Kinetics of the reduction of hematite to magnetite near its Curie transition

Abstract

I report the reduction of Fe 2O 3 to Fe 3O 4 in approximately 5% H 2 around the Curie transition temperature of 575°C of Fe 3O 4. Powder samples of hematite from J.T. Baker Chemical Co. were sintered in air at approximately 1000°C for 8 h to coarsen the material in order to ensure a reaction rate around 575°C. SEM and TEM measurements were performed to verify the particle size of these materials. Image analyses were performed using a desktop computer to calculate the particle size. X-ray data revealed that the starting samples were single-phase hematite with an impurity phase of less than 5% Fe 3O 4. The purpose is to investigate whether there is any anomalous behavior during the reduction of Fe 2O 3 to Fe 3O 4 in the vicinity of the magnetic transition temperature of either magnetite or gamma Fe 2O 3. Hydrogen reductions were performed in the temperature range of 500–630°C using a Perkin-Elmer TG-7. I will discuss the data in light of the regular Hedvall effect which occurs upon the oxidation of magnetite.