The effects of pH and citric acid concentration on the characteristics of nanocrystalline NiFe2O4 powder synthesized by a sol-gel autocombustion method

A novel sol-gel autocombustion process was used to synthesize ultrafine powders of nickel ferrite. This powder was prepared from metal nitrates and citric acid. The combustion process is an oxidation-reduction reaction in which the NO3- ion is the oxidant and the carboxyl group is the reductant. The results revealed that the nitrate - citrate gels exhibit a self-propagating behavior after ignition in air at room temperature. The ratio of metal nitrates to citric acid and different values of p H in the starting solution also affect the combustion process. The thermal decomposition and the phase evolution were investigated by DTA/TG and XRD techniques, respectively. By using this novel autocombustion method, an NiFe2O4 ferrite powder with crystallite sizes of 20 - 40 nm was obtained.