CN109628997B

CN109628997B - Preparation method of lanthanum hexaboride whisker

Info

Publication number: CN109628997B
Application number: CN201910125382.3A
Authority: CN
Inventors: 缪加巍; 伍岳; 高召顺; 肖立业; 韩立; 刘俊标; 左婷婷
Original assignee: Institute of Electrical Engineering of CAS
Current assignee: Institute of Electrical Engineering of CAS
Priority date: 2019-02-20
Filing date: 2019-02-20
Publication date: 2020-09-08
Anticipated expiration: 2039-02-20
Also published as: CN109628997A

Abstract

A lanthanum hexaboride whisker preparation method comprises the steps of taking metal lanthanum and simple substance boron powder as reaction raw materials, taking metal aluminum as a fluxing agent, fully mixing and uniformly grinding the metal lanthanum powder and the simple substance boron powder, adding a certain amount of metal aluminum, treating the aluminum cosolvent by a special method of a gap filling method, a layering method and a drilling method, removing an aluminum surface oxide film, relatively concentrating the raw materials, reducing the purification time and improving the lanthanum hexaboride whisker preparation efficiency.

Description

Preparation method of lanthanum hexaboride whisker

Technical Field

The invention relates to a preparation method of lanthanum hexaboride whisker.

Background

Lanthanum hexaboride, due to its unique structural characteristics, determines its particular properties. Six boron atoms of smaller volume form an octahedral framework structure, and eight boron framework structures wrap lanthanum atoms of larger volume at eight vertices of a cube. The unique structure determines that the composite material has higher melting point, higher hardness, better chemical stability and thermal stability, good conductivity and low work function, and simultaneously has the advantages of strong ion bombardment resistance, good resistance to toxicity, long service life and the like. Therefore, lanthanum hexaboride is a good hot cathode electron source and is widely applied to the fields of transmission electron microscopes, scanning electron microscopes, electron beam processing equipment and the like. Powdered, bulk and needle lanthanum hexaboride have been successfully prepared. Wherein, the aluminum fluxing agent method has lower culture temperature and simple process, and can prepare larger acicular monocrystal lanthanum hexaboride.

However, in the process of preparing lanthanum hexaboride by the flux method in the past, the prepared ingredients are directly put into a high-temperature furnace for sintering, and some problems can be caused: firstly, the added aluminum fluxing agent is granular, so that the total specific surface area of the aluminum fluxing agent is too large, a compact aluminum oxide film is formed on the surface after the aluminum fluxing agent is contacted with air, the aluminum is wrapped by the oxide film on the surface after being oxidized in a furnace, and the aluminum fluxing agent is difficult to contact with metal lanthanum powder and boron powder, so that the production efficiency is greatly reduced, and the problem that the lanthanum hexaboride whisker is prepared by the aluminum fluxing agent method is the largest; secondly, because the aluminum is excessive, the raw materials of lanthanum powder and boron powder are excessively dispersed in the aluminum cosolvent, and larger lanthanum hexaboride whiskers are not beneficial to growth; finally, after sintering is completed, the grown lanthanum hexaboride whiskers are distributed on each part of the aluminum block, and the aluminum block is purified only by completely dissolving the aluminum block, so that the time consumption is too long, and the efficiency is low.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method of lanthanum hexaboride whisker. The method takes metal lanthanum and simple substance boron powder as reaction raw materials, metal aluminum as a fluxing agent, the metal lanthanum powder and the simple substance boron powder are fully mixed and uniformly ground, a certain amount of metal aluminum is added, and the aluminum cosolvent is treated by a special method, so that the effects of removing an aluminum surface oxidation film, relatively concentrating the raw materials and reducing the purification time are achieved, and the preparation efficiency of the lanthanum hexaboride whisker is improved.

The method for preparing the lanthanum hexaboride whisker comprises the following specific steps:

1. preparing raw materials: grinding metal lanthanum powder with a certain mass in a glove box, mixing the metal lanthanum powder with boron powder with a certain mass, and grinding the metal lanthanum powder and the boron powder in a mortar for 25-30 min to enable the metal lanthanum powder and the boron powder to be fully ground and uniformly mixed.

