Safety & Usage Guide for Alumina Crucibles

This guide explains how to use Labmina high-purity alumina crucibles safely and get the longest life from them. Our crucibles are fired at 1800°C and rated for a working temperature of 1600°C. Please follow these instructions — the most common cause of breakage is heating or cooling too fast, or removing the crucible directly from a hot furnace.

Temperature ratings

Firing temperature: 1800°C. Maximum working temperature: 1600°C. Do not exceed the working temperature or hold near it longer than necessary — alumina creeps and deforms close to its limit.

Before first use: dry the crucible

Before the first use, place the crucible in an oven at about 105°C for 120 minutes to remove moisture. Trapped moisture can flash to steam on heat-up and crack the crucible.

Heating & cooling rates

Control the ramp rate carefully — this is the single most important rule:

• Below 1200°C: change temperature at less than 5°C per minute.
• Above 1200°C: change temperature at less than 4°C per minute.
• When cooling, reduce temperature under controlled power. Do not simply cut the power at high temperature — the early, fast cooling phase as the furnace cools can crack the product.

Do not use an open flame

Do not heat the crucible directly with a petrol/gasoline torch, acetylene torch or alcohol burner. Direct-flame heating is uneven and will cause the product to crack from thermal stress. Use a furnace that heats the crucible evenly.

Keep clearance from heating elements

Keep the product at least 5cm away from heating elements such as carbon (graphite) tubes, silicon-molybdenum (MoSi₂) rods or heating wire. Too close to a direct radiant source causes uneven heating and local overheating.

Support large crucibles on alumina feet

Large crucibles should not sit directly on the furnace hearth. Raise them on alumina (corundum) feet or similar refractory supports so air can circulate underneath. This even airflow reduces thermal gradients and extends the crucible’s life.

Quick do & don’t

For more on getting the most from your crucibles, see our cleaning & care guide. Need replacements or a custom size? Browse the alumina crucible range or request a quote.