Silicon Carbide Sic

Powder preparation
Silicon carbide (SiC) is a compound of silicon and carbon with a chemical formula of SiC. The simplest manufacturing process for producing silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1600°C (2910°F) and 2500°C (4530°F). Fine silicon particles can be converted to silicon carbide (SiC) by heating in the excess carbon from the organic material. The silica fume, which is a byproduct of producing silicon metal and ferrosilicon alloys, also can be converted to SiC by heating it with graphite at 1500°C (2730°F). The material formed in the Acheson furnace varies in purity. The silicon carbide “stones” and grains are turned into a fine powder by crushing, and then purified with halogens.

Kneading
The fine grain (sub-micron) powder is then homogeneously mixed with non-oxide sintering aids (a binder) to form a paste. Different binders including organosilicon binders may be used.

Shape forming
The resulting pasty mixture may be compacted and shaped either by extrusion or by cold isostatic pressing.

a: Extrusion consists in forcing the pasty mixture through a die with an opening. Silicon carbide tubes are produced through extrusion. The properties in the extrusion direction differ from the properties in other directions.

b: Cold isostatic pressing is the powder compaction method conducted at room temperature, and it involves applying pressure from multiple directions through a liquid medium surrounding the compacted part. A flexible mold immersed in a pressurized liquid medium is used. Materials with a uniform anisotropic structure are prepared using an isostatic pressing method. The materials used to produce silicon carbide plates and blocks are manufactured by cold isostatic pressing.

Computer numerical control (CNC) machining
CNC machining is used to machine the surface of the plates or drill the holes on process and services sides in the cylindrical blocks. Due to the very low mechanical strength of the green material, special care is required here. With the help of unique fixture, the components are turned, milled, and drilled according to specific machining parameters.

Sintering
Following the forming stage, the material is sintered in an inert atmosphere at temperatures up to 2300°C (4170°F). During the sintering process, and more precisely between approximately 1900°C (3450°F) and 2150°C (3900°F), the products shrink isostatically by a factor of roughly 20%. The block height, diameter and hole diameters all shrink by roughly 20%. The tube diameter, wall thickness and length also shrink.

Lapping or grinding
If required, the sintered silicon carbide parts can then be machined to precise tolerances using a very costly range of precision diamond grinding or lapping techniques.

Quality checks
The finished silicon carbide parts go through a series of dimensional checks, tests and inspections (leak detection, crack detection, pressure testing, etc…). Mechanical properties are carefully checked and monitored after each production batch.

Electric vehicles contribute towards decarbonization by directly reducing the number of pounds of CO2 that are emitted due to transportation. They have zero tailpipe emissions; however, they consume electricity that is produced by CO2 emitting sources. Including these emissions, the U.S. DoE averages the annual emissions of an EV to be 2,817 pounds of CO2 versus 12,594 pounds of CO2 from a vehicle that uses gasoline. That is a 78% reduction in the amount of CO2 emitted into the atmosphere.

EV charging stations do not have a direct impact on decarbonization, but without a robust infrastructure of DC fast charging stations, the adoption of EVs will be limited. Range anxiety remains a large contributor to the lack of EV adoption. Ninety percent of U.S. households that own an EV own another vehicle that is likely not an electric vehicle. These stats highlight that consumers do not have confidence that their EV can satisfy all their needs, specifically, long-distance trips.

Since 2009, the cost of photovoltaics (PV) solar energy generation has dropped nearly ninety percent, making it the lowest cost source of energy generation at $37/MWh as of 2020. Compare this to coal at $112/MWh and natural gas at $59/MWh. Solar is allowing the world to generate energy with zero emissions of CO2 all while doing it at the lowest cost of other energy sources. SiC cannot take credit for this cost reduction in its entirety, but it is a contributing reason to solar energy generation decreasing in cost.

The world is moving towards using more electric energy, so it is important to keep improving the efficiency of equipment that consumes this electric energy. Electric motors account for 40-50% of the world’s electricity consumption. It is critical to make these electric motors highly efficient as a small efficiency gain is amplified by the vast amount of these motors in the world.

Not only is SiC helping accelerate decarbonization in existing applications, but it is enabling applications that have not been feasible before. One example of this is electric vertical take-off and landing, eVTOL, aircraft. Just as SiC allows for extended range in EVs, it provides that extended range for eVTOLs as well, making them more practical.

SiC semiconductors help accelerate the adoption of these end-systems by making them more efficient, reliable, robust, smaller, lighter, and with an overall lower cost.

Compared to silicon that has a band-gap of 1.12 eV (electron-volts), GaN and SiC are compound semiconductors with band-gaps that are around three times higher at 3.39 eV and 3.26 eV respectively. This means that both can support higher voltages and higher frequencies, though there are a number of differences between the two technologies that impact how they work and where they are used.