2. Treating the aluminum cosolvent by adopting a gap filling method, a layering method or a drilling method:

(1) gap filling method: adding a certain amount of high-purity granular aluminum into an alumina crucible, pouring the uniformly mixed metal lanthanum powder and boron powder into the crucible, slightly shaking to fill the ingredients into gaps of the granular aluminum, and then adding a small amount of aluminum particles to cover the surfaces of the metal lanthanum powder and the boron powder. And (3) putting the crucible into an induction heating device, heating to 650-700 ℃ in an environment with a vacuum degree of 3pa, and stopping heating after the aluminum particles are fully melted. Then, the crucible was placed in a furnace to sinter, heated to 1350 ℃ and held for 12 hours. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

(2) A layering method: firstly, putting metal aluminum into an aluminum oxide crucible, then putting the aluminum oxide crucible into an induction heating device, heating the aluminum oxide crucible in an environment with the vacuum degree of 3pa, stopping heating after an aluminum block is melted, and taking out the aluminum block. Adding a layer of metal lanthanum powder and boron powder on the surface of the aluminum, and adding a layer of aluminum on the mixture. The alumina crucible was placed in an induction heating apparatus and heated in an atmosphere of a vacuum degree of 3 pa. Repeating the steps to obtain a structure with three layers of aluminum and two layers of ingredients. Then, the alumina crucible was put into a furnace to sinter, heated to 1350 ℃ and held for 12 hours. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

(3) Drilling: firstly, a certain amount of metal aluminum is put into an aluminum oxide crucible, then the aluminum oxide crucible is put into an induction heating device and heated in an environment with the vacuum degree of 3pa, and after an aluminum block is melted, the heating is stopped and the aluminum block is taken out. After cooling, punching holes in the vertical direction of the aluminum block, filling the holes with the uniformly mixed metal lanthanum powder and boron powder, and covering a layer of aluminum block on the metal lanthanum powder and the boron powder. Then, the alumina crucible was put into a furnace to sinter, heated to 1350 ℃ and held for 12 hours. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

The mass ratio of the metal lanthanum to the boron powder to the aluminum fluxing agent is 2:1: 27.

The heating rate of the sintered material in the furnace is 100 ℃/h.

The cooling rate of the furnace is 100 ℃/h.

The concentration of the dilute hydrochloric acid for soaking the sample is 5 mol/L.

Compared with the prior art, the invention has the following advantages and effects:

(1) the lanthanum hexaboride whisker prepared by the method has the advantages of large size, 1342-2700 microns in length, 57-152 microns in width, good quality and excellent performance.

(2) The raw materials adopted by the invention are metal lanthanum rod and boron powder, the cost is low, the acquisition is easy, the process is simple, and the growth condition is easy to realize.

(3) The method for specially treating the aluminum cosolvent adopted by the invention effectively removes the oxide film on the surface of the aluminum, and is beneficial to full contact between the raw material and the aluminum cosolvent.

(4) The method for specially treating the aluminum cosolvent adopted by the invention can relatively concentrate the ingredients and is beneficial to the growth of larger lanthanum hexaboride whiskers.

(5) The method for specially treating the aluminum cosolvent adopted by the invention is beneficial to improving the purification efficiency of the sintered lanthanum hexaboride whisker.

Drawings

FIG. 1a, FIG. 1b, FIG. 1c and FIG. 1d are optical microscope images of lanthanum hexaboride whisker prepared under the conditions of 100 ℃/h heating rate, 100 ℃/h cooling rate and 1350 ℃ maximum temperature preservation for 12h under the gap filling method;

FIG. 2a, FIG. 2b, FIG. 2c and FIG. 2d are optical microscope images of lanthanum hexaboride whisker prepared under the conditions of 100 ℃/h heating rate, 100 ℃/h cooling rate, 1350 ℃ maximum temperature and 12h heat preservation under the layering method;

FIG. 3 is an optical microscopic image of lanthanum hexaboride whisker with a length of 2325 μm and a cross-sectional width of 86 μm prepared under the conditions of a drilling method, a temperature rise rate of 100 ℃/h, a temperature drop rate of 100 ℃/h, a heat preservation time of 1350 ℃ at the highest temperature for 12 h;

