Advanced Ceramic Materials

Pros and Cons of Wurtzite Boron Nitride to Consider

Wurtzite boron nitride, often referred to as w-BN, is a remarkable material with a range of unique properties that have captured the interest of researchers and engineers. From its impressive thermal conductivity to its excellent electrical insulation, w-BN has found applications in various industries. However, like any material, it’s crucial to understand not only its advantages but also its limitations. In this blog post, we’ll delve into the benefits and cons of w-BN to provide you with a comprehensive overview.

The Pros of Wurtzite Boron Nitride

1. High Thermal Conductivity:

Wurtzite boron nitride boasts exceptional thermal conductivity, which is comparable to some metals. This property makes it an excellent choice for applications where efficient heat transfer is crucial. From thermal management in electronics to heat spreaders in aerospace, w-BN excels in dissipating heat effectively.

2. Electrical Insulation:

Unlike metals, w-BN is an electrical insulator. This characteristic is invaluable in electronics applications where electrical insulation is required alongside heat dissipation. It eliminates the risk of short circuits while efficiently managing heat.

3. Thermal Stability:

w-BN is stable at high temperatures, ensuring its performance in demanding thermal conditions. It doesn’t degrade or oxidize, making it suitable for aerospace and automotive applications, where exposure to extreme temperatures is common.

4. Chemical Inertness:

w-BN is chemically inert, meaning it doesn’t react with most chemicals. This property enhances its suitability for applications in harsh chemical environments. It remains stable and reliable even when exposed to aggressive substances.

5. Versatile Forms:

w-BN is available in various forms, including powders, coatings, and sheets. This versatility allows for customization to suit different applications, making it a highly adaptable material.

The Cons of Wurtzite Boron Nitride

1. Anisotropic Properties:

w-BN exhibits highly anisotropic properties, which means its characteristics can vary significantly depending on the crystallographic direction. This can make its behavior less predictable in certain applications and may require careful engineering.

2. Synthesis Challenges:

Producing high-quality w-BN can be challenging and may require specialized techniques. This can lead to higher production costs and limited availability, potentially impacting its commercial viability.

3. Thermal Conductivity Anisotropy:

While w-BN has excellent thermal conductivity, this property is also anisotropic. Heat may transfer more effectively in one direction than another, which could be a limitation in certain thermal management applications.

4. Brittleness:

Like other boron nitride materials, w-BN is brittle and can be prone to cracking or fracturing under mechanical stress. This may limit its use in applications requiring high mechanical strength.

5. Limited Electrical Conductivity:

w-BN is generally an insulator, which means it cannot conduct electricity. In applications where both thermal and electrical conductivity are required, w-BN may not be the best choice, and alternative materials may be more suitable.

6. Cost:

As a specialized material, w-BN can be relatively expensive compared to more common materials. This cost factor may influence its suitability for certain applications, particularly when budget constraints are significant.

Conclusion

In conclusion, wurtzite boron nitride (w-BN) presents a compelling solution for a wide range of applications, including electronics, aerospace, and automotive, where effective thermal management is essential. However, the choice of w-BN or another material depends on the specific requirements of the application and the trade-offs between its properties. Understanding both the benefits and limitations of w-BN is key to making informed decisions in selecting the right material for your particular needs.

Advanced Ceramic Materials (ACM) offers a wide range of boron nitride products with various specifications. For additional details, please visit our website.

Three Commonly Used Filaments for Electron Gun in SEM

The requirements of the electron gun in SEM are high brightness and small electron energy spread. There are three commonly used types at present, tungsten filament, lanthanum hexaboride (LaB6) filament, and field emission. Different filaments have differences in the size of the electron source, the amount of current, the current stability and the life of the electron source.

Thermal Dissociation Electron Gun

The thermal dissociation electron gun contains two kinds of tungsten filament and lanthanum hexaboride (LaB6) filament. It uses high temperature to make electrons have enough energy to overcome the work function barrier of the electron gun material and escape. The variables that have a significant effect on the emission current density are temperature and work function. Since it is desirable to operate the electron gun at the lowest temperature to reduce the volatilization of the material, it is necessary to use a material with a low work function to increase the emission current density without increasing the operating temperature.

