2. Introduction
Silicon carbide also known as carborundum.
It is a compound of silicon and carbon with chemical formula Sic. It occurs in
nature as the extremely rare mineral moissanite.
Silicon carbide powder has been mass-produced since 1893 for use as
an abrasive.
Grains of silicon carbide can be bonded together by sintering to form very
hard ceramics that are widely used in applications
3. Discovery
In 1891 Edward G Acheson produced a small amount of Silicon Carbide
while conducting experiments with the aim of obtaining a hard material
from the reaction of clay and carbon.
He passed a strong electric current from a carbon electrode through a mixture
of clay and coke contained in an iron bowl, which served as the second electrode.
Acheson recognized the abrasive value of the crystals obtained, had them
Analyzed, found the formula to be Sic, incorporated The Carborundum Company
in September 1891, and filed application for a patent on May 10, 1892.
4. Structure
Silicon carbide exists in about 250 crystalline forms. The polymorphism of Sic is characterized by a
large family of similar crystalline structures called polytypes.
Alpha silicon carbide (α-Sic) is the most commonly encountered polymorph. it is formed at
temperatures greater than 1700 °C and has a hexagonal crystal structure.
The beta modification (β-Sic), with a zinc blende crystal structure (similar to diamond), is formed
at temperatures below 1700 °C.
5. Properties
Pure Sic is colourless, . The crystals vary in colour from very pale green to black
depending on the amount of included impurities.
Black and green silicon carbide both with a shape of hex crystal. The material is extremely
hard and sharp, with excellent chemical properties. The hardness is between diamond
and fused alumina, but the mechanism hardness is higher than fused alumina. The micro
hardness is in the range of2840-3320kg/mm².
Silicon Carbide is sharp but fragile with good heat-resistance, heat-conductibility, can be
antacid and antalkali, lower dilatability and electrical conductivity.
6. Sic is quite stable chemically. It is stable to acids, not reacting with fuming
nitric acid, nor with boiling sulphuric hydrochloric or hydrofluoric acid.
Silicon Carbide dissociates in molten iron and the silicon reacts with the
metal oxides in the melt. This reaction is of use in the metallurgy of iron
and steel.
Sic has:
high hardness
high thermal consistency
very good resistance at high temperatures
low thermal expansion
electrical conductivity
is a semiconductor
non linear electrical resistance
Si and C as alloying additive.
7. production
Silicon carbide is made today in much the same way as it was when invented in 1891:
High purity quartz is mixed with a high quality coke or anthracite in large electric
resistance
furnaces at temperatures of over 2 000°C according to the following reaction:
SiO2 +3C=Sic +2CO
The process is an endothermic reaction requiring between 8000 – 10 000kWh per
tonne of product.
The simplest manufacturing process is to combine silica sand and carbon in
an Acheson graphite electric resistance furnace at a high temperature, between
1,600 °C and 2,500 °C
8. Applications
Silicon carbide forms natural crystals, which are very hard, very abrasive and dissociate or
sublimate at high temperatures. It is for these reasons that silicon carbide is used in the
following applications:
Abrasive industry:
With a good hardness, silicon carbide is the first choice raw material for manufacturing
abrasive pipe , pumping chamber etc. Its abrasiveness is 5-20 times than that of cast iron
and rubber.
9. Automobiles:
Silicon-infiltrated carbon-carbon composite is used for high performance "ceramic" brake
discs, as it is able to withstand extreme temperatures. The silicon reacts with the graphite
in the carbon-carbon composite to become carbon-fiber-reinforced silicon carbide
(C/Sic). These discs are used on some road-going sports cars, supercars, as well as other
performance cars including the Porsche Carrera GT , Bugatti Veyron, Bentleys, Ferraris,
Lamborghinis, some specific high performance Audis etc.
10. Electronics:
Silicon carbide is a semiconductor in research and early mass-production providing advantages
for fast, high-temperature and/or high-voltage devices. First devices available were Schottky
diodes, followed by Junction-gate FETs and MOSFETs for high-power switching. Bipolar
transistors and thyristors are currently developed.
It is also used in making LED’s.
Structural material:
Like other hard ceramics, silicon carbide is used in composite armour and in ceramic
plates in bulletproof vests.]
Silicon carbide is used as a support and shelving material in high temperature kilns such as for
firing ceramics, glass fusing, or glass casting. Sic kiln shelves are considerably lighter and more
durable than traditional alumina shelves.
11. Typical Silicon Carbide uses:
Suction box covers
Fixed and moving turbine components
Seals, bearings
Ball valve parts
Hot gas flow liners
Heat exchangers
Semiconductor process equipment
Jewellery
