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1.
Boron Nitride
Diborane and ammonia react at 873K to obtain hexagonal boron nitride with a layered structure
.
nB 2 H 6 +2 n NH 3 =2(BN) n +6 n H 2
The chemical formula of hexagonal boron nitride (BN) n is BN, which has a layered structure similar to graphite (Figure 13-17), except that the B atoms and N atoms in the layer are alternately arranged
.
Like graphite, layers are stacked in parallel by intermolecular forces
Figure 13-17 Layered structure of boron nitride and graphite
Pure boron nitride is a white powder, so it is also called "white graphite"
.
Hexagonal boron nitride has thermal conductivity, chemical stability, good electrical insulation, etc.
High-purity boron nitride is non-toxic and can be used as a filler for cosmetics, a heat shielding material in the aerospace industry, aluminizing of various capacitor films, and aluminizing of picture tubes.
Boron nitride products can be used as high temperature, high pressure, insulation, and heat dissipation components.
and so on
.
2.
Boron carbide
Boron carbide B 4 C has high hardness (Mohs hardness of 9.
3) and high melting point (over 2300°C)
.
It was discovered in the 19th century as a by-product of metal boride research
7C+2B 2 O 3 =B 4 C+6CO
Boron carbide has high hardness and can be used for grinding, grinding, drilling and polishing materials such as cemented carbide and gemstones
.
Boron carbide has good high temperature resistance and can be used as a ceramic coating for warships and helicopters
3.
Metal Borides
Many metal borides have excellent properties such as flame retardancy, high hardness, high temperature resistance, and wear resistance.
They have become important new materials and are widely used in radar, aerospace, instrumentation, medical equipment, home appliances, metallurgy and composite materials
.
With the advancement of science and technology, its use will continue to expand
Metal borides have a wide composition range, such as monoborides Mn 4 B, Co 3 B, etc.
, diborides ZrB 2 , TiB 2 , Ta 3 B 2, etc.
, triborides Cr 5 B 3 , Rh 7 B 3, etc.
, polyborides Compound Ti 3 B 4 , CaB 6 , LaB 6 , Ru 11 B 8 and so on
.
There are many methods for preparing metal borides, such as direct compounding from simple substances at high temperatures, reduction of mixed halides with hydrogen, and reduction of mixed metal oxides with carbon
.
Related link: Boron halide