Isothermal and non-isothermal reduction behaviors of iron ore compacts in pure hydrogen atmosphere and kinetic analysis

Abstract This study examines the isothermal and non-isothermal reduction behaviors of iron ore compacts in a pure hydrogen atmosphere and compares the results obtained during the reduction process by CO. The different phases accompanying the reduction reactions were identified using X-ray diffraction (XRD) and its morphology was microscopically examined. In isothermal experiments, temperature plays a significant role in the reduction process. At any given temperature, the reduction rate during the initial stages is higher than that during the final stages. The reduction rate in H₂ atmosphere was faster than in CO gas. The comparison of activation energy values suggested that reduction with H₂ is more efficient than with CO. At the same temperature, the time required to achieve a certain degree of reduction was lower when using H₂ gas than CO atmosphere. In non-isothermal tests, the heating rate has a significant effect on the reduction rate and reduction extent. At the same heating rate, the degree of reduction was higher in H₂ atmosphere than in CO gas. Based on experimental data, the parameters of reaction kinetics were deduced by application of model-free and model-fitting methods. The reduction in H₂ atmosphere was controlled by nucleation model (Avrami-Erofeev model), while the CO reduction reaction was controlled by gas diffusion

Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bi-layer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and possibility of using it to modify the electronic structure of few-layer graphene is discussed