Advanced Ceramic Materials

Application Prospects of Silicon Carbide in Automotive Industry

With the booming of modern industries, global energy consumption has increased year by year. Nowadays, motor vehicle pollution has become an important source of air pollution and an important cause of ash and photochemical smog pollution. The urgency of motor vehicle pollution prevention and control has become increasingly prominent, and energy conservation and emission reduction has become a major issue in the development of the automotive industry. Therefore, vigorously developing new energy vehicles is a strategic measure to achieve energy conservation and emission reduction and promote the sustainable development of the automotive industry.

At present, the electric drive parts of EV (Electric Vehicle) and HEV (Hybrid Electric Vehicle) are mainly composed of silicon (Si) based power devices. With the development of electric vehicles, higher requirements have been placed on the miniaturization and weight reduction of electric drives. However, due to material limitations, traditional Si-based power devices have approached or even reached the intrinsic limits of their materials in many respects. Therefore, various automotive manufacturers have high hopes for a new generation of silicon carbide (SiC) power devices.

Third-generation semiconductors, represented by silicon carbide, have significant advantages over traditional semiconductor materials such as monocrystalline silicon and gallium arsenide, such as high thermal conductivity, high breakdown field strength, high saturation electron drift rate, and high bonding energy, high chemical stability, strong radiation resistance, etc. These advantages determine that silicon carbide has an irreplaceable position in many fields. The advantages of SiC are mainly as follows:

(1) SiC has a high thermal conductivity (up to 4.9 W/cm•K), which is 3.3 times that of Si. Therefore, the SiC material has a good heat dissipation effect. In theory, SiC power devices can operate at temperatures of 175 ° C, making them suitable for high temperature devices.

(2) SiC has a high breakdown field strength, which is 10 times that of Si, and is therefore suitable for making high-production, high-power, high-current devices.

(3) SiC has a high saturation electron drift rate, which is twice that of Si. Its high field processing capability is strong, so SiC materials are suitable for high frequency devices.

In summary, the potential of silicon carbide devices in automotive industry is enormous. SiC devices can significantly reduce the size, weight and cost of power systems while increasing power density and system efficiency. This makes it an ideal device for EV and HEV electric drives and will revolutionize the electric drive system of electric vehicles.

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Common Materials for Ceramic Grinding Balls

The grinding ball is generally made of bauxite, roller powder, industrial alumina powder, high-temperature calcined alpha alumina powder after batching, grinding, milling (pulping, mud making), forming, drying, firing and other processes.

Ceramic grinding balls have the advantages of high mechanical strength, good wear resistance, environmental protection, and low price, so many ceramic materials are used to make grinding balls. This article focuses on common materials for ceramic grinding balls.

Silicon carbide grinding ball

Silicon carbide has stable chemical properties, high thermal conductivity, small thermal expansion coefficient and good wear resistance. It has been an important material for sandpapers, grinding wheels, and cutting tools. Silicon carbide grinding ball is used for milling same materials (silicon carbide ball to mill silicon carbide materials) to avoid contamination. They are available in 5mm, 10mm, 12mm, 15mm and 20mm sizes. Also, customized size is available.

Zirconia grinding ball

In the building materials, electronics, paint and other industries, zirconia grinding balls are used more and more widely. The zirconia grinding balls have high density (theoretical density value of 6.1 g/cm3), high toughness and high hardness (HRA of 90 or more). It has high grinding efficiency, less wear and less impurities in the production, showing more superior performance.

The coprecipitation method is a common method capable of producing zirconia powder (partially stable). The advantage of this method is that the raw material has high purity and high activity, and the obtained zirconia grinding ball has excellent performance and stable quality.

Yttria Stabilized Zirconia Grinding Ball

Alumina grinding ball

Alumina ceramic balls are an important engineering ceramic and are high-tech products. Alumina ceramic balls are widely used in white cement, minerals, ceramics, electronic materials, magnetic materials due to their suitable hardness, moderate density, wear resistance, corrosion resistance, low price, and the introduction of metal ball metal impurities. And the grinding and processing of raw materials in the paint, paint and other industries is a high-quality grinding media.

