Silicon Carbide

Silicon carbide

Edward G. Acheson
Edward G. Acheson
Silicon carbide (SiC) is a synthetic material with an exceptional hardness, highly wear resistance and chemically inert to alkalis and acids. It was discovered in 1893 by Henri Moissani (France) while examining rock samples from a meteorite crater located in Devil's Canyon (Arizona, United States).

Almost at the same time, Edward G. Acheson (United States) designed a method to manufacture from clay and coal coke a material that could replace diamond as abrasive and cutting material (Acheson method); he gave the product obtained (silicon carbide) the name of carborundum. In 1894 he created the company Carborundum Co to market his discovery.

Industrial process

The industrial process performed by Navarro SiC for the production of silicon carbide uses Acheson method, based on the following chemical reaction:

        SiO2 + 3·C -> SiC + 2·CO

A mixture of high purity sand or quartz and petroleum coke chemically react in Acheson furnace at temperatures up to 2,500 °C. The energy needed for the reaction is produced by the resistive heating of a graphite core connected to two electrodes at the ends of the furnace..

The reaction proceeds for about 36 hours, with the formation of ß-SiC (cubic silicon carbide) from 1,400 °C and the recrystallization and formation of α-SiC (hexagonal silicon carbide ) from 1.800 °C.

SiC reaction furnace α-SiC (hexagonal silicon carbide)
SiC reaction furnace
α-SiC (hexagonal silicon carbide)

Silicon carbide develops in the furnace as a solid cylindrical ingot around the graphite core, with concentric layers that decrease their SiC content with the distance from the core. It can be black or green depending on the composition of the raw materials used.

Characteristics of silicon carbide

Silicon carbide has an extreme hardness, second only to diamond and a few synthetic compounds. It is also highly resistant to heat. These properties make silicon carbide an irreplaceable material for abrasive and refractory applications.

Property Test Value

Physical properties

Color black, dark grey, green
Hardness UNE EN ISO 4545-1:2006 2,500 - 2,800 MPa
Density ASTM C20 3.21 g·cm-3
Moisture absorption ASTM C373 0.0 %
Refraction Index n0 2.65

Mechanical properties

Resistance to compression ASTM C773 1,725 - 2,500 MPa
Resistance to traction ACMA Test #4 310 MPa
Young's elasticity modulus ASTM C848 420 - 476 GPa
Flexural rupture modulus ASTM F417 324 - 450 MPa
Toughness to fracture Three-point flexural test 2.3 - 4.0 MPa·m1/2

Thermal properties

Thermal stability 1,400 ºC al aire
Resistance to thermal stress Tempering 350 - 500 ºC
Thermal conductivity (298 K) ASTM C408 41 - 90 W·m-1·K-1
Linear thermal expansion ASTM C372 4.7 - 5.1·10-6 K-1
Average specific heat ASTM C351 0.15 - 0.22 cal·g-1·K-1

Electrical properties

Dielectric constant ASTM D150 10.2 MHz
Electrical resistivity ASTM D1829 108 W·cm

Navarro SiC S.A.

Paseo de San Francisco de Sales 31 1º
28003 Madrid
Tel: +34 91 533 48 00
Fax: +34 91 554 70 27