substances 0.000 claims description 5
- 239000011812 mixed powder Substances 0.000 claims description 4
- 238000000498 ball milling Methods 0.000 claims description 3
- 230000015572 biosynthetic process Effects 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 238000012360 testing method Methods 0.000 claims description 3
- 239000006260 foam Substances 0.000 claims description 2
- 239000002994 raw material Substances 0.000 description 8
- 238000002485 combustion reaction Methods 0.000 description 7
- 239000013078 crystal Substances 0.000 description 5
- 150000002910 rare earth metals Chemical class 0.000 description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical group [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 238000002490 spark plasma sintering Methods 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 238000003746 solid phase reaction Methods 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052810 boron oxide Inorganic materials 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000005049 combustion synthesis Methods 0.000 description 1
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005551 mechanical alloying Methods 0.000 description 1
- 238000000133 mechanosynthesis reaction Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000013001 point bending Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 238000004062 sedimentation Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
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- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
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Abstract
LaB 6 The preparation method of the powder and the sintered body thereof comprises the following steps: weighing the reaction materials according to a preset proportion, and adding an inert diluent with a preset content to prepare an initial mixture; step (2) placing the initial mixture in a ball mill for uniform mixing, and then pressing the mixture on a press machine into a cake-shaped blank with the diameter of 80 mm and the height of about 40 mm; putting the cake-shaped blank into a reaction kettle, putting an ignition agent on the blank, filling protective gas for gas washing, then filling the protective gas for pressure maintaining, and continuously heating until the system generates a self-propagating reaction to obtain a blocky initial product; step (4) is toCrushing the primary product, leaching with hydrochloric acid solution and distilled water to reach the purification standard, and drying in a vacuum drying oven to obtain LaB 6 Powder; step (5) preparing the prepared LaB 6 Putting the powder into a high-strength graphite mould, putting the mould into a hot-pressing sintering furnace for sintering to obtain LaB 6 And (3) sintering the body.
Description
Technical Field
The invention relates to LaB 6 Preparation of powder and its sintered body.
Background
LaB 6 The rare earth metal has a simple cubic structure, six boron atoms are positioned at the vertexes of a crystal lattice to form an octahedral unit, and each octahedral unit is combined with an adjacent octahedral in an adjacent crystal lattice by a B-B covalent bond to form a three-dimensional cage-like structure. LaB 6 The surface is filled with a large number of rare earth metal atoms, and the barrier energy is greatly weakened by the active layer, so that electrons can easily leave the solid surface. When the material is heated to a high enough temperature, the rare earth metal atoms on the crystal surface are evaporated and can be rapidly filled with the rare earth metal atoms diffused from the crystal lattice, so that LaB 6 It is possible to continuously supply the electron emission sources to the outside. This makes LaB 6 The material has the advantages of good electrical conductivity, thermal conductivity, thermionic emission performance and the like, and forms the research and development focus in the field of hot cathode materials.
LaB 6 The emission performance of (a) is mainly influenced by the purity, compactness and grain size of the material. High purity, high density and smaller grain size samples have higher emission performance, and the density and grain size are influenced by the particle size of the powder, which means that more excellent and advanced production processes are needed, and the materials prepared by the preparation processes commonly used at the present stage are difficult to meet the standards of larger emission performance and preparation scale. LaB currently being prepared 6 The sample is exposed to large grain diameter, uneven size and more impurities, so that the density of a sintered body is low, the crystal grains are large, and the thermal emission current is denseSmall size and the like.
LaB 6 The main preparation method of the powder comprises the following steps: carbothermic, borothermic, solid phase reaction, and mechanosynthesis methods. The present situation of recent years is now under investigation using B 4 C and C are used as raw materials, and LaB with the particle size of about 200 nm is synthesized by a carbothermic method 6 And (3) powder. Using La 2 O 3 And B powder as raw material, synthesizing and preparing LaB with particle size from several nanometers to several micrometers by boron thermal reduction method 6 And (3) powder. Preparation of La by boron thermal reduction 2 O 3 And NaBH 4 Preparing LaB with average grain diameter less than 100 nm by solid phase reaction method 6 And (3) powder. Using La 2 O 3 、B 2 O 3 And Mg as raw materials, and obtaining LaB through mechanical alloying 6 And (3) powder, wherein the particle size of the powder is calculated to be 30-200 nm. From recent research work, most of the LaBs prepared in the reports 2 The powder particles can reach micron-scale and nano-scale, but the raw material cost is high, the preparation period is long, the purity is low, and the powder particles are prepared in trace amount, so that the powder particles are not suitable for large-scale production. Therefore, a preparation technique which can be mass-produced and has a small particle size of the powder is required.
