Magnesium carbonate, as an inorganic smoke suppressant, exhibits physical characteristics (especially particle size and morphology) that significantly influence the dispersibility, thermal decomposition behavior, reaction efficiency, and ultimate smoke suppression effect of coating systems. The behavior of magnesium carbonate varies greatly within coatings depending on its particle size:
- Smaller particle sizes lead to larger specific surface areas, enhanced reactivity, and increased adsorption.
- Larger particle sizes tend to agglomerate, are difficult to disperse, and result in a decline in smoke suppression effectiveness.
I. Influence of Different Particle Sizes of Magnesium Carbonate on Key Properties
1. Thermal Decomposition Behavior:
Smaller particle size magnesium carbonate, due to its large specific surface area, has a lower initial decomposition temperature and undergoes more rapid thermal decomposition. This allows for earlier release of CO₂, achieving smoke suppression earlier.
Larger particle sizes require higher temperatures for decomposition and exhibit higher thermal inertia, delaying the smoke suppression reaction.
2. Smoke Density Suppression Effect:
Smaller particle size materials are more likely to disperse uniformly and form a dense protective layer, enabling more effective dilution and adsorption of flammable gases and smoke particles.
3. Dispersibility and Application Suitability:
Nano-sized magnesium carbonate requires high-shear or ultrasonic equipment for dispersion. Surface modification (such as silane treatment) can improve agglomeration.
Micron-sized particles (1~5 μm) are commonly used industrial standards, offering a high cost-performance ratio and moderate dispersibility.
Larger particle size magnesium carbonate often leads to whitening, thickening, and increased grittiness in the coating, negatively impacting application and film formation quality.
4. Impact on Coating Performance:
Smaller particle sizes result in higher coating film transparency and gloss, increased system viscosity, and better leveling properties.
II. Application Recommendations and Engineering Selection
Recommended Particle Size Selection:
- Transparent Fire-Resistant Coatings: <1 μm (nano), to ensure transparency and high smoke suppression efficiency.
- Indoor Waterborne Coatings: 1~5 μm, for low cost and moderate dispersibility.
- High-Solids Industrial Coatings: ≤5 μm, for controllable viscosity and good workability.
- Powder Coatings: ≤10 μm, to ensure processing performance.
Synergistic Addition Strategies:
- Nano-sized magnesium carbonate + Micron-sized magnesium carbonate → Comprehensive particle size system to improve packing density and smoke suppression efficiency.
- Magnesium carbonate + Aluminum hydroxide/Ammonium polyphosphate → Synergistic flame retardancy and smoke suppression.
III. Future Research Directions
- Utilizing magnesium carbonate composites with graphene, expanded graphite, and montmorillonite to form novel multi-functional nano-composite smoke suppressants.
- Investigating the impact of particle size on coating carbonization behavior and the formation mechanism of fire-resistant residue structures.
- Designing intelligent controllable release magnesium carbonate (such as temperature-responsive encapsulated types).