CHEMICAL SYNTHESIS AND CHARACTERIZATION OF CALCIUM ALUMINATE POWDERS

The Pechini process was used to produce high-purity, monocalcium alumi nate (CaAl2O4) powders at temperatures as low as 900 degrees C. Absorp tion spectrometry and BET measurements revealed particles with sizes r anging 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 burnou t as a function of temperature. The growth kinetics of calcium alumina te crystallites from a polymeric precursor were studied during calcina tion as a function of temperature, using transmission electron microsc opy (TEM). At the early stages of crystallization, the activation ener gy for crystallite growth was found to be 118 kJ/mol. This is substant ially less than the 356 kJ/mol previously reported. A growth kinetic e xponent of n = 1.68 was determined for the amorphous-to-crystalline tr ansformation in the temperature range 700 degrees to 850 degrees C. Th ese values were consistent with growth by short-range diffusion.