Preparation of Ti2AlC and Ti(3)AlC(2)MAX Phases by Self-Propagating High-Temperature Synthesis with the Reduction Stage

摘要

This work is devoted to the preparation of powders of Ti2AlC and Ti(3)AlC(2)MAX phases by self-propagating high-temperature synthesis (SHS) using the magnesium-thermal reduction from oxide feedstock. Oxide TiO(2)is used as the titanium source, and magnesium is used as the reducing agent. Purification with the removal of magnesium oxide is performed in diluted hydrochloric acid at a temperature of 70 degrees C and concentration of 1 : 3. The target product yield with the magnesium-thermal reduction is 35-40%. It is revealed that the synthesis product with the stoichiometric component ratio after chemical leaching in hydrochloric acid consists of Ti2AlC, MgAl2O4, and TiC. The formation of spinel MgAl(2)O(4)is associated with the deficiency of the magnesium reducing agent in the charge; herewith, aluminum partially enters the reduction reaction of titanium from its oxide with the formation of Al2O3. This leads to the formation of spinel MgO . Al2O3. An increase in the content of excess magnesium in the charge from 20 to 30 wt % conditions the complete reduction of titanium from its oxide by magnesium with the formation of the Ti2AlC MAX phase and titanium carbide. A decrease of 10 wt % in the carbon content causes a decrease in the titanium carbide fraction to 4%. The product, containing Ti(3)AlC(2)and Ti2AlC MAX phases, as well as TiC, is formed at an excess soot content from 20 to 35%, and the Ti(3)AlC(2)weight fraction increases from 86 to 89%, respectively. These powders comprise agglomerates (87% of them are smaller than 65 mu m) consisting of thin plates of MAX phases 70-100 nm in thickness.