CaO: I, Fabrication and Characterization*

Two processes for hot‐pressing CaO to less than 1% porosity are described and discussed. One process is without additives at about 1200°C, and the other is with additives of NaF or LiF (preferably EiF) at about 1000°C. The dense bodies are characterized in terms of grain size, surface annealing, and the type and content of impurities and residual additives. Iron and silicon are prevalent impurities and undergo changes on subsequent firing, especially above 1650°C. Gaseous impurities, H 2 O and CO 2 , which are released from powders during hot‐pressing, may cause explosions if proper caution is not used. They are also trapped in varying small quantities in dense bodies as hydroxide and carbonate compounds and are surprisingly tenacious. Lithium is readily eliminated from bodies made with LiF. Fluorine, though more tenacious, can also be reduced with firing, but not as readily as in MgO. Some observations on possible densification mechanisms are presented, including possible effects of impurities.