Tungsten filament

The cheapest and most commonly used is tungsten filament. The tungsten filament emits electrons by thermal dissociation (Thermionization), the electron energy spread is 2 eV, and the work function of tungsten is about 4.5 eV. The tungsten filament is bent into a V-shaped thin wire, about 100µm in diameter, operating at about 2700K, and with a current density of 1.75A/cm2. In use, the diameter of the filament becomes smaller as the tungsten filament evaporates, and the service life is about 40 to 80 hours.

LaB6 filament

The work function of lanthanum hexaboride (LaB6) filament is 2.4eV, which is lower than that of tungsten filament. Therefore, the same current density can be achieved by using LaB6 at 1500K with higher brightness, so the service life is longer than that of tungsten filament. The electron energy spread of LaB6 filament is 1eV, which is better than that of tungsten filament. However, because LaB6 is very active when heated, it must be operated in a better vacuum environment, so the purchase cost of the instrument is high.

Field Emission Electron Guns

Field-emission electron guns are 10-100 times brighter than tungsten and lanthanum hexaboride filaments, respectively, while the electron energy spread is only 0.2-0.3 eV. Therefore, currently commercially available high-resolution scanning electron microscopes all use field emission electron guns, and their resolution can be as high as 1 nm or less.

Field emission electron guns can be subdivided into three types: cold field emission (FE), thermal field emission (TF), and Schottky emission (SE).

Introduction to Silicon Carbide Ball

Silicon carbide ceramics have high hardness, high melting point (2400 ° C), high wear resistance and corrosion resistance, as well as excellent oxidation resistance, high temperature strength, chemical stability, thermal shock resistance, thermal conductivity and good air tightness, etc. Thus, it has been widely used in energy, metallurgy, machinery, petroleum, chemical, aviation, aerospace, national defense and other fields.

Made of silicon carbide, the silicon carbide ball has the advantages of wear resistance, no pollution, and can improve the stability of the raw material. It can reduce the thickness of the mill and the volume of the ball, increasing the effective volume of the mill by 15%-30%. Silicon carbide balls are mainly used as deoxidizers in electric furnaces and cupolas. In addition, silicon carbide balls can also be used in the foundry and steelmaking industries (special steel, stainless steel, T-steel, G-steel, K-steel). It can be used in other factories to increase the temperature in the furnace, shorten the melting time, increase the steel output, and play the role of carbon addition, deoxidation, silicon addition and temperature rise. Silicon carbide balls can be used as a substitute for ferrosilicon. It does not generate dust pollution in the furnace, and the reaction speed is fast and the cost is reduced, which is a new way in the steel-making process. The heat of reaction generated when the silicon carbide element is oxidized can reduce the amount of electricity used, shorten the operation time, reduce the loss of molten steel, and increase the yield. In the process of producing manganese steel and chrome steel, the loss of manganese and chromium can be reduced.

The abrasive industry habitually divides silicon carbide into black silicon carbide and green silicon carbide according to color, both of which are hexagonal crystals, and all belong to α-SiC.

Black silicon carbide contains about 98.5% SiC. Black silicon carbide is made of quartz sand, petroleum coke and high-quality silica as the main raw materials, and is smelted by electric furnace at high temperature. Its hardness is between corundum and diamond, the mechanical strength is higher than corundum, and it is brittle and sharp. Its toughness is higher than that of green silicon carbide, and it is mostly used to process materials with low tensile strength, such as glass, ceramics, stone, refractory materials, cast iron and non-ferrous metals.

Green silicon carbide contains more than 99% SiC. Green silicon carbide is made of petroleum coke and high-quality silica. It is added with salt as an additive and is smelted by high temperature furnace. It is self-sharpening and is mostly used for machining hard alloys, alloys and optical glass. It is also used for wear-resistant cylinder liners and fine-grained high-speed steel tools.

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5 Metallization Processes of Alumina Ceramics

Because of its good electrical properties, alumina ceramics are widely used in electronic and electrical applications. As electronic and electrical substrate materials, the surface usually needs to be metallized. The following are five metallization processes for alumina ceramics.

1. Thick film method

This method uses screen printing to print various circuits, resistors and capacitors on the ceramic substrate. It is undeniable that this process is very widely used and can make the processed ceramic material carry a larger current.

2.DBC method

This process is often applied on high-power modules. The ceramic metallized by this method has a thicker copper layer, can load a larger current, has good thermal conductivity, high strength, strong insulation, and has a thermal expansion coefficient that matches that of semiconductor materials such as Si.

