LAUSR

Abstract The formation of iron oxide/iron composite compacts using mechanically activated and un-activated α-Fe 2 O 3 /Fe powder mixtures in various ratios by reactive spark plasma sintering – SPS is evidenced. Independent on the sintering temperature SPS of activated powders is leading to compacts with a microstructure consisting of iron clusters distributed in a continuous iron oxide matrix. The use of the un-activated powder is resulting in the fragmentation of the iron oxide matrix for several sintering temperatures by coalescence of the iron clusters. The carbon from graphite mould and punches has a significant influence on conserving the Fe/O ratio in compacts. The compact's microstructure and density, phase formation and crystallite size evolution during sintering, sintering mechanism and reactions which occur during sintering are discussed. The results are correlated with the free Gibbs energy of the system at various temperatures. The in-situ high-temperature X-ray diffraction has been performed. It is highlighted that in the case of the un-activated powder up to 1000 °C two or three iron oxides simultaneously coexist. In the temperature range of 550–580 °C in the material are present: α-Fe 2 O 3 , Fe 3 O 4 , and FeO. In the case of activated samples, in the temperature interval 250–530 °C only Fe 3 O 4 is present.