One difference between GaN and SiC is speed in terms of electron mobility – how quickly electrons can move through the semiconductor material. At 2,000 cm²/Vs, GaN’s electron mobility is 30% faster than that of silicon, while SiC has an electron mobility of 650 cm²/Vs. These differences play a part in dictating the benefits that each technology offers a target application.

The higher electron mobility of GaN, for example, makes it much more suitable for high-performance, high-frequency applications, something that is further supported thanks to a very, very small percentage of the chip being actually consumed by the gate electrode. This ensures very low capacitance meaning it is easy to achieve higher frequencies (which is why GaN semiconductors are widely used in RF devices that switch in the gigahertz range).

SiC, on the other hand, with its higher thermal-conductivity and lower-frequency operation is more suited for higher-power applications including the higher-end voltages required in EVs and data centers, some solar-power designs, rail traction, wind turbines, grid distribution and industrial and medical imaging that do not always require high-frequency switching but do need higher-voltage operation and improved heat dissipation.

What is clear is that for power processing and fast charging, both GaN and SiC are superior materials to legacy silicon. 650V-rated GaN offers faster switching, integration, and lower costs, and is optimized for applications up to 20kW. The higher voltage and temperature properties of SiC make it optimal for devices over 1,000V and applications up to 20MW.

Reaction-bonded silicon carbide (RB-SiC), sintered silicon carbide (SSiC), and recrystallized silicon carbide (RSiC) are three different types of silicon carbide (SiC) ceramics , each with its unique manufacturing process and properties. Here’s a comparison of these types:

Manufacturing process
RB-SiC: This form of SiC is produced by infiltrating molten silicon into a porous carbon preform. The reaction between the silicon and carbon forms silicon carbide.
SSiC: SSiC is created by sintering or densifying a mixture of silicon carbide powder and additives at high temperatures. The process forms a solid ceramic material.
RSiC: RSiC is produced through a process known as chemical vapor infiltration. In this method, silicon carbide is deposited on a porous carbon preform using chemical reactions.

Microstructure
RB-SiC: RB-SiC has a two-phase microstructure, consisting of silicon carbide and residual silicon.
SSiC: SSiC has a homogeneous microstructure, with densely packed silicon carbide grains.
RSiC: RSiC has a single-crystal or coarse-grained microstructure, depending on the manufacturing process.

Density and porosity
RB-SiC: RB-SiC generally has a higher porosity compared to SSiC and RSiC, resulting in lower density.
SSiC: SSiC has higher density due to the densification process during sintering.
RSiC: RSiC can have varying porosity levels depending on the desired application, but it is generally less porous compared to RB-SiC.

Mechanical properties
RB-SiC: RB-SiC exhibits good strength and thermal shock resistance but may have lower mechanical properties due to the presence of residual silicon.
SSiC: SSiC offers excellent mechanical properties, including high strength, hardness, and wear resistance. It also has good thermal conductivity.
RSiC: RSiC has good mechanical strength, high-temperature stability, and excellent oxidation resistance.

Applications
RB-SiC: RB-SiC is commonly used in applications where thermal shock resistance is important, such as kiln furniture, burner nozzles, and heat exchangers.
SSiC: SSiC is preferred in applications requiring high wear resistance and mechanical strength, including mechanical seals, bearings, and cutting tools.
RSiC: RSiC is often used in applications requiring high-temperature stability and resistance to corrosive environments, such as semiconductor processing equipment and furnace components.

Thermal conductivity
RB-SiC: RB-SiC has relatively lower thermal conductivity compared to SSiC and RSiC, primarily due to the presence of residual silicon.
SSiC: SSiC exhibits high thermal conductivity, making it suitable for applications requiring efficient heat transfer.
RSiC: RSiC typically has moderate to high thermal conductivity, depending on the specific manufacturing process and porosity.

Thermal expansion
RB-SiC: RB-SiC has a lower coefficient of thermal expansion (CTE) compared to SSiC and RSiC.
SSiC: SSiC has a relatively higher CTE compared to RB-SiC and RSiC.
RSiC: RSiC exhibits a higher CTE compared to RB-SiC but generally lower than SSiC.

Thermal shock resistance
RB-SiC: RB-SiC demonstrates good thermal shock resistance due to its lower thermal conductivity and higher porosity.
SSiC: SSiC has good thermal shock resistance, allowing it to withstand rapid temperature changes.
RSiC: RSiC also possesses good thermal shock resistance, making it suitable for high-temperature applications.

Maximum operating temperature
RB-SiC: RB-SiC can typically withstand temperatures up to around 1500°C (2732°F).
SSiC: SSiC has a higher maximum operating temperature compared to RB-SiC and can withstand temperatures up to approximately 1600°C (2912°F).
RSiC: RSiC exhibits excellent high-temperature stability and can endure temperatures exceeding 1600°C (2912°F) depending on the specific grade.

Our company adopts advanced equipment and technology in production and has advanced production lines and equipment to efficiently produce high-quality ferroalloy products. We focus on product quality management and ensure that our products comply with international standards and customer requirements through strict quality control and testing processes.