Combustion synthesis of nanocrystalline ceria (CeO2) powders by a dry route

In this study, ceria (CeO2) powders were synthesized with 50 g per batch via a combustion technique using two kinds of starting materials-urea [(NH2)(2)CO] (as a fuel) and ceric ammonium nitrate [Ce(NH4)(2)(NO3)(6)] (acting as both the source of cerium ion and an oxidizer). The starting materials were mixed thoroughly without adding water, and then ignited in the air at room temperature. It underwent a self-combustion process with a large amount of smoke, a voluminous loose product. The as-synthesized powders were characterized by X-ray diffraction (XRD) analysis, transmission electron microscope (TEM), scanning electron microscope (SEM), CHN elemental analyzer, surface area measurements, and sinterability. Experimental results revealed that the nanocrystalline CeO2 powders with low impurity content (< 0.2 wt%) can be obtained after combustion. Specific surface area and primary crystallite particle size of the ceria powder were similar to 50 m(2)/g and similar to 25 nm, respectively, through the stoichiometric fuel/oxidizer ratio reaction. The powder, when cold pressed and sintered in the air at 1250 degrees C for 1 h, was measured to attain the sintered density similar to 92% of theoretical density having submicron grain size. In addition, the thermal decomposition and combustion process of the reactant mixture were investigated using thermogravimetry (TG), differential scanning calorimetry (DSC), and mass spectrometry (MS) techniques simultaneously. Based on the results of thermal analysis, a possible mechanism concerning the combustion reaction is proposed. (c) 2006 Elsevier B.V All rights reserved.