CHEMICAL SYNTHESIS AND CHARACTERIZATION OF CALCIUM ALUMINATE POWDERS

The Pechini process was used to produce high-purity, monocalcium aluminate (CaAl2O4) powders at temperatures as low as 900 degrees C. Absorption spectrometry and BET measurements revealed particles with sizes ranging from submicrometer to 100 mu m, with specific surface areas as high as 10 m(2)/g. Auger electron spectrometry (AES) was used to study the progressive elimination of surface carbon from the organic burnout as a function of temperature. The growth kinetics of calcium aluminate crystallites from a polymeric precursor were studied during calcination as a function of temperature, using transmission electron microscopy (TEM). At the early stages of crystallization, the activation energy for crystallite growth was found to be 118 kJ/mol. This is substantially less than the 356 kJ/mol previously reported. A growth kinetic exponent of n = 1.68 was determined for the amorphous-to-crystalline transformation in the temperature range 700 degrees to 850 degrees C. These values were consistent with growth by short-range diffusion.