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Have you known all the structures boron nitride have?

Boron nitride is a crystal composed of nitrogen and boron atoms. Chemical composition of 43.5% boron and nitrogen atoms of gas, with four different variants: hexagonal boron nitride (HBN), amorphous boron nitride(ABN), cubic boron nitride (CBN) and boron nitride (WBN).

Nitrogen atoms and boron atoms communicate with each other in different ways, which can form different structures of boron nitride crystals. When the nitrogen and boron atoms in SP2 hybrid, because the bond angle is 120 o, the bond formed after the planar angle of six mesh structure with graphite like molecules, molecular plane mesh size of this large space take a different way of stacking, and can be a structure of hexagonal boron nitride (HBN) and amorphous boron nitride(ABN).

1. hexagonal boron nitride

The hexagonal boron nitride has graphite like structure, and its appearance is white, so it is sometimes referred to as some kind of boron nitride or white graphite. The structure of the hexagonal boron nitride, layered arrangement of AA, AA ... The grid type constant Alfa = 0.251 + 0.002nm, c = 0.670 + 0.004nm, the density is 2.25g / cm3. hexagonal boron nitride is very stable in air, high temperature power 2270K, sublimation at 3270K, boron nitride has good insulation, thermal conductivity, and chemical stability, insoluble in cold water, the water boils hydrolysis is very slow and produce a small amount of boric acid and hydrogen, and room temperature weak acid and alkali are no reaction. Poorly soluble in hot acid treatment can be decomposed by melting the sodium hydroxide, potassium hydroxide, using this property, cubic boron nitride can be separated from the hexagonal boron nitride.

2. amorphous boron nitride(ABN)

The structure of amorphous boron nitride(ABN), layered arrangement of ABCABC ... The type of lattice constant Alpha = 0.22556nm c = 0.4175nm, density 2.25 g / cm3.

It has the same properties as the hexagonal boron nitride and cannot be separated by physical methods. Inter layer ABCABC ... The scheme is more favorable for the transformation of cubic boron nitride, so it was used to obtain cubic boron nitride.

3. cubic boron nitride

In addition to the hexagonal boron nitride (HBN) and amorphous boron nitride(ABN) two structures, boron nitride diamond also has similar structure of two take SP 3 hybrid form, they are cubic boron nitride has zinc blende and Wurtzite structure of boron nitride (WBN) six.

The crystal structure of cubic boron nitride is similar to diamond, not only are similar lattice constants (0.3567nm diamond, cubic boron nitride, 0.3615nm) and bonding in crystals are basically the same, which is mixed along the four body covalent bond, which is something different with the diamond in a covalent bond between carbon atoms is the bond cubic boron nitride crystal is boron and nitrogen atom between covalent bond, in addition there is a weak ionic bond. In ideal cubic boron nitride crystals, the bond length of all four B-N bonds are equal to each other (0.157nm), the angle between the bond and the bond is 109o5 '.

Each layer of cubic boron nitride crystal is formed by the principle of compact ball stacking, which is composed of the same kind of atoms. The cubic boron nitride lattice has a continuous stacking of aa'bb 'cc' aa 'bb' with a constant grid of 3615 + 0.0001nm inhabitants and a population density of 3.48 g / cm3.

The most typical cubic boron nitride geometry is combined with tetrahedral crystal surface and negative tetrahedral surface, common shape: eight tetrahedron, false body, false hexahedron (flat tetrahedron).

According to the microstructure of cubic boron nitride B and N corrosion on the surface of the cubic boron nitride crystal tetrahedron can be divided into two types: one is that the four tetrahedral drill, drill surface surface; another example is that nitrogen tetrahedron, four surface is nitrogen surface. drill

4. Wurtzite boron nitride

Wurtzite boron nitride belongs to the six-crystal, the structure is shown in Figure 1-1. The structure of Wurtzite boron nitride is composed of a pair of atomic layers, one of which is a boron atom and the other is a nitrogen atom. If you only have the nearest neighbor atoms, it is impossible to say it is cubic or six-party structure, but as for the next nearest neighbor atoms, the difference can be between their structure. In these two structures, the length of the adjacent keys is almost equal. The grating constant of Wurtzite boron nitride a = 0.255 + 0.002nm, c = 0.