Silicon carbide (SiC) is a widely used high temperature material in the metallurgical and chemical industry. It boasts numerous properties that make it ideal for refractories and high temperature structural applications.
Nitride bonded silicon carbide is a widely used refractory material in the metallurgical and chemical industries due to its superior strength at elevated temperatures, remarkable erosion- and corrosion-resistance, as well as excellent thermal shock resistance.
Hardness
Nitride bonded silicon carbide is an advanced refractory ceramic with remarkable wear and abrasion resistance, exceptional thermal shock resistance, as well as excellent refractory and chemical properties. Generally composed of 20-30% Si3N4 and 70-80% SiC, NBSC exhibits remarkable wear- and abrasion resistance in demanding applications.
This material is available in a range of standard sizes and geometries, but can also be customized to meet individual requirements. It has applications such as waste to energy, kiln furniture and metal melting.
NBSC, with a Mohs hardness of 9 times that of diamond, can withstand temperatures ranging from 1200 – 1600 degrees C depending on its composition and grain size. Furthermore, this material exhibits excellent resistance to oxidation at elevated temperatures as well as excellent fracture toughness when exposed to extremes in temperature.
However, NBSC lacks the mechanical strength of dense silicon carbide ceramics and can only transmit compressive loads. Therefore, NBSC should not be used for components that must be capable of bending and stretching.
Other than NBSC, other types of refractory ceramic materials include recrystallized silicon carbide (RSIC), silicate-bonded silicon carbide and non-oxide bonded silicon carbide. Reaction bonded silicon carbide is produced by heating coarse-grained powdered SiC to temperatures above 1,200 deg C before bonding it with 5-15% aluminosilicate binder.
This method creates a relatively coarse material with low production costs and higher hardness than direct sintered or chemical vapour deposition (CVD) silicon carbide. It can be used in applications requiring high temperatures, making it an ideal choice for refractory bricks and plates.
Plate stackers often utilize this material due to its exceptional strength at room temperature and toughness when exposed to extreme temperatures. This is due to the sintered process which transforms fine and coarse grains into a compact SiC matrix without shrinkage.
NBSC exhibits an incredible modulus of rupture at 1350 degrees Celsius, making it suitable for many applications that need the ability to withstand extreme temperatures. Furthermore, NBSC can be molded into intricate shapes using the Blasch process.
Wear Resistance
Silicon carbide is one of the toughest ceramics and often used for seal faces and pump parts due to its superior wear resistance, high temperature strength, corrosion resistance and thermal shock resistance. Plus it can be fabricated into various shapes for optimal performance.
Crystalline silica has a close-packed structure covalently bonded between silicon and carbon atoms. This chemically stable material is resistant to most organic and inorganic acids, alkalis and salts at various concentrations. Furthermore, its high abrasion resistance makes it popular in metalworking, machining, chemical processing, mining and other industries requiring abrasive resistance.
Nitride bonded silicon carbide is a composite refractory ceramic material created by firing high-purity silicon carbide with silicon or mineral additives in a nitrogen atmosphere. NBSC exhibits superior refractory and chemical characteristics, is resistant to wetting by nonferrous metals, has excellent thermal shock resistance, and can be fired up to 1650 degC depending on its composition.
NBSC can be produced in a range of standard and custom forms, such as shaped, cast or forgings. It finds applications in mining, petrochemical processing and red metal extraction as well as monolithic cyclone liners.
The wear resistance of nitride-bonded silicon carbide depends on both the soil conditions being worked and its grain size distribution. Heavy soils tend to have less effective wear resistance since many top layer components of the surface are removed during abrasion; on the other hand, light soils typically experience improved protection due to smaller abrasive particles that won’t penetrate too deeply into the top layer of soil.
In all soil types tested, nitride-bonded silicon carbide proved more resistant to wear than steels such as boron steel and F-61 padding weld, including the steels under study. This suggests that nitride-bonded silicon carbide may serve as an effective replacement for steels resistant to abrasion.
Thermal Shock Resistance
Nitride bonded silicon carbide is an advanced refractory material with exceptional thermal shock resistance. This makes it suitable for applications requiring extreme temperatures, high stress levels and abrasion resistance as well as other harsh operating conditions.
This refractory material is typically composed of high purity silicon carbide and nitride additives. When fired, the nitride bonds to the silicon carbide, creating a strong bond between them. It finds applications in various industries such as mining and industry.
Microelectronics uses passivation layers to protect against water and sodium ions, which is essential for many processes like xerographic film printing and semiconductor manufacturing.
One of the remarkable properties of nitride-bonded silicon carbide is its resistance to thermal shock. Thermal shock occurs when an object experiences an abrupt change in temperature, leading to expansion or contraction in different directions – something which would usually crack brittle materials such as granite. Not so with silicon carbide though!
NB SiC’s nitride coating protects it against thermal shock due to extreme temperature changes, while still offering good thermal conductivity and mechanical strength. This makes the material ideal for applications requiring high thermal conductivity such as thermocouple protection tubes.
Nitride bonded silicon carbide can also be employed as a refractory in kilns due to its remarkable temperature resistance – up to 1,500 degrees C! Furthermore, this material boasts excellent oxidation resistance.
As such, nitride bonded silicon refractories are often preferred over traditional fire clay products in applications with extreme temperatures or harsh corrosives or erosives. This is because nitride bonded silicon carbide resists thermal shock much better than fire clay does.
Nitride bonded silicon carbide has an exceptionally high refractoriness compared to common refractory materials like glass or porcelain, making it ideal for furnaces where temperature fluctuations are large or where mechanical strength must be maintained at elevated temperatures.
Chemical Resistance
Nitride bonded silicon carbide has superior chemical resistance, making it the perfect material for refractory application. It can be used in process furnaces and kilns as well as cast components requiring high corrosion and oxidation resistance. Furthermore, NBSC boasts excellent thermal shock resistance and can be designed into complex shapes.
Different nitride-bonded silicon carbide compositions are available for use in various applications. Many of these compositions have been specifically engineered for maximum strength and corrosion resistance, with some even featuring double firing processes which reduce open porosity and enhance oxidation resistance.
These compositions can be manufactured into intricate shapes that cannot be achieved with other mixtures. Due to their low density and ease of workability, these compounds have a long service life and are durable enough for various applications such as mining, petrochemical, red metal production, monolithic cyclone liners and more.
NBSC is created by firing a mixture of high-purity silicon carbide and other additives in a nitrogen atmosphere. As such, it boasts superior wear resistance, thermal shock resistance, and corrosion resistance.
Nitride bonded silicon carbide is ideal for thermocouple protection tubes, particularly in oxygen atmosphere furnaces where they may come into direct flame impingement. Furthermore, this resistant material to wetting by nonferrous metals makes it suitable for insulators and valves as well.
This material has a maximum service temperature of 2730 deg F and an oxygen atmosphere furnace porosity of 14%, making it suitable for many industrial applications due to its excellent thermal conductivity. Furthermore, the primary tube should be gas tight to avoid oxidation damage.
Studies conducted to understand the oxidation kinetics of nitride bonded silicon carbide have revealed that when uncoated, untreated nitride bonded silicon carbide showed internal oxidation and parabolic growth rates; on the other hand, coated nitride bonded silicon carbide showed significant protection from oxygen oxidation.
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