Boron graphite-like

By subjecting boron nitride (a white powder) to high pressure and temperature small crystals of a substance harder than diamond, known as borazon, are obtained. This pressure-temperature treatment changes the structure from the original graphite-like layer structure (p. 163) to a diamond-like structure this hard form can withstand temperatures up to 2000 K. 

All three have similar cubic structures (although boron nitride also has a graphite-like structure). 

PI5.9 Boron nitride (BN) is isoelectronic with carbon and the B, C, and N atoms are about the same size. The result is that BN forms crystal structures similar to those of carbon, in that it crystallizes in a hexagonal (graphite-like hBN) and a cubic (diamond like cBN) structure. The data summarized at the end of the problem are available for the two forms of BN.17... 

Figure 1 2 9. The superlattice of metallic layers (B) made of graphite-like honeycomb boron planes separated by hexagonal Mg layers (A) forming a superlattice. ..ABABAB... where the c-axis is the period of the superlattice...

Hach CT, Jones LE, Crossland C, Thrower PA. An investigation of vapor deposited boron rich carbon—a novel graphite-like material—part I The structure of BCj (C6B) thin films. Carbon 1999 37 221-230. 

In graphite, which can be considered as a giant two-dimensional molecule from the series of condensed rings, the bonding between the separate layers is very weak, being due, as in molecular lattices, to Van der Waals-London interaction. The now infinite system of n electrons results in metallic conduction, only, however, in the plane of the rings Boron nitride has perhaps also a diamond-like form as well as the common graphite-like modification (p. 235). 

Boron carbide (B4C) is also an extremely hard, infusible, and inert substance, made by reduction of B203 with carbon in an electric furnace at 2500°C, and has a very unusual structure. The C atoms occur in linear chains of 3, and the boron atoms in icosahedral groups of 12 (as in crystalline boron itself). These two units are then packed together in a sodium chloride-like array. There are, of course, covalent bonds between C and B atoms as well as between B atoms in different icosahedra. A graphite-like boron carbide (BQ) has been made by interaction of benzene and BC13 at 800°C. 

These novel microstructures have extraordinary combination of physical and chemical properties [11-13], for this reason they become an important scheme of actually science work. One example of such nanomaterials is boron carbonitride (BNC) with graphite-like structure. Based on theoretical calculations, the existence of nanotube structures of BN was predicted in 1994, which was soon verified by the first synthesis of BN nanotubes in 1995. 

R. B. Kaner, J. Kouvetakis, G. E. Warble, M. L. Sattler and N. Bartlett, Boron-Garbon-Nitrogen Materials of Graphite-Like Structure, Mat. Res. Bull. 22 (1987) 399-404. 

Boron nitride (BN) exists in a hexagonal modification with a graphite-like crystal structure and a cubic high temperature/high pressure modification with a diamondlike structure. 

BN-powder is, due to its graphite-like properties, predestined for utilization as a high temperature lubricant or as a mold lubricant in metal casting. Formed articles of boron(III) nitride are used as melting crucibles for high purity metals or semiconductor alloys and as refractory linings for plasma burners, rocket jets and combustion chambers. 200 t/a of hexagonal BN were produced in 1995. 

The stereochemistry of boron is simple in many of its compounds with the halogens (but note BgClg), oxygen, nitrogen, and phosphorus, three coplanar or four tetrahedral bonds being formed. The more complex stereochemistry of the element in electron-deficient systems (elementary B, some borides, and the boranes) is dealt with separately. The planar arrangement of three bonds from a B atom has been demonstrated in many molecules BX3 and BR3 (Table 24.1), in cyclic molecules of the types noted in the previous section, in many oxy-ions (see later section), and in crystals such as the graphite-like form of BN (p. 847) and AlBj (p. 842). 

This designation is applied to boron nitride which has been converted from the microcrystalline, turbostratic state to an ordered layer-lattice, graphite-like structure by thermal treatment. 

Charles T.H., Linda EJ., Carl C. An Investigation of Vapor Deposited Boron Rich Carbon—A Novel Graphite-Like Material-Part 1 The Structure of BC fCsB) Thin Films. Carbon. 1999. V. 37. No2. P. 221-230. 

---