Mechanochemical synthesis and transformation of the polymorphic double carbonates fairchildite and buetschliite, (KCa(CO)): an X-ray powder diffraction study.

This study presents the mechanochemical synthesis of the two KCa(CO) polymorphs, fairchildite and buetschliite, from CaCO and KCO using a shaker mill. Unlike previous methods requiring high temperatures and prolonged heating, fairchildite, a high-temperature polymorph, is formed initially in all experiments, adhering to Ostwald's rule of stages. Notably, the transformation to the stable buetschliite phase can be achieved by varying milling parameters, particularly frequency and moisture content. The results suggest that pressure, rather than temperature, plays a significant role in this phase transition, with moisture further accelerating the transformation. These findings offer a new, efficient route for the synthesis of these polymorphs, highlighting the critical influence of milling conditions on the reaction pathway.