The application of magnesium carbonate (MgCO₃) in molten particle refining agent is mainly reflected in its high temperature decomposition characteristics, alkalinity regulation and physical and chemical synergy. The following is an analysis of its specific application and mechanism of action:
1. Application scenario
Melting particle refining agent is mainly used for purification of metal smelting (such as aluminum, steel, copper alloy, etc.), removing gas (H₂, O₂), non-metallic inclusions (such as oxides, sulfides) and impurity elements in the melt through adsorption or chemical reaction. Magnesium carbonate is often used as a key component in the following scenarios:
Aluminum alloy refining: removal of hydrogen and aluminum oxide inclusions in molten aluminum.
Steel smelting: desulfurization, dephosphorization and adjustment of slag composition.
Copper alloy treatment: reduce pores and impurity content.
2. Mechanism of action
(1) High temperature decomposition provides active components
Magnesium carbonate reacts at high temperatures (begins to decompose at about 350°C and completely decomposes above 500°C):
Magnesium oxide (MgO): As an alkaline oxide, it reacts with acidic impurities (such as SiO₂, P₂O₅) in the melt to form low-melting-point slag, which is easy to separate.
Carbon dioxide (CO₂): The released gas forms tiny bubbles, which carry away hydrogen and inclusions (such as Al₂O₃ particles in aluminum liquid) in the melt through flotation.
(2) Regulating melt fluidity
MgO produced by the decomposition of magnesium carbonate can adjust the viscosity of the refining agent and promote the separation of slag and metal melt.
The stirring effect of CO₂ bubbles can even out the temperature and composition of the melt and reduce segregation.
(3) Synergistic with other ingredients to enhance purification effect
When compounded with fluoride salts (such as Na₃AlF₆) or chloride salts (such as NaCl), MgO can reduce the melting point of the molten salt system and improve the activity of the refining agent.
In molten steel, MgO forms a composite slag system with CaO and Al₂O₃ to enhance the desulfurization ability.
3. Advantages of magnesium carbonate
Mild foaming: Compared with violent foaming agents (such as sodium carbonate), the CO₂ release rate is moderate to avoid melt splashing.
Environmental protection: The decomposition products (MgO, CO₂) have little impact on the environment, and MgO can be recycled.
Cost controllable: Magnesium carbonate raw materials are widely available and the price is lower than some rare earth-based refining agents.
4. Application precautions
Decomposition temperature matching: The particle size and purity of magnesium carbonate need to be selected according to the smelting temperature to ensure that the decomposition timing is synchronized with the refining stage.
Optimization of addition amount: Excessive magnesium carbonate will cause excessive foaming of the melt or excessive slag. The general addition amount is 5-15% of the total mass of the refining agent.
Moisture-proof treatment: Magnesium carbonate is easy to absorb moisture and agglomerate. The granular refining agent needs to be coated or dried to maintain fluidity.
5. Actual industrial case
Example of aluminum alloy refining agent formula:
Granular agents composed of magnesium carbonate (10%), potassium nitrate (20%), cryolite (50%), and graphite (20%) are used for dehydrogenation of aluminum liquid, and the hydrogen content can be reduced to less than 0.1mL/100g.
Steel refining slag system:
In the MgO-CaO-Al₂O₃ slag system, magnesium carbonate is used as a precursor of magnesium oxide, and the desulfurization rate can reach more than 80%.
6. Future development direction
Nano magnesium carbonate: Improve decomposition efficiency and dispersibility, and reduce the addition amount.
Composite functionalization: Composite with rare earth oxides and carbon materials to enhance multiple functions such as deoxidation and grain refinement.
Messi Biology stated that magnesium carbonate provides active magnesium oxide and carbon dioxide gas through high-temperature decomposition in molten particle refining agent, and has the functions of slag making, degassing and melt purification. Its application needs to be combined with specific metal systems and process parameters to optimize the formula. In the future, the performance can be further improved through material modification to meet high-end metallurgical needs.