Boron Nitride is an advanced ceramic known for its superior properties which is available both in Powder and solid forms. It is made up of Boron Nitrogen bonds with different structural forms of which one is Cubic Boron Nitride. We shall review this metal in detail in the ensuing paragraph.
Boron Nitride: An Overview
The other name of Boron Nitride is white graphene when it exists in the solid form. Boron Nitride offers good machinability, has higher heat capacity and is a good electrical insulator. Yet another specialty of Boron Nitride is, once machined they does not really require any heat sintering or treatment. Bn chemistry is almost like carbon due to the presence of isoelectronic phenomenon.
Boron Nitride chemical formula is given as “BN.” The BN compound has both Boron and Nitrogen atoms. The location of Boron a Nitrogen in the lattice generates different BN structures. There are different forms of Bn such as a-BN, h-BN, c-BN and w-BN.
Hexagonal Boron Nitride (h-BN)
Hexagonal boron nitride is a component of many industrial products, including cosmetics. In the structure of hexagonal boron nitride, the elements boron and nitrogen are fixed to the crystal lattice by strong covalent bonds. Its structure is similar to that of graphene.
Three nitrogen atoms are fixed to Boron Atom in the HBN structure. The similarity in the honeycomb hexagonal HBN structure is the reason for its analogy with carbon. The layers obey the wander Waals forces and the plate like geometry makes them ideal as lubricating mediums. The properties such as mechanical, chemical strength and electrical insulation are due to the planar triangular bonds
The other superior properties that correspond to the HBN structure are its thermal conductivity, and low frictional coefficient. Hexagonal Boron Nitride is popularly manufactured through Boric Oxide nitridation at elevated temperatures. H-BN is stable at 1000 degC under normal conditions that exceeds for vacuum or inert. Since the stability is closer to graphene, Hexagonal Boron Nitride is often acclaimed as the most advanced technical ceramic.
Applications of Hexagonal Boron Nitride
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It is used on nanoelectronics devices as a substitute to graphene substrate
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Hexagonal Boron Nitride in its thin form is used as coatings that resists corrosion
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It is often engaged in the manufacture of sensor materials
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It is used in electron tunneling due to its low value of dielectric constant.
Cubic Boron Nitride
What is c-BN?
c-BN is a derivative of Hexagonal Boron Nitride (h-BN) formed under high temperature and pressure.
The biggest specialty of Cubic Boron Nitride is that it holds the place of second hardest material in the world. The mechanical strength of Cubic Boron nitride is popular and is in par with diamond. It is one among the most popular polymorph of Boron Nitride.
The basic structure of c-Bn is crystalline with alternate arrangement of Boron and Nitrogen atoms. Here, Boron Nitrogen atoms follow covalent bonding which is the basic reason of the hardness and stability thermal. It has density around 3.5 g/cm3 and appears to be pale yellow or transparent.
Cubic Boron Nitride Properties
C-BN is also a brilliant semiconductor, upon increasing pressure while manufacturing c-BN bandgaps are often susceptible to changes greater. The bandgap helps to excel as electric insulator. Cubic Boron Nitride ‘s thermal conductivity is around 1300 KW/Mk. They remain inert and possesses low dielectric constant value.
The reactivity of c-BN is such that they remain even non respondent to ferrous materials. The optical range dealt by cubic boron nitride varies from Ultra violet to the visible spectrum. The two popular types of c-Bn available today in the market are dense cubic boron nitride and polycrystalline cubic Boron Nitride. Cubic Boron Nitride Formula is given as c-BN.
Cubic Boron Nitride Vs Diamond
What is harder that diamond.?
Although not harder than diamond, cubic Boron nitride has its place special when compared with diamond. Cubic boron Nitride hardness is 4500 Kg/mm2 which can be firmly compared with diamond of hardness around 600 Kg/mm2.The value of modulus both young’s and bulk is also in similar range of 800 – 1000 and 370 – 450.
Furthermore, when it comes to the structure, like diamond, c-BN has two base atoms that are different. The similarity of both diamond and c-BN is generally attributed to the lookalike structure they possess. However, c-BN and its electrical properties can be manipulated with the help of p and n type of impurities. This makes them different from that of diamond when it comes to functionality.
Cubic Boron Nitride uses
Cubic Boron Nitride exhibits both young’s and Bulk modulus greater Boron Carbide and Silicon Carbide. This very reason strongly contributes to the hardness of cubic Boron Nitride. The hardness makes them suitable as abrasives and make them an integral part of cbn cutting tool material. Generally Dense c-Bn is used for cutting application and porous type for grinding requirements.
C-BN is put across versatile applications of Cutting and machining due to its inert nature. Unlike diamond it doesn’t react to iron. The conventional c-Bn requires manipulation for utilising it in cutting application. This is generally done during the conversion of h-Bn to c-Bn while sintering.
Polycrystalline c-BN with binder often finds useful in highly abrasive environments, Image is shown below. Apart from hardness Cubic boron Nitride also excels in electrical applications. Bn because of its wide bandgap engages as electrical insulators. They also play a crucial role as heat sink in lasers, microelectronic devices and LEDs.
By coating Aluminium and Group 8 metals, c-BN functionality of becoming a sink is popular in electronic industry. C-BN also finds value during semiconductor synthesis to obtain p and N type by proper doping. The common materials used for doping are Silicon or Beryllium. These semiconductors work at high temperature and are used in UV sensors.
c-BN grinding wheels
The invention of c-BN grinding wheels merited precision manufacturing due to the increase in efficiency. Such wheels contributed to industries such as aerospace, machines, tool production and automobile. c-BN grinding wheels also offer high hardness and good performance on comparison with SiC and Alumina. They ensure integrity at higher working temperature without degradation unlike diamond.
The wheels of c-BN can withstand high temperature and hence deal with the amount of heat generated during the process. They also offer cost savings due to their higher resistance to wear and tear which is economically beneficial. The surface finish is appreciable and the work piece wastage is also less when in comes to c-BN grinding wheels. It also ensures lesser cycle time as the tasks are done quicker and precise.
Super abrasive wheels –or diamond cBN wheel
The super abrasive wheels are the ones differ from conventional wheel of Sic and Alumina. They are made of c-Bn and diamond. The super abrasive wheel offers better thermal conductivity limiting the rise in temperature of the workpiece. The diamond c-Bn wheel also offer high accuracy and precision cutting that contribute to better lifespan.
Conclusion
Cubic Boron Nitride is desirable in modern science and material manufacturing. They are competitive when compared to materials such as diamond. They excel in properties such as hardness, strength, and electrical insulation. The wide band gap, inert nature, low dielectric constant and optical specialities are the other factors of merit.