Understanding the Different Grades and Types of Silicon Carbide
Silicon Carbide, is one of the most versatile and durable materials in modern industry. Known for its extraordinary hardness, high thermal conductivity, and resistance to wear and chemical corrosion, Silicon Carbide is used across a vast range of applications—from abrasives and semiconductors to refractories and cutting tools.
However, not all Silicon Carbide is created equal. The material is produced in different grades and types, each tailored to specific industrial, mechanical, and electronic needs. Understanding these distinctions is essential for engineers, manufacturers, and researchers who want to select the right SiC material for their applications.
In this article, we’ll explore the different grades and types of Silicon Carbide, how they are manufactured, and their unique properties and applications.
What is Silicon Carbide?
Silicon Carbide (SiC) is a compound made from silicon (Si) and carbon (C) atoms bonded together in a crystalline structure. It occurs naturally in a rare mineral called moissanite, but industrial production of SiC is much more common today.
SiC is typically produced through the Acheson process, where high-purity silica sand (SiO₂) and petroleum coke (a carbon source) are heated together in an electric resistance furnace at temperatures above 2,000°C. The reaction forms Silicon Carbide crystals, which are then crushed, purified, and classified into different grades and particle sizes.
The Main Types of Silicon Carbide
There are two primary crystalline forms (polytypes) of Silicon Carbide used in industry: Alpha (α-SiC) and Beta (β-SiC).
Although both share the same chemical composition, they differ in crystal structure, which gives them unique physical properties and performance characteristics.
1. Alpha Silicon Carbide (α-SiC)
Alpha Silicon Carbide has a hexagonal or rhombohedral crystal structure and forms at temperatures above 1700°C. It is the most thermally stable and commonly used form of SiC in industrial applications.
Key Properties:
- High thermal conductivity
- Excellent chemical stability
- High hardness (Mohs 9.2–9.5)
- High temperature resistance (up to 1,900°C)
- Low thermal expansion coefficient
Common Applications:
- Abrasives: Grinding wheels, cutting tools, and sandpapers
- Refractories: Kiln furniture, crucibles, and furnace linings
- Ceramic components: Nozzles, bearings, and seals
Because of its durability and thermal stability, α-SiC is ideal for environments with extreme heat, friction, or corrosive substances.
- Beta Silicon Carbide (β-SiC)
Beta Silicon Carbide has a cubic (zinc blende) crystal structure and forms at temperatures below 1700°C. It is generally finer-grained, more uniform, and more easily sintered than alpha SiC.
Key Properties:
- Higher fracture toughness
- Better sinterability (useful for ceramics and semiconductors)
- Lower thermal expansion
- Excellent electrical properties
Common Applications:
- Semiconductors and electronics: Power devices, diodes, and transistors
- Advanced ceramics: Wear-resistant parts, heat exchangers, and structural components
- Nano and micro devices: MEMS sensors and substrates
β-SiC is widely used in electronic and high-tech applications due to its ability to handle high voltages, temperatures, and switching frequencies.
Grades of Silicon Carbide
Beyond crystal type, Silicon Carbide is classified into grades based on purity, manufacturing process, grain size, and intended use. These grades determine the performance and cost of the final material.
1. Metallurgical Grade Silicon Carbide
Metallurgical grade SiC is a relatively low-purity form of the material, typically containing 85–95% SiC with some free carbon and silica impurities.
Applications:
- Used as a deoxidizing and reducing agent in steelmaking and foundries
- Improves mechanical properties of metals by adding Si and C to the melt
- Acts as a source of heat in metallurgical reactions
This grade is cost-effective and suitable for bulk industrial use where ultra-high purity is not critical.
- Abrasive Grade Silicon Carbide
Abrasive grade SiC contains more than 98% purity and is manufactured for grinding, cutting, lapping, and polishing applications.
It is available in different grit sizes and colors, often categorized by the black and green types of SiC.
