A self-assembled spherical-like basic magnesium carbonate (Mg5(CO3)4(OH)2·4H2O) with diameters of 15−17 μm was synthesized in an aqueous solution system without using any organic additives during the precipitation process. Reaction parameters such as reaction time, stirring time, and reaction temperature were found to be important in controlling the final morphology of Mg5(CO3)4(OH)2·4H2O. By the investigation of the particles from time-dependent experiments, scanning electron microscopy observations and Fourier transform infrared spectra indicate that the formation of these spherical-like Mg5(CO3)4(OH)2·4H2O is via a complex process, in which the agglomerates built by many fine grains are first produced after the “burst” mixture of K2CO3 and Mg(NO3)2 solutions. Then the agglomerates tend to assemble into needlelike or other similar particles, and the latter, due to their unstable properties from the thermodynamic point of view, will transfer into sheetlike particles, which further assemble into spherical-like particles. During such a process, their corresponding compositions also change from (MgCO3)0.8(Mg(OH)2)0.2·1.3H2O to MgCO3·xH2O, then to Mg5(CO3)4(OH)2·4H2O. In addition, the stirring time and reaction temperature were found to play a comparative role in determining the final morphology of Mg5(CO3)4(OH)2·4H2O, and the morphology transition from spherical-like to nest-like, then to layered particles, as well as the decrease of particle size, can be well obtained by carefully adjusting the stirring time (0.5−4 min) of the initial solution and reaction temperature (333−363 K).

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