Activation on Ammonia Absorbing Reaction for Magnesium Chloride

Hexa-ammine complex (Mg(NH3)6Cl2) is directly formed at room temperature by the reaction between magnesium chloride (MgCl2) and ammonia (NH3) without formation of mono- and diammine complexes (Mg(NH3)Cl2 and Mg(NH3)2Cl2) even though these are more stable phases. The high kinetic barrier exists for the formation of low coordinated ammine complexes. The activation by using heat treatment and ball milling is carried out, and then the NH3 absorption properties are investigated to understand kinetic properties of the ammine complexes formation of MgCl2. At 373 K, the formation of Mg(NH3)2Cl2 is realized. Furthermore, it is found that a higher temperature than 573 K is required to form Mg(NH3)Cl2. Interestingly, the ball milled MgCl2 can transform into low coordinated ammine complexes even at room temperature, indicating that the structural disorder state generated by the ball milling induces the formation of the above phases with low activation energy. Therefore, it is expected that the kinetic barrier to form ammine complexes of MgCl2 is strongly related to the process on the structural change.