Combustion synthesis of gadolinia-doped ceria using glycine and urea fuels

Two different fuels, glycine and urea, along with metal nitrates (oxidant) have been used to prepare 12 mol% gadolinia (Gd2O3)-doped ceria powders by solution combustion route. Combined thermogravimetry-differential scanning calorimetry (TG-DSC) of the gel precursors has been carried out to study the combustion reactions. Phase pure-doped ceria powder is obtained after the combustion reaction when glycine is used as the fuel. However, when urea is used as the fuel the combustion reaction remains localized and the combustion-synthesized product is required to be calcined at 700 °C. For both the fuels theoretical calculations of exothermic heat and adiabatic flame temperature indicate favorable condition for combustion to occur. The incomplete combustion in urea route has been attributed to the formation of inhomogeneous precursor out of unstable gel. The powder produced by glycine route does not require any calcination step and can be sintered close to theoretical density at 1250 °C. Calcined powder of urea route shows relatively poor sinterability.