Synthesis of Aluminium Nitride using Urea-Precursor

We newly synthesized AlN using urea and aluminium chloride as the starting materials. By directly introducing aluminium chloride into a melted urea at 135°C, urea-precursor was formed under a non-aqueous condition and then no γ-Al₂O₃ was 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 1 hour. In this process the urea-precursor decomposed above 350°C, and the formation of AlN skeleton with a layer structure occurred 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. In our report we also discuss the preparation and decomposition processes of urea-precursor for the synthesis of AlN.