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Silicon Carbide, Good Refractory Materials

The silicon carbide refractory material is a material produced by using different binders as the main raw material of silicon carbide sand. Its thermal conductivity is high, about 10 to 14 times that of clay products; it has low expansion coefficient, good thermal stability, high temperature withstand voltage, high flexural strength and stable chemical properties. Coupled with the continuous improvement of adhesives in recent years, silicon carbide plates are now able to overcome their vulnerability to oxidation and alkali corrosion. Therefore, silicon carbide products are not only the necessary refractory materials for vertical tank zinc smelting, but also widely used in industrial furnaces such as iron and steel metallurgy, chemical industry, ceramics, as well as anti-corrosion wear-resistant pumps and pipeline linings.

Classification of Silicon Carbide

Industrial silicon carbide typically contains about 2% impurities (mainly silica, silicon, iron, aluminum, calcium, magnesium and carbon). According to the color and main use of silicon carbide, the classification of silicon carbide is as follows:

1 black silicon carbide, code TH, mainly used for making abrasive materials and refractory materials;

2 Green silicon carbide, code TL, can be used to make abrasive materials and refractory materials, and can also be used to manufacture resistive components (such as silicon carbon rods);

3 Bauxite silicon carbide is used in the manufacture of thermistors and arresters.

Production of Silicon Carbide and Its Products

Silicon carbide sand is made by using silica and carbonaceous raw materials in an electric furnace at high temperature, while silicon carbide products are made of silicon carbide sand as aggregate and oxide, silicate or silicon powder as high temperature bonding materials. It is formed and fired. When refining silicon carbide sand in an electric furnace, if petroleum coke and quartz sand are used as main raw materials, black silicon carbide sand is obtained; if an appropriate amount of salt is added during the compounding, green silicon carbide sand can be produced; if an appropriate amount of bauxite is blended, bauxite silicon carbide sand can be obtained.

Silicon Carbide Ceramic

Silicon carbide is a compound with strong covalent bond, and its Si-C bond has an ionic form of only about 12%. Therefore, it also has excellent mechanical properties, excellent oxidation resistance, high abrasion resistance and low friction coefficient. The biggest characteristic of SiC ceramics is high temperature strength. The strength of ordinary ceramic materials will be significantly reduced at 1200~1400 °C, but the flexural strength of silicon carbide at 1400 °C remains at a high level of 500~600MPa, so its working temperature can reach 1600~1700 °C. In addition, the thermal conductivity of silicon carbide ceramics is also higher (below ceramics in ceramics), so ceramic materials such as silicon carbide sheets have been widely used in high temperature bearings, bulletproof plates, nozzles, high temperature corrosion resistant parts, and high temperature and In the high-frequency range of electronic equipment parts and other fields.

A rare earth oxide such as Y2O3 can also be used as a sintering aid for silicon carbide ceramics to obtain dense silicon carbide by liquid phase sintering. Since the liquid phase sintering is to reduce the porosity and increase the density by the formation of the glass phase, the characteristics of the glass phase have a great influence on the microstructure obtained by sintering.

Application

The special properties of silicon carbide refractories determine that it can be used in different conditions and in different industrial fields. Due to its high thermal conductivity, silicon carbide refractories are widely used in the manufacture of muffle furnaces, heated hearths and heat exchangers, crucibles, carburizing tanks, thermowells, closed-end temperature measuring tubes and large bricks.

Silicon carbide products are also used in many non-direct heating furnace structures, such as zinc distillation columns, vertical and horizontal distillation tanks. In a wide temperature range, silicon carbide refractories are straightforward in mechanical strength and wear resistance, so they can be used to make mechanically wear-resistant parts, such as guide rails and tie rods for low temperatures, and highly abrasive rotating points. Inner lining of filters, dust collectors, pipes, chutes, furnace bottoms, lattice plates for tunnel kiln cars, porous products for filter gas, etc.

The special chemical properties of silicon carbide refractories make it very effective in various furnaces and plants in the non-ferrous metallurgical and chemical industries. Silicon carbide refractories are also used in steam boilers. In the industry, the use of silicon carbide refractories is far from enough. The scale of production of such refractories has increased in recent years, and the widespread use in the industry, particularly in the ceramics industry, non-ferrous and ferrous metallurgy, offers the possibility.

Three Silicon Carbide Powder Manufacturing Methods

Silicon carbide, chemical formula is SiC, belonging to the covalent bond material, C and Si belong to the same family, all have tetravalent bond, while Si also has metal characteristics, two elements composed of materials, the structure has The mesh shape and body shape have high strength in nature, so the properties of silicon carbide material are good high temperature strength, wear resistance, corrosion resistance, high thermal conductivity and high insulation.

