Silicon Carbide

Silicon carbide, a synthetic crystalline compound of silicon and carbon, has long been an industrial material, especially used as an abrasive and cutting tool material since the late 19th century. Silicon carbide can also be found in refractories or electric heating elements.

Edward Goodrich Acheson was responsible for pioneering mass-scale production beginning in 1890, using an electric resistance furnace and mixing silica sand powder with petroleum coke or anthracite coal as fuel sources.

Chemical Reactions

The Acheson Process is the standard method for producing silicon carbide today, originally devised by Edward Goodrich Acheson in 1893 and used widely today. It involves mixing silica with coal coke before heating to a very high temperature to cause the chemical reactions needed to form hard blue-black crystals containing SiC.

Chemical reaction that leads to SiC crystal production begins when silica and carbon in coal coke are heated above their respective melting points, approximately 2700 degrees Celsius. This causes SiO to be released as it melts away, producing SiC and producing some carbon monoxide gas as by-product. This reaction is endothermic and absorbs 624.7kJ per mole of crystal produced.

After SiO has been removed, any remaining silicon dioxide must be dissolved in water at high temperatures to dehydrate it into silica gel, before heating in an inert atmosphere such as argon to form a mixture of SiO and carbon that contains approximately the stoichiometric amounts needed to create silicon carbide.

At higher temperatures, reduction is controlled by diffusion; the rate at which silicon oxygen gas diffuses into carbon particles determines the overall rate of reaction. Many methods have been devised for producing silicon carbide using this approach; one such example includes methane as the carbon source.

Silicon carbide granules formed through this reaction are frequently employed as an abrasive. Crushing and adhering them to paper creates sandpaper while setting in clay can make grinding wheels. For more advanced uses such as in metallurgical or refractory processes, however, this coarse silicon carbide grit is compacted into its desired shape before being fused together using bonding agents such as silica nitride or nitride oxide for greater adhesion.

Chemical vapour deposition processes allow large single crystals of silicon carbide to be grown for use in nuclear reactors, producing an extremely wear-resistant and low neutron cross section material suitable for shielding applications in reactors.

Heat Treatment

Silicon Carbide, also referred to as Tungsten Carbide or Carborundum, is one of four chemical compounds formed from metals with carbon, as defined by salt-like carbides, metallic carbides and diamond-like carbides. While SiC occurs naturally in some meteorites and kimberlite deposits, most industrial-grade SiC used today is synthetic; with an approximate Mohs hardness rating of 9 at Mohs hardness test rating. SiC is highly thermal conductive material offering low expansion rate when temperatures increase and chemical reaction resistance capabilities as well as excellent thermal conductivity properties and resistance against chemical reaction resistance against chemical reaction with many properties that make SiC ideally suited to industrial-use today.

There are various methods for producing silicon carbide powder, each yielding different purity levels, crystal structures, particle sizes and shapes. One popular production process used by abrasives, metallurgical, and refractories industries involves creating a mixture of pure silica sand with carbon finely ground coke in brick electrical resistance furnaces using graphite rods that heat with current passing through them; once heated a layer of silicon carbide forms around each rod which manufacturers then remove and grind into powder form for powder production.

Granular material is the foundation for many other products and serves as the starting point for making functional ceramics, advanced refractories, abrasives and metallurgical raw materials. When producing abrasives from this granular material, binding agents are added before shaping it to create wheels, grinding sticks or other products used in various machining operations.

Sintering

Sintering is the process that occurs during densification of materials, determined by chemical composition of raw material and firing conditions. As part of this process, atoms move across different areas to fill vacant spaces which causes particles to change shape and density resulting in reduced volume of powder material.

Silicon carbide production begins by heating a mixture to temperatures ranging between 1700-2500 degrees Celsius, during which it transforms from powder into solid ingot form with radial layers. Depending on its purity, polycrystalline type and method of manufacture, SiC can have various layer structures; alpha variety with Wurtzite crystal structure is most popular and used for industrial applications; beta variety featuring zinc blende crystal structure are more suited to high grade metallurgical uses.

Initial green bodies are formed when sintering is underway. Two key processes in this phase include neck-connectivity between powder particles and pore elimination – both driven by variations in chemical potential energy between particle surfaces.

After the sintering process is complete, a solid with an average grain size of around 1 millimeter will emerge as a product. This grain size makes abrasives particularly suitable for shaping; loose or mixed with binder it can be formed into sheets, disks or belts; alternatively it may be compressed into blocks for use as grit abrasives; or adhered directly onto matrix materials as refractory materials.

Due to its exceptional hardness, chemical inertness and thermal conductivity properties, silicon carbide material finds application across numerous industrial fields. Grinding wheels use it for rough cutting materials such as chilled iron, marble and granite while its wear resistance makes it useful in bearings and cutters. Furthermore, its low coefficient of thermal expansion and resistance to corrosion make it an excellent refractory material suitable for boiler furnace walls, muffles, checker bricks and kiln furniture’s as well as linings in zinc purification plants while its electrical properties make it suitable for creating electric heating elements using recrystallized silicon carbide material.

Extrusion

An SiC ingot is produced by melting together silica sand and coke in an electrical resistance furnace under electric current, with carbon reacting with silica sand to produce SiC and carbon monoxide gas. Once formed, it forms into an irregular coarse crystalline structure with layers varying in composition that include graphite on the interior surface as well as layers such as a-SiC (abrasives), b-SiC (refractories and metallurgical grade) and unreacted material on all sides – each used differently for different applications depending on application needs.

C-SiC is widely utilized for industrial applications due to its hardness, high thermal conductivity and semiconductor behavior. Its properties allow it to be utilized as an abrasive product such as wheels or grits for grinding metals and minerals; or even be formed into blocks and disks shaped from it for longer service lives in harsh operating environments. Furthermore, its excellent wear resistance often comes paired with chemically inert ceramic coatings for extended longevity under harsh operating conditions.

SiC is widely used for cutting and machining tools as well as wear resistant parts in the automotive industry. SiC has become especially popular as an electrified vehicle battery management system component due to its superior heat dissipation properties compared to aluminum or titanium alloys – this allows more power storage capacity from batteries that last further on one charge cycle.

Silicon carbide can be produced through various processes. Reaction-bonded SiC can be formed by mixing powder with plasticizer and forming it into desired shapes before heating to burn off plasticizer. Alternatively, for advanced electronic applications single crystals of SiC may be grown from gaseous or molten silicon via chemical vapour deposition.

Sintering and extrusion methods used in silicon carbide production are highly energy efficient while remaining environmentally friendly. Furthermore, their production costs compare favorably with other ceramic processes. With increasing demand for silicon carbide material, manufacturers will likely strive to refine this production method and explore new applications such as carborundum printmaking; using carborundum grit applied directly onto an aluminium plate as an ink trap during printing process.