La température de fusion élevée du carbure de silicium

Silicon carbide is an extremely hard and strong non-oxide ceramic with excellent high temperature properties, widely utilized across multiple industries for demanding applications.

Fractographic examination of specimens tested in argon at 1500-2100 degC showed only the outermost layer was oxidized; only its oxide scale contained deformed and elongated boron grains with surrounding whiskers of WO3.

Thermodynamics

Silicon carbide (SiC) is an inert ceramic material which boasts many desirable industrial properties. These include high strength, wear resistance, thermal shock resistance and thermal conductivity – as well as being acid and alkali resistant and being capable of withstanding temperatures up to 1600 degC.

SiC can act either as an electrical insulator or semiconductor depending on its doping level and composition. Doping with nitrogen or phosphorus creates an n-type conductivity while doping with boron, gallium, or aluminium can generate p-type conductivity.

Silicon Carbide is widely utilized today, in industries ranging from steel production, heat treating of metals, float glass production and fabrication of ceramics and electronics components to composite armour (such as Chobham armour) and bulletproof vest production.

SiC melts as a function of both pressure and temperature, with its melting temperature determined by both variables. At low pressures, its phase diagram demonstrates incongruent melting that occurs as an equilibrium mixture of 3C cubic crystal and 6H hexagonal crystal (see [17]). At higher pressures however, studies have observed it congruently melting to form liquid with an unambiguous melting curve as seen in Figure 5. Its slow kinetics is likely due to large differences between carbon atomic radius differences vs silicon atomic radius differences (see [18].

Pressure

Silicon carbide has made headlines due to its semiconducting properties, particularly its superior voltage resistance performance compared with regular silicon. Furthermore, silicon carbide can also be used as an abrasive and in refractory applications like high performance brake discs for cars.

SiC is most frequently found as alpha silicon carbide (a-SiC), with its hexagonal crystal structure similar to Wurtzite. However, beta form can also form at lower temperatures but has limited commercial applications. SiC is known for being tough and hardwearing material with diamond-like qualities that is resistant to heat and corrosion.

Silicon carbide is produced as a powder or crystal for use in various refractory, abrasive and metallurgical applications. In combination with graphite it is often used to produce carbon-fiber-reinforced silicon carbide used in high performance brake discs for cars.

The Lely process is the go-to way of manufacturing silicon carbide. This involves heating a mixture of silica sand and coal (usually coke) at very high temperatures in a granite crucible with carbon conductor acting as electrode, while electrical current passes through coke, creating chemical reactions which allow sublimation at lower temperatures and deposit on graphite rods at cooler temperatures resulting in pure green crystals of SiC known as moissanite.

Diffusion

Silicon carbide (SiC) is an amorphous crystalline material with an extremely high melting point (2700oC). Due to the strong covalent bonds between Si and C atoms, Silicon Carbide exhibits extreme hardness and brittleness while not matching up with diamond’s hardness (9.5 Mohs scale). Found naturally as moissanite which was discovered at Canyon Diablo meteor crater in Arizona back in 1893; alternatively manufactured artificially using reduction silica-carbon in an electric furnace at high temperatures.

Silicon Carbide is widely utilized due to its exceptional physical and chemical properties. It boasts superior electrical characteristics such as 10 times higher voltage resistance than standard silicon and performing better in systems operating over 1000V than gallium nitride; additionally it demonstrates thermal shock resistance as well as wear resistance.

As part of efforts to enhance silicon carbide’s insulating ability, it is often covered with a layer of carbon (known as the C-cap) to mitigate degrade during high temperature annealing processes. Unfortunately, however, this coating may also have detrimental effects on self-diffusion by encouraging Frenkel pair formation and creating immobile antisites (see figure 4 for an illustration of this phenomenon). Figure 4 displays comparison between un-capped and C-capped samples annealed at 1700oC for one hour; 30 profile shapes differ between samples due to pinholes present on C-capped samples annealed at 1700oC for one hour in both samples, this evidenced by differences between their Arrhenius plots of self-diffusion curves (indicating pinholes present on C-capped sample).

Température

Silicon carbide (SiC), is a non-oxide ceramic material with remarkable thermal stability and strength at elevated temperatures. Composed of tightly packed carbon and silicon atoms bound by crystal lattice structures, SiC has a very high melting point – an attribute which makes it suitable for industrial uses where extreme temperatures exist.

Pure SiC is not an excellent electrical conductor; however, doping it with specific dopants significantly increases its conductivity. Furthermore, thermal shock resistance and creep resistance of SiC exceed other high-temperature ceramic materials such as alumina or boron carbide.

In the steel industry, 90% silicon carbide is an integral component of basic oxygen furnaces (BOF). It serves as fuel to increase scrap to hot metal ratio and raise tap temperature; furthermore it helps deoxidize steel while clearing away impurities from its melting pool – as well as being an effective means to control carbon content levels in steel melt.

SiC is not only used in the steel industry; it has many other applications as well. For instance, it serves as an efficient catalyst in producing polyvinyl chloride as well as other organic compounds. Furthermore, SiC can be used to produce alumina and boron carbides; furthermore it is an integral component in composite armour such as Chobham armor.