Alumina (Al2O3) crucibles can handle extremely high temperatures, making them perfect for various high-temperature applications in both oxidizing and reducing atmospheres.
The maximum operating temperatures for different types of alumina crucibles range from 1200°C to 1800°C.
This range depends on the purity of the alumina and the specific conditions of use.
These crucibles are inert to many substances, including hydrogen, carbon, and refractory metals.
They are also resistant to chemical attacks from most acids and alkaline solutions, with the exception of high concentration hydrofluoric acid.
4 Key Points Explained
Temperature Range for Alumina Crucibles
99.6% Alumina Crucible: Can be used at operating temperatures up to 1750°C in both oxidizing and reducing atmospheres.
85% Alumina Crucible: Shows excellent properties under reduction-oxidation atmosphere at temperatures between 1290°C and 1350°C. The maximum working temperature is 1400°C for short-term use.
99% Alumina Crucible: Performs well under reduction-oxidation atmosphere at temperatures between 1650°C and 1700°C. The maximum working temperature is 1800°C for short-term use.
99.7% Alumina Crucible: Ideal for very high temperature applications up to 1700°C.
Chemical Resistance
Alumina crucibles are inert to hydrogen, carbon, and refractory metals.
They are resistant to chemical attacks from most acids and alkaline solutions, with the exception of high concentration hydrofluoric acid.
Alumina crucibles should be kept away from hydrofluoric acid (HFA).
Application Considerations
Alumina crucibles are suitable for melting samples with acidic substances such as K2S2O7.
They are not applicable for melting samples with alkaline substances as molten solvent, such as NaOH, Na2O2, Na2CO3, which will cause corrosion to the crucible.
Protection tubes made of alumina or magnesia may be used to protect samples from strongly reducing atmospheres, especially at higher temperatures.
Thermal Properties
Alumina crucibles exhibit excellent high-temperature insulation properties and mechanical strength.
They have large thermal conductivity and low thermal expansion, making them suitable for long-term use in stable environments where temperature changes are not too fast.
Safety and Handling
It is safer and more desirable to protect the sample from strongly reducing atmospheres using a refractory tube of low porosity.
A slight current of air through the tube can serve to oxidize reducing gases and drive off smoke.
Porcelain tubes approximating the composition of sillimanite (Al2O3.SiO2) can be used up to temperatures as high as 1800°C, although they become soft and do not last long at this temperature.
In summary, the temperature at which an Al2O3 crucible can operate varies significantly based on the purity of the alumina and the specific conditions of use.
High-purity alumina crucibles can withstand temperatures up to 1750°C to 1800°C, making them ideal for very high temperature applications in both oxidizing and reducing atmospheres.
They are resistant to most chemical attacks, except for high concentration hydrofluoric acid, and are suitable for melting samples with acidic substances.
Care should be taken to protect the crucible and samples from alkaline substances and strongly reducing atmospheres.
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