Background

A chemical processing facility operating in an acidic environment was using components made from Reaction Bonded Silicon Carbide (RB-SiC) for pump seals and corrosion-resistant structural parts. The system was exposed to concentrated sulfuric acid (H₂SO₄) at elevated temperatures around 100°C.

After several months of operation, the plant observed gradual performance degradation, including surface erosion and dimensional changes in certain RB-SiC components.

To improve service life and operational stability, the engineering team evaluated Pressureless Sintered Silicon Carbide (SSiC) as an alternative material.

Problem Identified

Material analysis showed that the RB-SiC components contained approximately 10–15% free silicon phase. In strong acid environments, this free silicon can undergo selective corrosion.

As a result, the material structure gradually weakens, leading to:

• Surface corrosion
• Reduced mechanical strength
• Increased maintenance frequency
• Shorter component lifetime

Testing data under sulfuric acid conditions showed a significant difference in corrosion rate:

• SSiC: 1.8 mg/cm²·yr
• RB-SiC: 55.0 mg/cm²·yr

This difference became critical in long-term continuous operation.

Solution: Switching to SSiC Components

The facility replaced several RB-SiC parts with SSiC components manufactured with high densification control.

Key material characteristics included:

• Density ≥ 3.05 g/cm³
• Near-zero open porosity
• No free silicon phase
• Flexural strength ≥ 380 MPa
• High-temperature strength ≥ 420 MPa at 1300°C

Because SSiC is produced through high-temperature pressureless sintering (>2100°C), the resulting microstructure is more chemically stable in aggressive environments.

Results After Implementation

After switching to SSiC components, the plant observed several improvements:

• Improved corrosion resistance
  The absence of free silicon significantly reduced acid attack.
• Longer service life
  Component replacement intervals increased noticeably.
• More stable operation
  Dimensional stability under thermal and chemical stress improved.
• Reduced maintenance downtime
  Lower corrosion rates led to fewer shutdowns for part replacement.

Engineering Insight

The key difference between the two materials lies in the presence of free silicon.

• RB-SiC contains residual silicon formed during reaction infiltration.
• SSiC forms a fully sintered SiC structure without a secondary silicon phase.

In strongly corrosive environments, especially acids, the silicon phase in RB-SiC becomes the weak point of the material.

This makes SSiC a more suitable choice for:

• Chemical processing equipment
• Corrosion-resistant pump components
• High-temperature acid environments

Takeaway

When selecting between SSiC and Reaction Bonded SiC, the operating environment plays a critical role.

For applications involving:

• High temperature (>1200°C)
• Strong acids or corrosive chemicals
• Long-term structural stability requirements

SSiC typically provides better long-term performance.

RB-SiC remains a viable solution for applications where cost efficiency is a priority and the operating environment is less aggressive.