Nanocrystalline Cr2O3 and amorphous CrO3 produced by solution combustion synthesis

The synthesis of chromium oxides by solution combustion synthesis was investigated. Ammonium dichromate, glycine, urea and ammonium nitrate dissolved in aqueous solution were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. Amorphous CrO3 and crystalline Cr2O3 were synthesized. The results suggest that glycine is a better complexing/combustible agent for ammonium dichromate than urea. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The smallest crystallite size (≈20 nm) of Cr2O3 was obtained with glycine as fuel/complexant agent in fuel-lean mixtures. The highest specific surface area (63 m2/g) was observed with urea in fuel-rich mixtures, forming amorphous CrO3.