Synthesis of different morphological AlN from hydrated halloysite by aluminothermic reduction

Halloysite is a natural aluminum-rich nano-sized clay mineral, which can offer the aluminum source to synthesize aluminum nitride (AlN) in a low-cost and environmentally friendly manner. The micron-sized AlN with different morphology and structure, including self-assembled pine-like aggregates, hollow bayberry-like spheres, and high aspect ratio whiskers, were successfully synthesized at 700 °C under nitrogen atmosphere using natural hydrated halloysite (10 Å HNT). These three kinds of varying morphological AlN formed by different mechanism. The self-assembled-AIN pine-like aggregates formed by in-situ nitrogen substitution within the Al-O octahedra of 10 Å HNT thermal fragmentation through self-assembly. The formation of the bayberry-like hollow spheres is governed by a gas–liquid reaction pathway, whereas the development of whiskers with a high length-to-diameter ratio is driven by a gas–liquid-solid mechanism. The morphological comparison of AlN synthesized from 10 Å HNT with 7 Å HNT further confirms the validity of the in-situ substitution mechanism we previously proposed, as well as reflecting the critical influence of halloysite hydration state on structural evolution of AlN. This study offers a new insight into tailoring AlN nanostructures using clay mineral templates, with promising applications in thermally conductive composites and electronic packaging materials.