The low temperature fabrication of nanocrystalline MgAl₂O₄ spinel aerogel by a non-alkoxide sol-gel route

A novel nanorod-like spinel aerogel is synthesized by the sol-gel method combined with the supercritical technique. The Mg₄Al₂(OH)₁₄·3H₂O and boehmite is formed in the spinel precursor aerogel and Mg₄Al₂(OH)₁₄·3H₂O transforms into MgO and spinel at 350 °C. Structural transition of boehmite to γ-Al₂O₃ occurs at ca. 400 °C, which is favorable to the further solid reaction between MgO and γ-Al₂O₃ forming spinel aerogel at 500 °C. This formation temperature is much lower than the conventional methods. The highly pure nanorod spinel with length of 150–200 nm and width of 5–10 nm is well crystallized after 800 °C. The nanocrystal maintains a large specific surface of 81.87 m²/g after calcining at 1200 °C.