Care Guide

Magnesia (MgO) Crucibles: Handling Precautions

Factory guidance for getting the longest service life out of magnesium oxide crucibles — do not vacuum sinter, heat evenly, control the ramp rate at about 3 °C per minute, and respect the limited corrosion resistance of MgO.

1. Do Not Vacuum Sinter

Magnesia crucibles are not suitable for vacuum sintering. Do not run an MgO crucible in a vacuum furnace. If your process genuinely requires a vacuum atmosphere, select a crucible material that is rated for vacuum service instead.

2. Heat Evenly

Always heat the crucible evenly. Uneven heating concentrates thermal stress in one part of the wall and is one of the most common causes of cracking. Position the crucible so that heat reaches all sides uniformly, and avoid setting it directly against a heating element or inside a localised hot zone.

3. Never Heat or Cool Rapidly

Do not subject a magnesia crucible to sudden temperature change — neither rapid heating nor rapid cooling. Taking a hot crucible out into cold air, or placing a cold crucible directly into a hot furnace, will crack it. Ramp the temperature up and down gradually, and let the crucible cool down inside the furnace to near room temperature before you remove it.

4. Recommended Heating Rate: About 3 °C per Minute

Ramp the temperature at approximately 3 °C/min. This slow, controlled rate lets the whole crucible expand uniformly and is the single most effective thing you can do to extend its service life. Heating faster than this is the most common reason a magnesia crucible fails early.

Practical rule: if you are unsure whether your furnace programme is slow enough, make it slower. A few extra minutes on the ramp is far cheaper than a cracked crucible and a lost sample.

5. Limited Corrosion Resistance

Magnesia has limited corrosion resistance. MgO is a basic oxide and is attacked by acids and by strongly acidic melts — it is best suited to basic and neutral melts. Do not use a magnesia crucible with acidic fluxes or acidic sample matrices; for acidic work, choose an acid-resistant crucible material instead.

6. Practical Handling Tips

Inspect before every run. Check for hairline cracks, chips and flaking. A damaged crucible should be taken out of service, not risked.
Support it evenly. Set the crucible on a flat, stable setter so its base is fully supported at temperature.
Do not overfill. Leave headroom for the charge to expand and, where relevant, to release gas.
Use appropriate tongs. Handle hot crucibles with tongs rated for the working temperature, and grip the body rather than the rim.
Store dry and protected. Keep spare crucibles in a dry place, separated so they cannot knock against each other.

7. Quick FAQ

Can I vacuum sinter in an MgO crucible?
No. Magnesia crucibles are not intended for vacuum service — use an alternative material rated for vacuum.

What heating rate should I use?
About 3 °C/min. Ramp gradually rather than driving the furnace up quickly.

My crucible cracked — what most likely caused it?
In most cases it is thermal shock: heating or cooling too quickly, or heating unevenly. Review your ramp programme and the crucible's position in the furnace.

Can I use it with acidic samples?
No. MgO is a basic oxide with limited corrosion resistance and is attacked by acidic melts. Use it for basic and neutral melts only.

How do I cool it down?
Cool gradually inside the furnace to near room temperature before removing the crucible.

Need a hand? Tell us your working temperature, atmosphere and melt chemistry, and our engineers will help you choose the right crucible material — or supply custom sizes to your drawing. Contact Scuvette →