Silicon carbide ceramic is one of the hardest and strongest advanced ceramic materials, boasting excellent chemical resistance against acid, alkali corrosion and low thermal expansion rates. Reaction bonding and sintering are two methods used to fabricate material. These forming methods will have an immense influence on the microstructure of the finished product.
Production Processes
Silicon Carbide is an exceptionally hard material with excellent resistance to wear and corrosion, high heat tolerance, low expansion at elevated temperatures, making it the ideal material for refractory applications such as kiln shelves and burner nozzles. Furthermore, its superior electrical conductivity makes it an excellent alternative to metal in high temperature electronics applications like insulators and heaters.
Most silicon carbide is produced through the Acheson process. This involves mixing silica and carbon together in an electric furnace with a graphite rod at its core before subjecting this combination to high temperatures for chemical reaction to form silicon carbide – commonly referred to as green or black silicon carbide and used for various applications.
Grinding equipment must then be used to reduce this green or black SiC to finer particles for sintering, an essential process in creating quality silicon carbide ceramic products. Sintering takes place under very high temperature conditions within an atmosphere controlled environment for maximum adhesion between particles.
Reaction bonding (RBSC) and hot pressing sintering are two methods of sinering that can be accomplished. With reaction bonding, pieces are infiltrated with liquid or vapor silicon to react with carbon to form more silicon carbide which then bonds the original pieces. Reaction bonded SiC has lower thermal expansion coefficient and resistance to corrosion, wear, wear acids such as phosphoric, nitric and hydrochloric acids as well as corrosion.
Hot press sintering is another method for producing high-grade refractory silicon carbide. Similar to sintered silicon carbide production, but using different molding and heating processes. The end product features greater density compared to RBSC with reduced thermal expansion coefficient and greater strength; however it should still be treated as strong material.
Cold Isostatic Pressing
Cold Isostatic Pressing (CIP) is an efficient method of producing metal powders and ceramics. The CIP process begins by placing raw material inside an elastic container containing liquid. A uniformly distributed pressure is then applied, causing the liquid to solidify into green bodies ready to be processed further with rolling or machining processes. Quintus offers industrial solutions for CIP machinery to enable large volumes to be produced at lower costs.
CIP offers many advantages over uniaxial pressing, including being used to compact materials of various shapes and sizes, making it suitable for complex or hard-to-form components that require precise dimensional control. Furthermore, its lack of die walls permits materials to be compressed without using binder, further decreasing production steps and overall costs.
CIP can help ceramicists produce difficult shapes using traditional uniaxial pressing methods, including long and thin components like ceramic rods used as filaments in lamps and other electrical devices. Furthermore, this process can also compact refractory and electrical insulator powders for compacting purposes.
CIP can produce components with extremely high green strength. This allows CIP to quickly and efficiently handle various shapes while producing green parts with greater pressure-withstanding capacities than would be possible through uniaxial pressing, making handling and manipulation more straightforward and efficient.
CIP differs from uniaxial pressing in that its compaction process does not produce heat, which could compromise product strength and quality. This makes CIP particularly suitable for materials such as ceramics which tend to be fragile with limited ductility; as well as materials with higher melting points like nitrides, carbides or spinels which must remain fragile for proper compaction.
Due to not producing heat, CIP is safer to handle and manipulate molded powders than its counterpart. However, due to ceramic’s brittle nature it may still crack if pressure is released too rapidly or unevenly, leading to porosity or grain boundary shear defects if too quickly released; so in order to mitigate such risks it must be performed at lower temperature with controlled depressurization rates. To minimize these risks, CIP processes are usually done at lower temperatures with gradual pressure releases at controlled rates.
Hot Pressing
Silicon carbide is one of the hardest materials on Earth, offering superior corrosion-resistance and thermal properties. Thanks to these properties, silicon carbide ceramic can be found in an array of industrial products including refractories and heating devices; anti-abrasion components; automotive brake pads are among the many uses for silicon carbide as well.
Silicon Carbide ceramic can withstand temperatures of up to 1400 degrees Celsius, making it suitable for high-stress industrial applications. Furthermore, this material boasts excellent abrasion resistance and strength even at higher temperatures – two qualities which have made it popularly used in furnaces and kiln furniture applications.
While silicon carbide occurs naturally only rarely, there are various methods available to scientists who want to make it in the lab for manufacturing purposes. Reaction bonding is perhaps the most widely utilized manufacturing technique: mixing coarse silica and carbon together before heating to high temperatures before watching as their chemical reactions create sintered silicon carbide that can then be cut and formed into various shapes and sizes.
Hot pressing involves subjecting material to intense heat under pressure in a mold or die. This method helps eliminate voids and porosity in the material, helping it form into dense structures with sound structures. Elevated temperatures also promote atomic rearrangement within it for enhanced bonding between constituent particles.
Reactive sintering is another technique for producing silicon carbide. This involves mixing coarse silicon carbide with small amounts of carbon-containing material before placing it into a sintering furnace at 1600-1800 degC for 16-18 hours and heating. This creates dense sintered silicon carbide bodies comprising of a-SiC, b-SiC, and free silicon (10-15%) that resist wear-and-tear over time.
Reaction sintering is frequently employed for producing Ultra High Temperature Ceramic Matrix Composites (UHTCMCs), composed of SiC fibers/preforms enriched with UHTCs. This method is particularly beneficial when working with materials that do not achieve dense enough densities in standard sintering operations and when fabricating ceramics that have complex shapes that cannot be produced using cold isostatic press or other forms of sintering technology.
Reaction Sintering
Silicon Carbide ceramic is one of the hardest non-oxide materials, boasting superior thermal and mechanical performance in high temperature/heat shock environments and applications like abrasives and wear parts. Furthermore, SiC is highly thermally and electrically conductive which makes it often found in high voltage electric equipment, ceramic heaters and coolers.
Reaction sintering (also referred to as reaction bonding) is a process by which liquid silicon is infiltrated into carbon-containing porous ceramic bodies at low temperatures, reacting with carbon to form more SiC that bonds to original particles of silicon carbide and fills in any pores in the body. This densification method takes place at lower temperatures than conventional sintering techniques and makes for highly shaped products at an economically viable temperature range; additionally it’s an effective means of producing materials not accessible with conventional techniques alone.
Advantages of this sintering process include its incorporation of silicon infiltration within a preform of desired shape, providing control of both rate of sintering and final microstructure. Rapid sintering processes create bimodal grain size distribution, which has detrimental effects on mechanical and dielectric properties of finished products.
However, this sintering technique has several downsides, including its extreme sensitivity to changes in raw material composition and poor fracture toughness when porosity levels increase.
As such, it is preferable to utilize pressureless sintering processes when manufacturing ceramic components such as kiln furniture and crucibles. Energy-saving kiln furniture made of reaction sintered SiC is one such example of this application, such as its frame type energy saving kiln furniture that exhibits excellent oxidation resistance, bending strength, cold blast resistance as well as ease of maintenance over long periods. Such furniture can be utilized both high temperature tunnel kilns as well as double roller kilns.