The Vibrational Spectra and Decomposition ofα-Calcium Nitride (α-Ca3N2) and Magnesium Nitride (Mg3N2)

✍ Scribed by Anton M. Heyns; Linda C. Prinsloo; Klaus-Jürgen Range; Martin Stassen

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 342 KB
• Volume: 137
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7672

✦ Synopsis

Ca 3 N 2 has been characterized by X-ray powder diffraction and its structure confirmed by a crystal structure refinement with the Rietveld method. Ca 3 N 2 and the isostructural Mg 3 N 2 crystallize in the anti-bixbyite structure of the mineral (Mn, Fe) 2 O 3 in the body-centered space group of Ia3(T 7 h ), and the general appearance of their infrared and Raman spectra resembles that of the sesquioxides belonging to the same space group. The decomposition of M 3 N 2 (M ‫؍‬ -Ca, Mg) into M(OH) 2 and NH 3 , when exposed to the atmosphere, is reported. The presence of NH ؉ 4 vibrational bands in the decomposition products is explained in terms of the existence of Brønsted acid centers on the surface of the solid. During the initial stages of decomposition, infrared bands characteristic of adsorbed NH 3 were observed, showing that Lewis centers also exist on the surface. The decomposition product Mg(OH) 2 has weaker proton-donating centers than Ca(OH) 2 . The kinetics of the decomposition of Mg 3 N 2 , which is a much slower reaction than that of -Ca 3 N 2 , has been studied with FT-IR microspectrometry, and it is shown that the formation of Mg(OH) 2 is a three-dimensional diffusion process while the proton donation by the hydroxide to adsorbed NH 3 to form NH ؉ 4 ions is a quasi-first-order reaction.