Rearrangement of Porous CaO Aggregates During Calcite Decomposition in Vacuum

High‐resolution SEM photographs, N 2 adsorption isotherms, Hg porosimetry, and micrometer measurements were used to characterize CaO particle shapes and pore‐size distributions that result when calcite crystals are decomposed in vacuum at 686°C. The surface area of the CaO produced from large calcite crystals is constant at 116.4 m 2 /g independent of the extent of reaction. The volume occupied by a CaO aggregate is 98±2% that of the original calcite crystal. The ∼54% total porosity is comprised of 42% pores of ∼5 nm cross section and 12% pores of ∼10 μ m cross section. The duplex pore structure is formed by a diffusionless repacking of CaO particles that initially form with a more uniform distribution of particles and pores.