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Hydrothermally synthesized nano-size CeO2 powders, chemically precipitated CeO2 powders and commercial micron-size CeO2 powders were investigated by DTA/TGA and TEM. The sintering behavior of these powders was studied by continuous monitoring of the shrinkage kinetics. The microstructural features of the sintered specimens were observed by SEM. The sinterability of the CeO2 powder compact increased with decrease in particle size. During the high temperature sintering process a redox reaction occurred, i.e. CeO2 was reduced to Ce2O3, and oxygen gas was released. The redox reaction influenced the sintering behavior of CeO2, resulting in a decrease in density and microcracking for the hydrothermally synthesized nano-size CeO2 powder compacts, and sagged points in the sintering curves for the chemically precipitated and commercial micron-size CeO2 powder compacts. It was found that the redox reaction of ceria produced additional pores during the sintering process and thus a much higher temperature was needed to achieve a high density. (C) 1997 Acta Metallurgica Inc.