Why Do Alumina Crucibles Crack? Thermal Shock and Solutions

High-purity alumina (Al₂O₃ > 99%) crucibles are essential for melting precious metals, sintering advanced ceramics, and conducting laboratory tests at temperatures up to 1800°C. They offer exceptional chemical inertness and high-temperature stability.

However, users occasionally report that their alumina crucibles crack. In most cases, this is not due to a manufacturing defect, but rather a failure caused by thermal shock.

What is Thermal Shock?

Alumina is a ceramic material. While it can withstand absolute extreme heat, it is sensitive to sudden changes in temperature (rapid heating or rapid cooling). If a cold crucible is placed directly into a red-hot furnace, the inner and outer walls expand at different rates, creating stress that leads to cracking.

How to Prevent Cracking

• Pre-heating: Never place a cold alumina crucible directly into a hot furnace. Always place it in a cold furnace and bring it up to temperature gradually.
• Controlled Heating Rates: During the initial heating phase, keep the heating rate slow (e.g., 3-5°C per minute) until the crucible is glowing red. It can then handle faster heating.
• Avoid Rapid Cooling: Do not take a red-hot crucible out of the furnace and place it on a cold metal table. Allow it to cool down slowly inside the furnace or on a refractory board.

By following proper operational procedures, high-purity alumina crucibles will provide excellent service life. We supply a wide range of standard and custom-machined alumina crucibles and tubes, ready to meet the demands of your high-temperature processes.