What Is Silicon Carbide?

Silicon carbide is an extremely hard and strong material with high density, exceptional corrosion resistance and outstanding tribological properties. Available both sintered and reaction bonded forms.

Pressureless sintering provides high densification through reduction of surface energy of grains due to boron and carbon reaction1, but its high temperature leads to excessive grain growth that compromises mechanical properties.

Strength

Silicon carbide, commonly referred to as carborundum, is a hard chemical compound composed of silicon and carbon that occurs naturally in rare minerals like moissanite; however, more commonly it is mass-produced as powder and granules for use as an abrasive and ceramic plates in bulletproof vests. Carborundum can withstand high temperatures while remaining chemical resistant – including resistance against acids like phosphoric, sulphuric, and nitric acids.

Sintered silicon carbide has found widespread application across industries, from aerospace to astronomy, due to its remarkable thermal insulation properties. Sintered silicon carbide refractory material also boasts impressive durability and can be precisely machined using expensive equipment for precision tolerances.

Silicon carbide ceramic comes in two varieties, reactively bonded and sintered. Reactively bonded silicon carbide is manufactured by infiltrating compacts composed of SiC and carbon with liquid silicon, creating more SiC which bonds to initial particles forming more reaction bonded silicon carbide particles that adhere more easily than its sintered counterparts, yet remains cost-effective due to reduced strength and hardness.

Sintered silicon carbide is produced by heating raw materials to extremely high temperatures in an inert atmosphere, transforming them into an extremely strong material that can be used in various applications like wear parts for sand pumps and mining cyclones. Furthermore, it features excellent corrosion resistance as well as low thermal expansion properties.

Hardness

Reaction bonded silicon carbide (RSiC) is produced by pressing and sintering (heating) powder particles together, creating a solid piece of material with high strength, hardness, corrosion and oxidation resistance – though not as hard as sintered silicon carbide.

Sintered silicon carbide is a technical ceramic with strong covalent bonds, providing excellent mechanical properties at high temperatures. This material boasts great hardness and wear resistance as well as resistance against chemical corrosion, oxidation and thermal shock, along with very good thermal conductivity, making it suitable for use in harsh environments.

Liquid-phase sintering produces high-purity materials with an even microstructure, more compact than solid state sintering processes. Size changes during densification are minimal; precise parts with complex shapes can be produced. Sintering additives of boron and carbon can modify grain boundary energies and surface energies while improving volume diffusion rates and limiting glass formation between grains.

The results of solid-state sintering have superior compressive creep resistance than their conventional counterparts due to an increase in kinetic energy of crystalline silicon and acceleration of dislocation motion within granular regions, as well as an increase in metallic silicon concentration which helps decrease creep rates by slowing diffusion of SiC across grain boundaries.

Corrosion Resistance

Silicon carbide offers excellent resistance to corrosion, oxidation and wear – qualities which make it a suitable material choice for harsh environments where other materials might break down over time. Furthermore, silicon carbide can withstand temperatures up to 1,900 deg C which makes it suitable for chemical processing where equipment may come in contact with highly acidic chemicals and gases that corrode more readily than expected.

Both solid state-sintered silicon carbide (SSiC) and silicon-infiltrated silicon carbide ceramics have been found to be stable in various chemical solutions, although the latter has lower corrosion stability due to free silicon. To explore these mechanisms, we conducted both short-term and long-term corrosion experiments on SiSiC in NaOH solution using both accurate measurements of corrosion depth on polished surfaces as well as scanning electron microscopy on its corrosion products.

Reaction bonded silicon carbide (RBSiC) is produced by infiltrating liquid silicon into porous carbon or graphite preforms and reacting it into SiC. RBSiC differs from its more expensive SSiC counterpart in several respects; for one thing it has lower strength and hardness but costs significantly less to produce and is more permeable for gasses and liquids to pass through; it also features good resistance against abrasion, corrosion and thermal shock resistance to enable its use in applications such as burner nozzles or jet and flame tubes; finally it also features good thermal shock resistance to allow rapid temperature changes without being affected.

Thermal Conductivity

Sintered silicon carbide boasts one of the highest thermal conductivities among non-oxide ceramic materials, making it suitable for applications involving high temperatures such as chemical vapor deposition (CVD) SiC or reaction bonded silicon carbide applications.

Located near the core, its crystalline structure helps increase thermal conductivity for high thermal performance ceramic. Able to withstand high temperature loads with little damage and resistance to corrosion, oxidation and fatigue – this material makes an excellent material choice for pump seal applications as it can remain pressure and temperature resistant over extended periods.

This type of ceramic also boasts superior toughness, meaning that it can withstand impact and vibration better than other ceramic materials. Furthermore, its strength and oxidation resistance rank amongst the highest in its category.

Liquid Phase Sintering (LPS) is an innovative technique for densifying silicon carbide using eutectic oxide sintering additives to densify at lower temperatures than traditionally, thus saving production costs while simultaneously decreasing porosity in finished product.

HRTEM images of LPS-SiC samples with different sintering additives demonstrate how increased additive addition evened out the distribution of liquid phase among SiC grains, leading to densification, higher relative density, and improved electrical resistivity, which are properties critical for applications using microwave and millimeter wave frequencies.