Anhydrous magnesium carbonate (AMC) is a new inorganic flame retardant that can be used as an alternative to aluminum hydroxide and magnesium hydroxide. magnesium carbonate (MgCO3) is a common flame retardant for polymers commonly used in halogen-free flame-retardant wire and cable applications. It is suitable for occasions with high electrical insulation performance requirements.
Here, Alfa Chemistry summarizes the mechanism of action, preparation methods, innovative progress and applications of magnesium carbonate as a flame retardant additive.
The flame retardant mechanism of magnesium carbonate as a flame retardant additive is mainly based on its ability to release water when heated. When exposed to fire or high temperatures, magnesium carbonate undergoes a thermal decomposition reaction, releasing water vapor as a by-product. This endothermic reaction lowers the temperature of the surrounding area and dilutes the combustible gases, slowing or inhibiting the combustion process. The released water vapor also acts as a barrier between the ignited material and the surrounding oxygen, preventing the fire from spreading further.
In addition, magnesium carbonate can form stable metal oxide residues such as magnesium oxide (MgO) during the decomposition process. These metal oxide residues act as a protective layer or coating on the surface of the ignited material, preventing the entry of oxygen and heat, effectively inhibiting the spread of flames.
AMC can be prepared from magnesium carbonate trihydrate (MgCO3·3H2O) raw material through high-pressure and high-temperature dehydration method. The starting material MgCO3·3H2O (99.9%) was ground in an agate mortar with acetone. The sample pellet was made and sealed into a silver capsule. Using NaCl as pressure medium, the high pressure synthesis was performed on a cubic-anvil-type apparatus, and its pressure was calibrated by Bi phase transition and chloride (LiCl, KCl and NaCl) melting curves at high pressure. Then it was quenched to room temperature and released the pressure slowly. Upon cleaned up the silver coverage, the sample was obtained. 
Kesong Chai et al. proposed a synthesis strategy for hydrothermal anhydrous magnesium carbonate (AMC) from the perspective of ionic reactions, and explored the effects of pH value and carbon source form on the preparation of AMC. The results show that AMC prepared with urea as carbon source has smaller particle size in the presence of Na+/Cl- or K+/SO42− ion pairs. AMC prepared using magnesium chloride as the magnesium source has smaller constituent units than AMC prepared using magnesium sulfate as the magnesium source. 
Generally speaking, inorganic flame retardants require more addition, which will affect the mechanical properties of composite materials. Choosing nano-inorganic flame retardants with small size, uniform shape and high specific surface area can bring good flame retardant effects with a relatively small amount of addition. For example, nano-anhydrous magnesium carbonate (NAMC) has good flame retardant properties for polylactic acid/bamboo fiber composite materials, and its addition amount is only 5%.