3.DPC method

It is widely used in the LED field. The biggest advantage of this process is high circuit precision and smooth surface, which is more suitable for flip chip/eutectic packaging.

4.LTCC

Because LTCC uses thick film printing technology to complete the circuit production, the circuit surface is rough and the alignment is not accurate. In addition, the multilayer ceramic laminate sintering process has the problem of shrinkage ratio, which limits its process resolution, and the promotion and application of LTCC ceramic substrates are greatly challenged.

5.HTCC

Due to the high sintering temperature, this process has very few users and is basically replaced by LTCC.

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16 molding methods for advanced ceramics (4)

Advanced ceramics are new materials with a series of excellent properties such as wear resistance, corrosion resistance, high temperature resistance, oxidation resistance and high hardness. They are used in the fields of chemical industry, metallurgy, petroleum transportation, mechanical seals, information, energy, aerospace and defense widely. Advanced ceramics are also called special ceramics, modern ceramics, new ceramics, high-performance ceramics, high-tech ceramics and fine ceramics. There are mainly advanced ceramics such as boron nitride ceramics, alumina ceramics, and silicon nitride ceramics.

High-tech fields have high requirements on the shape and dimensional accuracy of advanced ceramics, while ceramic materials are essentially a brittle material, so subsequent processing of ceramic materials is difficult and costly. As a result, improving the performance and reliability of materials, realizing the precision molding of parts with complex shapes, and reducing the preparation and processing costs of materials have become important issues for the development of advanced ceramics.

Direct solidification molding

Direct solidification molding is a new concept of net-size in-situ ceramic molding technology invented by the research team of Professor Gauckler of the Federal Institute of Technology in Zurich, Switzerland, in the 1990s, combining bioenzyme technology, colloidal chemistry and ceramic technology.

Advantages: no or only a small amount of organic additives (less than 1% by weight), no degreasing of the body, uniform body density, relatively high density, and the ability to form large-size and complex-shaped ceramic parts.

Disadvantage: The strength of the green body is often not high enough.

Colloidal Vibration Injection Molding

Colloidal vibration injection molding is a colloidal molding technology invented by Professor F.F. Lange of the University of California, Santa Barbara in 1993. The prepared dilute suspension (20% -30% (vol)) containing high ionic strength is obtained by pressure filtration or centrifugation to obtain a blank with a high solid content, and then cast under vibration to achieve in-situ curing.

Advantages: Continuous production can be achieved, and complex shaped ceramic parts can be formed.

Disadvantages: The strength of the plain billet is low, and the billet is easy to crack and deform when demolding.

Temperature-induced flocculation

Temperature-induced flocculation molding is a net-size colloidal molding method invented by L. Bergstrom, Sweden, in 1994. DCC and colloidal vibration injection molding use the electrostatic stability characteristics of colloids, and this method uses the space (steric hindrance) stability characteristics of colloids.

Advantages: The unqualified body after demoulding can be reused as raw material, and it can be used to form almost all ceramic powder systems.

Solid Moldless Forming

The concept of modern solid moldless technology appeared around the late 1970s. In the early 1990’s, the University of Texas in the United States proposed the molding idea of free-form manufacturing and applied it to the ceramic field. Solid moldless technology breaks through the limitations of traditional molding ideas and is a molding method based on “growth”. In the field of ceramics, solid moldless forming processes can be further divided into: laser selective sintering, three-dimensional printing, fused deposition, layered manufacturing, and stereolithography.

Features: Highly flexible, highly integrated technology, fast, free-form manufacturing, etc. The main problems with this technology are: high equipment prices, software development, material development, molding accuracy and quality.

In the future, the future development of special ceramic molding technology will focus on the following aspects:

(1) Further develop the application of various moldless forming technologies that have been proposed in the preparation of different ceramic materials;

(2) The design of structural layers with more complex performance and the interpenetrating, interweaving, connecting structures and three-dimensional changes in composition within the layers

(3) Structural design and manufacturing of large shaped parts;

(4) Manufacturing and practical application of ceramic microstructures;

(5) Further develop new technologies for pollution-free and environmental coordination.

