NATURE OF CAO PRODUCED BY CALCITE POWDER DECOMPOSITION IN VACUUM AND IN CO2

Specially reactive (sr‐) CaO can be produced by decomposing 1‐ to 10‐μm particles of CaCO3 in vacuum at ∼650°C. Particles of sr‐CaO appear unchanged in dimension from the original CaCO3, but have internal pores with surface areas of 92 m2/g, more than twice the surface areas reported in a previous study for CaO made from calcite in vacuum at about the same temperature. Weak and broad X‐ray diffraction peaks in normal CaO first become discernible only after about half the CO2 content of a calcite sample has been lost, but the molar surface areas of samples decomposed in vacuum or in 0.1 torr CO2 are linear functions of the extent of reaction. The sr‐CaO, therefore, must be a phase with ion positions and spacings like those of normal CaO. Background pressures of CO2 (up to ∼1 torr) influence the surface area of the CaO by increasing the pore dimensions at the CaCO3‐CaO reaction interface. Sintering of the CaO is negligible at 650°C in CO2 pressures of≤0.1 torr, but sintering is pronounced in CO2, at 9 torr pressure. Copyright © 1979, Wiley Blackwell. All rights reserved