Sol–gel synthesis of Ti₂AlC and Ti₃AlC₂ MAX phases and their sinterability via spark plasma sintering

This study presents a novel sol-gel-based synthesis route for Ti–Al–C MAX phase raw materials in which alkoxide-derived gels not only provide homogeneous mixing of elements but also serve as an internal carbon source. Such a molecular-level control over precursor chemistry, together with the application of a controlled heat treatment, represents the first reported sol–gel-based route for Ti₃AlC₂ formation. Among the various precursor ratios investigated, the mixture with a Ti-/Al-alkoxide/C/Pr₄NOH (aq) molar ratio of 3.0:1.0:10:6.0 showed the best results for MAX phase formation. FTIR, XRD and TG analyses confirmed the presence of alkoxide groups, which also act as a carbon source necessary for the synthesis of the MAX phase, and the existence of Ti–O–Al bonds. The sol-gel raw materials were heated under argon atmosphere between 1150 and 1400 °C at a rate of 2 °C/min, held at these temperatures for 30–60 min, and then cooled in a controlled manner. As the temperature increased, the Ti₂AlC phase appeared first and at higher temperatures, especially around 1300–1350 °C, the Ti₃AlC₂ phase formed. At 1400 °C, decomposition of the MAX phases was observed. The highest purity of MAX phase (97 %) was obtained at 1300 °C with a 90 min dwell time. XRD and EDS results also showed small amounts of aluminum oxide (Al₂O₃) as secondary phase. Additional analyses using Raman, XPS, SEM, DSC, and TEM confirmed the successful synthesis of layered Ti₃AlC₂ with typical MAX phase structure.