FIG. 4 is an optical microscopic image of lanthanum hexaboride whisker with length of 2225 μm and cross-sectional width of 76 μm prepared under the conditions of 100 ℃/h heating rate, 100 ℃/h cooling rate, and heat preservation at the maximum temperature of 1350 ℃ for 12h under the drilling method;

FIG. 5 is an optical microscopic image of lanthanum hexaboride whisker with a length of 2210 μm and a cross-sectional width of 72 μm, prepared under the conditions of a drilling method, a temperature rise rate of 100 ℃/h, a temperature drop rate of 100 ℃/h, a heat preservation time of 1350 ℃ at the highest temperature for 12 h;

FIG. 6 is an optical microscopic image of lanthanum hexaboride whisker with a length of 2700 μm and a cross-sectional width of 120 μm prepared under the conditions of a drilling method, a temperature rise rate of 100 ℃/h, a temperature drop rate of 100 ℃/h, a temperature preservation of 1350 ℃ at the maximum temperature for 12 h.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1

In the glove box, the black oxide film on the surface of the metal lanthanum rod is removed to expose silver metal lanthanum. Then, 2g of metal lanthanum powder is filed and mixed with 1g of boron powder, and the metal lanthanum powder and the boron powder are put into a mortar for grinding for 30min, so that the metal lanthanum powder and the boron powder are fully mixed. Adding 20g of aluminum particles into an alumina crucible, pouring the uniformly mixed ingredients into the crucible, slightly shaking to fill the ingredients into gaps of the aluminum particles, and adding 7g of aluminum particles to cover the surfaces of the lanthanum metal powder and the boron powder. And (3) putting the alumina crucible into an induction heating device, heating to 700 ℃ in an environment with the vacuum degree of 3pa, and stopping heating after the aluminum particles are fully melted. Then the alumina crucible is put into a furnace for sintering, the heating rate is adjusted to be 100 ℃/h, the temperature is increased to 1350 ℃ and kept for 12 hours, and the cooling rate is 100 ℃/h. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid with the concentration of 5mol/L, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

The obtained lanthanum hexaboride whisker has the length of 1342-1507 mu m and the cross-sectional width of 64-152 mu m, and is the lanthanum hexaboride whisker with the length of 1507 mu m and the cross-sectional width of 64 mu m as shown in figure 1 a; FIG. 1b shows lanthanum hexaboride whisker with a length 1406 μm and a cross-sectional width of 110 μm; FIG. 1c shows lanthanum hexaboride whisker of length 1342 μm and cross-sectional width 152 μm; FIG. 1d shows lanthanum hexaboride whisker of length 1349 μm and cross-sectional width 100 μm.

Example 2

In the glove box, the black oxide film on the surface of the metal lanthanum rod is removed to expose silver metal lanthanum. Then, 3g of metal lanthanum powder is filed and mixed with 1.5g of boron powder, and the metal lanthanum powder and the boron powder are put into a mortar for grinding for 30min, so that the metal lanthanum powder and the boron powder are fully mixed. 14g of metal aluminum is put into an alumina crucible, then the alumina crucible is put into an induction heating device, the aluminum crucible is heated under the environment of 3pa of vacuum degree, the heating is stopped after an aluminum block is melted, and the alumina crucible is taken out. 2.25g of metal lanthanum powder and boron powder are added on the aluminum layer, 14g of aluminum is added on the metal lanthanum powder and the boron powder, and the aluminum is placed in an induction heating device to be heated under the vacuum degree of 3 pa. Repeating the steps to obtain a three-layer aluminum-sandwiched two-layer batching structure. Then the crucible is put into a furnace for sintering, the heating rate is adjusted to be 100 ℃/h, the temperature is increased to 1350 ℃ and kept for 12 hours, and the cooling rate is 100 ℃/h. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid with the concentration of 5mol/L, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

The length of the obtained lanthanum hexaboride whisker is 1622-1837 mu m, the width of the cross section is 57-86 mu m, and the lanthanum hexaboride whisker with the length of 1794 mu m and the width of the cross section of 72 mu m is shown in figure 2 a; FIG. 2b shows a lanthanum hexaboride whisker having a length of 1622 μm and a cross-sectional width of 86 μm; FIG. 2c shows lanthanum hexaboride whisker with length 1694 μm and cross-sectional width 86 μm; FIG. 2d shows lanthanum hexaboride whisker 1837 μm long and 57 μm wide in cross-section.