The structure determines the performance. The higher the performance,the finer the microstructure of the silicon carbide material is required. Therefore, the preparation method becomes the key to the acquisition of high-performance silicon carbide powder.

Carbothermal Reduction

The method was invented by Acheson. The specific method: in the Acheson electric furnace, the silicon dioxide in the quartz sand is reduced by carbon to obtain silicon carbide. The silicon carbide particles obtained by the method are coarser and consume a large amount of electricity, and the reaction equation is:

SiO₂+3C=SiC+2CO

Subsequently, the Acheson method was improved in various countries, such as using carbon black and water glass solution as raw materials, hydrogen as shielding gas, and reacting in a high temperature graphite furnace at 1550 ° C for 5 hours to obtain silicon carbide powder.

Self-propagating High Temperature Synthesis (SHS)

This method ignites the reactant body by an external heating source, and uses the chemical reaction heat released by the material during the synthesis process to maintain the synthesis process.

SiO₂+C+2M_g-SiC+2M_gO

The powder obtained by this method has high purity and small particle size, but requires a step such as pickling to remove Mg.

Mechanical Alloying

The carbon powder and the silicon powder were mixed into a powder according to a molar ratio of 1:1, and the grinding balls and the milling powder were packaged in an argon gas tank at a mass ratio of 40:1, and subjected to mechanical ball milling on a ball mill for 25 hours to obtain the silicon carbide powder with an average crystal grain of about 6 nm.

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Preparation of Hexagonal Boron Nitride Powder by Chemical Vapor Deposition (CVD)

Advanced Ceramic Materials (ACM) is an experienced boron nitride powder supplier. Our company always adheres to the principle of “Quality First” and everything is for the sake of users. We will continue to work hard, develop continuously, and strive to produce high-quality products, so that our products will eventually occupy the entire domestic market.

Hexagonal boron nitride powder is also known as white graphite because its various properties are similar to those of graphite.

Characteristics of boron nitride powder

• High activity and less impurities

• Product quality is stable

• Good electrical insulation

• Low dielectric constant and dielectric loss

• High temperature stability

• Good conductor of heat

• Good lubrication performance

• Chemically inert substances

• Does not wet the metal

Typical application of boron nitride products

• Solid lubricants in high temperature environments

• Cleavage agent in casting and injection molding

• Raw materials for the production of cubic boron nitride

• Used to prepare composite ceramics, such as evaporation boats for vacuum aluminum plating, etc.

• For cosmetics

• For electrical insulation

• For electrical instrument coating

Preparation of boron nitride powder

The preparation of h-BN powder by CVD usually employs a hot wall reactor. A gaseous substance containing B and N is charged into the reaction chamber through a carrier gas. A chemical reaction takes place between gaseous substances to produce boron nitride powder at high temperatures. Among them, the boron source generally uses B(OCH3)3, BF3, B2H6, BBr3 and BCl3 containing a boron compound, and the nitrogen source is generally N2 or NH3. Using ammonia water and trihydroxyborate as raw materials, hexagonal boron nitride nanoparticles were prepared by chemical vapor deposition at 1350 ° C. The selection of suitable raw materials can reduce the reaction temperature. Boron nitride nanospheres containing oxygen impurities were synthesized at 700 ° C using ethyl borate and ammonia as raw materials. Then, ammonia is removed by ammoniation at 1000 ° C in an ammonia gas atmosphere, and hexagonal boron nitride nanospheres having a particle diameter of 80 to 120 nm can be obtained.

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15 Applications for Silicon Carbide Powder (With Pictures)

Silicon carbide powder has high temperature strength, wear resistance,corrosion resistance, high thermal conductivity, high insulation and other properties. The application direction of silicon carbide powdermainly has the following categories:

1. Abrasive

Silicon carbide powder is often used in the manufacture of abrasive-abrasives due to its high temperature resistance and wear resistance. Artistically, silicon carbide is a popular abrasive for modern gemstones due to its low durability and low material cost. In the manufacturing industry, it is used for hardness during abrasive processing such as grinding, honing, water jet cutting and sand blasting. Silicon carbide particle composite paper can be used to make the grip of sandpaper and skateboard.

