A New Process for Silicon Carbide Recycling

Silicon carbide is an energy-efficient material that can enable electric vehicles to achieve greater driving distances without the need for active cooling systems and help decrease both size and weight of onboard battery management systems.

Rice University researchers have developed an innovative process for upcycling pulverformed SiC waste into high-quality raw materials, known as flash upcycling. It is energy-efficient and creates a green byproduct.

Recycled Silicon Carbide

Silicon carbide production can be energy intensive and produces significant waste material. Researchers at Fraunhofer Institute for Ceramic Technologies and Systems IKTS Dresden together with its industrial partner ESK-SiC GmbH have created an eco-friendly process that recycles this waste into high-grade silicon carbide – saving energy, reducing pollution levels and conserving raw materials in the process.

Recrystallized powdered SiC is well suited to applications involving machining processes, surface treatment, ballistic protective ceramics and filter materials. Furthermore, this recycled material is more impact resistant and crack-resistant than traditional SiC making it easier to work with; further enhancing recyclability through maintaining its hardness after heat treatment – an essential prerequisite for further processing into useful products.

Reprocessed SiC material typically ranges between 50 and 120 microns in grain size depending on its application, which makes it suitable for grinding and cutting applications, or even use as an alternative to natural sand for sanding where its lower particle volume provides equivalent grinding action with higher throughput.

Reprocessed silicon carbide can also be used in the production of reaction-bonded and nitride-bonded SiC crucibles due to its low reactivity and high hardness properties, making it better suited than conventional granular SiC for this purpose. Furthermore, its excellent sintering and molding performance makes reprocessed SiC an excellent replacement for current use in these applications.

Reprocessed silicon carbide typically boasts grain sizes between 60 microns and 90 percent porosity, with an impact-resistant porous structure more resistant than that found in traditional granular SiC granules. Furthermore, its production costs and energy usage can be lower compared to natural sand production methods; finally it also retains high hardness after heat treatment – essential properties for high temperature applications.

The Process

Production of silicon carbide requires energy-intensive processes that produce large volumes of powdery waste. Researchers from Fraunhofer IKTS have come up with a solution for recycling this powdery byproduct into high-grade silicon carbide material, decreasing industrial pollution while turning waste into valuable raw material resources. Their new process, called RECOSiC, significantly decreases industrial pollution levels while turning industrial pollution into valuable raw material sources.

SiC is produced through mixing silica sand with finely ground coke in an electrical furnace, where an electric current passes through a carbon conductor to cause chemical reaction that forms silicon and carbon monoxide gases that are later filtered off to leave pure silica sand mixture that can then be crushed and graded into various sizes of grains or powders.

Silicon carbide products have many applications in various fields. Silicon carbide offers various attractive characteristics, such as extremely high strength, corrosion resistance and thermal conductivity; furthermore it makes an excellent electrical insulator, aiding the creation of advanced electronic devices such as solid state circuit boards.

Silicon carbide’s unique crystal structure gives it its special properties. It forms in close-packed structures with covalent bonds between its atoms. They are organized into two primary coordination tetrahedra containing four silicon and four carbon atoms each, linked together and stacked to form polytypes with different physical properties.

Silicon carbide comes in various forms and sizes. Common examples are tetrahedra, spheres, rods and hexagons; wear-resistant layers infused with liquid silicon can produce silicon carbide-nitride (SiNx); it can even be grown as large single crystals known as Lely gems.

Silicon carbide is currently used in numerous industries, from abrasives and coated abrasives to power electronics for electric vehicles (EVs). Its use reduces friction, costs, improves efficiency and extends battery life – attributes which have made its use attractive in these applications. Silicon carbide has proven particularly effective at cutting friction costs while simultaneously cutting costs and improving performance compared to alternative materials.

The Materials

Silicon carbide, commonly referred to as carborundum, is a hard chemical compound made of silicon and carbon that occurs naturally as the rare mineral moissanite and has been mass produced since 1893 for use as an abrasive. Due to its long lifespan and minimal replacement needs, silicon carbide helps businesses and consumers decrease waste generation, thus helping reduce environmental impacts while saving costs in disposal fees and replacement needs.

Silicon carbidine has many industrial uses. It offers excellent electrical and thermal conductivity, high melting point, low density, strong mechanical strength and can withstand very high temperatures without cracking, thus making it useful for cutting, grinding and polishing operations. Silicon carbidine also serves as a key raw material in technical ceramics and refractories manufacturing; semiconductor electronics; high performance wheels/disks/wire saws/abrasive products as well as composite material applications with steel.

Silicon carbide production relies on two primary raw materials, quartz sand and petroleum coke. On an industrial scale, production takes place using the Acheson process, which involves heating a mixture in open-air furnaces to approximately 2,300 degC for carbothermic reduction before grinding into particles for further processing. Unfortunately, however, this method generates significant CO2 emissions: approximately 2.4 tons are released per ton produced of SiC produced using this technique.

As part of an effort to reduce its ecological impact, recycling the sludge produced during synthesis would be useful in producing high-grade SiC waste products and decreasing procurement from natural sources. This would allow production of abrasive sludge SiC waste products while simultaneously cutting costs associated with natural raw material acquisition.

This paper investigates the properties, particularly granulometry, of recycled silicon carbide waste for potential inclusion into new cementitious recipes. Our goal was to see if we could substitute recycled silicon carbide waste with minimal effects on overall granulometry and grain characteristics of concrete; our study results indicate this material can indeed serve this purpose, having similar values as other mineral aggregates.

The End Products

Silicon carbide, an industrial material commonly found in applications ranging from refractory components to semiconductors, is highly sought-after but its production requires energy intensive processes that release large amounts of CO2. Now, researchers have developed an environmentally-friendly way of recycling this material by turning by-products and waste products back into high quality silicon carbide material.

The RECOSiC (c) process recycles powdery SiC waste generated in production into silicon carbide that can be reused in known products and processes, increasing yields while decreasing reliance on raw material suppliers.

To create silicon carbide, quartz sand and petroleum coke must be heated in open-air Acheson furnaces. Unfortunately, this generates large quantities of by-products that cannot be used in high quality applications due to lack of grain size and cutting performance. Furthermore, contamination from airflow poses another serious threat when dealing with such gigantic open furnaces.

For recycling silicon carbide, waste products and sludges must first be separated and purified. The RECOSiC process employs flash Joule heating to quickly raise their temperature before combining it with liquid silicon to produce secondary Silicon Carbide which is then infiltrated with liquid silicon to decrease porosity and increase purity of primary SiC.

Once purified, silicon carbide undergoes a critical heat debinding and pyrolysis heat treatment process in a kiln, where oxygen-free conditions are used to heat it in order to extract its carbon content and burn off binder remnants – this step also increases purity to up to 98%!

Recycled Silicon Carbide can be utilized for many different uses, from abrasive products like sandpaper and grinding wheels or disks to composite materials with steel. Other applications for recycled SiC include high temperature refractories, ballistic protective ceramics for military technology and automotive/environmental technology (diesel particulate filter). Reprocessed SiC produced through the RECOSiC process contains predominantly hexagonal crystal structures (a-SiC), while beta silicon carbide (b-SiC).