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Polymorphs of calcium carbonate (CaCO3) have been easily synthesized in a water/pyridine mixed solvent system under mild conditions without using any other organic additives. The phase transition from pure aragonite to almost pure vaterite, and then to pure calcite, can be nicely captured by the choice of a suitable water to pyridine ratio. The formation mechanisms of calcium carbonate crystals have been proposed. A novel morphology of calcite, wire-like shaped, was found in pure pyridine solvent. A self-assembly process for the formation of wire-like calcite in pure pyridine solution has been proposed. The effect of experimental time on morphology of calcite is investigated in pure pyridine solvent. The results obtained proved that such reaction media could give an alternative and versatile tool for controlling both the structure and the polymorphism of inorganic materials.

A microcalorimeter was used to investigate the formation mechanism of MCM-41 mesoporous silica. The obtained results show that the formation processes of the sample contain three steps. On the basis of the calorimetric results, MCM-41 mesoporous silica was successfully synthesized under basic conditions at different experimental times, such as (1, 2, and 4) h, respectively. Associated with other analytical techniques, the formation mechanism of the produced silica is proposed. First, rodlike inorganic/surfactant complexes are formed which spontaneously pack into an ordered arrangement. Second, with the help of this new template, a new kind of pore structure is formed. Third, the interaction between the pore structures formed in steps 1 and 2 results in a new pore structure. This new pore structure is very similar to the structure formed in the first step. The present work proves that calorimetry can be used for investigations on the formation mechanism of materials.