Synthesis of aluminum nitride by a modified carbothermal reduction and nitridation method using basic dicarboxylate Al(III) complexes Al(OH)(Cn+2H2nO4)·xH2O (n=3, 6, 8)

Aluminum nitride (AlN) particles and whiskers were synthesized by using basic dicarboxylate Al(III) complexes Al(OH)(Cn+2H2nO4)·xH2O (n =3, 6, 8) as a precursor. AlN was obtained by calcining the glutarate complex (n=3, AG) without further additions of carbon source under flowing nitrogen in the temperature range 1200–1500°C and then burning out the residual carbon. In contrast, for suberate (n=6, ASu) and sebacate (n=8, ASe) complexes additional carbon was required for their complete conversion to AlN. The process of conversion of AG to AlN was investigated by 27Al magic-angle spinning (MAS) nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction. The complex began to decompose at ca. 400°C and then turned into γ-alumina at temperature above 600°C. Finally, the γ-alumina was converted to AlN without γ-α alumina phase transformation. The morphology of AlN powders was very similar to that of the precursor, indicating that conversion of alumina to AlN during the carbothermal reduction and nitridation does not proceed through gaseous intermediates but through solid-state Al–oxynitride compounds. The AlN powders obtained consisted of ultrafine particles or mixtures of particles and whiskers.