Ultrafine MnFe₂O₄ powder preparation by combusting the coprecipitate with and without Mg²⁺ or Zn²⁺ additives

Abstract

Ultrafine MnFe₂O₄ powder with its crystallites less than 100 nm was prepared using a combustion process. The coprecipitates containing the stoichiometric amount of Mn²⁺ and Fe³⁺ to form MnFe₂O₄ were prepared by dissolving the required metallic nitrates in de-ionized water and adding NH₄OH to adjust the pH of the solutions to 9. The collected dried precipitates were then heated up to predetermined temperatures and then quickly contacted with the acetone spray. Upon contacting with the heated precipitates, the acetone spray was ignited. The combustion of acetone caused the precipitates to form crystalline MnFe₂O₄ without chemical segregation. The crystallinity of MnFe₂O₄ powder so obtained depended on the ignition temperature of acetone spray. MnFe₂O₄ powder obtained at acetone ignition temperature of 773 K had higher crystallinity than that obtained at acetone ignition temperature of 523 K. The presence of a small amount of Mg²⁺ or Zn²⁺ in the composition of the coprecipitates promoted the mobility of constituent ions of the combusted powder and resulted in bigger MnFe₂O₄ crystallites at a lower acetone ignition temperature.