なぜ六方晶窒化ホウ素はとても滑りやすいのか

More than 100 years ago, there was a material that was very similar to graphite except for its structure and even its properties: hexagonal boron nitride (H-BN). It is a crystal composed of 56.4 percent nitrogen nucleus and 43.6 percent boron atoms. It is also called "white stone ink" because of its white color. Its structure is shown below.

The H-BN has many excellent features, most notably and most commendably "slippery". It can be seen from the above figure that the lattice structure of H-BN is very similar to that of graphite. Boron atoms and nitrogen atoms are staggered to form an infinite boundary network with hexagons as units, that is, monolayer H-Bn. When many of these layers of network along the C axis with ABAB... Which are infinitely stacked to form three-dimensional hexagonal boron nitride.

In each atomic layer, boron and nitrogen atoms are connected by a strong sp² hybrid covalent bond with a= B =0.2504nm. Each two adjacent atomic layers can be connected by weak interatomic force -- vanderWaals force, with bond length c=0.6661 LNM. Therefore, h-BN has a small binding force in the C-axis direction and a large distance between atoms. It is easy to slide between layers and has good lubricity even at high temperature.