Mechanothermal synthesis of cobalt, iron, and titanium aluminides

Resumo

The aluminides with compositions Al₁₃Co₄, Al₁₃Fe₄, Al₁₃Co₂Fe₂, and Al₃Ti are synthesized in air after mechanical activation of the precursor metals followed by thermosynthesis. The phase compositions of the synthesized aluminides as well as Al₁₃Co₄/SiO₂, Al₁₃Fe₄/SiO₂, and Al₃Ti/SiO₂ composites are analyzed before and after partial oxidation of methane (POM). According to the X-ray powder diffraction data, Al₁₃Co₄ crystallizes as the Y phase. During POM, the Z phase with low content of aluminum is formed along with the Y phase. The Al₁₃Fe₄ sample is the eutectic mixture of the Al_13–xFe₄ monoclinic M phase and aluminum, but the Al₁₃Co₂Fe₂ solid solution crystallizes as the homogeneous M phase. The formation of Al₃Ti in air is accompanied by oxidation. With SiO₂ as a substrate, intermetallics Al₁₃Co₄ and Al₁₃Fe₄, albeit corrosion-resistant to atmospheric oxygen up to 600°C, decompose to form corundum Al₂O₃, mullite Al₆Si₂O₁₃, and silicides CoSi₂, CoSi, Co₂Si, FeSi₂, and Fe₃Si. The phase transformations occurring during the coannealing of Al₁₃Co₄ and Al₁₃Fe₄ with SiO₂ are described by irreversible reactions. The aluminide Al₃Ti does not form silicides during the contact with SiO₂, and the phase composition of the 3Al–Ti–1.5SiO₂ composite does not change during POM.