LaB 6 The preparation method of the sintered body mainly comprises the following steps: hot press sintering and spark plasma sintering. To review the current state of the art, micron-sized LaBs were used 6 And (3) carrying out hot-pressing sintering on the powder at a sintering temperature of 1800 ℃, a sintering pressure of 50MPa and under the condition of keeping the temperature for 2h to obtain a sintered body with the density of 87.47%. Using micron-sized LaB 6 The powder is sintered by discharge plasma at 1400 ℃ and 50MPa for 10min to obtain 88.4 percent of sintered body. Since the change of the sintering method and parameters affects the properties of the sintered body, it is necessary to select an appropriate sintering method and parameters for preparation.
Disclosure of Invention
The invention aims to provide a LaB 6 A powder and a sintered body thereof.
The invention relates to a LaB 6 The preparation method of the powder and the sintered body comprises the following steps:
weighing the reaction materials according to a preset proportion, and adding an inert diluent with a preset content to prepare an initial mixture;
step (2) placing the initial mixture in a ball mill for uniform mixing, and then pressing the mixture on a press machine into a cake-shaped blank with the diameter of 80 mm and the height of about 40 mm;
putting the cake-shaped blank into a reaction kettle, putting an ignition agent on the blank, filling protective gas for washing gas, then filling the protective gas for maintaining the pressure, and continuously heating until the system generates a self-propagating reaction to obtain a blocky initial product;
and (4) crushing the primary product, leaching the crushed primary product with hydrochloric acid solution and distilled water to reach the purification standard, and drying the product in a vacuum drying oven to obtain LaB 6 And (3) powder.
Step (5) preparing the prepared LaB 6 Putting the powder into a high-strength graphite mould, putting the mould into a hot-pressing sintering furnace for sintering to obtain LaB 6 And (3) sintering the body.
The invention has the beneficial effects that: the raw material and energy consumption cost is low, the powder process is simple, the yield is high, the preparation period is short, and only the raw material and the energy consumption need to be heated to about 300 ℃; can prepare high-purity LaB with smaller granularity by kilogram grade at one time 6 Powder; the LaB with small grain size and high density can be obtained in a short time by spark plasma sintering 6 And (3) sintering the body.
Drawings
FIG. 1 shows LaB prepared by the present invention 6 XRD pattern of powder, FIG. 2 is LaB prepared by the invention 6 SEM image of powder, FIG. 3 is LaB prepared by the invention 6 The particle size distribution of the powder, FIG. 4 is the LaB prepared by the present invention 6 XRD pattern of the sintered body, FIG. 5 is LaB prepared by the present invention 6 SEM image of sintered body fracture morphology.
Detailed Description
The invention relates to a preparation method, which comprises the following steps:
weighing the reflecting materials according to a preset proportion, and adding NaCl with the corresponding material content to prepare an initial mixture;
step (2) placing the initial mixture into a ball mill for uniform mixing, and then pressing the mixture into a blank body with the diameter of 80 mm and the height of about 40 mm on a press machine;
putting the blank into a reaction kettle, putting a detonator on the blank, filling argon gas for washing, then filling argon gas for maintaining pressure, and continuously heating until a system generates a self-propagating reaction to obtain a gray block-shaped product;
crushing the primary product, washing with hydrochloric acid solution and distilled water to reach the purification standard, and drying in a vacuum drying oven to obtain LaB 6 And (3) powder.
Step (5) preparing the prepared LaB 6 Putting the powder into a sintering mold, then putting the powder into a sintering furnace, starting to heat up after vacuum pumping, wherein the heating rate is 80 ℃/min, the sintering pressure is 35MPa, the temperature is increased to 1960 ℃, the temperature and pressure are kept for 10min, then, starting to cool, and taking out a sample after cooling to room temperature.