Example 3

In the glove box, the black oxide film on the surface of the metal lanthanum rod is removed to expose silver metal lanthanum. Then, 3g of metal lanthanum powder is filed and mixed with 1.5g of boron powder, and the metal lanthanum powder and the boron powder are put into a mortar for grinding for 30min, so that the metal lanthanum powder and the boron powder are fully mixed. 30g of metal aluminum is put into an alumina crucible, then the alumina crucible is put into an induction heating device, the aluminum crucible is heated under the environment of 3pa of vacuum degree, and the aluminum crucible is taken out after the aluminum block is melted. After cooling, punching holes in the vertical direction of the aluminum block, filling metal lanthanum powder and boron powder into the holes, and covering 10g of aluminum block on the surfaces of the metal lanthanum powder and the boron powder. Then, the crucible is put into a furnace for sintering, the heating rate is adjusted to be 100 ℃/h, the temperature is increased to 1350 ℃, the temperature is kept for 12 hours, and the cooling rate is 100 ℃/h. And after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid with the concentration of 5mol/L, and filtering the sample after the aluminum fluxing agent is dissolved to obtain the lanthanum hexaboride whisker.

The obtained lanthanum hexaboride whisker has the length of 2210 to 2700 mu m and the section width of 72 to 120 mu m, and is shown as a lanthanum hexaboride whisker with the length of 2325 mu m and the section width of 86 mu m in figure 3; FIG. 4 shows lanthanum hexaboride whisker having a length of 2225 μm and a cross-sectional width of 76 μm; FIG. 5 shows lanthanum hexaboride whiskers 2210 μm in length and 72 μm in cross-sectional width; FIG. 6 shows lanthanum hexaboride whiskers that are 2700 μm long and 120 μm wide in cross-section.

Claims

1. A preparation method of lanthanum hexaboride whisker is characterized in that: the method for preparing the lanthanum hexaboride whisker comprises the following steps:

(1) preparing raw materials: grinding metal lanthanum powder in a glove box, mixing the metal lanthanum powder with boron powder, and grinding the metal lanthanum powder and the boron powder in a mortar for 25-30 min to fully grind and uniformly mix the metal lanthanum powder and the boron powder;

(2) treating the aluminum cosolvent by a layering method or a drilling method:

the layering method comprises the following steps: firstly, putting metal aluminum into an aluminum oxide crucible, then putting the aluminum oxide crucible into an induction heating device, heating the aluminum oxide crucible in an environment with the vacuum degree of 3pa, stopping heating after an aluminum block is melted, and taking out the aluminum block; adding a layer of metal lanthanum powder and boron powder on the surface of aluminum, and adding a layer of aluminum on the mixture; putting the alumina crucible into an induction heating device, and heating in an environment with the vacuum degree of 3 pa; repeating the steps to obtain a structure with three layers of aluminum and two layers of ingredients; then, putting the alumina crucible into a furnace for sintering, heating to 1350 ℃ and preserving heat for 12 hours; after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid, and filtering the sample after the aluminum fluxing agent is dissolved to obtain lanthanum hexaboride whisker;

the drilling method comprises the following steps: firstly, putting metal aluminum into an aluminum oxide crucible, then putting the aluminum oxide crucible into an induction heating device, heating the aluminum oxide crucible in an environment with the vacuum degree of 3pa, stopping heating after an aluminum block is melted, and taking out the aluminum block; after cooling, punching holes in the vertical direction of the aluminum block, filling the holes with the uniformly mixed metal lanthanum powder and boron powder, and covering a layer of aluminum block on the metal lanthanum powder and the boron powder; then, putting the alumina crucible into a furnace for sintering, heating to 1350 ℃ and preserving heat for 12 hours; after sintering, taking out the sample, soaking the sample in dilute hydrochloric acid, and filtering the sample after the aluminum fluxing agent is dissolved to obtain lanthanum hexaboride whisker;

the mass ratio of the metal lanthanum to the boron powder to the aluminum fluxing agent is 2:1: 27;

the heating rate of sintering in a furnace is 100 ℃/h;

the cooling rate of the furnace is 100 ℃/h;