A ceramic crucible can withstand different levels of heat depending on its composition and the specific conditions under which it is used.
For a 99.70% pure alumina crucible, it can withstand temperatures up to 1800°C in a redox atmosphere of 1650°C–1700°C. It has good high-temperature insulation and mechanical strength.
An 85% alumina ceramic crucible can withstand temperatures up to 1400°C in a reduction-oxidation atmosphere of 1290℃~1350℃. It also has excellent high-temperature insulation and mechanical strength, with large thermal conductivity and low thermal expansion.
A 99% alumina ceramic crucible, under a reduction-oxidation atmosphere of 1650℃~1700℃, can withstand temperatures up to 1800°C. It has excellent high-temperature insulation properties, mechanical strength, large thermal conductivity, and low thermal expansion. It does not react with air, water vapor, hydrogen, or CO even at 1700℃.
It is important to note that alumina ceramic crucibles are suitable for melting samples with acidic substances such as K2S2O7 but not applicable for melting samples with alkaline substances such as NaOH, Na2O2, Na2CO3, as these can cause corrosion to the crucible. Alumina ceramic crucibles should also be kept away from hydrofluoric acid (HFA).
Carbon-bonded and ceramic-bonded clay graphite and silicon carbide crucibles are widely used for melting and holding various metals and alloys. The temperature range for these crucibles varies from 400°C/750°F to 1600°C/2912°F, depending on the specific metal being melted.
A specific example is given for a >99.6% Alumina (Al2O3) High Form Crucible with a 1000 ml capacity, which can be used at operating temperatures up to 1750°C in both oxidizing and reducing atmospheres. It is inert to hydrogen, carbon, and refractory metals.
When using alumina crucibles, it is important to follow proper heating and cooling instructions to minimize the risk of thermal shock. Gradual warming up and cooling down are recommended, with heating rates of 150-300°C per hour and cooling rates often half of the heating rate (75-150°C per hour).
In summary, the heat tolerance of a ceramic crucible depends on its composition, with alumina crucibles capable of withstanding temperatures up to 1800°C in certain conditions. It is important to consider the specific application and follow the manufacturer's instructions for optimal use and longevity of the crucible.
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