2.2. Preparation of vaterite particles

Calcium carbonates consisting predominantly of vaterite were prepared using a carbonation process in methanol [37]. CO₂ gas was blown for 3 h at a flow rate of 300 ml min⁻¹ into a suspension consisting of 7.0 g of Ca(OH)₂ in 180 ml of methanol at 0°C in a Pyrex beaker. The resulting slurry was dried at 70°C in air, resulting in the formation of fine-sized powders. Figure 2 shows an SEM photograph of the powders. The surface area of the calcium carbonates obtained was determined to be 40 m² g⁻¹ through a nitrogen gas sorption analysis. Secondary particles of 0.5–1 mm in diameter were formed, and an agglomeration of primary particles of 20–100 nm in diameter was observed. XRD analysis (CuKα, 45 kV, 40 mA) showed that the calcium carbonate consists predominantly of vaterite with a trace amount of calcite (denoted as V hereafter).

SEM image of V particles.