2. Structural materials

In high temperature furnaces, silicon carbide is used as a support and shelf material, such as fired ceramics, glass fused or glass cast. Silicon carbide can be used to produce a new strong plastic alloy for aerospace, automotive and microelectronics.

3. Auto parts

Silicon infiltrated carbon-carbon composites are used in high performance “ceramic” brake discs because they can withstand extreme temperatures. Silicon carbide is also used to make sintered diesel particulate filters. SiC is also used as a lubricant additive to reduce friction and exhaust emissions.

4. Casting crucible

Silicon carbide crucibles have high temperature resistance and can be used for molten metals.

5. Electrical system

The earliest application of silicon carbide in electrical systems is the arrester. Silicon carbide has a voltage-dependent resistance, so a column of silicon carbide particles is connected between the high-voltage power line and the earth.

6. Electronic circuit components

Silicon carbide is the first commercially important semiconductor material. The crystal radio “Corundum” (synthetic silicon carbide) detector diode was invented in 1906.

7. Power electronics

SiC chips have higher power densities than silicon power devices and can handle temperatures in excess of 150 °C.

8. Light-emitting diode

SiC is an important LED component – it is a popular substrate and it can also be used as a heat sink for high power LEDs.

SiC is an important LED component – it is a popular substrate and it can also be used as a heat sink for high power LEDs.

9. Astronomy

With its low coefficient of thermal expansion, high hardness, high rigidity and thermal conductivity, silicon carbide is an ideal mirror material for astronomical telescopes.

10. Filament pyrometer

Silicon carbide fibers are used to measure the temperature of a gas in an optical technique called a filament pyrometer. It consists of placing filaments in a hot gas stream.

11. Heating element

Silicon carbide can be used as a heating element for glass, ceramics, electronic components, etc., such as an indicator igniter for producing gas heaters.

12. Jewelry

As a gemstone jewelry, silicon carbide is called “synthetic carbon silica”.

13. Steel production

Silicon carbide is dissolved in the basic oxygen furnace for steelmaking and acts as a fuel.

14. Catalyst carrier

The natural oxidation resistance exhibited by silicon carbide and the new new method of synthesizing cubic β-silicon carbide form have a large specific surface area, which has caused great interest in heterogeneous catalyst carriers.

15. Graphene production

Silicon carbide is used to graphitize graphene at high temperatures. This is considered to be a method for large-scale synthesis of graphene in practical applications.

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Detailed Introduction and Application Fields of Ceramic Tubes

The ceramic tube is a new type of material which is formed by sintering and sintering zirconia and alumina ceramic materials. The ceramic tube is formed by isostatic pressing, hot pressing, dry pressing and other processes, and then waxed or degreased and then sintered at a high temperature. Ceramic tubes are used in aerospace, medical equipment, military machinery and other fields.

Ceramic Tube Material Classification

Zirconia Tube

The zirconia ceramic tube is a new type of industrial ceramic material made of highly refined, high-purity, ultra-fine, non-polar compound. Compared with traditional ceramics, it has a wider range of applications and is more durable and suitable for industrial use. The zirconia tube has good high temperature strength, high breaking strength, high hardness and good thermal shock resistance.

Zirconia tube technical parameters:

Density ≈6g/cm3,

Hardness ≈ 13.2GPa,

Flexural strength ≈1000MPa,

The modulus of elasticity is 200Gpa,

The thermal conductivity is 2.6W/(m/K),

The coefficient of thermal expansion is 11×10-6/°C,

The maximum operating temperature is 2400 ° C.

Alumina Tube

Alumina ceramic tubes are a non-metallic material. Alumina ceramics are classified into 75, 85, 90, 92, 95, 97, 99 according to the content of aluminum. If the content is greater than 90, it is called high alumina ceramic, otherwise it is called ordinary alumina ceramic; if it is greater than 99, it is called super high alumina ceramic composite. Alumina ceramic tubes have the advantages of high temperature resistance and low transportation cost. The disadvantages are poor toughness and easy fracture.

Zirconia Toughened Alumina Tube

Zirconium oxide toughened alumina tube (ZTA tube) has mechanical strength and wear resistance and can be used as an ideal material between zirconia and alumina. It was established that ZTA ceramic tube is stronger and tougher than regular alumina ceramics.

