How Does Silicon Carbide Bond to Silicon Carbide?

Silicon carbide is an extremely hard, durable material with exceptional corrosion resistance, wear resistance and thermal conductivity – as well as serving as an effective semiconductor material.

Sintered silicon carbide offers many attractive properties that make it suitable for sealing applications, including chemical inertness, high temperature stability and a low coefficient of expansion.

Physical Properties

Silicon Carbide (SiC), a black-grey to green powder or solid grey material, is chemically inert, resisting corrosion in harsh environments. Furthermore, SiC’s density makes it less dense than ceramic materials but more than some metals; due to these physical characteristics it makes SiC ideal for applications subject to high thermal, mechanical and electrical stresses.

SiC’s primary crystalline structure is hexagonal with close-packed tetrahedral units covalently bonded together by covalent bonds. Because its constituent atoms have similar electronegativity values, the electrons shared rather than transfered completeing forms covalent bonds between silicon and carbon atoms which form covalent bonds within each tetrahedron forming its center part, creating polytype structures with various chemical and electrical properties.

Si-C is usually resistant to high temperatures, although at very high temperatures its tetrahedral structure can undergo phase changes due to oxidation forming SiO2 films that reduce thermal conductivity and raise melting point; these film layers may then need to be removed in order to expose its original tetrahedral shape and restore ductility of material.

SiC’s durable properties and low expansion rate make it a popular choice for ceramic components found in industrial furnaces, heat exchangers, rocket engines and semiconductor devices. Refractory and structural ceramics made with SiC have also found widespread application; its hardness makes it an important abrasive used in grinding wheels and cutting tools; it serves as an essential material in industrial furnace refractory linings as well as wear-resistant parts of pumps and rocket engines – it even forms key components in Europe’s bepiColombo mission to Mercury!

Reaction-bonded silicon carbide (RB SiC) is a multi-phase material comprised of 7-15% silicon metal and unreacted carbon, with its density making it suitable for high temperature applications, where its resistance to oxidation and deformation makes it particularly valuable. Reaction bonded SiC is commercially available, making this type of SiC easily formable into various shapes and sizes.

Chemical Properties

Silicon carbide is an exceptionally stable compound and one of the hardest known materials. With high chemical resistance and thermal conductivity, silicon carbide makes an excellent choice for industrial processing of harsh chemicals, but is also inert up to high temperatures, has low thermal expansion, and functions as a semiconductor – properties which make it suitable for applications as varied as cutting tools, structural materials (bulletproof vests), automobile parts (brake disks) lightning arresters, mirror materials in astronomical telescopes etc.

SiC is a close-packed hexagonal crystal composed of tetrahedra centered around silicon or carbon atoms, connecting through covalent bonds or single bonds respectively. SiC is classified as a wide band gap semiconductor; as such, electrons require more energy to enter its conduction band than would be needed with metal conductors like copper; this property makes SiC an invaluable heat removal solution essential for most electronic devices.

This substance is inert, stable and non-flammable – characteristics which highlight its stability and inertness – with an extremely low coefficient of thermal expansion. The gray to black-grey solid or powder does not emit any smell and weighs significantly less than most ceramics or metals while still being denser than them.

Modern methods for manufacturing silica-carbon compounds involve mixing pure silica sand with carbon in the form of ground coke in an electrical furnace and subjecting it to intense heat and electric current for several days; temperatures can reach as high as 2,500degC during this process.

With this method, various chemical compositions such as a-SiC and b-SiC can be manufactured, both of which find broad applications in electronics. Polytypes made using this process can also be tailored specifically for electronic use by doping them with impurities – an essential step in manufacturing processes such as this one. B-SiC offers lower breakdown voltage than a-SiC but has higher electron mobility.

Mechanical Properties

Silicon carbide’s chemical composition allows it to form a robust material with high Mohs hardness ratings (near diamond), thermal properties and chemical inertness; making it suitable for many applications requiring high temperature strength resistance and resistance against corrosion and chemical attacks. These qualities make silicon carbide ideal for applications requiring corrosion-resistance as well.

SiC is unique because its bonding between silicon and carbon atoms is covalent rather than ionic, due to their similar electronegativities resulting in electron sharing between atoms rather than complete transfer as would happen with ionic bonds. This structure accounts for its exceptional strength as well as high temperature tolerance.

Reaction bonded silicon carbide production is one of several ways of producing silicon carbide, with this approach producing multi-phase material containing refractory grade silicon carbide particles held together with ceramic matrix material and known as Reactive Bonded SiC (RB SiC) by its manufacturer containing between 7-15% silicon metal depending on your manufacturer. Reactivity Bonded SiC is used widely across many applications where its refractory properties are required – from furnace linings and wear resistant products.

Hydroxide bonding, an innovative new process used to produce SiC, offers several advantages over more traditional methods for its production of this material, including being capable of bonding silicon carbide to materials like sapphire and aluminium.

silicon carbide’s inherent hardness and high temperature strength enable it to have many beneficial industrial uses, with grinding, honing and water jet cutting being just some examples of its many applications. As it has exceptional wear resistance it has also become popular in modern lapidary work due to its durability. Furthermore, due to its electrical properties such as high thermal conductivity and semiconductor behavior it forms part of electrical heating elements like thermistors and varistors as well as being used for manufacturing checker bricks, muffles and kiln furniture for high temperature furnaces in addition to gas turbines and steam generators.

Thermal Properties

Silicon carbide, more commonly referred to as Carborundum, boasts an exceptional combination of physical and chemical properties that makes it an extremely robust material that’s used across a range of applications in high temperature, high voltage and abrasive environments. Its insolubility in water or other solvents speaks volumes for its corrosion-resistance while its excellent mechanical strength, high temperature resistance and thermal shock resistance all combine with excellent fatigue wear resistance for extended use. Silicon carbide also has great fatigue wear resistance making it great fatigue wear resistant than its counterparts such as ceramic counterparts like its cousin, Carborundum.

Chemical inertness of zirconia ceramics can be observed by their lack of odor and inability to dissolve in acid solutions, and its resistance to high temperature radiation exposure without degrading or cracking. With its outstanding physical and chemical properties, zirconia remains one of the most indispensable industrial ceramics today.

Silicon carbide’s chemical inertness stems largely from its molecular structure and close-packed lattice, featuring tetrahedra formed around carbon or silicon atoms. These tetrahedra can be found arranged into two distinct polymorphs: alpha silicon carbide (a-SiC), with its hexagonal wurtzite crystal structure; and beta silicon carbide (b-SiC), which possesses an iron blende crystal structure similar to diamond’s.)

Alpha-SiC is the most frequently produced form of silicon carbide and has become the material of choice due to its high melting point and resistance to oxidation, making it useful in many fields such as electrical furnace components. Due to their lower melting points, other polymorphs may offer more attractive solutions in some applications.

Silicon carbide’s narrow band gap between a-SiC and b-SiC makes it an effective semiconductor material at lower temperatures, due to its superior electron mobility in solid state over other engineering ceramics. Below is data detailing variations in this property while graph bars on material properties cards compare silicon carbide against non-oxide engineering ceramics.