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16 molding methods for advanced ceramics (3)

Advanced ceramics are new materials with a series of excellent properties such as wear resistance, corrosion resistance, high temperature resistance, oxidation resistance and high hardness. They are used in the fields of chemical industry, metallurgy, petroleum transportation, mechanical seals, information, energy, aerospace and defense widely. Advanced ceramics are also called precision ceramics, special ceramics, modern ceramics, new ceramics, high-performance ceramics, high-tech ceramics and fine ceramics. There are mainly advanced precision ceramics such as boron nitride ceramics, alumina ceramics, and silicon nitride ceramics.

High-tech fields have high requirements on the shape and dimensional accuracy of advanced precision ceramics, while ceramic materials are essentially a brittle material, so subsequent processing of ceramic materials is difficult and costly. As a result, improving the performance and reliability of materials, realizing the precision molding of parts with complex shapes, and reducing the preparation and processing costs of materials have become important issues for the development of advanced precision ceramics.

Centrifugal Grouting

Centrifugal grouting is developed on the basis of traditional grouting. It adjusts the process parameters such as pH value to make the powder uniformly dispersed in the liquid, and deposits and forms under the action of high-speed rotating centrifugal force. Centrifugal grouting combines wet chemical powder preparation with stress-free densification. On the one hand, this can prevent the agglomeration and other defects of the powder; on the other hand, it can achieve the purpose of separate deposition by virtue of the different particle size and speed of the powder, and can be used for the preparation of multilayer and gradient composite functional materials.

Electrophoretic deposition molding

Electrophoretic deposition molding uses a DC electric field to promote the migration of charged particles, and then deposits them on electrodes of opposite polarity to form.

Features: Simple operation, flexibility and high reliability, so it is suitable for the molding methods of multilayer ceramic capacitors, sensors, and gradient functional ceramics, but it is more sensitive to the influence of process parameter changes.

Gel injection molding

Injection molding involves adding a vinyl organic monomer in a suspension medium, and then using a catalyst and an initiator to crosslink the organic monomer through a free radical reaction, and the body is cured in situ. Gel injection molding technology is a new colloidal rapid prototyping technology first invented by researchers at Oak Ridge National Laboratory in the United States in the early 1990s.

Advantages: The body has high strength and is easy to machine.

Disadvantages: The shrinkage of the green body is relatively large during the densification process, which causes the green body to bend and deform. The organic monomer used is toxic and the reaction atmosphere is not easy to control.

Casting

Casting refers to a method of adding a solvent, a dispersant, a binder, a plasticizer and other components to a ceramic powder to obtain a uniformly dispersed and stable slurry, and obtaining a film of a desired thickness on a casting machine.

Advantages: simple equipment, continuous operation, high production efficiency, high level of automation, stable process, and uniform body performance.

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16 molding methods for advanced ceramics (2)

Extrusion

The powder, adhesive, lubricant and water are evenly mixed, and then the piston is pushed by a hydraulic press to squeeze the plasticized blank from the extrusion nozzle. As the inner shape of the extrusion nozzle gradually shrinks, the piston produces a large squeezing force on the mud mass, which makes the blank compact and shaped.

Advantages: The ceramic membrane tube obtained by extrusion has a large porosity, density and compressive strength, and the pore size distribution is concentrated, and the gas permeation flux is large. This method is suitable for manufacturing pipes or rods with round, elliptical, polygonal and other special fracture surfaces. Disadvantages: The material is low in strength and easily deformed, and may cause defects such as surface pits and blistering, cracking and internal cracks.

Injection molding

Injection molding is also called hot die casting.This technology adds metal powder, ceramic powder and polymer with similar fluidity by adding a certain amount of polymer and additive components and slightly heating. After cooling, it is descaled to obtain a blank. It is listed as an important “national key technology” by the United States and other developed countries.

Advantages: high utilization rate of raw materials, can be quickly and automatically mass-produced; special-shaped parts with small volume, complex shape and high dimensional accuracy can be prepared; due to the flow die, the density of the green body is uniform, the performance of the sintered product is superior; and the production cost is low.

Calendering

The powder material, additives and water are evenly mixed to make a plastic material, and then the material is rolled by two opposite rotating rolls, so as to form a plate-shaped plain blank. The density of the green body obtained by calendering forming is high, which is suitable for forming sheet and plate-shaped parts.

Grouting

The prepared mud is injected into the gypsum model, and the water in the mud will be gradually sucked into the model wall, and the fine particles in the mud will be evenly arranged into a thick mud layer with the shape of the model; when the expectations are reached, the excess mud in the model can be poured out.

