Synthesis of aluminium nitride using urea-precursors

We synthesized AlN using aluminium chloride hexahydrate and urea as the starting materials. By directly introducing aluminium chloride into melted urea at 135°C, a urea-precursor was formed under non-aqueous conditions with no γ-Al₂O₃ observed in any calcination steps. As a result, well-crystalline AlN powder was obtained by the pyrolysis of urea-precursor above 900°C under a stream of N₂ gas for 1hour. In this process the urea-precursor decomposed below 400°C, and an AlN skeleton with a layer structure formed above 800°C. The total yield of AlN powder based on the Al atom was only 80% due to production of volatile Al(NH₃)₆AlH₄Cl₂ as a by-product. The AlN powder was characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy (SEM). Morphological observation of the AlN powder by mean of SEM revealed large particles of about 30-μm diameter, which consisted of ultrafine particles of less than 1-μm diameter.