How to Maintain the Activity of Magnesium Oxide After Rework?

Reworked magnesium oxide should have an activity (active magnesium oxide content) of at least 60%. This has a direct impact on the material's reactivity, sintering density, and insulating performance and is one of the key indicators of the HG/T 3928-2012 standard.

 

1. Activity's Crucial Function

Encouraging Sintering Reaction: Active magnesium oxide has a higher surface energy and reactivity, which facilitates the formation of a thick ceramic structure through grain recrystallization during sintering at 900°C;

Enhancing Insulation Performance: Porosity reduces after adequate sintering, greatly increasing hot insulation resistance (goal ≥200 MΩ);

Improving Moisture Resistance: During operation, the solid structure successfully prevents moisture penetration, avoiding pipe bursts or malfunctions.

Insufficient activity can result in "false filling," which makes it vulnerable to failure in hot-state testing even if it passes cold-state testing.

 

2. Testing Procedures and Acceptance Standards

Standard Testing Procedure for Item Acceptance

Active Magnesium Oxide Content > 60% Hydration Technique (Titration following two hours of isothermal reaction)

Acid-Base Titration Method: Total MgO Content ≥ 95%

Ignition Loss < 5% Constant Weight Method at 950°C

A laboratory with CNAS certification, like Zhongxi Testing or Wuhan Kehai Testing Co., Ltd., must use the hydration method, which is the industry gold standard. The report is legitimate under the law.

 

3. Important Elements Influencing Activity

A factor

Requirements for Control

Risk Alert

Activity for Raw Materials

Make use of light magnesium oxide powder with high activity (≥60%).

When using heavy or aged powder, activity reduces.

Procedure for Sintering

Hold under high-purity nitrogen protection at 900±50°C for 1.5 hours.

The reaction is inhibited by an unclean atmosphere or a low temperature.

Cooling Technique

Using the furnace's natural cooling system to prevent thermal stress cracking

Structural flaws result from forced cooling.

Conditions of Storage

RH≤30%, sealed, and impervious to moisture

After absorbing moisture, activity drastically declines.

Experience has shown that the active reaction will be inhibited by Fe₂O₃＞0.05% or too much Cl⁻, resulting in incomplete sintering.

 

4. How Can Compliance Be Guaranteed? Source control: During procurement, suppliers (such as Liaoning Jiashun Technology and Dashiqiao Meier Magnesium Products) must submit active magnesium oxide testing reports;

Process monitoring: To guaranty process stability, temperature curves are captured utilising intelligent sintering furnaces;

Final examination and confirmation: Each batch's samples are sent to a CNAS facility for testing, and a special coded file is created.

The determined active magnesium oxide content usually reaches 62%–68% using standardised procedures, fully satisfying usage requirements.