Advantages: low process cost, simple process, easy to operate and control.

Disadvantages: rough forming shape, longer grouting time, and low body density and strength.

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16 molding methods for advanced ceramics (1)

Dry pressing

Dry pressing molding is to add a certain amount of organic additives (binders, lubricants, plasticizers, defoamers, water reducing agents, etc.) to the ceramic powder to form it in a mold under the effect of external pressure.

Advantages: It is easy to automate, so it is widely used in industrial production.

Disadvantages: During the forming process, the delamination of the green body is often caused by uneven pressure distribution in the radial and axial directions, and cracks and uneven density often occur.

Isostatic pressing

Isostatic pressing is a method in which the powder is molded while being compressed by applying isotropic pressure. According to different molding temperatures, isostatic pressing is divided into hot isostatic pressing and cold isostatic pressing. Cold isostatic pressing is an isostatic pressing method that forms a workpiece at room temperature. Hot isostatic pressing refers to an isostatic pressing method in which a workpiece is pressure-molded and sintered at high temperature and pressure.

Advantages: It can suppress parts with concave, hollow, slender and other complicated shapes; small friction loss, low molding pressure; pressure transmitted from all aspects, uniform compaction density distribution, high compaction strength, convenient mold making, and long life Long and low cost.

Disadvantages: The size and shape of the compact are not easy to accurately control, the productivity is low, the investment is large, the operation is complicated, the molding is operated under high pressure, and the container and other high-pressure parts need special protection.

Ultra-high pressure (UHP) molding

Ultrahigh pressure molding is a rapidly developing molding method, which is mostly used in the molding of nano-ceramics. The particle size of nanoceramics is greatly affected by the sintering temperature. The lower the sintering temperature and the smaller the particle size, the easier it is to obtain nanoceramics. By increasing the molding pressure and increasing the initial density of the green body, the sintering temperature of the nanoceramics can be reduced. Ultra-high pressure forming significantly changes the sintering properties of the green body, thereby making it easier to obtain nano-ceramics.

Powder electromagnetic forming

Powder electromagnetic pressing is a new high-efficiency molding process that uses strong pulsed electromagnetic force to act on the powder body to make it dense. This method is usually used for the molding of metal materials, and can obtain very high density. The density of the samples formed by the powder electromagnetic pressing method all reached more than 95%, and they have good piezoelectric and dielectric properties.

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Method for Preparing Silicon Carbide Powder

With the development of science and technology, modern defense, space technology and automobile industries not only require engineering materials to have good mechanical properties, but also require good physical properties. Silicon carbide (SiC) ceramics have the advantages of high-temperature strength and oxidation resistance, high wear resistance and thermal stability, small thermal expansion coefficient, high thermal conductivity and good chemical stability. It is, therefore, a widely applicated advanced engineering material, often used in the manufacture of combustion chambers, high-temperature exhaust devices, temperature-resistant patches, aircraft engine components, chemical reaction vessels, heat exchanger tubes and other mechanical components under severe conditions. It not only plays an important role in the high-tech fields being developed (such as ceramic engines, spacecraft, etc.), but also has a broad market and application fields to be developed in the fields of energy, metallurgy, machinery, building materials and chemicals.

For this reason, it is urgent to produce various silicon carbide products of different levels and different properties. However, the strong covalent bond of silicon carbide results in a high melting point, which makes it more difficult to prepare and densify the silicon carbide powder. At present, the preparation techniques of silicon carbide powder can be mainly divided into three categories: solid phase method, liquid phase method and gas phase method.

Solid phase method

The solid phase method is divided into a carbothermal reduction method and a silicon carbon direct reaction method. The carbothermal reduction method includes the Acheson method, the vertical furnace method, and the high temperature converter method. Among them, the Acheson method developed earlier, and its shortcoming is that the obtained powder has a large particle size (>1 mm), and the energy consumption is large and the process is complicated. 8In the 1980s, new equipment for synthesizing β-SiC powder such as vertical furnace and high temperature converter appeared. As the chemical substances in microwaves and solids are effective and the special polymerization is gradually being clarified, the technology of microwave heating synthesis of SiC powder is becoming more and more mature. The silicon-carbon direct reaction method includes self-propagating high-temperature synthesis (SHS) and mechanical alloying. Among them, the SHS reduction synthesis method utilizes an exothermic reaction between SiO2 and Mg to compensate for the lack of heat. The SiC powder obtained by the method has high purity and small particle size, but requires subsequent steps such as pickling to remove Mg from the product.

