Effects of Fe additions on self propagating high temperature synthesis characteristics of TiO2–Al–C system

Abstract

The aim of the present study was to investigate the effect of Fe additions on combustion velocity and phases that are formed after synthesis in the TiO2–Al–C system. Before experimental tests, thermodynamic calculations were performed to determine the range that Fe can be added to the reaction and remain self sustaining. According to the Merzhanov criterion, if the amount of Fe is lower than 53.13wt.%, the adiabatic temperature of the reaction is higher than 1800K and therefore the reaction proceeds in the self sustaining mode. But, experimental observations showed that the reaction became unstable when the amount of Fe was changed from 15 to 20wt.%, which was considerably lower than that was predicted by thermodynamic calculations. X-ray diffraction analysis indicated that Fe3Al, TiC and Al2O3 are the main phases formed in the products and additions of Fe decreased the lattice parameter of TiC. Also, Raman spectroscopy analysis showed that at higher Fe contents, oxygen dissolved in the TiC crystal structure leading to the formation of titanium oxy-carbide with lower lattice parameter and residual un-reacted carbon in the products. The adiabatic temperatures for the reactions containing 15 and 20wt.% Fe estimated using the thermodynamic data of the new products were in conformance with the Merzhanov criterion and experimental observations. Scanning electron microscopy examinations showed that the addition of Fe decreased TiC particle size and changed their growth controlling mechanism.