An Al2O3 (alumina) crucible is designed for high-temperature applications, with its maximum working temperature depending on its purity and composition. For example, a 99.7% Al2O3 crucible can withstand temperatures up to 1700°C for long-term use and up to 1800°C for short-term use. It exhibits excellent thermal insulation, mechanical strength, and resistance to chemical attacks, making it ideal for industries like metallurgy and materials science. Lower-purity alumina crucibles, such as 85% Al2O3, have slightly lower temperature limits, typically around 1350°C for long-term use and 1400°C for short-term use. The crucible's performance is influenced by factors like thermal conductivity, thermal expansion, and resistance to reducing or oxidizing atmospheres.
Key Points Explained:
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Temperature Limits Based on Alumina Purity:
- 99.7% Al2O3 Crucibles: These crucibles are ideal for very high-temperature applications, with a long-term working temperature of up to 1700°C and a short-term maximum of 1800°C. They are resistant to chemical attacks from acids, alkalis, and reducing gases, except for high-concentration hydrofluoric acid.
- 99% Al2O3 Crucibles: Similar to 99.7% crucibles, these can operate at 1650°C to 1700°C under reduction-oxidation atmospheres and up to 1800°C for short-term use.
- 85% Al2O3 Crucibles: These have lower temperature limits, with a long-term working range of 1290°C to 1350°C and a short-term maximum of 1400°C. They are suitable for stable environments with gradual temperature changes.
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Thermal and Mechanical Properties:
- Alumina crucibles exhibit excellent high-temperature insulation properties and mechanical strength, even at extreme temperatures.
- They have high thermal conductivity (about 3000 W/m·K) and low thermal expansion, which contribute to their durability and resistance to thermal shock.
- These properties make them harder than materials like iron or graphite and capable of withstanding higher internal pressures.
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Resistance to Chemical and Environmental Factors:
- Alumina crucibles are resistant to chemical attacks from most acids, alkalis, and reducing gases like hydrogen and CO.
- They do not react with air, water vapor, or hydrogen, even at temperatures as high as 1700°C.
- Their resistance to electrostatic discharge and other electrical hazards adds to their suitability for industrial applications.
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Applications in High-Temperature Processes:
- Alumina crucibles are widely used in industries for producing ferromagnetic materials like stainless steel and nickel alloys.
- They are also employed in casting, molding processes, and other high-temperature applications where thermal expansion and stability are critical.
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Considerations for Purchasers:
- When selecting an alumina crucible, consider the purity level (e.g., 99.7%, 99%, or 85%) based on the required temperature range and application.
- Evaluate the thermal conductivity and thermal expansion properties to ensure compatibility with the intended use.
- Assess the crucible's resistance to specific chemical environments, especially if the application involves exposure to acids, alkalis, or reducing gases.
By understanding these key points, purchasers can make informed decisions about the type of alumina crucible best suited for their specific high-temperature needs.
Summary Table:
| Feature | 99.7% Al2O3 Crucibles | 99% Al2O3 Crucibles | 85% Al2O3 Crucibles |
|---|---|---|---|
| Long-Term Temperature | Up to 1700°C | 1650°C - 1700°C | 1290°C - 1350°C |
| Short-Term Temperature | Up to 1800°C | Up to 1800°C | Up to 1400°C |
| Thermal Conductivity | ~3000 W/m·K | ~3000 W/m·K | ~3000 W/m·K |
| Chemical Resistance | Resistant to most acids, alkalis, and reducing gases | Similar to 99.7% | Suitable for stable environments |
| Applications | High-temperature metallurgy, materials science | Similar to 99.7% | Casting, molding processes |
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