How to Determine if Magnesium Oxide Has Absorbed Moisture

Changes in colour, shape, and the degree of clumping can be used to evaluate whether magnesium oxide has absorbed moisture. Magnesium oxide can clump or solidify after absorbing moisture, changing from a loose white powder to a dark grey colour.

1. Evaluation of Appearance and Properties

Colour Change: Magnesium oxide is often a white or somewhat white powder. The colour becomes dull or grayish-white after absorbing moisture.

Morphological Change: The particles stick to one another and form tiny clumps during the initial phases of moisture absorption. Hard lumps or a crusty covering that is challenging to smash by hand are the effects of further development.

Reduced Flowability: It pours readily and flows well when it isn't absorbing moisture. The powder clumps together and becomes much less flowable after absorbing moisture.

Deep moisture absorption produces a hard, stone-like substance that indicates a significant loss of activity, whereas slight moisture absorption appears as loose clumps that can be manually torn up.

2. Reference Standard for Moisture Content

Content of Moisture

State Evaluation

Impacts Usage

≤1.5%

Normal Range (includes crystallisation water)

No Impact

1.5%

Overabundance of External Moisture and Absorbed Moisture

Impacts Quality and Needs Treatment

When there is too much moisture in the air, magnesium oxide reacts with CO2 and water to generate basic magnesium carbonate, which lowers the MgO level.

3. Rapid On-Site Evaluation Technique

Test of Hand Squeezing

Squeeze a tiny sample gently:

It disperses easily and absorbs moisture only slightly.

Hard and unbreakable with moderate to severe moisture absorption.

Method of Spreading and Drying

After spreading the clumped sample out on a drying tray, let it air dry for two to four hours in a ventilated area:

recovers its looseness => It is still usable;

Downgrading is advised because activity is still difficult.

Inspection of the Storage Environment

damaged or open packing → extremely vulnerable to moisture absorption; warehouse humidity > 50%

when moisture-proofing techniques, including the use of desiccants or an inner plastic film liner, are employed.

4. Expert Testing Suggestions

It is advised to send samples to a CNAS-certified laboratory for active magnesium oxide content measurement if they are to be utilised for high-precision production (such as magnesium-based construction products or electronic materials) in order to guaranty activity ≥ 60%. Activity loss cannot be measured by visual observation alone.

For proper assessment, hydration testing (HG/T 3928-2012) should be combined with long-term storage or important applications.