Tech Team · Kintek Solution

A ceramic crucible's heat resistance depends on its material composition, with alumina-based crucibles being the most common. High-purity alumina crucibles (99% alumina) can withstand temperatures up to 1800°C for short-term use and 1700°C under reduction-oxidation atmospheres. Lower-purity alumina crucibles (85% alumina) are suitable for temperatures up to 1400°C for short-term use and 1350°C under stable conditions. Crucibles made from other materials, such as graphite, offer additional properties like thermal conductivity and corrosion resistance but may have different temperature limits. The choice of crucible depends on the specific application, including temperature requirements, chemical compatibility, and mechanical strength.

Key Points Explained:

1. Material Composition Determines Heat Resistance:

   • Ceramic crucibles are typically made from alumina (aluminum oxide) in varying purities, such as 85% or 99%. The purity level significantly impacts their thermal performance.
   • High-purity alumina crucibles (99%) have a higher melting point and can withstand extreme temperatures, making them suitable for high-temperature applications.
   • Lower-purity alumina crucibles (85%) are more cost-effective but have lower temperature limits.

2. Temperature Limits for Alumina Crucibles:

   • 99% Alumina Crucibles:
     • Short-term use: Up to 1800°C.
     • Reduction-oxidation atmosphere: Stable up to 1700°C.
     • Properties: Excellent high-temperature insulation, mechanical strength, thermal conductivity, and low thermal expansion.
   • 85% Alumina Crucibles:
     • Short-term use: Up to 1400°C.
     • Reduction-oxidation atmosphere: Stable up to 1350°C.
     • Properties: Suitable for stable environments with gradual temperature changes.

3. Chemical and Physical Stability:

   • Alumina crucibles exhibit excellent chemical stability, resisting reactions with air, water vapor, hydrogen, and CO even at high temperatures.
   • Their low thermal expansion and high thermal conductivity ensure durability and reliability under thermal stress.

4. Comparison with Other Crucible Materials:

   • Graphite Crucibles:
     • Offer superior thermal conductivity, corrosion resistance, and impact resistance.
     • Can significantly reduce melting time and energy consumption.
     • Temperature limits may vary depending on the specific graphite grade and application.
   • Alumina vs. Graphite:
     • Alumina crucibles are harder and can withstand higher internal pressures due to their higher thermal expansion coefficient.
     • Graphite crucibles are better suited for applications requiring rapid heat transfer and resistance to chemical corrosion.

5. Application Considerations:

   • The choice of crucible material depends on the specific requirements of the application, including:
     • Maximum operating temperature.
     • Chemical compatibility with the materials being processed.
     • Mechanical strength and thermal expansion properties.
     • Cost and availability.

6. Short-Term vs. Long-Term Use:

   • Crucibles have different temperature limits for short-term and long-term use. Short-term use allows for higher temperatures, while long-term use requires lower temperatures to ensure durability and prevent degradation.

7. Thermal Conductivity and Expansion:

   • High thermal conductivity ensures efficient heat transfer, reducing melting time and energy consumption.
   • Low thermal expansion minimizes the risk of cracking or damage due to rapid temperature changes.

By understanding these key points, purchasers can select the appropriate ceramic crucible based on their specific needs, ensuring optimal performance and longevity in high-temperature applications.

Summary Table:

Material	Purity	Short-Term Use (°C)	Long-Term Use (°C)	Key Properties
99% Alumina	99%	Up to 1800°C	Up to 1700°C	High-temperature insulation, mechanical strength, thermal conductivity, low expansion
85% Alumina	85%	Up to 1400°C	Up to 1350°C	Cost-effective, suitable for stable environments with gradual temperature changes
Graphite	-	Varies by grade	Varies by grade	Superior thermal conductivity, corrosion resistance, and impact resistance

Need help choosing the right ceramic crucible for your high-temperature applications? Contact our experts today for personalized guidance!