Obtaining of Ti2AlC and Ti3AlC2 MAX phases by SHS with reduction stage

Abstract

The paper focuses on obtaining Ti₂AlC and Ti₃AlC₂ MAX phase powders by self-propagating high-temperature synthesis (SHS) from oxide raw materials using magnesium-thermal reduction. The source of titanium was its oxide TiO₂ with magnesium used as a reducing agent. Cleaning from magnesium oxide was conducted in hydrochloric acid solution with a concentration of 1:3 at t = 70 °C. The yield of the target product in magnesium thermal reduction is 35–40 %. It was found that the synthesis product consisted of Ti₂AlC, MgAl₂O₄ and TiC after chemical leaching in hydrochloric acid at the stoichiometric ratio of components. MgAl₂O₄ spinel was formed due to the lack of magnesium reducing agent in the green mixture, while some part of aluminum reacted with titanium oxide reducing it and forming Al₂O₃ . It led to MgO·Al₂O₃ formation. An increase in the excess magnesium content in the green mixture from 20 wt.% to 30 wt.% leads to the complete reduction of titanium from its oxide by magnesium with the formation of Ti₂AlC MAX phase and titanium carbide. A decrease in carbon content by 10 wt.% in the green mixture leads to a decrease in titanium carbide content to 4 %. With an excess content of soot from 20 % to 35 %, a product containing Ti₃AlC₂ , Ti₂AlC and TiC MAX phases is formed, and the mass fraction of Ti₃AlC₂ increases from 86 % to 89 %, respectively. The resulting powders are agglomerates consisting of thin plates of 70–100 nm thick MAX phases. 87 % of such agglomerates are less than 65 μm in size.