(a) Black Silicon Carbide:
- Produced by the Acheson process with slightly less purity than green SiC
- Hard and tough, suitable for grinding iron, steel, and non-ferrous metals
- Often used in coated abrasives, grinding wheels, and refractory products
(b) Green Silicon Carbide:
- Made from high-purity silica and petroleum coke with the addition of salt as a flux
- Contains more than 99% SiC purity
- Sharper, harder, and more brittle than black SiC
- Ideal for grinding hard alloys, tungsten carbide, and glass
- Refractory Grade Silicon Carbide
This grade is optimized for thermal shock resistance, chemical stability, and high temperature strength.
It generally contains high-purity α-SiC grains, often bonded with clay or silicon nitride to form refractory bricks or shapes.
Applications:
- Furnace linings
- Crucibles
- Kiln furniture
- Burner nozzles
Refractory-grade SiC ensures long life and energy efficiency in high-temperature industrial processes.
- Ceramic Grade Silicon Carbide
Ceramic grade SiC is produced using fine powders of α- or β-SiC that are sintered or hot-pressed to form dense, high-strength ceramics.
Key Features:
- Exceptional wear resistance
- Low density
- Excellent mechanical strength
- Good thermal shock resistance
Applications:
- Mechanical seals and bearings
- Armor plates
- Heat exchangers
- Pump components
These ceramics are commonly used in aerospace, automotive, and chemical industries, where lightweight and high-performance materials are required.
- Electronic Grade Silicon Carbide
Electronic grade SiC is the highest purity form, typically exceeding 99.9999% (6N) purity. It is grown as single crystals using advanced techniques like the Physical Vapor Transport (PVT) method.
Key Features:
- High breakdown electric field
- High electron mobility
- High thermal conductivity
- Wide bandgap (3.26 eV)
Applications:
- Power electronics (MOSFETs, Schottky diodes, and IGBTs)
- LED substrates
- High-frequency and high-temperature electronics
- EV inverters and solar inverters
SiC semiconductors outperform traditional silicon-based devices, enabling faster switching, higher efficiency, and smaller form factors—key advantages in modern renewable energy and electric vehicle technologies.
Color and Purity Differences in Silicon Carbide
Color variations in Silicon Carbide often indicate differences in purity and manufacturing method:
| Color | Type | Typical Purity | Application |
| Black SiC | α-SiC | 95–98% | Abrasives, refractories |
| Green SiC | α-SiC | 98–99.9% | Fine abrasives, precision grinding |
| Yellow or Transparent SiC | β-SiC | 99.999% | Semiconductor-grade crystals |
These distinctions help industries select the correct type for specific requirements, balancing cost, performance, and material characteristics.
Choosing the Right Silicon Carbide Type
Selecting the right Silicon Carbide type depends on the application’s temperature, mechanical stress, electrical requirements, and environmental conditions.
| Application Area | Recommended SiC Type | Grade |
| Metal refining | Metallurgical | Low purity (85–95%) |
| Grinding tools | Black or Green SiC | Abrasive |
| High-temperature furnaces | α-SiC | Refractory |
| Mechanical seals, ceramics | β-SiC | Ceramic |
| Power semiconductors | β-SiC | Electronic (ultra-high purity) |
By matching the grade and type of Silicon Carbide to its end use, manufacturers can maximize performance and longevity while minimizing costs.
The Future of Silicon Carbide
With the rise of electric vehicles, renewable energy systems, and high-performance electronics, demand for high-purity electronic-grade Silicon Carbide is skyrocketing.
Next-generation SiC technologies are focusing on:
- Larger wafers (150mm and 200mm) for cost efficiency
- Improved defect control during crystal growth
- Integration with GaN (Gallium Nitride) for hybrid power devices
- Recycling and sustainability initiatives in SiC production
As innovation continues, Silicon Carbide will remain a cornerstone material for industries seeking high efficiency, durability, and sustainability.
Conclusion
Silicon Carbide is far more than just a hard material—it is a family of materials with diverse crystal structures, purities, and applications. From metallurgical additives to advanced semiconductors, SiC’s versatility and exceptional physical properties make it indispensable in today’s technological landscape.
Understanding the different grades and types of Silicon Carbide allows engineers, designers, and manufacturers to harness its full potential—choosing the right material for the right purpose and ensuring optimal performance across every application.