The preparation method comprises the steps of (1) and the mass ratio of the reaction materials is La 2 O 3 ：B 2 O 3 : mg = 4.9:29: 103; the inert diluent is NaCl; the diluent was added in an amount of 15 wt.% based on the total mass of the reaction mass.
According to the preparation method, the ball milling parameters in the step (2) are 8 hours, the rotating speed is 180 r/min, and the ball-to-material ratio is 2: 1; the pressure of the press is 30 MPa.
In the preparation method, the preheating temperature in the step (3) is 300 ℃; the protective atmosphere is argon, the gas washing pressure is 0.5 MPa, and the pressure maintaining pressure is 2 MPa.
The preparation method described above, wherein the hydrochloric acid solution in step (4) is 4 mol/L hydrochloric acid diluent, and the excess amount is 50 vol.%; the purification standard is as follows: the acid washing process, namely adding acid, stirring, releasing a large amount of heat with small foam formation, completely reacting HCl solution with MgO, and measuring the pH value by using a pH meter or pH test paper; and standing for 24 h, after the powder is precipitated, pouring out the upper layer solution, washing with distilled water to remove residual impurities, stirring for 20 min by using a magnetic stirrer, washing for 6 times, standing for 24 h, and then drying in a vacuum drying oven for 48 h to obtain the target powder.
In the step (5), the diameter of the mould is preferably within the range of 20-60mm, and in order to prevent the sintered body of the graphite mould from being adhered to the inner wall at high temperature, a thin layer of carbon paper is used between the graphite mould and the mixed powder to prevent the sintered body of the graphite mould from being adhered to the inner wall at high temperature.
Example 1:
(1) the reactant feedstock in this example was La 2 O 3 （>99.999 wt.%，3 μm）、B 2 O 3 （>99.9 wt.%）、Mg（>99.9 wt.%, 200 mesh), NaCl, (>99.99 wt%), experimental conditions: the ball milling time is 8h, the pressurizing pressure is 30 MPa, the pressure of the protective atmosphere is 2MPa, NaCl is selected as a diluent, the adding amount is 15 wt.%, and the method specifically comprises the following steps: lanthanum oxide, boron oxide and magnesium powder are used as raw materials, and the mass ratio of the three raw materials is La 2O 3: B2O 3: mg = 4.9:29:103, weighing the materials by using an analytical balance, wherein the initial mixture is 2 kg; (ii) a
(2) Mixing the initial mixture with QM-ISP4 planetary ball mill at rotation speed of 180 r/min and ball-to-material ratio of 2:1 for 8 hr to contact the reaction materials fully and raise the activity of the reaction materials;
(3) pressing the uniformly mixed reaction materials in a Y32-100t hydraulic press under the pressure of 30 MPa in a die to form a cake-shaped blank with the diameter of 80 mm and the height of about 40 mm;
(4) and (3) putting the cake-shaped blank into a combustion synthesis reaction kettle, filling 0.5 MPa of argon, and discharging gas when the temperature is raised to 180 ℃. Argon gas at 2MPa was again introduced into the vessel, and the temperature was further raised. When the temperature is increased to about 300 ℃, the temperature is changed, the air pressure in the reaction kettle is rapidly increased to about 4 MPa from 2MPa before the reaction, the temperature is rapidly increased by one or two hundred degrees, the reaction is completed within a few minutes, and then the temperature-increasing switch is cut off. After 24 hours, the combustion products are taken out to obtain cylindrical bodies containing the target products, and then crushing treatment is carried out to obtain the combustion products before immersion cleaning.
(5) Putting the powdery combustion product into 12 mol/L hydrochloric acid, diluting the powdery combustion product into 4 mol/L hydrochloric acid for acid washing, continuously stirring the powdery combustion product by using a glass rod, putting the powdery combustion product into a heat collection type magnetic stirrer for stirring for 30 min when the powdery combustion product is cooled to room temperature, and allowing HCl and MgO to react more fully along with the formation of small foamsMeasuring the pH value by a pH meter or pH test paper; if the pH paper or the pH meter shows a pH value of 4 or less, the reaction is completely acidic. Standing for 24 h for powder sedimentation, pouring the pickling solution into a beaker, washing the settled powder in the beaker with distilled water to remove the foreign matter MgCl 2 And putting the mixture into a heat collection type constant-temperature magnetic stirrer for stirring for 30 min, standing for 8h, and leading out upper-layer liquid. Sequentially and circularly carrying out the steps until the purification standard is reached, standing for 24 h, and then putting the mixture into a vacuum drying oven for drying for 24 h to obtain pure LaB 6 And (3) ultrafine powder.
