Silicon Carbide Refractories
Introduction
Silicon Carbide Aggregate Refractories, (also be called silicon carbide Raw Material) are a refractory raw materials is made of SiC (Silicon Carbide). Silicon Carbide is also known as Carborundum, the silicon carbide content is from 72% to 99%. Generally, black silicon carbide (SiC content above 96%) is used as the raw material, and the binder is added (or no binder), and then it is prepared by batching, mixing, molding and firing. The main crystal phase is silicon carbide. Silicon carbide refractories are mainly divided into several types of clay bonding, Si3N4 bonding, Sialon bonding, β-SiC bonding, Si2ON2 bonding and recrystallization. It is stable to acidic slag and has good wear resistance, corrosion resistance, high temperature strength, good thermal shock stability, high thermal conductivity, and low thermal expansion coefficient. They are high-performance refractory materials.
The silicon carbide can be made into SIC Bricks. The main crystal phase is SiC. The silicon carbide brick is formed by matching the binding agent, mixing, molding and firing process. The moth hardness of silicon carbide brick is 9.5, between that of corundum and diamond.
The silicon carbide castables do not weaken on heating and display superior operational properties: the compressive strength is 40–80 MPa at sintering temperature 400°C and 50–85 MPa at 1300°C, the strain onset temperature under a load of 0.2 MPa is 1700–1510°C; thermal stability (1300°C - water) is better than 45 heating/cooling cycles (1300°C - water); no change in linear and volume dimensions was observed on heating. The newly-developed castables can find application in various sectors of industry, in particular, as the refractory material for the lining of Whiting furnaces and porcelain kilns.
In view of its high mechanical strength and abrasiveness over a wide temperature range, SiC is used extensively in the production of silicon carbide refractories.
Silicon carbide refractories have high physicomechanical properties and endurance, high mechanical strength, resistance to deformation at high temperature, and as a result of the absence of polymorphic transformations, it has a low linear thermal expansion coefficient (LTEC) and high thermal conductivity.
Silicon carbide refractories are mainly manufactured from granular semidry or plastic mixes by compaction, ramming, or stretching. In industry there is extensive use of silicon carbide based on silica, high-alumina, argillaceous and nitride binders.
Silicon carbide is a semiconductor, which can be doped n-type by nitrogen or phosphorus and p-type by beryllium, boron, aluminium, or gallium. Metallic conductivity has been achieved by heavy doping with boron, aluminium or nitrogen.
Superconductivity has been detected in 3C-SiC:Al, 3C-SiC:B and 6H-SiC:B at similar temperatures ~1.5 K. A crucial difference is however observed for the magnetic field behavior between aluminium and boron doping: 3C-SiC:Al is type-II. In contrast, 3C-SiC:B is type-I, as is 6H-SiC:B. Thus the superconducting properties seem to depend more on dopant (B vs. Al) than on polytype (3C- vs 6H-). In an attempt to explain this dependence, it was noted that B substitutes at C sites in SiC, but Al substitutes at Si sites. Therefore, Al and B "see" different environments, in both polytypes.
Alpha silicon carbide (α-SiC) is the most commonly encountered polymorph, and is formed at temperatures greater than 1700 °C and has a hexagonal crystal structure (similar to Wurtzite). The beta modification (β-SiC), with a zinc blende crystal structure (similar to diamond), is formed at temperatures below 1700 °C. Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for heterogeneous catalysts, owing to its higher surface area compared to the alpha form.
Properties of major SiC polytypes | |||
Polytype | 3C (β) | 4H | 6H (α) |
Crystal structure | Zinc blende (cubic) | Hexagonal | Hexagonal |
Space group | T2d-F43m | C46v-P63mc | C46v-P63mc |
Pearson symbol | cF8 | hP8 | hP12 |
Lattice constants (Å) | 4.3596 | 3.0730; 10.053 | 3.0810; 15.12 |
Density (g/cm3) | 3.21 | 3.21 | 3.21 |
Bandgap (eV) | 2.36 | 3.23 | 3.05 |
Bulk modulus (GPa) | 250 | 220 | 220 |
Thermal conductivity (W⋅m−1⋅K−1) @ 300 K (for temp. dependence) | 320 | 348 | 325 |
Pure SiC is colorless. The brown to black color of the industrial product results from iron impurities. The rainbow-like luster of the crystals is due to the thin-film interference of a passivation layer of silicon dioxide that forms on the surface.
The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for bearings and furnace parts. Silicon carbide does not melt but begins to sublimate near 2700 °C like graphite, having an appreciable vapor pressure near that temp. It is also highly inert chemically, partly due to the formation of a thin passivated layer of SiO2. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices. SiC also has a very low coefficient of thermal expansion (4.0 × 10−6/K) and experiences no phase transitions that would cause discontinuities in thermal expansion.
Properties
1.The more SiC content, the better the alkali resistance
2.Silicon carbide in silicon carbide castables is especially advantageous at high temperatures (1100℃).
3.Produce partial gaps around the SiC particles to improve the thermal shock resistance and strength of the refractory castable.
4.The important chemical properties of silicon carbide are oxidation resistance, corrosion resistance, and the first reaction. When heated to 1000℃, the surface of SiC is oxidized and a SiC 2 film is formed. This film hinders the diffusion of oxygen, delays the oxidation rate, protects the silicon carbide covered by the film, improves the service life of the silicon carbide material.
5.Because the substrate is SIC, silicon carbide is wear resistant, silicon carbide has high hardness.
6.Silicon carbide is widely used in abrasives, heating elements, structural ceramics and refractory materials due to its high hardness, electrical conductivity, high temperature resistance and high strength.
Chemical & Physical Index
Polytype | 3C (β) | 4H | 6H (α) |
Crystal structure | Zinc blende (cubic) | Hexagonal | Hexagonal |
Space group | T2d-F43m | C46v-P63mc | C46v-P63mc |
Pearson symbol | cF8 | hP8 | hP12 |
Lattice constants (Å) | 4.3596 | 3.0730; 10.053 | 3.0810; 15.12 |
Density (g/cm3) | 3.21 | 3.21 | 3.21 |
Bandgap (eV) | 2.36 | 3.23 | 3.05 |
Bulk modulus (GPa) | 250 | 220 | 220 |
Thermal conductivity (W⋅m−1⋅K−1) @ 300 K (see [36][37] for temp. dependence) | 320 | 348 | 325 |
Characteristics:
l Corrosion resistance
l Good wear resistance
l High thermal conductivity
l High temperature strength
l Good thermal shock resistance
l Low thermal expansion coefficient
l Strong corrosion resistance
l Good anti-oxidation resistance
Application :
Black Silicon Carbide is suitable for make grinding wheels, cutting wheels, mounted wheels, oil stone, abrasive media, and also suitable for surface grinding, lapping or polishing.
The abrasive products made of it are suitable for working on Cast Iron, Non-ferrous Metal, Rock, Leather, Rubber, Wood, Ceramic, etc.
Black Silicon Carbide is also broadly used as high-grade refractory material and metallurgical additive.
Package
1 ) . In 1MT Big Bag
2 ) . 25KG PP Big Bag In 1MT Big Bag
3 ) . customized packing as required