Liquid phase method

The liquid phase method mainly includes a sol-gel method and a polymer thermal decomposition method. The sol-gel method utilizes Si-containing and C-containing organic polymer materials to obtain a gel containing uniformly mixed Si and C by a suitable sol-gelation process, followed by pyrolysis and high-temperature carbothermal reduction to obtain silicon carbide. Pyrolysis of organic polymers is also an effective technique for the preparation of silicon carbide: One type is to heat the gel polysiloxane, which decomposes to release small monomers, finally forms SiO2 and C, and then carbon reduction reaction to obtain SiC powder; the other is to heat the polysilane or polycarbosilane to release the small monomer to form a skeleton, which finally forms SiC powder.

Gas phase method

Gas phase synthesis of silicon carbide ceramic ultrafine powder is currently mainly used in gas phase reactive deposition (CVD), plasma (Plasma Induced CVD), laser induced gas phase (Laser Induced CVD) and other technologies. These types of methods all decompose organic matter by high temperature, and the obtained powder has high purity, small particle size, less particle agglomeration, and easy control of components, but they are high in cost and low in yield, and are difficult to achieve mass production. The gas phase method is more suitable for the preparation of laboratory materials and products for special requirements.

The currently used SiC ceramic powders are mainly submicron or even nanometer grade powders, and their powders have small particle size and high surface activity. The main problem currently faced is that the powder is prone to agglomeration, and it is necessary to modify the surface of the powder to prevent or inhibit the secondary aggregation of the powder. At present, the methods for dispersing SiC powder mainly include the following types: high energy surface modification, washing, dispersant treatment powder, inorganic coating modification, and organic coating modification.

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Detailed Introduction to Boron Nitride Structure

Boron nitride is a compound of boron and nitrogen with the chemical formula BN. It forms cubic and hexagonal structures which correspond to carbon in the form of diamond and graphite respectively. Because of their excellent thermal stability, thermal shock stability and chemical stability, boron nitride ceramics are often used as parts of high-temperature equipment (a typical melting range is 2700-3000oC). They are stable in air to ~1000℃ whereas carbon-graphite based materials would have long since ignited! This article detailed introduces two kinds of boron nitride structures.

Cubic Boron Nitride

In the cubic form of boron nitride ceramic, boron and nitrogen atoms are alternately linked to form a tetrahedral bond network, exactly like carbon atoms do in diamond. So it is a 3D giant covalent lattice. The B-N-B or N-B-N bond angle is 109°. Nitrogen’s lone pair of electrons can accepted by boron to give the tetrahedral bond network shown in the diagram. Cubic boron nitride ceramic is the second hardest material only to diamond. It has extremely high hardness and can even scratch diamond. CBN has very high thermal conductivity, excellent wear resistance and good chemical inertness, making it a perfect material used in extreme conditions. Because of its hardness, chemical inertness, high melting temperature (2973℃), cBN is used as cutting tools and abrasive components for shaping/polishing with low carbon ferrous metals. BN based tools behave in a similar way to diamond tools but can be used on iron and low carbon alloys without risk of reaction because CBN is chemically inert. CBN doesn’t lose its cutting properties until 1100-1200℃.

Hexagonal Boron Nitride

Hexagonal boron nitride is a white slippery solid with a layered structure, physically similar to graphite as a 2D planar giant covalent network. HBN has good thermal and electrical properties and is chemically inert. It melts under pressure at ~3000℃ testament to its great thermal stability.

In the hexagonal form of boron nitride, boron and nitrogen atoms are alternately linked to form interlocking hexagonal rings, just like the carbon atoms in graphite do. The B-N-B or N-B-N bond angle is 120°. The B-N bonding in the 2D layers is very strong, but the layers are held together by weak intermolecular forces (Van der Waal forces, instantaneous dipole – induced dipole forces) and the layers are 0.334 nm apart. HBN can be used as a lubricant, and can have semiconductor properties after doping. Hexagonal boron nitride can be incorporated in ceramics, alloys, resins, plastics, rubbers to give them self-lubricating properties.

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