Example 2:
mixing LaB 6 Placing the powder into a graphite die, using a thin layer of carbon paper between the graphite die and the mixed powder, placing the graphite die and the mixed powder into a spark plasma sintering device, applying mechanical pressure to the die along a vertical axis, passing low-voltage and high-ampere pulse current through the die, controlling the sintering temperature by a thermocouple or an optical pyrometer, increasing the temperature rate to 80 ℃/min, the sintering pressure to 35MPa, increasing the temperature to 1960 ℃, preserving heat and pressure for 10min, then starting cooling, and obtaining a sample with the relative density of 95.76% after cooling to room temperature. The bending strength of the sample measured by the three-point bending resistance method was 174.2 MPa.
Claims (8)
1. LaB 6 The preparation method of the powder and the sintered body thereof is characterized by comprising the following steps:
weighing the reaction materials according to a preset proportion, and adding an inert diluent with a preset content to prepare an initial mixture;
step (2), uniformly mixing the initial mixture in a ball mill, and pressing the mixture into a cake-shaped blank with the diameter of 80 mm and the height of about 40 mm on a press machine;
putting the cake-shaped blank into a reaction kettle, putting an ignition agent on the blank, filling protective gas for gas washing, then filling the protective gas for pressure maintaining, and continuously heating until the system generates a self-propagating reaction to obtain a blocky initial product;
and (4) crushing the primary product, leaching the crushed primary product with hydrochloric acid solution and distilled water to reach the purification standard, and drying the product in a vacuum drying oven to obtain LaB 6 Powder;
step (5) preparing the prepared LaB 6 Putting the powder into a high-strength graphite mould, putting the mould into a hot-pressing sintering furnace for sintering to obtain LaB 6 And (3) sintering the body.
2. The LaB of claim 1 6 The preparation method of the powder and the sintered body thereof is characterized in that the reaction materials in the step (1) and the mass ratio thereof are La 2 O 3 ：B 2 O 3 : mg = 4.9:29: 103; the inert diluent is NaCl; the amount of diluent added was 15 wt.% of the total mass of the reaction mass.
3. The LaB of claim 1 6 The preparation method of the powder and the sintered body thereof is characterized in that the ball milling parameters in the step (2) are 8 hours, the rotating speed is 180 r/min, and the ball-to-material ratio is 2: 1; the pressing pressure of the press is 30 MPa.
4. The LaB of claim 1 6 The preparation method of the powder and the sintered body thereof is characterized in that the preheating temperature in the step (3) is 300 ℃; the protective atmosphere is argon, the washing pressure is 0.5 MPa, and the pressure maintaining pressure is 2 MPa.
5. The LaB of claim 1 6 The preparation method of the powder and the sintered body thereof is characterized in that the hydrochloric acid solution in the step (4) is 4 mol/L hydrochloric acid diluent, and the hydrochloric acid is excessive by 50 vol.%; the purification standard is as follows: the acid washing process, namely adding acid, stirring, releasing a large amount of heat with small foam formation, completely reacting HCl solution with MgO, and measuring the pH value by using a pH meter or pH test paper; and standing for 24 h, after the powder is precipitated, pouring out the upper layer solution, washing with distilled water to remove residual impurities, stirring for 20 min by using a magnetic stirrer, washing for 6 times, standing for 24 h, and then drying in a vacuum drying oven for 48 h to obtain the target powder.
6. The LaB of claim 1 6 Preparation of powder and sintered body thereofIn the method, the diameter of the mould in the step (5) is preferably in the range of 20-60mm, and in order to prevent the sintered body of the graphite mould from being adhered to the inner wall at high temperature, a thin layer of carbon paper is used between the graphite mould and the mixed powder to prevent the sintered body of the graphite mould from being adhered to the inner wall at high temperature.
7. The LaB of claim 1 6 The powder and the sintered body thereof are characterized in that LaB 6 The average particle diameter of the powder is about 483 nm.
8. The LaB of claim 1 6 The preparation method of the powder and the sintered body thereof is characterized in that the LaB 6 The sintered body had a relative density of 95.76%.
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