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

Autor: Klaus-Jürgen Range, Linda C. Prinsloo, Anton M. Heyns, Martin Stassen
Rok vydání: 1998
Předmět:
Zdroj: Journal of Solid State Chemistry. 137:33-41
ISSN: 0022-4596
DOI: 10.1006/jssc.1997.7672
Popis: α -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 Ia 3( 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 = α -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 Bronsted 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 α -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.
Databáze: OpenAIRE
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