Background

A chemical equipment manufacturer required a material solution for components operating in both acidic and alkaline environments.

The application involved:

• Strong acids (e.g., H₂SO₄, HCl)
• Alkaline media (e.g., NaOH solutions)
• Operating temperatures up to 100°C
• Continuous immersion conditions with fluid agitation

The key requirement was to identify a material with predictable corrosion behavior and long-term stability under mixed chemical exposure.

Test Method

To evaluate material performance, pressureless sintered silicon carbide (SSiC) samples were tested under controlled laboratory conditions:

• Test type: Immersion with continuous stirring
• Duration: 125–300 hours
• Evaluation metric: Corrosion weight loss (mg/cm²·yr)

This method simulates long-term exposure in industrial chemical systems.

Corrosion Performance Results

Acid Environments

• 98% H₂SO₄ (100°C): 1.8 mg/cm²·yr
• 85% H₃PO₄ (100°C): <0.2 mg/cm²·yr
• 70% HNO₃ (100°C): <0.2 mg/cm²·yr
• 25% HCl (70°C): <0.2 mg/cm²·yr

Engineering interpretation:
Corrosion rates below 2 mg/cm²·yr indicate suitability for long-term operation with minimal material degradation.

Alkali Environments

• 50% NaOH (100°C): 2.5 mg/cm²·yr
• 45% KOH (100°C): <0.2 mg/cm²·yr

Result:
SSiC maintains stable performance in most alkaline conditions, with slightly higher corrosion rates in strong NaOH environments but still within acceptable industrial limits.

Material Behavior Analysis

The corrosion resistance of SSiC is primarily determined by its microstructure:

• SiC content ≥ 98.5%
• No free silicon phase
• Open porosity ≈ 0

These characteristics result in:

• No preferential corrosion phase (unlike RB-SiC)
• Limited penetration pathways for corrosive media
• Stable chemical bonding in aggressive environments

Comparison with Alternative Materials

Under similar conditions:

• Reaction Bonded SiC shows higher corrosion rates in acids due to free silicon
• Alumina (Al₂O₃) may degrade in specific acid environments
• Tungsten carbide exhibits rapid corrosion in strong acids

SSiC demonstrates lower corrosion rates across a broader range of chemical conditions.

Application Outcome

Based on the test results, SSiC was selected for:

• Chemical pump components
• Reactor internal linings
• Heat exchanger parts

After implementation, the system achieved:

• Stable operation under continuous chemical exposure
• Reduced maintenance frequency
• Consistent dimensional performance

Conclusion

This case confirms that SSiC provides reliable corrosion resistance across both acidic and alkaline environments when:

• Corrosion rate remains below 2 mg/cm²·yr
• Material structure is fully dense and free of secondary phases

For applications involving mixed chemical exposure, SSiC offers a predictable and stable material solution.