Silicon carbide is the foundation of several new technologies such as electric vehicles, 5G networks and solar panels. With over 250 crystalline forms available and numerous unique properties it serves as the backbone for these emerging industries.
Producing SiC can be done through various processes, but the Acheson process is the most popular one. This involves heating silica sand with carbon in coke at high temperatures in order to produce pure SiC crystals through chemical reactions that create pure crystals of SiC.
Acheson Process
The Acheson process commercially produces silicon carbide by mixing silica and coke before heating it to high temperatures, producing hard and abrasive silicon carbide which has various applications across multiple industries.
Acheson furnaces consist of graphite slabs layered with carbon black heat insulation for efficient silica-coke reaction, while their walls are lined with the insulating material to create a confined space around a central resistor for energy savings and reduced emission of toxic and organic pollutants.
Mathematical modeling has confirmed that silicon carbide formation in the Acheson process is dominated by solid-gas reactions at the interface between raw materials, with gas phase composition and low vapor pressure at reaction temperatures being major influences on their formation.
Acheson is a multi-step process that begins by mixing powdered silica and coke in a graphite crucible, then heating at high temperatures in either vacuum or an inert gas environment. Once heated, crystals formed from this mix are then consolidated using cold isostatic pressing technology – in which powder is compacted by pressurizing under flexible mold immersed in liquid medium.
Reaction Bonded SiC
RB SiC is used in applications where it must withstand high levels of friction, impact, abrasion and erosion – such as semiconductor manufacturing equipment such as wafer carriers and susceptors, protective gear for workers in industries like aerospace and military; it even helps minimize thermal shock due to rapid temperature changes.
Sintered silicon carbide (SSiC), however, is made by pressing and sintering SiC powder; while reaction bonded silicon carbide (RBSiC) is produced by infiltrating compacts of carbon and silicon with liquid silicon to bond it with initial particles of SiC to produce additional silicon carbides which then form RBSiC with excellent hardness, strength, corrosion and oxidation resistance properties.
Making Reaction-Bonded Silicon Carbide involves mixing 70-99% weight of 10 5000mm silicon powder with 1- 10% weight of thermosetting resin as bonding agent in a solvent, then drying this slurry to obtain granules, before shaping these to meet predetermined shape specifications. After drying, plasticizing by adding a higher carbon rate bonding agent (such as phenol resin ) creates a silicon supplying body. Finally this body is brought together with fused silicon carbide/carbon preform and heat processed to produce reaction-bonded silicon carbide.
Chemical Vapour Deposition
Silicon carbide, composed of silicon and carbon atoms, is the hardest naturally occurring substance known. Due to its low thermal expansion rate and excellent corrosion resistance properties, silicon carbide finds use in various applications due to its low thermal expansion rate, excellent corrosion resistance properties, superior physical and chemical properties as well as resistance against wear and abrasion compared to most metals; in fact its density is comparable with diamond.
Chemical vapour deposition (CVD) is the preferred process to create b-SiC. Powder SiC is converted to vapor by heating it in either vacuum or gaseous plasma environments before being introduced into a CVD furnace for further reaction with other materials loaded into it and eventually turning out as freestanding SiC articles.
A method is provided for producing b-SiC in which multiple graphite deposition mandrels are assembled within a graphite isolation tube and gas is introduced through its upper end in such a manner that reaction gases sweep over each mandrel at approximately 1 micron per minute or faster. This facilitates deposition of the compound onto these mandrels at an increasing rate until final product has been achieved.
TevTech’s patented process for deposition of conformal and superconformal 3C-SiC coatings at high temperatures with low pressure is tailored to achieve conformal and superconformal coating of vias and trenches in micrometer or submicrometer scale vias and trenches, relevant for electronic materials used within them. In contrast to previous studies, higher temperature allows slower precursor consumption kinetics while the addition of HCl helps achieve improved step coverage at lower temperatures by minimizing surface site blocking.
Large Furnace Technology
SiC epitaxy furnaces are used to produce silicon carbide wafers that are then utilized in power electronics and other energy-efficient applications, including electric vehicles and renewable energy systems. Global demand has seen this product type become an integral component of modern living.
An improved Acheson type furnace structure with insulated gates for carrying forward silica-coke reactions under conditions that result in increased proportionate yield of coarsely crystalline material while decreasing fire sand recycled after each production run. Studies conducted have demonstrated that when this insulated gate construction is used, much greater conversion of silica, coke and fire sand to coarsely crystalline silicon carbide occurs than with portions taken from surrounding carbon black wall structures.
Graphite thermal field heating is an ideal choice for industrial furnaces due to its ability to maintain excellent temperature stability and controllability, non-contamination, easy cleanup and resistance against chemical attacks. Furthermore, graphite can withstand extreme temperatures and pressures and can withstand even extreme pressures and temperatures. Pressed SiC powder blanks are sintered into high-strength components before being subjected to rigorous quality checks, tests and inspections before being coated with different materials to provide wear resistance, corrosion protection or performance advantages.
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