Cubic boron nitride and its properties

Physical and mechanical properties of cubic boron nitride.

Cubic boron nitride is a new synthetic superhard material with a hardness close to diamond, but with higher heat resistance. Cubic boron nitride is a compound of boron (43.6%) and nitrogen (56.4%). It has a lattice with almost the same structure and parameters as diamond.

Cubic boron nitride is derived from boron nitride (BN), which is similar in many respects to graphite in its properties. Like graphite, boron nitride crystallizes into a hexagonal lattice. The distance between the atoms at the vertices of the regular hexagon is 1.45 A for boron nitride and 1.42 A for graphite, and the distance between the planes is Z.ZZA and 3.35A, respectively. At the same time, in each hexagon, boron and nitrogen atoms alternate with each other, with each nitrogen atom connected to three boron atoms and vice versa. In contrast to the structure of graphite, in which the hexagonal layers move relative to each other so that the vertices of the hexagons are above the center of the adjacent hexagons, in boron nitride the layers are just below one another and the boron and nitrogen atoms alternate vertically. Boron nitride and graphite have similar densities of 2.20-2.25 g/cm3 and 2.20-2.35 g/cm3, respectively

There are significant differences between graphite and boron nitride. Graphite is black and boron nitride is white. Graphite is a good conductor electricity, boron nitride is bad, it's a great insulator at high temperatures. These differences are due to significant semi-metallic properties inherent in graphite and not present in boron nitride.

There are common properties between graphite and boron nitride, in particular the fact that both substances have hexagonal lattices with similar parameters, suggesting that the lattice of boron nitride may be cubic, similar to diamond. But this was experimentally confirmed only after the invention of high-pressure technology, which made it possible to synthesize diamonds and other superhard materials.

Boron nitride is treated at high temperature and pressure in a special chamber to obtain a cubic lattice variant similar to diamond, the only difference is that the cubic lattice parameters of boron nitride are slightly larger than diamond. They are equal to 3.616A and 3.567A respectively, with interatomic distances of 1.56A and 1.54A respectively. The structural lattice of diamond consists of atoms of one element (carbon and cubic boron nitride) and atoms of two elements (boron and nitrogen). Each boron atom is bound to four nitrogen atoms.

The literature provides various data on the hardness of cubic boron nitride. Based on these data, its microhardness ranges from 7500 to 9500 kg/mm 2. The wide range of microhardness values of cubic boron nitride is due to the fact that it is measured on a Vickers or PMT-3 instrument using a diamond pyramid and its hardness is close to that of cubic boron nitride. The microhardness of diamond is J 0000 kg/mm 2, and that of feldspar zeolite is 9250 kg/mm 2. These values are determined with an accuracy of +5%. The actual density of cubic quartz is slightly less than that of diamond, at 3.45 g/cm 9. The strength of CBN corresponds to the strength of ASO and ACP diamonds.

The grain of cubic boron nitride is dark brown, yellow, gray or milky white. They come in a variety of shapes - mostly octahedrons and tetrahedrons.

Practice has shown that cubic boron nitride cannot compete with diamond when processing hard and brittle materials (cermet carbide, glass, ceramics, granite and other non-metallic materials), at the same time, because of its high heat resistance, it is a promising tool steel processing material, especially high-speed normal and improve productivity, as well as other metals and alloys. The advantages of cubic boron nitride when processing these materials are high wear resistance and productivity at low power consumption and low grinding temperatures, which ensures a high quality surface layer.

China's cubic boron nitride, according to the Institute of High pressure physics of the Soviet Academy of Sciences, was first obtained in parallel with artificial diamond in 1960 under laboratory conditions at the Institute of High pressure Physics of the Soviet Academy of Sciences. The original technology for the industrial production of CBN, the dedicated high-pressure chamber and the semi-automatic synthesis device were developed at the Institute of Superhard Materials. Since 1964, in the experimental plant, cubic boron nitride and its grinding tools began to pilot industry, post-industrial production. In 1966, the Leningrad Ilich Abrasive Plant began production of cubic boron nitride and its tools.

Research conducted in recent years has opened up the possibility of altering the physical, mechanical and operational properties of CBN as a tool abrasive over a fairly wide range, depending on the main starting material, synthesis parameters (pressure, temperature, holding time), solvents (catalysts) and additives. As a result, the CBNS synthesized by various manufacturers differ significantly and are produced under various trademarks: borazone (General Electric), cubonite (ISM Experimental Plant), elbor (Ilich Abrasive Plant, Leningrad).

In the Soviet Union, cubic boron nitride (cubonite and elbor) has been produced industrially for 6 years and is used in tools, pastes and powders in various industries in more than 500 enterprises throughout the country.

There are two types of cubic grinding powders: KO with particle sizes from 160/125 to 50/40 and KR with particle sizes from 250/200 to 50/40 - and KM micropowders with particle sizes from 60/40 to 1/0. They all have different physical, mechanical and operational characteristics and are suitable for various types of processing. The ISM pilot plant also produces KN-grade oblong zeolite, which has a higher abrasive capacity and is mainly composed of single crystals. Elbor grinding powder is divided into LO, LI and micro-powder - LM grades.

The operational performance of cubic quartz grinding powder depends on the shape, surface properties and mechanical strength of the particles. The grain surface of KO grade feldspar is more developed. The KR brand grain has a rounder shape. The mechanical strength of the KR grade cubonite is higher, while the KO grade is lower.

Particle size of cubic zeolite powder. Like synthetic diamonds, CBN is broken and then sorted into different parts by size. The powder consists of a group of grains of different sizes and configurations, which are single crystals, crystal fragments, and grain aggregates (polycrystalline). The main characteristics of cubic quartz powder are granularity, strength and grinding ability, and its determination method is the same as that of diamond powder.

The group, grain name and grain size of the main part of cubic quartz powder are the same as that of diamond powder.

The particle composition criteria (number of particles expressed as a percentage) for grinding and micropowder are the same as for diamond powder of the corresponding particle size. In powder compositions ranging in size from 256/200 to 60/40, no more than 2% of layered and acicular grains are allowed, the size of which exceeds the particle size of the main part of the powder by more than 2 times. The content of soluble impurities in the powder should not exceed 5%, caking and moisture - • 0.2%.

The strength of KO and KR grade powders with particle sizes from 250/200 to 60/40 is approximately the same as that of ASO and ACP grade synthetic diamond powders, respectively. The grinding capacity of cubic quartz powder is determined by the ratio of the weight of ground corundum to the weight of waste powder and must be at least 2. Superabrasive materials like cubic boron nitride (CBN) are essential for industrial applications. As leading lapping powder suppliers, we offer high-quality CBN abrasive micron powder. Our products ensure efficient grinding and superior finish, making us a trusted choice in the industry.

TU 258-66 specifies additional technical requirements for cubic zeolite powders and test methods for these powders.