Ceramic Tube Application Field

Ceramic tubes are widely used in instrumentation, medical equipment, watches, abrasive tools, energy and power, construction, mechanical hardware, automotive, military, aerospace and other fields.

Ceramic Tube Color

The common color of ceramic tubes is white, also known as ivory. White tubes are also the most widely used of all ceramic rods. Of course, there are other colors of ceramic tubes, such as blue, black, gray ceramic rods, yellow, etc. The density and hardness of ceramic rods of different colors are different.

Ceramic Tube Forming Process

Isostatic Molding

Process: fill the powder into the rubber mold→ isostatic pressing → sintering → grinding and polishing

Advantages: high density, good quality, high volume molding

Disadvantages: high cost, unable to make special shapes

Injection Molding

Process: purchase airflow powder → with chemical components → stir evenly → dry → break → injection molding

→ Discharge → Sintering → Post-processing

Advantages: special ceramic materials with special shapes and small sizes can be made, which can be mass-produced;

Disadvantages: Can not make products with large size

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Lanthanum Hexaboride Cathodes From Different Manufacturers

Lanthanum hexaboride (LaB6) single crystal is a special structure crystal, which has good conductivity and low work function. When working at 1400~1680 °C, it can obtain DC emission current of 0-100A/cm2, far better than oxide and other pure metal cathodes.

The cathode characteristics of lanthanum hexaboride are as follows:

– Extended Life – Thousands of Hours in Clean Vacuum. Guaranteed Life (Measured in Surface Loss). Guaranteed Against Mounting Structure Failure.

– Exceptional Stability – Thermal/Chemical/Electrical. Precision Machined Carbon Mounting. High over-temperature Tolerance.

– High Brightness/Low Energy Spread – Oriented Single Crystal. Best-Quality/High-Purity Material.

– Accurate Microflats – Superior Optics/Controlled Source Size Standard Diameter Available.

The applications of lanthanum hexaboride are as follows:

-Thermionic emission (cathode)
-Plasma source for plasma enhanced coating(PECVD)
-Vacuum electron beam welding machine
-Electron beam surface reforming device
-Electron beam lithography device
-Transmission electron microscope
-Scanning electron microscope
-Surface analysis device
-Radio therapy devices

The lanthanum hexaboride cathode processed by LaB6 single crystal is usually 90° or 60° vertebral body, and then divided into 15um, 6um, 20um plane according to the microfacet. The filament bases of common electronic mirrors of different manufacturers are as follows:

Base Type	Diameter of Ceramic disc in mm	Diameter of Pins in mm	Center Distance of Pins in mm
ACM	12.0	1.0	6.45
FEI/PHILIPS	26.0	1.0	5.0
JEOL K-type	28.0	1.2	8.0
HITACHI S-type	9.8	1.2	2.7
ZEISS (DSM & TEM) LEO (1450 & TEM) TESCAN	19.8	1.0	5.0
AMRAY (except 1200)	26.1	1.0	5.0
ISI/ABT/TOPCON 2 pins	23.3	1.2	11.9
ISI/ABT/TOPCON	23.4	1.2	12.0

Information is provided by Advanced Ceramic Materials (ACM) Corporation.

Silicon Carbide Plate Heating Principle

Silicon carbide products can be used in various industries. The characteristics of the silicon carbide plate are that it is outstanding in all aspects, with good wear and tear resistance, good quality and strong bearing capacity. The industrial application of silicon carbide plate is very extensive and environmentally friendly. Today we will introduce the principle of silicon carbide heating and the industrial application of silicon carbide.

Silicon Carbide Plate – Heating Principle

The service life of silicon carbide plate is largely determined by the rationality of the silicon carbide production process. When making sanitary ceramics, high-voltage electromagnetic products, etc., the scaffolding on the kiln car needs to bear a large load. Therefore, the strength of silicon carbide products is of great significance.

It is preferable to use a dense silicon carbide material having high oxidation resistance depending on the thermal stress at the time of firing. According to relevant information, many industrial ceramics in the United States use silicon carbide materials as the main pillar and flat plate of the scaffold. The thickness of the silicon carbide plate used in the production is 25-30mm, which is quite good for baking.

