Chinese name: Lanthanum hexaboride

English name: lanthanum hexaboride

CAS number: 12008-21-8

Molecular formula: B6La

Molecular weight: 203.7715

Density (g/mL, 20 ℃): 4.76

Mohs scale hardness: 9.5

Room temperature resistance: 15-27 μ Ω

Vickers hardness: 27.7GPa

Work function: 2.66eV

Emission constant: 29A/cm2 · K2

Melting point (º C): 2715

CAS number: 12008-21-8

MDL number: MFCD00151350

EINECS number: 234-531-6

PubChem number: 24854496

Solubility: insoluble in water and hydrochloric acid

Chemical properties: The chemical properties are very stable and do not react with water, oxygen, or even hydrochloric acid; At room temperature, it only reacts with nitric acid and aqua regia; Under aerobic atmosphere, oxidation only occurs at 600-700 ℃. In a vacuum atmosphere, LaB6 material is prone to react with other substances or gases to form low melting point substances; At high temperatures, the formed substances will continuously volatilize, exposing the low escape power surface of Lanthanum hexaboride crystal to the emission surface, thus making Lanthanum hexaboride have excellent anti poisoning ability.

The crystal structure of Boride determines a series of unique properties:

1) Because of the strong bonding force between boron atoms (Lattice constant 4.145 ∨), it is a refractory compound, with a melting point of 2210 ℃.

2) The chemical properties are very stable and do not react with water, oxygen, or even hydrochloric acid; At room temperature, it only reacts with nitric acid and aqua regia; Oxygen only undergoes oxidation at 600-700 ℃.

3) Within a certain temperature range, the coefficient of expansion approaches zero.

4) Good stability in the air, and surface contamination during use can be restored by vacuum heat treatment.

5) Good resistance to ion bombardment and able to withstand high field strength.

6) Since there is no valence bond between the metal atom and the boron atom, the Valence electron of the metal atom is free. Therefore, Boride has high conductivity, and the resistance of Lanthanum hexaboride is roughly the same as that of metal lead. The temperature coefficient of its resistivity is positive.

7) If six Boride is allowed to contact with Refractory metals at high temperature, boron will diffuse into the metal lattice and form interstitial boron alloy with the metal. At the same time, the boron framework will collapse and allow the metal atoms to evaporate.

8) When the Boride is heated to a certain temperature, the metal atoms on the crystal surface evaporate, but are immediately supplemented by the metal atoms diffused from the interior of the lattice, while the boron framework remains unchanged, minimizing the loss of surfactant.

Synthesis method:

Chemometrically mix and stir a small amount of Lanthanum oxide, boron and carbon black powder (about 1g in total) until uniform, and press the reactant into thin sheets [1in (1in=0.0254m) × 1/2in × 1/16 inch]. Place thin slices into a 1.5-inch high and 1.7-inch diameter graphite crucible. The latter is then placed in a larger graphite crucible (4 inches high and diameter), filled with hydrogen gas, and heated at 1500 ℃ for 2 hours or 1800 ℃ for 1 hour.

Structural properties:

Since the B6 Octahedron network needs two electrons to stabilize its structure, the three Valence electron of La will have one rich, and LaB6 behaves as a metal conductor. The surface plasmon resonance absorption of metal conductor LaB6 nanomaterials is around 1000nm, which can compensate for the poor barrier effect of infrared barrier materials such as ITO (indium tin oxide) in the near-infrared region, making LaB6 an important infrared barrier material. Due to the strong Covalent bond between B atoms in LaB6 structure, a close spatial network is formed, which makes it have the characteristics of low volatility, low work escape, high melting point, high strength and high stability.

Purpose: It has a wide range of applications and has been successfully applied in more than 20 military and high-tech fields such as radar, aerospace, electronic industry, instrumentation, medical equipment, home appliance metallurgy, environmental protection, etc. 1) Electron emission cathode. Due to the low work of electron escape, the cathode material with the highest emission current at medium temperature can be obtained, especially high-quality single crystals, which are ideal materials for high-power electron emission cathodes. 2) High brightness point light source. It is used to prepare the core elements of electron microscope, such as optical filter, soft X-ray diffraction Monochromator and other electron beam light sources. 3) High stability and long life system components. Its excellent comprehensive performance has enabled it to be applied in various electron beam systems, such as electron beam engraving, electron beam heat sources, electron beam welding guns, and accelerators, for the production of high-performance components in engineering fields.

Packaging and storage:

Sealed and stored in a dry, cool environment, not suitable for exposure to air, to prevent oxidation and aggregation caused by moisture, which affects dispersion performance and usage effect