What is cubic boron nitride powder?

Cubic boron nitride (CBN) is a synthetic superhard material, whose atomic structure is similar to that of carbon atoms in diamond, so it has the characteristics of high density and the hardness is second only to diamond. It is mainly used as abrasive and tool material.

As early as 1957, researchers from GE Company in the United States used artificial methods to synthesize cubic boron nitride for the first time under ultra-high temperature and high pressure conditions, but the natural cubic boron nitride has not been discovered, so cubic boron nitride is considered to be a synthetic product, does not exist in nature.

It wasn't until 2009 that scientists from the University of California, Riverside and Lawrence Livermore National Laboratory, together with colleagues from institutions in China and Germany, found the mineral in chromium-rich rocks in the ancient oceanic crust about 306 kilometers beneath the mountains of the southern Tibetan Plateau in China. The crystals formed at temperatures of about 1,300 degrees Celsius and pressures of 118,430 atmospheres.

The new mineral, cubic boron nitride, was officially recognized by the International Mineralogical Association in August 2013.

History of cubic boron nitride

In 1957, the United States GE General Electric Company was the first to develop cubic boron nitride.

In 1960, the Soviet Union successfully developed cubic boron nitride.

In 1964, Japan successfully developed cubic boron nitride.

In 1966, the first cubic boron nitride was born in China.

In 1969, the United States General Electric began to promote cubic boron nitride, under the trade name "Brasson" (BZN) appeared in the international market.

In 1974, De Beers developed an amber cubic boron nitride.

Natural cubic boron nitride was first discovered on the Tibetan Plateau in 2009.

Structure of cubic boron nitride

Cubic boron nitride has a similar crystal structure to diamond and the lattice coefficients of the two are similar (0.3567nm for diamond and 0.3615nm for cubic boron nitride).

Cubic boron nitride is a compound composed of nitrogen atoms and boron atoms. The chemical composition is 43.6% boron and 56.4% nitrogen. From the way the atoms are arranged in the crystal, the structure of cubic boron nitride is composed of a face-centered cubic lattice of B atoms and a face-centered cubic lattice of N atoms staggered by 1/4 along the diagonal.

Properties of cubic boron nitride

(1) High hardness. It is the second hardest material in nature, second only to diamond. Mohs hardness 9.7 (diamond 10), Vickers hardness 7500 (diamond 10000).

(2) Strong thermal conductivity. Cubic boron nitride has excellent thermal conductivity, its thermal conductivity is 79.54w/m·k, lower than diamond, but much higher than high speed steel, hard alloy and other ceramic materials.

(3) High thermal stability. Cubic boron nitride has high thermal stability, better than synthetic diamond, can withstand the cutting temperature above 1200℃.

(4) High chemical stability. Cubic boron nitride is chemically inert and has high chemical stability against acids and bases in neutral and reducing gaseous media.

Synthesis of cubic boron nitride

At present, the synthesis of cubic boron nitride single crystal is mainly synthesized by static high pressure catalyst method, usually with hexagonal boron nitride (hBN) and different catalysts as raw materials, under high temperature (1400℃~1800℃) and high pressure (4~8GPa) CBN single crystal powder, the color is mostly black or amber.

The earliest synthesized cubic boron nitride in China used metal magnesium as catalyst, and later mainly used metal nitride borides. The cubic boron nitride synthesized by nitride is light in color, mostly light yellow, amber or colorless transparent crystals, with complete crystal type, smooth crystal surface and high compressive strength of single particle.

The commonly used catalysts for the synthesis of cubic boron nitride are: Li3N, Mg3N2, Ca3N2, Li3BN2, Mg3B4N4, Cs3B2N4.

Application of cubic boron nitride

Because of its excellent properties, cubic boron nitride can play a very important role in the field of material processing. At present, cubic boron nitride is mainly used as abrasive materials and tool materials.

(1) Used as abrasive material. Small particles of cubic boron nitride single crystal is mainly used as abrasive materials, cubic boron nitride abrasive is bonded to cubic boron nitride abrasive with a certain geometric shape products, with a very high service life, can be divided into metal binder CBN abrasive, resin binder CBN abrasive, electroplating binder CBN abrasive, ceramic binder CBN abrasive four categories.

Cubic boron nitride abrasives are mainly used for grinding, which can be used for the processing of ferrous materials and non-ferrous metal materials. Their application scope is wider than diamond abrasives in the field of metal materials processing. Cubic boron nitride abrasive has good grinding performance for ferrous metals, especially for materials with high hardness, high toughness, high strength and low heat conductivity at high temperature, and its metal grinding rate is 10 times that of diamond.

Cubic boron nitride abrasive is used for high speed and efficient grinding and honing, which can greatly improve the grinding efficiency, high grinding precision, long grinding wheel life, and save many auxiliary time such as grinding wheel replacement and dressing, machine tool adjustment and workpiece detection.

(2) Used as tool materials. Polycrystalline cubic boron nitride (PCBN) was prepared by using CBN single crystal powder with appropriate particle size and sintering together at high temperature and high pressure. The micrograins in PCBN structure are disordered with uniform hardness and no directionality, which overcomes the defects of CBN single crystal such as easy cleavage and anisotropy.

There are three kinds of PCBN cutting tools: the first is the whole pure PCBN sintered sheet; The second is a composite sheet sintered with CBN as the wear-resisting layer and cemented carbide as the substrate. The third is the first sintering PCBN blade blank, and then welded to the carbide matrix welding blade.

PCBN tool is particularly effective in the processing of iron group metals and their alloys. It is not only capable of rough and fine turning of hardened steel, high speed steel, cast iron and other materials, but also capable of high-speed cutting of high temperature alloy, thermal spraying materials, hard alloy and other difficult materials. It is one of the best tools to realize the grinding by turning instead of turning.