Silicon carbide (SiC) ceramics are a leading class of advanced industrial ceramics, widely recognized for their exceptional high-temperature performance in extreme service environments. Among them, high-purity hot-pressed silicon carbide ceramic supports stand out for maintaining more than 80% of their room-temperature strength at 1200°C. This article provides a practical and technical analysis of their physical and chemical properties, compares them with other structural ceramics, outlines the manufacturing process, and explores key industrial applications.

1. Physical and Chemical Properties of High-Purity Hot-Pressed SiC

Silicon carbide is a predominantly covalent compound with a stable crystal structure, which provides outstanding hardness, strength, and wear resistance. Through hot-press sintering, high-purity SiC ceramics can achieve densities close to the theoretical value and extremely low porosity, significantly enhancing mechanical reliability.

Key Performance Parameters

• Room-temperature flexural strength: ≥ 500 MPa

• Elastic modulus: ~ 400 GPa

• Thermal conductivity (at 1200°C): ~ 80 W/m·K

• Coefficient of thermal expansion: ~ 4.5 × 10⁻⁶ /°C

• Oxidation resistance: Up to approximately 1600°C

• Strength retention at 1200°C: > 80% of room-temperature value

The outstanding high-temperature strength retention is primarily attributed to:

1. High raw material purity, which minimizes intergranular glassy phases.

2. Hot-press sintering, which suppresses excessive grain growth.

3. Near-full densification, reducing creep and high-temperature softening.

As a result, the material maintains structural integrity and dimensional stability during prolonged exposure to elevated temperatures.

Chemically, SiC ceramics exhibit excellent corrosion resistance against most acids, alkalis, and molten salts, making them suitable for harsh chemical environments.

2. Comparison with Other Structural Ceramics

To better understand its positioning, high-purity hot-pressed SiC can be compared with common engineering ceramics:

Compared with Alumina (Al₂O₃)

Advantages of SiC:

• Higher high-temperature strength retention

• Higher thermal conductivity

• Superior thermal shock resistance

Limitations:

• Higher material and processing cost

• More demanding machining requirements

Alumina strength at 1200°C typically drops below 50% of its room-temperature value, and its lower thermal conductivity reduces resistance to thermal gradients.

Compared with Silicon Nitride (Si₃N₄)

Advantages of SiC:

• Better corrosion resistance

• Higher thermal conductivity

• Superior oxidation stability at extreme temperatures

Limitations:

• Slightly lower fracture toughness

• Lower impact resistance

Silicon nitride generally offers higher fracture toughness, making it more suitable for impact-loaded applications, whereas SiC excels in corrosive high-temperature environments.

Compared with Zirconia (ZrO₂)

Advantages of SiC:

• Superior high-temperature stability

• No phase transformation at elevated temperatures

• Higher thermal conductivity

Limitations:

• Lower room-temperature toughness

Zirconia can undergo phase transformations above 1000°C, potentially leading to long-term property degradation, whereas SiC remains structurally stable.

Overall Assessment

Core Advantages:

• Excellent high-temperature strength retention

• High thermal conductivity

• Strong corrosion and oxidation resistance

• Outstanding wear resistance

Main Challenges:

• Intrinsic brittleness

• Sensitivity to micro-defects

• Relatively high production cost

These factors demand strict process control during manufacturing.

3. Manufacturing Process Overview

The production of high-purity hot-pressed SiC ceramic supports involves several precision-controlled steps:

1. Raw Material Selection

High-purity SiC powder (typically ≥ 99.5%) is selected to minimize impurities that could degrade high-temperature performance.

2. Powder Processing

The powder is finely milled and homogenized. Small amounts of sintering aids (such as boron or carbon) are added to promote densification.

3. Forming

Green bodies are shaped through dry pressing or isostatic pressing, ensuring uniform density distribution.

4. Hot-Press Sintering (Core Process)

The compact is placed in a graphite die and sintered under:

• Temperature: 1900–2100°C

• Pressure: 20–40 MPa

• Atmosphere: Inert

Simultaneous high temperature and pressure facilitate particle rearrangement and diffusion, resulting in near-full densification and refined microstructure.

5. Precision Machining

Post-sintering machining is performed using diamond tools to achieve strict dimensional tolerances and surface finish requirements.

The combination of high purity, controlled grain growth, and low porosity ensures consistent high-temperature mechanical performance.

4. Industrial Applications

Due to its ability to retain over 80% of room-temperature strength at 1200°C, hot-pressed SiC ceramic supports are widely used in high-temperature and corrosive environments.

Aerospace

• Engine hot-end structural components

• Combustion chamber liners

• Thermal protection elements

Energy and Power Generation

• Gas turbine components

• High-temperature reactor structures

• Advanced thermal system supports

Chemical and Metallurgical Industries

• Furnace linings and support fixtures

• Corrosion-resistant rollers and structural parts

• Molten salt handling components

Semiconductor Processing

• High-temperature wafer supports

• Heat-treatment fixtures

• Contamination-sensitive structural carriers

Its high purity and thermal stability make it particularly suitable for contamination-controlled environments.

Conclusion

High-purity hot-pressed silicon carbide ceramic supports combine exceptional thermal stability, mechanical strength, and corrosion resistance. With strength retention exceeding 80% at 1200°C, they are among the most reliable materials for demanding high-temperature structural applications.

Although production costs are relatively high and the material remains inherently brittle, precise processing and microstructural control enable outstanding long-term performance. As industries continue to push operational limits in temperature, efficiency, and durability, high-temperature SiC ceramics will remain a critical material solution in advanced manufacturing and energy systems.