Silicon Carbide Purity Grades Explained | SiC Composition & Testing

Quick Answer

Silicon carbide (SiC) purity grades are defined by the percentage of SiC crystal content and impurity levels (Fe₂O₃, SiO₂, free Si, free C, Al₂O₃, CaO). Standard commercial grades range from 88–99.9% SiC. Lower-purity SiC (88–95%) is used for metallurgical and refractory applications, while high-purity grades (97–99.9%) are preferred for abrasives, polishing, and semiconductors. Purity is verified through XRF or chemical analysis, with exporters reporting each batch in a Certificate of Analysis (COA).

Table of Contents

• 1. What Defines Silicon Carbide Purity
• 2. Key Impurities and Their Effects
• 3. Typical Purity Grades and Their Applications
• 4. International Standards and Classification
• 5. Testing and Analysis Methods
• 6. How Purity Affects Application Performance
• 7. Selecting the Right SiC Grade for Your Industry
• 8. FAQ

1. What Defines Silicon Carbide Purity

Purity in silicon carbide refers to the weight percentage of crystalline SiC in the total material composition. It is the most critical parameter affecting hardness, electrical resistance, oxidation resistance, and suitability for specific applications. SiC purity is controlled by the quality of raw materials, furnace conditions, and post-processing such as magnetic separation and acid washing.

Typical commercial SiC grades contain small amounts of impurities such as Fe, Al, SiO₂, and free carbon. These residual elements influence both color and mechanical behavior. Green SiC typically achieves the highest purity (up to 99.9%), while black SiC ranges from 97–99% depending on refining intensity.

2. Key Impurities and Their Effects

The following table summarizes common impurities found in SiC and how they affect performance:

3. Typical Purity Grades and Their Applications

SiC is commercially available in several purity bands, each optimized for a distinct market sector. Exporters like CanAbrasive classify and certify SiC powders according to both chemical and physical parameters. Below is an indicative table used in export documentation:

4. International Standards and Classification

Purity and particle size are standardized globally to ensure consistent performance. Major standards include:

• FEPA (Europe): Defines F-grit ranges for abrasives with minimum SiC purity thresholds of 97% for black and 99% for green grades.
• JIS R6001 (Japan): Common in Asia; sets both grit size and purity limits for W and GC grades (equivalent to black and green SiC).
• ANSI B74.12 (USA): Outlines particle size and classification but often cross-referenced with FEPA for export products.
• ISO 9001 / ISO 8486: Required for quality management and grit tolerance verification.

High-purity semiconductor SiC (4N–6N, i.e., 99.99–99.9999%) follows specialized ASTM or proprietary standards, not commercial abrasive specifications.

5. Testing and Analysis Methods

Reliable exporters use standardized analytical techniques to verify each batch. Typical methods include:

• XRF (X-ray Fluorescence): Measures elemental composition to ±0.01% accuracy; used for Fe, Si, Al, Ca, Mg, etc.
• Chemical Wet Analysis: Determines free carbon, moisture, and LOI (loss on ignition).
• LECO or ICP-OES: Quantifies trace metallic impurities.
• Magnetic Testing: Detects residual ferromagnetic particles after magnetic separation.
• PSD & Morphology: Particle size distribution and shape affect surface area and reactivity; measured by laser diffraction and SEM imaging.

Each shipment should include a Certificate of Analysis (COA) showing SiC %, Fe₂O₃ %, SiO₂ %, and testing method. Advanced exporters also provide Material Safety Data Sheet (SDS) and Technical Data Sheet (TDS) with storage and handling instructions.

6. How Purity Affects Application Performance

The correlation between purity and performance is direct: higher SiC purity enhances thermal conductivity, oxidation resistance, and stability at elevated temperatures. However, higher purity also raises cost due to longer furnace runs and post-processing steps.

• Low-Purity (88–95%): Economical; suitable for metallurgical and refractory uses where trace oxides are acceptable.
• Medium-Purity (95–97%): Balanced performance; commonly used for industrial refractories and coarse abrasives.
• High-Purity (97–99.5%): Required for coated abrasives, lapping, and precision grinding.
• Ultra-High-Purity (99.9%+): Used in semiconductors, optics, and high-frequency ceramic components where contamination cannot be tolerated.

For example, in polishing LED wafers or ceramics, a 99.9% green SiC microgrit reduces scratching and improves yield, whereas 97% black SiC would introduce metallic residues. In contrast, for a furnace lining, the small amount of Fe₂O₃ in 95% SiC improves thermal shock resistance and bonding strength—showing that “highest purity” is not always “best choice.”

7. Selecting the Right SiC Grade for Your Industry

To choose the right silicon carbide grade, consider these five decision factors:

1. End Use: Polishing and semiconductors need 99.9%+ purity; refractories typically 95–97%.
2. Contamination Sensitivity: Electronics and optics cannot tolerate metallic or oxide residues.
3. Thermal Environment: High-temperature furnaces perform better with medium-purity grades due to enhanced toughness.
4. Budget: Each additional 1% purity increase can add 10–15% to cost.
5. Exporter Capability: Reputable suppliers such as CanAbrasive provide both black and green SiC with verified COAs for different grades, ensuring consistent quality and documentation.

8. FAQ

Q1: What does “SiC purity” mean?

It refers to the percentage of silicon carbide (SiC) crystals in the material, excluding oxides and impurities. High-purity grades (≥99%) have fewer defects and superior performance in precision applications.

Q2: How is SiC purity tested?

Purity is analyzed via XRF or chemical analysis. Exporters report SiC content, Fe₂O₃, SiO₂, and other impurities in Certificates of Analysis (COA) accompanying each shipment.

Q3: What is the difference between black and green SiC purity?

Green SiC is produced under more refined conditions, achieving 99–99.9% purity, while black SiC typically contains 97–99% SiC and trace Fe₂O₃. Green SiC is preferred for applications needing minimal contamination.

Q4: Does higher purity always mean better performance?

Not always. While higher purity improves surface finish and chemical stability, medium-purity grades can offer better toughness and cost efficiency for refractory or heavy-duty grinding applications.

Q5: Which purity grade is best for refractory materials?

Grades in the 95–97% range are commonly used for refractories and kiln furniture because they balance cost, toughness, and thermal performance.

Q6: What purity is required for semiconductor use?

Semiconductor-grade SiC requires 99.9%–99.9999% purity (4N–6N), far exceeding commercial abrasive specifications. These are produced via chemical vapor deposition or specialized purification routes.

Q7: How does Fe₂O₃ content affect quality?

Higher Fe₂O₃ increases the risk of oxidation and surface contamination, particularly during high-temperature use. For precision polishing, Fe₂O₃ should remain ≤0.1–0.2%.

Q8: How can buyers confirm the declared purity?

Request third-party verification or a COA with clear test methods. Reputable exporters like CanAbrasive provide XRF reports and maintain batch traceability for each lot.