Silicon carbide (SiC), nearly as hard as diamonds, is used as an abrasive in grinding wheels
and metal-cutting tools, for lining furnaces, and as a refractory in producing nonferrous
metals.
Description
Silicon carbide is a hard covalently bonded material predominantly produced by the carbothermal reduction of silica. Silicon carbide is made by heating silica sand and petroleum coke packed around electrodes in an electric resistance furnace to above 2200°C. Depending on the exact reaction conditions the resulting silicon carbide is either a fine powder or a bonded mass that requires crushing and milling to produce a usable feedstock. This material is very resistant to abrasion and to corrosion with a molten slag. It also has excellent resistance to thermal spalling. However as it is a carbide, it will oxidise readily, silicon carbide has a fairly high conductivity.
Several hundred structures of silicon carbide (polytypes) have been identified which have different stacking arrangements for the silicon and carbon atoms. The simplest structure is a diamond structure which is designated /3-SiC. Other structures are either hexagonal or rhombic and are referred to as a-SiC.
Chemical Properties
light grey powder
Chemical Properties
Silicon carbide is a yellow to green to bluishblack, iridescent crystalline substance. Colorless when pure.
Physical properties
the properties of silicon carbide are that it is a refractory material (high melting point), it has excellent thermal conductivity and low thermal expansion, consequently it displays good thermal shock resistance. In addition, the high hardness, corrosion resistance and stiffness lead to a wide range of applications where wear and corrosion resistance are primary performance requirements. Silicon carbide possesses interesting electrical properties due to its semiconductor characteristics, the resistance of different compositions varying by as much as seven orders of magnitude.
Characteristics
Silicon carbide is a premium-priced unit which is employed in lining work for its uniformity, abrasion resistance and dimensional stability. It is resistant to most organics, inorganic acids, alkalis and salts in a variety of concentrations except to hydrofluoric acid and acid fluorides. The permeable units have the lowest resistance.
Uses
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Industry
Application
Role/benefit
Abrasive machining processes
Processing of glass, ceramic, stone, refractory, hard alloy, etc.
Abrasive and cutting tools/durability and low cost
Electronic
Light-emitting diodes
Component/electroluminescence property
Semiconductor devices
Component/has wide forbidden band (2.86 EV) and p and n two conductive types
Electric systems
Gapped SiC lightning arresters
Resistance/voltage-dependent property
Sic switches and SiC Schottky diodes
Raw material/anti high-temperature and high-voltage properties
Ceramics
Hard ceramics used for composite armor, bulletproof vests, etc.
Raw material/low density and high strength
Temperature ceramics
Raw material/has high intensity at High temperature
Astronomy
Astronomical telescopes
Mirror material/low thermal expansion coefficient, high hardness, rigidity and thermal conductivity
Aerospace
Gas filter and combustion chamber nozzle
Raw material/anti high-temperature property
Silicon carbide fibre
Reinforcing of metal,resin,alloy,glass,etc.
Reinforcing material/helps to improve all kinds of features
Heat shield material, high temperature filter cloth and conveyor belt
Raw material/anti high-temperature property
Automobile
Brake discs
Ingredient/helps to increase temperature resistance
Sintered form for diesel particulate filters
Ingredient/anti high-temperature property
Oil additive
Helps to educe friction, emissions, and harmonics
Carbon
Graphene production
Raw material
Manufacture of biochar
Coating material/helps to improve the Hardness, strength and wear resistance
Alchemy blast furnace brick
Raw material/anti high-temperature property
Graphite electrode production
Coating component/increase the coating capacity of rapid temperature change
Others
Thin filament pyrometry
Filament material/anti high-temperature property
Nuclear fuel particles
Ingredient/anti high-temperature property
Nuclear fuel cladding
Synthetic moissanite gemstone
Raw material/similar to diamond in several important respects
Steel production
Additional fuel/allows the furnace to process more scrap with the same charge of hot metal
Catalyst support
Support material/large surface area
Carborundum printmaking
Paste material for ink plate
Uses
Silicon carbide is widely used as an abrasive in grinding and cutting glasses; in polishing glass and sharpening stones. It is used in the manufacture of porcelain, refractory brick, furnace linings, and emery paper. The compound also is used in semiconductor technology.
Uses
Manufacture of abrasives and refractories,
brake linings, heating elements, and
thermistors.
Preparation
Silicon carbide is prepared by fusing a mixture of silica (sand) and carbon (coke) with some salt and saw dust in an electric arc furnace at 3000°C.
SiO2(Sand)+3C(Coke)--(3000℃)--Sic+2CO
Salt and saw dust is added to infuse air into the product so that it can be broken into pieces easily. The product obtained is first washed with strong acid followed by strong base to remove basic and acidic impurities respectively. Finally, it is washed with water.
Definition
Bluish-black, iridescent crystals. Insoluble in water and alcohol; soluble in fused alkalies and molten iron. Excellent thermal
conductivity, electrically conductive, resists oxida-
tion at high temperatures. Noncombustible, a nui-
sance particulate.
Production Methods
Silicon carbide, also known by the trade name Carborundum,
has been manufactured and used as an abrasive material for
more than a century. It combines desirable properties of
hardness and thermal resistance. It is produced by heating
high-grade silica sand with finely ground carbon at 2400°C in
an electric furnace. In its powdered or granular form, it
has been used as the abrasive material in “paper and wheels.”
It is used as an abrasive in sandblasting and engraving. It has
been incorporated into ceramics and glass and especially into
refractory ceramic materials.
General Description
Yellow to green to bluish-black, iridescent crystals. Sublimes with decomposition at 2700°C. Density 3.21 g cm-3. Insoluble in water. Soluble in molten alkalis (NaOH, KOH) and molten iron.
Reactivity Profile
Silicon carbide is non-combustible. Generally unreactive. Soluble in molten alkalis (NaOH, KOH) and in molten iron.
Silicon carbide, in certain forms,
may be a cause of pneumoconiosis in exposed
workers.
Silicon carbide has generally been considered
to be an inert dust with little adverse effect
on the lungs.
Flammability and Explosibility
Nonflammable
Industrial uses
Silicon carbide is one of the very few totally man-made minerals used in refractory work. These are:
Oxide-bonded-(S102, A1201, Si02 or silicate glass), silicon oxynitride (Si2 ON2), silicon nitride (S13N4)
The first three of these four bonding systems result in a permeable product, and when failure occurs in such masonry systems due to chemical degradation, it is usually due to attack on the bond. Thus, permeable units (where the corrodent penetrates the mass) are far more rapidly damaged.
Self-bonded”—(silicon carbide to silicon carbide) impermeable ones, where the attack is limited to the surface.
The self-bonded product can be manufactured by either of two methods: reaction bonded or sintered. Both will produce an impermeable unit, and they have roughly comparable chemical resistances, but they do not have identical physical properties.
Safety Profile
Suspected carcinogen with experimental neoplastigenic data. A nuisance dust.
Potential Exposure
A potential danger to those involved in the manufacture of silicon carbide abrasives, refractories, and semiconductors. Silicon carbide fibers are also produced in fibrous form as reinforcing fibers for composite materials.
Incompatibilities
Dust may form explosive mixture with air. Sublimes with decomposition @ 2700C.