Of course, the silicon carbide plate price will be more expensive than that of clay bricks, but from the economical point of view, silicon carbide has a longer service life. In the market, although the silicon carbide price is slightly higher than other high temperature resistant materials, according to the detailed understanding, silicon carbide materials have very unique properties, high temperature strength, high thermal stability of silicon carbide, and silicon carbide High conductivity, some good characteristics of silicon carbide, have a decisive effect on the extension of the life of silicon carbide board. Therefore, silicon carbide board has a long service life. The recycling of silicon carbide is quite feasible!

Silicon Carbide Plate – Features

1. Good oxidation resistance: It can be adapted to the oxidizing atmosphere of ceramic and the reducing atmosphere. In the case of normal operation and normal firing, the number of turnovers is used 500-1000 times or more.

2. The silicon carbide plate has high density and smooth surface, and does not fall into the slag when used.

3, High temperature compression and flexural strength: the slab can be used for a long time on one side, no need to turn over, no deformation.

4, Resistant to rapid cooling, good heat, not easy to crack when used.

5, the use of firing temperature range is wide: It is used in the range of 800 ° C to 1400 ° C.

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Introduction to the Properties of Boron Nitride Ceramics

Boron nitride ceramics (BN) is a new type of ceramic material with excellent performance and great development potential. It is generally believed that there are mainly five isomerides of boron nitride: hexagonal boron nitride (h-BN), wurtzite boron nitride (w-BN), three isomers of trigonal boron nitride (r-BN), cubic boron nitride (c-BN) and orthorhombic boron nitride (o-BN). The most common of these isomerides are h-BN and c-BN.

The crystal structure of BN and the B-N bond characteristics determine that BN has many excellent physical and chemical properties: low density, high temperature resistance, thermal shock resistance, oxidation resistance, high thermal conductivity, high electrical resistivity, high electric field breakdown strength, excellent room temperature and high temperature dielectric properties, chemical resistance, non-toxic white, self-lubricating, good processability, low density, high temperature oxidation resistance, high heat of vaporization and excellent lubrication properties. Boron nitride ceramics are widely used in high-tech fields such as machinery, metallurgy, electronics, space science, etc., and have a very broad application prospect.

Structural features of Boron Nitride

High covalent bond composition and strong chemical stability. Boron Nitride is composed of elements with similar electronegativity. According to the semi-empirical method of determining the type of chemical bond in the crystal by Pauling (Valence bond theory), the compound formed by the atom with large difference in electronegativity is basically an ionic crystal, and a compound composed of atoms having substantially the same electronegativity values is basically a covalent bond compound.

According to the relationship between the electronegativity difference ΔX of the compound and the ion binding condition, in several commonly used ceramic materials, the proportion of BN ion bond is the smallest and the covalent bond component is the highest. Covalently bonded crystals generally have the characteristics of stable structure and low reactivity, so boron nitride is a structurally stable high-quality ceramic material.

Common Boron Nitride Products

Boron Nitride Powder

Boron Nitride powders, also referred to as white graphite are non-abrasive, white powders with a hexagonal platy crystal structure similar to graphite, but with a much higher oxidation resistance at 800ºC. Boron Nitride ceramic powders have high thermal conductivity, low coefficient of friction, high dielectric constant and are chemically inert. Due to those unique properties Boron Nitride powders find use in a broad range of applications ranging from electronics, aerospace, oil and gas, ceramic manufacturing and cosmetics.

Boron Nitride Rod

Boron Nitride rod is used as a container for most molten metals like aluminum, iron, steel, silicon, tin germanium and copper due to its properties like corrosion resistance, electrical resistance and the fact that it can withstand temperatures of about 20000. It plays an important role in nanotechnology to produce nanotubes, which find applications in the aerospace industry. It is widely utilized in evaporator boats, nozzles for nonferrous metals, electric insulators in vacuum system, induction heating coil supports, crucibles and radar components and antenna windows and insulators for high temperature furnace.

Boron Nitride Nanotube

Boron nitride nanotubes (BNNTs) are a polymorph of boron nitride. They were predicted in 1994 and experimentally discovered in 1995. Structurally they are similar to carbon nanotubes, which are cylinders with sub-micrometer diameters and micrometer lengths, except that carbon atoms are alternately substituted by nitrogen and boron atoms. However, the properties of BN nanotubes are very different: whereas carbon nanotubes can be metallic or semiconducting depending on the rolling direction and radius, a BN nanotube is an electrical insulator with a bandgap of ~5.5 eV, basically independent of tube chirality and morphology.

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